Validation of a polynomial regression model: the thermal inactivation of Bacillus subtilis spores in milk.
OBJECTIVE
The predicted survival of Bacillus subtilis 168 spores from a polynomial regression equation was validated in milk.


RESULTS
Bias factor suggested as an index of model performance was used to validate the polynomial model predictions in ultrahigh temperature (UHT) treated and sterilized whole and skim milk. Model predictions were fail safe, predicting higher D-values (decimal reduction times) in buffer than actually noted in milk.


CONCLUSIONS
The D-values for spores were lower in milk as compared with those predicted in potassium phosphate buffer contrary to the popular expectation of better spore survival in complex food systems. The Bias factor, a quantitative measure of the model performance, indicated that on average the model predictions exceed the observations by 40% in the case of whole milk and by 60% in the case of skim milk.


CONCLUSIONS
The present work is an attempt to ascertain the extent of reliability that one can safely place in polynomial model predictions, without compromising on the safety or palatability of foods where it is eventually intended to be applied. The work has also highlighted the differences in the thermal inactivation pattern of spores in buffer and in milk with a possible influence of the various constituents of milk. The work will assist the dairy industry to better design thermal processes to ensure longer shelf life of dairy foods.
Jagannath
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Department of Biotechnology, Faculty of Engineering, Kansai University, Suita, Osaka, Japan. jagann10@yahoo.com
Tsuchido
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D000818:Animals; D001412:Bacillus subtilis / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology; D006358:Hot Temperature; D008892:Milk / Q000737:chemistry / Q000382:microbiology*; D008954:Models, Biological; D013171:Spores, Bacterial / Q000187:drug effects / Q000502:physiology