Application of Phenolic Extracts for Inhibition of Polyphenol Oxidase Activity and Enzymatic Browning in Food Systems.

Enzymatic browning is a major problem during food processing and storage, as it degrades the sensory characteristics, and nutritional value of fruits and vegetables, leading to waste generation. Natural inhibitors, such as phenolic extracts, have emerged as a promising solution to address this issue. Based on this, the present research aims to evaluate the phenolic extract from collard greens (CGs) as a potential inhibitor of polyphenol oxidase (PPO), which is the main enzyme behind enzymatic browning. The CG extract, prepared using an optimized extraction method, showed a total phenolic content of 2.35 ± 0.23 mmol gallic acid equivalent/L and a ferric-reducing antioxidant power of 3.35 ± 0.06 mmol Trolox equivalent/L. To improve the extract’s ability to inhibit PPO, it was treated with acid (0.3 and 0.6 M HCl) for 2 hours at 80 °C. This process helped break down glycosidic phenolics into aglycones. As a result, the content of flavonoids, such as catechins, increased significantly, along with the extract’s ability to cupric chelating activity (p ≤ 0.05). The acid-treated and untreated extracts were tested as natural PPO inhibitors, using PPO sourced from Jerusalem artichoke tubers (JAT). Ascorbic acid (AA) was used as a standard for comparison. Enzyme activity assay showed that the untreated extract and AA acted as competitive inhibitors, increasing the Michaelis-Menten constant (Km) value but not affecting maximum velocity (Vmax). In contrast, the acid-treated extract showed mixed-type inhibition, increasing Km and decreasing Vmax. To evaluate their real-world effect, these extracts were applied to fresh-cut JAT slices, and color properties were investigated. The acid-treated extract showed significantly better browning inhibition than the untreated extract and AA. These results suggest that phenolic extracts, especially after acid treatment, could work well as a natural solution to inhibit enzymatic browning in food.