Orange Juice Color And Its Discolor During Sterilization And Storage

In this study, varieties of sweet oranges were used as experimental material, including Earlygold, Hamlin, Valencia, Jincheng and so on. The research was focused on the analysis of juice color in sweet orange by Color i5 spectrophotometer as to establish the database of orange juice. Furthermore, in order to explore the trend of color changes in orange juice, the content of carotenoid, vitamin C and the browing-index in orange juice after sterilization and refrigerated were also studied. Through the studies above, indication were made as follows.(1) In order to research thoroughly into the orange juice color, the color properties (CIE L*a*b*, hue, chroma and OJ) of hundreds of orange juices from different area were studied by Color i5 spectrophotometer in this study. Orange juice color database is fundamentally established in our country, from which we find that orange juice color number in our country is very high (CN>36) and which will be propitious to the export of orange juice to the international market.(2) Very wide varietal, interlocal and mature variations on juice color were observed, but the seasonal difference is not significant (P>0.05). First, the juice color in different area presents discrepancy. The juice color in Chongqing is the most vivid, which will be favor of the development in orange juice industry . Moreover, there is great difference between the juice color in different varieties: the juice color of Navel orange and blood orange were higher than others, especially the color of blood orange juice is higher than 42.(3) Changes in color parameters CIE (L*, a*, b*) in juice were significant (P < 0.05) as a function of fruit maturity. Along with the maturity, significant differences (P < 0.01) were presetented in juice color CIE (L*, a*, b* values) at different maturity stages. Decrease in CIE L* in juice color and increases in CIE a*, b*, C*, hue and OJ values from analysis of orange juices were the characteristic color changes, indicating that the juice color became more attractive. The increases in juice color could be associated with the ascent in carotenoid and vitamin C. The overall color change (ΔE*) at maturity indicated that the color of orange juice is variational. So in the industrial production, more importance should be attached on the effect of maturity on product quality, and orange harvest and classification and selection should be well done, so that orange juice with better quality can be produced.(4) The effects of sterilization on juice color, carotenoid, and vitamin C content on orange juice were studied. Results showed that sterilization resulted in decreasing in CIE a*and OJ values in juice color, increasing in CIE L*, b*, C*and hue values. The profile of the main carotenoid and vitamin C related to the color of the juices was destroyed after sterilization. Besides, the effect of themal processing (95℃, 1min) on orange juice color was stronger than sterilized method, but the effect of microwave is comparatively small.(5) Color changes in orange juice during storage at -4°C for 12 week were studied. Decrease in CIE a*in juice color and increases in CIE L*, b*, C*and hue values from analysis of orange juices were the characteristic color changes during refrigerated storage. With respect to fresh juice, juice color in stored shifted toward the direction to negativeΔOJ, indicating the color became slightly paler. The overall color change (ΔE*) is higher than 2, indicated that the color of orange juice is variational and the noticeable visual difference during storage.(6) The content of carotenoids, vitamin C and browing-index in orange juices is unstable and easily susceptible to change during sterilization and storage, which were detrimental to juice quality, leading to a dull and weak juice color. The Significant correlations between color parameter and the content of carotenoid, vitamin C and browing-index were also explored, suggesting that the natural color break was characterized by a reduction in carotenoid concentration, a decrease in vitamin C, and an increase in browing-index.