Examining the polyphenol content, antioxidant activity and fatty acid composition of twenty-one different wastes of fruits, vegetables, oilseeds and beverages

Abstract

One of the most abundantly available, cost-effective valuable resources that are of all-time concern for minimization and economical re-utilization is food waste, and quantifying the phenolic compounds and identifying the principle chemical constituents will favour their industrial exploitation potential. Water, methanol and ethanol extracts of 21 common food wastes of four different classes (fruits, vegetables, oilseeds and beverages) were screened by determination of their antioxidant activity (measured by DPPH activity, reducing power and phosphomolybdenum method) as well as total phenol, flavonoid and ascorbic acid contents. Further predominant chemical constituents (essential fatty acid composition and elemental contents) of the top four phytochemical-rich food wastes were investigated by GC–MS and ICP–MS. Water was more efficient for polyphenol extraction, and ethanol extracts for antioxidant power. Onion peel, pineapple skin and date seed had the highest phenolic content and antioxidant activity. Radish peel showed the highest ascorbic acid content (48.9 ± 1.5 mg/g). Onion peel emerged as a unique source of flavonoids (> 80%). Onion peel, radish peel and pineapple skin were identified to be the sources of essential fatty acid, i.e., linoleic acid, particularly radish peel being the rich source of alpha-linoleic acid highlighting its potential for human dietary intake or as animal feed. Moreover, the screened polyphenol and unsaturated omega fatty acid-rich food wastes constituted considerable quantities of essential macro- and micronutrients. Our study demonstrates the possibility of recovering large amounts of natural phytochemicals from food wastes as alternatives to synthetics and for industrial applications.