This work aims to study the regulatory mechanism of calcium fortification on the texture of kelp pickle during the shelf-life period in order to provide theoretical support for improving its texture quality using exogenous calcium. The effects of fermentation acidity and sodium/calcium ratio on the texture of kelp pickle during its shelf life at 4 ℃ were studied, and the evolution of water distribution and the structure of calcium ion bridge was analyzed. The results showed the hardness of kelp pickle decreased with increasing fermentation acidity, but its changes were effectively slowed down by exogenous calcium lactate. The rate of hardness preservation of kelp pickle with a sodium/calcium of 1.5:1 increased by 92.8% compared with the control group. The results of scanning electron microscopy (SEM) and low-frequency nuclear magnetic resonance (NMR) spectroscopy showed calcium lactate alleviated the morphological damage of kelp tissues caused by acid produced during fermentation, and inhibited the transition of bound water to free water during the shelf-life period. The proportion of free water in kelp pickle with a sodium/calcium ratio of 2:1 increased by only 10.29 percentage points after six months of storage. The results of X-ray photoelectron spectroscopy (XPS) showed that the mechanism by which calcium lactate enhanced the texture of kelp pickle during its shelf-life might be related to the formation of a stable calcium ion bridge at a sodium/calcium ratio of 2:1 or 1.5:1.

Thermally resistant peptides were obtained from enzymatical hydrolysis of Hongqu rice distiller’s grains and evaluated for its effect on resistance to thermally induced oxidative stress in Saccharomyces cerevisiae. Various proteases were screened for the survival rate of S. cerevisiae under heat stress. The enzymatic hydrolysis conditions were optimized based on the yield of thermally resistant peptides, and the peptides were identified by mass spectroscopy and its antioxidant activity was investigated. The expression of genes in the pentose phosphate pathway and the contents of intracellular coenzyme, glutathione (GSH) and reactive oxygen species (ROS) were analyzed to explore the protective effects of the peptides on S. cerevisiae from heat-induced oxidative stress. The results indicated that the optimal enzymatic hydrolysis conditions were as follows: Hongqu rice distiller’s grains/water ratio 1:10, hydrolysis temperature 50 ℃, hydrolysis time 3 h, protamex dosage 3000 U/g, and pH 8.5. Under these conditions, the yield of thermally resistant peptides was 62.44%, and the survival rate of S. cerevisiae in the presence of the prepared peptides under heat stress was 73.97%, which was 22.76% higher than that of the control group (pure water). Sequence identification showed that 16 out of the top 20 most abundant peptides had hydrophobic amino acid contents of over 50%. The peptides exhibited 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) cation radical scavenging activity with a half-maximal effective concentration (EC₅₀) of 4.53 and 1.82 mg/mL, respectively, indicating good antioxidant activity. Besides, the thermally resistant peptides upregulated gene expression in the pentose phosphate pathway, elevated NADH kinase activity, increased GSH content by 5.74 times, and restored intracellular ROS to almost the same level as before heat stress treatment, thus enhancing resistance to heat-induced oxidative stress in S. cerevisiae.

The effect of nanosized bamboo dietary fiber (NBDF) on whey syneresis in yogurt during shelf storage was studied. The milk wettability of micro- and nano-modified NBDF with different particle sizes was analyzed. The inhibitory mechanism of the modified NBDF exhibiting the best milk wettability on whey syneresis during the shelf storage of yogurt was investigated. The results showed that the morphology of NBDF changed from blocky to filamentous after sequential ultrasound, pressurized heating and enzymatic hydrolysis. The microfibrils were fractured after high-energy mechanical ball milling, forming nanoclusters. The milk wettability of modified NBDF initially increased and then decreased with the decrease in particle size. The microfibrils with a particle size of 10–30 μm had the strongest milk wettability. Addition of the microfibrils at a mass concentration of 9 g/L improved the oscillation stability of set yogurt. After 28 days of shelf storage, the whey separation rate was 5.84%, which was only 57.87% of that of the control group. This may be related to the fact that the microfibrils effectively increased the proportion of bound water in yogurt (by 41.4%), improved the casein network structure, and increased the coatability, contributing to the formation of tiny and uniform whey pore channels in yogurt.