Comparative analysis of enzymatic defence mechanisms in Sapindus mukorossi Gaertn. and Acacia concinna (Willd.) DC. using a Michaelis–Menten kinetic model

This study compares the enzymatic antioxidant defence responses of two saponin-rich species, Sapindus mukorossi Gaertn. and Acacia concinna (Willd.) DC. Dried fruit powders were analysed for catalase, peroxidase, and polyphenol oxidase activities using standard spectrophotometric assays. Distinct interspecific variations were observed Acacia concinna (Willd.) DC. showed higher enzymatic activity, whereas Sapindus mukorossi Gaertn. exhibited comparatively higher polyphenol oxidase activity. Enzyme kinetic parameters (Vmax and Km) were estimated using Michaelis-Menten modelling and Lineweaver-Burk plots. Acacia concinna (Willd.) DC. demonstrated lower Km and higher Vmax values for most enzymes, indicating superior catalytic efficiency and substrate affinity. Linear Discriminant Analysis (LDA) revealed that the first two discriminant functions accounted for 96.53% of the total variance, and post hoc test (P = 0.05) confirmed significant differences in enzymatic profiles. The present study highlights the residual enzymatic potential, kinetic adaptability and biochemical composition of these saponin-rich species, emphasizing the role of enzyme efficiency in physiological stress defence response.