# Potential Applications of Yeast Biomass Derived from Small-Scale Breweries
## 5 Yeast Biomass Processing Technologies  
Since brewery yeast sludge may contain different impurities, the initial processing focuses on removing undesirable particles. Large particles such as hops may be separated via mechanical sieving [32]. The remaining beer may be removed by centrifugation or filtration followed by washing with water [40]. Removal of hop-derived compounds bound to the yeast cell walls may be achieved with washing in basic solutions (pH > 9) [12]. Traditionally, yeast extract is prepared using an autolysis process. In this method, a yeast suspension containing around 10% of dry yeast biomass is heated up to around 50 \({}^{\circ}\)C in acidic conditions (pH = 5) and then incubated for 24 h [38]. During this process, biological membranes are disrupted and vacuolar proteolytic enzymes (such as proteinase \begin{table}
\begin{tabular}{l l l} \hline Cell wall & 11–25 & \% cell DW \\ \hline Chitin & 1.4–6.9 & \% cell wall \\ \hline Mannan & 28–67 & \% cell wall \\ \hline Total beta-glucan & 32–57 & \% cell wall \\ \hline
1–6 beta-glucan & 4.5–11.5 & \% cell wall \\ \hline \end{tabular}
\end{table} 
Table 4: Composition of yeast cell wall [35]. \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline \multicolumn{1}{c}{**Vitamin**} & \multicolumn{1}{c}{**Yeast Biomass**} & \multicolumn{5}{c}{**Yeast Extracts**} \\ \hline Biotin (B7) & 0.0013 & 0.5 & 1.14 & 1.28 & 1.38 & 6.19 \\ \hline Folic acid (B9) & 0.0130 & 0.01 & 0.045 & 0.049 & 0.013 & 0.053 \\ \hline Niacin (B3) & 0.3000 & nd & 0.94 & 1.04 & 0.68 & 0.79 \\ \hline Pantothenic acid (B5) & 0.0700 & 0.08 & 0.2 & 0.19 & 0.16 & 0.43 \\ \hline Riboflavin (B2) & 0.0400 & 0.13 & 0.002 & 0.002 & 0.001 & 0.011 \\ \hline Thiamine (B1) & 0.1200 & 0.11 & 0.069 & 0.07 & 0.052 & 0.075 \\ \hline Pyridoxine (B6) & 0.0280 & 1.76 & 0.049 & 0.051 & 0.031 & 0.059 \\ \hline Cobalamin (B12) & 0.000001 & 0.17 & 0.0018 & 0.0012 & 0.011 & 0.0016 \\ \hline \multirow{4}{*}{Source material type} & \multirow{2}{*}{\begin{tabular}{} \end{tabular} } & \begin{tabular}{} \end{tabular} & \begin{tabular}{} \end{tabular} & \begin{tabular}{} \end{tabular} & \begin{tabular}{} \end{tabular} & \begin{tabular}{} \end{tabular} & \begin{tabular}{} \end{tabular} & \begin{tabular}{} \end{tabular} \\ \cline{1-1} \cline{3-6}  & & \begin{tabular}{} \end{tabular} & \begin{tabular}{} \end{tabular} & \begin{tabular}{} \end{tabular} & \begin{tabular}{} \end{tabular} & \
\begin{tabular}{} \end{tabular} &
\begin{tabular}{} \end{tabular} \\ \hline Reference & [38] & [39] & [30] & [30] & [30] & [30] & [30] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Vitamin content in brewery yeast biomass and yeast extracts [mg/g DW]. A and B, carboxopeptidase Y) are released and start to degrade proteins in the cell. This process produces a mixture of low-mass peptides and free amino acids. DNA and RNA also undergo hydrolysis, resulting in the production of oligonucleotides, nucleotides, and nucleosides. Enhanced production of monophosphate nucleotides, which are important flavor enhancers, may be achieved in altered autolysis conditions [41]. During autolysis, polymers present in the cell wall are partially hydrolyzed by the beta-glucanase enzyme, resulting in the disruption of cell walls. General degradation of cell elements finally leads to the release of hydrolysis products to the solution. The efficiency of the autolysis process may be improved by the addition of sodium chloride (up to 3%), ethyl acetate, or isopropanol [38]. NaCl causes the separation of the plasma membrane from the cell wall due to reductions in cytoplasmic volume caused by differences in osmotic pressure. This process finally leads to the disruption of the lipid membrane and the release of hydrolytic enzymes. It may also be stimulated by the addition of Alcalase [42]. The hydrolysis of biopolymers derived from yeast may be enhanced by the addition of hydrolytic enzymes (proteases: trypsin, pepsin, papain, and others).