Changes in isoflavones concentrations in cheese during processing and ripening

The aim of the study was to determine possible changes in isoflavones concentration in cheese made from either control or isoflavone-enriched milk during manufacturing and ripening. The experiment was carried out on four high-yielding lactating Holstein cows that were divided into two groups with similar mean milk yield. The control group of cows was fed a diet based on extruded rapeseed cake (C) while the experimental group of animals was fed a diet based on extruded full-fat soya (S). The experiment was carried out in the form of a cross-over design and was divided into 2 periods of 14 days (a 10-d preliminary period and a 4-d experimental period). Cows were fed individually twice daily ad libitum the diet based on maize silage, lucerne hay and supplemental mixture. In each period 20 kg of morning milk was collected from each group for cheese processing. After pasteurisation (65 °C, 30 min.) a total of 5 kg of milk from each sample in each period was weighed out to make cheese with a low-heated curd. Cheeses were salted in 20% solution of NaCl for 3.5 h and allowed to ripen for 90 days at 15 °C. During technological processing samples were taken to determine isoflavones content. Data concerning the nutrients intake, milk yield and concentration of isoflavones were analysed by means of multifactor analysis of variance using the GLM procedure of the Statgraphics 7.0 package. Average daily isoflavones intake in S (1284.7 mg/d) was higher than in C (2.9 mg/d, P < 0.001). Milk yield expressed in 4% FCM did not differ significantly between groups (P > 0.05). Concentration of daidzein, genistein and glycitein in pasteurised full fat milk was similar in both groups. Milk from S group had higher concentration of equol (26.7 µg/L) in comparison to C group (4.0 µg/L). After processing cheese in C contained 32.1 µg/kg daidzein and 5.6 µg/kg of equol while cheese in S contained 17.5 µg/kg of daidzein and 24.3 µg/kg of equol. During a 90-day ripening percentage decrease in isoflavones concentration was lower in S than in C. Concentration of daidzein was reduced by 47% in C and 37% in S. Concentration of genistein decreased by 51% in C and 31% in S, concentration of glycitein by 46% in C and 29% in S and concentration of equol by 50% in C and 38% in S.