Extraction and determination of flavonoid compounds in citrus fruit waste

Abstract Citrus is a globally cultivated fruit crop that has been heavily industrialised to manufacture food products. It is commonly sought out for its nutritional benefits. However, parallel to rapid industrialisation, parts of the crop’s physical composition (inner and outer peel, seeds etc.) are often discarded to the environment as waste. Recent advancement in technology has led researchers to look for alternatives to recover potential therapeutic compounds from citrus fruit waste, directly extending the life of the waste and indirectly solving waste management concerns. Citrus fruit peels are especially rich in flavonoid compounds, a subclass of the many phytochemicals largely present in the body of the fruit. Flavonoid compounds have the capacity to be act as antioxidants, leaving room for the potential of the flavonoids present in fruit waste to be commercialized as a natural bioresource. This study aims to extract and recover the flavonoid compounds present in the peels of citrus fruits calamansi ( Citrus microcarpa ), kaffir lime ( Citrus hystrix ), and key lime ( Citrus aurantiifolia ) via ethanolic extraction and test the presence of recovered flavonoid compounds via alkaline reagent test. In addition, this study also aims to measure the antioxidant activities of all three citrus fruit peel samples via the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay. This study hopes to shed light on the therapeutic potential of citrus fruit peel waste as a bioresource which could benefit communities in the future.