Properties of co-precipitates obtained by different acids and distribution of milk nitrogen matter

Abstract

For the production of co-precipitates, skim milk (0.05 % milk fat) was used. The chemical complex between casein and whey protein was formed by heating of milk at 87°C during 10 min, and at 95°C during 20 min, respectively. The pasteurised milk (80-85°C during 20 sec) was used as a probe. Co-precipitates were obtained from heat-treated milk by coagulation with 2.8 M HC1, 1.4 M H2SO4, 2.8 M lactic and 2.8 M acetic acids, respectively. Co-precipitates obtained by acetic acid were rather dry, lax and white, while co-precipitates obtained by H2SO4 and HC1, respectively, were a little sticky, compact and had pronounced yellow undertone. Co-precipitates obtained by lactic acid were compact and softer, probably due to higher moisture content (67.32%). As a measure of recoveries of milk nitrogen matter into co-precipitates, sera nitrogen content was used. Milk sera obtained by separation of co-precipitates, had a little nitrogen matter content, regardless of the acid used (0.0440% for HC1; 0.0465% for H2SO4; 0.0500% for acetic acid and 0.0464% for lactic acid). Nitrogen matter that remained in sera represents non-protein nitrogen, which represents 4-6% of total nitrogen matter of milk. Utilisation of nitrogen matter was greater when milk was treated at 87°C during 10 min than by pasteurisation of milk. Co-precipitates obtained from heat treated milk (87°C; 10 min) by HC1 had 11.61%. Co-precipitates obtained from pasteurised milk had 11.38% nitrogen matter. Nitrogen matter utilisation was greater when lactic acid was used (11.62%). .

Za dobijanje koprecipitata korišćeno je obrano mleko sa 0.05 % mlečne masti. Hemijski kompleks između kazeina i serum proteina obrazovan je zagrevanjem mleka na 87°C u toku 10 min, i na 95°C u toku 20 min. Kao referentni uzorak korišćeno je pasterizovano mleko (80-85°C, 20 sec). Koprecipitati su dobijeni koagulacijom tehnički tretiranog mleka pomoću 2.8 M HCl, 1.4 M H2SO4, 2.8 M mlečne i 2.8 M sirćetne kiseline. Koprecipitati dobijeni pomoću sirćetne kiseline bili su suvi i rastresiti, bele boje, dok su koprecipitati dobijeni pomoću HC1 i H2SO4 bili malo lepljivi, kompaktni, sa izraženom žućkastom nijansom. Koprecipitati dobijeni pomoću mlečne kiseline bili su kompaktni, mekši i imali su najveći sadržaj vode (67.32%). Kao merilo prelaska azotnih materija iz mleka u koprecipitate korišćen je sadržaj azota u mlečnom serumu. Mlečni serum posle izdvajanja koprecipitata imao je mali sadržaj azota, bez obzira na korišćenu kiselinu (0.0440% za HC1; 0.0465% za H2SO4; 0.0500% za sirćetnu i 0.0464% za mlečnu kiselinu). To znači da azotne materije koje su zaostale u serumu predstavljaju praktično neproteinski azot, koga prema literaturnim podacima ima 4-6% u odnosu na ukupne azotne materije mleka. Istraživanja su pokazala da se zagrevanjem mleka na 87°C u toku 10 min postiže znatno veće iskorišćenje azotnih materija mleka u obliku koprecipitata dobijenih pomoću HC1 (11.61%), nego kod pasterizovanog mleka (11.38%) i da je ono nešto veće kada se koprecipitati dobijaju koagulacijom pomoću mlečne kiseline (11.62%).