Viscosity of set-style yogurt as influenced by heat treatment of milk and added demineralized whey powder

• Main Authors: Đurđević-Denin Jelena D., Maćej Ognjen D., Jovanović Snežana T.
• Format: Article
• Language: English
• Published: University of Belgrade - Faculty of Agriculture, Belgrade 2002-01-01
• Series: Journal of Agricultural Sciences (Belgrade)
• Subjects: demineralized whey powder; skim milk powder; heat treatment; viscosity; set-style yogurt
• Online Access: http://www.doiserbia.nb.rs/img/doi/1450-8109/2002/1450-81090201045D.pdf

Skim milk powder was reconstituted to obtain milk A (with 8.44% TS). Milk sample A was standardized with different amounts of demineralized whey powder (DWP) to obtain milk B (with 9.71% TS) and milk C (with 10.75% TS). Milk samples were heat treated at 85ºC/20 min and 90ºC/10 min, respectively. Untreated milk was used as control. Milk samples were inoculated with 2.5% of commercial yogurt culture (containing Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus in the ratio 1:1) at 43ºC. Samples were incubated until pH 4.6 was reached. Samples were immediately cooled to 4ºC and held at that temperature until analyses. Measurements of viscosity were done with Brookfield DV-E Viscometer. Spindle No 3 at 20 rpm was used for all samples. After 1 day of storage, set-style yogurt samples produced from untreated milk had the highest, while samples produced from milk heat treated at 90ºC/10 min the smallest initial viscosity, regadless of the dry matter content and composition. Average viscosity of set-style yogurts decreased with intensifying temperature of applied heat-treatment. During storage, set-style yogurt samples produced from milk heat treated at 90ºC/10 min had the least pronounced decrease of viscosity during shearing. After 14 days of storage, set-style yogurt samples produced from milk standardized with demineralized whey powder had higher viscosity than samples produced from basis milk.