Yogurt characteristics as effected by added lactose
Enrichment of yogurt with lactose addition may increase growth of the yogurt starter culture (Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus) and enhance yogurt physico-chemical and sensory attributes. The objectives of this study were: to determine the influence of added lactose on (1) the growth of the yogurt starter culture during yogurt´s shelf life, (2) the physico-chemical characteristics of yogurt during shelf life, (3) the final lactose content of yogurt during its shelf life, and (4) the sensory attributes of yogurt. Fat free plain set-type yogurt was manufactured using 0, 1, 3 and 5% w/w added lactose to accomplish objectives 1, 2 and 3. For objective 4, a blueberry yogurt was manufactured using the same lactose levels. Analyses for plain set-type yogurt were done at 7 days intervals during 35 days of storage period. Three replications were conducted. Sensory evaluation was conducted by 100 consumers of yogurt on day 3 of its manufacture. Data were analyzed using Proc Mixed model of SAS® 9.3 program. Significant differences between means were analyzed at α = 0.05 using Tukey adjustment. Addition of lactose to yogurt at 5% w/w significantly increased growth of Streptococcus thermophilus ST-M5 but had no effect on growth of Lactobacillus bulgaricus LB-12. Lactose added at 5% w/w showed significantly the highest lactose content during entire storage period as expected, the lowest pH values, and also the highest syneresis values over storage period of 35 days. Lactose addition had no effect on appearance and color of blueberry yogurt. Samples containing added lactose showed significantly higher scores for taste, sourness and sweetness. Lactose added at 3 and 5% w/w had significantly the highest overall liking scores. Acceptability of yogurts and purchase intent markedly increased with the addition of lactose. Added lactose in yogurt manufacture favorably influenced some attributes of yogurt.
Keywords: added lactose, yogurt, probiotic properties, starter culture, lactic acid bacteria