Kemijski sastav i reološka svojstva čvrstog jogurta dobivenog od obranog mlijeka tretiranog peroksidazom iz hrena

The aim of this work is to determine the impact of an enzymatic treatment on the fermentation and rheological properties of set yoghurt prepared from skimmed milk. Skimmed bovine milk was treated with horseradish peroxidase added at the level of 645 U per g of proteins in the presence (addition level of 7.8 mmol per L of milk) or absence of ferulic acid as a cross-linking agent, and used to prepare set yoghurt with commercial direct vat set starter culture. The evaluation showed that the treatment of skimmed milk with horseradish peroxidase enhanced its apparent viscosity, and storage and loss moduli. The prepared yoghurt contained protein, fat and total solids at 3.49–3.59, 0.46–0.52 and 15.23–15.43 %, respectively, had titratable acidity of 0.83–0.88 %, and no significant difference in the composition was found among the yoghurt samples (p>0.05). Compared to the control yoghurt, the yoghurt prepared from the milk treated with horseradish peroxidase had a higher apparent viscosity, storage and loss moduli and flow behavior indices, especially when ferulic acid was added. Yoghurt samples from the skimmed milk treated either with horseradish peroxidase only or with the additional ferulic acid treatment had better structural reversibility, because their hysteresis loop area during rheological analysis was larger (p0,05). U usporedbi s kontrolnim jogurtom, jogurt dobiven od mlijeka tretiranog peroksidazom iz hrena imao je veću prividnu viskoznost, modul pohrane i modul gubitka, te indeks tečenja, naročito nakon dodatka ferulične kiseline. Uzorci jogurta dobiveni od mlijeka tretiranog samo peroksidazom iz hrena ili kombinacijom peroksidaze i ferulične kiseline imali su bolja strukturna svojstva, tj. veću petlju histereze utvrđenu reološkom analizom