Agro-Based Waste Materials as Novel Sources of Antioxidants and Alpha-Amylase Inhibitors: An In Vitro Evaluation

Background: Agro-based Waste Materials (AWM) contain phytochemicals, including vitamins, dietary fibers, and polyphenols, some of which have significant antioxidant properties. Despite this, the evaluation of the complex array of phenolic compounds present in various AWMs is limited. This research aimed to investigate the polyphenol content, antioxidant capacity, and alpha-amylase inhibition of eight distinct fruit and vegetable peel/pomace, namely amla, mango, pomegranate, orange, lemon, potato, tomato, and carrot. Methods: Samples of AWM were analyzed for total phenolic and flavonoid content using standard colorimetric assays. Antioxidant activity was evaluated by using FRAP, DPPH-RSA, and ABTS-RSA assays. The inhibition of α-amylase was also tested. Correlations among the parameters were determined using Pearson's correlation, and Principal Component Analysis (PCA) was used to identify patterns and relationships within the dataset. Results: The observed data showed that amla pomace contained the highest level of phenolic content, while the highest flavonoid content was found in pomegranate peel. In terms of antioxidant capacity, pomegranate peel exhibited higher radical scavenging activity for DPPH, whereas amla pomace showed the highest potential to scavenge ABTS, with FRAP values ranging from 8.60 to 556.41 mg TE/g. Total phenolic content was significantly and positively correlated with both DPPH-RSA and ABTS-RSA (r > 0.7, p ≤ 0.01). The results also showed that amla pomace possessed the highest inhibitory activity, i.e., 64.34%. Principal Component Analysis (PCA) was used to investigate the correlations between the antioxidant assays and AWM. PCA reduced the dimensionality of the dataset to two components, which accounted for 89.36% of the total variance Discussion: AWM peels and pomaces are good sources of polyphenols, especially amla and pomegranate. Phenolic content showed strong links with antioxidant activity. Amla pomace also showed the highest α-amylase inhibition. Thus, AWM can be used in functional food. Conclusion: The study indicates that different AWM may alter the natural structure of α- amylase, thereby inhibiting its activity, and suggests that phenolic compounds are the key antioxidant agents in these plants. These findings emphasize the significance of AWM as an excellent source of polyphenols, which may be utilized in the development of food, feed, and nutraceutical products.