Effect of thermal and non-thermal treatments on the color of citrus juice: A review

Citrus juice is widely consumed due to its high nutritional values, desirable taste, and color. The juice color is the key indicator for quality attributes affecting the consumer's attention. Conventional thermal treatment is the common method in juice processing which adversely affects its nutritional value and appearance. Measuring the color properties of the juice is an intelligent way to control the juice quality and estimating the alteration in chemicals. In this study, the effects of different treatments on the color aspects of citrus juice including L*, a* & b* values, browning index, total color difference, chroma, and hue index were reviewed. New thermal methods such as microwave, ohmic heating, and infrared radiation are used which result in the shortened process come up time (CUT). In addition, non-thermal treatments such as pulsed electric fields, high-pressure processing, high-pressure carbon dioxide, sonication, and ultraviolet are applied to process the juice, which results in better preservation of the nutritional values. These methods are less effective in the inactivation of the enzymes playing a key role in the juices stability. Therefore, a combination of thermal and non-thermal methods is suggested to increase the effectiveness of the process as well as preserving the juice quality.