The Problem of DEFT on Dairy Industry and Its Applications

Abstract

The estimation of bacterial counts in raw milk was studied using Direct Epifluorescent Fitler Technique (DEFT). The milk inoculated with Bacillus cereus was detected 10³ to 10⁷ counts/ml using DEFT. In the case of raw milk, the regression line was log(DEFT)=0.86log(SPC)+0.91; r=0.81, and 10⁵ to 10^6.5 counts/ml were detected. Application of DEFT to the sterilizing effect of LTLT (low temperature long time) pasteurized milk and to the post pasteurization contamination of UHT (ultra high temperature) sterilized milk may be useful. The differential determination of sublethal injured bacterial cells was tested by DEFT. The RNA (ribonucleic acid) of viable cells was stained orange by acridine orange, but inactive cells and DNA (deoxyribonucleic acid) were stained green. When sublethal injured cells were prepared by heat treatment, the ratio (injured cells/unharmed cells, green cells/orange cells) were as follows: Enterobacter cloacae: (1.89, 1.36), (14.71, 19.75), Bacillus cereus (vegetative form): (1.18, 0.88), (2.71, 2.06), and Staphylococcus aureus: (0.92, 0.90), (0.50, 0.40), but with poor agreement for Candida krusei. Acid producing activity and acridine orange-staining characteristics of lactic starter culture (Lactobacillus bulgaricus, Streptococcus thermophilus) and its concentrates (L. acidophilus) were determined. There was a high correlation between acid production and staining characteristics.