MATHEMATICAL-MODELING OF SURVIVAL AND WEIGHT-LOSS OF BAKERS-YEAST DURING DRYING

Drying and death rates of Baker's yeast were studied in a computer-con trolled laboratory scale tunnel drier with varying air velocity betwee n 2.0-3.0 ms-1 and temperatures within the range of 40-60 degrees C. T wo falling rate periods were observed during the drying process. A sin gle first-order expression described the death rate of the microorgani sms during both drying phases. Arrhenius-type expressions described th e effects of the temperature on the first falling rate period drying a nd death rate constants. Compensation relations were also found betwee n the parameters of these Arrhenius expressions. A single linear relat ion was observed between the first falling rate period drying constant and the death rate constant at 2.5 with 3.0 m s(-1) for air velocity. A similar relation was also observed with the data obtained at 2.0 m s(-1) of air velocity. It was concluded that the death rate of yeast w as lower with a slower air velocity. The second falling rate period is a diffusion-controlled process. It was confirmed by the experimental results that the velocity of air flow does not affect the drying rare constants in the second falling rate period, Within the range of the e xperiments, no temperature effects were observed on the second falling rate period drying constant.