Organic acids profiles in lactose-hydrolyzed yogurt with different matrix composition

The composition of the dairy matrix used in yogurt manufacture could influence the metabolic activity of yogurt starter and the compounds produced during fermentation. In this way, the lactose hydrolysis with a beta-galactosidase enzyme and the supplementation with dairy powders to obtain different types of delactosed yogurts for lactose-intolerant people modifies the milk base composition. In this work, we studied the influence of the addition of different doses of beta-galactosidase and levels of dairy powders on organic acids profile during the manufacture and storage of two varieties of yogurt (natural and sweetened). Lactose, glucose, galactose, titratable acidity, fermentation time, and microbiological counts were also evaluated. The mean proportions of lactose/glucose/galactose in relation to the total sugars were 18: 36: 46 in hydrolyzed yogurts, while they were 81: 4: 15 in unhydrolyzed ones. In supplemented yogurts, the content of lactose, citric, orotic, and hippuric acids were significantly increased. The starter population was similar in all yogurts, but some changes in their activity were evidenced due to both factors studied. The fermentation time was slightly increased, and the lactic acid content and the titratable acidity were significantly increased due to fortification while they were decreased by enzyme addition. These results are probably due to the increase in the buffer properties of the milk base by the dairy powder addition and due to an inhibition of the starter activity caused by changes in the carbohydrate profile. The results demonstrated that the changes in the matrix composition of the yogurt affected the organic acids profile, above all the lactic acid content.