Effect of Ultrasound on the Microbial Flora and Physicochemical Parameters of Yogurt Added to Native Mexican Plants

There is a growing trend in food fortification to use natural products to improve quality during production and processing. We study the effect of high-intensity ultrasound (HIU), applied at different processing times to fresh raw cow's milk supplemented with dried plant material (DPM), on the gel fermentation kinetics and the physicochemical profile of yogurt during storage. The results showed a significant reduction in milk fermentation with the application of HIU after inoculation (INOC). The counts of <i>Lactobacillus delbrueckii</i> ssp. <i>bulgaricus</i> and <i>Streptococcus thermophilus</i> increased with the use of HIU, producing a synergistic effect in the presence of DPM due to the phenolic acids and flavonoids present. Syneresis was reduced and the water holding capacity (WHC) significantly increased in gels obtained with milk to which DPM had been added and which was sonicated after INOC. This led to the formation of a denser and more homogeneous protein network that retained more serum during storage. The luminosity of gels produced with milk sonicated at 40 °C increased, improving their appearance. However, saturation was reduced, shifting the yellow color to a neutral hue. In gels produced with non-sonicated milk, the fat separated, forming a yellow upper layer. HIU applied after INOC in milk to which DPM had been added reduced the milk processing time, producing stable and better-quality yogurts during refrigerated storage.