Impact of thermal inactivation conditions on the residual proteolytic activity and the viscosity properties of whey protein concentrate enzymatic hydrolysates

The rationale for enzymatically hydrolysis of whey proteins includes enhancement of their technofunctional properties and the release of bioactive peptide sequences. This study investigated the impact of thermal treatments, i.e., heating using a water bath, using a tubular heat exchanger and heating during spray drying, on the residual proteolytic activity (RA), apparent viscosity (eta(app)) and gelation temperature (Tg) of whey protein concentrate hydrolysates (WPH) generated with Alcalase (R) (WPH-Alc), Neutrase (TM) (WPH-Neu) and Debitrase (R) (WPH-Deb). The WPHs generated showed different degrees of hydrolysis (DH, 2.60-11.13%) and chromatographic profiles. Thermal inactivation studies showed different impacts on RA dependent on the thermal treatment conditions. The eta(app) of unheated WPHs were significantly lower (16-18%) than that of the unhydrolysed whey protein concentrate (WPC). Thermal inactivation (80 degrees C waterbath) increased eta(app) of all samples producing aggregates. Tubular heat exchanger inactivation increased eta(app) of WPH-Alc and WPH-Deb at different rates, whereas no significantly changes were observed for WPH-Neu for holding times lower than 10 min. At 45% (w/v) total solids (TS) the viscosity of WPC was 1.0 Pa s, whereas the equivalent viscosity for WPC-Alc and WPHDeb was achieved at 49.5 and 50.1% TS. Different trends were observed in Tg of the WPHs which were dependent on the enzyme and thermal treatment. Overall, this study demonstrates that judicious choice of thermal treatments during WPH enzyme inactivation is required in order to achieve an appropriate balance between RA, eta(app) and Tg.