Influence of different acids on ph changes of heat-treated skim milk with formed complex casein/whey protein

Abstract

The skim milk has been subjected to high heat treatment (95ºC during 20 min) to form chemical comples between caseir and whey proteins (coaggregates of milk proteins). Influence of the addition of two organic (lactic and acetic) and two inorganic (HCl and H2SO4) acids on the rate of pH changes of heat-treated skim milk and formation of co-precipitates have been investigated. Addition of 7 ml HCl and about 7,2 ml H2SO4 respectively, reduces pH of heat-treated skim milk to 4,6. The buffer capacity of skim milk is lower in relation to these acids, when pH decreased below 4,5. On the other hand, lactic and acetic acids indicated sigfiicantly slower pH reduction of heat-treated skim milk. The milk buffer capacity to these acids is particularly significant below pH 5,0. At pH below 4,85 buffer capacity is greater to acetic than to lactic acid. Titration curves become parallel with abscise milk buffer capacity is greatest in this pH region to these acids. For production of co-precipitates, all four acids can be used, but when HCl is used, produced coprecipitates have two most important parameters necessary for application of co-precipitates, the smallest level of calcium the best solubility. .

Ispitivan je uticaj 2,8M HCl, 1,4 M H2SO4, 2,8 M CH3CHOHCOOH i 2,8 M CH3COOH na brzinu promene pH vrednosti obranog mleka kod kojeg je zagrevanjem na 95ºC u toku 20 minuta obrazovan hemijski kompleks između kazeina i serum proteina (koagregati proteina mleka). Već sa dodatih 7 ml HCl i nešto više od 7 ml H2SO4 postignuta je pH vrednost od 4,6. Ispod pH vrednosti 4,5 puferni kapacitet mleka prema ovim kiselinama je bio slabije izražen. CH3COOH i CH3CHOHCOOH znatno sporije snižavaju pH vrednost mleka u poređenju sa HCl i H2SO4. Puferni kapacitet mleka prema ovim kiselinama naročito je izražen pri pH vrednostima ispod 5,0. Ispod pH 4,85 veći puferni kapacitet sastojaka mleka je prema CH3COOH nego prema mlečnoj kiselini. Pri pH vrednosti nižim od 4,40 za CH3COOH i 4,05 za CH3CHOHCOOH obe krive su u svom daljem toku skoro paralelne sa apscisnom osom, što govori da je puferni kapacitet mleka prema ovim kiselinama u ovoj oblasti pH najveći. U praksi se za proizovdnju koprecipitata mogu koristiti sve četiri kiseline. Hlorovodonična kiselina ima određenu prednost, jer se dobijaju koprecipitati sa manjim sadržajem kalcijuma i imaju najbolju rastvorljivost, što je sa stanovišta prakse i njihove primene veoma značajno. .