Effects of Neutral Protease on the Texture and Flavor of High-protein Fermented Milk

The objective of this study was to investigate the effects of neutral proteases from different sources on the textural properties and flavor compounds of high-protein fermented milk, so as to improve the taste, flavor, and drinking experience of high-protein fermented milk. In this study, two neutral proteases—ADMIL (AD) and Galaya smooth (GS)—were added at mass concentrations of 0.02% and 0.012%, respectively, to a high-protein yogurt base with a protein content of 6 g/100 g. After fermentation at 42 ℃, the final products were characterized for textural properties including viscosity, gel strength, hardness, friction coefficient, and water-holding capacity, while changes in flavor compounds induced by the two enzymes were also analyzed. Results showed that compared with the control sample without protease addition, the AD-treated and GS-treated samples exhibited decreases in viscosity by 8.9% and 5.3%, respectively, a 42.1% reduction in gel strength, and decreases in hardness by 33.3% and 41.7%, respectively. Particle size and friction coefficient were also reduced, while water-holding capacity slightly decreased with no significant difference (P > 0.05). Sensory evaluation indicated that the addition of neutral proteases improved the drinking experience of high-protein fermented milk. Further analysis of volatile compounds revealed an increase in the content and variety of flavor compounds in both enzyme-treated samples. Among them, the concentrations of flavor compounds such as n-pentanoic acid, hydroxyacetone, butyric acid, 2-hydroxy-3-pentanone, sec-butanol, myristic acid, benzoic acid, 2,3-pentanedione, (+)-limonene, and 3-hydroxy-2-butanone were significantly increased in the AD-treated sample. In the GS-treated sample, the concentrations of n-pentanoic acid and butyric acid were significantly increased.The AD-treated sample showing a more pronounced flavor enhancement. In conclusion, neutral proteases effectively reduced the viscosity, particle size, and friction coefficient of high-protein fermented milk, significantly improved its flavor, and demonstrated substantial application potential.