# Yeast as a By-Product from Wine and Beer Production: Comparative Evaluation of Physico-Chemical Composition

## TL;DR

This study compares the nutritional and chemical properties of yeast by-products from wine and beer production in Moldova, focusing on their potential as sustainable food sources.

## Contribution

The novelty lies in the comparative physico-chemical and antioxidant analysis of wine lees and spent brewer’s yeast under different drying methods.

## Key findings

- Cricova wine lees had the highest protein content (45.35–46.81%).
- Efes spent brewer’s yeast (oven-dried) had the highest total polyphenol content (3.98 mg GAE/g).
- Wine lees contained the highest B vitamins, with vitamin B3 being the most abundant.

## Abstract

The trend toward sustainable protein substitutes is driven by growing concerns about food security, sustainability, and human health. Spent brewer’s yeast and wine lees are two by-products of the beer and wine industry with high potential, owing to their complex composition, which remains insufficiently exploited. The purpose of this study was to perform a comparative analysis of the two by-products under two different drying techniques to observe if there are significant changes in composition: oven-drying and freeze-drying. Two samples of wine lees from producers in the Republic of Moldova were used—Asconi Winery and Cricova Winery (Republic of Moldova)—as well as a sample of spent brewer’s yeast offered by Efes Vitanta Moldova Brewery. The samples were characterized in terms of physicochemical properties, antioxidant activity (total polyphenol content (TPC), individual polyphenol content, and DPPH assay scavenging activity), color, mineral content, structural composition (FT-IR analysis), and microstructure, as well as organic acid and B vitamin content. The highest protein content was recorded in the samples from Cricova (45.35–46.81%). Regarding the polyphenols, the oven-dried Efes sample exhibited a TPC value of 3.98 mg GAE/g, while the highest DPPH value of 88.92% was observed in the Asconi sample. All analyzed samples showed a diverse composition of individual phenolic compounds, including 4-hydroxybenzoic acid, vanillic acid, caffeic acid, and rosmarinic acid. Wine lees samples have the highest content of B vitamins, with vitamin B3 being the most abundant across all samples, followed by vitamin B6. The microstructural examination revealed autolyzed yeast cells, with more permeable cell walls, favorable to subsequent valorization treatments, and in some cases, cells form clusters in a mother-daughter junction due to serial re-pitching.