Proteolysis in pork loins during superchilling and regular chilling storage

Effect of Static Magnetic Field on the Quality of Pork during Super-Chilling Storage

Fresh pork tenderloin was stored at -3 °C under different static magnetic fields (SMF) of 0, 4, and 10 mT (control, MF-4, and MF-10) to investigate their physicochemical properties changes during storage of 8 days. The initial equilibrium temperature of the samples stored with 4 mT MF was found to be -2.3 °C, which was slightly lower (0.3 °C) than that the control value. The super-chilling phenomenon on the pork was then observed, as the samples stored under the magnetic field did not freeze throughout storage period, but the control experienced a sudden change in temperature after 138 h and then froze. The preservation effect of MF-4 on meat quality was the best in all treatment groups. MF-4 achieved a higher water-retention rate, with drip and cook losses of 6.5% and 29.0% lower than the control, respectively. Meanwhile, the MF-4 effectively delayed the color change in the meat during the storage and the texture hardening after cooking, and effectively controlled the growth of the total volatile saline nitrogen content on the samples. In addition, MF-4 delayed the reduction in myofibrillar protein solubility, sulfhydryl content, and emulsification capacity, indicating that this field inhibited the denaturation of myofibrillar protein. This study can be considered as an application reference of magnetic fields during meat storage at a super-chilled temperature.

Effect of temperature fluctuation during superchilling storage on the microstructure and quality of raw pork

The effect of different temperature fluctuations on the microstructure and quality of pork loins during superchilling storage was investigated. Based on the dynamic monitoring of ice crystal formation and melting in pork through cryomicroscope, the changes of ice crystals in pork were observed at different temperature points, and there was no obvious phase transition in pork at -3 °C for a short period of time, but the freeze-thaw cycles were obviously found in the samples of -3 ± 3 °C and -3 ± 5 °C groups. Results of microstructure observation showed that temperature fluctuations resulted in muscle fiber fracture and the decrease of water holding capacity of superchilling pork, where stronger temperature fluctuation showed more significant changes. The temperature fluctuation groups exhibited higher thiobarbituric acid reactive substances (TBARS) values after 20 days of storage, and contributed to the reduction of immobilized water and the increase of free water in raw pork, and had more serious drip loss. These indicated that increased temperature fluctuation promoted lipid oxidation and drip loss of pork during storage. This study provided supports to precise temperature control in cold chain logistics of raw meat.

Modeling of Chilled/Supercooled Pork Storage Quality Based on the Entropy Weight Method

Simple Summary

The quality of chilled meat is difficult to predict because many quality indexes need to be considered. The waste of meat resources caused by improper storage has caused huge economic losses in the meat industry. The entropy weight method (EWM) was widely used as an effective method of infusion of multiple attributes into a single index of food quality. In this study, the model based on the entropy weight method was used to predict and comprehensively evaluate the quality changes in chilled pork, and the relative error range between the measured and predicted shelf life was lower than 11%. The modeling based on EWM integrates the information from each quality index and provides accurate quality prediction, which will enable the food industry to enhance accurate judging of the shelf life and safety of meat.

Abstract

The entropy weight method (EWM) was developed and used to integrate multiple quality indexes of pork to generate a comprehensive measure of quality. The Arrhenius equation and chemical kinetic reaction were used to fit and generate the shelf life prediction model. The pork was stored at the temperatures of 7 °C, 4 °C, 1 °C and −1 °C. Quality indexes, such as drip loss, color, shear force, pH, TAC, TVB-N and TBARS were measured. The results show that low temperatures effectively delay microbial growth and lipid oxidation. The regression coefficients (R²) for the comprehensive scores at each temperature were greater than 0.973 and the activation energy Ea was 9.7354 × 104 kJ mol⁻¹. The predicted shelf life of pork stored at 7 °C, 4 °C, 1 °C and −1 °C was 4.35 d, 6.85 d, 10.88 d and 14.90 d, respectively. In conclusion, EWM is an effective method to predict the shelf life of chilled/supercooled pork.

Development of temperature control algorithm for supercooling storage of pork loin and its feasibility for improving freshness and extending shelf life

Supercooling storage refers to lowering the product temperature below its freezing point without phase transition and has the potential to extend shelf life. Nevertheless, supercooled objects are in a thermodynamically unstable state, and nucleation can occur spontaneously. To achieve supercooling storage, slow cooling and insulation are essential. Hence, a stepwise algorithm for the supercooling storage of pork loins was designed and validated in this study. Pork loins were stored at 3°C, −18°C, and −3°C (freezing), and supercooled for 16 days. All samples remained in a supercooled state and were unfrozen at the end of storage. Supercooled pork loins were superior in terms of drip loss, cooking loss, and water-holding capacity compared to frozen samples. Additionally, supercooling treatment prevented discoloration, increase of volatile basic nitrogen, and microbial growth. Thus, supercooling of pork loin was achieved using a stepwise program and was effective to maintain meat quality.

Metabolites Analysis on Water-Holding Capacity in Beef Longissimus lumborum Muscle during Postmortem Aging

Currently, the metabolomic research on water-holding capacity (WHC) of beef during postmortem aging is still insufficient. In this paper, the kit method was adopted for energy metabolites testing, the ultra-high-performance liquid chromatography (UHPLC) system was used for sample separation, and the mass spectrometer was applied to collect the primary and secondary spectra of the samples. The results showed that lactic acid reached saturation at day 2 postmortem, while energy metabolites changed significantly within day 2 postmortem (p < 0.05). Based on these findings, it was suggested that the energy metabolism qualities of the beef had already achieved a largely stable state at around day 2 postmortem. Then, through metabolomic analysis, 25 compounds were differentially abundant at days 0, 0.5, 1, and 2 during postmortem aging. Within the period of day 0−2 postmortem, the purine metabolism in beef was relatively active until 0.5 d postmortem, while glycolysis metabolism remained active until day 2 postmortem. The functions of the identified metabolites contribute to a more detailed molecular view of the processes behind WHC and are a valuable resource for future investigations into the flavor of postmortem beef.

Effects of Different Storage Temperatures on the Physicochemical Properties and Bacterial Community Structure of Fresh Lamb Meat

This study was aimed to compare the physicochemical properties and bacterial community structure of tray-packaged fresh lamb meat under different storage temperatures, such as 4°C (chilling), −1.5°C (supercooling), −4°C (superchilling) and −9°C (sub-freezing). The total viable counts (TVC), total volatile base nitrogen (TVB-N), bacterial diversity and metabolic pathways were investigated. The results indicated that the shelf life of superchilling and sub-freezing storage was over 70 d, which was significantly longer than that of chilling and supercooling storage. TVC and TVB-N values showed an increasing trend and were correlated well (R²>0.92). And the TVB-N values of lamb meat were exceeded the tolerable limit (15 mg/100 g) only found under chilling and supercooling storage during storage period. At the genus level, Pseudomonas was the core spoilage bacteria then followed Brochothrix for chilling and supercooling storage. Pseudomonas, Ralstonia, Psychrobacter and Acinetobacter were the dominant spoilage bacteria for superchilling and sub-freezing storage. Furthermore, the bacterial community diversity of lamb meat stored at chilling and supercooling storage decreased with the storage time prolonged, which was opposite to the outcome of meat stored under superchilling and sub-freezing storage. For chilling and supercooling storage, the abundance of main metabolisms (carbohydrate metabolism and amino acid metabolism, etc.) of bacteria increased with the storage time prolonged, which was opposite to superchilling storage. This may be related to the bacteria community diversity and the formation of dominant spoilage bacteria. In conclusion, this work provides data for the preservation of fresh lamb meat which will benefit the meat industry.

Myofibrillar protein characteristics of fast or slow frozen pork during subsequent storage at -3 °C

This study aimed to investigate the effect of storage at -3 °C on myofibrillar protein in fast or slow frozen pork. Five pork loins at 48 h post-mortem were subjected to either fast (cold metal plate/-80 °C) or slow freezing (still air/-20 °C) followed by storage at -3 °C for 0, 1, 3, and 7 days before thawing. Freezing rate significantly influenced myofibrillar proteins within 3 days at -3 °C, evidenced by higher thaw loss, higher surface hydrophobicity and reduced water-holding of myofibrils, and accelerated appearance of a myosin-4 fragment (160 kDa) in slow freezing. However, these observed differences disappeared after 7 days of storage at -3 °C. The meat pH after thawing did not differ between fast and slow freezing rate. However, the pH values after thawing in both groups decreased with extended storage at -3 °C. Our results suggest that the beneficial effects of fast freezing are gradually lost by holding at -3 °C due to more extensive protein denaturation.

Protein degradation and structure changes of beef muscle during superchilled storage

This study investigated the effect of superchilled storage (-4 °C) on protein degradation and structural changes of beef steaks from M. longissimus lumborum compared with traditional chilling (2 °C) and frozen storage (-18 °C). Traditional chilling induced significantly greater degradation of troponin T and desmin, and more rapid loss of calpain activity, compared to superchilled or frozen storage treatments. The proteolysis of key myofibrillar proteins resulted in a sharp decline of WBSF values during traditional chilled storage. For frozen beef samples, no major changes were observed with respect to protein degradation or muscle structure during storage. However, superchilled samples exhibited wider gaps between muscle fibers at 12 weeks storage, associated with muscle fiber shrinkage.

The influence of marinade composition on pork tenderness

The aim of the study was to identify the effect of marinating meat on selected quality determinants. Fifty-four pork samples were prepared from longissimus dorsi muscles, each 2.5-cm-thick; they were subsequently marinated for 24 hours (n = 12) and control samples were also prepared (n = 6). The following marinades were used: base marinade (M) whose ingredients included a mixture of herbs and condiments (salt, pepper, juniper berries, rosemary, bay, pimento, garlic) and 3 liquid marinades obtained by adding to the base marinade of apple cider vinegar (MV), light beer (MB) and buttermilk (MM). In the samples pH, marinade absorption, drip loss, cooking loss, WBSF and tenderness by sensory assessment were measured(1,2).

The pH value of the material used for the study was 5.8 ± 0.02. The use of the base marinade increased the pH to 6.37 ± 0.03, whereas the liquids used in the marinades decreased the pH to 5.5 ± 0.05. Marination resulted in an increase in the material weight by 2.87 ± 0.05% (MB), 4.45 ± 0.07% (MM), 0.87 ± 0.03% (M). The addition of vinegar resulted in exuding meat juice and a decrease in the material weight by 2.53 ± 0.06% (MV). Using the base marinade reduced drip loss (0.53 ± 0.01%) compared with the control (1.37 ± 0.03%). Sour marinade (MV) increased cooking loss by 18% compared to the control, the MB and MM marinades did not affect this parameter significantly, and the base marinade had a significant effect on reducing cooking loss by 24%. Each of the marinades used had a significant effect on reducing the maximum shear strength by 31% (liquid marinades) and by as much as 46% – base marinade. This relationship was confirmed in a sensory assessment, where higher notes for tenderness were given when base marinade (9.2 ± 0.3pts), marinade with buttermilk (8.1 ± 0.2pts), and marinades with vinegar and beer (7.3 ± 0.3pts) was used compared with control samples (5.7 ± 0.4pts).

This study has shown a beneficial effect of the marinades on the tenderness of the products. The most beneficial effect on the quality determinants under study was exerted by the base marinade, which consisted of herbs and condiments only.

Effect of superchilled storage on shelf life and quality characteristics of M. longissimus lumborum from Chinese Yellow cattle

The effect of superchilled storage (SC, -4 °C) on shelf life and quality characteristics of M. longissimus lumborum from Chinese Yellow cattle compared with traditional chilling (TC, 2 °C) and frozen storage (-18 °C) was studied. The shelf life of beef steaks held at -4 °C extended to 12 weeks based on the total volatile basic nitrogen (TVB-N) value, which was 2.4 times longer than steaks stored at 2 °C. As the storage time increased, SC samples showed a lower increase of the total aerobic count (TAC), pH and thiobarbituric acid reactive substances (TBARS) values compared to TC samples. Further, L^⁎ and a^⁎ values of SC samples changed more slowly than that of TC samples. Beef steaks held frozen had a longer shelf life than SC steaks, however, the shear force of frozen steaks remained above 55 N throughout the storage time indicative of toughness. Consequently, SC offers an effective approach for maintaining better shelf life and quality of beef steaks.