Comparison of DNA quality in raw and reconstituted milk during sterilization.

Responses to milk sterilization are usually evaluated only in terms of physicochemical properties and microbial safety, thus undervaluing the importance of DNA quality in an authentication process by methods based on PCR. Because DNA is a heat-sensitive molecule, we hypothesized that the heating process may impair the detection or quantification of DNA in raw fresh milk (FM) or reconstituted milk (RM), and that differences in DNA quality might exist between FM and RM. We thus investigated the effects of sterilization on the quality of DNA extracted from FM or RM; differences in DNA quality between FM and RM were also evaluated. The quality of extracted DNA from FM or RM was assessed by the specific detection of FM or RM composition in goat milk mixtures using primers targeting the bovine 12S gene, as well as by monitoring DNA yield, purity, ratio of mitochondrial (mt) to nuclear (n) DNA, and the level of DNA degradation. Polymerase chain reaction readily detected both untreated and heat-treated FM or RM in cow-goat milk mixtures, and gave a good sensitivity threshold (0.1%) under all sterilization conditions. The DNA yield and mtDNA:nDNA ratio of FM and RM varied significantly during the sterilization process. These results demonstrated that the sterilization altered the quantification of DNA in FM or RM during sterilization, but DNA could still be readily detected in sterilized FM or RM by PCR. Furthermore, we noted significant differences in DNA integrity, yield, and mtDNA:nDNA ratio between FM and RM during sterilization, which may have potential as a means to distinguish FM and RM.