FERMENTATION KINETICS OF YOGURT PRODUCED WITH A2 MILK

Yogurt is one of the most important dairy products worldwide, as it is a healthy and nutritious food, increasingly present in the diet of consumers. With the increase in the production of A2 milk and the dissemination of the various health benefits, to the detriment of A1 milk, the trend is also for growth in dairy products. The objective of this study was to evaluate the fermentation kinetics of yogurt produced with A2 milk, evaluating the multiplication of lactic acid bacteria (LAB), pH and titratable acidity. Three fermentations were carried out, for which we used pasteurized A2 milk with the addition of 7% sugar, the commercial culture of Rica Nata® (Lactobacillus delbrueckii subsp. bulgaricus associated with Streptococcus thermophilus), which was added at 42 °C, and maintained at this temperature until pH 4.6 was reached. During fermentation, pH, titratable acidity and BAL count were measured every 20 minutes for the first two hours and every 30 minutes until pH 4.6 was reached. For the BAB count, serial dilutions were performed in 0.1% peptone water (up to a dilution of 10⁻¹¹), and then seeded on MRS agar (Man Rogosa and Sharpe) and M17 agar (Seg Terzaghi), incubated for 72 hours in microaerophilia. The titratable acidity was expressed in Dornic degrees (°D) and the pH was measured with the aid of a properly calibrated pH meter (MPA-210). After the three fermentation processes, an increase in lactic acid bacteria (LAB) was observed over the course of fermentation (the average initial LAB count was 6.11 log CFU/mL, reaching 12.12 log CFU/mL at the end), accompanied by a gradual decrease in pH due to lactose consumption (average initial pH of 6.6 and final pH of 4.6), and consequently, a progressive increase in titratable acidity (initial average of 15 and final of 58 °D). The fermentation processes lasted between 4 hours and 30 minutes and 5 hours. The increase in LAB populations, the decrease in pH, and the rise in titratable acidity in the yogurt produced with A2 milk followed the expected pattern for traditional fermentation. Based on these results, it can be confirmed that the fermentation kinetics of yogurt processed with A2 milk are within the expected standards, promoting LAB growth, acidification of the medium, and thereby resulting in the desirable characteristics of yogurt.