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The use of gases in different food applications has increased in the last decades. The incorporation of hydrogen into yogurt was reported to improve the organoleptic properties of some dairy products. A study is needed to understand the effect of this application on the behavior of yogurt bacteria during the fermentation stage. The effects of H2- and N2-incorporation into milk on the acidification and reducing capacities of Lactobacillus delbrueckii subsp. bulgaricus (LB) and Streptococcus thermophilus (ST) were envisaged. A data acquisition multiparameter interface equipped with pH and redox electrodes was used for continuously measuring and recording values. H2 increased the acidification capacity of ST (+10%) and the reducing capacity of LB (+13.7%), whereas N2 increased the acidification capacity of ST (+13.3%) and decreased the reducing capacity of LB (-21.47%) and ST (-18.88%). H2 increased the coagulation time of LB (+12.96%) and ST (+6.15%). Results could reveal the promotive role of hydrogen on the metabolic activity of yogurt bacteria in single cultures and these bacteria grow better in the presence of hydrogen in milk. These results will allow yogurt manufacturers to better understand the behavior of yogurt bacterial strains when the preparation of gas-incorporated yogurt is envisaged and better control its quality attribute notes. [ABSTRACT FROM AUTHOR]

The acidification and reducing capacities of yoghurt bacteria were evaluated in different plant extract‐enriched milk samples. The milk samples enriched with thyme and grape seed extracts exhibited the highest values of acidification capacity for Lactobacillus delbrueckii subsp. bulgaricus (LB) (0.0065 pH unit/min) and Streptococcus thermophilus (ST) (0.0068 pH unit/min). The highest values of reducing capacity were observed in thyme (−0.98 mV/min), grape (−1.92 mV/min) and green tea (−0.75 mV/min)‐enriched samples for LB, ST and mixed culture of LB + ST, respectively. The fortification of yoghurt with plant extracts modified the acidification and reducing activities of starters, thus changing the fermentation time and quality attributes of the product. [ABSTRACT FROM AUTHOR]