Effects of processing and storage on walnut (Juglans regia L) tannins

Kar Wai Clara Sze-Tao, Julie E. Schrimpf, Suzanne S Teuber, Kenneth H. Roux, Shridhar K. Sathe

Research output: Contribution to journalArticlepeer-review

39 Scopus citations


Walnut tannins were maximally extracted with absolute methanol and an extraction time of 60min. Storage (21 days at 25°C) significantly reduced (20-40% reduction) the assayable tannin content in walnuts. The ranges of tannin content in freshly cracked inshell and shelled walnuts were respectively 372-1095 and 363-667mg catechin equivalent per 100g dry weight. The assayable tannin content in inshell and shelled walnuts was 10-20% higher when the particle size was reduced from 2- to 8-mesh. Using 0.5 as compared to 2% (w/v) vanillin as colour development reagent yielded 15-20% higher assayable tannin contents. The assay colour development reached a maximum after 20min of incubation at 25°C. Roasting (204°C for 5min) caused a small (14%) but significant reduction in assayable tannins. Soaking in aqueous alkali solutions was more effective (44-100% reduction) than soaking in aqueous acid solutions (6-76% reduction) in decreasing the assayable tannin content in walnuts. Microwave heating in distilled deionised water resulted in 93-98% reduction in walnut assayable tannins. Blanching at 100°C for 2min 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 (r=0.92).

Original languageEnglish (US)
Pages (from-to)1215-1222
Number of pages8
JournalJournal of the Science of Food and Agriculture
Issue number13
StatePublished - 2001
Externally publishedYes


  • Astringency
  • Processing
  • Tannins
  • Walnuts

ASJC Scopus subject areas

  • Agricultural and Biological Sciences (miscellaneous)
  • Food Science
  • Chemistry (miscellaneous)


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