Deterioration in quality of quick-frozen pork patties induced by changes in protein structure and lipid and protein oxidation during frozen storage

Integrated Lipidomic and Metabolomics Analysis Revealing the Effects of Frozen Storage Duration on Pork Lipids

Frozen storage is an important strategy to maintain meat quality for long-term storage and transportation. Lipid oxidation is one of the predominant causes of the deterioration of meat quality during frozen storage. Untargeted lipidomic and targeted metabolomics were employed to comprehensively evaluate the effect of frozen duration on pork lipid profiles and lipid oxidative products including free fatty acids and fatty aldehydes. A total of 688 lipids, 40 fatty acids and 14 aldehydes were successfully screened in a pork sample. We found that ether-linked glycerophospholipids, the predominant type of lipids, gradually decreased during frozen storage. Of these ether-linked glycerophospholipids, ether-linked phosphatidylethanolamine and phosphatidylcholine containing more than one unsaturated bond were greatly influenced by frozen storage, resulting in an increase in free polyunsaturated fatty acids and fatty aldehydes. Among these lipid oxidative products, decanal, cis-11,14-eicosenoic acid and cis-5,8,11,14,17-dicosapentaenoic acid can be considered as potential indicators to calculate the freezing time of unknown frozen pork samples. Moreover, over the three-month frozen storage, the first month was a rapid oxidation stage while the other two months were a slow oxidation stage.

Effects of starch/polyvinyl alcohol active film containing cinnamaldehyde on the quality of large yellow croaker (Pseudosciaena crocea) proteins during frozen storage

This study aimed to investigate the effects of starch/polyvinyl alcohol (starch/PVA) film containing cinnamaldehyde (CIN) with different humidity treatment on the quality changes of large yellow croaker (Pseudosciaena crocea) under vacuum packaging during frozen storage. It was evaluated by measuring the water loss, water migration, total volatile basic nitrogen (TVB-N), thiobarbituric acid (TBA), free amino acids (FAA) content, myofibril secondary and tertiary structure and microstructure of large yellow croaker. Compared with control group, the starch/PVA films could inhibit the water loss, water migration, protein degradation, lipid oxidation and microstructure damage of fish. The film containing CIN with higher humidity treatment showed the best protective effect for large yellow croaker. The film with higher humidity treatment showed better to maintain the quality of fish than that with low humidity treatment. Therefore, starch/PVA active film containing CIN with high humidity treatment showed good fresh-keeping potential in the frozen storage of aquatic products.

Water distribution and key aroma compounds in the process of beef roasting

The key aroma compounds and water distribution of the beef at different roasting times (0, 3, 6, 9, 12, 15, and 18 min) were identified and analyzed. The results showed that the L^* value increased considerably before peaking and then decreased. On average, a^* values decreased significantly first and then kept stable, while b^* values increased first and then decreased. A total of 47 odorants were identified in all samples, including 14 alcohols, 18 aldehydes, 6 ketones, 1 ester, 3 acids, 4 heterocyclic compounds, and 1 other compound. Among them, 11 key aroma compounds were selected and aldehydes and alcohols predominantly contributed to the key aroma compounds. The fluidity of the water in the beef during the roasting process was decreased, and the water with a high degree of freedom migrated to the water with a low degree of freedom. The correlation analysis showed that water content and L^* were negatively correlated with key aroma compounds of the samples, while M₂₁ was positively correlated with key aroma compounds.

Inhibitory effect of chitosan coating on oil absorption in French fries based on starch structure and morphology stability

The effect of chitosan (CS) coating on oil absorption, water migration, starch structure and morphology in French fries was evaluated. The penetrated surface oil, structure oil, total oil content, and a* of coated fries decreased, while the water content, L*, b*, and hardness significantly (P < 0.05) increased compared to uncoated samples. 1 % CS-coated fries had the lowest oil content, which decreased by 43.0 % compared to uncoated samples. CS-coated fries had higher free water, and lower T₂ relaxation time, immobile and binding water than the control. CS coating reduced the pores on the fries' surface and the interaction between oil and the component of fries, which was observed by confocal laser scanning microscopy and scanning electron microscopy (SEM). As for starch morphology, the pores and cracks of starch granules in the coated samples reduced. As for the starch structure, the relative crystallinity, R_1047/1022 respectively increased by 47.2 % and 2.35 times, and ΔH of CS-coated fries increased from 0 to 2.09 J/g, indicating that the long-range crystalline structure, short-range ordered structure, and hydrogen bonds between the double helices in starch increased. Therefore, CS coating reduced oil penetration into fries by reducing water migration and increasing starch ordered structure and morphological integrity.

A strategy for accurately and sensitively quantifying free and esterified fatty acids using liquid chromatography mass spectrometry

Fatty acid (FA) composition of foods dictates a diversity of aspects regarding food quality, ranging from product shelf life, sensory properties to nutrition. There is a challenge to quantitate FAs using liquid chromatography-mass spectrometry due to poor ionization efficiency and matrix effects. Here, an isotopic-tagged derivatization strategy was established to accurately and sensitively quantify free and esterified FAs. After derivatization reaction, the detection sensitivity of FAs was remarkably improved and the limit of quantitation was lower than 100 ng/L. The quantitative errors caused by matrix effects were diminished benefiting from isotope-derivatized internal standards. The established quantitation strategy was successfully applied to verify both free and esterified FA contents in meat after different post-harvest procedures, finding that free polyunsaturated FAs increased significantly during freezing process.

Inhibitory Effect of Guava Leaf Polyphenols on Advanced Glycation End Products of Frozen Chicken Meatballs (-18 °C) and Its Mechanism Analysis

The inhibitory effect of guava leaf polyphenols (GLP) on advanced glycation end products (AGEs) of frozen chicken meatballs (−18 °C) and its possible inhibitory mechanism was investigated. Compared with control samples after freezing for 6 months, acidic value (AV), lipid peroxides, thiobarbituric acid reactive substance (TBARS), A294, A420, glyoxal (GO), Nε-carboxymethyl-lysine (CML), pentosidine, and fluorescent AGEs of chicken meatballs with GLP decreased by 11.1%, 22.3%, 19.5%, 4.30%, 8.66%, 8.27%, 4.80%, 20.5%, and 7.68%, respectively; while free sulfhydryl groups the content increased by 4.90%. Meanwhile, there was no significant difference between meatballs with GLP and TP in AV, A294, GO, and CML (p > 0.05). Correlation analysis indicated that GO, CML, pentosidine, and fluorescent AGEs positively correlated with AV, TBARS, A294, and A420, while GO, CML, pentosidine, and fluorescent AGEs negatively correlated with free sulfhydryl groups. These results manifested GLP could inhibit AGEs formation by inhibiting lipid oxidation, protein oxidation, and Maillard reaction. The possible inhibitory mechanism of GLP on the AGEs included scavenging free radicals, capturing dicarbonyl compounds, forming polyphenol−protein compounds, and reducing the formation of glucose. Therefore, the work demonstrated that the addition of plant polyphenols may be a promising method to inhibit AGEs formation in food.

Quality changes and deterioration mechanisms in three parts (belly, dorsal and tail muscle) of tilapia fillets during partial freezing storage

The quality changes in tilapia belly muscle (BM), dorsal muscle (DM) and tail muscle (TM) were studied and the hypothesis of browning of the fillets was revealed during partial freezing. Compared with DM and TM groups, BM samples had higher thiobarbituric acid reactive substances (TBARS) (0.41 mg malondialdehyde eq/kg at 49 d) and K values (61.81% at 42 d) (P < 0.05). The microstructure of the BM group deteriorated most obviously during storage. Therefore, the BM group was considered to be the fastest to oxidize and deteriorate. In addition, 54 different micromolecular metabolites were identified from tilapia fillets by UHPLC-Q-TOF-MS analysis, and there were significant differences in the micromolecular metabolites in the three parts of tilapia. Therefore, proteins and lipids were degraded by the action of enzymes and microorganisms to produce some amines and small molecular acids, leading to the deterioration of the quality of tilapia fillets.

Vacuum Impregnation Process Optimization for Tilapia with Biopreservatives at Ice Temperature

The vacuum impregnation (VI) process was used to pretreat tilapia fillets with biopreservatives at −2 °C. Response surface methodology (RSM) was utilised to optimize processing conditions, including vacuum pressure (p_v), vacuum maintenance time (t₁), and atmospheric pressure recovery time (t₂), which were determined to be 67.73 kPa, 23.66 min, and 8.87 min, respectively. The anticipated values for the aerobic plate count (APC), total volatile basic nitrogen (TVB-N), and comprehensive score (CS) were 5.17 lg CFU/g, 14.04 mg/100 g, and 0.98, respectively. Verification experiments were conducted, and the experimental results for APC and TVB-N deviated from the predicted values by 0.19% and 0.64%, respectively. After 30 days of storage following VI and atmosphere impregnation (AI) pretreatment, the water-holding capacity (WHC), APC, TVB-N, hardness, and whiteness were determined. On the 30th day, the results for VI pretreatment were 63.38%, 6.27 lg CFU/g, 17.41 mg/100 g, 3.11 N, and 47.73, respectively. Compared with AI pretreatment, WHC, hardness, and whiteness increased by 14.8%, 18.6%, and 6.3%, respectively, whereas APC and TVB-N decreased by 11.3% and 29.6%, respectively. This study demonstrates that when biopreservatives are applied during the pretreatment process, VI technology can be utilised to facilitate their penetration into the interior of tilapia, hence significantly enhancing the effect of ice-temperature preservation.

Astaxanthin Extract from Shrimp (Trachypenaeus curvirostris) By-Products Improves Quality of Ready-to-Cook Shrimp Surimi Products during Frozen Storage at -18 °C

The effects of astaxanthin extract (AE) from shrimp by-products on the quality and sensory properties of ready-to-cook shrimp surimi products (RC-SSP) during frozen storage at −18 °C were investigated. Changes in 2-thiobarbituric acid reactive substances (TBARS) value, sulfhydryl groups, carbonyls, salt-soluble protein content, textural properties, color, and sensory quality over specific storage days were evaluated. The AE from shrimp by-products contained 4.49 μg/g tocopherol and 23.23 μg/g astaxanthin. The shrimp surimi products supplemented with 30 g/kg AE had higher redness values and greater overall acceptability and texture properties after cooking (p < 0.05). AE showed higher oxidative stability in RC-SSP than the control, as evidenced by lower TBARS and carbonyl content, and higher sulfhydryl and salt-soluble protein content. AE from shrimp by-products had positive effects on the antioxidant activity and color difference of RC-SSP, and could be used as a potential multifunctional additive for the development of shrimp surimi products.

Storage and Packaging Effects on the Protein Oxidative Stability, Functional and Digestion Characteristics of Yak Rumen Smooth Muscle

The objective of this study was to investigate the effects on protein oxidative stability, functional and digestion characteristics of yak rumen smooth muscle with overwrap packaging using oxygen-permeable film (OWP) and vacuum packaging bag (VP) during storage (0, 7, 14, 28, 42, 56, 84, 168 and 364 days) at −18 °C. The results show that yak rumen smooth muscle was oxidized with frozen storage through the formation of protein carbonyls and disulfide bonds, the loss of total sulfhydryl. The emulsifying activity of yak rumen smooth muscle protein (SMP) under VP began to perform a higher level than that under OWP after 14 days, and the foaming capacity under VP showed the highest level on the 28th day of 111.23%. The turbidity under VP reached the minimum 0.356 on the 28th day as well, followed by significantly increasing on the 56th day compared with OWP. The digestibility of yak rumen SMP under both OWP and VP reached the maximum on the 28th day of frozen storage. Moreover, yak rumen under VP at 28–56 days of frozen storage had good functional properties and high digestibility of SMP, which showed better edible value.

Interrelationship among protein structure, protein oxidation, lipid oxidation and quality of grass carp surimi during multiple freeze-thaw cycles with different pork backfat contents

Storing at -18°C, the surimi was processed from fresh grass carp, supplemented with pork backfat of 50, 100, or 150 g kg^-1 (groups F₀ , F₅₀ , F₁₀₀ , and F₁₅₀ , respectively). The surimi was thawed and refrozen weekly afterward, with changes in surimi protein structure (primary structure, secondary structure, and tertiary structure), protein oxidation index (carbonyl and sulfhydryl), lipid oxidation index (TBARS), protein solubility, as well as surimi quality (texture characteristics and whiteness), were determined. The results showed that the texture characteristics of surimi increased after the first freezing and thawing (F-T) cycle and then decreased. The whiteness of the surimi decreased with the increase of F-T cycle times, while the whiteness of the surimi increased with the increase in fat content. With the F-T cycle times and fat content rising, the relative content of α-helix structures, sulfhydryl content, and protein solubility decreased. In contrast, carbonyl content was in reverse, being an increasing trend. The free amino content showed a decrease after an increase at the early stage with the F-T cycles growing, while it showed a decrease with an increase in fat content. Meanwhile, the redshift in the maximum absorption peak of the tryptophan fluorescence was caused by the F-T cycles, so was the decline in fluorescence intensity; however, there was little difference in tryptophan spectra with the same fat content. The association among protein structure, protein oxidation, lipid oxidation and surimi quality were elucidated by Pearson's two-tailed correlation. The lipid oxidation in the repeated freezing and thawing process of surimi led to the decrease in whiteness. The protein oxidation led to the change of protein structure and the decrease of protein solubility. Lipid oxidation caused by the increase of fat content led to the decrease of free amino content and protein solubility, and finally led to the increase of whiteness and the deterioration of texture characteristics. PRACTICAL APPLICATIONS: In this study, changes in various components of surimi were measured to examine the interrelationship among protein structure, protein oxidation, lipid oxidation and surimi quality. Freeze-thaw cycle and high-fat content are easy to cause lipid oxidation, protein oxidation, a decrease in protein solubility, and deterioration of surimi quality. Therefore, temperature fluctuations must be avoided to extend the shelf life of such products. An appropriate fat content level must be selected to prevent protein and lipid oxidation and maintain quality.

The Effect of Pressure-Shift Freezing versus Air Freezing and Liquid Immersion on the Quality of Frozen Fish during Storage

In this study, a self-cooling laboratory system was used for pressure−shift freezing (PSF), and the effects of pressure−shift freezing (PSF) at 150 MPa on the quality of largemouth bass (Micropterus salmoides) during frozen storage at −30 °C were evaluated and compared with those of conventional air freezing (CAF) and liquid immersion freezing (LIF). The evaluated thawing loss and cooking loss of PSF were significantly lower than those of CAF and LIF during the whole frozen storage period. The thawing loss, L* value, b* value and TBARS of the frozen fish increased during the storage. After 28 days storage, the TBARS values of LIF and CAF were 0.54 and 0.65, respectively, significantly higher (p < 0.05) than the 0.25 observed for PSF. The pH of the samples showed a decreasing trend at first but then increased during the storage, and the CAF had the fastest increasing trend. Based on Raman spectra, the secondary structure of the protein in the PSF-treated samples was considered more stable. The α-helix content of the protein in the unfrozen sample was 59.3 ± 7.22, which decreased after 28 days of frozen storage for PSF, LIF and CAF to 48.5 ± 3.43, 39.1 ± 2.35 and 33.4 ± 4.21, respectively. The results showed that the quality of largemouth bass treated with PSF was better than LIT and CAF during the frozen storage.

Quality changes in fish sausages supplemented with pangas protein isolates as affected by frozen storage and casing material

Influence of pangas protein isolates (10PI) and casing material on frozen storage (-18 °C) characteristics of pangas mince sausages was studied for a period of three months along with control sausages (CO). The expressible fluid content of sausage emulsion increased as storage progressed to 3 months, reaching 31.32 and 17.57 g 100 g^-1 for control and 10% PI emulsions, respectively. Water holding capacity and cooking yield values showed a gradual and significant (p < 0.05) reduction with progress in the storage time. The G' and G″ values decreased during storage, indicating the change in protein structure and gelling ability. Sausages packed in LDPE casings had higher oxidation and bacterial counts than sausages packed in cellulose casings. Irrespective of the casing material and protein isolates, the sensory scores varied non-significantly in all the sausages during the initial storage phase. After three months, sausages from COCL and 10PICL were still acceptable with sensory scores of 5.6 and 5.8, respectively, indicating better quality of sausages stuffed into cellulose casings than LDPE casings.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-021-05222-1.

Differentiation of Penaeus vannamei from different thermal processing methods in physico-chemical, flavor and sensory characteristics

Differentiation in physico-chemical, flavor and sensory characteristics of shrimps (Penaeus vannamei) after direct roasting (DR, 200 °C), boiling (100 °C/2 min) + roasting (BR), steaming (100 °C/2 min) + roasting (SR) and microwaving (280 W/2 min) + roasting (MR) was investigated. BR, SR, and MR endowed shrimps with better texture to varying degrees and significantly (P < 0.05) increased lightness when compared to DR, which closely related to their different water status. High correlations between nuclear magnetic resonance data and quality properties were found by partial-least-squares regression (PLSR). Shrimps possessed by SR significantly (P < 0.05) increased the proportion of sweet amino acids (63.89 ± 0.92%), with superior umami and richness detected by electronic tongue. Compared with DR, both SR and MR endowed shrimps with richer ester, while BR endowed shrimps with richer hydrocarbons. Roasting combined with other thermal processing would favor improving the quality of shrimp products.

Assessing the Gel Quality and Storage Properties of Hypophythalmalmichthys molitrix Surimi Gel Prepared with Epigallocatechin Gallate Subject to Multiple Freeze-Thaw Cycles

Epigallocatechin gallate (EGCG) with concentrations of 0-0.03% was added to manufacture surimi gels, respectively, while effects on gel quality and storage properties indicators during freeze-thaw (F-T) cycles were investigated. The results implied that the gel quality and storage properties of surimi gels added without EGCG were seriously destroyed during F-T cycles. The addition of EGCG could inhibit the decline of texture and gel strength. Moreover, EGCG has effect on inhibiting the microbial growth and the formation of off-odor compounds such as total volatile basic nitrogen (TVB-N) and malondialdehyde (MDA). Low-field nuclear magnetic resonance (LF-NMR) and water-holding capacity (WHC) results showed that immobilized water migrated to free water with the extension of F-T cycles. The scanning electron microscope (SEM) observed denser protein networks and smaller holes from the surimi gels added with EGCG. However, excessive (0.03%) EGCG showed the loose network structure and moisture loss. Overall, EGCG in 0.01-0.02% addition was good for resisting damage of surimi gels during F-T cycles.

Comparison of Effects from Ultrasound Thawing, Vacuum Thawing and Microwave Thawing on the Quality Properties and Oxidation of Porcine Longissimus Lumborum

The effects of vacuum thawing (VT), ultrasound thawing (UT) and microwave thawing (MT) on the quality, protein and lipid oxidation, internal temperature distribution and microstructure of porcine longissimus lumborum were compared. The results showed that a significant decrease (p < 0.05) in quality compared with those of fresh meat (FM) occurred for all of the thawing samples, especially for the MT samples. Changes in quality of the VT and UT samples were less significant than those of the MT samples. The increases in carbonyl content and TBARS value indicated that proteins and lipids in the thawing samples were oxidized. The decreases in uniform degrees of internal temperature distributions of muscles from the thawing samples were analysed by infrared thermography. Scanning electron microscopy images showed that the myofibril arrangements of thawing samples were looser than those of the FM samples with compact and ordered structure, which was proven by the obvious increase in the myofibril gap value of the thawing samples.

Impact of Ultrasound-assisted Saline Thawing on the Technological Properties of mirror carp (Cyprinus carpio L.)

The aim of the study was to evaluate the positive effect of ultrasound-assisted saline thawing (UST) on the technological properties (water mobility, water holding capacity, colour, pH, shear force, TVB-N, oxidation reaction and microstructure) of mirror carp (Cyprinus carpio L.). The results present in the study showed that different thawing methods had negative impacts on the quality of mirror carp to varying degrees. Among them, UST samples had significant lower thawing loss, centrifugal loss and cooking loss than ultrasound thawing (UT) and air thawing (AT) samples (P < 0.05). The analysis result of low-field nuclear magnetic resonance illustrated that UST inhibited the mobility and distribution of water effectively. Decrease in shear force and TVBN values were observed in all thawing samples, and the UST samples maintained the significant better texture property and freshness than UT and AT samples did (P < 0.05). In addition, the treatment of UST obtained 1% salt concentration inhibited the oxidation reactions effectively. Investigation of the microstructure of samples demonstrated that the treatment of UST kept the relatively complete structure of tissue than other thawing methods. Therefore, UST can be an alternative strategy to the traditional thawing of meat.

Improving the Flavor of Fermented Sausage by Increasing Its Bacterial Quality via Inoculation with Lactobacillus plantarum MSZ2 and Staphylococcus xylosus YCC3

This research aims to investigate the effects of Staphylococcus xylosus YCC3 (Sx YCC3) and Lactobacillus plantarum MSZ2 (Lp MSZ2) on lipid hydrolysis and oxidation, the bacterial community’s composition, and the volatile flavor compounds in fermented sausage. The bacterial community was examined by plate counting and high-throughput sequencing. Differential flavor compounds in non-inoculated and inoculated sausages were identified by principal component analysis (PCA) and orthogonal partial least squares discrimination analysis (OPLS-DA). The results showed that the free fatty acid (FFA) content was increased after inoculating with Sx YCC3 or Lp MSZ2. The pH, peroxide value (POV), thiobarbituric acid reactive substances (TBARS) value, lipoxygenase activity, and the counts of Enterobacteriaceae were lower in the inoculated sausage than in the non-inoculated sausage. The bacterial inoculation enhanced the competitiveness of Staphylococcus and Lactobacillus and restricted the growth of unwanted bacteria. The OPLS-DA revealed that (Z)-hept-2-enal, (E)-2-octenal, 1-nonanal, octanal, and 1-octen-3-ol were common differential flavor compounds that were found in the inoculated sausages but were not found in the non-inoculated sausages. A positive correlation was observed between the differential flavor compounds and the relative abundance of Staphylococcus or Lactobacillus, or the FFA content. Our results indicated that inoculation with Sx YCC3 or Lp MSZ2 can improve fermented sausages’ flavor by enhancing their bacterial quality and increasing their FFA content.

Effect of protein oxidation in meat and exudates on the water holding capacity in bighead carp (Hypophthalmichthys nobilis) subjected to frozen storage

This study aimed to investigate the effect of myofiber changes and protein oxidation on water holding capacity (WHC) of bighead carp fillets stored at -20 °C. WHC, microstructure, protein oxidation parameters, and specific modifications of oxidized amino acids were analyzed during 9 months of frozen storage. Results indicated that WHC decreased accompanied by myofibers' structural changes (including the formation of cavities among myofibers, breakage of myofibrils and myofibers, and shortening of sarcomeres) and protein oxidation. SDS-PAGE and carbonyl and sulfhydryl content determination of myofibrillar proteins and exudates gave a detailed description of the protein oxidation. LC-MS/MS analysis demonstrated that oxidation, di-oxidation, and 4-hydroxy-2-nonenal (HNE) and malondialdehyde (MDA) adduction were the top four oxidative modifications of proteins. Oxidative modifications impaired configuration and polarity of proteins, which may further affect WHC. This study provides plausible explanations to support the role of protein oxidation in the decrease of WHC in frozen fillets.

The quality properties of frozen large yellow croaker fillets during temperature fluctuation cycles: improvement by cellobiose and carboxylated cellulose nanofibers

Frozen aquatic products undergo unavoidable quality changes owing to temperature fluctuations during frozen storage and distribution. This study investigated the effects of 1% cellobiose (CB), and 0.5 and 1% carboxylated cellulose nanofibers (CNF) on ice crystal growth and recrystallization of frozen large yellow croaker fillets exposed to temperature fluctuations. Denser and more uniformly distributed ice crystals were observed in the CB- and CNF-treated samples than in the water-treated samples. Furthermore, the addition of CB and CNF suppressed the conversion of bound water to frozen water in the samples during temperature fluctuation cycles, played a positive role in fixing the ionic and hydrogen bonds that stabilize the protein structure, limited the conformational transition from α-helix to β-sheet, and improved protein thermal stability. Based on turbidity, zeta potential, and confocal laser scanning microscopy (CLSM) analyses, the presence of CB and CNF restricted the protein aggregation. Compared with CB, CNF molecules with abundant carboxyl functional groups and longer morphology exhibited better cryoprotective effects. Moreover, the fillets were more improved protected from mechanical damage induced by large ice crystals at a higher CNF concentration. This study reveals the potential of CB and CNF as novel cryoprotectants.

Mechanisms of Change in Emulsifying Capacity Induced by Protein Denaturation and Aggregation in Quick-Frozen Pork Patties with Different Fat Levels and Freeze-Thaw Cycles

Herein, we discuss changes in the emulsifying properties of myofibrillar protein (MP) because of protein denaturation and aggregation from quick-frozen pork patties with multiple fat levels and freeze-thaw (F-T) cycles. Protein denaturation and aggregation were confirmed by the significantly increased surface hydrophobicity, turbidity, and particle size, as well as the significantly decreased solubility and absolute zeta potential, of MPs with increases in fat levels and F-T cycles (p < 0.05). After multiple F-T cycles, the emulsifying activity and emulsion stability indices of all samples were significantly reduced (p < 0.05). The emulsion droplets of MP increased in size, and their distributions were dense and irregular. The results demonstrated that protein denaturation and aggregation due to multiple F-T cycles and fat levels changed the distribution of surface chemical groups and particle sizes of protein, thus affecting the emulsifying properties.

The role of trifunctional cryoprotectants in the frozen storage of aquatic foods: Recent developments and future recommendations

Freeze-induced changes including protein denaturation, ice crystals formation and lipid oxidation are mainly responsible for the quality deterioration persistent in aquatic foods. Here, for the first time, the cryoprotectants with trifunctional properties have been suggested for aquatic food cryopreservation and have exhibited exceptional cryoprotective abilities. In this study, in-depth discussion of protein denaturation, ice crystal formation and lipid oxidation is added in order to understand their mechanism, emphasizing on the necessity and use of trifunctional cryoprotectants in aquatic foods during frozen storage. Trifunctional cryoprotectants have strong abilities to prevent the formation of malondihaldehyde and aldehydes resulting from lipid oxidation, which further interact with proteins, subsequently lead to protein denaturation. Besides these all cryoprotective properties, ice crystal binding abilities distinguish trifunctional cryoprotectants from conventional cryoprotectants. Moreover, this study added with recent advances in cryoprotectants including antifreeze proteins and protein hydrolysates with their role in retarded freeze-induced changes. This study concluded that trifunctional cryoprotectants are effective owing to their hydrophilic amino acid chains, radical scavenging, water entrapping abilities, as well as the hydroxyl groups, which interact at the functional sites of protein molecules. Furthermore, polysaccharides and protein hydrolysates are the potential ingredients with trifunctional cryoproperties. However, more scientific research is required for material optimization to attain the desired level of cryoprotection.

Crystallization Behavior and Quality of Frozen Meat

Preservation of meat through freezing entails the use of low temperatures to extend a product’s shelf-life, mainly by reducing the rate of microbial spoilage and deterioration reactions. Characteristics of meat that are important to be preserve include tenderness, water holding capacity, color, and flavor. In general, freezing improves meat tenderness, but negatively impacts other quality attributes. The extent to which these attributes are affected depends on the ice crystalline size and distribution, which itself is governed by freezing rate and storage temperature and duration. Although novel technology has made it possible to mitigate the negative effects of freezing, the complex nature of muscle tissue makes it difficult to accurately and consistently predict outcome of meat quality following freezing. This review provides an overview of the current understanding of energy and heat transfer during freezing and its effect on meat quality. Furthermore, the review provides an overview of the current novel technologies utilized to improve the freezing process.

The impact of quick-freezing methods on the quality, moisture distribution and microstructure of prepared ground pork during storage duration

The aim of present study was to investigate the influences of ultrasound-assisted immersion freezing (UIF), immersion freezing (IF) and air freezing (AF) on the quality, moisture distribution and microstructure properties of the prepared ground pork (PGP) during storage duration (0, 15, 30, 45, 60, 75 and 90 days). UIF treatment significantly reduced the freezing time by 60.32% and 39.02%, respectively, compared to IF and AF (P < 0.05). The experimental results of quality evaluation revealed that the L* and b* values, juice loss, cooking loss, TBARS values and carbonyl contents were decreased in the UIF treated samples, while the a* value, peak temperatures (Tm), enthalpy (ΔH) and sulfhydryl contents were significantly higher than those of IF and AF treated samples (P < 0.05). In addition, low-field nuclear magnetic resonance (LF-NMR) and differential scanning calorimetry (DSC) analysis demonstrated that UIF inhibited the mobility of immobilized water and reduced the loss of immobilized and free water, and then a high water holding capacity (WHC) was achieved. Compared to the IF and AF treatments, the UIF treated PGP samples possessed better microstructure. Therefore, UIF could induce the formation of ice crystals with smaller size and more even distribution during freezing process, which contributed to less damage to the muscle tissue and more satisfied product quality.

Freezing of meat and aquatic food: Underlying mechanisms and implications on protein oxidation

Over the recent decades,protein oxidation in muscle foods has gained increasing research interests as it is known that protein oxidation can affect eating quality and nutritional value of meat and aquatic products. Protein oxidation occurs during freezing/thawing and frozen storage of muscle foods, leading to irreversible physicochemical changes and impaired quality traits. Controlling oxidative damage to muscle foods during such technological processes requires a deeper understanding of the mechanisms of freezing-induced protein oxidation. This review focus on key physicochemical factors in freezing/thawing and frozen storage of muscle foods, such as formation of ice crystals, freeze concentrating and macromolecular crowding effect, instability of proteins at the ice-water interface, freezer burn, lipid oxidation, and so on. Possible relationships between these physicochemical factors and protein oxidation are thoroughly discussed. In addition, the occurrence of protein oxidation, the impact on eating quality and nutrition, and controlling methods are also briefly reviewed. This review will shed light on the complicated mechanism of protein oxidation in frozen muscle foods.

Dynamics of heat transfer and moisture in beef jerky during hot air drying

The aim of this study was to investigate the surface temperature, moisture migration, muscle shrinkage and microstructure of beef jerky during hot air multi-stage drying. Temperatures were sequentially increased from 40 to 50 to 60 °C, and corresponding times were 0.5 h - 1 h - 2.5 h, 0.5 h - 2 h - 1.5 h, 1 h - 1 h - 2 h and 1 h - 2 h - 1 h in 4 groups. With increasing temperature, moisture content and diffusivity of the sample decreased, the surface temperature, moisture migration, muscle shrinkage and the gaps (spacing) between muscle fibres increased. The jerky in groups 3 and 4 attained high overall acceptability. The jerky dried at 40 °C for 1 h, 50 °C for 1 h and 60 °C for 2 h had highest quality. The results cover the range of temperature and time used in beef drying and can be used to optimize the drying process of beef.

Effect of roasting temperature on lipid and protein oxidation and amino acid residue side chain modification of beef patties

Beef is rich in nutrients and is one of the most important ingredients in the world. But in the process of cooking and heating, the nutrients of beef will change to varying degrees. How temperature affects the oxidation of lipids and proteins in beef, and the modification of amino acid residues is unclear. This study intended to heat beef at different roasting temperatures (150 °C, 190 °C, 230 °C, 270 °C, 310 °C), measure parameter including colour, peroxide value (PV), thiobarbituric acid-reactive substances (TBARS), thiol and carbonyl content, protein solubility, tryptophan and Schiff base content, protein molecular weight distribution and modification of amino acid residues to discussed the effects of different temperatures on the lipid and protein oxidation of beef patties, as well as the modification of amino acid residues. The results showed that the values of L* and b* increased with the temperature increased, and the values of a* decreased. With the increase of temperature, the lipid oxidation indexes PV and TBARS, Schiff base and carbonyl content also increased, and the thiol content and protein solubility decreased significantly (p < 0.001). SDS-PAGE showed that the band of myosin heavy chain (MHC, 220 kDa) was significantly degraded, while the band of actin (42 kDa) was still clearly visible. The analysis of UPLC-MS/MS results found that the aromatic amino acid residues in all samples were oxidized to a certain extent, especially tryptophan. Other oxidative modifications, including α-amiooadipic acid (AAA), hydroxyethyl lysine (CEL) and malondialdehyde (MDA), were only present in roasted samples and not in raw meat. The results suggested that lipid oxidation and protein oxidation were closely related to colour parameters. The oxidation of proteins and lipids was aggravated at higher temperature. Amino acid side chains were also modified at high temperature, and this change was particularly evident in aromatic amino acids. These results provided new insights for the oxidation of proteins and lipids of beef and the modification level of amino acid residues under high temperature conditions, which will help us to improve the cooking quality of meat foods.

Effects of dietary resveratrol supplementation on the chemical composition, oxidative stability and meat quality of ducks (Anas platyrhynchos)

The effects of dietary resveratrol (0, 300, 400 and 500 mg/kg) on the chemical composition, antioxidative capacity, meat quality and volatile compound concentrations of duck meat were investigated. The results showed that dietary resveratrol had no significant effects on the chemical composition. Dietary resveratrol supplementation increased superoxide dismutase, glutathione peroxidase, catalase activity, pH_{15 min}, pH_{24 h} and color, and reduced the malondialdehyde, and carbonyl contents and shear force, thereby improving water mobility and distribution (T_2b, T₂₁, T₂₂), drip loss, cooking loss and volatile compounds concentration of duck meat. In conclusion, dietary resveratrol supplementation improved the meat quality of ducks by enhancing the antioxidant capacity, improving the color and shear force, and suppressing lipid and protein oxidation, and 500 mg/kg dietary resveratrol had the greatest effect in this study.

Impact of ice structuring protein on myofibrillar protein aggregation behaviour and structural property of quick-frozen patty during frozen storage

The goal of this study was to explore the cryoprotective effect of ice structuring protein (ISP) on the aggregation behaviour and structural changes of myofibrillar protein (MP) from quick-frozen pork patties during frozen storage. Frozen storage causes the formation of large protein aggregates and weakens MP structures. After adding ISP into patties, MP had a more stable aggregation system, which was manifested by a uniform particle size distribution and significantly higher absolute zeta potential (11.71 mV) than the control (9.56 mV) (P < 0.05). Atomic force microscopy results showed that the surface roughness of MP aggregation decreased by 9.78% with ISP after freezing for 180 d. Additionally, compared to patties without ISP, the MP carbonyl content from the ISP-treated patty decreased by 32%, and the free amino content increased by 14.99% during frozen storage. Results from circular dichroism spectroscopy and fluorescence spectroscopy showed that MP secondary and tertiary structure stability in patties improved with ISP. Overall, ISP has the potential to improve MP aggregation and structural stability during frozen storage.

Dynamic changes in the qualities and heterocyclic aromatic amines of roasted pork induced by frying temperature and time

The effects of different frying temperatures (150, 175, 200, 225 and 250 °C) and times (0.5, 1.0, 1.5, 2.0 and 2.5 min) on yield, shear force, color and sensory characteristics, and heterocyclic aromatic amine (HAA) contents of roasted pork were investigated. The results showed significant decreases in yield, shear force and L* and increases in a*, b* and the amounts of HAA of roasted pork with increased frying temperature and time (P < 0.05). The highest score of overall acceptability in crispy and darker roast pork fried at 225 °C for 1 min was obtained. However, the principal component analysis demonstrated that higher HAA contents of roasted pork under high frying temperature (225-250 °C) and long frying time (2-2.5 min) occurred. Considering the various qualities and the amounts of HAA, frying roasted pork at 175 °C for 1.5-2 min was the most suitable condition for preparing roasted pork.

Changes in the thermal stability and structure of myofibrillar protein from quick-frozen pork patties with different fat addition under freeze-thaw cycles

Changes in thermal stability and structure of myofibrillar protein from pork patties with different fat addition (0%, 5%, 10%, 15% and 20%) under freeze-thaw (F-T) cycles were discussed. The results showed that the total sulfhydryl, reactive sulfhydryl, free amino group, α-helix and β-sheet contents, fluorescence intensity (FI), and protein thermal stability (T_max, ∆H_total) of samples with the same fat content were significantly decreased, while the β-turn and random-coil content and the maximum fluorescence emission wavelength (λ_max) were significantly increased with increasing F-T cycles (P < 0.05). These changes in samples with 20% fat at the 5th F-T cycle were obvious and were verified by the decreases in ∆H_total (26.1%), reactive sulfhydryl (16.1%), and FI (16.8%) compared with the patties without fat. Therefore, repeated F-T cycles could decline the thermal stability of protein, destroy the protein structure of patty, and the changes were positively correlated with fat content of patty.

Inhibiting effect of ice structuring protein on the decreased gelling properties of protein from quick-frozen pork patty subjected to frozen storage

The effect of ice structuring protein (ISP) on the gelling properties of myofibrillar protein from quick-frozen pork patty during frozen storage was investigated by determining and comparing protein solubility, turbidity and gel properties. Protein solubility was increased by 10.23% and turbidity was decreased after ISP treated. The gel whiteness and strength of myofibrillar protein from patty with ISP were 8.38% and 13.70% higher than that of the control after frozen for 180 days. And the addition of ISP could weaken the influence of frozen storage on water mobility and reduce the water loss. Furthermore, ISP retrained the decrease in the maximum elastic (G') value and loss factor (tan δ) value of samples. Through observing by scanning electron microscope (SEM), ISP retarded the destruction of gel microstructure and maintained the relatively complete tissue of gel. These findings confirmed the importance of ISP in myofibrillar protein gel quality assurance of pork patty during frozen storage.

The Formation and Control of Ice Crystal and Its Impact on the Quality of Frozen Aquatic Products: A Review

Although freezing has been used to delay the deterioration of product quality and extend its shelf life, the formation of ice crystals inevitably destroys product quality. This comprehensive review describes detailed information on the effects of ice crystals on aquatic products during freezing storage. The affecting factors (including nucleation temperature, freezing point, freezing rate, and temperature fluctuation) on the size, number, distribution, and shape of ice crystals are also elaborated in detail. Meanwhile, the corresponding technologies to control ice crystals have been developed based on these affecting factors to control the formation of ice crystals by inhibiting or inducing ice crystallization. In addition, the effects of ice crystals on the water, texture, and protein of aquatic products are comprehensively discussed, and the paper tries to describe their underlying mechanisms. This review can provide an understanding of ice crystallization in the aquatic products during freezing and contribute more clues for maintaining frozen food quality.

Effect of ice structuring protein on the quality of quick-frozen patties subjected to multiple freeze-thaw cycles

The inhibitory effect of ice structuring protein (ISP) on the quality deterioration of quick-frozen pork patties subjected to multiple freeze-thaw (F-T) cycles was investigated. The inhibitory effect of ISP on patty quality deterioration was obvious after five F-T cycles (P < 0.05). The hardness and springiness of patties with 0.20% ISP were 3.84% and 10.61% higher than those of patties without ISP, and the thawing loss of patties with 0.20% ISP was 43.64% lower than that of patties without ISP (P < 0.05). In addition, ISP effectively restrained moisture migration and destruction of pork patty microstructure during F-T cycles. More importantly, thiobarbituric acid reactive substance levels and carbonyl contents in the patties with 0.20% ISP were 25% and 32% lower than those in the control group (no significant difference with patties with 0.30% ISP) after five F-T cycles. Therefore, these results illustrated the potential benefits of ISP in meat products.

Effect of freeze-thaw cycles on the quality of quick-frozen pork patty with different fat content by consumer assessment and instrument-based detection

The change in quality of quick-frozen patties containing different amounts of added fat (0%, 5%, 10%, 15%, and 20%) under different freeze-thaw (F-T) cycles (a F-T cycle was performed by freezing at -18 °C and thawing at 4 °C) was evaluated. The results showed that the a*-values of samples were significantly decreased, while L*-values, b*-values, thawing loss, and cooking loss were notably increased after 3 F-T cycles. Low-field nuclear magnetic resonance (LF-NMR) results showed that the water mobility of patties was enhanced. Textural properties (hardness, springiness, cohesiveness, and chewiness) of patties were significantly decreased after 5 F-T cycles (P < 0.05). Lipid and protein oxidation were aggravated with increasing fat content and number of F-T cycles, as confirmed by the increase in lipid peroxides, TBARS, and carbonyl content. Therefore, the results from instrument-based detection and consumer scores indicated that repeated F-T cycles accelerated the quality deterioration of quick-frozen pork patties, and rendered them unacceptable after 3 F-T cycles.