Diversity of sugar alcohols produced by Aureobasidium spp. and the influence of selected nutrients on mannitol synthesis

Sugar alcohols are a group of diverse polyols derived from monosaccharides that have been used in many commercial products. Mannitol, a six-carbon sugar alcohol, is a natural sweetener produced by many plants such as pumpkin, celery and olive, and microorganisms including yeast, bacteria, fungi, lichen and algae. Mannitol has been widely used as a sugar substitute in food and pharmaceutical industries, especially the products for diabetic patients, since it does not affect blood sugar and insulin levels. Mannitol can be produced via fermentation by yeasts such as Candida spp. and Aureobasidium spp. In nature, most microorganisms produce mannitol from glucose, fructose, sucrose and glycerol with different efficacies. Thus, this study was aimed to (i) study the diversity of polyols produced by seven Aureobasidium strains including A. pullulans (NRRL Y-2311-1, CBS 135684, PBUAP55 and PBUAP102) A. thailandense (NRRL58543, PBUAP17 and PBUAP70) (ii) select the best strain for mannitol production and (iii) investigate the effect of carbon and nitrogen sources on the mannitol production. It was found that these Aureobasidium strains were able to produce a variety of sugar alcohols including mannitol, arabitol, xylitol and glycerol in the strain-dependent manner. Aureobasidium thailandense PBUAP70 produced the highest yield of mannitol at 14% conversion comparing with the rest by using glucose as substrate. Glucose and ammonium sulphate were found to be enhanced the mannitol production of this strain up to 16% conversion which was the highest of the carbon and nitrogen sources tested.