Unsuspected role of pH in the development of texture and functionalities in Swiss-cheese

The αs1-casein hydrolysis has been shown to greatly influence the texture and techno-functionalities of hard cooked cheeses. This hydrolysis can be performed by the proteinases of the thermophilic lactobacilli since rennet, also implied, is denatured during the cooking step. However, it is unclear whether these changes are only due to the proteolytic activity of lactobacilli, the pH decrease in cheese or both. Small scale Swiss-cheeses were made from microfiltered milk using various combinations of starters including or not lactobacilli: i) Streptoccocus thermophilus alone (STH cheeses), ii), S. thermophilus in enriched lactose cheesemilk (STH-LACT cheeses) to reach pH level similar to cheese with lactobacilli and iii) S. thermophilus and lactobacilli either L helveticus (STH/LH cheeses), or L. delbrueckii subsp lactis (STH/LL cheeses). As S. thermophilus does not metabolize the galactose moiety of lactose, the pH at day 1 of these STH-LACT cheeses was similar to those made with lactobacilli (pH 5.15-5.25) while pH values of the STH cheeses were higher (pH 5.40). Higher firmness and chewiness of the melted ripened STH cheeses were correlated with a higher pH at day 1 and with a lower proteolysis (twofold amount of remaining intact αs1-casein) compared to the STH-LACT cheeses as well as the cheeses with lactobacilli. Conversely, the stretchability showed different behaviors depending both on the quantitative and qualitative proteolysis and on the pH value. The lower pH and content in small peptides led to higher stretchability of the STH-LACT and STH/LH cheeses in contrast to the cheeses STH (high pH and few small peptides) and STH/LL (low pH and high amount of small peptides). In conclusion, the decrease in pH due to the use of lactobacilli plays a key role in the texture of raw and melted Swiss-cheese. Beside the pH, the proteolytic activity of lactobacilli is also a determinant factor for stretchability.