Influência da técnica de semeadura e da atmosfera de incubação nas contagens de lactobacilos em iogurtes naturais

Abstract

Natural yogurts are obtained from the fermentation of milk by the action of two lactic bacteria added as starter cultures: Streptococcus thermophilus and Lactobacillus bulgaricus. The consumption of these microorganisms in yogurts can confer health benefits, provided they are ingested in adequate quantities (minimum:107 CFU/g). Due to this requirement, there are numerous researches on monitoring the viability of lactic bacteria during the refrigerated storage of yogurts. Although there is a standardized methodology to perform counts of these microorganisms, there are many studies that adopt variations in this method, including changes in incubation atmosphere conditions and seeding technique. Thus, the objective was to verify if there is a difference between the counts of lactobacilli in natural yogurt in different seeding techniques and incubation atmosphere. For this, the count of L. bulgaricus was performed using the MRS agar by varying the seeding technique (surface, depth and depth with coverage) and the incubation atmosphere (aerobic and microaerophilic). In addition, the pH and acidity of the samples were also checked. Based on the results, the analyzed brands met the requirements of the legislation regarding the acidity limits, ranging from 1.03 to 1.35%. The pH ranged from 3.76 to 4.45, being within the limits recommended in the literature. As for the counts, the results ranged from 5 to 8 log CFU/g in the different seeding techniques and from 6 to 8 log CFU/g in the two incubation atmospheres. Therefore, it was possible to conclude that the lower the oxygen exposure, the better the recovery of lactobacilli, evidenced in the counts or the size of the colonies. Furthermore, the incubation applying the deep seeding technique in aerobiosis proved to be effective, since it did not show significant difference when compared to microaerobiosis.