Comparisons between the electrophoretic pattern and textural assessment of aged Cheddar cheese made using various levels of calf rennet or microbial coagulant (Rennilase 46L)

Abstract

The set-to-cut time, rennet concentration and set temperature were varied during the commercial manufacture of Cheddar cheese in nine Damrow cheese vats on each of three consecutive days. In addition, in two separate pilot plant trials, the setting conditions and coagulant type (calf rennet or Rennilase) were varied during early and mid-season manufacture of Cheddar cheese. The effect of variations on proteolysis were assessed by measuring the non-casein nitrogen (NCN) and the non-protein nitrogen (NPN) content of the cheese. Protein degradation was also estimated by determining the breakdown of αS1 and β-caseins using polyacrylamide gel electrophoresis (PAGE), at intervals over a six-month period. At the same time, changes in cheese texture were assessed by a trained panel. NPN levels were similar in all cheeses and tended to increase slightly over the six month period. The NCN level increased markedly in cheese from both pilot plant trials but less so in cheese from the commercial trial due to a lower moisture content and a higher pH. The specificity and activity of Rennilase differed from that of calf rennet and this was reflected in sharply elevated NCN levels during early maturation. The breakdown of αS1-casein was both rapid and extensive when calf rennet was used as the coagulant. The degradation of β-casein was greater in cheese produced with Rennilase than with calf rennet. Higher residual coagulant levels in the cheese due to the increasing concentrations of rennet (10·6, 16·0 and 24·0 ml/100 litres milk) and Rennilase (4·6, 7·0 and 10·5 ml/100 litres milk) used initially were reflected in the significant (P < 0·001) early breakdown of αS1-casein. In spite of the significant variation in the early breakdown of αS1-casein, sensory evaluation of the textural characteristics of the cheese was not sensitive to a variation in coagulant concentration. Cheese made using Rennilase was significantly (P < 0·001) less rubbery, less smooth, firmer and grittier than cheese made using calf rennet but differences were small, suggesting that the type of coagulant had little effect on sensory scores. Independent of rennet concentration and set temperature during commercial cheese manufacture, the rate of breakdown of αS1-casein was higher for a 50-min set-to-cut time than for a 30-min set-to-cut time. The degradation of β-casein was not influenced to the same extent. As the variation in αS1-casein breakdown was of a similar magnitude to that found for varying levels of coagulant, the strong correlations (r2 = +0·800, −0·914 and −0·651) between αS1-casein breakdown and changes in curdiness, stickiness and smoothness with time do not fully explain the increase in smoothness and decrease in curdiness with increasing set-to-cut time. However, increasing the set-to-cut time from 30 to 50 min significantly (P < 0·1) increased the cheese moisture content and significantly (P < 0·001 to P < 0·1) reduced the cheese salt content, the pH and the calcium level. Consequently, cheese texture is determined primarily by its pH and chemical composition. Subsequent, early changes in texture are determined by αS1-casein breakdown. Downgrading for body defects such as curdiness at 35 days does not accurately predict what the cheese texture will be after (6 months) storage. The results of this work have shown that the body of a cheese can be singled out from others on the basis of a curdy texture at 1 month, but is indistinguishable at 6 months.