CHEESE YIELD EXPERIMENTS AND PROTEOLYSIS BY MILK-CLOTTING ENZYMES

Accurate estimates of differences in yield of cheese are important in experiments comparing treatments. Small differences (.l%) are economically important. Estimates of least significant difference are appropriate for evaluating those differences; expression as a percentage of yield is preferred to expression as weight. A low least significant difference is essential to prevent a Type II error in statistical inference, viz., concluding no difference when an economically important difference exists. The results of an experiment showing no effect of a treatment, but with a high LSD, are misleading. A least significant difference of ± .l% seems to be a practical lower limit, although lower values would be desirable. Important factors in accurate yield estimates are: accuracies of estimating quantities of milk and cheese; accuracy of sampling and analysis; and experimental design, replication of trials, and statistical analysis. Adjustments of yields to constant moisture (whey) and to constant fat losses in whey are useful. The significance of yield experiments should include both statistical and economical inferences; the least significant difference should be low to conclude no effect of a treatment on yield. Most milk-clotting enzymes are more proteolytic than chymosin, when compared on casein substrates, at levels that would be economically important. Differences are less clear when compared on milk or during cheese making, likely due to inherently greater inaccuracies of measurement. Lab-scale cheese making in beakers and accurate measurement of protein levels in whey appear to be satisfactory for estimation a basic yield loss due to proteolysis; losses of fat and curd fines may be additional. Many studies on milk-clotting enzymes and yield either had no statistical analyses or showed no significant effect (P=.05) on yield. A critical review of the literature indicates that most milk-clotting enzymes are likely to affect yield of many varieties of cheese relative to calf rennet. Based on protein losses in whey, relative losses for Cheddar were, compared with calf rennet: bovine pepsin, –.14%; chicken pepsin, –.44%; Mucor miehei, –.63 to –.68%; Mucor pusillus, –.49; Endothia parasitica, –1.24; these data are qualified by assuming an equal value for milk fat and cheese, milk containing 3.6% fat and 2.464% casein, cheese moisture and salt of .37 and .017, and whey solids of .065. Other varieties would likely have similar losses, but of different magnitude; these need to be determined. An exception may be swine pepsin, which is destroyed during cooking. Lower yields may be offset by lower enzyme prices or other factors. © 1990, American Dairy Science Association. All rights reserved.