Enzymatic hydrolysis of yeast cell walls for the production of value-added products

Abstract

Currently at Ohly GmbH, the insoluble yeast cell wall (YCW) fraction is generated as a side-stream product from the Saccharomyces cerevisiae yeast extract production, which is sold for a low profit margin as an additive and supplement for animal feed. The YCW structure exhibits a great source of health-promoting activity and bioactive properties in humans and animals. Therefore, the main aim of this dissertation was to hydrolyse the autolysed YCW through enzymatic digestion, altering its composition and structure, and thereby obtaining different types of unique hydrolysates, which may be used for possible innovative and valuable applications. As there wasn’t any previous work with YCWs at Ohly GmbH, the first step was to develop an enzymatic conversion method establishing the reaction conditions and a hydrolysate product analysis protocol to standardize the process. Once the protocol was determined, the second step was screening 56 commercial enzyme mixtures, which present different hydrolytic activities (such as phospholipase, β-glucanase, chitinase, mannanase, etc) and also characterize the obtained hydrolysates in visual, analytical and chemical terms, such as viscosity, turbidity, solubilisation and phase separation, reducing and free sugars over reaction time. Afterwards, a characterization of glucan- and mannan-oligosaccharides was performed, in order to establish a hydrolysate product selection according to the respective number-average degree of polymerization (DPn), which was also estimated. The DPn values obtained from the enzymatic hydrolysates were also compared and related by their molecular weight (MW) profile, which was analysed by HPLC-SEC. Thus, with a full and detailed report of each hydrolysate product, ideas of new products development were generated, since different DPn values can lead to different product applications. In addition, to obtain a hydrolysate product with an immune-stimulant activity to animal feed, a process optimization (variation of the enzymatic reaction conditions) for a specific commercial enzyme mixture was performed and studied in detail.