Evaluation of fermentative activity of lactic cultures for dehydrated yogurt with the use of different additives

Objective: To evaluate the fermentative activity of dehydrated lactic cultures with the use of various additives and vacuum drying, using yogurt as a model system. Design/methodology/approach: The yogurt was made with commercial lactic cultures (YF-L705 Yo-Flex CHR HANSEN) inoculated in whole milk incubated for 4 h/42°C. The yogurt was centrifuged at 6,000 rpm/15 min/4°C. The supernatant was removed, and the following additives were added to the precipitate: 1) SN, without additives, 2) Glycerol, 3) Calcium carbonate, 4) Yeast extract, 5) Glycerol and calcium carbonate, 6) Glycerol, calcium carbonate and yeast extract. The drying of 6 treatments was done up to 96h inside vacuum desiccators. Weight and moisture loss were recorded at 0, 24, 48, 72 and 96h. The dehydrated portions with the additives 1,2,3,4,5,6 was used as inoculums in milk for the production of yogurt; recording the drop in pH up to 24h and FTIR. As a control, non-dehydrated and lyophilized portion of yogurt were used. Results: The drying time at constant weight was 3 days. Dehydrated cultures containing yeast extract and calcium carbonate are associated with faster milk fermentation activity (p ≤ 0.05). Yoghurts manufactured with fresh cultures take 4 hours to ferment, dehydrated ones take over 12 hours. Infrared spectra show that yogurts produced with fresh or dried strains are of similar qualities. Study limitations/implications: The fermentative activity in dehydrated foods improves when alkalis are added, such as calcium carbonate, which is an antacid and releases CO2 upon contact with water and acid, stimulating anaerobiosis. Infrared spectra show that yogurts produced with fresh or dried strains are of similar qualities. Findings/conclusions: The best model to present the fermentation pH change curve is a Boltzman sigmoidal function. Yogurts with fresh or dried cultures differed in the time at which the milk is fermented. The fermentative activity in dehydrated foods improves when alkalis are added, such as calcium carbonate, which is an antacid and releases CO2 on contact with water, stimulating anaerobiosis. Infrared spectra show that yogurts produced with fresh or dried strains are of similar qualities.Objective: To evaluate the fermentative activity of dehydrated lactic cultures with the use of different additives and vacuum desiccation, using yogurt as model system. Design/methodology/approach: The yogurt was elaborated with commercial lactic cultures (YF-L705 Yo-Flex CHR HANSEN) and whole milk incubated at 42 °C for 4 h. Yogurt was centrifuged at 6,000 rpm/15 min/4 °C. The supernatant was eliminated and with the precipitate, 6 treatments were established by addition of additives: T1, Without additive, T2, Glycerol, T3, Calcium carbonate, T4, Yeast extract, T5, Glycerol, and T6, Glycerol, Calcium carbonate and Yeast extract; non-dehydrated and freeze-dried yogurt was used as control: T7 and T8, respectively. The precipitate of the treatments with additives was dehydrated in a silica gel in a desiccator and under vacuum conditions. The weight loss was recorded at 0, 24, 48, 72 and 96 h. The precipitate with dehydrated additives was used as milk inoculates for yogurt elaboration. The change of pH was recorded at 0, 1, 2, 3, 4, 5, 6, 7, 8 and 24 h. With the pH and the fermentation time, a model was established to present the change curve in fermentation pH and the Fourier transform infrared spectroscopy (FTIR). Results: The drying time to constant weight was 3 days. The fermentation pH change curve was a Boltzman sigmoidal function and analysis of variance was conducted with its parameters to assess the different fermentation speeds of the different treatments. The dehydrated cultures with Yeast Extract and Calcium Carbonate are associated with a higher fermentation activity of the milk (p < 0.05). The yogurts manufactured with fresh cultures take 4 to 5 h to ferment and the dehydrated ones take more than 10 h. The infrared spectra showed that the quality of the yogurts produced with fresh or dry cultures are similar, which agrees with other studies. Limitations on study/implications: The dehydrated inoculated with the additives can be used to make yogurt with similar quality as to when inoculate with fresh culture is used, with the disadvantage of the fermentation time being longer. It is possible that this methodology can be used to dehydrate other inoculates based on lactic bacteria, but their effectiveness would have to be assessed experimentally. Findings/conclusions: This study shows an alternative method to dehydrate lactic bacteria in the laboratory with equipment of relatively easy access for any laborator