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Thanyaporn Kleekayai

University of Limerick, Limerick, Ireland

Heat stability of whey protein hydrolysates generated under pH- and non pH-controlled conditions, and contribution of UHT processing on hydrolysate properties

The growing demand for ready-to-drink beverages has drawn attention to the development of high content whey protein beverages with enhanced functional properties. The aim of this work was to investigate the effect of enzymatic hydrolysis on the technofunctional properties, including the heat stability at 140?C, and the impact of UHT processing on the physicochemical characteristics of whey protein hydrolysates (WPHs). A 10% (w/v, protein) whey protein concentrate (WPC) solution was hydrolysed using a commercially food-grade proteinase preparation at enzyme to substrate (E:S) ratios of 0.5-1.0% (v/w, protein). Hydrolysis was conducted at 50?C for 4 h with the pH controlled at pH 7.0 (ST7) and free-fall pH starting at pH 8.0 (FF8) and 9.0 (FF9). Heat stability was analysed in an oil-bath at 140?C and reported as heat coagulation time (HCT). Enzymatic hydrolysis resulted in a significant improvement (p<0.05) in heat stability comparing to unhydrolysed WPC, with HCT values ranged from 56 to 114 sec and 32 sec for the WPHs and WPC, respectively. Generally, the ST7 WPHs had significantly higher (p<0.05) HCT values than the FF8/9 WPHs. Changing the hydrolysis conditions did not affect the extent of viscosity and turbidity reduction. At similar extents of hydrolysis, the different hydrolysis conditions resulted in different reverse-phase liquid chromatographic profiles. UHT processing (140?C, 3 sec) of the 1.0ST7 WPH led to an increase in turbidity and particle size without gel formation. Homogenisation reduced viscosity, particle size and sediment formation in the UHT treated WPH. In conclusion, enzymatic hydrolysis enhanced the heat stability of whey protein ingredients by preventing gel formation during UHT treatment. Moreover, regulation of pH during hydrolysis modified the peptide profile and therefore the heat stability of WPHs. This study demonstrated that WPHs could be formulated in ready-to-drink protein dense beverage applications.

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