عنوان مقاله [English]
Background and objective: Strained or concentrated yoghurt is a traditional milk product that its popularity and consumption has increased during recent years due to its higher nutritional value, longer shelf life, desirable textural and sensory properties, and today it is widely produced industrially. This product can be produced from many different animal milks such as buffalo, cow, goat, ewe and camel. The milk of various animals differs in composition and therefore this factor can affect the characteristics of the final product. Identical to the other dairy products, strained yoghurt manufactured from buffalo milk has the higher quality than those produced from cow milk due to the higher total solids and fat content; but its utilization has limited because of its higher cost. Transglutaminase enzyme (TG), by createing inter- and intra-molecular cross linkages among proteins is known as an effective strategy to improve the functional properties of dairy products. TG treatment has been considered as a practical technique instead of increasing the total solids of utilized milk (by adding skim milk powder). Therefore, the aim of this study was to investigate the effect of TG enzyme treatment on physicochemical and sensory properties of strained yoghurt prepared from cow and buffalo milk mixture and to introduce the best product with the lower buffalo milk substitution (the lower of cost).
Materials and methods: Strained yoghurt samples with different amounts of buffalo milk replacement with cow (0, 25, 50, 75 and 100%, v/v) and using TG enzyme (0 and 0.015%, w/v) were produced and 10 experimental treatments evaluated for physicochemical (pH, acidity (% lactic acid), syneresis (%) and dry matter (%)) and sensory properties (texture, colour, odour and flavour) during 21 days of storage (1, 7, 14 and 21 days) under refrigeration conditions. The obtained mean values were analyzed using a random factorial design and compared by Duncan test at 5% level.
Results: The results showed that increasing the substitution amount of buffalo milk with cow milk caused a significant increase in acidity and dry matter while it expressively reduced the pH and syneresis of yoghurt samples (p<0.0001). Also, with increasing the TG enzyme concentration, the amount of acidity and syneresis decreased and the pH increased significantly (p<0.0001), but this variable had no significant effect on dry matter (p>0.005). Over time, the pH decreased significantly and its initial value of 4.11 at the first day of storage reached to 3.98 at the end of 21 days of storage. The initial values of acidity, dry matter and syneresis as 0.98%, 20.69% and 4.45% increased till the end of storage and reached to 1.23%, 22.16% and 10.35%, respectively. In terms of sensory acceptability, increasing the concentration of enzyme caused a significant increase in texture score of the samples (p<0.0001), while the enzyme had no significant effect on other sensory scores of the samples. With increasing the mixing rate of buffalo milk, the texture, colour and flavour scores of the samples increased significantly (p<0.0001) and the aroma score decreased (p<0.0001). Furthermore, during the storage period, the sensory properties of the samples decreased significantly (p<0.0001).
Conclusion: According to the results of this study, by replacing 75% of buffalo milk with cow milk and using transglutaminase enzyme treatment (0.015%), it is possible to produce a strained yoghurt with suitable quality characteristics.