Yeast cell wall hydrolysis by enzymes for the production of value-added products

Abstract

Yeast cell walls (YCW) are side-stream products from yeast extract production and are usually lower value products. In the first part of the project, we explored the potential of enzymes in converting Ohly’s YCW into high(er) added value new products. Accordingly, a better understanding of the enzymatic hydrolysis of YCW and the subsequent hydrolysates properties was obtained. An enzymatic assay was developed in lab-scale by standardizing process conditions such as enzyme dosage, temperature, pH and reaction time. Over 56 Carbohydrases and 4 Phospholipases were tested. The hydrolysates characterization was done by visual, analytical and chemical analysis. The following Ohly starting materials were used: YCW from the S. cerevisiae (hydrolysis process) and from C. utilis a.k.a Torula (Prime process). Hydrolysates were clustered using a PCA into 6 groups based on their profile of: free reducing sugars, free glucose, and free mannose. From all enzymes the most interesting were AO3, NC5, SN7, SN8, ET4, NC1 and ST3. In the second part of the project, the Torula YCW were used as a starting material for the production of a new yeast extract due to their high protein content. An enzymatic assay was performed by standardizing process conditions such as enzyme dosage, combination of different enzymes, temperature, pH and reaction time. The hydrolysates characterization was done by analytical and chemical analysis, and by sensory analysis. Proteolytic enzymes (9), Carbohydrases (2), Phospholipases (4) from various manufactures were tested. Results show that the optimal recipe to produce a new yeast extract from Torula YCW consisted of: 0.5% NS11 + 0.5% EN1 + 0.1% AO5 as the best combination when tested in an application (vegetable broth).