PPubMed29 Apr 2021Cited 9×

Chemical and biochemical bleaching of oat hulls: The effect of hydrogen peroxide, laccase, xylanase and sonication on optical properties and chemical composition

Eva Schmitz, Juanita Francis, Katarina Gutke, Eva Nordberg Karlsson, Patrick Adlercreutz, Magnus Paulsson

Abstract

'Patrick Adlercreutz' 'Magnus Paulsson'] Title: Graphical abstract

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Alkaline hydrogen peroxide bleaching whitens oat hulls while preserving fibre composition, making them suitable as food fibre supplements.

What’s new

i.Assessed chemical and biochemical bleachability of oat hulls, including sonication
ii.Optimized alkaline hydrogen peroxide bleaching achieving up to ~20 brightness units increase with <10% yield loss
iii.Showed bleaching does not significantly alter fibre, carbohydrate, or phenolic composition
iv.Demonstrated high consumer acceptance (91%) for cookies containing bleached hulls
v.Evaluated laccase and xylanase enzyme effects, finding limited benefit and issues with mediators

How they did it

The study treated oat hull batches with chemical bleaching using alkaline hydrogen peroxide at varying NaOH and H2O2 loadings, and with biochemical bleaching combining laccase, xylanase, and sonication. Optical properties were measured with a Technidyne Color Touch X spectrophotometer, and fibre, carbohydrate, lignin, and phenolic contents were analyzed using NREL protocols, HPAEC‑PAD, and HPLC. A design‑of‑experiments explored sonication time and enzyme concentration ranges.

What they found

Brightness increased by up to ~20 units and L* by up to ~22 units after optimal chemical bleaching
65‑85% of loaded H2O2 was consumed during bleaching
Total yield loss during bleaching and washing was less than 10%
Consumer acceptance of cookies with bleached hulls reached 91%
Milled hulls showed brightness gains of 7‑12 units (Swe17) and 5‑7 units (Swe19)

Caveats

✕The optical property measurement method underestimated brightness and L* values by ~5 and 2‑3 units respectively
✕Enzyme laccase with ABTS mediator caused irreversible blue staining, limiting its use
✕Oven drying after enzymatic treatment caused darkening that could not be reversed by subsequent bleaching
✕Milling introduced iron, potentially affecting colour and optical results

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