Quantitative PCR Analysis for Fruit Juice Authentication Using PCR and Laboratory-on-a-Chip Capillary Electrophoresis According to the Hardy−Weinberg Law

DNA-based analysis for the authentication of fruit juices was evaluated using the Polymerase Chain Reaction (PCR) and laboratory-on-a-chip capillary electrophoresis (LOC). A PCR restriction fragment length polymorphism (RFLP) assay demonstrated the detection of grapefruit juice in orange juice, although the assay was relatively insensitive with a limit of detection of 10% v/v. A PCR heteroduplex assay for detecting mandarin juice in orange juice was successfully applied to the LOC system and demonstrated greater sensitivity with a limit of detection of 2.5% v/v. Results for both assays using authentic juice mixtures were consistent with that expected following the random reannealing of PCR-amplified DNA at PCR plateau according to the principles of the Hardy-Weinberg law. Calculations of theoretical and expected yields of homoduplex and heteroduplexes indicated that the heteroduplexes were underestimated by 1.5-fold on the LOC. Although the LOC can provide good quantitative end-point analytical data from PCR methods, care must be taken in data interpretation because different data interpretation applies dependent on the attainment of the PCR plateau.