Procurement of fermentable sugars from cardboard waste for the cultivation of yeasts for biotechnological use

Abstract

The effect of different acid hydrolysis conditions (acid concentration, solid:liquid ratio and temperature) on the production of fermentable sugars from cardboard waste was studied. The hydrolysate so obtained was characterized with regard to the sugar concentration and specific monosaccharides composition as well as to the phenolic compounds content. Next its use as carbon source for the growth of the yeasts Rhodotorula glutinis and Cryptococcus curvatus was evaluated. The hydrolysate was previously detoxified with activated charcoal in order to decrease the concentration of growth-inhibitory compounds, such as phenolics produced during the acid hydrolysis process. An hydrolysate with a maximum fermentable sugars concentration of 20.9 g L-1 was obtained under the following conditions: catalyst, sulfuric acid 10 %, temperature, 125 °C, solid:liquid ratio, 60 g L-1. The main carbohydrate present in the hydrolysate was glucose. Concerning to the hydrolysis byproducts it was found 328.7 mg L-1 of phenolic compounds. About the microbial growth, the results suggest that R. glutinis is able to tolerate the inhibitory compounds present in the hydrolysate producing up to 8.1 g L-1 of biomass, while C. curvatus was unable to growth on this carbon source. It is concluded that the findings of the present study demonstrated that the cardboard waste is a potential source of fermentable sugars to be used in biotechnology processes for obtaining microbial metabolites of commercial interest.