Effect on phenolics, hmf and some physico-chemical properties of apple juice concentrate of activated carbon applied at the different temperatures

In this research, the effect of different temperature, time and activated carbon doses on hydroxymethylfurfural (HMF) level on apple juice concentrate was examined. Changing in total phenolic content, oBrix, pH, titratable acidity, electrical conductivity, total invert sugar, reflectance color (L*, a*, b*, h, C*), spectrophotometric color, clearness, viscosity and mineral content were also determined. The values of HMF in the apple juice samples decreased with increasing activated carbon doses and application time. However, the application time of activated carbon had no significant effect on HMF content. While the application temperature of activated carbon had no significant effect on HMF, it had a highly important effect on total phenolic content (P < 0.05). Total phenolic content in the apple juice decreased significantly with increasing doses, application time and temperature of activated carbon (P < 0.05). Transmittances at 440 nm of apple juice were increased by activated carbon applications with increasing doses and application time at all temperatures. Parallel to increase in the activated carbon doses and application time, hue (h) values of all apple juice decreased at all temperatures. Hydroxymethylfurfural (HMF), formed by the Maillard reaction and dehydration of ketopentoses, particularly in acidic and/or high temperature environments, is an important quality parameter in fruit juices and other foods. In fresh unheated juices, the HMF content is normally zero. However, it occurs during processing which requires high temperature, and storage. High HMF and dark color of apple juices could be improved with a proper clarifying agent such as activated carbon. The results of this study showed that the activated carbon can be useful in making a significant improvement in the apple juice by decreasing its HMF content and enhancing color properties without considerable loss in the levels of phenolic compounds, which are important constituents for color and flavor of fresh fruit, could be achieved in the apple juice.