The purpose of this study was to clarify factors affecting the browning of a model processed cheese during storage. Model processed cheese samples (pH 4.5-6.0) which were composed of sugars (galactose, glucose, or lactose; 0-1.8%), amino acids (0-2.8%), sodium caseinate (26.0-31.2%), fat from butter (22.0-28.5%), water (44.1%), emulsifying salts (trisodium citrate, disodium tartrate dihydrate, or disodium hydrogen phosphate; 0 or 1.4%), and salt (0-5.0%) were prepared. Each model processed cheese was stored at 50ºC for 4-7 d. The L*-, a*-, and b*-values of model cheese samples before and after storage were measured and the ΔE-value was calculated to estimate the browning. All model cheese samples turned brown during storage. The ΔE-value strongly correlated with the concentration of galactose (r=0.99), and pH (r=0.94), respectively. The galactose-added model cheese turned more intensively brown than glucose or lactose-added ones. The browning was not dependent on the amount of free amino acids, but on the amount of added sodium caseinate. The browning was repressed by the addition of 1 to 3% of NaCl. The model cheese added with disodium hydrogen phosphate as an emulsifying salt turned more intensively brown than those added with disodium tartrate dihydrate or trisodium citrate. The ΔE-values of model cheese samples containing galactose strongly correlated with the decrease in galactose. These results showed that galactose was one of the most important factors for regulating the browning of processed cheese during storage and that the browning was also dependent on pH, protein, NaCl, and an emulsifying salt.
Keywords: Maillard reaction; discoloration; emulsifier; galactose; non-enzymatic.