Microcalorimetry as a Tool for Monitoring Food Fermentations

Abstract

Food fermentations are important to obtain different products such as bread, beer, mead, wine, yogurt, among other. The rate of fermentation is generally monitored by the measurement of simple variables like pH, Brix, titratable acidity and volume increase (in case of bread’s dough). Isothermal microcalorimetry has been used to evaluate bacterial growth in medical, clinical, environmental and food fields. This work aims to show the potentiality of isothermal microcalorimetry as a tool for monitoring different fermentations. Yogurt fermentations were performed on 100 mL milk in isothermal conditions at 45°C with types of pasteurized milk (cow and goat), fermented by two activated commercial yogurt starters (with a different combination of Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus and a dose of 0.4 % w/v). Apricot juice fermentations were performed on 4 mL glass vials (15 Bx, pH 4.5) in isothermal conditions at 15°C with six different type of commercial yeasts (Saccharomyces cerevisiae with a dose of 0.3 % w/v). Dough fermentations were performed on 4mL Hastelloy vials in isothermal conditions at 30°C with different flours (wheat, cornstarch, teff, commercial gluten free mixture and buckwheat) and commercial bread yeast (Saccharomyces cerevisiae with a dose of 1.0 % w/w). All fermentations evaluated show a different behaviour for heat flow and accumulated heat: (1) for yogurt has a strong influence related to kind of milk as well as starter used. (2) for apricot juice has a strong influence related to kind of yeast used as well as its concentration. (3) for dough has a strong influence related to kind of flour used as well as the inclusion of wheat flour. These results confirm isothermal calorimetry can be combined with other techniques in order to be useful for monitoring different industrial fermentations and evaluating changes in formulation and process