Abstract

Bovine milk was spiked with seven organophosphorus pesticides, denthion, dimethoate, malathion, methyl parathion, monocrotophos, phorate and trichlorphon, and subjected to heat treatment at 63, 80 and 100°C or lactic acid fermentation at 42°C with commercial directed vat set (DVS) starters to investigate the degradation kinetics of the pesticides in bovine milk during heat treatment and yoghurt processing. The pesticides spiked were extracted from the prepared samples, purified and analyzed with gas chromatograph technique. Then the kinetic parameters of degradation of them were calculated accordingly. Comparing this to that of the pesticides in the bovine milk heated at 42°C, the degradation of the pesticides in the bovine milk during yoghurt processing was found to be totally accelerated by the starters of lactic bacteria applied, because the half live periods of six pesticides decreased except for malathion, and two commercial DVS starters which showed different effects somewhat on the degradation of the pesticides. Analysis results also indicated that the pesticides degraded faster at higher temperature in bovine milk during heat treatment; and among the pesticides methyl parathion and phorate were the most unstable and stable one. Heat treatment and lactic acid fermentation could reduce the level of organophosphorus pesticide in dairy products.

Key words: Bovine milk, organophosphorus pesticide, degradation, yoghurt, starter, heat treatment.