Identification of antioxidant compounds from fresh and frozen mango peels using spectrophotometric and HPLC methodologies

A huge amount of mango peels (7 – 9 million tons) is produced annually [1]. Most of them are discarded in landfills or incinerated, leading to severe environmental problems. The chemical characterization of mango peels and the identification of their bioactive properties are essential to find potential applications for this byproduct. Hence, this study aimed to perform diZerent HPLC and spectrophotometric methodologies that enable the identification of the main antioxidant compounds in fresh and frozen mango peels and the evaluation of their antioxidant activity. To accomplish that, firstly, fresh and frozen (-20 ºC for 30 days) mango peels were submitted to diZerent extraction processes. A methanolic extraction followed by an alkaline and acid hydrolysis was performed to obtain free and bound phenolic compounds, while vitamin C and carotenoids were extracted with water and acetone:hexane (50%:50% / v:v), respectively. Then, three diZerent HPLC methodologies were performed to identify and quantify phenolic compounds, vitamin C, and carotenoids. The antioxidant activity of phenolic extracts was determined using spectrophotometric methodologies (DPPH and ABTS assays). The vitamin C content varied between 4.57 – 4.82 mg/ 100 g fresh weight (FW). Regarding carotenoids, the most abundant was b-carotene (17.87 – 19.64 μg/ gFW). Concerning phenolics, thirteen different compounds were identified. Mangiferin (162 – 167 μg/ gFW) and gallic acid (basic hydrolysis: 11.30 – 89.71μg / gFW; acid hydrolysis: 5.26 – 15.62 μg/ gFW) were the main free and bound phenolic compounds, respectively. Both fresh and frozen mango peels showed a high antioxidant activity. Freezing increased and reduced free and bound phenolics, respectively. Fresh and frozen mango peels can be wholly used as added value ingredients (pulps) or to extract natural food preservatives, contributing to mango processing companies' environmental and financial sustainability. Freezing is a preservation method advantageous for releasing free polyphenols with strong antioxidant capacity, generated through the break of bound phenolics present in antioxidant fiber.