BACKGROUND: The potential use of polyphenols to improve the functional characteristics of dairy products has gained much
attention. However, the effects of the polyphenols on naturally occurring enzymes in milk have not been studied extensively.
Excess plasmin activity in dairy products might result in several quality defects. The objective of this study was to assess the
ability of polyphenols to inhibit plasmin inmilk using a molecular and kinetic approach.
RESULTS: Epicatechin gallate (ECG), epigallocatechin gallate (EGCG), quercetin (QUER), andmyricetin (MYR) caused a significant
decrease in plasmin activity by 60, 86, 65, and 90%, respectively. The inhibition rates were alleviated in the presence of milk
proteins. EGCG, QUER, and MYR, exhibited noncompetitive inhibition against plasmin, whereas ECG caused a mixed-type
inhibition. A decrease in the random structure of plasmin upon the complex formation with ECG, EGCG, QUER, and MYR was
found. The other phenolics that were evaluated did not cause any significant changes in plasmin conformation. The observed
inhibitory phenolic-plasmin interactions were dominated by H-bonds and electrostatic attractions. Green tea extract (GTE) rich
in catechins also inhibited plasmin activity in the milk.
CONCLUSION: Significant changes in the secondary structure of plasmin upon binding of ECG, EGCG, QUER, and MYR led
to diminished plasmin activity both in the absence and presence of milk proteins. These flavonoids with promising plasmin
inhibitory potential could be used in new dairy formulations leading to controlled undesired consequences of plasmin activity.