Collard Green Extracts as Potential Inhibitors of Enzymatic Browning

Abstract

This study seeks to assay the phenolic extract of collard greens (CGs) as a new source of inhibitor for polyphenol oxidase (PPO), the primary enzyme responsible for enzymatic browning. The extract of CGs obtained under optimized extraction conditions had a total phenolic content (TPC) and a ferric-reducing antioxidant power (FRAP) value of 2.35 ± 0.23 mmol gallic acid equivalent/L and 3.35 ± 0.06 mmol Trolox equivalent/L, respectively. To enhance the extracts’ inhibitory activity, an acid hydrolysis treatment (0.3–0.6 M HCl, 2 h at 80°C) was applied to convert glycosidic phenolic compounds into aglycones. This treatment significantly increased the concentration of flavonoids, including catechin and its derivatives, as well as the cupric chelating activity of the extract (p ≤ 0.05). The acid-hydrolyzed and nonhydrolyzed extracts were tested as natural inhibitors of PPO, sourced from Jerusalem artichoke tubers (JAT), with ascorbic acid (AA) as a reference inhibitor. Kinetic analysis indicated that the nonhydrolyzed extract and AA performed as competitive inhibitors (increased Michaelis–Menten constant [K_m] and stable maximum velocity [V_max]), whereas the acid-hydrolyzed extract exhibited mixed-type inhibition (increased K_m and decreased V_max). To validate the effect of the extracts on the real food models, the effect of the inhibitors was tested on the fresh-cut slices of JAT by measuring colorimetric parameters, and the results revealed that the acid-hydrolyzed extract had a significantly higher browning inhibition compared to nonhydrolyzed extract and AA. These findings highlight the potential of extracts of CGs, particularly in their hydrolyzed form, as effective natural inhibitors of enzymatic browning in food applications.