Valorization of Malus domestica L. (Apple) peels: A case study of circular bioeconomy

Abstract

Sustainable food production by agricultural and food processing industries has gained importance in last decade, which essentially requires good management of the wastes generated during processing. In this regard, sustainable handling of any agro waste using the concept of “circular bioeconomy” is important. Present work depicts a case study on circular bioeconomy of Apple peels (AP) utilization for its value addition with zero waste at the end. AP was exposed to four different Deep eutectic solvents synthesised using HBA Choline Chloride with varoius HBDs like malic acid, glycerol, ethelene glycol and urea as well as a benchmark solvent Ethanol:water (50% v/v) resulting in extracts with TPC ranging between 1040 and 4302.6 mg GAE 100 g-1. Polyphenolic profiling of the extracts using developed HPLC method, confirmed the presence of polyphenols such as Phlordizin, Rutin, Syringic acid, Paracoumaric acid, Chlorogenic acid, Catechin, Epicatechin, Ferulic acid. The chemistry behind the ability of DESs for the extraction of the polyphenols in varying amount is explained using Hole theory and computational modeling of DES. Antioxidant potential of the extracts towards FRAP (7.76- 20.7 mM L−1)/ABTS (2.31- 8 mM L−1) assay and antibacterial activity against gram negative/positive bacterias with zone of inhibition between 12.2 and 14.9 mm, confirmed extracts to be biologically active, promoting their use as nutraceutical. Moreover, total dietary fiber in the residue (27.31- 45.44%) can find application as probiotics, thus complying with zero waste generation at the end. DES could be recycled six times with 15% decrease in efficiency.