Influence of ultrasound-assisted immersion freezing on the freezing rate and quality of porcine longissimus muscles

Accepted Manuscript Influence of ultrasound-assisted immersion freezing on the freezing rate and quality of porcine longissimus muscles

Mingcheng Zhang, Niu Haili, Qian Chen, Xiufang Xia, Baohua Kong PII: DOI: Reference:

S0309-1740(17)30967-1 doi:10.1016/j.meatsci.2017.10.005 MESC 7381

To appear in:

Meat Science

Received date: Revised date: Accepted date:

1 July 2017 28 September 2017 9 October 2017

Please cite this article as: Mingcheng Zhang, Niu Haili, Qian Chen, Xiufang Xia, Baohua Kong , Influence of ultrasound-assisted immersion freezing on the freezing rate and quality of porcine longissimus muscles. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Mesc(2017), doi:10.1016/j.meatsci.2017.10.005

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ACCEPTED MANUSCRIPT Influence of ultrasound-assisted immersion freezing on the freezing rate and quality of porcine longissimus muscles

, Haili, Niu a, Qian Chen a, Xiufang Xia a, *, Baohua Kong a,*

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College of Food and Pharmaceutical Engineering, Suihua University, Suihua,

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Heilongjiang 152061, China

Corresponding author: Tel: +86-451-55191794; fax: +86-451-55190577. E-mail address:[email protected] (B. -H. Kong).

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b

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China

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College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030,

Corresponding author. Tel: +86-451-55191289; fax: +86-451-55190577. E-mail address: [email protected] (X. -F. Xia)

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a

a,b

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Mingcheng Zhang

ACCEPTED MANUSCRIPT Abstract The objective of this study was to evaluate the effect of ultrasound-assisted immersion freezing (UIF) on the freezing rate and quality of porcine longissimus muscles under different ultrasound powers. UIF with a certain level of ultrasound power significantly (P > 0.05)

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accelerated the freezing rate. The phase transition times of samples treated with UIF at 180 W (UIF-180) were the shortest. There were no significant differences (P > 0.05) in a* (redness),

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b* (yellowness), pH values or cooking loss among UIF, IF, and control (fresh muscle)

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samples. Investigation of the microstructure of frozen muscles demonstrated that UIF-180

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remarkably reduced the size of ice crystals and made their distribution more uniform. UIF-180 samples showed a significant (P < 0.05) reduction in thawing loss and T21 and T22

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relaxation times compared with other treatments, which meant that UIF at certain powers could reduce the mobility and loss of immobilized and free water. The results showed that

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improved meat quality.

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UIF at certain powers significantly increased the freezing rate of muscle samples and

Keywords: Ultrasound-assisted immersion freezing; Freezing rate; Porcine longissimus

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muscle; Freezing rate; Quality

ACCEPTED MANUSCRIPT Introduction Frozen is an effective method for extending the shelf-life of meat and meat products by inhibiting microbial growth and reducing biochemical reactions. However, deterioration in quality occurs, including flavour loss, decolouration, and lipid and protein oxidation (Sebranek,

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1982). The quality of frozen meat is influenced by the extent of freezing-induced cellular dehydration, the size of the ice crystals and their location inside the meat (Dalvi-Isfahan,

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Hamdami, Xanthakis, & Le-Bail, 2007). It is generally known that rapid freezing results in

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the formation of fine ice crystals, which is helpful for avoiding muscle tissue damage.

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Immersion freezing (IF) uses a liquid coolant as a heat-transfer medium, which can drastically increase freezing speed of samples due to the high thermal coefficient of liquid media

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(Zarkadas & Mitrakas, 1999; Ribero, Rubiolo, & Zorrilla, 2009). Compare with air freezing (AF), IF has some advantages in providing a good product quality due to form small ice

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crystals (Delgado et al, 2009; Galetto, Verdini, Zorrilla, & Rubiolo, 2010; Anese et al, 2012). In recent decades, several novel and emerging freezing technologies have been employed in

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order to provide the potential means to optimize crystallisation of frozen meat. These methods can alter the nucleation, crystal growth, and nucleation rate of food materials during freezing,

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including high pressure freezing (Otero, Sanz, Guignon, & Aparicio, 2009), radio frequency-assisted freezing (Anese et al., 2012) microwave-assisted freezing (Dorward, Raaenielsen, Hansen, & Fischer. 2013), and ultrasound-assisted freezing (Cheng, Zhang, Xu, Adhikari, & Sun, 2015). Ultrasound, as a relatively innovative technology, is increasingly applied in both the analysis and preservation of food (Alarcon-Rojo, Janacua, Rodriguez, Paniwnyk, Mason, 2015). Ultrasound is defined as sound waves at higher frequencies than those that can be detected by the human ear (20 kHz). When sound crosses an aqueous substance, it generates

ACCEPTED MANUSCRIPT waves of compression and rarefaction of the molecules in the medium, with the result being the formation of cavities and/or bubbles during rarefaction. These cavitation bubbles can serve as nuclei for ice nucleation once they reach the critical nucleus size (Zheng & Sun, 2006; Cheng et al., 2015). The motion of cavitation bubbles can lead to microstreaming, which is

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another significant acoustic phenomenon associated with cavitation, and could be used to enhance heat and mass transfer in the medium (Simal, Benekito, Sanchez, & Rossello, 1998).

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If the time spent in compression and rarefaction cycles exceeds certain limits, cavitation

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bubbles will become unstable and violently collapse, which can release notably high pressures

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(up to 100 MPa) and temperatures (up to 5000 K). Accordingly, the ultrasonic waves travel along the liquid medium and cause severe turbulence in the immediate surroundings and thus

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improve the heat transmission efficiency (Cheng et al., 2015). Several studies have confirmed that ultrasound has ability to improve heat transfer and accelerate the freezing process of food

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materials (Zheng & Sun, 2006). Both acoustic streaming and cavitation were two major factors which affected the heat transfer (Cheng et al., 2015). Kiani et al. (2013) evaluated the

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effect of ultrasound irradiation on the convective heat transfer between a stationary copper sphere and a cooling medium at different Reynolds (Re) and Prandtl (Pr) numbers. The results

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confirmed that the application of ultrasound enhances the rate of heat transfer between a submerged object and cooling medium. Hu et al. (2013) investigated that application of power ultrasound during phase-transition stage of freezing process significantly increased the freezing rate of dough cylinders and the freezing time was shortened by more than 11%. Similar results were also reported by Li and Sun (2012), Delgado, Zheng, & Sun, (2009) and Xin, Zhan, & Bhandari (2014). The size and size distribution of ice crystals are important parameters in frozen foods. In general, smaller size and even distribution of ice crystals helps improve the quality of frozen

ACCEPTED MANUSCRIPT foods (Xia et al., 2009). Ultrasound is able to induce nucleation at higher temperature during freezing process. This effect can be utilized to control the size and distribution of ice crystals in frozen foods (Xu, Zhang, Bhandari, & Cheng, 2014). Moreover, application of ultrasound can fragment the ice crystals, which increases the number of nuclei and reduces the size of ice

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crystals. The fast freezing brought about by the application of ultrasound contribute to the formation of smaller ice crystals thus improves the quality of frozen food. Sun and Li (2003)

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found that the tissue of potatoes frozen using ultrasound assisted freezing exhibited superior

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cellular structure compared to the samples frozen without applying power ultrasound. In

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addition, Islam et al. (2014) applied power ultrasound at different levels during immersion freezing of three mushroom varieties. They found that the application of ultrasound reduced

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the drip loss during the thawing process.

Meat is rich in protein, which is prone to modification by ultrasound. Several studies

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have shown that power ultrasound treatment induces modifications of food protein leading to improved functional properties, such as solubility, emulsification and gel properties, which are

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considered to be closely related to changes in protein structure, particle size and hydrophobicity (Alarcon-Rojo et al., 2015; Gülseren, Güzey, Bruce, & Weiss, 2007;

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Alarcon-Rojo et al., 2015). Over nearly ten years, several studies have investigated the application of ultrasound-assisted freezing in food, and the results demonstrated improvement in the freezing rate (Li, & Sun, 2002; Xin et al., 2014), initiation of nucleation (Xu, Zhan, Bhandari, Cheng, & Islam, 2015), and minimization of ice crystals (Kiani, Zhang, & Sun, 2013). Most of the studies focused on fruit and vegetable products (Xin et al., 2014; Islam, Zhang, Adhikari, Cheng, & Xu, 2014; Cheng, Zhang, Adhikari, & Islam, 2014; Xu et al., 2015), fish (Santacatalina, Guerrero, Garcia-Perez, Mulet, & Carcel, 2016), and gluten (Song, Hu, & Li, 2008). To the best of our knowledge, few studies have been conducted on meat and

ACCEPTED MANUSCRIPT meat products. The purpose of this study was to evaluate the effect of ultrasound-assisted freezing on the freezing rate and quality of porcine longissimus muscles during immersion freezing.

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2. Materials and Methods 2.1. Sample

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Porcine longissimus muscles(lumborum) were obtained from pig carcasses of

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approximately 24 weeks of age within 24 h after slaughter from the Beidahuang Meat Corporation

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(Harbin, Heilongjiang, China). The pigs were slaughtered in compliance with the operating procedures of pig-slaughtering (GB/T 17236-1998) in China. The samples were kept on ice and

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transported to the laboratory. The muscles were sliced into approximately 30-mm-thick chops perpendicular to the direction of the fibre. The weight of each sample was approximately 120

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± 2 g. The muscle chops were separately packaged with poly nylon pouches (Nylon/Poly ethylene coextrusion, 0.3 mm thick). To achieve uniform initial temperature, muscle chops

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were kept in a 4 °C refrigerator for up to a further 6 h prior to treatment.

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2.2. Freezing process and freezing time measurement There were seven treatments. For each treatment, 12 chops were used at a minimum. The seven treatments were the control (fresh samples stored in a 4 °C refrigerator), AF, IF, and IF with different ultrasound powers (120, 180, 240, and 300 W). A pilot-scale ultrasonic bath system (Fig. 1, Nanjing Xian ou Co., Ltd., Nanjing, China) with a coolant including 95% ethanol and 5% fluoride was used for IF and ultrasound-assisted immersion freezing (UIF). Ten ultrasound transducers are installed at the bottom of the freezing tank (30 × 22 × 26 cm3 ), through which a continuous flow (1.5 L/min) of coolant was maintained by a low temperature

ACCEPTED MANUSCRIPT circulation pump. The control system for the equipment was modified such that the output power could be precisely adjusted within the range of 0 to 300 W at a frequency of 30 kHz. For AF, muscle chops were placed in a refrigerator (-20 °C) until the geometric centre temperature reached approximately -18 °C without air circulation. For UIF, muscle chops

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were fully immersed in the coolant (-20.0 ± 0.5 °C) with ultrasound powers of 0 (IF), 120 W (UIF-120), 180 W (UIF-180), 240 W (UIF-240), or 300 W (UIF-300) until the geometric

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centre temperature reached approximately -18 °C.

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An ultrasonic field was applied perpendicular to the muscle fibres because the ultrasound

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emission was unidirectional. Muscle chops were located approximately 10 cm from the bottom of the tank to maintain the uniformity of the ultrasound wave intensity around the

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samples. Ultrasound with a 30 sec on/30 sec off cycle was applied for 8 min when the temperature of the chops decreased to 0 °C. Samples were exposed to the ultrasound at 30 sec

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intervals to prevent excessive heat generation from continuous ultrasound. A K-type thermocouple (1.0 mm diameter, with an accuracy of ± 0.1 °C) was inserted into the

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geometrical centre of each sample and connected to an Applent AT4500 temperature testing instrument (Applent Precision Instrument Co., Ltd., Changzhou, China), and ATS45 data

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acquisition software was used to monitor and record freezing rate data. The temperatures of the samples were recorded at 1 sec intervals. After freezing, samples were stored at -18 ± 1 °C.

2.3. Thawing loss measurement Thawing loss was measured immediately after the frozen porcine chops were thawed to an internal temperature of 4 °C (Xia, Kong, Liu, & Liu, 2009) and expressed as Thawing loss (%) = (W0 －W1 )/ W0×100%

ACCEPTED MANUSCRIPT where W0 and W1 represent the weight of the of porcine chop before and after thawing, respectively.

2.4. Cooking loss measurement

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Thawed muscle chops were individually packed in polyethylene bags and cooked in an 85 °C water bath until the centre temperature reached 75 °C. Cooking loss was expressed as

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Cooking loss (%) = (W1 －W2 )/ W1 ×100%,

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where W1 and W2 represent the weight of the of porcine chop before and after cooking,

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respectively.

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2.5. Cutting force measurement

After evaluating cooking loss, the muscle samples were used to measure cutting force

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according to the method described in Xia et al. (2009) using a texture analyser (Stable Micro System; TA: XT2i, England) with a knife blade (HDP/BSW). A 25 kg load cell was used, and

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the crosshead speed of the knife blade was 5 mm/s. The cutting force (N) was recorded as the maximum force to cut transversally into the sample. From each cooked chop, six cylindrical

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cores (1.27 cm in diameter) were obtained parallel to the muscle fibres, and a minimum of 3 chops were analysed.

2.6. pH measurement The pH of the muscles was measured based on the method described by Choi, Min, and Hong (2016) with slight modification. Briefly, thawed muscle (10 g) was homogenized in a blender with 100 ml deionized water (4 °C). A standard pH metre (FE20, Mettler-Toledo Instruments Co., Ltd., China) was used to measure the pH of the mixture.

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2.7. Colour measurement A ZE-6000 colourimeter (Juki Corp, Tokyo, Japan) was used to evaluate the surface colour of the porcine longissimus muscles using a D65 light source and a 10° observer with

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an 8 mm diameter measuring area and a 50 mm diameter illumination area according to the method described in Jia, Kong, Liu, Diao, and Xia (2012). Four different locations on the

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surface of each sample were used to measure the L* (lightness), a* (redness), and b*

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(yellowness) values, and a minimum of 3 chops were analysed. The instrument was calibrated

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with a white reference tile (L*=95.26, a*=-0.89, b*=1.18).

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2.8. Microstructure of frozen samples

The microstructure of the frozen samples was observed according to the method described by Choi, Park, Chung, Park, Kim, & Chun (2017) with certain modifications. The

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frozen muscles (0.5 × 0.5 × 1 cm3 ) were rapidly moved into a Leica CM1850 cryostat

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(CM1850, Leica, Germany) and were excised perpendicular or parallel to the orientation of the muscle fibres at -20 °C. The cross-sections or longitudinal sections (4-μmthick) of the

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samples were obtained and placed horizontally on the glass slides. Samples were first stained with haematoxylin staining solutions for 15 min, and the stained samples were differentiated by 1% hydrochloric acid alcohol solution in order to make the colour uniform. The acid on the slice was washed with running tap water for 1 h. After eosin staining for 10 minutes, samples were dehydrated with 70%, 80%, and 90% ethanol for 2 min at each concentration and finally with 100% ethanol for 5 min. The dehydrated samples were then cleared in xylene two times and mounted in a resinous medium and stored at 37 °C for 3 h. The specimens were examined under a light microscope (magnification 10 × 10) (Olympus BX41, Olympus

ACCEPTED MANUSCRIPT Optical Co. Ltd., Tokyo, Japan), and images were obtained by a digital camera (Olympus, Japan). The average radiuses of ice crystals in images were quantitatively analyzed by using an Image-Pro Plus software (Media Cybernetics, Silver Spring, MD, USA). 2.9. Nuclear magnetic resonance

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Low field-nuclear magnetic resonance (LF-NMR) relaxation measurements were conducted according to the method described by Aursand, Gallart-Jornet, Erikson, Axelson,

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and Rustad (2008) with an LF-NMR analyser minispec mq 20 (Bruker Optik GmbH,

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Ettlingen, Germany) with a magnetic field strength of 0.47 T corresponding to a proton

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resonance frequency of 20 MHz. When the core temperature of the muscle chops reached 4 °C, they were cut into parallelepipeds (1 × 1 × 2 cm3 ) and placed in NMR tubes (18 mm of The

transverse

relaxation

time

(T2 )

was

measured

using

the

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diameter).

Carr-Purcell-Meiboom-Gill pulse sequence. For each sample, 16 scans were obtained at 2 sec

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intervals with 3000 echoes in total. The continuous distribution of exponentials related to water located in different muscle compartments was fitted for a ll Carr-Purcell-Meiboom-Gill

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curves using the CONTIN algorithm after normalizing the raw data. Each measurement was performed in triplicate. The mean apparent relaxation times (T2i) for each detected population

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in CONTIN were recorded.

2.10. Statistical analysis Three batches of samples subjected to different freezing treatments were processed independently to study the effects of the different freezing treatments on thawing loss, cooking loss, cutting force, frozen microstructure, and moisture migration in porcine longissimus muscles. For each batch of samples, all of the specific experiments were conducted in triplicate (triplicate observations). The results were expressed as the mean values

ACCEPTED MANUSCRIPT ± standard deviations. Each triplicate was included as a random term, and different freezing treatments were included as fixed terms. The data were analysed using the General Linear Model procedure in the Statistix 8.1 software package (Analytical Software, St. Paul, MN, USA). The significance of the main effects was determined using one-way analysis of

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variance (ANOVA), and determination of significant differences (P < 0.05) among the means

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was performed by the Tukey post hoc procedure.

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3. Results and Discussion

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3.1. Freezing time

It is generally known that freezing rate has a remarkable impact on the quality of frozen

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meat. The faster the freezing rate, the smaller the ice crystals produced. Temperature change curves during freezing were used to intuitively describe the influence of different freezing

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treatments on muscle chop freezing time (Fig. 2). In this study, the total freezing time of the samples was defined as the time required for the temperature to drop from 4 °C to -18 °C. It

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can be seen that the total freezing time of AF samples was 18248 sec, which was more than 6.5-fold the time needed by IF samples (P < 0.05). As the heat transfer coefficient in liquid

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media is far higher than in air, IF drastically increased freezing speed and reduced total freezing time (Galetto et al, 2010; Lucas, & Raoult-Wack, 1998). When ultrasonic power was applied, the freezing time decreased at first and later increased with the increase in ultrasonic power, and 180 W of ultrasonic power (UIF-180) produced the shortest total freezing time (P < 0.05). These results confirmed that UIF at certain powers significantly increased the freezing rate of muscle chops compared with IF. To understand the influence of different freezing treatments on the freezing rate of muscle more accurately, as shown from Table 1, the course of freezing was divided into three

ACCEPTED MANUSCRIPT stages: a pre-cooling stage (4 − -1 °C), a phase transition stage (the largest formation of ice crystals, -1 − -5 °C), and a sub-cooling stage (-5 − -18 °C) (Xu et al, 2015). During the pre-cooling stage, ultrasonic power was not applied, and there were no significant differences in the pre-cooling times between IF and UIF. When the temperature decreased to 0 °C,

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freezing entered the phase transition stage, which could directly determine product quality because most of the water would crystallise in this stage (Li and sun, 2002). The phase

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transition time increased at first and later decreased with the increase in ultrasonic power

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(Table. 1), which was in accordance with the total freezing time. The samples treated with 180

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W ultrasonic power (UIF-180) had the shortest phase transition time, which was shortened by 12.6% compared to IF (P < 0.05). Such a trend can be linked to the enhancement of the

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convective heat transfer rate due to both microstreaming and cavitation (Cheng et al, 2015). Li and Sun (2002) studied UIF of potatoes and reported that ultrasound power applied during

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the phase transition stage significantly accelerated the freezing process and thereby decreased the freezing time. Similar results were also reported by Hu, Liu, Li, Li, and Hou (2013), Tu et

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al. (2015), and Xu et al. (2015). These investigations demonstrated that ultrasonic treatment is helpful for increasing the freezing rates of food materials, such as dough, apple and red radish.

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During UIF, higher intensity agitation is produced by ultrasonic cavitation with increased ultrasound power (Li & Sun, 2002), with the heat transfer coefficient increasing and the freezing time decreasing. In the present study, the rate of heat transfer was the fastest at 180 W of ultrasonic power. Kiani et al. (2012) found that proper ultrasound intensities cause higher cooling rates which depend on the intensity of ultrasound and the position of the sphere. However, the application of ultrasound at high intensities led to the generation of heat at the surface of the sphere, thus limiting the possibility of achieving lower final temperature. In this study, the phase transition times were significantly prolonged (P < 0.05) when ultrasound

ACCEPTED MANUSCRIPT power was at relatively high levels (UIF-240 and UIF-300), and the corresponding freezing efficiency decreased compared with UIF-180. The excessive heat generated on the sample surface due to ultrasonic power of high intensities became an obstacle to heat exchange between the muscle and coolant (Cheng et al., 2015). At this point, the higher ultrasound

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power had a negative effect on freezing efficiency. In the sub-cooling stage, because large amounts of water inside the muscle had frozen, the thermal conductivity increased, and a

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rapid temperature reduction occurred compared to the phase transition stage. The amount of

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time in the sub-cooling stage was not significantly different (P > 0.05) among IF and UIF

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samples, except UIF-300 samples. The UIF-300 had more additional heat produced from the

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ultrasonic power, which led to prolonged sub-cooling times (Li and Sun, 2002).

3.2. Thawing loss, cooking loss, and cutting force

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The effects of different freezing treatments on thawing loss, cooking loss and cutting force of thawing muscles are presented in Fig. 3. Thawing loss influenced the weight,

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appearance, and sensory properties of the meat product (Xia et al., 2009). As shown in Fig. 3, the thawing loss of AF samples was 4.63% and significantly decreased (P < 0.05) to 2.52%for

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the samples treated with IF. The thawing loss decreased at first and later increased with the increase in ultrasonic power. The samples treated with 180 W ultrasonic powers had the lowest thawing loss (P < 0.05). Islam et al. (2014) investigated the effect of UIF on the quality of mushrooms and reported that ultrasound (0.39 W cm2 , 20 kHz) significantly reduced the thawing loss by 10%. Xin et al. (2014) investigated the effect of UIF on the quality of broccoli and found that more than 1% reduction (P < 0.05) in the thaw loss were achieved after UIF compared to normal freezing products. Similar results were reported by Hu et al. (2013) and Xu et al. (2015). The reduced thawing loss is related to the increased freezing rate

ACCEPTED MANUSCRIPT caused by appropriate ultrasonic power, which leads to more small ice crystals that are uniformly distributed in the muscle (Xu et al., 2015). For samples with slow freezing in air, by contrast, intracellular water gradually moves to the extracellular space, and larger extracellular ice crystals are formed, leading to severe tissue deformation and cell atrophy, and part of the

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melted water could not go back into the intracellular space after thawing (Xia et al., 2009; Lebovka, Bazhal, &Vorobiev, 2001). The samples with more thawing loss may reduce meat

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acceptability and quality due to textural deterioration and reduced taste.

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There were no significant differences in cooking loss among control, IF and UIF samples

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(P > 0.05). Compared to the fresh meat (control), IF, and UIF samples, AF samples had significantly greater (P < 0.05) cooking loss (32.44%) (Fig. 3), which may be associated with

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the intense cell damage from slow freezing procedures (Lagerstedt, Enfält, Johansson, &Lundström., 2008; Anese et al., 2012).

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Tenderness is an important organoleptic trait that affects acceptance of meat and meat products (Xia et al., 2009). Cutting force was measured as an objective evaluation of meat

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tenderness. The cutting force of AF samples was the highest, which was increased by approximately 20% compared to control samples (P < 0.05). Hale and Waters (1981) reported

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that thawed meat by AF treatment had higher (P < 0.05) cutting force than fresh meat samples, which was attributed to the water loss caused by slow freezing and therefore less water available to hydrate the muscle fibres (Leygonie, Britz, & Hoffman, 2012). The cutting force of samples treated with IF was not significantly different (P > 0.05) from UIF samples, except for UIF-300. In this study, cutting force results were consistent with cooking loss results from frozen muscle. The UIF-300 samples showed a significantly lower (P < 0.05) cutting force, which might be because UIF-300 treatment lowered the freezing speed and caused large ice crystal formation in muscle tissue, which could result in greater mechanical damage to the

ACCEPTED MANUSCRIPT muscle microstructure (larger intercellular spaces and muscle fibre fragmentation) (Zhang, Li, Diao, Kong, & Xia, 2017). Furthermore, the higher intensity ultrasonic power also led to loss of integrity of muscle fibres (Jayasooriya, Bhandari, Torley, &D'Arey, 2004). Dickens, Lyon, and Wilson (1991) reported that the application of ultrasound irradiation could improve

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broiler pectoralis muscle tenderness by breakdown of muscle fibres. Jørgensen, Christensen, and Ertbjerg (2008) also demonstrated that ultrasound treatment (25 kHz, 500 W for 40

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minutes) improved pork tenderness.

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3.3. Colour and pH

Colour plays an important role in the appearance, presentation and acceptability of

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frozen pork and is an attribute directly used for evaluating visual quality. The influence of the different freezing conditions on the colour of thawed porcine longissimus muscles is

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presented in Table 2. The L* values of AF and UIF-300 samples were significantly higher than those of control samples (P < 0.05), and there were no significant differences among

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control, IF, and UIF samples at 120, 180 and 240 W (P > 0.05). Farouk, Wieliczko, and Merts (2003) reported that slowly frozen and thawed beef was lighter in colour than fast-frozen meat.

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This notable change in the L* value affected by the freezing and thawing processes might be attributed to the changes in the distribution and chemical-physical state of water in the thawed muscle. The larger amounts of thaw drip may result in greater light reflection and lighter colour in the slowly frozen samples (Muela, Sañudo, Campo, Medel, & Beltrán, 2010). Moreover, a higher intensity ultrasound could increase the L* values of the muscles because more water moved outside the cells. Pohlman, Dikeman, and Kropf, (1997) reported that a specific intensity of ultrasonic irradiation (22 W/cm2 at 20 kHz) resulted in an increased L* in bovine pectoralis muscles. The different freezing treatments had no remarkable influence on

ACCEPTED MANUSCRIPT a*or b* values. This result was similar to the results of Lind, Harrison, and Kropf (1971), who reported that freezing rates had no significant influence on a* values in lamb, which might be because myoglobin had recovered its natural conformation and recovered its colour after sample thawing (Fernández et al., 2007).

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As shown in Table 2, there were no significant differences (P > 0.05) in pH values among the samples after different freezing treatments. In general, the change in pH value was mainly

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dominated by the content of ammonia, organic sulphides and amines, which were produced

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after meat protein degradation by microorganisms and endogenous enzymes (Muela et al,

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2010). In this study, freezing time was short and did not result in a significant change in pH values. We can also assume that the changes in thawing and cooking losses were not caused

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3.4. Microstructure of frozen muscles

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by pH values.

The size and distribution of ice crystals have the great influence on the quality of frozen

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muscles. In general, small ice crystals and a uniform distribution are desirable because they can minimize the mechanical damage to frozen foods (Chevalier, Sentissi, Havet, & Bail,

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2000). The cross-sections (Fig. 4A) and longitudinal sections (Fig. 4B) of the frozen muscle tissue, and average radius of ice crystal (Fig. 4C) were observed in order to clearly measure the size and distribution of ice crystals inside the muscles and how the size and distribution were influenced by different freezing treatments. As shown in Fig. 4, the ice crystals formed in AF samples were most irregular and average radius of ice crystals were the largest (29.51 μm) due to the longer freezing time. Compared with the AF samples, smaller ice crystal cavities (average radius 13.17 μm) were observed in the IF samples (P < 0.05). Ultrasound power further affected ice crystal size and distribution in frozen muscles. The smallest and

ACCEPTED MANUSCRIPT most uniform distribution of ice crystals was detected in samples treated with UIF-180, which significantly reduced the average radius of ice crystals to 5.02 μm (Fig. 4C). As shown in Fig. 4B, muscle fibres from UIF-180 samples were arranged neatly and appeared to be more compact and dense. This finding reflected that samples treated with UIF-180 had less

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structural damage, which also gave explained the reduced thawing loss and cooking loss discussed above. Therefore, UIF at the proper power has the ability to induce nucleation at

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higher temperatures and significantly increase the ice nucleus number in foods during

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freezing, which results in smaller ice crystals (Cheng et al., 2015; Kiani et al., 2013). Zhang,

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Inada, Yabe, Lu, and Kozawa (2001) suggested that microstreaming resulting from the motion of stable cavitation bubbles by ultrasound can also be a primary driving force of nucleation

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during freezing. Moreover, ice crystals will fracture when they are subjected to certain intensities of ultrasonic irradiation, leading to a reduction in ice crystal size (zheng & Sun,

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2006). However, further increases in ultrasonic power to 240 W and 300 W caused increases in the size of the ice crystals (Fig 4A), and the average radius of the ice crystals increased to

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8.83 μm and 18.42 μm, respectively (Fig 4C). For UIF-240 samples, the gap between muscle fibres was wider compared to UIF-180 samples (Fig. 4B), but neither shrinkage nor

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deformation of cells was evident. For UIF-300 samples, atrophy and derangement of muscle fibres began to appear (Fig. 4B). Ultrasound irradiation is known to generate heat within water-containing materials through cavitation (Kiani et al, 2013). At high ultrasonic power, the destructive role of ultrasonic cavitation and the vibration of the ultrasonic waves themselves can lead to muscle physical structure weakening (Jayasooriya, Torley, D’Arcy, & Bhandari, 2007).

3.5. Low-field NMR analysis

ACCEPTED MANUSCRIPT Freezing and frozen storage can alter both the content and distribution of moisture in meat tissue (Leygonie et al., 2012). LF-NMR is an effective method for evaluating water distribution and mobility inside frozen muscle after different freezing treatments (Zhang et al, 2017). Three peaks were observed and directly assigned to three distinct water populations

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(Fig. 5A). T2b (0-2 ms) represents bound water that is tightly bound to hydrophilic groups on macromolecules. T21 (10-100 ms) mainly corresponds to immobilized water that is entrapped

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in the myofibrillar network or within the space among the thick and thin filaments and is

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recognized as the predominant water component among the three types of water in muscle.

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T22 (100-1000 ms) represents free water that exists in the space among fibre bundles depending on capillary force (McDonnell et al., 2013).

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The influence of different freezing treatments on the T2b relaxation characteristics of thawed fresh meat is shown in Fig. 5B. There were no significant differences (P > 0.05)

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among the control, AF, IF and UIF samples in T2b relaxation. Zhang et al. (2017) found that the T2b relaxation time of porcine longissimus muscle after one freeze and thaw cycle did not

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significantly change (P > 0.05) compared to that of fresh muscle. This finding is mainly due to the presence of bound water that is independent of any mechanical stress and

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micro-structural change in the muscle tissue. The amount of bound water changes very little, and it is very resistant to freezing or heating (McDonnell et al., 2013). As shown in Fig. 5C, the T21 of the control samples was 35.96 ms, which was significantly lower than AF (48.95 ms), IF (45.34 ms), and UIF-300 (47.12 ms) (P < 0.05). This finding could be associated with the size and distribution of the ice crystals. Formation of large and extracellular ice crystals disrupts the physical structure, largely breaking myofibrils apart. After thawing, the water from melting ice in the extracellular spaces was reabsorbed with difficulty by the damaged myofibrils. Thus, the amount of previously immobilized water converted to free water, and

ACCEPTED MANUSCRIPT the released water was then redistributed into the sarcoplasmic and extracellular spaces (Leygonie et al., 2012). In addition, as the water froze, the concentration of the remaining solutes (proteins, carbohydrates, lipids, vitamins, and minerals) increased, thereby disrupting the homeostasis of the complex meat system, which was the key driver for water migration

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(Lawrie, 1998; Zhang et al., 2017). When the freezing rate accelerated, more intracellular water formed ice but could not infiltrate into the extracellular regions (Leygonie et al., 2012).

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In the present study, UIF-180 and UIF-240, especially UIF-180, remarkably shortened the

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freezing time and led to smaller and more uniformly distributed ice crystals, which would be

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beneficial for keeping muscle tissue intact after thawing. Accordingly, water molecules were securely trapped in muscle tissue, leading to immobilized water with lower mobility. It can be

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observed in Fig. 5C that the T21 relaxation time of samples with UIF-180 was significantly shortened to 37.47 ms, which was not significantly different from fresh samples (control) (P >

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0.05). As shown in Fig. 5D, the free water (T22 ) changes in all treatments were similar to immobilized water (T21 ). This result suggested that, for UIF-180 samples, free water had

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lower mobility and was more closely associated with muscle tissue than other freezing

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treatments, thereby reducing the amount of exudate (thawing loss).

4. Conclusions

UIF at certain powers significantly increased the freezing rate of muscle chops, and samples with UIF-180 had the shortest total freezing time. The thawing loss from frozen samples decreased at first and later increased with the increase in ultrasonic power, and the samples treated with 180 W ultrasonic powers had the lowest thawing loss. The different freezing treatments had no significant effect on a*, b* or pH values. Microstructure observation of frozen muscles showed that, compared with the IF samples, the smallest and

ACCEPTED MANUSCRIPT most uniformly distributed ice crystals were observed in samples treated with UIF-180 W. Low-field NMR analysis revealed that the T21 and T22 relaxation times of muscle samples treated with UIF-180 were the shortest, which means that UIF at a certain power could reduce the mobility and decrease the losses of immobilized and free water. In summation, the

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appropriate ultrasonic power treatment is beneficial for increasing the freezing rate and

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improving frozen meat quality.

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Acknowledgements

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This study was supported by the National Natural Science Foundation (grant No. 31571859 and No. 31771903) and the National Key Research and Development Plan for the

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13th Five-Year Plan Period (grant No. 2016YFD0401504).

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References

Anese, M., Manzocco, L., Panozzo, A., Beraldo, P., Foschia, M., & Nicoli, M. C. (2012).

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Effect of radiofrequency assisted freezing on meat microstructure and quality. Food Research International, 46, 50-54.

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Alarcon-Rojo, A. D., Janacua, H., Rodriguez, D., Paniwnyk, L. K., & Mason, T. J. (2015). Power ultrasound in meat processing. Meat Science, 107, 86-93. Aursand, I. G., Gallart-Jornet, L., Erikson, U., Axelson, D. E., & Rustad, T. (2008). Water distribution in brine salted cod (Gadusmorhua) and salmon (Salmo salar): A Low-Field 1 H NMR study. Journal of Agricultural and Food Chemistry, 15, 6252-6260. Cheng, X. F., Zhang, M., Adhikari, B., & Islam, M. N. (2014). Effect of ultrasound irradiation on some freezing parameters of ultrasound-assisted immersion freezing of strawberries. International Journal of Refrigeration, 44, 49-55.

ACCEPTED MANUSCRIPT Cheng, X. F., Zhang, M., Xu, B. G., Adhikari, B., & Sun, J. (2015). The principles of ultrasound and its application in freezing related processes of food materials: A review. Ultrasonics Sonochemistry, 27, 576-585. Chevalier, D., Sentissi, M., Havet, M., & Bail, A. L. (2000). Comparison of air-blast and

PT

pressure shift freezing on Norway lobster quality. Journal of Food Science, 65(2), 329-333. Choi, M. J., Min, S. G., & Hong, G. P. (2016). Effects of pressure-shift freezing conditions on

RI

the quality characteristics and histological changes of pork. LWT-Food Science and

SC

Technology, 67, 194-199.

NU

Choi, E. J., Park, H. W., Chung, Y. B., Park, S. H., Kim, J. S., & Chun, H. H. (2017). Effect of tempering methods on quality changes of pork loin frozen by cryogenic immersion.

MA

Meat Science, 124, 69-76.

Dalvi-Isfahan, M., Hamdami, N., Xanthakis, E., & Le-Bail, A. (2017). Review on the control

ED

of ice nucleation by ultrasound waves, electric and magnetic fields. Journal of Food Engineering, 195, 222-234.

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Delgado, A. E., Zheng, L., & Sun, D. (2009). Influence of ultrasound on freezing rate of immersion-frozen apples. Food and Bioprocess Technology, 2, 263-270.

AC C

Dickens, J. A., Lyon, C. E., & Wilson, R. L. (1991). Effect of ultrasonic radiation on some physical characteristics of broiler breast muscle and cooked meat. Poultry Science,70, 389-396.

Dorward, D. W., Raaenielsen, J., Hansen, B. T., Nair, V., & Fischer, E. R. (2013). Advances in microwave-assisted freeze substitution. Microscopy & Microanalysis, 19, 560-561. Farouk, M. M., Wieliczko, K. J., & Merts, I. (2003). Ultra-fast freezing and low storage temperatures are not necessary to maintain the functional properties of manufacturing beef. Meat Science, 66(1), 171-179.

ACCEPTED MANUSCRIPT Fernández, P. P., Sanz, P. D., Molina-García, A. D., Otero, L., Guignon, B., & Vaudagna, S. R. (2007). Conventional freezing plus high pressure-low temperature treatment: Physical properties, microbial quality, and storage stability of beef meat. Meat Science, 77(4), 616-625.

PT

Galetto, C. D., Verdini, R. A., Zorrilla, S. E, & Rubiolo, A. C. (2010). Freezing of strawberries by immersion in CaCl2 solutions. Food Chemistry, 123, 243-248.

RI

Gülseren, I., Güzey, D., Bruce, B. D., & Weiss, J. (2007). Structural and functional changes in

SC

ultrasonicated bovine serum albumin solutions. Ultrasonics Sonochemistry, 14, 173-183.

NU

Hale, M. B., & Waters, M. E. (1981). Frozen storage stability of whole and headless freshwater prawns, Macrobrachium rosenbergii. Marine Fish Review, 42, 18-21.

MA

Hu, S. Q., Liu, G., Li, L., Li, Z. X., & Hou, Y. (2013). An improvement in the immersion freezing process for frozen dough via ultrasound irradiation. Journal of Food Engineering,

ED

114, 22-28.

Islam, M. N, Zhang, M., Adhikari, B., Cheng, X. F., & Xu, B. G. (2014). The effect of

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ultrasound-assisted immersion freezing on selected physicochemical properties of mushrooms. International Journal of Refrigeration, 42, 121-133.

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Jayasooriya, S. D., Bhandari, B. R., Torley, P., & D'Arey, B. R. (2004). Effect of high power ultrasound waves on properties of meat: A review. International Journal of Food Properties, 7, 301-319. Jayasooriya, S. D., Torley, P. J., D’Arcy, B. R., & Bhandari, B. R. (2007). Effect of high power ultrasound and ageing on the physical properties of bovine semitendinosus and longissimus muscles. Meat Science, 75, 628-639. 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

ACCEPTED MANUSCRIPT protein oxidation of pork patties during chilled storage. Meat Science, 91, 533-539. Jørgensen, A. S., Christensen, M., & Ertbjerg, P. (2008). Marination with kiwifruit powder followed by power ultrasound tenderizes porcine M. biceps femoris. ICoMST 2008, 10-15 August, Cape Town, South Africa.

PT

Kiani, H., Zhang, Z., & Sun, D. W. (2012). The effect of ultrasound irradiation on the convective heat transfer rate during immersion cooling of a stationary sphere, Ultrasonics.

RI

Sonochemistry. 19, 1238-1245.

SC

Kiani, H., Zhang, Z., & Sun, D. W. (2013). Effect of ultrasound irradiation on ice crystal size

NU

distribution in frozen agar gel samples. Innovative Food Science & Emerging Technologies, 18, 126-131.

MA

Lagerstedt, Å., Enfält, L., Johansson, L., & Lundström. K. (2008). Effect of freezing on sensory quality, shear force and water loss in beef M. longissimus dorsi. Meat Science, 80,

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457-461.

Lawrie, R. A. (1998). In Anonymous (Ed.), Lawrie's meat science (pp. 1-336). (6th ed.).

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Lancaster, PA: Technomic Publishing Inc. Leygonie, C., Britz, T. J., & Hoffman, L. C. (2012). Impact of freezing and thawing on the

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quality of meat: review. Meat Science, 91, 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, 277-282. Lind, M. L., Harrison, D. L., & Kropf, D. H. (1971). Freezing and thawing rates of lamb chops: Effects on palatability and related characteristics. Journal of Food Science, 36(4), 629-631. Lucas, T., & Raoult-Wack, A. L. (1998). Immersion chilling and freezing in aqueous refrigerating media: review and future trends. International Journal of Refrigeration, 21(6),

ACCEPTED MANUSCRIPT 419-429. McDonnell, C. K., Allen, P., Duggan, E., Arimi, J. M., Casey, E., Duane, G., & Lyng, J. G. (2013). The effect of salt and fibre direction on water dynamics, distribution and mobility in pork muscle: A low field NMR study. Meat Science, 95, 51-58.

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Muela, E., Sañudo, C., Campo, M. M. Medel, I., & Beltrán, J. A. (2010). Effect of freezing method and frozen storage duration on instrumental quality of lamb throughout display.

RI

Meat Science, 84, 662-669.

SC

Otero, L., Sanz, P. D., Guignon, B., & Aparicio, C. (2009). Experimental determination of the

NU

amount of ice instantaneously formed in high-pressure shift freezing. Journal of Food Engineering, 95, 670-676.

MA

Pohlman, F. W., Dikeman, M. E., & Kropf, D. H. (1997). Effects of high intensity ultrasound treatment, storage time and cooking method on shear, sensory, instrumental color and

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cooking properties of packaged and unpackaged beef pectoralis muscle. Meat Science, 46(1), 89-100.

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Ribero, G. G., Rubiolo, A. C., & Zorrilla, S. E. (2009). Microstructure of Mozzarella cheese as affected by the immersion freezing in NaCl solutions and by the frozen storage. Journal

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of Food Engineering, 91(4), 516-520. Santacatalina, J. V., Guerrero, M. E., Garcia-Perez, J.V., Mulet, A., & Carcel, J. A. (2016). Ultrasonically assisted low-temperature drying of desalted codfish. LWT-Food Science and Technology, 65, 444-450. Sebranek, J. G. (1982). Use of cryogenics for muscle foods. Food Technology, 36(4), 121-127. Simal, S., Benekito, J., Sanchez, E. S., & Rossello, C. (1998). Use of ultrasound to increase mass transport rates during osmotic dehydration. Journal of Food Engineering, 36,

ACCEPTED MANUSCRIPT 323-336. Song, G. S., Hu, S. Q., & Li, L. (2008). Effect of ultrasound-assisted freezing on changes in protein secondary structure studied by Fourier transform infrared spectroscopy. Journal of Shanxi University of Science & Technology. 26, 132-137.

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Sun, D. W. & Li, B. (2003). Microstructural change of potato tissues frozen by ultrasound assisted immersion freezing. Journal of Food Engineering, 57, 337-345.

RI

Tu, J., Zhang, M., Xu, B. G., & Liu, H. H. (2015). Effects of different freezing methods on

SC

the quality and microstructure of lotus (Nelumbo nucifera) root. International Journal of

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Refrigeration, 52, 59-65.

Xin, Y., Zhan, M., & Bhandari, B. (2014). The effects of ultrasound-assisted freezing on the

MA

freezing time and quality of broccoli (Brassica oleracea L. var. botrytis L.) during immersion freezing. International Journal of Refrigeration, 41, 82-91.

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Xu, B., Zhang, M., Bhandari, B., & Cheng, X. (2014). Influence of power ultrasound on ice nucleation of radish cylinders during ultrasound-assisted immersion freezing. International

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Journal of Refrigeration, 46, 1-8.

Xu, B. G., Zhan, M., Bhandari, B., Cheng, X. F., & Islam, M. N. (2015). Effect of

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ultrasound-assisted freezing on the physico-chemical properties and volatile compounds of red radish. Ultrasonics Sonochemistry, 27, 316-324. Xu, Z. Y., Sun, D. W., & Zhu, Z. W. (2016). Potential life cycle carbon savings for immersion freezing of water by power ultrasound. Food Bioprocess Technology, 9, 69-80. Zarkadas, D., & Mitrakas, M. (1999). On the applicability of a plug flow immersion freezer: Theoretical considerations. LWT-Food Science and Technology, 32(8), 548-552. 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

ACCEPTED MANUSCRIPT of bubble nuclei. International Journal of Heat & Mass Transfer, 44(23), 4533-4539. Zhang, M. C., Li, F. F., Diao, X. P., Kong, B. H., & Xia, X. F. (2017). Moisture migration, microstructure damage and protein structure changes in porcine longissimus muscle as influenced by multiple freeze-thaw cycles. Meat Science, 133, 10-18.

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Zheng, L. Y. & Sun, D. W. (2006). Innovative applications of power ultrasound during food

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freezing processes-a review. Trends in Food Science & Technology, 17, 16-23.

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Fig. 1. Three-dimensional perspective drawing of ultrasound-assisted freezing apparatus. 1.

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Ultrasonic tank; 2. Ultrasonic transducer; 3. Refrigeration compressor; 4. Coolant storage tank; 5. Circulating pump; 6. Control panel; 7. Ultrasonic generator; 8. Temperature testing

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instrument; 9. K-type thermocouple.

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10

(A)

(B)

5

Temperature (° C)

Temperature (° C)

5 0 -5 AF -10 -15

0 -5 IF UIF-120 UIF-180 UIF-240 UIF-300

-10 -15

-20

-20 0

5000

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Time (S)

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Fig. 2. Freezing curves of porcine longissimus muscles during freezing. AF, air freezing; IF,

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immersion freezing; UIF, ultrasound-assisted immersion freezing at different ultrasound

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powers (120, 180, 240, and 300 W).

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35

a

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Thawing loss (%)

b

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30 Cutting force (N)

Cutting force Thawing loss Cooking loss (%)

25 2 0

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00

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Treatment

Fig. 3. Influence of different freezing methods on the thawing loss, cooking loss, and cutting

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force of porcine longissimus muscles. The means in the same index with different letters differ significantly (P < 0.05). Control, fresh meat; AF, air freezing; IF, immersion freezing;

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UIF, ultrasound-assisted immersion freezing at different ultrasound powers (120, 180, 240, and 300 W).

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a 30 25

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(C)

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Average radius of ice crystal (μ m)

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b

cd d e

5 0

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AF

IF

0 0 0 0 12 18 24 30 FFFFI I I I U U U U Treatment

Fig. 4. Influence of different freezing treatments on the microstructures (A and B) of frozen porcine longissimus muscles and average radius of ice crystal (C). AF, air freezing; IF, immersion freezing; UIF, ultrasound-assisted immersion freezing at different ultrasound powers (120, 180, 240, and 300 W). Scale bars indicate 200 µm."a-e" means with different letters differ significantly (P< 0.05).

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1.4

a

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Fig. 5. Distribution of the LF-NMR T2 relaxation times of porcine longissimus muscles under

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different freezing treatments (A) and changes in the T2b relaxation times (B), T21 relaxation times (C) and T22 relaxation times (D). The means in the same T2 with different letters differ

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Table 1. Time the porcine longissimus muscles spent at each freezing stage as affected by different freezing treatments. Pre-cooling stage (sec)

Phase transition stage (sec)

Sub-cooling stage (sec)

IF

772 ± 9a

1239 ± 13b

677 ± 24b

UIF-120

775 ± 5

UIF-180

785 ± 13

UIF-240

776 ± 8a

1160 ± 13c

UIF-300

790 ± 16a

1387 ± 22a

b

646 ± 12

1083 ± 18

d

608 ± 27

b

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a

1210 ± 16

b

2688 ± 19b 2632 ± 21

c

2476 ± 21

e

641 ± 13b

2578 ± 15d

748 ± 35a

2925 ± 20a

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Total freezing time (sec)

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Treatment

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The means in the same column with different superscript letters differ significantly (P < 0.05).

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The results are mean ± standard deviation (n = 3). IF, immersion freezing; UIF, ultrasound-assisted immersion freezing at different ultrasound powers (120, 180, 240, and 300

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W).

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Table 2 Changes in colour and pH values of frozen porcine longissimus muscle treated with different freezing conditions. Colour

pH

L*

a*

b*

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Treatment

49.43 ± 0.79

c

17.87 ± 1.06

a

13.15 ± 0.56

a

5.70 ± 0.02

AF

52.71 ± 0.49

ab

17.30 ± 0.71

a

15.29 ± 0.59

a

5.73 ± 0.02

IF

51.69 ± 1.38abc

17.48 ± 0.82a

UIF-120

51.39 ± 1.09bc

17.09 ± 0.43a

UIF-180

49.91 ± 0.46

UIF-240

51.78 ± 2.14bc

UIF-300

54.46 ± 1.07

a

a

17.40 ± 0.86a

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17.80 ± 0.55

14.14 ± 0.45a 13.83 ± 0.52a 14.51 ± 1.26

17.19 ± 0.37

a

a

14.83 ± 1.87a

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bc

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Control

14.68 ± 0.65

a

a a

5.72 ± 0.01a 5.74 ± 0.02a a

5.73 ± 0.01

5.72 ± 0.02a a

5.72 ± 0.02

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The means in the same column with different superscript letters differ significantly (P < 0.05). The results are mean ± standard deviation (n = 3). AF, air freezing; IF, immersion freezing;

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UIF, ultrasound-assisted immersion freezing at different ultrasound powers (120, 180, 240,

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and 300 W).

ACCEPTED MANUSCRIPT Highlights UIF at certain powers significantly increased the freezing rate of muscle chops

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Samples treated with 180 W ultrasonic power had the least thawing loss

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The smallest ice crystals were formed in samples treated with UIF-180

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Ultrasonic power at 180 W could significantly shorten the T2 relaxation time

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Using the appropriate ultrasonic power is beneficial for improving frozen meat quality

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