- Email: [email protected]
Changes in microstructure, quality and water distribution of porcine longissimus muscles subjected to ultrasound-assisted immersion freezing during frozen storage
Meat Science 151 (2019) 24–32
Contents lists available at ScienceDirect
Meat Science journal homepage: www.elsevier.com/locate/meatsci
Changes in microstructure, quality and water distribution of porcine longissimus muscles subjected to ultrasound-assisted immersion freezing during frozen storage Mingcheng Zhanga,b,c,1, Xiufang Xiaa,1, Qian Liua, Qian Chena, Baohua Konga,
T
⁎
a
College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China College of Food Science and Technology, Bohai University, China c Food Safety Key Lab of Liaoning Province, National & Local Joint Engineering Research Center of Storage, Processing and Safety Control Technology for Fresh Agricultural and Aquatic Products, Jinzhou, Liaoning 121013, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Ultrasound-assisted immersion freezing Porcine longissimus muscle Quality characteristic Microstructure Water distribution
The effect of ultrasound-assisted immersion freezing at 180 W (UIF-180) on the microstructure, quality and water distribution of porcine longissimus muscles during frozen storage was evaluated. The size of the ice crystals increased with extended storage time, and UIF-180 samples had a smaller size and uniform distribution of ice crystals. The thawing and cooking losses in the UIF-180 sample were significantly lower than that in air freezing (AF) and immersion freezing (IF) samples (P < 0.05). AF samples had a higher cutting force at 0 days. During the 60–180 days of the storage period, the cutting force of UIF-180 samples was significantly higher than that of AF and IF samples (P < 0.05). Low field-nuclear magnetic resonance results showed that UIF-180 decreased water migration during frozen storage. UIF-180 samples had significantly lower lipid oxidation and higher redness than that of the AF and IF samples (P > 0.05). Overall, UIF at particular powers is an efficient method in reducing quality deterioration of muscles during long-term frozen storage.
1. Introduction Freezing and frozen storage are important methods for the longterm preservation of meat and meat production, which can inhibit microbial growth, slow enzymatic activity, and preserve the original taste and nutritional value (Ngapo, Babare, Reynolds, & Mawson, 1999). However, some adverse changes such as protein denaturation and lipid oxidation still happen, which are the primary causes of declining sensory quality of frozen products, and these changes can be accelerated by freezer burn when the frozen meat is unpacked and exposed to air (Turgut, Işıkçı, & Soyer, 2017). Freezing methods and storage conditions, such as freezing rate and storage time, substantially influence the quality of frozen meat. Furthermore, ice crystal growth within muscle tissue during frozen storage is a quality issue because recrystallization of ice crystals can lead to muscle physical structure weakening (Damodaran & Wang, 2017). Additionally, drip loss and nutritional value loss in muscle can still occur during the freeze/thaw process, which negatively modifies the final product quality and consumer acceptability of meat products (Figueirêdo, Trad, Mariutti, &
Bragagnolo, 2014). Ultrasound is a new technology being used in food preservation and analysis. The ultrasonic waves cause severe turbulence in liquid medium and increase heat transmission efficiency (Cheng, Zhang, Xu, Adhikari, & Sun, 2015). Ultrasound-assisted immersion freezing (UIF) is an effective method to increase the heat transfer coefficient and accelerate the freezing process of food (Li & Sun, 2002). The cavitation and microstreaming produced by power ultrasound are the major reasons to shorten the freezing time of food (Islam, Zhang, Adhikari, Cheng, & Xu, 2014). Additionally, ultrasound can increase the probability of nucleation in supercooled water and induce nucleation at higher temperatures during the freezing process, which is very useful for controlling the size and distribution of ice crystals in frozen materials (Cheng et al., 2015). Therefore, UIF is an effective method for maintaining the quality of frozen foods. There are some reports about the effect of UIF on food quality and freezing speed. Li and Sun (2002) found that the tissue of potatoes frozen using ultrasound assisted freezing exhibited superior cellular structure compared to the samples frozen without applying power ultrasound. Islam et al. (2014) reported
⁎
Corresponding author at: College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China. E-mail addresses: [email protected], [email protected] (B. Kong). 1 These authors contributed to this work equally. https://doi.org/10.1016/j.meatsci.2019.01.002 Received 21 September 2018; Received in revised form 27 December 2018; Accepted 9 January 2019 Available online 11 January 2019 0309-1740/ © 2019 Elsevier Ltd. All rights reserved.
Meat Science 151 (2019) 24–32
M. Zhang et al.
2.3. Thawing loss, cooking loss, and cutting force measurement
that the application of ultrasound at different levels during immersion freezing significantly reduced the freezing time of mushroom and better preserved the microstructure of frozen samples. Similar results were also found in the freezing of fish (Santacatalina, Guerrero, Garcia-Perez, Mulet, & Cárcel, 2016), gluten (Song, Q, & Lin, 2008), and meat (Zhang, Niu, Chen, Xia ＆ Kong, 2018). In a previous study, we investigated the effect of UIF on the quality and freezing rate of porcine longissimus muscle at various ultrasound powers. The results showed that UIF at certain powers significantly increased the freezing rate of muscles, and samples treated with UIF at 180 W (UIF-180) had a shorter freezing time, smaller and uniformly ice crystal distribution, and lower thawing loss (Zhang et al., 2018). This result indicated that UIF-180 treatment increases the freezing rate of muscle samples and improves meat quality. However, there were little reports about the changes of microstructure, quality and water distribution of meat which subjected to UIF during frozen storage. Therefore, the objective of our present study was to investigate the changes of microstructure, thawing loss, colour attributes, cutting force, cooking loss, lipid oxidation, as well as water migration and distribution of porcine longissimus muscles during 180 days of frozen storage as influenced by different freezing methods, such as UIF-180, AF and IF.
The frozen samples were air thawed overnight at 4 °C. The thawing loss was determined as described by Xia, Kong, Liu, and Liu (2009) and expressed as:
Thawing loss (%) = (M0 − M1)/ M0 where M0 and M1 represent the weight of the sample before and after thawing, respectively. Thawed muscle samples were packed and cooked at 85 °C in a water bath until the centre temperature reached 75 °C. Cooking loss was calculated according to the following equation:
Cooking loss (%) = (M1 − M2)/ M1 where M1 and M2 represent the weight of the sample before and after cooking, respectively. After determining cooking loss, the cooked samples were used to measure cutting force as described by Zhang et al. (2018). Briefly, cylindrical cores (1.27 cm in diameter) from each cooked sample were cut using a texture analyser (Stable Micro System; TA: XT2i, England) with a knife blade (HDP/BSW). The maximum force which cut transversally into the chops was recorded as cutting force (N).
2. Materials and methods
2.4. Thiobarbituric acid-reactive substance measurement
2.1. Frozen sample preparation
Thiobarbituric acid-reactive substance (TBARS) was measured based on the method of Xia et al. (2009). Briefly, a sample of 2 g was homogenized and mixed in 3 mL of 1% thiobarbituric acid, and then, 17 mL of 2.5% trichloroacetic acid was added. The mixture was boiled for 30 min and cooled in cold water. The mixture was centrifuged at 3000 g for 10 min at room temperature, and the absorbance was recorded at 532 nm (A532). The TBARS value was expressed as the following:
Porcine longissimus muscles (lumborum) were purchased from the Beidahuang Meat Corporation (Harbin, Heilongjiang, China) within 24 h after slaughter. The pigs (approximately 24 weeks of age) were slaughtered according to the pig slaughtering operating procedures (GB/T 17236-1998) in China. The muscle samples were wrapped at 0–4 °C and transported to the laboratory. Approximately 3-cm-thick chops (120 ± 2 g) of pork loin were manually cut perpendicular to the direction of the muscle fibres and packaged with poly nylon pouches. Sample preparation was conducted at 4 °C. There were three treatments including air freezing (AF), immersion freezing (IF), and ultrasound-assisted immersion freezing at 180 W power (UIF-180). The UIF freezer was made by Nanjing Xianou Co., Ltd. Nanjing, China with 10 ultrasound transducers at the bottom of the freezing tank. The structure of the freezer was same as described by Zhang et al. (2018) with 5% fluoride plus 95% ethanol as a coolant. The size of the freezing tank was 30 × 22 × 26 cm3. The muscle samples were frozen according to our previous descriptions (Zhang et al., 2018). The AF process was conducted at −20 ± 0.5 °C and ended when the geometric centre temperature of the chops reached approximately −18 °C. For IF and UIF-180, chops were immersed in the coolant (−20.0 ± 0.5 °C) with 0 W and 180 W ultrasound powers, respectively, until the geometric centre temperature reached approximately −18 °C. After freezing, muscle samples were stored at −18 ± 1 °C for 0, 30, 60, 90, 120, 150, and 180 d. For each treatment, at least 42 chops were used, and for each storage time, 6 chops were used for analysis.
TBARS (mg malondialdehyde/kg of muscle) = (A532 /weight of muscle) × 9.48 where “9.48” was a constant derived from the dilution factor and the molar extinction coefficient (152,000 M−1 cm−1) of the red, TBA arbituric acid reaction product. 2.5. Low field-nuclear magnetic resonance measurement Low field-nuclear magnetic resonance (LF-NMR) relaxation measurements were performed as described by Zhang et al. (2018) with an LF-NMR analyser minispec mq 20 (Bruker Optik GmbH, Ettlingen, Germany). Briefly, the thawed muscle chops (1 × 1 × 2 cm3) were put into 18 mm NMR tubes for determination. The transverse relaxation time (T2) was measured using the Carr-Purcell-Meiboom-Gill pulse sequence. Bi-exponential fitting resulted in three water populations, A2b, A21 and A22, with corresponding relaxation times T2b, T21 and T22 via the software provided by Bruker instruments. 2.6. Colour measurement
2.2. Microstructure of frozen samples The colour of the thawed muscle samples was evaluated by a ZE6000 colourimeter (Juki Corp, Tokyo, Japan) according to the method of Jia, Kong, Liu, Diao, and Xia (2012). A minimum of 3 chops were used to analyse the L* (lightness)-, a* (redness)- and b* (yellowness) values. For each chop, four different locations on the surface were used to determine colour.
The frozen samples (0.5 × 0.5 × 1 cm3) were excised perpendicularly or parallel to the direction of the myofibres at −20 °C using a Leica CM1850 cryostat (CM1850, Leica, Germany). The cross-sections or longitudinal sections of the samples (4 μm thick) were obtained and stained following a method described previously (Zhang et al., 2018). Three micrographs of each specimen were observed using a light microscope connected to a digital camera (Olympus BX41, Olympus Optical Co. Ltd., Tokyo, Japan). The average radiuses of ice crystals in the three images of each specimen were quantitatively analyzed using Image-Pro Plus software (Media Cybernetics, Silver Spring, MD, USA).
2.7. Statistical analysis Three batches of samples subjected to different freezing treatments were processed independently to study the effects of the different 25
Meat Science 151 (2019) 24–32
M. Zhang et al.
(caption on next page)
26
Meat Science 151 (2019) 24–32
M. Zhang et al.
Fig. 1. Changes in microstructural cross section (A), longitudinal section (B), and average radius of ice crystal (C) of frozen porcine longissimus muscles affected by different freezing methods during frozen storage. AF, air freezing; IF, immersion freezing; UIF-180, ultrasound-assisted immersion freezing at 180 W. Scale bars indicate 400 μm. Means with different letters (A-E) are significantly different (P < 0.05) in different frozen storage durations for the same treatment, and means with different letters (a-c) indicate significant differences between freezing method at the same time point (P < 0.05).
3.2. Thawing loss and cooking loss
freezing treatments on quality characteristics of porcine longissimus muscles during frozen storage. For each batch of samples, all experiments were performed in triplicate. The results are expressed as the mean ± standard deviations which analyzed using the General Linear Model procedure of the Statistix 8.1 software package (Analytical Software, St. Paul, MN, USA). Data was subjected to one-way analysis of variance (ANOVA). And mean comparison was performed (P < 0.05) using Tukey procedures.
Thawing loss substantially influences the appearance, weight, colour, and sensory quality of meat and meat products (Xia et al., 2009). Thawing loss increased with extended storage time (Fig. 2A). The thawing losses of the AF, IF, and UIF-180 samples were 4.63%, 2.52%, and 1.23% at 0 days, and they significantly increased to 11.32%, 9.51%, and 7.49% at 180 days, respectively (P < 0.05). The UIF sample had the smallest thawing loss, followed by IF and AF samples during frozen storage. Thawing loss is related to the rate of thawing, ice crystal location and size, and the integrity of muscle tissue (Farouk, Wieliczko, & Merts, 2004; Kim, Liesse, Kemp, & Balan, 2015). The disruption of muscle fibres caused by the growth of ice crystals during frozen storage can diminish the water binding capacity of muscle (Rahelić, Puač, & Gawwad, 1985). The reduced thawing loss in the UIF-180 samples is related to the formation of small and even ice crystals, which results in less damage to the muscle structure during frozen storage. For AF samples, the slow freezing rate caused water migration to the extracellular space, which can lead to the formation of irregular and large ice crystals and destruction of muscle structure (Muela, Sanudo, Campo, Medel, & Beltran, 2010). Therefore, the AF sample had a weak ability to re-absorb melted water back into the cells after thawing. Cooking loss usually includes a mixture of liquid and soluble substances from muscle during cooking (Hong et al., 2011). Products with low cooking loss may have better eating quality (Aaslyng, Bejerholm, Ertbjerg, Bertram, & Andersen, 2003). The influence of different freezing methods and storage time on the cooking loss of samples is shown in Fig. 2B. The cooking losses of samples exhibited similar trends to thawing loss. The cooking losses of the AF, IF, and UIF-180 samples were 37.44%, 32.39%, and 31.35% at 0 days and significantly increased to 42.48%, 40.59%, and 38.64% at 180 days, respectively (P < 0.05). The UIF-180 sample had the smallest cooking loss during frozen storage. Hong et al. (2011) found that the thawing loss of bighead carp (Aristichthys nobilis) by different freezing methods increased with the increase in frozen storage time. According to the results of the muscle microstructures (Fig. 1), the UIF-180 samples had uniform and fine ice crystals, which effectively maintain the integrity of muscle tissue during freezing and frozen storage and contribute to smaller cooking loss.
3. Results and discussion 3.1. Microstructure of frozen muscles The size of ice crystals is crucial to the final quality of frozen foods. The expansion pressure of ice crystals can cause irreversible damage to the structure of the muscle, thereby destroying muscle quality, colour, taste and nutritional value (Hong, Zhu, Luo, & Yu, 2011). The distribution and size of ice crystals inside the muscles and changes of the muscle during frozen storage were evaluated using image analysis. Fig. 1A and Fig. 1B represent the cross-sections and longitudinal sections of the frozen muscle tissue with different freezing treatments, respectively, and Fig. 1C represents the average radius of the ice crystals. As shown in Fig. 1A and B, different freezing treatments substantially influenced the size and distribution of ice crystals inside the muscles during frozen storage (P < 0.05). Muscle fibres from UIF-180 samples were arranged neatly and appeared to be more compact and denser. The size of ice crystals increased with an increase in frozen storage time (Fig. 1C). The average radius of the ice crystals of AF, IF, and UIF-180 samples were 29.43, 13.42, and 5.08 μm at 0 days, which increased to 124.28, 85.25, and 46.65 μm at 180 days, respectively (P < 0.05). At 180 days, UIF-180 samples still had the regular and uniform distribution of ice crystals, the average radius of the ice crystals in the UIF-180 samples was 62.46% lower than that in the AF sample and 45.27% smaller than that in the IF sample (P < 0.05). This result suggests that UIF-180 can effectively maintain a smaller ice crystal size within the muscle and cause minimal damage to the muscle fibres during the entire frozen period. Additionally, AF samples presented seriously twisted and narrowed fibres with large intra and extracellular ice crystals. After 90 days of frozen storage, as the shape of the ice crystals presented more irregular, an increased amount of breakages and even fractures occurred in the muscle fibres of the AF samples, which resulted in textural change, and thawing loss increased as shown in Fig. 2A. Both intra- and extra cellular ice crystals in the AF sample squeezed the muscle fibres into a very narrow space, resulting in a widened distance between the fibres. Bevilacqua and Zaritzky (1986) found that even if the diameter of the ice crystals is very small, the recrystallization phenomenon will occur with the prolongation of freezing time. The diffusion of water molecules from bulk to the crystal surface and surface integration were continuing to form some larger sized ice crystals (Tironi, Lamballerie, & Lebail, 2010). Zhang, Inada, Yabe, Lu, and Kozawa (2001) discussed that ultrasound can produce microstreaming, which can promote nucleation during freezing. Zheng and Sun (2006) suggested that certain intensities of ultrasonic power induce ice crystal fracture and lead to ice crystal size reduction. The small ice crystals and their uniform distribution during frozen storage can benefit the quality of frozen foods (Chevalier, Sentissi, Havet, & Bail, 2000).
3.3. Cutting force The cutting force reflects the muscle tenderness, such that lower cutting forces are associated with better tenderness (Xia et al., 2009). As shown in Fig. 2C, AF samples had the highest cutting force at 0 day, which was 18.73% and 22.77% higher than that of the IF and UIF-180 samples, respectively (P < 0.05). This results may be attributed to the greater fluid loss after thawing, which resulted in less water available to hydrate the muscle fibres; thus, a greater force was needed to cut off the muscle fibres (Leygonie, Britz, & Hoffman, 2012). However, the cutting force of AF samples sharply decreased with the increasing storage time until 180 days (P < 0.05), which related to the destruction of muscle tissue. Combined with the above microstructure analysis, the formation of large, extracellular ice crystals in the AF samples disrupt the physical structure, largely breaking myofibrils apart, resulting in decreased cutting force (Leygonie et al., 2012). Liu, Xiong, and Chen (2010) also indicated that the loss in membrane strength due to ice crystal formation could subsequently reduce the force needed to cut the meat. Moreover, for IF and UIF-180 samples, no significant differences of cutting force were observed at 0 day and 30 days (P > 0.05). After 27
Meat Science 151 (2019) 24–32
(A)
12
Thawing loss (%)
Aa
AF IF UIF
10
Ca
Cb Da
8 6
Ea
Cc
Fa
Ba Ab
Ab Ac
Bb Bc
Bc
Cc Db
4 Eb 2
TBARS (mg malonaldehyde/kg of muscle)
M. Zhang et al.
Ec
Eb
Dc
Ec
0 0
(B)
Cooking loss (%)
35
60
90
120
150
180
AF IF UIF-180
0.4
Ba
Ab
Ca Bb Da
0.3
Bc
Db
0.2
Ea
DEa
Cc Dc
DEb
Fb
Fb
0.1
Ea Eb
Ea
Ac
Cb
Fb
0
30
60
90
120
150
180
Frozen storage time (days)
AF IF UIF-180
45 40
30
Aa
0.5
Aa BCa Ba DEa CDa DEa ABb Ab BCa Bab Bb Ea Bc CDb Db Cb Cb Cb
Aa Ab Ac
Fig. 3. Changes in thiobarbituric acid-reactive substance (TBARS) of frozen porcine longissimus muscles affected by different freezing methods during frozen storage. AF, air freezing; IF, immersion freezing; UIF-180, ultrasoundassisted immersion freezing at 180 W. Means with different letters (A-F) are significantly different (P < 0.05) in different frozen storage durations for the same treatment, and means with different lowercase letters (a-c) indicate significant differences between freezing method at the same time point (P < 0.05).
30 that, during the 60–180 days of the storage period, the cutting force of the UIF-180 samples were significantly higher than that of the AF and IF samples (P < 0.05), indicating that the UIF-180 samples were more effective in maintaining the original muscle tissue state. Bueno et al. (2013) used three different methods to freeze the mutton, namely, liquid nitrogen freezing, refrigerator freezing, and blast freezing. They reported that frozen muscles with a faster freezing speed (liquid nitrogen freezing) have higher hardness than the other two methods after frozen storage for 10 months.
25 20 0
30
60
90
120
150
180
Frozen storage time (days)
(C) 35 Aa
Cutting force (N)
30
Ba Bb Aa Ab Bb Ab Cb
25
Bc
20
AF IF UIF-180
3.4. Lipid oxidation Lipid oxidation of frozen muscle was evaluated by measuring TBARS. As shown in Fig. 3, the TBARS formation of three groups increased with increased storage time, and the frozen storage time has a stronger influence on the oxidative degree than freezing method. TBARS values of AF, IF, and UIF-180 samples at 0 days were 0.144, 0.142, and 0.164 mg/kg and increased to 0.489, 0.454, and 0.359 mg malondialdehyde/kg at 180 day, respectively. Previous studies have verified that 0.5 mg malondialdehyde/kg of TBARS value in fresh meat was a borderline which impacting on meat quality/sensory attributes (Lanari, Schaefer, & Scheller, 1995; Tarladgis, Watts, & Younathan, 1960; Turner et al., 1954). Thus, each freezing method did not affect the quality of the meat during 180 days of frozen storage. However, a higher level of TBARS values in the UIF-180 samples at 0 days may be a result of ultrasonic treatment during the freezing process. Kang et al. (2016) found that ultrasound can cause lipid oxidation of beef during curing processing, which was attributed to the hydroxyl radicals produced by brine decomposition, which are caused by the cavitation of ultrasonic waves. However, the TBARS values of the UIF-180 samples were significantly lower than that of the AF and IF samples from 60 to 180 days, which means for UIF-180 samples, fat oxidation increased at the initial frozen storage duration, but its oxidation rate was lower than that of the AF and IF samples. The TBARS values of the IF samples were significantly lower than that of the AF samples from 90 to 180 days. The small ice crystals and a uniform distribution were formed by relative fast freezing rates (UIF-180) and maintained well during the frozen
Ba Cb BbCa Ca Da Db Cb Cb DEc DEc Ec
15 10 0
30
60
90
120
150
180
Frozen storage time (days) Fig. 2. Changes in thawing loss (A), cooking loss (B), and cutting force (C) of frozen porcine longissimus muscles affected by different freezing methods during frozen storage. AF, air freezing; IF, immersion freezing; UIF-180, ultrasound-assisted immersion freezing at 180 W. Means with different letters (AF) are significantly different (P < 0.05) in different frozen storage durations for the same treatment, and means with different lowercase letters (a-c) indicate significant differences between freezing method at the same time point (P < 0.05).
28
Meat Science 151 (2019) 24–32
M. Zhang et al.
storage, which possibly contributed to lipid oxidation to a lower extent over a long duration of frozen storage. Oxidation is a major cause of meat quality deterioration during storage, which can lead to discoloration, flavour deterioration, and nutrient destruction. The lipid oxidation of muscle food during frozen storage may be related to the damage of cellular structures caused by freezing (Boonsumrej, Chaiwanichsiri, Tantratian, Suzuki, & Takai, 2007). Similar results were found by Soyer, Özalp, Dalmış, and Bilgin (2010) in chicken leg and breast meats during frozen storage. Oxidation of samples increased significantly with prolonged storage up to 6 months. Lipid oxidation occurred during frozen storage might cause the denaturation of proteins. Proteins exposed to oxidizing environments are very susceptible to chemical modification, such as amino acid destruction, peptide scission and formation of protein-lipid complexes (Saeed & Howell, 2002). 3.5. Low field-nuclear magnetic resonance analysis LF-NMR can be used to evaluate the migration and distribution of water molecules in meat and meat products. There were three peaks which were assigned to three relaxation components. T2b (0–2 ms) corresponds to the bound water which was closely bound to macromolecules, T21 (10–100 ms) represents the immobilized water trapped within the myofibrillar protein network, and T22 (100–1000 ms) corresponds to the free water existing in the space amongst the fibre bundles (Zhang, Regenstein, Zhou, & Yang, 2017). Fig. 4A-C shows the changes in T2 relaxation characteristics of thawed muscles with different freezing treatments during frozen storage. The relaxation time corresponding to the three peaks in all samples had different degrees of right shift (increase of relaxation time) with increased frozen storage time (P < 0.05), suggesting that the capillary force of the muscle tissue was impaired (Xue et al., 2018). As shown in Fig. 5A, T2b had no obvious differences amongst all samples (P > 0.05) at 0 days. With the increase in frozen storage time, the T2b of all the samples became gradually longer. Amongst them, the T2b relaxation time of the AF samples increased the fastest and was significantly longer than that of the IF and UIF-180 samples (P < 0.05), and the UIF-180 samples had the shortest T2b from 30 to 180 days of storage (P < 0.05). For T21, changes in the three treatments were similar to T2b (bound water) except at 0 days (Fig. 5B). T21 of the AF, IF, and UIF-180 samples were 57.03, 48.95, and 40.44 ms at 0 days, and it increased to 68.62, 62.84 and 56.95 ms at 180 days, respectively. T21 relaxation times of the UIF-180 samples were significantly shorter than that of the AF and IF samples during 180 days of frozen storage (P < 0.05). The increased T21 suggested that the capillary force of the muscle tissue was impaired (Xue et al., 2018). Similar results were reported by Sanchez-Alonso, Martinez, Sanchez-Valencia, and Careche (2012), who found that there was a significant increase in the T21 of hake muscle with increased frozen storage time. During freezing and frozen storage, large and extracellular ice crystals disrupt the physical structure of muscle tissue. After the meat thaws, the damaged myofibrils have difficulty reabsorbing the melted water in the extracellular spaces due to the destruction of the cell membrane, which leads to partly immobilized water converting to free water (Leygonie et al., 2012). In this study, during the freezing and frozen storage, UIF-180 showed minimal damage to the muscle fibres because of their small and evenly distributed ice crystals; thus, the T21 was shorter than that of AF and IF. Moreover, the corresponding areas A21 of the three samples were decreased (P < 0.05) with increasing storage time (P < 0.05), and UIF-180 had significantly higher A21 than that of AF and IF (Fig. 5E). This result also indicates the UIF-180 can combine more immobilized water than other samples in the same storage period. The change in the T22 relaxation time is similar to that of the T21 during frozen storage (Fig. 5C). However, the T22 relaxation areas (A22) were increased gradually with the increase of storage time (Fig. 5F).
Fig. 4. Changes in LF-NMR T2 relaxation times of frozen porcine longissimus muscles affected by different freezing methods during frozen storage. AF, air freezing; IF, immersion freezing; UIF-180, ultrasound-assisted immersion freezing at 180 W.
29
Meat Science 151 (2019) 24–32
M. Zhang et al.
(D)
AF IF UIF-180
3.5 3.0
Aa Ba BCa Bab Ab BCb Bc
T2b (ms)
2.5 CDa
2.0 1.5
Da
Ea Db Dc
AF IF UIF-180
0.06
Aa Ab
0.05
ABa Aa
Aa ABa ABa ABa Aa Aa ABa ABa Ba Aa ABa Ba
Ac
Bb Ab
A2b (%)
(A)
Cb Cb Cc CDc
0.04
0.02
0.5
0.01
Ac
30
60
90
120 150 180
0
30
Frozen storage time (days) AF IF UIF-180
80 70
T21 (ms)
Da
Da
Cb
BCa
Bb
Cab CDc
Bb
Ab
100
Ab Ac
Bc
BCc
BCc
Aa
ABa
Aab
DEc Ec
40
20
20
450
Aa
Aa
Ba Ca Aa Bb Cab CDa Cab BCb BCb CDc CDb Da Db DEc EFc
30
40
CDa Ca
Da
Ba Cb
BC
Bb
A22 (%)
Bb BCa Cab Cb
90
120 150 180
AF IF UIF-180
50
Ab
350
60
Frozen storage time (days)
Aa
400
300
0
F)
AF IF UIF-180
120 150 180
0
30 60 90 120 150 180 Frozen storage time (days)
(C)
Aa Ba Ab Ac Bb ABb
60 40
10
T22 (ms)
80
30
0
90
AF IF UIF-180
120 BCa
Ca
60
Frozen storage time (days)
(E)
A21 (%)
(B)
50
Ab Cb
0.00
0
60
Aa Bb
0.03
1.0
0.0
ABb
Aa
Ac ABc
Bb
Ca Ea
30 Da Fb
20
Ca Da
Ba Ba Cb Ca Bb Bc
Aa Bb
Aa Aa Ab
Bc
Cb
Cb
Dc
Dab Db
Db
10
250
0
200 0
30
60
90
0
120 150 180
30
60
90
120 150 180
Frozen storage time (days)
Frozen storage time (days)
Fig. 5. Changes in LF-NMR T2 relaxation times and the corresponding peak area A21 of frozen porcine longissimus muscles affected by different freezing methods during frozen storage. AF, air freezing; IF, immersion freezing; UIF-180, ultrasound-assisted immersion freezing at 180 W. Means with different letters (A-F) are significantly different (P < 0.05) in different frozen storage durations for the same treatment, and means with different lowercase letters (a-c) indicate significant differences between freezing method at the same time point (P < 0.05).
were 52.58, 51.17, and 49.28 at 0 days and increased to 57.10, 54.88, and 52.48 at 180 days, respectively (P < 0.05). The L*-value of the UIF-180 samples were always lower (P < 0.05) than that of AF and IF during the frozen storage. The change in the L*-value is affected by the freezing rate and method, which is related to the water state and distribution in the thawed muscle. The muscle with slow freezing rate (AF samples) had more thawing loss, which leads to greater light reflection and lighter colour. Muela et al. (2010) also proved that slowly frozen lamb after thawing was lighter in colour than fast frozen meat. As proven in the above LF-NMR analysis, water migration in the UIF-180 samples was the smallest, thus less thawed water was attached to the surface of the meat, which reduced the light reflection intensity and decreased the lightness (Farouk et al., 2004). Additionally, muscle fibre
Renou, Monin, and Sellier (1985) showed that there was a relationship between relaxation time and quality characteristics of pork, and they confirmed that muscle samples with a longer T2 relaxation time had a higher thawing loss (drip loss). This study revealed that free water in the UIF-180 samples had lower mobility and was more tightly bound to muscle tissue than other AF and IF samples, thus decreasing thawing loss. 3.6. Colour Colour has an important influence on appearance and acceptability of food. As shown in Table 1, the L*- value increased with increased storage time. Lightness (L*- value) of the AF, IF, and UIF-180 samples 30
Meat Science 151 (2019) 24–32
M. Zhang et al.
Table 1 Changes in colour of frozen porcine longissimus muscles affected by different freezing methods during frozen storage. Colour parameters
Samples
Frozen storage time (days) 0
L*
a*
b*
AF IF UIF-180 AF IF UIF-180 AF IF UIF-180
52.58 51.17 49.28 17.26 17.47 17.87 15.32 14.29 14.31
30 ± ± ± ± ± ± ± ± ±
Ea
0.15 0.11Eb 0.06Ec 0.12Ab 0.10Ab 0.06Aa 0.12Da 0.15Fb 0.09Eb
53.54 51.16 50.22 17.27 17.15 17.73 16.16 15.08 15.36
60 ± ± ± ± ± ± ± ± ±
Da
0.12 0.14Eb 0.11Dc 0.06Ab 0.03Bb 0.08Ba 0.11Da 0.07Eb 0.13Db
53.51 52.82 52.52 15.45 16.71 17.15 18.82 17.15 16.21
90 ± ± ± ± ± ± ± ± ±
Da
0.11 0.11Db 0.11Cc 0.10Bc 0.14Cb 0.08Ca 0.06Ca 0.07Dab 0.05Cb
54.45 52.76 52.79 15.55 16.43 16.84 18.94 18.87 17.56
120 ± ± ± ± ± ± ± ± ±
Ca
0.18 0.07Db 0.08Cb 0.11Bc 0.08Db 0.09Da 0.10BCa 0.11Ca 0.08Bb
57.10 54.88 52.48 15.04 15.36 16.24 19.80 18.62 17.41
150 ± ± ± ± ± ± ± ± ±
Ba
0.72 0.38Cb 0.17Cc 0.21Cb 0.09Eb 0.11Da 0.04Ba 0.13Cb 0.15Bc
57.60 56.52 54.28 12.92 14.45 15.88 20.14 19.53 18.80
180 ± ± ± ± ± ± ± ± ±
ABa
0.23 0.11Bb 0.23Bc 0.19Dc 0.08Fb 0.13Ea 0.07ABa 0.15Bb 0.13Ac
58.45 57.53 55.25 12.72 13.72 15.14 21.39 20.77 18.56
± ± ± ± ± ± ± ± ±
0.15Aa 0.22Aa 0.24Ab 0.10Dc 0.11Gb 0.07Fa 0.06Aa 0.09Ab 0.08Ac
AF, air freezing; IF, immersion freezing; UIF-180, ultrasound -assisted immersion freezing at 180 W. Values are given as the means ± SE from triplicate determinations; A-G means in the same row with different letters differ significantly (P < 0.05); a-c means in the same column within same index with different letters differ significantly (P < 0.05).
results of cutting force indicated that the UIF-180 was more effective in maintaining the original muscle tissue. The TBARS values of the UIF180 samples were significantly lower than those of the AF and IF samples from 60 to 180 days. Low-field NMR analysis showed that the T2 relaxation times (T2b,T21 and T22) of the UIF-180 samples were the shortest, which revealed that UIF-180 could decrease water migration during frozen storage. The UIF-180 samples also had a higher a* value and lower L* value. Overall, ultrasonic treatment at a certain power is beneficial for maintaining frozen muscle quality.
shrinkage of the UIF-180 samples was less severe than that of AF and IF, which helps decrease the light scattering on the meat surface and increase the L*-value (Hector, Brew-Graves, Hassen, & Ledward, 1992). Redness (a*-value) was influenced by both freezing method and frozen storage time, and it has an opposite change trend to that of L*value. The a*-values significantly decreased with the increasing frozen storage time (P < 0.05). For example, a*-values of AF and IF were 12.92, 12.72 and 14.45, 13.72 for 150 and 180 days frozen storage, respectively. Holman, Van, Mao, Coombs, and Hopkins (2017) indicated that a*-value of 14.50 was the minimum threshold of acceptability of fresh meat, which reflected that longer frozen storage time obviously impacted the quality of AF and IF samples. However, the UIF180 samples had a significant lower reduction rate in a*-value than the AF and IF samples during the frozen storage (P < 0.05). Muela et al. (2010) found that the redness of frozen muscle was negatively related to frozen storage time because frozen storage reduces the activity of metmyoglobin-reducing enzymes, and this reduction rate increases with prolonged storage time (Farouk & Swan, 1998). Finally, metmyoglobin formation and accumulation on meat surfaces changes meat colour from red to brown (Utrera, Parra, & Estévez, 2014). According to the above microstructure characteristics of frozen muscles (Fig. 1), the tissue damage of the UIF-180 samples is less than that of the AF and IF samples, which could maintain the activity of metmyoglobin-reducing enzymes well and thus lead to a redder appearance. In contrast, a large amount of oxidase released from serious cellular disruption after thawing, which caused the AF samples to have a high degree of myoglobin oxidation, and metmyoglobin were thought to contribute to the brown (a*-value reduction) appearance (Muela, Monge, Sañudo, Campo, & Beltrán, 2015). In addition, UIF-180 could induce the lower degree of lipid oxidation which indicated by lower TBARS values, and prevent the formation of metmyoglobin (Jeong, Kim, Yang, & Joo, 2011). The change in b*-value is similar to that of the L*-value during frozen storage. The b*- value increased with increased storage time, and the UIF-180 samples always had lower b*-values than that AF and IF samples during storage (P < 0.05). Coombs et al. (2017) revealed that protein oxidation could decrease colour stability and increase b*-values during frozen storage. This result could be related to increases in TBARS during frozen storage (Fig. 3).
Acknowledgements This study was supported by the National Natural Science Foundation of China (grant No. 31571859 and No. 31771903) and the National Key Research and Development Plan for the 13th Five-Year Plan Period in China (grant No. 2016YFD0401504). References Aaslyng, M. D., Bejerholm, C., Ertbjerg, P., Bertram, H. C., & Andersen, H. J. (2003). Cooking loss and juiciness of pork in relation to raw meat quality and cooking procedure. Food Quality & Preference, 14(4), 277–288. Bevilacqua, A., & Zaritzky, N. E. (1986). Rate of pigment modifications in packaged refrigerated beef using reflectance spectrophotometry. Journal of Food Processing & Preservation, 10(1), 1–18. Boonsumrej, S., Chaiwanichsiri, S., Tantratian, S., Suzuki, T., & Takai, R. (2007). Effects of freezing and thawing on the quality changes of tiger shrimp (Penaeus monodon) frozen by air-blast and cryogenic freezing. Journal of Food Engineering, 80(1), 292–299. Bueno, M., Resconi, V. C., Campo, M. M., Cacho, J., Ferreira, V., & Escudero, A. (2013). Effect of freezing method and frozen storage duration on odor-active compounds and sensory perception of lamb. Food Research International, 54(1), 772–780. Cheng, X., Zhang, M., Xu, B. G., Adhikari, B., & Sun, J. C. (2015). The principles of ultrasound and its application in freezing related processes of food materials: A review. Ultrasonic Sonochemisry, 27, 576–585. Chevalier, D., Sentissi, M., Havet, M., & Bail, A. L. (2000). Comparison of air-blast and pressure shift freezing on Norway lobster quality. Journal of Food Science, 65(2), 329–333. Coombs, C., Holman, B., Collins, D., Kerr, M. J., Friend, M. A., & Hopkins, D. L. (2017). Effects of chilled-then-frozen storage (up to 52 weeks) on an indicator of protein oxidation and indices of protein degradation in lamb M. longissimus lumborum. Meat Science, 135, 134–141. Damodaran, S., & Wang, S. Y. (2017). Ice crystal growth inhibition by peptides from fish gelatin hydrolysate. Food Hydrocolloids, 70, 46–56. Farouk, M. M., & Swan, J. E. (1998). Effect of rigor temperature and frozen storage on functional properties of hot-boned manufacturing beef. Meat Science, 49(2), 233–247. Farouk, M. M., Wieliczko, K. J., & Merts, I. (2004). Ultra-fast freezing and low storage temperatures are not necessary to maintain the functional properties of manufacturing beef. Meat Science, 66(1), 171–179. Figueirêdo, B. C., Trad, I. J., Mariutti, L. R. B., & Bragagnolo, N. (2014). Effect of annatto powder and sodium erythorbate on lipid oxidation in pork loin during frozen storage. Food Research International, 65, 137–143. Hector, D. A., Brew-Graves, C., Hassen, N., & Ledward, D. A. (1992). Relationship between myosin denaturation and the colour of low-voltage-electrically-stimulated beef. Meat Science, 31(3), 299–307. Holman, B. W., Van, R. J., Mao, Y., Coombs, C. E., & Hopkins, D. L. (2017). Using instrumental (CIE and reflectance) measures to predict consumers' acceptance of beef
4. Conclusions UIF-180 had an obvious influence on microstructure, quality and water distribution of porcine longissimus muscles during frozen storage. UIF-180 effectively maintained the smaller ice crystal size within the muscle during the frozen storage period. The thawing and cooking losses increased with extended storage time, and the UIF-180 sample had the smallest thawing loss, followed by the IF and AF samples. The 31
Meat Science 151 (2019) 24–32
M. Zhang et al.
Sanchez-Alonso, I., Martinez, I., Sanchez-Valencia, J., & Careche, M. (2012). Estimation of freezing storage time and quality changes in hake (Merluccius merluccius, L.) by low field NMR. Food Chemisty, 135(3), 1626–1634. Santacatalina, J. V., Guerrero, M. E., Garcia-Perez, J. V., Mulet, A., & Cárcel, J. A. (2016). Ultrasonically assisted low-temperature drying of desalted codfish. LWT - Food Science and Technology, 65, 444–450. Song, G. S., Q, H. S., & Lin, L. (2008). Effect of ultrasound-assisted freezing on changes in protein secondary structure studied by fourier transform infrared spectroscopy. Journal of Shaanxi University of Science & Technology, 26, 132–137. Soyer, A., Özalp, B., Dalmış, Ü., & Bilgin, V. (2010). Effects of freezing temperature and duration of frozen storage on lipid and protein oxidation in chicken meat. Food Chemistry, 120(4), 1025–1030. Tarladgis, B. G., Watts, B. M., & Younathan, M. T. (1960). A distillation method for the quantitative determination of malonaldehyde in rancid foods. The Journal of the American Oil Chemists'Society, 37, 44–48. Tironi, V., Lamballerie, M. D., & Lebail, A. (2010). Quality changes during the frozen storage of sea bass (Dicentrarchus labrax) muscle after pressure shift freezing and pressure assisted thawing. Innovative Food Science & Emerging Technologies, 11(4), 565–573. Turgut, S. S., Işıkçı, F., & Soyer, A. (2017). Antioxidant activity of pomegranate peel extract on lipid and protein oxidation in beef meatballs during frozen storage. Meat Science, 129, 111–119. Turner, E. W., Paynter, W. D., Montie, E. J., Bessert, M. W., Struck, G. H., & Olson, F. C. (1954). Use of the 2-thiobarbithuric acid reagent to measure rancidity in frozen pork. Food Technology, 8(7), 326–330. Utrera, M., Parra, V., & Estévez, M. (2014). Protein oxidation during frozen storage and subsequent processing of different beef muscles. Meat Science, 96(2), 812–820. Xia, X. F., Kong, B. H., Liu, Q., & Liu, J. (2009). Physicochemical change and protein oxidation in porcine longissimus dorsi as influenced by different freeze-thaw cycles. Meat Science, 83(2), 239–245. Xue, S. W., Xu, X. L., Shan, H. M., Wang, H. H., Yang, J., & Zhou, G. H. (2018). Effects of high-intensity ultrasound, high-pressure processing, and high-pressure homogenization on the physicochemical and functional properties of myofibrillar proteins. Innovative Food Science & Emerging Technologies, 45, 354–360. Zhang, M. C., Niu, H. L., Chen, Q., Xia, X. F., & Kong, B. H. (2018). Influence of ultrasound-assisted immersion freezing on the freezing rate and quality of porcine longissimus muscles. Meat Science, 136, 1–8. Zhang, X., Inada, T., Yabe, A., Lu, S., & Kozawa, Y. (2001). Active control of phase change from supercooled water to ice by ultrasonic vibration 2. Generation of ice slurries and effect of bubble nuclei. International Journal of Heat & Mass Transfer, 44(23), 4533–4539. Zhang, Z. Y., Regenstein, J. M., Zhou, P., & Yang, Y. L. (2017). Effects of high intensity ultrasound modification on physicochemical property and water in myofibrillar protein gel. Ultrasonics Sonochemistry, 34, 960–967. Zheng, L. Y., & Sun, D. W. (2006). Innovative applications of power ultrasound during food freezing processes-a review. Trends in Food Science & Technology, 17, 16–23.
colour. Meat Science, 127, 57–62. Hong, H., Zhu, S. C., Luo, Y. K., & Yu, J. (2011). Quality changes of bighead carp (Aristichthys nobilis) during chilled and partial freezing storage. South China Fisheries Science, 7(6), 7–12. Islam, M. N., Zhang, M., Adhikari, B., Cheng, X. F., & Xu, B. G. (2014). The effect of ultrasound-assisted immersion freezing on selected physicochemical properties of mushrooms. International Journal of Refrigeration, 42, 121–133. Jeong, J. Y., Kim, G. D., Yang, H. S., & Joo, S. T. (2011). Effect of freeze–thaw cycles on physicochemical properties and color stability of beef semimembranosus muscle. Food Research International, 44, 3222–3228. Jia, N., Kong, B. H., Liu, Q., Diao, X. P., & Xia, X. F. (2012). Antioxidant activity of black currant (ribesnigrum L.) extract with aqueous ethanol and its inhibitory effect on lipid and protein oxidation of pork patties during chilled storage. Meat Science, 91, 533–539. Kang, D. C., Zou, Y. H., Cheng, Y. P., Xing, L. J., Zhou, G. H., & Zhang, W. G. (2016). Effects of power ultrasound on oxidation and structure of beef proteins during curing processing. Ultrasonic Sonochemistry, 33, 47–53. Kim, Y. H., Liesse, C., Kemp, R., & Balan, P. (2015). Evaluation of combined effects of ageing period and freezing rate on quality attributes of beef loins. Meat Science, 110, 40–45. Lanari, M. C., Schaefer, D. M., & Scheller, K. K. (1995). Dietary vitamin E supplementation and discoloration of pork bone and muscle following modified atmosphere packaging. Meat Science, 41(3), 237–250. Leygonie, C., Britz, T. J., & Hoffman, L. C. (2012). Impact of freezing and thawing on the quality of meat: Review. Meat Science, 91(2), 93–98. Li, B., & Sun, D. W. (2002). Effect of power ultrasound on freezing rate during immersion freezing of potatoes. Journal of Food Engineering, 55(3), 277–282. Liu, Z. L., Xiong, Y. L., & Chen, J. (2010). Protein oxidation enhances hydration but suppresses water-holding capacity in porcine longissimus muscle. Journal of Agricultural and Food Chemistry, 58(19), 10697–10704. Muela, E., Monge, P., Sañudo, C., Campo, M. M., & Beltrán, J. A. (2015). Meat quality of lamb frozen stored up to 21 months: Instrumental analyses on thawed meat during display. Meat Science, 102, 35–40. Muela, E., Sanudo, C., Campo, M. M., Medel, I., & Beltran, J. A. (2010). Effect of freezing method and frozen storage duration on instrumental quality of lamb throughout display. Meat Science, 84(4), 662–669. Ngapo, T. M., Babare, I. H., Reynolds, J., & Mawson, R. F. (1999). Freezing rate and frozen storage effects on the ultrastructure of samples of pork. Meat Science, 53(3), 159–168. Rahelić, S., Puač, S., & Gawwad, A. H. (1985). Structure of beef longissimus dorsi muscle frozen at various temperatures: Part 1-histological changes in muscle frozen at −10, −22, −33, −78, −115 and −196°C. Meat Science, 14(2), 63–72. Renou, J. P., Monin, G., & Sellier, P. (1985). Nuclear magnetic resonance measurements on pork of various qualities. Meat Science, 15(4), 225–233. Saeed, S., & Howell, N. K. (2002). Effect of lipid oxidation and frozen storage on muscle proteins of Atlantic mackerel (Scomber scombrus). Journal of the Science of Food & Agriculture, 82(5), 579–586.
32
Contents lists available at ScienceDirect
Meat Science journal homepage: www.elsevier.com/locate/meatsci
Changes in microstructure, quality and water distribution of porcine longissimus muscles subjected to ultrasound-assisted immersion freezing during frozen storage Mingcheng Zhanga,b,c,1, Xiufang Xiaa,1, Qian Liua, Qian Chena, Baohua Konga,
T
⁎
a
College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China College of Food Science and Technology, Bohai University, China c Food Safety Key Lab of Liaoning Province, National & Local Joint Engineering Research Center of Storage, Processing and Safety Control Technology for Fresh Agricultural and Aquatic Products, Jinzhou, Liaoning 121013, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Ultrasound-assisted immersion freezing Porcine longissimus muscle Quality characteristic Microstructure Water distribution
The effect of ultrasound-assisted immersion freezing at 180 W (UIF-180) on the microstructure, quality and water distribution of porcine longissimus muscles during frozen storage was evaluated. The size of the ice crystals increased with extended storage time, and UIF-180 samples had a smaller size and uniform distribution of ice crystals. The thawing and cooking losses in the UIF-180 sample were significantly lower than that in air freezing (AF) and immersion freezing (IF) samples (P < 0.05). AF samples had a higher cutting force at 0 days. During the 60–180 days of the storage period, the cutting force of UIF-180 samples was significantly higher than that of AF and IF samples (P < 0.05). Low field-nuclear magnetic resonance results showed that UIF-180 decreased water migration during frozen storage. UIF-180 samples had significantly lower lipid oxidation and higher redness than that of the AF and IF samples (P > 0.05). Overall, UIF at particular powers is an efficient method in reducing quality deterioration of muscles during long-term frozen storage.
1. Introduction Freezing and frozen storage are important methods for the longterm preservation of meat and meat production, which can inhibit microbial growth, slow enzymatic activity, and preserve the original taste and nutritional value (Ngapo, Babare, Reynolds, & Mawson, 1999). However, some adverse changes such as protein denaturation and lipid oxidation still happen, which are the primary causes of declining sensory quality of frozen products, and these changes can be accelerated by freezer burn when the frozen meat is unpacked and exposed to air (Turgut, Işıkçı, & Soyer, 2017). Freezing methods and storage conditions, such as freezing rate and storage time, substantially influence the quality of frozen meat. Furthermore, ice crystal growth within muscle tissue during frozen storage is a quality issue because recrystallization of ice crystals can lead to muscle physical structure weakening (Damodaran & Wang, 2017). Additionally, drip loss and nutritional value loss in muscle can still occur during the freeze/thaw process, which negatively modifies the final product quality and consumer acceptability of meat products (Figueirêdo, Trad, Mariutti, &
Bragagnolo, 2014). Ultrasound is a new technology being used in food preservation and analysis. The ultrasonic waves cause severe turbulence in liquid medium and increase heat transmission efficiency (Cheng, Zhang, Xu, Adhikari, & Sun, 2015). Ultrasound-assisted immersion freezing (UIF) is an effective method to increase the heat transfer coefficient and accelerate the freezing process of food (Li & Sun, 2002). The cavitation and microstreaming produced by power ultrasound are the major reasons to shorten the freezing time of food (Islam, Zhang, Adhikari, Cheng, & Xu, 2014). Additionally, ultrasound can increase the probability of nucleation in supercooled water and induce nucleation at higher temperatures during the freezing process, which is very useful for controlling the size and distribution of ice crystals in frozen materials (Cheng et al., 2015). Therefore, UIF is an effective method for maintaining the quality of frozen foods. There are some reports about the effect of UIF on food quality and freezing speed. Li and Sun (2002) found that the tissue of potatoes frozen using ultrasound assisted freezing exhibited superior cellular structure compared to the samples frozen without applying power ultrasound. Islam et al. (2014) reported
⁎
Corresponding author at: College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China. E-mail addresses: [email protected], [email protected] (B. Kong). 1 These authors contributed to this work equally. https://doi.org/10.1016/j.meatsci.2019.01.002 Received 21 September 2018; Received in revised form 27 December 2018; Accepted 9 January 2019 Available online 11 January 2019 0309-1740/ © 2019 Elsevier Ltd. All rights reserved.
Meat Science 151 (2019) 24–32
M. Zhang et al.
2.3. Thawing loss, cooking loss, and cutting force measurement
that the application of ultrasound at different levels during immersion freezing significantly reduced the freezing time of mushroom and better preserved the microstructure of frozen samples. Similar results were also found in the freezing of fish (Santacatalina, Guerrero, Garcia-Perez, Mulet, & Cárcel, 2016), gluten (Song, Q, & Lin, 2008), and meat (Zhang, Niu, Chen, Xia ＆ Kong, 2018). In a previous study, we investigated the effect of UIF on the quality and freezing rate of porcine longissimus muscle at various ultrasound powers. The results showed that UIF at certain powers significantly increased the freezing rate of muscles, and samples treated with UIF at 180 W (UIF-180) had a shorter freezing time, smaller and uniformly ice crystal distribution, and lower thawing loss (Zhang et al., 2018). This result indicated that UIF-180 treatment increases the freezing rate of muscle samples and improves meat quality. However, there were little reports about the changes of microstructure, quality and water distribution of meat which subjected to UIF during frozen storage. Therefore, the objective of our present study was to investigate the changes of microstructure, thawing loss, colour attributes, cutting force, cooking loss, lipid oxidation, as well as water migration and distribution of porcine longissimus muscles during 180 days of frozen storage as influenced by different freezing methods, such as UIF-180, AF and IF.
The frozen samples were air thawed overnight at 4 °C. The thawing loss was determined as described by Xia, Kong, Liu, and Liu (2009) and expressed as:
Thawing loss (%) = (M0 − M1)/ M0 where M0 and M1 represent the weight of the sample before and after thawing, respectively. Thawed muscle samples were packed and cooked at 85 °C in a water bath until the centre temperature reached 75 °C. Cooking loss was calculated according to the following equation:
Cooking loss (%) = (M1 − M2)/ M1 where M1 and M2 represent the weight of the sample before and after cooking, respectively. After determining cooking loss, the cooked samples were used to measure cutting force as described by Zhang et al. (2018). Briefly, cylindrical cores (1.27 cm in diameter) from each cooked sample were cut using a texture analyser (Stable Micro System; TA: XT2i, England) with a knife blade (HDP/BSW). The maximum force which cut transversally into the chops was recorded as cutting force (N).
2. Materials and methods
2.4. Thiobarbituric acid-reactive substance measurement
2.1. Frozen sample preparation
Thiobarbituric acid-reactive substance (TBARS) was measured based on the method of Xia et al. (2009). Briefly, a sample of 2 g was homogenized and mixed in 3 mL of 1% thiobarbituric acid, and then, 17 mL of 2.5% trichloroacetic acid was added. The mixture was boiled for 30 min and cooled in cold water. The mixture was centrifuged at 3000 g for 10 min at room temperature, and the absorbance was recorded at 532 nm (A532). The TBARS value was expressed as the following:
Porcine longissimus muscles (lumborum) were purchased from the Beidahuang Meat Corporation (Harbin, Heilongjiang, China) within 24 h after slaughter. The pigs (approximately 24 weeks of age) were slaughtered according to the pig slaughtering operating procedures (GB/T 17236-1998) in China. The muscle samples were wrapped at 0–4 °C and transported to the laboratory. Approximately 3-cm-thick chops (120 ± 2 g) of pork loin were manually cut perpendicular to the direction of the muscle fibres and packaged with poly nylon pouches. Sample preparation was conducted at 4 °C. There were three treatments including air freezing (AF), immersion freezing (IF), and ultrasound-assisted immersion freezing at 180 W power (UIF-180). The UIF freezer was made by Nanjing Xianou Co., Ltd. Nanjing, China with 10 ultrasound transducers at the bottom of the freezing tank. The structure of the freezer was same as described by Zhang et al. (2018) with 5% fluoride plus 95% ethanol as a coolant. The size of the freezing tank was 30 × 22 × 26 cm3. The muscle samples were frozen according to our previous descriptions (Zhang et al., 2018). The AF process was conducted at −20 ± 0.5 °C and ended when the geometric centre temperature of the chops reached approximately −18 °C. For IF and UIF-180, chops were immersed in the coolant (−20.0 ± 0.5 °C) with 0 W and 180 W ultrasound powers, respectively, until the geometric centre temperature reached approximately −18 °C. After freezing, muscle samples were stored at −18 ± 1 °C for 0, 30, 60, 90, 120, 150, and 180 d. For each treatment, at least 42 chops were used, and for each storage time, 6 chops were used for analysis.
TBARS (mg malondialdehyde/kg of muscle) = (A532 /weight of muscle) × 9.48 where “9.48” was a constant derived from the dilution factor and the molar extinction coefficient (152,000 M−1 cm−1) of the red, TBA arbituric acid reaction product. 2.5. Low field-nuclear magnetic resonance measurement Low field-nuclear magnetic resonance (LF-NMR) relaxation measurements were performed as described by Zhang et al. (2018) with an LF-NMR analyser minispec mq 20 (Bruker Optik GmbH, Ettlingen, Germany). Briefly, the thawed muscle chops (1 × 1 × 2 cm3) were put into 18 mm NMR tubes for determination. The transverse relaxation time (T2) was measured using the Carr-Purcell-Meiboom-Gill pulse sequence. Bi-exponential fitting resulted in three water populations, A2b, A21 and A22, with corresponding relaxation times T2b, T21 and T22 via the software provided by Bruker instruments. 2.6. Colour measurement
2.2. Microstructure of frozen samples The colour of the thawed muscle samples was evaluated by a ZE6000 colourimeter (Juki Corp, Tokyo, Japan) according to the method of Jia, Kong, Liu, Diao, and Xia (2012). A minimum of 3 chops were used to analyse the L* (lightness)-, a* (redness)- and b* (yellowness) values. For each chop, four different locations on the surface were used to determine colour.
The frozen samples (0.5 × 0.5 × 1 cm3) were excised perpendicularly or parallel to the direction of the myofibres at −20 °C using a Leica CM1850 cryostat (CM1850, Leica, Germany). The cross-sections or longitudinal sections of the samples (4 μm thick) were obtained and stained following a method described previously (Zhang et al., 2018). Three micrographs of each specimen were observed using a light microscope connected to a digital camera (Olympus BX41, Olympus Optical Co. Ltd., Tokyo, Japan). The average radiuses of ice crystals in the three images of each specimen were quantitatively analyzed using Image-Pro Plus software (Media Cybernetics, Silver Spring, MD, USA).
2.7. Statistical analysis Three batches of samples subjected to different freezing treatments were processed independently to study the effects of the different 25
Meat Science 151 (2019) 24–32
M. Zhang et al.
(caption on next page)
26
Meat Science 151 (2019) 24–32
M. Zhang et al.
Fig. 1. Changes in microstructural cross section (A), longitudinal section (B), and average radius of ice crystal (C) of frozen porcine longissimus muscles affected by different freezing methods during frozen storage. AF, air freezing; IF, immersion freezing; UIF-180, ultrasound-assisted immersion freezing at 180 W. Scale bars indicate 400 μm. Means with different letters (A-E) are significantly different (P < 0.05) in different frozen storage durations for the same treatment, and means with different letters (a-c) indicate significant differences between freezing method at the same time point (P < 0.05).
3.2. Thawing loss and cooking loss
freezing treatments on quality characteristics of porcine longissimus muscles during frozen storage. For each batch of samples, all experiments were performed in triplicate. The results are expressed as the mean ± standard deviations which analyzed using the General Linear Model procedure of the Statistix 8.1 software package (Analytical Software, St. Paul, MN, USA). Data was subjected to one-way analysis of variance (ANOVA). And mean comparison was performed (P < 0.05) using Tukey procedures.
Thawing loss substantially influences the appearance, weight, colour, and sensory quality of meat and meat products (Xia et al., 2009). Thawing loss increased with extended storage time (Fig. 2A). The thawing losses of the AF, IF, and UIF-180 samples were 4.63%, 2.52%, and 1.23% at 0 days, and they significantly increased to 11.32%, 9.51%, and 7.49% at 180 days, respectively (P < 0.05). The UIF sample had the smallest thawing loss, followed by IF and AF samples during frozen storage. Thawing loss is related to the rate of thawing, ice crystal location and size, and the integrity of muscle tissue (Farouk, Wieliczko, & Merts, 2004; Kim, Liesse, Kemp, & Balan, 2015). The disruption of muscle fibres caused by the growth of ice crystals during frozen storage can diminish the water binding capacity of muscle (Rahelić, Puač, & Gawwad, 1985). The reduced thawing loss in the UIF-180 samples is related to the formation of small and even ice crystals, which results in less damage to the muscle structure during frozen storage. For AF samples, the slow freezing rate caused water migration to the extracellular space, which can lead to the formation of irregular and large ice crystals and destruction of muscle structure (Muela, Sanudo, Campo, Medel, & Beltran, 2010). Therefore, the AF sample had a weak ability to re-absorb melted water back into the cells after thawing. Cooking loss usually includes a mixture of liquid and soluble substances from muscle during cooking (Hong et al., 2011). Products with low cooking loss may have better eating quality (Aaslyng, Bejerholm, Ertbjerg, Bertram, & Andersen, 2003). The influence of different freezing methods and storage time on the cooking loss of samples is shown in Fig. 2B. The cooking losses of samples exhibited similar trends to thawing loss. The cooking losses of the AF, IF, and UIF-180 samples were 37.44%, 32.39%, and 31.35% at 0 days and significantly increased to 42.48%, 40.59%, and 38.64% at 180 days, respectively (P < 0.05). The UIF-180 sample had the smallest cooking loss during frozen storage. Hong et al. (2011) found that the thawing loss of bighead carp (Aristichthys nobilis) by different freezing methods increased with the increase in frozen storage time. According to the results of the muscle microstructures (Fig. 1), the UIF-180 samples had uniform and fine ice crystals, which effectively maintain the integrity of muscle tissue during freezing and frozen storage and contribute to smaller cooking loss.
3. Results and discussion 3.1. Microstructure of frozen muscles The size of ice crystals is crucial to the final quality of frozen foods. The expansion pressure of ice crystals can cause irreversible damage to the structure of the muscle, thereby destroying muscle quality, colour, taste and nutritional value (Hong, Zhu, Luo, & Yu, 2011). The distribution and size of ice crystals inside the muscles and changes of the muscle during frozen storage were evaluated using image analysis. Fig. 1A and Fig. 1B represent the cross-sections and longitudinal sections of the frozen muscle tissue with different freezing treatments, respectively, and Fig. 1C represents the average radius of the ice crystals. As shown in Fig. 1A and B, different freezing treatments substantially influenced the size and distribution of ice crystals inside the muscles during frozen storage (P < 0.05). Muscle fibres from UIF-180 samples were arranged neatly and appeared to be more compact and denser. The size of ice crystals increased with an increase in frozen storage time (Fig. 1C). The average radius of the ice crystals of AF, IF, and UIF-180 samples were 29.43, 13.42, and 5.08 μm at 0 days, which increased to 124.28, 85.25, and 46.65 μm at 180 days, respectively (P < 0.05). At 180 days, UIF-180 samples still had the regular and uniform distribution of ice crystals, the average radius of the ice crystals in the UIF-180 samples was 62.46% lower than that in the AF sample and 45.27% smaller than that in the IF sample (P < 0.05). This result suggests that UIF-180 can effectively maintain a smaller ice crystal size within the muscle and cause minimal damage to the muscle fibres during the entire frozen period. Additionally, AF samples presented seriously twisted and narrowed fibres with large intra and extracellular ice crystals. After 90 days of frozen storage, as the shape of the ice crystals presented more irregular, an increased amount of breakages and even fractures occurred in the muscle fibres of the AF samples, which resulted in textural change, and thawing loss increased as shown in Fig. 2A. Both intra- and extra cellular ice crystals in the AF sample squeezed the muscle fibres into a very narrow space, resulting in a widened distance between the fibres. Bevilacqua and Zaritzky (1986) found that even if the diameter of the ice crystals is very small, the recrystallization phenomenon will occur with the prolongation of freezing time. The diffusion of water molecules from bulk to the crystal surface and surface integration were continuing to form some larger sized ice crystals (Tironi, Lamballerie, & Lebail, 2010). Zhang, Inada, Yabe, Lu, and Kozawa (2001) discussed that ultrasound can produce microstreaming, which can promote nucleation during freezing. Zheng and Sun (2006) suggested that certain intensities of ultrasonic power induce ice crystal fracture and lead to ice crystal size reduction. The small ice crystals and their uniform distribution during frozen storage can benefit the quality of frozen foods (Chevalier, Sentissi, Havet, & Bail, 2000).
3.3. Cutting force The cutting force reflects the muscle tenderness, such that lower cutting forces are associated with better tenderness (Xia et al., 2009). As shown in Fig. 2C, AF samples had the highest cutting force at 0 day, which was 18.73% and 22.77% higher than that of the IF and UIF-180 samples, respectively (P < 0.05). This results may be attributed to the greater fluid loss after thawing, which resulted in less water available to hydrate the muscle fibres; thus, a greater force was needed to cut off the muscle fibres (Leygonie, Britz, & Hoffman, 2012). However, the cutting force of AF samples sharply decreased with the increasing storage time until 180 days (P < 0.05), which related to the destruction of muscle tissue. Combined with the above microstructure analysis, the formation of large, extracellular ice crystals in the AF samples disrupt the physical structure, largely breaking myofibrils apart, resulting in decreased cutting force (Leygonie et al., 2012). Liu, Xiong, and Chen (2010) also indicated that the loss in membrane strength due to ice crystal formation could subsequently reduce the force needed to cut the meat. Moreover, for IF and UIF-180 samples, no significant differences of cutting force were observed at 0 day and 30 days (P > 0.05). After 27
Meat Science 151 (2019) 24–32
(A)
12
Thawing loss (%)
Aa
AF IF UIF
10
Ca
Cb Da
8 6
Ea
Cc
Fa
Ba Ab
Ab Ac
Bb Bc
Bc
Cc Db
4 Eb 2
TBARS (mg malonaldehyde/kg of muscle)
M. Zhang et al.
Ec
Eb
Dc
Ec
0 0
(B)
Cooking loss (%)
35
60
90
120
150
180
AF IF UIF-180
0.4
Ba
Ab
Ca Bb Da
0.3
Bc
Db
0.2
Ea
DEa
Cc Dc
DEb
Fb
Fb
0.1
Ea Eb
Ea
Ac
Cb
Fb
0
30
60
90
120
150
180
Frozen storage time (days)
AF IF UIF-180
45 40
30
Aa
0.5
Aa BCa Ba DEa CDa DEa ABb Ab BCa Bab Bb Ea Bc CDb Db Cb Cb Cb
Aa Ab Ac
Fig. 3. Changes in thiobarbituric acid-reactive substance (TBARS) of frozen porcine longissimus muscles affected by different freezing methods during frozen storage. AF, air freezing; IF, immersion freezing; UIF-180, ultrasoundassisted immersion freezing at 180 W. Means with different letters (A-F) are significantly different (P < 0.05) in different frozen storage durations for the same treatment, and means with different lowercase letters (a-c) indicate significant differences between freezing method at the same time point (P < 0.05).
30 that, during the 60–180 days of the storage period, the cutting force of the UIF-180 samples were significantly higher than that of the AF and IF samples (P < 0.05), indicating that the UIF-180 samples were more effective in maintaining the original muscle tissue state. Bueno et al. (2013) used three different methods to freeze the mutton, namely, liquid nitrogen freezing, refrigerator freezing, and blast freezing. They reported that frozen muscles with a faster freezing speed (liquid nitrogen freezing) have higher hardness than the other two methods after frozen storage for 10 months.
25 20 0
30
60
90
120
150
180
Frozen storage time (days)
(C) 35 Aa
Cutting force (N)
30
Ba Bb Aa Ab Bb Ab Cb
25
Bc
20
AF IF UIF-180
3.4. Lipid oxidation Lipid oxidation of frozen muscle was evaluated by measuring TBARS. As shown in Fig. 3, the TBARS formation of three groups increased with increased storage time, and the frozen storage time has a stronger influence on the oxidative degree than freezing method. TBARS values of AF, IF, and UIF-180 samples at 0 days were 0.144, 0.142, and 0.164 mg/kg and increased to 0.489, 0.454, and 0.359 mg malondialdehyde/kg at 180 day, respectively. Previous studies have verified that 0.5 mg malondialdehyde/kg of TBARS value in fresh meat was a borderline which impacting on meat quality/sensory attributes (Lanari, Schaefer, & Scheller, 1995; Tarladgis, Watts, & Younathan, 1960; Turner et al., 1954). Thus, each freezing method did not affect the quality of the meat during 180 days of frozen storage. However, a higher level of TBARS values in the UIF-180 samples at 0 days may be a result of ultrasonic treatment during the freezing process. Kang et al. (2016) found that ultrasound can cause lipid oxidation of beef during curing processing, which was attributed to the hydroxyl radicals produced by brine decomposition, which are caused by the cavitation of ultrasonic waves. However, the TBARS values of the UIF-180 samples were significantly lower than that of the AF and IF samples from 60 to 180 days, which means for UIF-180 samples, fat oxidation increased at the initial frozen storage duration, but its oxidation rate was lower than that of the AF and IF samples. The TBARS values of the IF samples were significantly lower than that of the AF samples from 90 to 180 days. The small ice crystals and a uniform distribution were formed by relative fast freezing rates (UIF-180) and maintained well during the frozen
Ba Cb BbCa Ca Da Db Cb Cb DEc DEc Ec
15 10 0
30
60
90
120
150
180
Frozen storage time (days) Fig. 2. Changes in thawing loss (A), cooking loss (B), and cutting force (C) of frozen porcine longissimus muscles affected by different freezing methods during frozen storage. AF, air freezing; IF, immersion freezing; UIF-180, ultrasound-assisted immersion freezing at 180 W. Means with different letters (AF) are significantly different (P < 0.05) in different frozen storage durations for the same treatment, and means with different lowercase letters (a-c) indicate significant differences between freezing method at the same time point (P < 0.05).
28
Meat Science 151 (2019) 24–32
M. Zhang et al.
storage, which possibly contributed to lipid oxidation to a lower extent over a long duration of frozen storage. Oxidation is a major cause of meat quality deterioration during storage, which can lead to discoloration, flavour deterioration, and nutrient destruction. The lipid oxidation of muscle food during frozen storage may be related to the damage of cellular structures caused by freezing (Boonsumrej, Chaiwanichsiri, Tantratian, Suzuki, & Takai, 2007). Similar results were found by Soyer, Özalp, Dalmış, and Bilgin (2010) in chicken leg and breast meats during frozen storage. Oxidation of samples increased significantly with prolonged storage up to 6 months. Lipid oxidation occurred during frozen storage might cause the denaturation of proteins. Proteins exposed to oxidizing environments are very susceptible to chemical modification, such as amino acid destruction, peptide scission and formation of protein-lipid complexes (Saeed & Howell, 2002). 3.5. Low field-nuclear magnetic resonance analysis LF-NMR can be used to evaluate the migration and distribution of water molecules in meat and meat products. There were three peaks which were assigned to three relaxation components. T2b (0–2 ms) corresponds to the bound water which was closely bound to macromolecules, T21 (10–100 ms) represents the immobilized water trapped within the myofibrillar protein network, and T22 (100–1000 ms) corresponds to the free water existing in the space amongst the fibre bundles (Zhang, Regenstein, Zhou, & Yang, 2017). Fig. 4A-C shows the changes in T2 relaxation characteristics of thawed muscles with different freezing treatments during frozen storage. The relaxation time corresponding to the three peaks in all samples had different degrees of right shift (increase of relaxation time) with increased frozen storage time (P < 0.05), suggesting that the capillary force of the muscle tissue was impaired (Xue et al., 2018). As shown in Fig. 5A, T2b had no obvious differences amongst all samples (P > 0.05) at 0 days. With the increase in frozen storage time, the T2b of all the samples became gradually longer. Amongst them, the T2b relaxation time of the AF samples increased the fastest and was significantly longer than that of the IF and UIF-180 samples (P < 0.05), and the UIF-180 samples had the shortest T2b from 30 to 180 days of storage (P < 0.05). For T21, changes in the three treatments were similar to T2b (bound water) except at 0 days (Fig. 5B). T21 of the AF, IF, and UIF-180 samples were 57.03, 48.95, and 40.44 ms at 0 days, and it increased to 68.62, 62.84 and 56.95 ms at 180 days, respectively. T21 relaxation times of the UIF-180 samples were significantly shorter than that of the AF and IF samples during 180 days of frozen storage (P < 0.05). The increased T21 suggested that the capillary force of the muscle tissue was impaired (Xue et al., 2018). Similar results were reported by Sanchez-Alonso, Martinez, Sanchez-Valencia, and Careche (2012), who found that there was a significant increase in the T21 of hake muscle with increased frozen storage time. During freezing and frozen storage, large and extracellular ice crystals disrupt the physical structure of muscle tissue. After the meat thaws, the damaged myofibrils have difficulty reabsorbing the melted water in the extracellular spaces due to the destruction of the cell membrane, which leads to partly immobilized water converting to free water (Leygonie et al., 2012). In this study, during the freezing and frozen storage, UIF-180 showed minimal damage to the muscle fibres because of their small and evenly distributed ice crystals; thus, the T21 was shorter than that of AF and IF. Moreover, the corresponding areas A21 of the three samples were decreased (P < 0.05) with increasing storage time (P < 0.05), and UIF-180 had significantly higher A21 than that of AF and IF (Fig. 5E). This result also indicates the UIF-180 can combine more immobilized water than other samples in the same storage period. The change in the T22 relaxation time is similar to that of the T21 during frozen storage (Fig. 5C). However, the T22 relaxation areas (A22) were increased gradually with the increase of storage time (Fig. 5F).
Fig. 4. Changes in LF-NMR T2 relaxation times of frozen porcine longissimus muscles affected by different freezing methods during frozen storage. AF, air freezing; IF, immersion freezing; UIF-180, ultrasound-assisted immersion freezing at 180 W.
29
Meat Science 151 (2019) 24–32
M. Zhang et al.
(D)
AF IF UIF-180
3.5 3.0
Aa Ba BCa Bab Ab BCb Bc
T2b (ms)
2.5 CDa
2.0 1.5
Da
Ea Db Dc
AF IF UIF-180
0.06
Aa Ab
0.05
ABa Aa
Aa ABa ABa ABa Aa Aa ABa ABa Ba Aa ABa Ba
Ac
Bb Ab
A2b (%)
(A)
Cb Cb Cc CDc
0.04
0.02
0.5
0.01
Ac
30
60
90
120 150 180
0
30
Frozen storage time (days) AF IF UIF-180
80 70
T21 (ms)
Da
Da
Cb
BCa
Bb
Cab CDc
Bb
Ab
100
Ab Ac
Bc
BCc
BCc
Aa
ABa
Aab
DEc Ec
40
20
20
450
Aa
Aa
Ba Ca Aa Bb Cab CDa Cab BCb BCb CDc CDb Da Db DEc EFc
30
40
CDa Ca
Da
Ba Cb
BC
Bb
A22 (%)
Bb BCa Cab Cb
90
120 150 180
AF IF UIF-180
50
Ab
350
60
Frozen storage time (days)
Aa
400
300
0
F)
AF IF UIF-180
120 150 180
0
30 60 90 120 150 180 Frozen storage time (days)
(C)
Aa Ba Ab Ac Bb ABb
60 40
10
T22 (ms)
80
30
0
90
AF IF UIF-180
120 BCa
Ca
60
Frozen storage time (days)
(E)
A21 (%)
(B)
50
Ab Cb
0.00
0
60
Aa Bb
0.03
1.0
0.0
ABb
Aa
Ac ABc
Bb
Ca Ea
30 Da Fb
20
Ca Da
Ba Ba Cb Ca Bb Bc
Aa Bb
Aa Aa Ab
Bc
Cb
Cb
Dc
Dab Db
Db
10
250
0
200 0
30
60
90
0
120 150 180
30
60
90
120 150 180
Frozen storage time (days)
Frozen storage time (days)
Fig. 5. Changes in LF-NMR T2 relaxation times and the corresponding peak area A21 of frozen porcine longissimus muscles affected by different freezing methods during frozen storage. AF, air freezing; IF, immersion freezing; UIF-180, ultrasound-assisted immersion freezing at 180 W. Means with different letters (A-F) are significantly different (P < 0.05) in different frozen storage durations for the same treatment, and means with different lowercase letters (a-c) indicate significant differences between freezing method at the same time point (P < 0.05).
were 52.58, 51.17, and 49.28 at 0 days and increased to 57.10, 54.88, and 52.48 at 180 days, respectively (P < 0.05). The L*-value of the UIF-180 samples were always lower (P < 0.05) than that of AF and IF during the frozen storage. The change in the L*-value is affected by the freezing rate and method, which is related to the water state and distribution in the thawed muscle. The muscle with slow freezing rate (AF samples) had more thawing loss, which leads to greater light reflection and lighter colour. Muela et al. (2010) also proved that slowly frozen lamb after thawing was lighter in colour than fast frozen meat. As proven in the above LF-NMR analysis, water migration in the UIF-180 samples was the smallest, thus less thawed water was attached to the surface of the meat, which reduced the light reflection intensity and decreased the lightness (Farouk et al., 2004). Additionally, muscle fibre
Renou, Monin, and Sellier (1985) showed that there was a relationship between relaxation time and quality characteristics of pork, and they confirmed that muscle samples with a longer T2 relaxation time had a higher thawing loss (drip loss). This study revealed that free water in the UIF-180 samples had lower mobility and was more tightly bound to muscle tissue than other AF and IF samples, thus decreasing thawing loss. 3.6. Colour Colour has an important influence on appearance and acceptability of food. As shown in Table 1, the L*- value increased with increased storage time. Lightness (L*- value) of the AF, IF, and UIF-180 samples 30
Meat Science 151 (2019) 24–32
M. Zhang et al.
Table 1 Changes in colour of frozen porcine longissimus muscles affected by different freezing methods during frozen storage. Colour parameters
Samples
Frozen storage time (days) 0
L*
a*
b*
AF IF UIF-180 AF IF UIF-180 AF IF UIF-180
52.58 51.17 49.28 17.26 17.47 17.87 15.32 14.29 14.31
30 ± ± ± ± ± ± ± ± ±
Ea
0.15 0.11Eb 0.06Ec 0.12Ab 0.10Ab 0.06Aa 0.12Da 0.15Fb 0.09Eb
53.54 51.16 50.22 17.27 17.15 17.73 16.16 15.08 15.36
60 ± ± ± ± ± ± ± ± ±
Da
0.12 0.14Eb 0.11Dc 0.06Ab 0.03Bb 0.08Ba 0.11Da 0.07Eb 0.13Db
53.51 52.82 52.52 15.45 16.71 17.15 18.82 17.15 16.21
90 ± ± ± ± ± ± ± ± ±
Da
0.11 0.11Db 0.11Cc 0.10Bc 0.14Cb 0.08Ca 0.06Ca 0.07Dab 0.05Cb
54.45 52.76 52.79 15.55 16.43 16.84 18.94 18.87 17.56
120 ± ± ± ± ± ± ± ± ±
Ca
0.18 0.07Db 0.08Cb 0.11Bc 0.08Db 0.09Da 0.10BCa 0.11Ca 0.08Bb
57.10 54.88 52.48 15.04 15.36 16.24 19.80 18.62 17.41
150 ± ± ± ± ± ± ± ± ±
Ba
0.72 0.38Cb 0.17Cc 0.21Cb 0.09Eb 0.11Da 0.04Ba 0.13Cb 0.15Bc
57.60 56.52 54.28 12.92 14.45 15.88 20.14 19.53 18.80
180 ± ± ± ± ± ± ± ± ±
ABa
0.23 0.11Bb 0.23Bc 0.19Dc 0.08Fb 0.13Ea 0.07ABa 0.15Bb 0.13Ac
58.45 57.53 55.25 12.72 13.72 15.14 21.39 20.77 18.56
± ± ± ± ± ± ± ± ±
0.15Aa 0.22Aa 0.24Ab 0.10Dc 0.11Gb 0.07Fa 0.06Aa 0.09Ab 0.08Ac
AF, air freezing; IF, immersion freezing; UIF-180, ultrasound -assisted immersion freezing at 180 W. Values are given as the means ± SE from triplicate determinations; A-G means in the same row with different letters differ significantly (P < 0.05); a-c means in the same column within same index with different letters differ significantly (P < 0.05).
results of cutting force indicated that the UIF-180 was more effective in maintaining the original muscle tissue. The TBARS values of the UIF180 samples were significantly lower than those of the AF and IF samples from 60 to 180 days. Low-field NMR analysis showed that the T2 relaxation times (T2b,T21 and T22) of the UIF-180 samples were the shortest, which revealed that UIF-180 could decrease water migration during frozen storage. The UIF-180 samples also had a higher a* value and lower L* value. Overall, ultrasonic treatment at a certain power is beneficial for maintaining frozen muscle quality.
shrinkage of the UIF-180 samples was less severe than that of AF and IF, which helps decrease the light scattering on the meat surface and increase the L*-value (Hector, Brew-Graves, Hassen, & Ledward, 1992). Redness (a*-value) was influenced by both freezing method and frozen storage time, and it has an opposite change trend to that of L*value. The a*-values significantly decreased with the increasing frozen storage time (P < 0.05). For example, a*-values of AF and IF were 12.92, 12.72 and 14.45, 13.72 for 150 and 180 days frozen storage, respectively. Holman, Van, Mao, Coombs, and Hopkins (2017) indicated that a*-value of 14.50 was the minimum threshold of acceptability of fresh meat, which reflected that longer frozen storage time obviously impacted the quality of AF and IF samples. However, the UIF180 samples had a significant lower reduction rate in a*-value than the AF and IF samples during the frozen storage (P < 0.05). Muela et al. (2010) found that the redness of frozen muscle was negatively related to frozen storage time because frozen storage reduces the activity of metmyoglobin-reducing enzymes, and this reduction rate increases with prolonged storage time (Farouk & Swan, 1998). Finally, metmyoglobin formation and accumulation on meat surfaces changes meat colour from red to brown (Utrera, Parra, & Estévez, 2014). According to the above microstructure characteristics of frozen muscles (Fig. 1), the tissue damage of the UIF-180 samples is less than that of the AF and IF samples, which could maintain the activity of metmyoglobin-reducing enzymes well and thus lead to a redder appearance. In contrast, a large amount of oxidase released from serious cellular disruption after thawing, which caused the AF samples to have a high degree of myoglobin oxidation, and metmyoglobin were thought to contribute to the brown (a*-value reduction) appearance (Muela, Monge, Sañudo, Campo, & Beltrán, 2015). In addition, UIF-180 could induce the lower degree of lipid oxidation which indicated by lower TBARS values, and prevent the formation of metmyoglobin (Jeong, Kim, Yang, & Joo, 2011). The change in b*-value is similar to that of the L*-value during frozen storage. The b*- value increased with increased storage time, and the UIF-180 samples always had lower b*-values than that AF and IF samples during storage (P < 0.05). Coombs et al. (2017) revealed that protein oxidation could decrease colour stability and increase b*-values during frozen storage. This result could be related to increases in TBARS during frozen storage (Fig. 3).
Acknowledgements This study was supported by the National Natural Science Foundation of China (grant No. 31571859 and No. 31771903) and the National Key Research and Development Plan for the 13th Five-Year Plan Period in China (grant No. 2016YFD0401504). References Aaslyng, M. D., Bejerholm, C., Ertbjerg, P., Bertram, H. C., & Andersen, H. J. (2003). Cooking loss and juiciness of pork in relation to raw meat quality and cooking procedure. Food Quality & Preference, 14(4), 277–288. Bevilacqua, A., & Zaritzky, N. E. (1986). Rate of pigment modifications in packaged refrigerated beef using reflectance spectrophotometry. Journal of Food Processing & Preservation, 10(1), 1–18. Boonsumrej, S., Chaiwanichsiri, S., Tantratian, S., Suzuki, T., & Takai, R. (2007). Effects of freezing and thawing on the quality changes of tiger shrimp (Penaeus monodon) frozen by air-blast and cryogenic freezing. Journal of Food Engineering, 80(1), 292–299. Bueno, M., Resconi, V. C., Campo, M. M., Cacho, J., Ferreira, V., & Escudero, A. (2013). Effect of freezing method and frozen storage duration on odor-active compounds and sensory perception of lamb. Food Research International, 54(1), 772–780. Cheng, X., Zhang, M., Xu, B. G., Adhikari, B., & Sun, J. C. (2015). The principles of ultrasound and its application in freezing related processes of food materials: A review. Ultrasonic Sonochemisry, 27, 576–585. Chevalier, D., Sentissi, M., Havet, M., & Bail, A. L. (2000). Comparison of air-blast and pressure shift freezing on Norway lobster quality. Journal of Food Science, 65(2), 329–333. Coombs, C., Holman, B., Collins, D., Kerr, M. J., Friend, M. A., & Hopkins, D. L. (2017). Effects of chilled-then-frozen storage (up to 52 weeks) on an indicator of protein oxidation and indices of protein degradation in lamb M. longissimus lumborum. Meat Science, 135, 134–141. Damodaran, S., & Wang, S. Y. (2017). Ice crystal growth inhibition by peptides from fish gelatin hydrolysate. Food Hydrocolloids, 70, 46–56. Farouk, M. M., & Swan, J. E. (1998). Effect of rigor temperature and frozen storage on functional properties of hot-boned manufacturing beef. Meat Science, 49(2), 233–247. Farouk, M. M., Wieliczko, K. J., & Merts, I. (2004). Ultra-fast freezing and low storage temperatures are not necessary to maintain the functional properties of manufacturing beef. Meat Science, 66(1), 171–179. Figueirêdo, B. C., Trad, I. J., Mariutti, L. R. B., & Bragagnolo, N. (2014). Effect of annatto powder and sodium erythorbate on lipid oxidation in pork loin during frozen storage. Food Research International, 65, 137–143. Hector, D. A., Brew-Graves, C., Hassen, N., & Ledward, D. A. (1992). Relationship between myosin denaturation and the colour of low-voltage-electrically-stimulated beef. Meat Science, 31(3), 299–307. Holman, B. W., Van, R. J., Mao, Y., Coombs, C. E., & Hopkins, D. L. (2017). Using instrumental (CIE and reflectance) measures to predict consumers' acceptance of beef
4. Conclusions UIF-180 had an obvious influence on microstructure, quality and water distribution of porcine longissimus muscles during frozen storage. UIF-180 effectively maintained the smaller ice crystal size within the muscle during the frozen storage period. The thawing and cooking losses increased with extended storage time, and the UIF-180 sample had the smallest thawing loss, followed by the IF and AF samples. The 31
Meat Science 151 (2019) 24–32
M. Zhang et al.
Sanchez-Alonso, I., Martinez, I., Sanchez-Valencia, J., & Careche, M. (2012). Estimation of freezing storage time and quality changes in hake (Merluccius merluccius, L.) by low field NMR. Food Chemisty, 135(3), 1626–1634. Santacatalina, J. V., Guerrero, M. E., Garcia-Perez, J. V., Mulet, A., & Cárcel, J. A. (2016). Ultrasonically assisted low-temperature drying of desalted codfish. LWT - Food Science and Technology, 65, 444–450. Song, G. S., Q, H. S., & Lin, L. (2008). Effect of ultrasound-assisted freezing on changes in protein secondary structure studied by fourier transform infrared spectroscopy. Journal of Shaanxi University of Science & Technology, 26, 132–137. Soyer, A., Özalp, B., Dalmış, Ü., & Bilgin, V. (2010). Effects of freezing temperature and duration of frozen storage on lipid and protein oxidation in chicken meat. Food Chemistry, 120(4), 1025–1030. Tarladgis, B. G., Watts, B. M., & Younathan, M. T. (1960). A distillation method for the quantitative determination of malonaldehyde in rancid foods. The Journal of the American Oil Chemists'Society, 37, 44–48. Tironi, V., Lamballerie, M. D., & Lebail, A. (2010). Quality changes during the frozen storage of sea bass (Dicentrarchus labrax) muscle after pressure shift freezing and pressure assisted thawing. Innovative Food Science & Emerging Technologies, 11(4), 565–573. Turgut, S. S., Işıkçı, F., & Soyer, A. (2017). Antioxidant activity of pomegranate peel extract on lipid and protein oxidation in beef meatballs during frozen storage. Meat Science, 129, 111–119. Turner, E. W., Paynter, W. D., Montie, E. J., Bessert, M. W., Struck, G. H., & Olson, F. C. (1954). Use of the 2-thiobarbithuric acid reagent to measure rancidity in frozen pork. Food Technology, 8(7), 326–330. Utrera, M., Parra, V., & Estévez, M. (2014). Protein oxidation during frozen storage and subsequent processing of different beef muscles. Meat Science, 96(2), 812–820. Xia, X. F., Kong, B. H., Liu, Q., & Liu, J. (2009). Physicochemical change and protein oxidation in porcine longissimus dorsi as influenced by different freeze-thaw cycles. Meat Science, 83(2), 239–245. Xue, S. W., Xu, X. L., Shan, H. M., Wang, H. H., Yang, J., & Zhou, G. H. (2018). Effects of high-intensity ultrasound, high-pressure processing, and high-pressure homogenization on the physicochemical and functional properties of myofibrillar proteins. Innovative Food Science & Emerging Technologies, 45, 354–360. Zhang, M. C., Niu, H. L., Chen, Q., Xia, X. F., & Kong, B. H. (2018). Influence of ultrasound-assisted immersion freezing on the freezing rate and quality of porcine longissimus muscles. Meat Science, 136, 1–8. Zhang, X., Inada, T., Yabe, A., Lu, S., & Kozawa, Y. (2001). Active control of phase change from supercooled water to ice by ultrasonic vibration 2. Generation of ice slurries and effect of bubble nuclei. International Journal of Heat & Mass Transfer, 44(23), 4533–4539. Zhang, Z. Y., Regenstein, J. M., Zhou, P., & Yang, Y. L. (2017). Effects of high intensity ultrasound modification on physicochemical property and water in myofibrillar protein gel. Ultrasonics Sonochemistry, 34, 960–967. Zheng, L. Y., & Sun, D. W. (2006). Innovative applications of power ultrasound during food freezing processes-a review. Trends in Food Science & Technology, 17, 16–23.
colour. Meat Science, 127, 57–62. Hong, H., Zhu, S. C., Luo, Y. K., & Yu, J. (2011). Quality changes of bighead carp (Aristichthys nobilis) during chilled and partial freezing storage. South China Fisheries Science, 7(6), 7–12. Islam, M. N., Zhang, M., Adhikari, B., Cheng, X. F., & Xu, B. G. (2014). The effect of ultrasound-assisted immersion freezing on selected physicochemical properties of mushrooms. International Journal of Refrigeration, 42, 121–133. Jeong, J. Y., Kim, G. D., Yang, H. S., & Joo, S. T. (2011). Effect of freeze–thaw cycles on physicochemical properties and color stability of beef semimembranosus muscle. Food Research International, 44, 3222–3228. Jia, N., Kong, B. H., Liu, Q., Diao, X. P., & Xia, X. F. (2012). Antioxidant activity of black currant (ribesnigrum L.) extract with aqueous ethanol and its inhibitory effect on lipid and protein oxidation of pork patties during chilled storage. Meat Science, 91, 533–539. Kang, D. C., Zou, Y. H., Cheng, Y. P., Xing, L. J., Zhou, G. H., & Zhang, W. G. (2016). Effects of power ultrasound on oxidation and structure of beef proteins during curing processing. Ultrasonic Sonochemistry, 33, 47–53. Kim, Y. H., Liesse, C., Kemp, R., & Balan, P. (2015). Evaluation of combined effects of ageing period and freezing rate on quality attributes of beef loins. Meat Science, 110, 40–45. Lanari, M. C., Schaefer, D. M., & Scheller, K. K. (1995). Dietary vitamin E supplementation and discoloration of pork bone and muscle following modified atmosphere packaging. Meat Science, 41(3), 237–250. Leygonie, C., Britz, T. J., & Hoffman, L. C. (2012). Impact of freezing and thawing on the quality of meat: Review. Meat Science, 91(2), 93–98. Li, B., & Sun, D. W. (2002). Effect of power ultrasound on freezing rate during immersion freezing of potatoes. Journal of Food Engineering, 55(3), 277–282. Liu, Z. L., Xiong, Y. L., & Chen, J. (2010). Protein oxidation enhances hydration but suppresses water-holding capacity in porcine longissimus muscle. Journal of Agricultural and Food Chemistry, 58(19), 10697–10704. Muela, E., Monge, P., Sañudo, C., Campo, M. M., & Beltrán, J. A. (2015). Meat quality of lamb frozen stored up to 21 months: Instrumental analyses on thawed meat during display. Meat Science, 102, 35–40. Muela, E., Sanudo, C., Campo, M. M., Medel, I., & Beltran, J. A. (2010). Effect of freezing method and frozen storage duration on instrumental quality of lamb throughout display. Meat Science, 84(4), 662–669. Ngapo, T. M., Babare, I. H., Reynolds, J., & Mawson, R. F. (1999). Freezing rate and frozen storage effects on the ultrastructure of samples of pork. Meat Science, 53(3), 159–168. Rahelić, S., Puač, S., & Gawwad, A. H. (1985). Structure of beef longissimus dorsi muscle frozen at various temperatures: Part 1-histological changes in muscle frozen at −10, −22, −33, −78, −115 and −196°C. Meat Science, 14(2), 63–72. Renou, J. P., Monin, G., & Sellier, P. (1985). Nuclear magnetic resonance measurements on pork of various qualities. Meat Science, 15(4), 225–233. Saeed, S., & Howell, N. K. (2002). Effect of lipid oxidation and frozen storage on muscle proteins of Atlantic mackerel (Scomber scombrus). Journal of the Science of Food & Agriculture, 82(5), 579–586.
32