Isothermal calorimetry for monitoring of grape juice fermentation with yeasts immobilized on nylon-6 nanofibrous membranes

Isothermal microcalorimetry is often used to monitor microbiological activity and growth in various types of biological samples. Usually, it is useful to convert the isothermal microcalorimetry data into biologically meaningful data such as growth rate, lag phase or maximum growth. In this work, isothermal calorimetry was applied for monitoring of grape juice fermentation by Saccharomyces cerevisiae immobilized in nylon-6 nanofibrous membranes (NFM) prepared by electrospinning in comparison with freely dispersed yeasts. The resulting heat flow can be fitted using various approaches applying graphical, exponential, Gompertz, modified logistic and Michaelis-Menten models. Advantages and drawbacks of each approach for monitoring of the immobilized yeasts have been discussed in relation to the S. cerevisiae yeasts. Analysis of the fitting parameters showed that immobilized yeasts had the highest growth rate and maximum growth in comparison with freely dispersed yeasts. Parallel measurements of sugar and oxygen consumption rates for immobilized and free yeasts cells confirmed the calorimetric data. The results of this work demonstrate practical approach to analysis and modeling of calorimetric data in food analysis and advantages of application of NFM as solid support for yeast immobilization.