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Effect of drying methods and antioxidants on the flavor and lipid oxidation of silver carp slices
Accepted Manuscript Effect of drying methods and antioxidants on the flavor and lipid oxidation of silver carp slices Xiangjin Fu, Qinglu Lin, Shiying Xu, Zhang Wang PII:
S0023-6438(14)00670-7
DOI:
10.1016/j.lwt.2014.10.035
Reference:
YFSTL 4233
To appear in:
LWT - Food Science and Technology
Received Date: 12 October 2009 Revised Date:
2 August 2014
Accepted Date: 14 October 2014
Please cite this article as: Fu, X., Lin, Q., Xu, S., Wang, Z., Effect of drying methods and antioxidants on the flavor and lipid oxidation of silver carp slices, LWT - Food Science and Technology (2014), doi: 10.1016/j.lwt.2014.10.035. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Effect of Drying methods and Antioxidants on the Flavor and Lipid
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Oxidation of Silver Carp Slices
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Xiangjin Fu1,2, Qinglu Lin1, Shiying Xu2,3 *,Zhang Wang2,3
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1 School of Food Science and Technology, Central south University of forestry and technology. Changsha 410004, PR China
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2 State key laboratory of food science and safety. Jiangnan University. Wu Xi 214122, PR China 1
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3 School of Food Science and Technology, Jiangnan University. Wu Xi 214122, PR China
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Running title: Effect of Drying and Antioxidants on the Quality of Silver Carp Slices
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Author E-mail address: [email protected]
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*Corresponding author address: Tel 086-0510-85884496, Fax 086-0510-85884496, E-mail: [email protected]
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Abstract Silver carp slices were dried using hot air, microwave, and microwave-vacuum
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(MV). The drying kinetics, lipid oxidation, flavor, and content of fat, eicosapentaenoic
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acid (EPA), docosahexaenoic acid (DHA), and earthy-musty off-odour compounds
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were compared among the dried slices. Furthermore, the effect of vitamin C (Vc) and
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tea polyphenols (TP) on the microwave-dried fish slices was investigated. The
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Exponential models gave good fit for the drying data. Compared with hot air drying,
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microwave and MV drying reduced the drying time drastically. Drying removed part
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of the fishy off-odour, produced grilled flavor and “Oxidated oil” off-odour. Hot air
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dried fish slices had better grilled flavor. The TP restrict the formation of fishy and
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“Oxidated oil” off-odours effectively. Microwave drying removed a large part of
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“Earthy-musty” off-odour, and marinating with Vc or TP help to remove this
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off-odour. The slices dried with microwave or MV had less thiobarbituric acid
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reactive substance (TBARS). The TBARS decreased with power intensity during
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microwave drying but increased with the vacuum during MV drying. All drying
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processes largely decreased the contents of fat, EPA and DHA (P < 0.05). Microwave
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drying retained more fat (P < 0.05). The Vc and TP protected the EPA and DHA
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effectively.
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Key words: Microwave drying; microwave-vacuum drying; drying kinetics; Lipid
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oxidation; Flavor
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Chemical compounds studied in this article
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Vitamin C (Pub Chem CID: 5785); Tea polyphenols (Pub Chem CID: 65064);
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2723628); Eicosapentaenoic acid (Pub Chem CID: 446284); Docosahexaenoic acid
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(Pub Chem CID: 445580); Geosmin (Pub Chem CID: 29746); 2-Methylisoborneol
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(Pub Chem CID: 16913)
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1. Introduction Silver carp (Hypophthalmichthys molitrix) is widely raised in China, India and
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Mexico, due to its quick growth and resistance to stress, diseases and rough handling
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(Siddaiah, Raju & Chandrasekhar, 2001; Barrera, Ramirez, Gonzalez & Vazquez,
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2002). It is a new resource for fish products, due to its huge stock (statistical data
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show that 3,687,751 tons were caught in China in 2012 (Anonymous, 2013), excellent
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white color, low market price, high quality nutritious protein (15~18 g / 100 g) and
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unsaturated fatty acids (Siddaiah et al., 2001; Barrera et al., 2002). However, the
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silver carp is not particularly liked by consumers due to its fishy and earthy–musty
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off-odour. The fishy odour has been attributed to the oxidation of lipid (Siddaiah et.
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al., 2001), while the earthy–musty odour is caused by the semivolatile cyclic alcohols
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geosmin (GEO) and 2-methylisoborneol (MIB) (Lloyd & Grimm, 1999).
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Initiation and propagation of lipid oxidation are catalyzed by exposure to oxygen,
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exposure to light, the presence of pigments such as chlorophyll, riboflavin and hemo
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proteins, the presence of metals, and the contact with lipoxygenase (Mistry & Min,
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1997). When oxygen is present, unsaturated fatty acid decomposition occurs more
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readily. These suggest low temperature, low oxygen and quick processing can help to
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avoid the lipid oxidation. The microwave-vacuum (MV) heating technology not only
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have the advantages of microwave heating (heating rapidly, high efficiency, good
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controllable and sanitation) (Cui, Xu & Sun, 2003), but the lower boiling point of
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water and less oxygen caused by the vacuum environment. It implies that MV may be
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a suitable technology for drying silver carp. In fact, several reports have been focused
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microwave-dried samples showed lower fat loss, less lipid oxidation than hot air-dried
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samples (Wu & Mao, 2008). And there are numerous studies on the application of MV
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drying to the fruits and vegetables, such as the carrot (Cui, Xu & Sun, 2003), garlic
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(Cui, Xu & Sun, 2004), mushroom (Giri & Prasad, 2007). The dried products were
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found to be more excellent in terms of taste, aroma and rehydration than products
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dried by the hot-air method. Bighead carp (Hypo. nobilis) slices were also dried by
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MV; the higher vacuum degree could enhance the puffing effect, and improve the
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crispness of the fish slices (Zhang, Zhang, Shan & Fang, 2007). However, limited
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literature is available about the effect of MV drying on the lipid oxidation of fish.
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Tea polyphenols (TP) have beneficial anti-oxidative activities, which demonstrate
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potential for their use as anti-oxidants in food industry. Fan, Chi & Zhang (2008)
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reported that TP dip treatment on silver carp lead to retention of the good quality
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characteristics for longer and an extension of the shelf life during iced storage.
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However, there have been few studies on the use of TP to protect the unsaturated fatty
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acids and improve the flavor of silver carp during drying.
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Peroxide value defines the initial stage of the oxidative changes. However,
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peroxides are unstable and decompose via fission, dehydration and the formation of
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free radicals, to form a variety of chemical products, such as alcohols, aldehydes,
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ketones, and acids compounds at elevated temperatures, and thus, peroxide value was
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found to be a poor indicator for heated samples (Wu & Mao, 2008). Alternatively,
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TBARS (thiobarbituric acid reactive substance) value could be reliable and
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(Siddaiah et. al, 2001) found the significantly positively relationship between TBARS
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and off-odour in silver carp, thus, the present study used TBARS to evaluate the
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intensity of the lipid oxidation.
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The present work investigates the effect of drying methods (hot air, microwave, and
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MV) on the drying kinetics, lipid oxidation, poly-unsaturated fatty acids (EPA and
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DHA) and flavor of silver carp slices. And the treatments with TP and Vc (Vitamin C)
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were used to improve the quality of dried silver carp slices.
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2. Materials and methods
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2.1 Materials
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Fresh silver carps were purchased from local market. The silver carps were brought
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to the laboratory on ice. The approximate weight of the individual fish was 1000 ± 50
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g. Upon arrival to the laboratory the fish were washed, scaled, gutted, and filleted.
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Before drying, the white muscle was collected and cut into slices of about 5×5×10–
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mm by hands and their weight were determined by an electronic balance (Model
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MP2000D, Shanghai Electronic Balance Instrument Co. Ltd., Shanghai, China). The
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average moisture content of raw slices was 80.5 ± 0.5 g/ 19.5 ± 0.5 g (g water/g dry
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matter) and fat content 5.82 ± 0.65 g/ 100 g (g fat/g dry matter).
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2.2 Marinating
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The Vc and TP (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China)were
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dissolved in cold distilled water (4 oC). The fish slices (50 g) were marinated in 100
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mL solution of the Vc (0.2 g/100 mL and 0.4 g/100 mL) or TP (0.1 g/100 mL and 0.2
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g/100 mL) for 2 h. The marinated fish slices were placed on a stainless steel wire
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mesh for 10 min before drying.
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2.3 Microwave–vacuum drying and microwave drying The lab scale MV dryer in which the materials to be dried can be rotated in the
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cavity was developed by Cui et al. (2003, 2004) and described in details elsewhere
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(Cui et al., 2003, 2004). The rotation speed of the turntable was 5 rpm. The MV dryer
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could be operated without applied vacuum for microwave-only drying. The standard
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procedure described by Cui et al. (2003) was used to determine the power output. In
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the current study, the set power outputs of the microwave dryer were H (460.5±1.5 W),
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HM (350.0±2.0 W), M (210.3±2.3 W), ML (122.1±3.1 W) and L (52.3±2.0 W).
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2.4 Drying procedure
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Fish slices (about 10 g samples) were spread in a single layer in a dish made of
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tetrafluoroethylene and subjected to various experimental conditions: (1) The hot air
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drying was conducted in an oven (Model 101-2-BS, Shanghai Yuejin Medical
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Instrument Co. Ltd., Shanghai, China) at 60 and 90 oC for 6 and 4 h, respectively; (2)
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For microwave drying, the fish slices were heated at microwave power output of H
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(460.5±1.5 W), HM (350.0±2.0 W), M (210.3±2.3 W), ML (122.1±3.1 W) and L
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(52.3±2.0 W) for 7 min, 10 min, 10 min, 16 min and 40 min, respectively; (3) For MV
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drying, the fish slices were heated at constant microwave power output of HM
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(350.0±2.0 W) for 7 min at vacuum of 0.02 MPa, 0.04 MPa and 0.06 MPa,
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respectively; (4) For marinated fish slices, they were heated at microwave power
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output of HM (350.0±2.0 W) for 10 min without vacuum applied.
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then weighed by electronic balance, continuous drying experiment on similar weight
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was conducted to examine the effect of this interruption during drying on weight loss
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and it was found the effect was negligible (Cui et al., 2003, 2004). The temperatures
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of the fish slices during drying were monitored by a digital probe-like thermometer
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(Model XMD-16, Automatic equipment Ltd. Co., Shanghai, China).
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The moisture of the dried sample at the end of every drying period was calculated
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from dry weight determined by drying at 105 oC to constant weight. Three replicates
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were carried out for each experiment, and the mean value of moisture content at each
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experimental point were determined. The raw samples were described as RAW; the
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hot air-dried samples were described as HAD; the microwave dried samples were
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described as MD; the MV dried samples were described as MVD.
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2.5 Modeling drying data
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The empirical Page’s model Eq. (1) and exponential model Eq. (2) (Giri, Prasad.
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2007) have been used to describe the drying kinetics of various agricultural materials
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in convective and microwave-convective drying, thus these two models were used to
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describe the drying kinetics of silver carp slices:
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r = A*exp (-kt n),
(1)
r = A*exp (-Kt),
(2)
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Where r = sample moisture content (g water/g dry matter) at time t; and t = drying
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time in min, A = initial moisture content (g water/g dry matter), K = drying rate
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constant (min-1), k and n is the parameter of empirical Page’s model.
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ACCEPTED MANUSCRIPT The parameters K, k and n of the above equations were evaluated through
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non-linear regression analysis using computer program (Origin 7.0, Origin Lab
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Corporation, USA). The goodness of fit of the tested mathematical model to the
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experimental data was evaluated from the coefficient of determination (R2). The
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higher the R2 -value, the better is the goodness of fit.
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2.6 Determination of thiobarbituric acid reactive substance (TBARS)
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The TBARS was assessed according to the method of Richards & Hultin (2000).
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Solution of trichloroacetic acid-thiobarbituric acid (TCA-TBA) (dissolve 15g TCA
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and 1.3g TBA in 100ml water) (Sinopharm Chemical Reagent Co., Ltd., Shanghai,
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China) was heated at 95 oC for 10 min on the day of use to dissolve the TBA.
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Approximately 300 mg of sample was added to 2.2 mL of the TCA-TBA mixture and
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incubated for 1 h at 65 oC. After centrifugation (5000×g for 10 min) (SIGMA 4K-15,
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Germany), the absorbance at 532 nm (UV-1800, Shimadzu, Japan) of the supernatant
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was determined. A standard curve was constructed using malondialdehyde (MDA),
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and results are expressed as micrograms of MDA equivalents per kilogram of dried
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matter. All experiments were run in triplicates.
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2.7 Sensory evaluation
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Five trained panelists (aged from 23 to 35, 2 male and 3 female) sniffed the
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samples, using a scale of 0-9 to value the odours, with 9 being the strongest (Richards
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& Hultin, 2000). The average value was defined as the final score. In the training
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sessions assessors smelt the samples, discussing among themselves the best
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descriptions and agreeing on the meaning of their elected descriptors (Table 1).
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2.8 Determination of fatty acids About 4 g of each sample was homogenized for lipid extraction (Siddaiah et al.,
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2001). Extracted oil were analyzed for methyl esters of fatty acids by gas
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chromatography (Agilent 6890, Agilent, Santa Clara, USA) on a capillary column (HP
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1, Agilent, Santa Clara, USA) according to the method of Wu & Mao (2008).
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Retention time and peak areas were recorded with the help of a microcomputer.
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2.9 Determination of geosmin (GEO) and methylisoborneol (MIB)
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The earthy-musty off-odour compounds, and were extracted according to the
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method of Lloyd & Grimm (1999), using microwave mediated distillation and
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solid-phase
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Spectrometer (GC/MS) analysis. Gas chromatograph grade GEO and MIB (Sigma
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Aldrich Co. Ltd, St. Louis, USA) were used as external standards.
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The microwave mediated distillation apparatus were made according to Lloyd &
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Grimm (1999). The microwave oven used was a CEM (Matthews, NC, USA) Model
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300. The distillation was done at microwave power of 350 W for 10 min; the flow rate
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of N2 was 80 mL/min. The liquid distillate was collected in a 10 mL glass vial. SPME
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fiber used was divinylbenzene/Carboxen/poly (dimethylsiloxane) (Supelco, PA, USA),
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and the extraction conditions were: 60 oC, 30 min. GC-MS was carried out in a gas
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chromatography system (TRACE MS, Finnigan, USA), using the PEG-20M capillary
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column (30 m×0.25 mm×0.25 um). The ion trap was operated in the electron impact
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(EI) ionization mode with a filament current of 10 mA and a mass scan range of 60 to
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250 daltons.
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2.10 Statistical analysis Data represent the mean and standard deviation from two or three independent
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experiments. Statistical significance of data was determined by using analysis of
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variance, using the SAS program, version 6.0 (SAS Institute Inc., Cary, N.C., U.S.A.).
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3 Results
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3.1 Drying kinetics of silver carp slices
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The drying curves for silver carp slices under hot-air drying, microwave drying and
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MV drying conditions are shown in Fig.1, Fig.2 A, and Fig.3 A respectively. The
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drying kinetics was dependent on the method and parameters (temperature, power
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intensity, and pressure). Silver carp slices having 80.5 ± 0.5 g/19.5 ± 0.5 g (g water/g
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dry matter) (r = 4.13 ± 0.13) initial moisture content were dried to a final moisture
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content of 20 g/80 g (r = 0.25, China aquatic product standard of dried fish fillet,
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SC/T 3203-2001, 2001) within 8.5 min by the microwave drying at power intensity
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HM (350.0±2.0 W) (Fig. 2A). And it took about 6 min for MV drying at the power
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intensity HM, at vacuum of 0.06 MPa (Fig. 3A). By comparison, for convective
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hot-air drying, it took about 165 min at 90 oC (Fig. 1), thus, the MV drying time at
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HM power intensity and vacuum of 0.06 MPa was around 94.8% shorter than the
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convective air drying (90 oC) time.
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The temperatures of the fish slices during microwave and MV drying are shown in
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figure 2 B and figure 3 B, respectively. The power intensity had considerable effect on
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the temperature of the fish slices during microwave drying (Fig. 2 B). At L power
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output, the temperature reached 77 oC in 5 min and then remained about 75 oC for 15
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the temperature reached 75 oC in 3 min and then remained about 75 oC until 10 min,
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followed by decreasing to about 60 oC in the last 5 min. At the power outputs of M,
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HM, and H, the temperature reached 78 oC in 1.5 min, and then decreased to about 60
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C in the followed stage.
The pressure had considerable effect on the temperatures of the fish slices during
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MV drying (Fig. 3 B). At vacuum of 0.02 MPa, the temperature increased to 55 oC in
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1.5 min, and then increased slowly to about 60 oC until the end (7 min) of the drying
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procedure. At vacuum of 0.04 and 0.06 MPa, the temperature increased to 50 and 44
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o
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drying procedure, respectively. Therefore, at the HM power intensity, the temperature
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of fish slices during microwave drying was higher than that of MV drying.
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Table 2 lists the model constants obtained by application of Empirical Page’s
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equation and Exponential equation to the experimental drying data. The Exponential
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models give better fit for the drying data under all conditions tested with higher R2
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values (>0.99).
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3.2 Lipid oxidation of silver carp during drying
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The results of TBARS are shown in table 3. The lipid oxidation during microwave
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and MV drying was milder than that of hot air drying, significantly (P < 0.05). The
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TBARS was decreased with the increasing of power intensity during the microwave
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drying. However, it is surprising that the TBARS increased with the decreasing
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pressure during the MV drying. At the same power intensity of HM, the fish slices
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ACCEPTED MANUSCRIPT dried by MV had higher TBARS, especially at vacuum of 0.04 MPa and 0.06 MPa,
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thus, the vacuum did not protect the lipid from oxidation. The fish slices dried by
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microwave at HM or H power intensity and the samples dried by MV at HM power
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intensity and vacuum of 0.02 MPa had the lowest TBARS. Take the energy
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consumption into account, the microwave drying at HM power intensity is the
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economic method to dry the silver carp slices, with the least TBARS.
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3.3 Effect of antioxidants on the lipid oxidation during microwave drying
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Because the vacuum did not protect the lipid from oxidation, the effect of
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antioxidants on the lipid oxidation of fish slices was only investigated during
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microwave drying at the power intensity of HM. The lipid oxidation was considerably
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inhibited by marinating with Vc and TP (Fig. 4). The final TBARS were decreased
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with the increasing of Vc and TP. The microwave dried fish slices (MD) pretreated
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with TP (0.2 g/ 100 mL) achieved the lowest TBARS (0.73 mg/kg).
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3.4 Effect of drying method and antioxidants on the content of fat, EPA and DHA
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After drying, there was a significant decrease in fat content that was revealed by the
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data expressed on a dry matter basis (P < 0.05) (Table 4). Microwave dried slices
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(MD) retained a higher fat content than hot air (HAD) and MV (MVD) dried samples
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(P < 0.05). All drying processes largely decreased the relative contents of EPA and
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DHA in silver carp slices (P < 0.05). The Vc and TP protected the EPA and DHA
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effectively. The MD added TP (0.2 g/ 100 mL) showed the highest level of EPA (5.42
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g/100 g fat) and DHA (4.36 g/100 g fat) (Table 4).
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3.5 Effect of drying method and antioxidants on the flavor of dried silver carp slices
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ACCEPTED MANUSCRIPT The odour scores of raw and dried samples are presented in table 5. Drying
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increased the oxidized oil odour except for microwave dried samples (MD) with a TP
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pretreatment. The MVD received the highest score of oxidized oil odour. However,
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drying decreased the fishy odour evidently; there was no fishy odour present in the
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fish slices treated with TP, especially. Furthermore, drying produced grilled protein
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flavor. The grilled protein flavor scores of HAD (8.4) and MD (7.1) were higher than
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MVD (5.3) (Table 5). However, the TP treatments inhibited the increase of grilled
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protein flavor. The earthy-musty odour was removed slightly by drying treatments.
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The marinating with Vc evidently decreased the scores of earthy-musty odour (from
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4.5 to 0.4, Table 5).
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3.6 The content of earthy-musty compounds
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Quantitative information of MIB and GEO from the integrated peak areas using
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external standard plots is shown in Table 6. The result revealed the concentration of
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the off-odour compounds at 2.31±0.25 ug/kg MIB and 1.29 ± 0.15 ug/kg GEO for
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RAW (raw fish). The treatment of Vc (0.4 g/ 100 mL) combined with microwave
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drying reduced about MIB to 0.73 ± 0.12 ug/kg (70% reduction) and GEO to 0.57 ±
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0.08 ug/kg (50% reduction).
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4 Discussions
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4.1 Drying kinetics of silver carp slices
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Various transport properties like moisture and thermal diffusivity and mass and heat
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transfer coefficients, describe well the mechanisms involved in drying. A good
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agreement was found between the experimental and fitted values with high R2-values
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seen that the drying constant K-values of microwave and MV drying were higher than
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hot-air drying. In microwave drying, K-value was found to increase with the
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increasing power, while in MV drying, K-value was found to increase with the
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decreasing pressure. And in hot air drying, the K-value was found to increase as the
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temperature was increased. This can be attributed to the fact that higher temperature,
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higher microwave power and lower pressure, help in increasing the driving force of
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heat and mass transfer.
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4.2 Lipid oxidation
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Thermal oxidation is one of the greatest threats to unsaturated fatty acids in foods.
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The EPA and DHA are especially susceptible to oxidation. The oxidations of
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unsaturated fat acids are catalysed by heat, light, trace metals or enzymes and involve
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free radical generation. Free radicals propagate autooxidation by reacting with oxygen
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to form hydroperoxides, which breakdown to generate other new free radicals (Weber,
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Bochi, Ribeiro, Victorio & Emanuelli, 2008) and TBARS (Stewart, Raghavan, Orsat
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& Golden, 2003).
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High temperatures accompanying drying processes could speed up the breakdown
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of peroxides into their carbonyl components, thus the TBARS of the dried fish slices
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was higher at 90 oC than 60 oC during hot air drying (Table 3). The temperature of
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samples during microwave and MV drying were lower than that of hot air drying (Fig.
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2B, Fig. 3B), thus, the slices dried by microwave and MV obtained lower TBARS.
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However, the temperature in microwave drying (Fig. 2 B) was higher than that of
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ACCEPTED MANUSCRIPT MV drying at vacuum of 0.04 MPa and 0.06 MPa (Fig. 3 B) for the same power
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intensity (HM), while the TBARS of the former were lower (Table 3). And it is very
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surprising that the TBARS increased with the increasing vacuum during the MV
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drying. It looks likely that fat exuded to the surface with the moisture evaporation in
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the low pressure condition of MV drying, which enhanced the contact of fat and
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oxygen, and promoted the lipid oxidation. On the other hand, the pro-oxidative
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components such as lipoxygenase and hemoglubin proteins were likely to keep their
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activity at the low temperature of MV drying (Fig. 3B). In contrast, the lipoxygenase
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and hemoglubin proteins should be denatured at the higher temperatures of hot air and
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microwave drying (Turhan, Ustun & Altunkaynak, 2004).
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The antioxidants, Vc and TP, exhibited a good ability of anti-oxidation (Fig. 4).
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This is explained by the fact that Vc and TP have potent free radical quenching
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activity. The TP has been used to inhibit the increase of TBARS of silver carp fillets
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during ice storage, after approximately 35 days of iced storage, the final TBARS was
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0.85 mg /kg, while the samples without TP had 3.09 mg/kg TBARS (Fan et al., 2008).
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In the present study, the microwave dried fish slices (MD) pretreated with TP (0.2 g/
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100 mL) achieve the lowest TBARS of 0.73 mg/kg (Fig. 4), that is of great practical
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importance, provides a possible application of microwave drying as an efficient
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drying process for fish slices.
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4.3 Content of fat acids, EPA and DHA
AC C
EP
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323
333
Drying decreased the content of fat, EPA and DHA. Microwave dried slices (MD)
334
retained higher content of fat, EPA and DHA than hot air (HAD) and microwave
16
ACCEPTED MANUSCRIPT 335
vacuum (MVD) dried samples (P < 0.05) (Table 4). Similar results were achieved by
336
other researchers (Stewart et al., 2003) for soybean. Weber et al. (2008) also observed
337
cooking led to a lower fat loss, when compared to the raw silver catfish. The loss of volatile free fat acids probably occurred during heating, leading to a
339
decreased fat content. Furthermore, fat may exude with the moisture evaporation. The
340
extended heating treatment during hot air drying and low pressure in the MV drying
341
seems to enhance this phenomenon. On the other hand, oxidation is another way the
342
fat is lost. According to the results of lipid oxidation (Table 3 and Fig. 4), the fat lose
343
is in accordance with increased lipid oxidation, except in the case of MD samples
344
treated with Vc, which retained the lowest content of fat (Table 3) while limiting lipid
345
oxidation, since part of fat was lost in the marinating stage (data not shown).
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The TP protected the EPA and DHA effectively may be due to the TP inhibit the
347
lipid oxidation (Fig. 4), with its structural features that may specifically interfere with
348
the unsaturated fat acid cascade (Banerjee, 2006).
349
4.4 Flavor of dried silver carp slices
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346
Cooking methods have significant effect on the flavor of foods. The grilled protein
351
flavor is the favored aroma. The HAD (8.4) and MD (7.1) fish samples received
352
higher score of grilled protein flavor than MVD (5.3) (Table 5) which may due to the
353
high temperature during hot air drying and microwave drying (Fig. 2 B), since the
354
products of Millard reaction occur at high temperatures and they have been shown to
355
contribute to a “meat-like” flavor (Weber et al., 2008).
356
AC C
350
The ‘oxidated oil’ and ‘fishy’ odour notes are caused by aldehydes and ketones,
17
ACCEPTED MANUSCRIPT which are the products of lipid oxidation; and there is a significantly positively
358
relationship between TBARS and off-odour in silver carp (Siddaiah et al., 2001). Two
359
mg TBARS/kg is usually regarded as the limit beyond which the fish will normally
360
develop an objectionable odour (Fan et al., 2008). The MVD (dried at HM power
361
intensity and vacuum of 0.06 MPa) received high score of fishy and oxidated oil
362
odour, due to its severe lipid oxidation (TBARS 2.735 mg/kg, Table 3). In contrast,
363
the Vc and TP treatments reduced the fishy and oxidated oil off-odour because they
364
effectively protected the lipid from oxidation (TBARS<1.5 mg/kg, Fig. 4).
365
4.5 Earthy–musty odour
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Earthy–musty odour in fresh water-farmed fish represents one of the most
367
significant economic problems encountered in aquaculture. It is suggested that
368
differences between acceptability of silver carp from different ponds may be due to
369
earthy-musty off-odour resulting from the presence of GEO and MIB in the pond
370
environment, when either compound is present in tissue at concentrations exceeding
371
0.7 ug/kg, they render fish unfit for retail sale (Andelkovic, Aleksic & Baltic, 2001).
372
Attempts to mask harvested tainted fish with chemical treatments, various cooking
373
methods and flavourings have achieved limited success (Yamprayoon & Noomhorm,
374
2000).
EP
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TE D
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After drying, these undesirable odorous compounds were partially removed, but
376
slight taint still existed (Table 6). Because GEO and MIB are lipophilic compounds,
377
and fish have fat, their removal is very difficult.
378
The treatment of Vc (0.4 g/100 mL) combined with microwave drying reduced
18
ACCEPTED MANUSCRIPT about 70% MIB and 50% GEO (Table 6). Yamprayoon & Noomhorm (2000) reported
380
that marinating tilapia in acetic acid solution resulted in decreased earthy-musty odour,
381
partly because the acid enhances the desorbing of MIB and GEO from the muscle
382
proteins, partly because the acid marinating treatment remove considerable fat from
383
the muscle, so the fat-soluble MIB and GEO were removed too. The Vc is an acidic
384
substance (ascorbic acid) which may play a similar role as acetic acid in removing the
385
earthy-musty odour compounds of silver carp slices.
386
5 Conclusions
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The MV drying caused severe lipid oxidation and oxidized off-odours while on the
388
other hand the microwave drying could reduce the drying time, avoid lipid oxidation.
389
The marinating with Vc and TP significantly inhibited the lipid oxidation during
390
drying. Samples treated with TP (0.2 g/ 100 mL) retained the most of DHA and EPA
391
while preventing the production of fishy off-odours. A large part of the earthy-musty
392
off-odour compounds were removed by marinating with Vc (0.4 g/100 mL) combined
393
with microwave drying.
394
Reference
396 397 398 399 400
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TE D
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Andelkovic R., Aleksic J. & Baltic M. (2001). The investigation of the acceptability of carp and silver carp meat from different ponds. Tehnologija Mesa, 42, 33-38. Anonymous. (2013). The fishery yearbook of china, China Agricultural Press, 31.
Banerjee S. (2006) Inhibition of mackerel (Scomber scombrus) muscle lipoxygenase by green tea polyphenols. Food Research International, 39, 486-491. Barrera A. M., Ramirez J. A., Gonzalez C. J. J. & Vazquez M. (2002). Effect of
19
ACCEPTED MANUSCRIPT 401
pectins on the gelling properties of surimi from silver carp. Food hydrocolloid, 16,
402
441-447.
404 405 406
Cui Z. W., Xu S. Y. & Sun D. W. (2003). Dehydration of garlic slices by combined microwave–vacuum and air drying. Drying Technology, 21(7), 1173–1185.
RI PT
403
Cui Z. W., Xu S. Y. & Sun D. W. (2004). Microwave–vacuum drying kinetics of carrot slices. Journal of Food Engineering, 65, 157–164.
Fan W. J., Chi Y. L. & Zhang S. (2008). The use of a tea polyphenol dip to extend
408
the shelf life of silver carp (Hypophthalmicthys molitrix) during storage in ice. Food
409
Chemistry, 108, 148–153.
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407
410
Giri S. K. & Prasad S. (2007). Drying kinetics and rehydration characteristics of
411
microwave-vacuum and convective hot-air dried mushrooms. Journal of Food
412
Engineering, 78, 512
TE D
521.
Lloyd S. W. & Grimm C. C. (1999). Analysis of 2-methylisoborneol and geosmin in
414
catfish by microwave distillation-solid-phase microextraction. Journal of Agricultural
415
& Food Chemistry, 47, 164-169.
417
Mistry B. S. & Min D. B. (1997). Proxidant effects of monoglycerols and
AC C
416
EP
413
diglycerols in soybean oil. Journal of Food science, 53, 1896-1897.
418
Richards M. P. & Hultin H. O. (2000). Effect of pH on lipid oxidation using trout
419
hemolysate as a catalyst: a possible role for deoxyhemoglobins. Journal of
420
Agricultural & Food Chemistry, 48, 3141-3147.
421 422
SC/T 3203-2001. (2001). China aquatic product standard: Dried seasoned fish fillet (2nd ed.). Beijing: Ministry of Agriculture of the People’s Republic of China.
20
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Siddaiah D., Reddy G. V. S., Raju C. V. & Chandrasekhar T. C. (2001). Changes in
424
lipids, proteins and kamaboko forming ability of silver carp (Hypophthalmichthys
425
molitrix) mince during frozen storage. Food Research International, 34 (1), 47-53. Stewart O. J., Raghavan G. S.V., Orsat V. & Golden K.D. (2003). The effect of
427
drying on unsaturated fatty acids and trypsin inhibitor activity in soybean. Process
428
Biochemistry, 39, 483-489.
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Turhan S., Ustun N. S. & Altunkaynak T. B. (2004). Effect of cooking methods on
430
total and heme iron contents of anchovy (Engraulis encrasicholus). Food Chemistry,
431
88, 169–172.
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Weber J., Bochi V. C., Ribeiro C. P., Victorio A. de M. & Emanuelli T. (2008).
433
Effect of different cooking methods on the oxidation, proximate and fatty acid
434
composition of silver catfish (Rhamdia quelen) fillets. Food Chemistry, 106, 140–146.
435
Wu T. & Mao L. (2008). Influences of hot air drying and microwave drying on
436
nutritional and odorous properties of grass carp (Ctenopharyngodon idellus) fillets,
437
Food Chemistry, 110, 647-653.
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Yamprayoon J. & Noomhorm A. (2000). Effects of preservation methods on
439
geosmin content and off-flavor in Nile tilapia (Oreochromis niloticus). Journal of
440
Aquatic Food Product Technology, 9(4), 95-107.
441
AC C
438
Zhang J., Zhang M., Shan L. & Fang Z. (2007). Microwave-vacuum heating
442
parameters for processing savory crisp bighead carp (Hypophthalmichthys nobilis)
443
slices. Journal of Food Engineering, 79, 885
891.
21
ACCEPTED MANUSCRIPT Table 1 Descriptors used in the sensory evaluation Oxidated oil
Odour associated with rancid pork fat
Fishy
Odour associated with the chopped silver carp mince stand at 25 C for 0.5 h
Earthy/musty
Odour associated with mud
Grilled protein
Odour associated with grilled fish meat
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ACCEPTED MANUSCRIPT Table 2 Model constants of Logarithmic equation and Exponential equation Exponential equation
Page’s equation k
R2
K
R2 0.992
0.005
1.027
0.979
0.006
Hot air (90 oC)
0.012
1.026
0.929
0.014
0.995
Microwave (La)
0.052
0.971
0.989
0.049
0.992
Microwave (ML)
0.187
0.867
0.989
0.146
0.990
Microwave (M)
0.208
1.041
0.996
0.225
0.993
Microwave (HM)
0.321
Microwave (H)
0.443
MVb (HM, 0.02 MPa)
0.325
MV (HM, 0.04 MPa)
0.350
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0.987
0.334
0.997
1.085
0.983
0.516
0.997
1.027
0.998
0.340
0.999
1.123
0.998
0.355
0.999
0.997
0.409
0.999
TE D 0.382
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Hot air (60 oC)
MV (HM, 0.06 MPa) a
n
0.929
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The power intensity of microwave: H, 460.5±1.5 W; HM, 350.0±2.0 W; M, 210.3±2.3 W; ML, 122.1±3.1 W; and L, 52.3±2.0 W. b MV: Microwave-vacuum drying.
ACCEPTED MANUSCRIPT
Table 3 Effect of drying method on the Lipid oxidation of dried silver carp Temperature or Drying method
Vacuum (M Pa)
TBARS (mg/kg)
\
90 oC
\
Lc
\
ML
\
M HM H
a
HM
4.990 ± 0.169G 3.025 ± 0.130E
2.527 ± 0.118 D
\
2.120 ± 0.080C
\
1.375 ± 0.152A
\
1.273 ± 0.115A
0.02
1.450 ± 0.052A
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MV b
4.534 ± 0.112F
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Microwave a
60 oC
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Hot air
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Power intensity
0.04
1.797 ± 0.044B
0.06
2.735 ± 0.247D
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The drying time at L, ML, M, HM, H power intensity were 40, 16, 10, 10, 7 min, respectively. b Microwave-vacuum drying at HM for 7 min. c The power intensity of microwave: H, 460.5±1.5 W; HM, 350.0±2.0 W; M, 210.3±2.3 W; ML, 122.1±3.1 W; and L, 52.3±2.0 W. A-G Means in column having different superscript letters are significantly different (P< 0.05) (n=3).
ACCEPTED MANUSCRIPT Table 4 Fat, EPA and DHA of dried silver carp slices
EPA
DHA
matter)
(g/100g fat)
(g/100g fat)
RAWA
5.82 ±0.65a
5.08± 0.09b
3.87± 0.08b
HADB
4.58 ±0.16c
4.05±0.08d
2.61±0.05c
MVDC
4.65 ±0.12c
4.09± 0.17d
2.75± 0.15c
MDD
5.14±0.10b
4.12± 0.09d
2.96± 0.14c
Vc 0.2 g/100 mL
4.10±0.16d
4.65± 0.05c
3.62± 0.21b
Vc 0.4 g/100 mL
4.15±0.14d
4.98± 0.15b
3.78±0.11b
TP 0.1 g/100 mL
4.78±0.15c
4.80±0.14b
3.85± 0.08b
TP 0.2 g/100 mL
4.65±0.08c
5.42± 0.11a
4.36± 0.13a
A
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Fat (g/100g dry
Raw fish slices. Fish slices were dried by hot air at 90 oC for 2.5 h. C Fish slices were dried by microwave-vacuum at HM (power intensity, 350.0±2.0 W) and vacuum 0.06 Mpa for 7 min. D Fish slices were dried by microwave at HM (power intensity, 350.0±2.0 W) for 10 min. E Fish slices were marinated in Vc or TP solution for 2 h, followed by being dried by microwave at power intensity of HM (350.0±2.0 W) for 10 min. Vc: Vitamin C; TP: Tea polyphenols. a-d Means in each column having different superscript letters are significantly different (P< 0.05) (n=2).
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ACCEPTED MANUSCRIPT Table 5 Effect of drying method and antioxidants on the odour of silver carp slices Fishy
Oxidated oil Earthy-musty Grilled protein
5.0
1.0
4.5
0
HADb
2.2
3.8
3.8
8.4
MVDc
3.0
4.0
3.6
5.3
MDd
2.6
3.7
1.9
7.1
Vc 0.2 g/100 mL
2.3
2.4
1.1
6.2
Vc 0.4 g/100 mL
1.2
1.2
0.4
6.9
TP 0.1 g/100 mL
0
TP 0.2 g/100 mL
0
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MD
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RAWa
1.0
1.6
3.5
0.5
1.5
3.4
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The odour was valued using a scale of 0-9, with 9 being the strongest. a Raw fish slices. b Fish slices dried by hot air at 90 oC for 2.5 h. c Fish slices dried by microwave-vacuum at HM (power intensity, 350.0±2.0 W) and vacuum 0.06 Mpa for 7 min. d Fish slices dried by microwave at HM (power intensity, 350.0±2.0 W) for 10 min. e Fish slices were marinated in Vc or TP solution for 2 h, followed by being dried by microwave at power intensity of HM (350.0±2.0 W) for 10 min. Vc: Vitamin C; TP: Tea polyphenols.
ACCEPTED MANUSCRIPT Table 6 The effect of drying method and pretreatment with Vc on the content of earthy-musty compounds MIB and GEO (ug/kg) GEO
RAWa
2.31±0.25A
1.29±0.15A
MDb
2.62±0.20A
MDc (Vc 0.4 g/100 mL)
0.73±0.12B
a
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MIB
0.85±0.11B
0.57±0.08C
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Raw fish slices. Fish slices dried by microwave at power intensity of HM (350.0±2.0 W) for 10 min, c Fish slices were marinated in Vc solution (0.4 g/100 mL) for 2 h, followed being dried by microwave at power intensity of HM (350.0±2.0 W) for 10 min. Vc: Vitamin C. A-C Means in each column having different superscript letters are significantly different (P< 0.05) (n=2).
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b
ACCEPTED MANUSCRIPT 1
Captions
2
Figure 1 Kinetics of hot air drying at 60 oC (●) and 90 oC (■). (r: moisture content, g
3
water/g dry matter), (n=3).
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Figure 2 Effect of power intensity on the drying kinetics of microwave drying (■ L,
6
52.3±2.0 W; ○ML, 122.1±3.1 W; ▲ M, 210.3±2.3 W; ▼HM, 350.0±2.0 W; □ H,
7
460.5±1.5 W) , (n=3).
8
A: The r of the samples during drying (r: moisture content, g water/g dry matter)
9
B: The temperature of the samples during drying
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10
Figure 3 Effect of vacuum degree on the drying kinetics of microwave-vacuum
12
drying at power intensity of HM (350.0±2.0 W), (■ 0.02 MPa; ○ 0.04 MPa; ▲ 0.06
13
MPa), (n=3).
14
A: The r of the samples during drying (r: moisture content, g water/g dry matter)
15
B: The temperature of the samples during drying
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17
Figure 4 Effect of antioxidants on the lipid oxidation of silver carp slices during
18
microwave drying (■ control;
19
g/100 mL; △ TP, 0.2 g/100 mL) (n=3).
20
(Fish slices were marinated in Vc or TP solution for 2 h, followed by being dried by
21
microwave at power intensity of HM (350.0±2.0 W) for 10 min. Vc: Vitamin C; TP:
22
Tea polyphenols)
23
●
Vc, 0.2 g/100 mL; ○ Vc, 0.4 g/100 mL; ▲TP, 0.1
ACCEPTED MANUSCRIPT 24 25
Figure 1
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4 3
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r
2
0 0
1
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1
2
3
Time (h)
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27
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26
4
5
6
ACCEPTED MANUSCRIPT 29
Figure 2
4
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r
3 2
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1
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0 0
10
20
30
40
Time (min)
30
A
31
60
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Temperature ( C)
70
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80
50
AC C
40 30 20
0
10
20 Time (min)
32 33 34
B
30
40
ACCEPTED MANUSCRIPT 35
Figure 3
4
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r
3 2
SC
1
-1
0
1
M AN U
0 2
3
4
5
6
7
8
Time (min)
36
A
70
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AC C
Temperature (C)
60
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37
40 30 20
0
2
4 Time (min)
38 39 40
B
6
8
ACCEPTED MANUSCRIPT 41 42
Figure 4
43
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2.5
SC
1.5 1.0 0.5 0.0
2
4
6
EP
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Time (min)
AC C
44
0
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TBARS (mg/kg)
2.0
8
10
ACCEPTED MANUSCRIPT 1. Microwave dried fish slices retained more fat, EPA and DHA. Tea polyphenols (TP) treated fish slices retained the most of DHA and EPA, achieved non-fishy products. 2. The thiobarbituric acid reactive substance (TBARS) of dried fish slices
vacuum during microwave-vacuum drying.
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decreased with power intensity during microwave drying but increased with the
3. Marinating with Vc combined with microwave drying removed the
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earthy-musty off-odour effectively.
S0023-6438(14)00670-7
DOI:
10.1016/j.lwt.2014.10.035
Reference:
YFSTL 4233
To appear in:
LWT - Food Science and Technology
Received Date: 12 October 2009 Revised Date:
2 August 2014
Accepted Date: 14 October 2014
Please cite this article as: Fu, X., Lin, Q., Xu, S., Wang, Z., Effect of drying methods and antioxidants on the flavor and lipid oxidation of silver carp slices, LWT - Food Science and Technology (2014), doi: 10.1016/j.lwt.2014.10.035. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Effect of Drying methods and Antioxidants on the Flavor and Lipid
2
Oxidation of Silver Carp Slices
3
Xiangjin Fu1,2, Qinglu Lin1, Shiying Xu2,3 *,Zhang Wang2,3
4 5 6
1 School of Food Science and Technology, Central south University of forestry and technology. Changsha 410004, PR China
7
2 State key laboratory of food science and safety. Jiangnan University. Wu Xi 214122, PR China 1
8
3 School of Food Science and Technology, Jiangnan University. Wu Xi 214122, PR China
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Running title: Effect of Drying and Antioxidants on the Quality of Silver Carp Slices
18
Author E-mail address: [email protected]
19 20
*Corresponding author address: Tel 086-0510-85884496, Fax 086-0510-85884496, E-mail: [email protected]
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ACCEPTED MANUSCRIPT 22
Abstract Silver carp slices were dried using hot air, microwave, and microwave-vacuum
24
(MV). The drying kinetics, lipid oxidation, flavor, and content of fat, eicosapentaenoic
25
acid (EPA), docosahexaenoic acid (DHA), and earthy-musty off-odour compounds
26
were compared among the dried slices. Furthermore, the effect of vitamin C (Vc) and
27
tea polyphenols (TP) on the microwave-dried fish slices was investigated. The
28
Exponential models gave good fit for the drying data. Compared with hot air drying,
29
microwave and MV drying reduced the drying time drastically. Drying removed part
30
of the fishy off-odour, produced grilled flavor and “Oxidated oil” off-odour. Hot air
31
dried fish slices had better grilled flavor. The TP restrict the formation of fishy and
32
“Oxidated oil” off-odours effectively. Microwave drying removed a large part of
33
“Earthy-musty” off-odour, and marinating with Vc or TP help to remove this
34
off-odour. The slices dried with microwave or MV had less thiobarbituric acid
35
reactive substance (TBARS). The TBARS decreased with power intensity during
36
microwave drying but increased with the vacuum during MV drying. All drying
37
processes largely decreased the contents of fat, EPA and DHA (P < 0.05). Microwave
38
drying retained more fat (P < 0.05). The Vc and TP protected the EPA and DHA
39
effectively.
40
Key words: Microwave drying; microwave-vacuum drying; drying kinetics; Lipid
41
oxidation; Flavor
42
Chemical compounds studied in this article
43
Vitamin C (Pub Chem CID: 5785); Tea polyphenols (Pub Chem CID: 65064);
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2
ACCEPTED MANUSCRIPT Trichloroacetic acid (Pub Chem CID: 6421); Thiobarbituric acid (Pub Chem CID:
45
2723628); Eicosapentaenoic acid (Pub Chem CID: 446284); Docosahexaenoic acid
46
(Pub Chem CID: 445580); Geosmin (Pub Chem CID: 29746); 2-Methylisoborneol
47
(Pub Chem CID: 16913)
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3
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1. Introduction Silver carp (Hypophthalmichthys molitrix) is widely raised in China, India and
51
Mexico, due to its quick growth and resistance to stress, diseases and rough handling
52
(Siddaiah, Raju & Chandrasekhar, 2001; Barrera, Ramirez, Gonzalez & Vazquez,
53
2002). It is a new resource for fish products, due to its huge stock (statistical data
54
show that 3,687,751 tons were caught in China in 2012 (Anonymous, 2013), excellent
55
white color, low market price, high quality nutritious protein (15~18 g / 100 g) and
56
unsaturated fatty acids (Siddaiah et al., 2001; Barrera et al., 2002). However, the
57
silver carp is not particularly liked by consumers due to its fishy and earthy–musty
58
off-odour. The fishy odour has been attributed to the oxidation of lipid (Siddaiah et.
59
al., 2001), while the earthy–musty odour is caused by the semivolatile cyclic alcohols
60
geosmin (GEO) and 2-methylisoborneol (MIB) (Lloyd & Grimm, 1999).
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50
Initiation and propagation of lipid oxidation are catalyzed by exposure to oxygen,
62
exposure to light, the presence of pigments such as chlorophyll, riboflavin and hemo
63
proteins, the presence of metals, and the contact with lipoxygenase (Mistry & Min,
64
1997). When oxygen is present, unsaturated fatty acid decomposition occurs more
65
readily. These suggest low temperature, low oxygen and quick processing can help to
66
avoid the lipid oxidation. The microwave-vacuum (MV) heating technology not only
67
have the advantages of microwave heating (heating rapidly, high efficiency, good
68
controllable and sanitation) (Cui, Xu & Sun, 2003), but the lower boiling point of
69
water and less oxygen caused by the vacuum environment. It implies that MV may be
70
a suitable technology for drying silver carp. In fact, several reports have been focused
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4
ACCEPTED MANUSCRIPT on the drying of fish using microwave. During the drying of grass carp,
72
microwave-dried samples showed lower fat loss, less lipid oxidation than hot air-dried
73
samples (Wu & Mao, 2008). And there are numerous studies on the application of MV
74
drying to the fruits and vegetables, such as the carrot (Cui, Xu & Sun, 2003), garlic
75
(Cui, Xu & Sun, 2004), mushroom (Giri & Prasad, 2007). The dried products were
76
found to be more excellent in terms of taste, aroma and rehydration than products
77
dried by the hot-air method. Bighead carp (Hypo. nobilis) slices were also dried by
78
MV; the higher vacuum degree could enhance the puffing effect, and improve the
79
crispness of the fish slices (Zhang, Zhang, Shan & Fang, 2007). However, limited
80
literature is available about the effect of MV drying on the lipid oxidation of fish.
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Tea polyphenols (TP) have beneficial anti-oxidative activities, which demonstrate
82
potential for their use as anti-oxidants in food industry. Fan, Chi & Zhang (2008)
83
reported that TP dip treatment on silver carp lead to retention of the good quality
84
characteristics for longer and an extension of the shelf life during iced storage.
85
However, there have been few studies on the use of TP to protect the unsaturated fatty
86
acids and improve the flavor of silver carp during drying.
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Peroxide value defines the initial stage of the oxidative changes. However,
88
peroxides are unstable and decompose via fission, dehydration and the formation of
89
free radicals, to form a variety of chemical products, such as alcohols, aldehydes,
90
ketones, and acids compounds at elevated temperatures, and thus, peroxide value was
91
found to be a poor indicator for heated samples (Wu & Mao, 2008). Alternatively,
92
TBARS (thiobarbituric acid reactive substance) value could be reliable and
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ACCEPTED MANUSCRIPT meaningful for evaluating the fat quality of heated samples. And previous study
94
(Siddaiah et. al, 2001) found the significantly positively relationship between TBARS
95
and off-odour in silver carp, thus, the present study used TBARS to evaluate the
96
intensity of the lipid oxidation.
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The present work investigates the effect of drying methods (hot air, microwave, and
98
MV) on the drying kinetics, lipid oxidation, poly-unsaturated fatty acids (EPA and
99
DHA) and flavor of silver carp slices. And the treatments with TP and Vc (Vitamin C)
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were used to improve the quality of dried silver carp slices.
101
2. Materials and methods
102
2.1 Materials
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Fresh silver carps were purchased from local market. The silver carps were brought
104
to the laboratory on ice. The approximate weight of the individual fish was 1000 ± 50
105
g. Upon arrival to the laboratory the fish were washed, scaled, gutted, and filleted.
106
Before drying, the white muscle was collected and cut into slices of about 5×5×10–
107
mm by hands and their weight were determined by an electronic balance (Model
108
MP2000D, Shanghai Electronic Balance Instrument Co. Ltd., Shanghai, China). The
109
average moisture content of raw slices was 80.5 ± 0.5 g/ 19.5 ± 0.5 g (g water/g dry
110
matter) and fat content 5.82 ± 0.65 g/ 100 g (g fat/g dry matter).
111
2.2 Marinating
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The Vc and TP (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China)were
113
dissolved in cold distilled water (4 oC). The fish slices (50 g) were marinated in 100
114
mL solution of the Vc (0.2 g/100 mL and 0.4 g/100 mL) or TP (0.1 g/100 mL and 0.2
6
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g/100 mL) for 2 h. The marinated fish slices were placed on a stainless steel wire
116
mesh for 10 min before drying.
117
2.3 Microwave–vacuum drying and microwave drying The lab scale MV dryer in which the materials to be dried can be rotated in the
119
cavity was developed by Cui et al. (2003, 2004) and described in details elsewhere
120
(Cui et al., 2003, 2004). The rotation speed of the turntable was 5 rpm. The MV dryer
121
could be operated without applied vacuum for microwave-only drying. The standard
122
procedure described by Cui et al. (2003) was used to determine the power output. In
123
the current study, the set power outputs of the microwave dryer were H (460.5±1.5 W),
124
HM (350.0±2.0 W), M (210.3±2.3 W), ML (122.1±3.1 W) and L (52.3±2.0 W).
125
2.4 Drying procedure
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Fish slices (about 10 g samples) were spread in a single layer in a dish made of
127
tetrafluoroethylene and subjected to various experimental conditions: (1) The hot air
128
drying was conducted in an oven (Model 101-2-BS, Shanghai Yuejin Medical
129
Instrument Co. Ltd., Shanghai, China) at 60 and 90 oC for 6 and 4 h, respectively; (2)
130
For microwave drying, the fish slices were heated at microwave power output of H
131
(460.5±1.5 W), HM (350.0±2.0 W), M (210.3±2.3 W), ML (122.1±3.1 W) and L
132
(52.3±2.0 W) for 7 min, 10 min, 10 min, 16 min and 40 min, respectively; (3) For MV
133
drying, the fish slices were heated at constant microwave power output of HM
134
(350.0±2.0 W) for 7 min at vacuum of 0.02 MPa, 0.04 MPa and 0.06 MPa,
135
respectively; (4) For marinated fish slices, they were heated at microwave power
136
output of HM (350.0±2.0 W) for 10 min without vacuum applied.
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138
then weighed by electronic balance, continuous drying experiment on similar weight
139
was conducted to examine the effect of this interruption during drying on weight loss
140
and it was found the effect was negligible (Cui et al., 2003, 2004). The temperatures
141
of the fish slices during drying were monitored by a digital probe-like thermometer
142
(Model XMD-16, Automatic equipment Ltd. Co., Shanghai, China).
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The moisture of the dried sample at the end of every drying period was calculated
144
from dry weight determined by drying at 105 oC to constant weight. Three replicates
145
were carried out for each experiment, and the mean value of moisture content at each
146
experimental point were determined. The raw samples were described as RAW; the
147
hot air-dried samples were described as HAD; the microwave dried samples were
148
described as MD; the MV dried samples were described as MVD.
149
2.5 Modeling drying data
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The empirical Page’s model Eq. (1) and exponential model Eq. (2) (Giri, Prasad.
151
2007) have been used to describe the drying kinetics of various agricultural materials
152
in convective and microwave-convective drying, thus these two models were used to
153
describe the drying kinetics of silver carp slices:
155
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r = A*exp (-kt n),
(1)
r = A*exp (-Kt),
(2)
156
Where r = sample moisture content (g water/g dry matter) at time t; and t = drying
157
time in min, A = initial moisture content (g water/g dry matter), K = drying rate
158
constant (min-1), k and n is the parameter of empirical Page’s model.
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ACCEPTED MANUSCRIPT The parameters K, k and n of the above equations were evaluated through
160
non-linear regression analysis using computer program (Origin 7.0, Origin Lab
161
Corporation, USA). The goodness of fit of the tested mathematical model to the
162
experimental data was evaluated from the coefficient of determination (R2). The
163
higher the R2 -value, the better is the goodness of fit.
164
2.6 Determination of thiobarbituric acid reactive substance (TBARS)
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The TBARS was assessed according to the method of Richards & Hultin (2000).
166
Solution of trichloroacetic acid-thiobarbituric acid (TCA-TBA) (dissolve 15g TCA
167
and 1.3g TBA in 100ml water) (Sinopharm Chemical Reagent Co., Ltd., Shanghai,
168
China) was heated at 95 oC for 10 min on the day of use to dissolve the TBA.
169
Approximately 300 mg of sample was added to 2.2 mL of the TCA-TBA mixture and
170
incubated for 1 h at 65 oC. After centrifugation (5000×g for 10 min) (SIGMA 4K-15,
171
Germany), the absorbance at 532 nm (UV-1800, Shimadzu, Japan) of the supernatant
172
was determined. A standard curve was constructed using malondialdehyde (MDA),
173
and results are expressed as micrograms of MDA equivalents per kilogram of dried
174
matter. All experiments were run in triplicates.
175
2.7 Sensory evaluation
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Five trained panelists (aged from 23 to 35, 2 male and 3 female) sniffed the
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samples, using a scale of 0-9 to value the odours, with 9 being the strongest (Richards
178
& Hultin, 2000). The average value was defined as the final score. In the training
179
sessions assessors smelt the samples, discussing among themselves the best
180
descriptions and agreeing on the meaning of their elected descriptors (Table 1).
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2.8 Determination of fatty acids About 4 g of each sample was homogenized for lipid extraction (Siddaiah et al.,
183
2001). Extracted oil were analyzed for methyl esters of fatty acids by gas
184
chromatography (Agilent 6890, Agilent, Santa Clara, USA) on a capillary column (HP
185
1, Agilent, Santa Clara, USA) according to the method of Wu & Mao (2008).
186
Retention time and peak areas were recorded with the help of a microcomputer.
187
2.9 Determination of geosmin (GEO) and methylisoborneol (MIB)
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The earthy-musty off-odour compounds, and were extracted according to the
189
method of Lloyd & Grimm (1999), using microwave mediated distillation and
190
solid-phase
191
Spectrometer (GC/MS) analysis. Gas chromatograph grade GEO and MIB (Sigma
192
Aldrich Co. Ltd, St. Louis, USA) were used as external standards.
(SPME)
followed
by
gas
chromatograph-Mass
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microextraction
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The microwave mediated distillation apparatus were made according to Lloyd &
194
Grimm (1999). The microwave oven used was a CEM (Matthews, NC, USA) Model
195
300. The distillation was done at microwave power of 350 W for 10 min; the flow rate
196
of N2 was 80 mL/min. The liquid distillate was collected in a 10 mL glass vial. SPME
197
fiber used was divinylbenzene/Carboxen/poly (dimethylsiloxane) (Supelco, PA, USA),
198
and the extraction conditions were: 60 oC, 30 min. GC-MS was carried out in a gas
199
chromatography system (TRACE MS, Finnigan, USA), using the PEG-20M capillary
200
column (30 m×0.25 mm×0.25 um). The ion trap was operated in the electron impact
201
(EI) ionization mode with a filament current of 10 mA and a mass scan range of 60 to
202
250 daltons.
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2.10 Statistical analysis Data represent the mean and standard deviation from two or three independent
205
experiments. Statistical significance of data was determined by using analysis of
206
variance, using the SAS program, version 6.0 (SAS Institute Inc., Cary, N.C., U.S.A.).
207
3 Results
208
3.1 Drying kinetics of silver carp slices
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The drying curves for silver carp slices under hot-air drying, microwave drying and
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MV drying conditions are shown in Fig.1, Fig.2 A, and Fig.3 A respectively. The
211
drying kinetics was dependent on the method and parameters (temperature, power
212
intensity, and pressure). Silver carp slices having 80.5 ± 0.5 g/19.5 ± 0.5 g (g water/g
213
dry matter) (r = 4.13 ± 0.13) initial moisture content were dried to a final moisture
214
content of 20 g/80 g (r = 0.25, China aquatic product standard of dried fish fillet,
215
SC/T 3203-2001, 2001) within 8.5 min by the microwave drying at power intensity
216
HM (350.0±2.0 W) (Fig. 2A). And it took about 6 min for MV drying at the power
217
intensity HM, at vacuum of 0.06 MPa (Fig. 3A). By comparison, for convective
218
hot-air drying, it took about 165 min at 90 oC (Fig. 1), thus, the MV drying time at
219
HM power intensity and vacuum of 0.06 MPa was around 94.8% shorter than the
220
convective air drying (90 oC) time.
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The temperatures of the fish slices during microwave and MV drying are shown in
222
figure 2 B and figure 3 B, respectively. The power intensity had considerable effect on
223
the temperature of the fish slices during microwave drying (Fig. 2 B). At L power
224
output, the temperature reached 77 oC in 5 min and then remained about 75 oC for 15
11
ACCEPTED MANUSCRIPT min, followed by decreasing to about 50 oC in the last 20 min. At ML power output,
226
the temperature reached 75 oC in 3 min and then remained about 75 oC until 10 min,
227
followed by decreasing to about 60 oC in the last 5 min. At the power outputs of M,
228
HM, and H, the temperature reached 78 oC in 1.5 min, and then decreased to about 60
229
o
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C in the followed stage.
The pressure had considerable effect on the temperatures of the fish slices during
231
MV drying (Fig. 3 B). At vacuum of 0.02 MPa, the temperature increased to 55 oC in
232
1.5 min, and then increased slowly to about 60 oC until the end (7 min) of the drying
233
procedure. At vacuum of 0.04 and 0.06 MPa, the temperature increased to 50 and 44
234
o
235
drying procedure, respectively. Therefore, at the HM power intensity, the temperature
236
of fish slices during microwave drying was higher than that of MV drying.
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C in 1.5 min, and then decreased slowly to 43 and 38 oC until the end (7 min) of the
Table 2 lists the model constants obtained by application of Empirical Page’s
238
equation and Exponential equation to the experimental drying data. The Exponential
239
models give better fit for the drying data under all conditions tested with higher R2
240
values (>0.99).
241
3.2 Lipid oxidation of silver carp during drying
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The results of TBARS are shown in table 3. The lipid oxidation during microwave
243
and MV drying was milder than that of hot air drying, significantly (P < 0.05). The
244
TBARS was decreased with the increasing of power intensity during the microwave
245
drying. However, it is surprising that the TBARS increased with the decreasing
246
pressure during the MV drying. At the same power intensity of HM, the fish slices
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ACCEPTED MANUSCRIPT dried by MV had higher TBARS, especially at vacuum of 0.04 MPa and 0.06 MPa,
248
thus, the vacuum did not protect the lipid from oxidation. The fish slices dried by
249
microwave at HM or H power intensity and the samples dried by MV at HM power
250
intensity and vacuum of 0.02 MPa had the lowest TBARS. Take the energy
251
consumption into account, the microwave drying at HM power intensity is the
252
economic method to dry the silver carp slices, with the least TBARS.
253
3.3 Effect of antioxidants on the lipid oxidation during microwave drying
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Because the vacuum did not protect the lipid from oxidation, the effect of
255
antioxidants on the lipid oxidation of fish slices was only investigated during
256
microwave drying at the power intensity of HM. The lipid oxidation was considerably
257
inhibited by marinating with Vc and TP (Fig. 4). The final TBARS were decreased
258
with the increasing of Vc and TP. The microwave dried fish slices (MD) pretreated
259
with TP (0.2 g/ 100 mL) achieved the lowest TBARS (0.73 mg/kg).
260
3.4 Effect of drying method and antioxidants on the content of fat, EPA and DHA
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After drying, there was a significant decrease in fat content that was revealed by the
262
data expressed on a dry matter basis (P < 0.05) (Table 4). Microwave dried slices
263
(MD) retained a higher fat content than hot air (HAD) and MV (MVD) dried samples
264
(P < 0.05). All drying processes largely decreased the relative contents of EPA and
265
DHA in silver carp slices (P < 0.05). The Vc and TP protected the EPA and DHA
266
effectively. The MD added TP (0.2 g/ 100 mL) showed the highest level of EPA (5.42
267
g/100 g fat) and DHA (4.36 g/100 g fat) (Table 4).
268
3.5 Effect of drying method and antioxidants on the flavor of dried silver carp slices
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ACCEPTED MANUSCRIPT The odour scores of raw and dried samples are presented in table 5. Drying
270
increased the oxidized oil odour except for microwave dried samples (MD) with a TP
271
pretreatment. The MVD received the highest score of oxidized oil odour. However,
272
drying decreased the fishy odour evidently; there was no fishy odour present in the
273
fish slices treated with TP, especially. Furthermore, drying produced grilled protein
274
flavor. The grilled protein flavor scores of HAD (8.4) and MD (7.1) were higher than
275
MVD (5.3) (Table 5). However, the TP treatments inhibited the increase of grilled
276
protein flavor. The earthy-musty odour was removed slightly by drying treatments.
277
The marinating with Vc evidently decreased the scores of earthy-musty odour (from
278
4.5 to 0.4, Table 5).
279
3.6 The content of earthy-musty compounds
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Quantitative information of MIB and GEO from the integrated peak areas using
281
external standard plots is shown in Table 6. The result revealed the concentration of
282
the off-odour compounds at 2.31±0.25 ug/kg MIB and 1.29 ± 0.15 ug/kg GEO for
283
RAW (raw fish). The treatment of Vc (0.4 g/ 100 mL) combined with microwave
284
drying reduced about MIB to 0.73 ± 0.12 ug/kg (70% reduction) and GEO to 0.57 ±
285
0.08 ug/kg (50% reduction).
286
4 Discussions
287
4.1 Drying kinetics of silver carp slices
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288
Various transport properties like moisture and thermal diffusivity and mass and heat
289
transfer coefficients, describe well the mechanisms involved in drying. A good
290
agreement was found between the experimental and fitted values with high R2-values
14
ACCEPTED MANUSCRIPT (greater than 0.99, Table 2) for Exponential model. In the Exponential model, it can be
292
seen that the drying constant K-values of microwave and MV drying were higher than
293
hot-air drying. In microwave drying, K-value was found to increase with the
294
increasing power, while in MV drying, K-value was found to increase with the
295
decreasing pressure. And in hot air drying, the K-value was found to increase as the
296
temperature was increased. This can be attributed to the fact that higher temperature,
297
higher microwave power and lower pressure, help in increasing the driving force of
298
heat and mass transfer.
299
4.2 Lipid oxidation
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Thermal oxidation is one of the greatest threats to unsaturated fatty acids in foods.
301
The EPA and DHA are especially susceptible to oxidation. The oxidations of
302
unsaturated fat acids are catalysed by heat, light, trace metals or enzymes and involve
303
free radical generation. Free radicals propagate autooxidation by reacting with oxygen
304
to form hydroperoxides, which breakdown to generate other new free radicals (Weber,
305
Bochi, Ribeiro, Victorio & Emanuelli, 2008) and TBARS (Stewart, Raghavan, Orsat
306
& Golden, 2003).
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High temperatures accompanying drying processes could speed up the breakdown
308
of peroxides into their carbonyl components, thus the TBARS of the dried fish slices
309
was higher at 90 oC than 60 oC during hot air drying (Table 3). The temperature of
310
samples during microwave and MV drying were lower than that of hot air drying (Fig.
311
2B, Fig. 3B), thus, the slices dried by microwave and MV obtained lower TBARS.
312
However, the temperature in microwave drying (Fig. 2 B) was higher than that of
15
ACCEPTED MANUSCRIPT MV drying at vacuum of 0.04 MPa and 0.06 MPa (Fig. 3 B) for the same power
314
intensity (HM), while the TBARS of the former were lower (Table 3). And it is very
315
surprising that the TBARS increased with the increasing vacuum during the MV
316
drying. It looks likely that fat exuded to the surface with the moisture evaporation in
317
the low pressure condition of MV drying, which enhanced the contact of fat and
318
oxygen, and promoted the lipid oxidation. On the other hand, the pro-oxidative
319
components such as lipoxygenase and hemoglubin proteins were likely to keep their
320
activity at the low temperature of MV drying (Fig. 3B). In contrast, the lipoxygenase
321
and hemoglubin proteins should be denatured at the higher temperatures of hot air and
322
microwave drying (Turhan, Ustun & Altunkaynak, 2004).
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The antioxidants, Vc and TP, exhibited a good ability of anti-oxidation (Fig. 4).
324
This is explained by the fact that Vc and TP have potent free radical quenching
325
activity. The TP has been used to inhibit the increase of TBARS of silver carp fillets
326
during ice storage, after approximately 35 days of iced storage, the final TBARS was
327
0.85 mg /kg, while the samples without TP had 3.09 mg/kg TBARS (Fan et al., 2008).
328
In the present study, the microwave dried fish slices (MD) pretreated with TP (0.2 g/
329
100 mL) achieve the lowest TBARS of 0.73 mg/kg (Fig. 4), that is of great practical
330
importance, provides a possible application of microwave drying as an efficient
331
drying process for fish slices.
332
4.3 Content of fat acids, EPA and DHA
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333
Drying decreased the content of fat, EPA and DHA. Microwave dried slices (MD)
334
retained higher content of fat, EPA and DHA than hot air (HAD) and microwave
16
ACCEPTED MANUSCRIPT 335
vacuum (MVD) dried samples (P < 0.05) (Table 4). Similar results were achieved by
336
other researchers (Stewart et al., 2003) for soybean. Weber et al. (2008) also observed
337
cooking led to a lower fat loss, when compared to the raw silver catfish. The loss of volatile free fat acids probably occurred during heating, leading to a
339
decreased fat content. Furthermore, fat may exude with the moisture evaporation. The
340
extended heating treatment during hot air drying and low pressure in the MV drying
341
seems to enhance this phenomenon. On the other hand, oxidation is another way the
342
fat is lost. According to the results of lipid oxidation (Table 3 and Fig. 4), the fat lose
343
is in accordance with increased lipid oxidation, except in the case of MD samples
344
treated with Vc, which retained the lowest content of fat (Table 3) while limiting lipid
345
oxidation, since part of fat was lost in the marinating stage (data not shown).
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The TP protected the EPA and DHA effectively may be due to the TP inhibit the
347
lipid oxidation (Fig. 4), with its structural features that may specifically interfere with
348
the unsaturated fat acid cascade (Banerjee, 2006).
349
4.4 Flavor of dried silver carp slices
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Cooking methods have significant effect on the flavor of foods. The grilled protein
351
flavor is the favored aroma. The HAD (8.4) and MD (7.1) fish samples received
352
higher score of grilled protein flavor than MVD (5.3) (Table 5) which may due to the
353
high temperature during hot air drying and microwave drying (Fig. 2 B), since the
354
products of Millard reaction occur at high temperatures and they have been shown to
355
contribute to a “meat-like” flavor (Weber et al., 2008).
356
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The ‘oxidated oil’ and ‘fishy’ odour notes are caused by aldehydes and ketones,
17
ACCEPTED MANUSCRIPT which are the products of lipid oxidation; and there is a significantly positively
358
relationship between TBARS and off-odour in silver carp (Siddaiah et al., 2001). Two
359
mg TBARS/kg is usually regarded as the limit beyond which the fish will normally
360
develop an objectionable odour (Fan et al., 2008). The MVD (dried at HM power
361
intensity and vacuum of 0.06 MPa) received high score of fishy and oxidated oil
362
odour, due to its severe lipid oxidation (TBARS 2.735 mg/kg, Table 3). In contrast,
363
the Vc and TP treatments reduced the fishy and oxidated oil off-odour because they
364
effectively protected the lipid from oxidation (TBARS<1.5 mg/kg, Fig. 4).
365
4.5 Earthy–musty odour
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Earthy–musty odour in fresh water-farmed fish represents one of the most
367
significant economic problems encountered in aquaculture. It is suggested that
368
differences between acceptability of silver carp from different ponds may be due to
369
earthy-musty off-odour resulting from the presence of GEO and MIB in the pond
370
environment, when either compound is present in tissue at concentrations exceeding
371
0.7 ug/kg, they render fish unfit for retail sale (Andelkovic, Aleksic & Baltic, 2001).
372
Attempts to mask harvested tainted fish with chemical treatments, various cooking
373
methods and flavourings have achieved limited success (Yamprayoon & Noomhorm,
374
2000).
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After drying, these undesirable odorous compounds were partially removed, but
376
slight taint still existed (Table 6). Because GEO and MIB are lipophilic compounds,
377
and fish have fat, their removal is very difficult.
378
The treatment of Vc (0.4 g/100 mL) combined with microwave drying reduced
18
ACCEPTED MANUSCRIPT about 70% MIB and 50% GEO (Table 6). Yamprayoon & Noomhorm (2000) reported
380
that marinating tilapia in acetic acid solution resulted in decreased earthy-musty odour,
381
partly because the acid enhances the desorbing of MIB and GEO from the muscle
382
proteins, partly because the acid marinating treatment remove considerable fat from
383
the muscle, so the fat-soluble MIB and GEO were removed too. The Vc is an acidic
384
substance (ascorbic acid) which may play a similar role as acetic acid in removing the
385
earthy-musty odour compounds of silver carp slices.
386
5 Conclusions
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The MV drying caused severe lipid oxidation and oxidized off-odours while on the
388
other hand the microwave drying could reduce the drying time, avoid lipid oxidation.
389
The marinating with Vc and TP significantly inhibited the lipid oxidation during
390
drying. Samples treated with TP (0.2 g/ 100 mL) retained the most of DHA and EPA
391
while preventing the production of fishy off-odours. A large part of the earthy-musty
392
off-odour compounds were removed by marinating with Vc (0.4 g/100 mL) combined
393
with microwave drying.
394
Reference
396 397 398 399 400
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Andelkovic R., Aleksic J. & Baltic M. (2001). The investigation of the acceptability of carp and silver carp meat from different ponds. Tehnologija Mesa, 42, 33-38. Anonymous. (2013). The fishery yearbook of china, China Agricultural Press, 31.
Banerjee S. (2006) Inhibition of mackerel (Scomber scombrus) muscle lipoxygenase by green tea polyphenols. Food Research International, 39, 486-491. Barrera A. M., Ramirez J. A., Gonzalez C. J. J. & Vazquez M. (2002). Effect of
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pectins on the gelling properties of surimi from silver carp. Food hydrocolloid, 16,
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441-447.
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Cui Z. W., Xu S. Y. & Sun D. W. (2003). Dehydration of garlic slices by combined microwave–vacuum and air drying. Drying Technology, 21(7), 1173–1185.
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Cui Z. W., Xu S. Y. & Sun D. W. (2004). Microwave–vacuum drying kinetics of carrot slices. Journal of Food Engineering, 65, 157–164.
Fan W. J., Chi Y. L. & Zhang S. (2008). The use of a tea polyphenol dip to extend
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the shelf life of silver carp (Hypophthalmicthys molitrix) during storage in ice. Food
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Chemistry, 108, 148–153.
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Giri S. K. & Prasad S. (2007). Drying kinetics and rehydration characteristics of
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microwave-vacuum and convective hot-air dried mushrooms. Journal of Food
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Engineering, 78, 512
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521.
Lloyd S. W. & Grimm C. C. (1999). Analysis of 2-methylisoborneol and geosmin in
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catfish by microwave distillation-solid-phase microextraction. Journal of Agricultural
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& Food Chemistry, 47, 164-169.
417
Mistry B. S. & Min D. B. (1997). Proxidant effects of monoglycerols and
AC C
416
EP
413
diglycerols in soybean oil. Journal of Food science, 53, 1896-1897.
418
Richards M. P. & Hultin H. O. (2000). Effect of pH on lipid oxidation using trout
419
hemolysate as a catalyst: a possible role for deoxyhemoglobins. Journal of
420
Agricultural & Food Chemistry, 48, 3141-3147.
421 422
SC/T 3203-2001. (2001). China aquatic product standard: Dried seasoned fish fillet (2nd ed.). Beijing: Ministry of Agriculture of the People’s Republic of China.
20
ACCEPTED MANUSCRIPT 423
Siddaiah D., Reddy G. V. S., Raju C. V. & Chandrasekhar T. C. (2001). Changes in
424
lipids, proteins and kamaboko forming ability of silver carp (Hypophthalmichthys
425
molitrix) mince during frozen storage. Food Research International, 34 (1), 47-53. Stewart O. J., Raghavan G. S.V., Orsat V. & Golden K.D. (2003). The effect of
427
drying on unsaturated fatty acids and trypsin inhibitor activity in soybean. Process
428
Biochemistry, 39, 483-489.
RI PT
426
Turhan S., Ustun N. S. & Altunkaynak T. B. (2004). Effect of cooking methods on
430
total and heme iron contents of anchovy (Engraulis encrasicholus). Food Chemistry,
431
88, 169–172.
M AN U
SC
429
Weber J., Bochi V. C., Ribeiro C. P., Victorio A. de M. & Emanuelli T. (2008).
433
Effect of different cooking methods on the oxidation, proximate and fatty acid
434
composition of silver catfish (Rhamdia quelen) fillets. Food Chemistry, 106, 140–146.
435
Wu T. & Mao L. (2008). Influences of hot air drying and microwave drying on
436
nutritional and odorous properties of grass carp (Ctenopharyngodon idellus) fillets,
437
Food Chemistry, 110, 647-653.
EP
TE D
432
Yamprayoon J. & Noomhorm A. (2000). Effects of preservation methods on
439
geosmin content and off-flavor in Nile tilapia (Oreochromis niloticus). Journal of
440
Aquatic Food Product Technology, 9(4), 95-107.
441
AC C
438
Zhang J., Zhang M., Shan L. & Fang Z. (2007). Microwave-vacuum heating
442
parameters for processing savory crisp bighead carp (Hypophthalmichthys nobilis)
443
slices. Journal of Food Engineering, 79, 885
891.
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ACCEPTED MANUSCRIPT Table 1 Descriptors used in the sensory evaluation Oxidated oil
Odour associated with rancid pork fat
Fishy
Odour associated with the chopped silver carp mince stand at 25 C for 0.5 h
Earthy/musty
Odour associated with mud
Grilled protein
Odour associated with grilled fish meat
AC C
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TE D
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o
ACCEPTED MANUSCRIPT Table 2 Model constants of Logarithmic equation and Exponential equation Exponential equation
Page’s equation k
R2
K
R2 0.992
0.005
1.027
0.979
0.006
Hot air (90 oC)
0.012
1.026
0.929
0.014
0.995
Microwave (La)
0.052
0.971
0.989
0.049
0.992
Microwave (ML)
0.187
0.867
0.989
0.146
0.990
Microwave (M)
0.208
1.041
0.996
0.225
0.993
Microwave (HM)
0.321
Microwave (H)
0.443
MVb (HM, 0.02 MPa)
0.325
MV (HM, 0.04 MPa)
0.350
SC
M AN U 1.080
0.987
0.334
0.997
1.085
0.983
0.516
0.997
1.027
0.998
0.340
0.999
1.123
0.998
0.355
0.999
0.997
0.409
0.999
TE D 0.382
RI PT
Hot air (60 oC)
MV (HM, 0.06 MPa) a
n
0.929
AC C
EP
The power intensity of microwave: H, 460.5±1.5 W; HM, 350.0±2.0 W; M, 210.3±2.3 W; ML, 122.1±3.1 W; and L, 52.3±2.0 W. b MV: Microwave-vacuum drying.
ACCEPTED MANUSCRIPT
Table 3 Effect of drying method on the Lipid oxidation of dried silver carp Temperature or Drying method
Vacuum (M Pa)
TBARS (mg/kg)
\
90 oC
\
Lc
\
ML
\
M HM H
a
HM
4.990 ± 0.169G 3.025 ± 0.130E
2.527 ± 0.118 D
\
2.120 ± 0.080C
\
1.375 ± 0.152A
\
1.273 ± 0.115A
0.02
1.450 ± 0.052A
TE D
MV b
4.534 ± 0.112F
SC
Microwave a
60 oC
M AN U
Hot air
RI PT
Power intensity
0.04
1.797 ± 0.044B
0.06
2.735 ± 0.247D
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The drying time at L, ML, M, HM, H power intensity were 40, 16, 10, 10, 7 min, respectively. b Microwave-vacuum drying at HM for 7 min. c The power intensity of microwave: H, 460.5±1.5 W; HM, 350.0±2.0 W; M, 210.3±2.3 W; ML, 122.1±3.1 W; and L, 52.3±2.0 W. A-G Means in column having different superscript letters are significantly different (P< 0.05) (n=3).
ACCEPTED MANUSCRIPT Table 4 Fat, EPA and DHA of dried silver carp slices
EPA
DHA
matter)
(g/100g fat)
(g/100g fat)
RAWA
5.82 ±0.65a
5.08± 0.09b
3.87± 0.08b
HADB
4.58 ±0.16c
4.05±0.08d
2.61±0.05c
MVDC
4.65 ±0.12c
4.09± 0.17d
2.75± 0.15c
MDD
5.14±0.10b
4.12± 0.09d
2.96± 0.14c
Vc 0.2 g/100 mL
4.10±0.16d
4.65± 0.05c
3.62± 0.21b
Vc 0.4 g/100 mL
4.15±0.14d
4.98± 0.15b
3.78±0.11b
TP 0.1 g/100 mL
4.78±0.15c
4.80±0.14b
3.85± 0.08b
TP 0.2 g/100 mL
4.65±0.08c
5.42± 0.11a
4.36± 0.13a
A
SC
M AN U
MDE
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Fat (g/100g dry
Raw fish slices. Fish slices were dried by hot air at 90 oC for 2.5 h. C Fish slices were dried by microwave-vacuum at HM (power intensity, 350.0±2.0 W) and vacuum 0.06 Mpa for 7 min. D Fish slices were dried by microwave at HM (power intensity, 350.0±2.0 W) for 10 min. E Fish slices were marinated in Vc or TP solution for 2 h, followed by being dried by microwave at power intensity of HM (350.0±2.0 W) for 10 min. Vc: Vitamin C; TP: Tea polyphenols. a-d Means in each column having different superscript letters are significantly different (P< 0.05) (n=2).
AC C
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ACCEPTED MANUSCRIPT Table 5 Effect of drying method and antioxidants on the odour of silver carp slices Fishy
Oxidated oil Earthy-musty Grilled protein
5.0
1.0
4.5
0
HADb
2.2
3.8
3.8
8.4
MVDc
3.0
4.0
3.6
5.3
MDd
2.6
3.7
1.9
7.1
Vc 0.2 g/100 mL
2.3
2.4
1.1
6.2
Vc 0.4 g/100 mL
1.2
1.2
0.4
6.9
TP 0.1 g/100 mL
0
TP 0.2 g/100 mL
0
SC
MD
M AN U
e
RI PT
RAWa
1.0
1.6
3.5
0.5
1.5
3.4
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The odour was valued using a scale of 0-9, with 9 being the strongest. a Raw fish slices. b Fish slices dried by hot air at 90 oC for 2.5 h. c Fish slices dried by microwave-vacuum at HM (power intensity, 350.0±2.0 W) and vacuum 0.06 Mpa for 7 min. d Fish slices dried by microwave at HM (power intensity, 350.0±2.0 W) for 10 min. e Fish slices were marinated in Vc or TP solution for 2 h, followed by being dried by microwave at power intensity of HM (350.0±2.0 W) for 10 min. Vc: Vitamin C; TP: Tea polyphenols.
ACCEPTED MANUSCRIPT Table 6 The effect of drying method and pretreatment with Vc on the content of earthy-musty compounds MIB and GEO (ug/kg) GEO
RAWa
2.31±0.25A
1.29±0.15A
MDb
2.62±0.20A
MDc (Vc 0.4 g/100 mL)
0.73±0.12B
a
RI PT
MIB
0.85±0.11B
0.57±0.08C
SC
Raw fish slices. Fish slices dried by microwave at power intensity of HM (350.0±2.0 W) for 10 min, c Fish slices were marinated in Vc solution (0.4 g/100 mL) for 2 h, followed being dried by microwave at power intensity of HM (350.0±2.0 W) for 10 min. Vc: Vitamin C. A-C Means in each column having different superscript letters are significantly different (P< 0.05) (n=2).
AC C
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M AN U
b
ACCEPTED MANUSCRIPT 1
Captions
2
Figure 1 Kinetics of hot air drying at 60 oC (●) and 90 oC (■). (r: moisture content, g
3
water/g dry matter), (n=3).
RI PT
4
Figure 2 Effect of power intensity on the drying kinetics of microwave drying (■ L,
6
52.3±2.0 W; ○ML, 122.1±3.1 W; ▲ M, 210.3±2.3 W; ▼HM, 350.0±2.0 W; □ H,
7
460.5±1.5 W) , (n=3).
8
A: The r of the samples during drying (r: moisture content, g water/g dry matter)
9
B: The temperature of the samples during drying
M AN U
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5
10
Figure 3 Effect of vacuum degree on the drying kinetics of microwave-vacuum
12
drying at power intensity of HM (350.0±2.0 W), (■ 0.02 MPa; ○ 0.04 MPa; ▲ 0.06
13
MPa), (n=3).
14
A: The r of the samples during drying (r: moisture content, g water/g dry matter)
15
B: The temperature of the samples during drying
EP
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16
TE D
11
17
Figure 4 Effect of antioxidants on the lipid oxidation of silver carp slices during
18
microwave drying (■ control;
19
g/100 mL; △ TP, 0.2 g/100 mL) (n=3).
20
(Fish slices were marinated in Vc or TP solution for 2 h, followed by being dried by
21
microwave at power intensity of HM (350.0±2.0 W) for 10 min. Vc: Vitamin C; TP:
22
Tea polyphenols)
23
●
Vc, 0.2 g/100 mL; ○ Vc, 0.4 g/100 mL; ▲TP, 0.1
ACCEPTED MANUSCRIPT 24 25
Figure 1
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4 3
SC
r
2
0 0
1
M AN U
1
2
3
Time (h)
EP
28
AC C
27
TE D
26
4
5
6
ACCEPTED MANUSCRIPT 29
Figure 2
4
RI PT
r
3 2
SC
1
M AN U
0 0
10
20
30
40
Time (min)
30
A
31
60
EP
o
Temperature ( C)
70
TE D
80
50
AC C
40 30 20
0
10
20 Time (min)
32 33 34
B
30
40
ACCEPTED MANUSCRIPT 35
Figure 3
4
RI PT
r
3 2
SC
1
-1
0
1
M AN U
0 2
3
4
5
6
7
8
Time (min)
36
A
70
EP 50
AC C
Temperature (C)
60
TE D
37
40 30 20
0
2
4 Time (min)
38 39 40
B
6
8
ACCEPTED MANUSCRIPT 41 42
Figure 4
43
RI PT
2.5
SC
1.5 1.0 0.5 0.0
2
4
6
EP
TE D
Time (min)
AC C
44
0
M AN U
TBARS (mg/kg)
2.0
8
10
ACCEPTED MANUSCRIPT 1. Microwave dried fish slices retained more fat, EPA and DHA. Tea polyphenols (TP) treated fish slices retained the most of DHA and EPA, achieved non-fishy products. 2. The thiobarbituric acid reactive substance (TBARS) of dried fish slices
vacuum during microwave-vacuum drying.
RI PT
decreased with power intensity during microwave drying but increased with the
3. Marinating with Vc combined with microwave drying removed the
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TE D
M AN U
SC
earthy-musty off-odour effectively.