Abstract
Walnut tannins were maximally extracted with absolute methanol and an extraction time of 60βmin. Storage (21 days at 25βΒ°C) significantly reduced (20β40% reduction) the assayable tannin content in walnuts. The ranges of tannin content in freshly cracked inshell and shelled walnuts were respectively 372β1095 and 363β667βmg catechin equivalent per 100βg dry weight. The assayable tannin content in inshell and shelled walnuts was 10β20% higher when the particle size was reduced from 2β to 8βmesh. Using 0.5 as compared to 2% (w/v) vanillin as colour development reagent yielded 15β20% higher assayable tannin contents. The assay colour development reached a maximum after 20βmin of incubation at 25βΒ°C. Roasting (204βΒ°C for 5βmin) caused a small (14%) but significant reduction in assayable tannins. Soaking in aqueous alkali solutions was more effective (44β100% reduction) than soaking in aqueous acid solutions (6β76% reduction) in decreasing the assayable tannin content in walnuts. Microwave heating in distilled deionised water resulted in 93β98% reduction in walnut assayable tannins. Blanching at 100βΒ°C for 2βmin was as effective as alkali soaking in significantly reducing the amount of extractable walnut tannins (98% reduction). The tannin content in blanched walnuts was positively related to astringency scores (rβ
β=β0.92).
Β© 2001 Society of Chemical Industry