Significant effects of two pesticides on the bacteriostatic activity and antioxidant ability of green tea polyphenols

Green tea polyphenols (GTPs) are widely used in food preservation because of their strong bacteriostatic activity and antioxidant ability, and whether pesticides as common pollutants in food will affect the function of GTPs is worthy of attention. Therefore, GTPs and two pesticides, namely, acetamiprid (ACE) and diquat dibromide (DIQ) commonly used on food crops were selected as research objects and Vibrio qinghaiensis sp.-Q67 (Q67) as the test organism to explore the effects of pesticide pollutants on the bacteriostatic activity of GTPs by the time-dependent microplate toxicity analysis method (t-MTA). The binary mixture systems of GTPs and two pesticides were designed by the direct equipartition ray design method (EquRay). The effect residual ratio (ERR) method was used to quantify the toxicity interactions of binary mixture systems. Besides, the effects of these two pesticides on the antioxidant capacity of GTPs were investigated. The results indicated that the bacteriostatic activity of GTPs upon interaction with the two pesticides shows certain time characteristics. These two pesticides can affect the bacteriostatic activity of GTPs, which is enhanced or weakened with prolonged duration, i.e. time-dependent synergism or antagonism. The bacteriostatic mechanism of the three substances and their mixtures is produced by affecting the cell morphology or destroying the cell structure, and the long-term antagonism of the three substances may be due to the competition for the active site. The two pesticides can greatly reduce the antioxidant capacity of GTPs. ACE reduces the free radical scavenging ability of GTPs by 14–24% and DIQ by 39–63% in the experimental concentration ratios. In addition, the free radical scavenging ability of GTPs decreases with the increase in the concentration ratio of the two pesticides in the mixture systems.