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.

The objective of the study reported in this Research Communication was to investigate the effects of pectin and whey protein concentrate (WPC) on the generation of acid whey during Greek-style yogurt (GSY) processing. Yogurt samples were prepared using pectin (0·05%, w/v) and whey protein concentrate (WPC-80) (1%, w/v) as possible ingredients that reduce the acid whey production. Control yogurt sample was prepared without addition of these ingredients. The results showed that yogurt made with pectin plus WPC had significantly higher water holding capacity (~56%) than the control (33%). Similarly, yogurt supplemented with pectin plus WPC exhibited 15% less susceptibility to syneresis compared to the control (P < 0·05). Viability of L. bulgaricus and S. thermophilus in all yogurts remained ≥7·0 and ≥8·0 log CFU/g respectively. Native PAGE analysis showed an interaction between pectin and WPC. Pectin hinders the formation of large oligomeric aggregates of whey protein which correlates with an increase in WHC and a decrease in syneresis. Our results demonstrated that a combination of pectin and WPC have the potential to limit the quantity of acid whey generation in GSY manufacturing. Thus, these ingredients have positive implications for dairy industry in the production of GSY.

Contradictory statements about the effects of pH change on crystallisation behaviour of lactose exist in the literature. Considering the importance of addressing the processability issue of acid whey, a systematic study is required to establish lactose crystallisation behaviour in the presence of LA and Ca at concentrations present in real acid whey waste streams emphasising impact of pH. Structural modifications of lactose were evident at elevated, more neutral pH in the presence of 1% w/w LA and 0·12% w/w Ca. These structural changes led to changes in the anomeric equilibrium of lactose, which manipulated the water–lactose behaviour and increased the crystallinity. Therefore, altering pH to 6·5 may be the solution to proper industrial processing of acid whey, enhancing the ability of lactose to crystallise properly.

Two types of diet – standard and atherogenic – were used to study the effect of wheat or wheat–rye breads supplemented with 20 % acid whey concentrate after ultrafiltration on the physiological response of growing rats. The acid whey concentrate after ultrafiltration used in rat diets caused reduced weight gain (for atherogenic diet with wheat bread); growth of caecum tissue and digesta weight; a decrease in the pH of caecum digesta (for atherogenic diet); reduced activity of bacterial glycolytic enzymes; and a significant increase in total SCFA for both types of diet with wheat–rye breads containing acid whey concentrate. For wheat bread with acid whey, in standard diet, a statistically significant increase was found in the population of bifidobacteria. The results showed that the acid whey concentrates could be used as a valuable food ingredient.

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.

Physical properties of lactose appeared influenced by presence of lactic acid in the system. Some other components such as Ca may further attenuate lactose behaviour and impact its phase transition. A model-based study was thus implemented with varying concentrations of Ca (0·12, 0·072 or 0·035% w/w) and lactic acid (0·05, 0·2, 0·4 or 1% w/w) in establishing the effects of these two main acid whey constituents on lactose phase behaviour. Concentrated solutions (50% w/w) containing lactose, lactic acid and Ca were analysed for thermal behaviour and structural changes by Differential Scanning Colorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR), respectively. Presence of 1% (w/w) lactic acid and 0·12% (w/w) Ca in lactose solution significantly increased the evaporation enthalpy of water, delayed and increased the energy required for lactose crystallisation as compared to pure lactose. FTIR analysis indicated a strong hydration layer surrounding lactose molecules, restricting water mobility and/or inducing structural changes of lactose, hindering its crystallisation. The formation of calcium lactate, which restricts the diffusion of lactose molecules, is also partly responsible. It appears that Ca removal from acid whey may be a necessary step in improving the processability of acid whey.