Rajka Božanić

Chymotrypsin selectively digests β-lactoglobulin in whey protein isolate away from enzyme optimal conditions: Potential for native α-lactalbumin purification

The present study examines the resistance of the α-lactalbumin to α-chymotrypsin (EC 3.4.21.1) digestion under various experimental conditions. Whey protein isolate (WPI) was hydrolysed using randomised hydrolysis conditions (5 and 10% of WPI; pH 7.0, 7.8 and 8.5; temperature 25, 37 and 50 °C; enzyme-to-substrate ratio, E/S, of 0.1%, 0.5 and 1%). Reversed-phase high performance liquid chromatography (RP-HPLC) was used to analyse residual proteins. Heat, pH adjustment and two inhibitors (Bowman-Birk inhibitor and trypsin inhibitor from chicken egg white) were used to stop the enzyme reaction. While operating outside of the enzyme optimum it was observed that at pH 8.5 selective hydrolysis of β-lactoglobulin was improved because of a dimer-to-monomer transition while α-la remained relatively resistant. The best conditions for the recovery of native and pure α-la were at 25 °C, pH 8.5, 1% E/S ratio, 5% WPI (w/v) while the enzyme was inhibited using Bowman-Birk inhibitor with around 81% of original α-la in WPI was recovered with no more β-lg. Operating conditions for hydrolysis away from the chymotrypsin optimum conditions offers a great potential for selective WPI hydrolysis, and removal, of β-lg with production of whey protein concentrates containing low or no β-lg and pure native α-la. This method also offers the possibility for production of β-lg-depleted milk products for sensitive populations.

Reduction in aflatoxin M1 concentration during production and storage of selected fermented milks

This study focused on monitoring changes in aflatoxin M1 (AFM1) concentrations during production and storage of different fermented milks using selected probiotic and non probiotic combined cultures. Milk samples intended for fermentation were intentionally contaminated by adding a standard of AFM1. All of the tested cultures caused remarkable reductions in AFM1 concentrations during the fermentation process. Probiotic cultures were more effective than non probiotic cultures, with Lactobacillus casei LC-01 strain being the most efficient , achieving a reduction level of approximately 58%. Among the non probiotic cultures, yogurt culture YC-380 was the most efficient, with a reduction level of approximately 41%.