Stimulating effect of sorbitol and xylitol on germination and growth of some xerophilic fungi.

Sorbitol and xylitol are polyols often used in foods as naturally occurring sugar substitutes. They provide sweet taste and reduced calories in products of intermediate moisture. This type of food is susceptible to spoilage by xerophilic molds which affect shelf life of foods and produce significant losses. The aim of the present work was to study the effect of glycerol, sorbitol and xylitol on the germination and growth of four xerophilic fungi at different temperatures and water activity levels. Penicillium chrysogenum, Wallemia sebi, Eurotium chevalieri and Eurotium repens were cultivated on malt extract agar with the addition of the respective polyols and a(w) adjusted to 0.85, 0.88, 0.90 and 0.93. Incubation was made at 25, 30 and 35 °C. Results of the present study demonstrated that sorbitol and xylitol affect the growth kinetics of the four fungal species. The observed tendency was that these solutes shortened the germination times and increased the growth rates. The effect of each solute depended on the fungal species and the a(w)/temperature combinations. At lower a(w) the influence was more evident on the germination times while the effect on growth rates was more pronounced at higher a(w) levels.