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

Resumen

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 laboratory