Pressure Induced Structural Changes of Proteins Affecting the Ice Nucleation Temperature of Pork Loins

Effect of high pressure pretreatment on the inhibition of ice nucleation and biochemical changes in pork loins during supercooling preservation

In this study, the effect of high pressure (HP) pretreatment on the stability of pork loins during supercooling (SC) preservation was investigated, and the freshness and postmortem metabolism of pork loins preserved by SC was evaluated. Based on the differential scanning calorimetry (DSC), the peak enthalpies of 200 MPa treatment were lower than those of 50 MPa treatment (P < 0.05). For the nuclear magnetic resonance (NMR) relaxometry, extramyofibrillar water in pork loins was decreased with increasing intermyofibrillar water at >100 MPa (P < 0.05). Compared to unpressurized control all HP treatment had less α-helix structure while random coil was dominated from the Fourier transform infrared (FTIR) spectroscopy (P < 0.05). A 200 MPa was selected to estimate the relationship between HP pretreatment and stability of SC preservation of pork loins. The HP-treated pork loins showed high stability during SC preservation under the relatively low temperature algorithm. Compared to fresh control, HP pretreatment caused physicochemical changes of pork loins which did not recover even after 2 weeks of preservation. Nevertheless, HP followed by SC preservation was able to reduce property changes better than pork loins preserved by normal refrigeration. According to the analyses of transmission electron microscopy (TEM), the HP pretreatment influenced the postmortem biochemical metabolism of pork loins, however, it did not affect the freshness and quality parameters of pork loins due to the subsequently applied low preservation temperature of SC. Therefore, this study demonstrated that moderate HP pretreatment was a potential pretreatment for SC preservation of pork loins.

Conditions of the Stepwise Cooling Algorithm for Stable Supercooling Preservation and Freshness of Pork Loin

Supercooling has the advantage of maintaining the freshness of foods without a phase transition. However, it is hard to sustain the supercooled state. Static temperature control, one of the various supercooling technologies, is used for stable supercooling storage. In this experiment, the effect of following external factors in maintaining the supercooled state of foods was investigated. Three main parameters had an effect on the supercooled state of food: (1) properly setting the lower-temperature limit of the supercooling algorithm, (2) slow cooling to the target temperature, and (3) minimizing temperature fluctuation. Accordingly, the following stepwise cooling algorithm for pork loin was designed: a lower-temperature limit of −3.0 °C and a storage period = 36 h followed by a lower-temperature limit of −3.5 °C for 24 h. The samples conserved at −3.0 °C displayed a 100% supercooled state. Physicochemical properties including drip loss, cooking loss, texture, color, total volatile basic nitrogen (TVBN), and total aerobic count (TAC) of pork loin were analyzed. The drip loss values of the supercooled meat samples were lower than those of the superchilled ones. Furthermore, TVBN and TAC of the treated samples were not significantly different from those of the fresh samples (p > 0.05). In conclusion, supercooling storage extended the freshness and quality of pork loin better than refrigerated storage.

Comparison of Superchilling and Supercooling on Extending the Fresh Quality of Beef Loin

This study compared the effects of superchilling and supercooling preservations for 15 days on the freshness and quality characteristics of beef loin. Beef freshness was evaluated by total aerobic count (TAC), total volatile basic nitrogen (TVB-N), and thiobarbituric acid reactive substances (TBARS), and instrumental color, drip loss, cooking loss, and texture profile analysis (TPA) were determined as quality parameters. All assays were compared with fresh control and normal chilling conditions (4 °C). The mean preservation temperatures of superchilling and supercooling were −3.9 °C and −2.1 °C, respectively. The freshness parameters indicated that both superchilling and supercooling extended the freshness of beef loin for 15 days, while chilled beef could not maintain the standard of freshness conditions. For quality parameters, there was no difference between the control and supercooling treatments, whereas superchilling exhibited higher drip loss and toughness compared to the control (p < 0.05). Therefore, this study demonstrated that supercooling was the best preservation technique to extend the freshness and quality of beef loin, but superchilling was not suitable to guarantee the quality of beef.

Functional Properties of Extracted Protein from Edible Insect Larvae and Their Interaction with Transglutaminase

Global concern about food supply shortage has increased interest on novel food sources. Among them, edible insects have been studied as a potential major food source. This study aimed to improve the functional properties of protein solutions extracted from Protaetia brevitarsis (PB) by use of transglutaminase (TG) as a cross-linking agent. After various incubation times (10, 20, 30, 60, and 90 min) with TG, the protein solutions were assessed with regard to their amino acid composition, protein nutritional quality, pH, color (yellowness), molecular weight distribution, thermal stability, foam ability (capacity and stability), and emulsion ability (capacity and stability). Incubation with TG changed the amino acid composition of the proteins and shifted the molecular weight distribution towards higher values, while improving the rest of the aforementioned properties. Since the incubation time for 90 min decreased the protein functionality, the optimum incubation time for cross-linking PB-derived protein with TG is 60 min. The application of TG to edible insect proteins ultimately increases its functionality and allows for the development of novel insect processing technology.