Rambutan peel as a source of food antioxidant extracts

Abstract

Valorization is defined as the procedure to recover the natural resources contained in by-products, without endangering human health or damaging the environment. Commercial processing of tropical fruit leads to large amounts of waste products (peels, seeds, kernels and rinds) that can be revalorized. Therefore, the total phenolic and flavonoid content, as well as the antioxidant activity of tropical fruit by-products (mango peel and kernel, rambutan peel, pineapple peel and crown leaf, pitahaya peel, banana peel and cocoa pod husk) have been investigated. Although all the extracts have proven to be interesting sources of bioactive compounds, the rambutan peel showed the highest level of phenolic compounds (10.9 g GAE 100 g-1 d.w. (dry weight)) and antioxidant activity (9.8 g Trolox 100 g-1 dw). Afterwards, the extraction process was modelled and optimized using the response surface methodology (RSM). The conditions that maximized the responses in a Soxhlet extraction were: 50% ethanol:water (v:v), 140°C, and 35 min. The rambutan extracts obtained under these conditions reported up to 17.3 g 100 g-1 dw of gallic acid, 3.2 g catechin 100 g-1 dw, and 12.3 g Trolox 100 g-1 dw, with ellagic acid as the principal benzoic acid with 1.6 g 100 g-1 dw. Moreover, this extract significantly increases the induction period of virgin olive oil in an accelerated stability experiment, showing its potential as a food antioxidant.