Journal of Agricultural Sciences (Belgrade) (Jan 2006)
Change of juice color during raspberry processing in fruit juice and fruit juice concentrate
Abstract
A change of anthocyanins under different conditions of enzymatic treatments, clarification and concentration was determined. A pectin preparation Klerzyme®120, manufactured by DSM, France, specific for "sour fruits" with pH below 3.2, was used for maceration and depectinization. Experiments were carried out by a laboratory hydraulic press. Raw raspberry juice was clarified either by membranes separation processes or by traditional treatments using gelatin and bentonite. For microfiltration and ultrafiltration processes, membrane cut-off should not be below 30,000 g/mol to prevent any color loss. Experiments with membrane separations processes were carried out with five different membranes. A raw depectinized raspberry juice was clarified by cross-flow microfiltration and ultrafiltration using ceramic tubular membranes and hollow fiber polymeric membranes of a molecular weight cut-off of 300, 50 and 30 kg /mol or with a mean pore size of 0.2 urn in the case of microfiltration. Fruit juice concentrations were carried out by a laboratory equipment for vacuum evaporation. Extraction yield by a laboratory hydraulic press was the same in case of single-stage maceration and two-stage maceration. However, due to a lower viscosity, it was observed that single-stage process provides raspberry juice with more color and high efficiency of extraction. It was noticed that thermal breaks of raspberry pulp provide juice containing more total anthocyanins. The clarification using gelatin and bentonite removed about 50% total anthocyanins, while a clarification by a cross-flow ultrafiltration using Carbosep M9, M8 and M7 membranes achieved the highest level of color loss. Total color loss after concentration was 70%. The best results in color protection were observed by a microfiltration through Kerasep membrane, due to its relatively large pores (0.2μm). .
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