Influence of selected factors on the viscosity of set style yogurt and acid casein gel at constant speed of spindle rotation

The influence of milk dry matter (DM) content (8.20%, 9.27% and 10.28%) and applied heat treatments (untreated milk and milk heat-treated at 90oC/10?) on the viscosity of set-style yogurt and acid casein gel gained by acidification with GDL (glucono-d-lactone) has been investigated. Viscosity was measured during the time of 3 minutes at constant speed of spindle rotation of 20 rpm. The results have shown that yogurt samples produced from untreated milk had higher viscosity values than samples produced from heat-treated milk. An increase of dry matter content influenced the increase of viscosity of yogurt samples produced from both untreated milk and heat-treated milk. Samples with 10.28% DM had the highest viscosity values. An increase of DM content in samples of acid casein gel produced by acidification with GDL had an opposite influence. The samples with smallest DM content had the highest viscosity values. There is no linear relationship between the period of storage of set-style yogurt produced from heat-treated milk and viscosity value. Istrazivanja su obuhvatila uticaj suve materije mleka (8.20%, 9.27% i 10.28%) i primenjenih termickih tretmana (termicki netretirano mleko i termicki tretirano mleko na 90oC/10 min) na viskozitet cvrstog jogurta i kiselog kazeinskog gela dobijenog acidifikacijom pomocu glukono-?-laktona (GDL-a). Viskozitet je odredjivan tokom vremena pri brzini rotacije vretena od 20 o/min u toku 3 minuta. Rezultati su pokazali da su uzorci cvrstog jogurta proizvedeni od termicki netretiranog mleka imali vece vrednosti viskoziteta od uzoraka proizvedenih od termicki tretiranog mleka. Povecanje sadrzaja suve materije mleka utice na povecanje viskoziteta uzoraka cvrstog jogurta proizvedenih od termicki netretiranog mleka i termicki tretiranog mleka. Najvece vrednosti viskoziteta imali su uzorci sa 10.28% suve materije. Kod uzoraka kiselog kazeinskog gela proizvedenih acidifikacijom pomocu GDL-a uticaj povecanja suve materije mleka je suprotan. Uzorci sa najmanjim sadrzajem suve materije imaju najvece vrednosti viskoziteta. Nije utvrdjena linearna zavisnost izmedju duzine perioda skladistenja i vrednosti viskoziteta cvrstog jogurta proizvedenog od termicki tretiranog mleka.