Studies on the Browning of Dehydrated Foods as a Function of Water Activity-I : Effect of Aw on Browning in Amino Acid-Lipid Systems

The effect of Aw on browning resulting from the oxidation of linoleate was studied in freeze-dried model systems. The systems were adjusted to various Aw, and stored at 35°C. Brown pigments were extracted from the model systems and fractionated into lipophilic and hydrophilic fractions. Water played an important role in the browning reaction. In the humidified system not only lipophilic but also hydrophilic brown pigments were found, whereas in the dry system only a lipophilic brown pigment was found. The formation of lipophilic brown pigment was fastest at Aw≈0, and decreased with increasing Aw to the critical value of 0. 41, but, when Aw was higher than 0. 41, browning increased with increasing Aw up to 0. 84. On the other hand, the formation of hydrophilic brown pigment differed from that of lipophilic brown pigment: the browning increased with increasing Aw from Aw≈O to the maximum region of 0. 41-0. 67, then decreased with increasing Aw. The observed effect of Aw on the formation of lipophilic and hydrophilic brown pigments was discussed based on the effect of Aw on the pattern of linoleate oxidation.