Effects Of Concentration Prior To Cold-Stabilization On The Color Of Concord Grape Juice

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Anthocyanins are ubiquitous in nature, found in many fruits and vegetables. Concerning Concord grape juice, anthocyanins are the prominent color pigment, giving the juice its characteristic purple hue. They contribute to color as both a free, unbound species, and also through reactions with other compounds, forming copigmented complexes or polymeric pigments. Color is often a defining factor of consumer acceptance; therefore, understanding the effect of processing on the color of the juice is extremely pertinent to the success of the industry. Recently, there has been anecdotal evidence that concentration prior to cold storage may significantly impact the overall color of Concord grape juice produced form concentrate. The color of Concord grape juice produced by concentration before coldstabilization/detartration (direct-to-concentrate, DTC) was compared to juice produced via cold stabilization prior to concentration (standard concentrate, SC). Following reconstitution, DTC juice had a 63% greater absorbance at 520 nm than SC juice. A significant loss of anthocyanins was observed using a paired t-test during coldstabilization of single-strength juice during SC processing (averaging 79 mg/L as cyanidin-3-glucoside, 23% of total anthocyanins), while no significant loss of anthocyanins or color was observed during cold stabilization of DTC concentrate. The concentration of anthocyanins in the SC bitartrate crystals was 0.80% w/w compared to 0.13% w/w in the DTC bitartrate crystals. Based on changes in titratable acidity during processing, the loss of anthocyanins in SC juice due to coprecipiation was estimated to be 64 mg/L. The decrease in coprecipitation of anthocyanins with bitartrate crystals during DTC cold-stabilization may be due to lower water concentration and decreased pH, hindering the adherence of colored flavylium ions to the bitartrate crystal.
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