Food Ingredients for the Future: In-Depth Analysis of the Effects of Lactic Acid Bacteria Fermentation on Spent Barley Rootlets

Repurposing by-products to alternative applications has become a vital part of food research. Barley rootlets (BRs) are a side-stream of malting and brewing industries. This study focuses on processing BRs into food ingredients, using fermentation with five lactic acid bacteria (LAB) as a valorisation technique. The strains used were Lactiplantibacillus plantarum FST 1.7, Lactobacillus amylovorus FST2.11, Weissella cibaria MG1, Leuconostoc citreum TR116 and Limosilactobacillus reuteri R29. The influence of fermentation on sugar/FODMAP/acid compositions and microbial metabolites in BRs was analysed. A variety of techno-functional properties were also evaluated. Results showed BRs were a suitable substrate for LAB, particularly for Lactiplantibacillus plantarum FST 1.7 and Lactobacillus amylovorus FST2.11. Sugar, acid and the FODMAP composition of the fermented BRs demonstrated various traits imparted by LABs, including high mannitol production from Leuconostoc citreum TR116 and Limosilactobacillus reuteri R29. Limosilactobacillus reuteri R29 also produced fructans using BRs as a substrate. A techno-functional analysis of BRs showed a significant reduction in α-amylase activity post sterilisation and fermentation. Fermentation reduced water-binding capacity and significantly increased oil-binding capacity. The LAB used displayed great potential in improving the functionality of BRs as a food ingredient while also showcasing LAB fermentation as a viable processing aid for BR valorisation.