Epifluorescence Light Microscopy as a New Method for Evaluation of Fermentation Activity of Bakery’s Yeast

Introduction: Technological performance of Bakery’s yeast is closely related to its viability. In order to predict the performance of baker's yeast, observations concerned with accurate and fast detection of viable and nonviable yeast in the fermentation environment is essential. Materials and Methods: In this study, three samples of instant dry yeast were investigated by epifluorescence light microscopy (EFLM) using 0.02 % FDA and 0.1% Evans blue. Gasograph apparatus was employed to measure CO2 produced by the Saccharomyces cerevisiae during fermentation. Microbial tests were carried out in order to count the number of yeasts colonies formed. Bread volume and height were assessed after baking process. Results: Baker’s yeast (A) had the highest number of green cells (177.8±7.36) and baker’s yeast (C) had the lowest number of green cells (102.2±8.97). The number of yeast colonies formed in baker’s yeast (A) was the highest (15×1010 cfu/mg) while the bakery’s yeast (C) was the least (12×1010 cfu/mg). Gasograph test showed that baker’s yeast (A) produced the highest amount of CO2 (163.3± 1.9 ml CO2/3h) and bakery’s yeast (C) produced the lowest amount during fermentation process (139.67±1.6 ml CO2/3h). Bread (A) produced the highest volume (132.22±1.0 cm3) and height (4.72±0.35 cm) while bread (C) had the lowest volume (108.33±6.21 cm3) and height (3.81± 0.3 cm). Conclusion: The tests concerned indicated that high survivability and bioactivity of bakery’s yeast leads to more production of CO2 and higher volume and height of bread. The results showed a direct correlation between the percentage of live yeasts and ability of CO2 production. Utilization of EFLM can help to predict the bakery yeast bioactivity without the need for baking tests.