Metin Atamer

Effects of lactoperoxidase and hydrogen peroxide on rheological properties of yoghurt

The effects of activation of the lactoperoxidase (LPO) system by H2O2-NaSCN and hydrogen peroxide (H2O2) on the accessibility of sulphydryl groups (SH) in skimmed milk, and on the dynamic rheological properties of the resulting yoghurt were investigated. Four different concentrations of each reagent (20-80 mg H2O2-NaSCN/kg milk and 100-400 mg H2O2/kg milk) were compared. Clear negative correlations were noted between the accessibility of SH groups and both LPO activation rate and H2O2 concentration. Also the native PAGE pattern of the heat-treated samples showed that with increase in the H2O2-NaSCN and H2O2 concentrations, the level of interaction between beta-lactoglobulin (beta-lg) and kappa-casein (kappa-CN) decreased. The complex modulus (G*) of skimmed milk yoghurts declined gradually with the decrease in the concentration of accessible SH groups accordingly. Tan delta values of yoghurt samples were found to be different from the control, but close to each other, indicating that protein interaction forces taking place in the formation of gel networks of treated yoghurts were different from the control.

Effects of season on vitamins A and E contents and colour of Turkish butter

Butter is a product that consists of roughly the same constituents asmilk, but their distribution is different. In buttermaking, the fat contentof the milk is concentrated approximately 20 times. Milk and butter aregood sources of the fat solublevitamins A, D and E.Vitamin A (retinol) is a primary alcohol derivative of a polymer con-sisting of four isoprene units. Vitamin A is present in cow’s milk as reti-nol, retinol esters and carotenes. The content of vitamin A dependsstrongly on the amount of carotenoids in the feed. The ratio of retinol tocarotene in cow’s milk varieswith breed [1–3].Vitamin E consists of a group of tocopherols. The most potent ofthese and the principal one in milk is alpha-tocopherol. This is a strongreductant and serves as an antioxidant protecting lipids from oxidation.It is stable to heat but may be partly destroyed by intensive illuminationin the presence of O

Yayik Butter Profiles from Different Species of Mammals’ Milk

Yayik butter is one of the traditional dairy products of Turkey. The type of milk used in the manufacture of Yayik butter is one of the most important parameters determining the characteristics of the end product. The present study investigated the effects of different milk species (cow, sheep, goat) on some properties of Yayik butters made from yogurts produced using milks of these species. While the sheep Yayik butter had the highest value of lactic acid, the goat Yayik butter had a significantly higher peroxide value than those of cow and sheep Yayik butters, indicating weaker oxidative stability. The accumulation of free fatty acids was highest in goat Yayik butter. On the first day of storage, the use of different milk species did not have any effect on sensory properties of Yayik butters, but some flavor defects in goat Yayik butter were perceived on day 30.