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A high degree of hydrolysis can reduce the allergenicity of milk, while lactic acid bacteria (LAB) fermentation can further enhance the antioxidant ability of enzymatic milk. LAB with a strong antioxidant ability was screened, and the effects of LAB on the bitterness, taste and flavor of enzymatic skim milk (ESM) with a high degree of hydrolysis were investigated in this paper, in addition to the response surface methodology optimized the conditions of the LAB fermentation of ESM. The results indicate that the skim milk hydrolyzed by Protamex has a higher degree of hydrolysis and lower bitterness. The scavenging rate of 2,2-Diphenyl-1-picrylhydrazyl (DPPH) free radical, the inhibition rate of hydroxyl radical (·OH) and the superoxide dismutase (SOD) activity of Lactiplantibacillus plantarum 16 and Lactococcus lactis subsp. lactis m16 are significantly higher than those of other strains (p < 0.05), while the improvement effect of L. plantarum 16 on the bitterness and flavor of ESM is better than that of L. lactis subsp. lactis m16. The fermented ESM has a strong antioxidant ability and low bitterness when the inoculum quantity of L. plantarum 16 is 5%, fermentation at 37 °C for 18 h and the pH of the ESM is 6.5, for which the DPPH free radical scavenging rate is 61.32%, the ·OH inhibition rate is 83.35%, the SOD activity rate is 14.58 and the sensory evaluation is 4.25. The contents of amino acids related to bitterness and antioxidants were reduced and increased, respectively. The ESM fermented by L. plantarum 16 has a good flavor, antioxidant ability and low bitterness. [ABSTRACT FROM AUTHOR]

Pathogenic microorganisms have been detected in fermented food. Combining the enormous class of the pathogens and their continuously appearing mutants or novel species, it is important to select suitable and safe antibacterial agents for fermented food safety. Lactic acid bacteria (LAB) which produce diverse imperative antimicrobial metabolites have an immense number of applications in the food industry. Here, the human-derived strain YT was isolated due to its cell-free supernatant (CFS-YT) and cells (Cs-YT), respectively performed obvious inhibitory ring to Gram-positive and -negative spoilage bacteria. Strain YT was identified as Lacticaseibacillus rhamnosus by the 16s rDNA sequence and morphology. The antibacterial activity of CFS-YT was demonstrated to be growth-dependent, pHs-sensitive, broadly thermostable and enzyme-insensitive. Cs-YT displayed a broad antibacterial spectrum with the action mode of bacteriostasis. The antibacterial activity of Cs-YT was due to substances located at the cell surface which were sensitive to heat, stable at broad pH gradients and sensitive to specific enzymes. These data suggested that L. rhamnosus YT could be used as an alternative antimicrobial agent in fermented food biopreservation. [ABSTRACT FROM AUTHOR]

The effects of MRS, whey protein and blueberry alone, and mixed fermentation on the survival rate of lactic acid bacteria under various freeze-drying conditions were investigated. The surface structure of the freeze-dried powders was also investigated to explore the anti-freezing protection mechanism of mixed whey protein and blueberry fermentation on the bacteria. It was found that the mixed fermentation medium of blueberry and whey protein has a protective effect on the freeze-drying bacteria and is better than the traditional MRS and whey protein medium. The optimal concentration of blueberry juice addition was 9%. The survival rate of the pre-freezing temperature at −80 °C was higher than at −20 °C after the pre-freezing and freeze-drying processes. The freeze-drying thickness of 0.3 cm could improve the survival rate of the bacteria. The Fourier transform infrared spectroscopy results indicated the interaction between the whey protein, anthocyanins, and the surface composition of the lactic acid bacteria. [ABSTRACT FROM AUTHOR]