## 1 Introduction  
The loss of fruit and beverages due to microbial spoilage impacts negatively on the economy of the producing countries [1; 2]. In developing countries, such losses are severe due to poor conservation and transportation facilities available to producers [3]. Some of the common microorganisms that are associated with fruit and beverage spoilage are _Botrytis_, _Colletotrichum_, _Rhizopus_, _Dekera_, _Zygosaccharomyces_, _Pichia_ and _Hansenispora_ species [4; 5; 6]. The current methods for the preservation of beverages and fruits are mainly based on synthetic chemicals. However, due to the serious health concerns associated with the use of synthetic chemicals [7], there is an urgent need for their replacement with less harmful preservatives, which are a healthier alternative for humans and cost effective. Recently, yeasts were identified as potential producers of biopreservation compounds and potential biocontrol agents against several spoilage organisms [2; 8; 9; 10; 11]. These investigations lacked an industrial engineering approach for sustainable production of these biopreservation compounds, and used expensive refined media that is not cost-effective [12]. However, yeasts also have the ability to produce useful metabolites while growing in inexpensive media [13; 14; 15].  
Grape pomace extract (GPE) is an inexpensive potential raw material that could be used for the production of value-added products like biopreservation compounds. South Africa has a thriving wine industry [16] and large quantities of grape pomace are generated, essentially as a waste product. The chemical composition of GPE could make a suitable alternative medium for the growth of various microorganisms, since it contains fermentable reducible sugars [17] such as glucose, fructose and yeast-assimilable nitrogen (YAN) that can fulfil the nutritional requirements for microbial growth of producers of biopreservatives.  
During microbial growth, the relationship between growth rates and the production kinetics of extracellular metabolites, is key in assessing the general physiological requirements of yeasts, including substrate utilization and extracellular metabolites formation rates. The process for the production of biopreservation compounds needs to be optimized for higher product yield and minimal cost of production. Optimization approaches such as response surface methodology (RSM) and Box-Behnken have been used previously [18; 19; 20]. However, based on the number of experimental runs required when developing suitable response surface models, the central composite design is the most preferred design with regard to response surface methodology [21; 20; 22].  
As supported by the literature, the nature of the growth inhibition by yeasts have been attributed to its higher growth rate, which makes them competitive for nutrient and space [14]. Another attribute is the production of extracellular compounds such as killer toxins and volatile organic compounds (VOCs) [9; 10; 14]. Since the current literature has demonstrated the potential of yeasts as producers of VOCs with growth inhibition properties mostly at the screening level without much production using renewable bioresources, this research forms part of a larger project investigating the use of wild yeasts as producers of biopreservation compounds. This study's aim was to understand the kinetics of biopreservation compound production by _C. pyralidae_ and _P. kluyveri_ and to optimize the production process, using grape pomace extracts, a cheap, readily available raw material, as a fermentation medium.