Liquid submerged fermentation by selected microbial strains for onion skins valorization and its effects on polyphenols

Abstract

Onion skins, actually recycled as organic fertilizers, could be used as a substrate in environmental-friendly bioprocesses to recover high-value bioactive compounds and food ingredients.In this work, a bioprospecting method was carried out including 94 bacterial and 45 yeast strains from several agri-food and environmental niches to verify their ability to grow on onion skins as unique nutrients source.Red and yellow onion skins were assessed by newly selected starter-driven liquid submerged fermentation assays mainly aimed at the release and modification of polyphenols through microbial activities. Fermented onion skins were also investigated as a inexpensive favourable source of microbial enzymes (amylases, proteases, lipases, esterases, cellulases, xylanases).In red onion skins, the treatment with Lactiplantibacillus plantarum TB 11–32 produced a slight increase of bioactive compounds in terms of total phenolics, whereas with the yeast strain Zygosaccharomyces mrakii CL 30 − 29 the quercetin aglycone content increased of about 25% of the initial raw material.In yellow onion skins inoculated, the highest content of phenolic compounds was detected with the yeast strain Saccharomyces cerevisiae En SC, while quercetin aglycone increased of about 60% of the initial raw material in presence of the bacterial strain L. plantarum C 180 − 34.In conclusion, the proposed microbial pre-treatment method can be a potential strategy to re-use onion skins as a fermentation substrate, and as a first step in the development of a biorefinery process to produce value-added products from onion by-products.

Novel Fermentation Strategies of Strawberry Tree Arbutus unedo Fruits to Obtain High Nutritional Value Products

“…The determination of total phenolic content (TPC) in the extracts was performed by Folin-Ciocalteu (FC) assay as described in Ramires et al [52], and TPC was expressed as mg gallic acid equivalent (GAE), per 100 g dry weight of strawberry tree samples. The total flavonoid content (TFC) was determined according to Jia et al [53].…”

“…Lipase, esterase and endo-xylanase activity assays were carried out according to the procedure described by Maiorano et al [38]; α-amylase and protease activity tests followed the method described by Ramires et al [52]. Finally, cellulases were determined using a cellulase assay kit (CellG5, Megazyme, Bray, Ireland), according to the method provided by the manufacturer.…”