Efeito do uso de ultrassom na viabilidade das culturas tradicionais do iogurte e culturas probióticas.

Abstract

Emerging technologies such as High-Intensity Ultrasound (HIUS) have been applied to foods, in addition to achieving effects such as microbial inactivation, but also, at sublethal levels, to cause changes in the fermentation process of microorganisms, such as Lactic Acid Bacteria. (BAL) and optimize your metabolic activities. To have this effect, it is necessary to understand the factors that can impact the proportion of HIUS treatment in different products, such as the physical, biological or morphological properties of each microorganism, as well as the process parameters and type of food matrix. Therefore, this study sought to evaluate the effect of HIUS on fermentation time on the microbial viability of the following Fermented Milks (LF): yogurt (only with the protosymbiotic culture of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus), a fermented milk containing only Lactobacillus acidophilus La 5, and a third yoghurt co-culture product plus Lactobacillus acidophilus La 5. Three different Energy Densities (DE) were used to sonicate each product in the bath (0.08, 0.26 and 0.08 J.mL-1 in the bath and another three DE of 1600, 640 and 200 J.mL-1 in the probe, in both equipment with the samples submerged in a temperature bath of 10 and 25°C. All samples treated with HIUS in the bath did not show significant effects between them and compared to the control. But using the probe, the LF with the yogurt culture alone had its fermentation time reduced with the energy density of 640 J.mL-1 while fermented milk containing only Lactobacillus acidophilus La 5 with the probe also had its final fermentation time reduced using the energy density of 200 J.mL-1. The LF containing the yogurt culture and the probiotic culture had its final fermentation time increased in the samples treated with ultrasound. The HIUS application temperatures did not differ, therefore, the temperature of 25°C would be the most indicated for the treatment with DE of 640 J.mL-1 in the LF only with the traditional culture of yogurt and with DE of 200 J.mL-1 in the LF with the culture traditional yogurt and probiotic culture, for saving more energy resources to have a cold chain at this stage. Thus, predictive microbiology was used to evaluate the effect of HIUS on LAB metabolism in fermented milks, this time using only the probe and sonication temperature of 25°C. The samples that performed faster in the fermentation showed an increase in the microbial growth rate, in these cases it can be related to an increased LAG (adaptation period of the microorganism in hours) phase. However, the fermented milk containing the yogurt culture and the probiotic culture showed lower microbial concentrations at the beginning of fermentation than the control samples, indicating that HIUS inactivated some cells, which were unable to compensate and excel in metabolism. Therefore, it becomes more interesting to apply the ultrasound separately to fermented milks only with traditional yogurt cultures or only with Lactobacillus Acidophilus La 5 using the DE of 640 and 200 J.mL-1 respectively at 25°C in the probe.