5-hydroxymethyl furfural (HMF) accumulation and brown pigment formation (BPF) were studied in the presence and absence of some hydrocolloids in concentrated orange juice. The influence of addition of 1.5% xanthan gum (XG) and 1.5% XG and 0.5% microcrystalline cellulose (MCC) were observed on the nonenzymic browning reactions in concentrated orange juice at 45, 60, and 75 degrees C. The effect of water activity was also observed by replacing the samples into different water activity media (0.11 +/- 0.01, 0.30 +/- 0.01, 0.50 +/- 0.01, 0.75 +/- 0.01, and 0.80 +/- 0.01). It was observed that the samples containing 1.5% XG and 0.5% MCC showed the lowest BPF and HMF accumulation, whereas the browning rate and HMF accumulation in pure orange juice were the highest at all temperatures. Maximum BPF and HMF accumulation were observed in the range of water activity between 0.30 and 0.75. The lowest values were observed at aw 0.80.