The effect of γ-irradiation on the non-enzymatic browning reaction in the aqueous model solutions

Aqueous solutions of sugars (xylose, arabinose, fructose, glucose or sucrose), alone or in the presence of amino acid (lysine), were γ-irradiated at 0, 5, 10, 20 and 30 kGy at room temperature. Also evaluated were differences between irradiation and heat treatment. Absorbances at 420 nm, of the irradiated sugar–amino acid solutions, were increased although no browning was observed in the irradiated sugar or amino acid alone. The degree of browning of the irradiated sugar–amino acid solution increased with increasing irradiation dose and was dependent on the type of sugar. The non-reducing sugar, sucrose, did not react with lysine by heating for 4 h at 80 °C; however, the irradiated sucrose–lysine solution showed the non-enzymatic browning reaction and it had a higher reactivity than other sugars. For the sugar–lysine solution irradiated at 30 kGy, browning was in the following order of intensity: sucrose > fructose > arabinose > xylose > glucose. Furfural compounds (5-hydroxymethylfurfural and 2-furaldehyde) were not detected in any irradiated samples.