The influence of GDL concentration on milk pH change during acid coagulation

Abstract

Skim milk powder was reconstituted to obtain milk A (with 8.01% TS). Milk A was standardized with 3% of skim milk powder and 3% of demineralized whey powder (DWP), respectively, to obtain milk B (with 11.15% TS) and milk C (with 11.10% TS). Milk samples were heat treated at 85ºC/10 min, 90ºC/10 min and 95ºC/10 min, respectively. Untreated milk was used as control. Acidification was carried out at 25ºC, 35ºC and 45ºC during 240 min with GDL (glucono-d-lactone), namely with the amount of 0.5%, 0.75%, 1.0%, 1.25% 1.5%, 1.75%, 2.0% and 3.0% of GDL, respectively. The results showed that all investigated factors, explicitly GDL concentration, acidification temperature and applied heat treatment of milk as well as added DWP influence the change of pH during acidification. Milk samples standardized with DWP had smaller buffer capacity and faster change of pH than samples standardized with skim milk powder. Only at acidification temperature of 25ºC, added DWP did not influence the change of milk buffer capacity regardless of the change of casein:whey protein ratio. Under this acidification condition, both milk samples standardized with skim milk powder and DWP had similar final pH values.

Obrano mleko u prahu je rekonstituisano da se dobije mleko sa 8.01% SM (mleko A). Mleko A je standardizovano sa 3% obranog mleka u prahu (mleko B sa 11.15% SM) i sa 3% demineralizovane surutke u prahu (mleko C sa 11.10% SM). Uzorci su termički tretirani na 85ºC/10 min, 90ºC/10 min i 95ºC/10 min respektivno, a kao kontrolno mleko su korišćeni uzorci termički netretiranog mleka. Acidifikacija je vršena pomoću različitih koncentracija GDL-a (glukono-d-laktona) i to 0.5%, 0.75%, 1.0%, 1.25%, 1.5%, 1.75%, 2.0% i 3.0%. Acidifikacija je vršena pri temperaturama 25ºC, 35ºC i 45ºC u vremenu od 240 min. Rezultati su pokazali da promena pH vrednosti zavisi od količine dodatog GDL-a, temperature acidifikacije i primenjenog režima termičke obrade mleka, kao i od dodate demineralizovane surutke u prahu. Uzorci mleka kojima je dodata demineralizovana surutka u prahu imali su manji puferski kapacitet, što je indukovalo brže sniženje pH vrednosti u odnosu na uzorke kojima je dodato obrano mleko u prahu. Jedino pri temperaturi acidifikacije od 25ºC, dodata demineralizovana surutka u prahu nije uticala na promenu puferskog kapaciteta bez obzira na izmenjen odnos kazein:serum proteini. Pri ovim uslovima acidifikacije, uzorci mleka kojima je dodato obrano mleko u prahu i demineralizovana surutka u prahu u istoj količini imali su približno iste krajnje pH vrednosti.