The influence of dry matter and heat treatment on the viscosity of set-style yogurt produced from reconstituted skim milk powder

Abstract

Skim milk powder was reconstituted in distilled water to obtain reconstituted milk A (8.44% TS), milk B (9.65% TS) and milk C (10.84% TS). The yogurts were produced from untreated milk and milk heat treated at 85°C/20 and 90°C/10 min, respectively. Milk samples were inoculated with 2.5% commercial yogurt culture and incubated at 43°C until pH 4.6 was reached. Viscosity measurements were performed at 20°C after 1, 7 and 14 days of storage at 4°C. Brookfield DV-E Viscometer (spindle No 3 at 20 rpm) was used for measurement. Initial viscosity of yogurt samples produced from milk treated at 85720 were greater, but yogurt samples produced from milk treated at 90°C/10 min showed a smaller decrease of viscosity during time of shearing. Viscosity of stored samples showed the smaller reduction during time of shearing.

Obrano mleko u prahu je rekonstituisano sa destilovanom vodom da bi se dobilo mleko A (sa 8.44% SM), B (sa 9.65% SM) i C (sa 10.84% SM). Ogledi su vršeni sa termički netretiranim mlekom i mlekom termički tretiranom na 85°C/20 min i 90°C/10 min, respektivno. Viskozitet je određivan pomoću viskozimetra Brookfield DV-E, na temperaturi od 20°C, nakon 1., 7. i 14. dana skladištenja. Vrednost viskoziteta je nakon 1. dana skladištenja bila najveća kod uzoraka proizvedenih od termički netretiranih mleka. Početna vrednost viskoziteta uzoraka čvrstog jogurta proizvedenih od mleka termički tretiranih na 85°C/20 min, bila je nešto veća, u odnosu na uzorke proizvedene od mleka termički tretiranih na 90°C/10 min. S druge strane uzorci čvrstog jogurta proizvedeni od mleka termički tretiranog na 90°C/10 min, imali su manje izraženo smanjenje viskoziteta tokom vremena delovanja sile smicanja. Kod uzoraka koji su skladišteni 14 dana, smanjenje viskoziteta je bilo najmanje izraženo.