• Enzymatic Hydrolysis of Heat-induced Aggregates of Whey Protein Isolate

      O'Loughlin, Ian B.; Murray, Brian A.; Kelly, Philip; Fitzgerald, Richard J.; Brodkorb, Andre (American Chemical Society, 26/04/2012)
      The effects of heat induced denaturation and subsequent aggregation of Whey Protein Isolate (WPI) solutions on the rate of enzymatic hydrolysis was investigated. Denaturation of whey proteins was monitored by reversed-phase and size exclusion HPLC and observed by native- and SDS-PAGE. Treated and un-treated WPI solutions (100 g L-1 protein) were hydrolysed to a target degree of hydrolysis (DH) of 5 % with Corolase® PP. Aggregate formation was monitored using light microscopy, with size distribution determined by particle size. Viscosity and surface hydrophobicity exhibited large increases with heat-treatment and the major protein components in WPI showed differences in their rates of aggregation. Results revealed an increased rate of hydrolysis of protein solutions, which were subjected to a pre-hydrolysis heattreatment. Light and Confocal Laser Scanning Microscopy (CLSM) images illustrated the optical clarification of the solution, weakening of the gel network and disintegration of aggregates indicative of hydrolysis. Comparison of samples where there was a heat-treatment prior to hydrolysis and a control non-treated hydrolysis reaction, revealed significant differences in the time to reach 5 %DH (P < 0.001). The heat-treatments ≥ 75 ºC for 5 min produced significantly (P < 0.001) more rapid reactions than the other 5 heat-treatments and the control un-treated reaction. The viscosity, surface hydrophobicity, and insolubility of the heat-treated WPI solutions subsequently declined upon their hydrolysis. The extensive aggregation in some heattreated solutions was postulated to relate to the congruent increased rate of hydrolysis. This study demonstrated that prior thermal treatment of ≥ 75 ºC for 5 min can accelerate the enzymatic hydrolysis reaction of WPI with Corolase® PP.
    • Preparation of modified whey protein isolate with gum acacia by ultrasound maillard reaction

      Chen, Weijun; Ma, Xiaobin; Wang, Wenjun; Lv, Ruiling; Guo, Mingming; Ding, Tian; Ye, Xingqian; Miao, Song; Liu, Donghong; National Key Research and Development Program of China; et al. (Elsevier, 2018-10-18)
      Effect of ultrasound treatment on whey protein isolate (WPI)-gum Acacia (GA) conjugation via Maillard reaction was investigated. And the physicochemical properties of the conjugates obtained by ultrasound treatment were compared with those obtained by classical heating. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis, high-performance size exclusion chromatography and fourier transform infrared spectroscopy provided evidence on the formation of the Maillard type conjugation. Compared with classical heating, ultrasound treatment could accelerate the glycation reaction between WPI and GA. A degree of graft of 11.20% was reached by classical heating for 48 h, whereas only 20 min was required by ultrasound treatment. Structural analyses suggested that the conjugates obtained by ultrasound treatment had less α-helix content, higher surface hydrophobicity and fluorescence intensity than those obtained by classical heating. Significantly lower level of browning intensity and significantly higher (p < 0.05) level of solubility (under alkaline conditions), thermal stability, emulsifying activity and emulsifying stability were observed for the conjugates obtained by ultrasound treatment as compared with those obtained by classical heating.
    • Whey protein isolate polydispersity affects enzymatic hydrolosis outcomes

      O'Loughlin, Ian B.; Murray, Brian A.; Brodkorb, Andre; Fitzgerald, Richard J.; Robinson, A. A.; Holton, T. A.; Kelly, Tom A.; Teagasc Walsh Fellowship Programme; Enterprise Ireland; CC/2008/0001/A. (Elsevier, 24/05/2013)
      The effects of heat-induced denaturation of whey protein isolate (WPI) on the enzymatic breakdown of α-La, caseinomacropeptide (CMP), β-Lg A and β-Lg B were observed as hydrolysis proceeded to a 5% degree of hydrolysis (DH) in both unheated and heat-treated (80 °C, 10 min) WPI dispersions (100 g L−1). Hydrolysis of denatured WPI favoured the generation of higher levels of free essential amino acids; lysine, phenylalanine and arginine compared to the unheated substrate. LC–MS/MS identified 23 distinct peptides which were identified in the denatured WPI hydrolysate – the majority of which were derived from β-Lg. The mapping of the detected regions in α-La, β-Lg, and CMP enabled specific cleavage points to be associated with certain serine endo-protease activities. The outcomes of the study emphasise how a combined approach of substrate heat pre-treatment and enzymology may be used to influence proteolysis with attendant opportunities for targeting unique peptide production and amino acid release