## 4 Conclusions  
The use of cheap, readily available agricultural waste (i.e., grape pomace extracts) for the production of potential biopreservation compounds by yeasts presents a cost-effective and realistic alternative to synthetic chemical preservatives. Yeasts have proven to be a potential source of biopreservation compounds with inhibition properties against various spoilage organisms. _C. pyralidae_ Y1117 showed growth inhibition activity against _Z. baillii_, _D. bruxellensis_ and _D. anomala_, while the two _P. kluyveri_ strains only showed inhibition activity against _D. bruxellensis_ and _D. anomala_. The production process was optimized for _C. pyralidae_ Y1117, _P. kluyveri_ Y1125 and _P. kluyveri_ Y1164 and the biopreservation compounds produced identified. The models developed for the production of biopreservation compounds under the optimum conditions for each yeast were shown to be appropriate and statistically sound to mathematically explain the production process for potential biopreservation compounds, using GPE as fermentation medium.  
The following are available online at [[http://www.mdpi.com/2304-8158/8/2/51/s1](http://www.mdpi.com/2304-8158/8/2/51/s1)]([http://www.mdpi.com/2304-8158/8/2/51/s1](http://www.mdpi.com/2304-8158/8/2/51/s1)).  
Conceptualization, M.M.N., H.W.d.P.; methodology and software, M.M.N., S.K.O.N. and B.S.C.; validation, S.K.O.N., H.W.d.P., B.S.C. and N.P.J.; formal analysis, M.M.N., L.M. and U.F.H.; investigation, M.M.N. and U.F.H.; resources, N.P.J., H.W.d.P. and S.K.O.N.; data curation, B.S.C., M.M.N. and L.M.; writing--original draft preparation, M.M.N.; visualization, review and editing, S.K.O.N., H.W.d.P., N.P.J., B.S.C., L.M. and U.F.H.; supervision, S.K.O.N., H.W.d.P. and N.P.J.; project administration, N.P.J., H.W.d.P. and S.K.O.N. funding acquisition, N.P.J., H.W.d.P. and S.K.O.N.  
The financial support was provided by the National Research Foundation (NRF) and the Agricultural Research Council (ARC) of South Africa.  
The authors would like to thank the Agricultural Research Council, the National Research Foundation (NRF) and the Bioresource Engineering Research Group (_BioERG_), Department of Biotechnology, Cape Peninsula University of Technology for funding and infrastructure. The authors thank all students, interns, technicians and research assistants for their contribution.  
The authors hereby declare that they have no conflicts of interest.  
\begin{table}
\begin{tabular}{c c c c} \hline  & \multicolumn{3}{c}{**VOCs and Concentrations (mg/L)**} \\ \hline
**Compound** & **C. _pyralidae_ Y1117** & _P. kluyveri_ Y1125** & _P. kluyveri_ Y1164** \\ \hline Isoamyl acetate & not detected & 16.51 & 17.73 \\ Isoamyl alcohol & 1.73 & 1.74 & 1.89 \\ Butyric acid & 1.24 & 1.25 & 1.25 \\
2-Phenyl ethylacetate & 1.47 & 1.97 & 1.99 \\ Hexanoic acid & 0.93 & 0.93 & 0.93 \\
2-Phenyl ethanol & 1.61 & 1.66 & 1.68 \\ Octanoic acid & 1.32 & 1.32 & 1.32 \\ Decanoic acid & 1.44 & 1.44 & 1.44 \\ \hline \end{tabular}
\end{table}
Table 3: List of quantified volatile organic compounds (VOCs) identified to be produced by _Candida pyralidae_ Y1117, _Pichia kluyveri_ Y1125 and _P. kluyveri_ Y1164 when grape pomace extract is used as fermentation medium.