Effect of thermal processing on tristimulus colour changes of fruits

Purpose of review: C olour is an import ant attribu te because it is usually the f irst property the consumer observes. Various factors are r esponsible for loss of colour during the processing of food products. This review covers the latest research on visual (tristimu lus) colour change of whole fruit, fruit pulp, puree and concentrate dur ing thermal processing such as drying and pasteurisation. Fin dings: The visual colour of fruits and their products changed significan tly regardless of the processing method applied. This change w as basically attributed to non-enzymatic browning. Osmotically pre-treated samples exhibited less colour change during drying. How ever, vacuum- and microwave-dried sam ples suffered extensive browning. D irection for future research: In g eneral, fruits have been suggested to offer h ealth benefits beyond basic nutritional requirements. Th e benefit comes from the natural antioxidants they contain. Care m ust be taken during thermal treatment in such a way as to min im ise antioxidant deterioration and colour change. Further research is required on quantitative determination of pigment destructi on, and r eactions involving phenolic substances and proteins in order to establish relationships with the tristimulus colour parameters L, a and b. Further research needs to focus on enzymatic activity and destruction of vitamin C in order to identify whether colour change is enzym atic or non-enzymatic. Thus, process parameters could be optimised. Ke ywords: C olour change; thermal processing; tristim ulus; fruit; juice; puree; concentrate