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Changes in antioxidant flavonoids during freeze-drying of red onions and subsequent storage.

Author(s) : PÉREZ-GREGORIO M. R., REGUEIRO J., GONZÁLEZ-BARREIRO C., et al.

Type of article: Article

Summary

The aim of this study was to elucidate the effect of the freeze-drying process and storage on onion flavonoids content. Major flavonols of a mature red onion bulb were confirmed as quercetin derivatives (3,4'-O-diglucoside (Qdg) and 4'-O-monoglucoside (Qmg)) using a combination of chromatographic comparisons, UV–visible spectra and scientific literature data. These two components account for about a 93% of the total flavonols (334 ± 60 mg Q kg-1, fresh weight), and are the main responsible for the IC50 antioxidant activity of 15.84 ± 3.73 g/kg. The remaining flavonol fraction (approx. 7%) comprises up to 8 different components of which quercetin-3-O-glucoside and isorhamnetin-4-glucoside are prominent members although each contribute less than 3% of the total flavonol fraction; instead, quercetin represents less than 1% of total flavonols. In this red onion, eight anthocyanins (which represent less than 1% of total flavonols) were also found at a total level of 2.1 ± 0.05 mg C3g kg-1 (fresh weight). Anyway, 4 of them (cyanidin 3-glucoside (C3g) > cyanidin 3-(6''-malonylglucoside) (C3,6mg) > cyanidin 3-(6''- malonyl-laminaribioside) (C3,6mlmb) > cyanidin 3-laminaribioside (C3lmb)) account for the 95% of total anthocyanins. Freeze-drying process concludes in an increase in the extraction of flavonoids up to a 32% for flavonols and 25% for anthocyanins. Freeze-dried onion powder storage at room temperature, in dark, in air- and water-tight glass bottles for up to 6 months was keeping rather stable all flavonoids. [Reprinted with permission from Elsevier. Copyright, 2011].

Details

  • Original title: Changes in antioxidant flavonoids during freeze-drying of red onions and subsequent storage.
  • Record ID : 30001783
  • Languages: English
  • Source: Food Control The International Journal of HACCP and Food Safety - vol. 22 - n. 7
  • Publication date: 2011/07
  • DOI: http://dx.doi.org/10.1016/j.foodcont.2011.01.006

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