Repurposing citrus peel waste and its positive effects on our health and communities

Every year, more than 30% of food products go to waste. This is approximately 1.3 billion tons of food, which is equivalent to 1.3 trillion U.S. dollars. While conventional solid waste treatments and fertilization of food waste are common, citrus fruit peels require secondary applications and advanced disposal management due to their low pH values and high antimicrobial characteristics. Since citrus fruits are well-known sources of vitamin C and antioxidants, we hypothesized that their peels also contain high amounts of vitamin C and antioxidants. In our study, five common citrus peels including grapefruit, lemon, lime, orange, and tangerine, were used to determine the amounts of vitamin C and total soluble antioxidants. Experimental results showed that lemon peels contain the highest vitamin C concentration (39.68 mg/g sample), closely followed by tangerine peels (37.23 mg/g sample). Lower vitamin C concentrations were extracted from the grapefruit, lime, and orange peels within a 3-hour reaction period with the average concentrations of 26.36 mg/g, 25.20 mg/g, and 24.53 mg/g sample, respectively. Despite containing a relatively low level of vitamin C, grapefruit peels demonstrated the highest antioxidant capacity (48.142 µmol Trolox/g peel sample), followed by orange, lemon, tangerine, and lime. Based on our results, if we were able to repurpose fruit peels and utilize them as a nutrient source, each U.S. individual would be able to meet the daily amount of the recommended vitamin C with 2-3 teaspoons of citrus peels reducing 4.8 pounds of the carbon dioxide (CO2) equivalent annually at the same time.