Influence of milk heating intensity on consistency of yoghurt

Autor proučava utjecaj intenziteta zagrijavanja mlijeka namijenjenog preradi u jogurt na konzistenciju tog proizvoda. Radna hipoteza temelji se na pretpostavci da intenzivnije zagrijavanje mlijeka pozitivno utječe na konzistenciju i kvalitetu jogurta koagulacijom bjelančevina sirutke. U pokusnoj se proizvodnji, u industrijskim uvjetima, koristilo isto sirovo zbirno mlijeko. Deset skupina uzoraka jogurta proizvedeno je od ukupno 100 000 litara sirovog mlijeka. Svaki se uzorak sastojao od po 10 000 litara homogeniziranog (150 bar/65 °C), pasteriziranog (85 °C/20 sekundi) i standardiziranog (2,8% masti) mlijeka kome je dodano 1% obranog mlijeka u prahu. Svaki je uzorak mlijeka podijeljen na četiri jednaka dijela, pa je prvi dio grijan do 85 °C, drugi do 90 °C, treći do 95 °C i četvrti do 100 °C i to 5 minuta. Zatim se mlijeko ohladilo do 45 °C, inokuliralo s 3% kulture za jogurt, prelilo u čašice, zatvorilo i prenijelo u komoru za zrenje (43 °C). Zrenje je jogurta prekinuto naglim hlađenjem. Viskozitet uzoraka jogurta određen je prvog, trećeg i sedmog dana poslije proizvodnje i skladištenja u hladnjači u jednakim uvjetima. U pravilu se viskozitet jogurta povećavao od prvog do sedmog dana i bio to veći što se intenzivnije zagrijavalo mlijeko u doba pripreme. Razlike viskoziteta jogurta sve četiri skupine uzoraka i sva tri razdoblja starosti većinom su bile signifikantne. Rezultati istraživanja i statističke obrade podataka potvrdili su pretpostavku da intenzitet zagrijavanja mlijeka utječe na konzistenciju i kvalitetu jogurta.The study refers to the influence of heat treatment intensity of milk used for making yoghurt on its consistency. Working hypothesis implied that milk heating intensity had positive influence on yoghurts consistency and quality due to coagulation of whey proteins. The same raw, bulk milk was used in experiments carried out under industrial conditions. For production of ten groups of yoghurt samples 100 000 litres of raw bulk milk was used. Each sample consisting of 10 000 litres of homogenized (150 bar/65 °C), pasteurized (85 °C/20 seconds) and standardized milk to a finished milk fat content of 2.8 % and added 1 % of nonfat milk powder, was divided in four parts, each part was heated to 85 °C, 90 °C, 95 °C and 100 °C during 5 minutes. Milk was cooled to 45 °C, inoculated with 3% of yoghurt culture, and incubated in incubating room (45 °C). Viscosity of yoghurt samples was determined the first, the third and the seventh day after production and storage in cold room under the same conditions. As a rule, viscosity of yoghurt increased from, the first to the seventh day after making. This increase followed the intensity of milk heating. Differences in viscosity of yoghurt were usually significant. Results of investigation and statistical data confirmed the working hypothesis that intensity of milk heating influence consistency and quality of yoghurt