Enhancement of Radical Quenching Ability of Sweet Whey and Casein Hydrolyzate: Mutual Supplementation with Thermally Generated Maillard Reaction Products

Abstract Text: Copiously available sweet whey is a source of nutritious proteins, peptides, free amino acids, and lactose.  Abundant N-terminal, ε-amino-groups and the reducing sugar, allows thermal generation of Maillard reaction products (MRPs) on heating. With an aim to develop powerful natural antioxidative foods, this research investigates the enhancement of short (Antioxidative Activity)(AA) and long term (Antioxidative Persistence)(AP) ROS quenching ability of two types of sweet whey, Cheddar (ChWPC) and Edam (EWPC) whey and enzymatic hydrolyzate of casein (CH) through mutual supplementation with freshly heat-generated MRPs.  Whey and CH dispersions (3 and 2%, respectively, w/v) were heated for 0 to 4 hours at 90^OC in McIlvaine’s iso-ionic buffer (pH 7.0), with and without added lactose (1%, w/v), to generate MRPs.  AA and AP were determined from luminol-induced chemiluminescence (CL) caused by unquenched hydroxyl radicals generated by pyrolysis of 2,2’-azobis(2-methylpropionamidine) dihydrochloride (ABAP).  Decrease in CL, measured as relative light units (RLU), compared to control (without the test materials) at maximal radical generation within one and two hours, were respectively measures of AA and AP.  Thermal generation of MRPs tended to enhance AA and AP in both sweet wheys though this effect was more dramatic for  ChWPC. This was conceivably due to its greater peptide content.  CWPC and EWPC heated for one hour exhibited radical induced CL maxima of 99 and 141 RLU, respectively. Whereas values for ChWPC+lactose and EWPC+lactose were 90 and 140 RLU, respectively. Furthermore, a direct correlation was observed between added lactose induced MRP formation and AA of ChWPC though this was not so clear for EWPC.  AA of CH after heating for four hours showed a CL of 79 RLU. However, this decreased when lactose, ChWPC and EWPC were added to CH as seen from increasing CL of  164, 107 and 121, respectively. The AP values for the same treatments were 53, 87, 57 and 62 RLU, respectively. The study not only indicated the variable effect of MRPs on antioxidative properties of the sweet wheys and CH, but also depicted the dramatic time-dependent thermal enhancement of AA and AP of ChWPC on MRP formation with added lactose.  These data can potentially lead to the development of powerful new antioxidants to alleviate the detrimental effects of cellular oxidative stress.

Keywords: Antioxidants, free radicals, reactive oxygen species.