The Impact of Pasteurisation and Sterilisation on Bioactive Compounds of Onion By-products

Abstract

Onion (Allium cepa L.) waste disposal represents a worldwide environmental problem. A solution to this issue could be the use of onion waste as food-grade ingredients, which could be added to processed foods for their enrichment in bioactive compounds. For this purpose, onion waste should be adequately processed and stabilised. Thus, the objective of this work was to study the composition of processed onion waste, assessing the effects of processing and thermal stabilisation on onion waste bioactive compounds. Onion waste was triturated (‘Paste’) and triturated + pressed (‘Bagasse’, solid residue and ‘Juice’, liquid fraction). All by-products were stabilised by pasteurisation and sterilisation. Results indicated that bagasse was an enriched dietary fibre product (361–453 mg/g dry weight (DW)); paste showed high alkyl or alkenyl cystein sulphoxide (ACSO) content (5.6 mg/g DW); and juice showed large fructans concentration (205–221 mg/g DW). In paste and bagasse, pasteurisation and sterilisation improved soluble/insoluble fibre ratio, with no changes in total dietary fibre concentration in pasteurised products and a slight decrease (8 % on average) in the sterilised ones. In juice, thermal treatments produced fructans losses, more pronounced after sterilisation (59 % on average) than after pasteurisation (36 % on average). However, sterilisation provided by-products with better ACSO results than pasteurisation. As a conclusion, industrial processing has an important impact on the bioactive composition, generating products with different functional applications. Moreover, pasteurisation resulted to be the most suitable treatment to obtain safe products enriched in dietary fibre and fructans, while sterilisation could be used to produce products rich in ACSOs.