Production of xylitol and ethanol by Hansenula polymorpha from hydrolysates of sunflower stalks with phosphoric acid

This research analyses the effect exerted by the phosphoric acid concentration (CAo) in sunflower-stalk hydrolysis at 95 °C, considering the results in relation to the yields in d-glucose and total reducing sugars (TRS). Besides to display the behavior of the yeast in generating bioalcohols from hydrolysates rich in nutrients such as phosphate, essential for the growth of yeasts in fermentation processes. The results show that the hydrolysis of the hemicellulose fraction was almost complete at CAo = 2.67 mol/L (25.3%), at which conversion reached 82.7%. The percentage of converted cellulose also increased with the acid concentration, reaching a value of 13.9% in the hydrolysis process of 2.67 mol/L. The hydrolysis rate (rH) was calculated from the values of the concentration of total reducing sugars generated over the process. For a value of CAo = 1.67 mol/L, it was determined that (rH)max = 3.5 g TRS/(L h) at the beginning of the hydrolysis process. After being detoxified, the hydrolysates were fermented with Hansenula polymorpha, ATCC 34438, registering better results in the production of ethanol that of xylitol. For an initial concentration of total reducing sugars of 13.3 g/L, xylitol yield was 0.023 g/g, and ethanol yield was 0.14 g/g.