Physico-Chemical, Microbiological and Sensory Characteristics of Yogurt as Affected by Added Lactose

Abstract

Enrichment of yogurt with lactose addition may increase the 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 the 1) physico-chemical characteristics, including the final lactose content of yogurt, during its shelf life; 2) growth of the yogurt starter culture over yogurt shelf life and 3) 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 and 2. For objective 3, a blueberry yogurt was manufactured using the same lactose levels. Analyses for plain set-type yogurt were conducted at 7 days intervals during 35 days of storage. Sensory evaluation was conducted on flavored yogurt three days after 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. Lactose addition influenced some of the yogurt characteristics in a positive manner. Lactose contents of yogurts with lactose added at 1%, 3% and 5% stayed higher in that proportion than control throughout the 35 days of storage. Yogurts containing 5% w/w added lactose had the lowest pH. Yogurts containing 5% w/w added lactose had significantly the highest syneresis values compared to 0%, 1% and 3% w/w added lactose during storage period at day 7 and from day 21 onwards. Use of 5% w/w added lactose resulted in significantly higher counts of Streptococcus thermophilus compared to control and this bacterial survival was the highest for 1% w/w added lactose compared to the rest. The overall liking scores indicated that yogurts containing added lactose were preferred over control. For taste, sourness and sweetness samples containing added lactose had higher scores than control. The consumer acceptability of yogurts increased as lactose addition increased. The acceptability of yogurts and purchase intent frequency scores markedly increased with the addition of lactose.