A zero-waste approach towards a sustainable waste management of apple: Extraction of value-added products and their application as edible coating

Abstract

This study aimed to valorize apple pomace (AP) for the production of value-added products in a zero-waste system. A Box-Behnken design was used to optimize the microwave-assistant extraction factors on simultaneous extraction of pectin (APP) and phenolic compounds (APPC). Under optimum conditions (microwave power of 600 W, irradiation time of 6 min, liquid/solid ratio of 45, and pH of 1.5), the APP and APPC yields were 28.37 ± 1.19% and 3.42 ± 0.48%, respectively. The solid residue after co-extraction was used as a carbon source for microbial production of pullulan and single cell protein (SCP) and the maximum production yields of pullulan (43.7 g/L) and SCP (33.5%) were gained after sequential homogenization, ultrasonication and enzymatic treatment (H + U + E). The molecular weight of APP and pullulan were found to be 690.293 and 366.246 kDa, respectively. Also, the FT-IR and 1H NMR analysis confirmed the presence of pectin and pullulan in the resulting sample and their XRD pattern showed an amorphous structure. The results of DPPH, ABTS and FRAP assays indicated that the antioxidant capacity of apple pomace phenolics was comparable with vitamin C and BHA at high concentrations. Moreover, the coating with 50:50 ratios of APP and pullulan enriched with 15% APPC was selected as the best edible coating for strawberry that prolonged its shelf life until 24 days at 4 °C. The outcomes revealed that the extraction of these valuable compounds from AP in line with the sustainable agriculture development not only reduces environmental problems, but also the obtained products can be used to coat fruits.