The study of heat-stable protease : effects on cheddar cheese quality and on the total bacterial counts during ripening

Tye, Teik Mien (1986) The study of heat-stable protease : effects on cheddar cheese quality and on the total bacterial counts during ripening. Masters thesis, Memorial University of Newfoundland.

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Abstract

A heat-stable protease T25 secreted by Pseudomonas fluorescens from raw milk was used to accelerate the ripening process of Cheddar cheese. Its effects on the growth and activity of starter cultures used in Cheddar cheese manufacturing were also tested. The presence of bacteria protease (T25) exerted indirect influence on the growth of starter cultures. The addition of the protease to milk used for Cheddar cheese manufacturing caused differences in the growth patterns of bacteria during the first month of ripening. There was a trend in the lowering of percent total fat, protein, nitrogen, moisture content and yield (dry weight) of the cheese to which bacteria protease was added. The pH changes observed in the control cheese sample during aging were slightly higher than the sample containing the bacterial protease. A gradual degradation of αS₁-casein fraction was observed in the protease treated cheese during aging. Also, T25 protease gives better activity with α-casein as a substrate compared to other casein fractions. Addition of this bacterial protease (5 mg/L, 9.45 mg/L, 10 mg/L and 20 mg/L) to pasteurized milk prior to the addition of renneting agent (porcine pepsin) in the manufacture of Cheddar cheese by the conventional method, results in a product which is able to achieve higher intensity of cheddaring flavour (P<0.05) and higher preference score (P<0.01) within 6 months of aging when compared to that of the control cheese not containing the bacterial protease. No off-flavour or bitterness was detected in the protease treated cheese throughout the ripening period. The texture of the cheeses remained fine during aging. The results of this study indicates that the protease T25 secreted by Pseudomonas fluorescens is a suitable agent to accelerate the ripening process of Cheddar cheese.

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