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 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.

This study aimed to investigate the effects of different freezing temperatures and storage durations on the digestive and structural properties of chicken meat proteins. The texture, protein digestibility, particle size, and microstructure of the digested samples were used to characterize their digestive properties. Conformational changes in the digested samples were confirmed by infrared spectroscopy, circular dichroism, and endogenous tryptophan fluorescence spectra. The results revealed that the moisture and protein contents decreased with extended storage and increased temperature. Compared to fresh chicken breasts, protein digestibility decreased as the duration of frozen storage increased. Moreover, the samples stored at −40 °C had higher digestibility than those stored at −18 °C, and the protein structure of the samples stored at −18 °C exhibited more damage and was more likely to aggregate compared to the protein of samples stored at −40 °C. Therefore, a higher freezing temperature and an extended frozen storage duration result in greater structural damage to the protein and lower protein digestibility.