Greek strained yogurt is produced in high quantities worldwide. This production leaves behind acid whey, a by-product that is an environmental challenge. Hence, efforts are made to minimize the acid whey generation. In this study, the combined effect of the different heat treatment levels of milk and the different time of straining on the composition of the produced strained yogurt, as well as on the quantity and composition of the expelled acid whey, was investigated. The initial yogurts were prepared with bovine milk heated at 85 °C/16 s or 100 °C/16 s or 90 °C/5 min, and the acid whey was removed by centrifugation (5500 rpm, 5 min, 25 °C) either immediately after incubation or after 24 h. The results showed that, regardless of the heat treatment of milk, straining after 24 h resulted in an 8% increase in the yield in strained yogurt and about an 11% decrease in the generated acid whey, compared to straining immediately after incubation. The heat treatment level of milk significantly influenced the fat, lactose, and total solids contents of the strained yogurts, as well as the residual whey proteins, protein, and total solids contents of acid whey. Yogurt's sensory properties were not affected significantly. It was concluded that the quantity of the acid whey expelled during the production of Greek strained yogurt could be decreased without affecting the general quality of the yogurt.
Keywords: Greek yogurt; acid whey; milk heat treatment; yogurt centrifugation.