Lactic Acid Fermentation as a Valorising Agent for Brewer’s Spent Yeast—Improving the Sensory Quality and Nutritional Potential

Abstract

Brewer’s spent yeast (BSY) is one of the brewing industry’s most plentiful side-streams. Abundant, low-cost and high in nutrients, it has great potential for application in food technology and human nutrition. With the ever-increasing interest in sustainability, waste reduction and circular food systems, the use of BSY as a novel food ingredient may be the route to add exponential value while reducing the environmental impact. However, negative flavour characteristics and high amounts of alcohol severely limit the current applications of BSY. This study explores the use of processing involving lactic acid bacteria (LAB) fermentation technology as a means of improving BSY quality characteristics and examines the effects of this process on the chemical, nutritional and sensory characteristics of BSY. The results reveal that BSY is a suitable substrate for LAB fermentation, successfully supporting the growth of Lactobacillus amylovorus FST 2.11. Compared to the unfermented BSY (CBSY), fermentation significantly reduced the perceptible bitterness of the BSY as detected by a sensory panel, from 6.0 ± 2.8 units to 0.9 ± 0.7 units, respectively. Fermented BSY (PBSY) had enhanced sour and fruity flavours, and a variety of other volatile compounds and metabolites were determined. Protein profiles showed significant protein degradation, and free amino acid levels were greatly increased following fermentation, from 2.8 ± 0.2 g/100 g to 10.5 ± 0.4 g/100 g, respectively. Protein quality was high, with the CBSY and PBSY providing well over the required level (>100%) of essential amino acids per gram protein, with the exception of sulphur amino acids (98%). Major physical differences were observed using scanning electron microscopy. This study concludes that LAB fermentation positively affects the sensory and nutritional characteristics of BSY and can aid in the incorporation of brewer’s spent yeast into foods for human consumption.

Valorisation Process Using Lactic Acid Bacteria Fermentation Induces Significant Changes in the Physical and Functional Properties of Brewers Spent Yeast

“…The basic composition of the control brewer's spent yeast (CBSY) and the processed brewer's spent yeast (PBSY) are described in a previous study [13] and are reported in Table 1. The current study builds on these known compositional data, further investigating the carbohydrate and lipid composition of CBSY and PBSY.…”

“…Control brewers' spent yeast (CBSY) and processed brewers' spent yeast (PBSY) were prepared as described by Jaeger et al [13]. Briefly, the processing of the BSY consisted of standardisation, autolysis, sterilisation, and fermentation with Lactobacillus amylovorus FST 2.11.…”

“…The dried and fermented BSY is referred to as processed BSY (PBSY), and the unfermented BSY is referred to as control BSY (CBSY). The composition of these powders was then analysed and is presented in Table 1 [13].…”

“…This research, in particular, ties into Goal 12-'Responsible production and consumption'-which aims to substantially reduce food waste along production chains through prevention, reduction, recycling, and reuse. A previous study employed a process including lactic acid bacteria (LAB) fermentation to successfully improve the sensory and quality characteristics of brewers' spent yeast [13]. LAB fermentation with Lactobacillus amylovorus FST 2.11 significantly reduced the bitterness of BSY as perceived by a sensory panel while increasing the intensity of fruity and sour flavours.…”

“…LAB fermentation with Lactobacillus amylovorus FST 2.11 significantly reduced the bitterness of BSY as perceived by a sensory panel while increasing the intensity of fruity and sour flavours. In addition to changes in sensory characteristics, significant protein degradation was observed as a result of the processing, which likely affected functional behaviour [13]. Thus, processing, including LAB fermentation, is a successful means of upcycling BSY into a more palatable, nutritious food ingredient.…”