We investigated sonication as a pre-processing step to reduce acid whey generation during Greek yoghurt manufacture. The generation of a large amount of acid whey during the production of Greek yoghurt is an ongoing problem in the dairy industry and many studies are currently focusing on reducing it. We focused on the use of ultrasonication as a novel approach to minimize the casein fraction in the acid whey stream and simultaneously improve the gel properties. Ultrasound applied before the fermentation modified the structural properties and bonding behaviours of milk proteins, and enhanced the retention of casein in the yoghurt gel after the fermentation and straining steps. Therefore, the use of low-frequency ultrasonication as a pre-processing step may have the potential to provide significant economic benefits to the Greek yoghurt manufacturing process. Moreover, it improved the nutritional and physicochemical properties compared to regular Greek yoghurts.

Greek yoghurt, a popular dairy product, generates large amounts of acid whey as a by-product during manufacturing. Post-processing treatment of this stream presents one of the main concerns for the industry. The objective of this study was to manipulate initial milk total solids content (15, 20 or 23 g/100 g) by addition of milk protein concentrate, thus reducing whey expulsion. Such an adjustment was investigated from the technological standpoint including starter culture performance, chemical and physical properties of manufactured Greek yoghurt and generated acid whey. A comparison was made to commercially available products. Increasing protein content in regular yoghurt reduced the amount of acid whey during whey draining. This protein fortification also enhanced the Lb. bulgaricus growth rate and proteolytic activity. Best structural properties including higher gel strength and lower syneresis were observed in the Greek yoghurt produced with 20 g/100 g initial milk total solid compared to manufactured or commercially available products, while acid whey generation was lowered due to lower drainage requirement.