Effects of sulphur dioxide preservation of flax straw on fibre components and microbial colonisation during dew-retting

The changes in flax straw structure when treated with sulphur dioxide (SO₂) and consequent effect on dew-retting of the treated straw were investigated. The active oxoanions released by sulfurous acid degraded phenolics bound to the polysaccharides and lipids leading to an increase in water-soluble carbohydrates and polyphenols. As a result, proportions of hemicellulose, nitrogen, sulphur, ash and caustic weight loss were higher in treated straw while lipid was reduced. The coarseness of treated fibre was possibly caused by in situ dryback of the hydrolysed polysaccharides. The deposition of salts containing high concentrations of sulphur, calcium and potassium in the vicinity of the fibre bundles and epidermal layer was observed and investigated. In a dew-retting trial comprising SO₂-treated and untreated samples, the SO₂ treatment delayed microbial colonisation and, consequently, retting by nearly 2 wk compared to the controls. The changes in pH, fungal population and polysaccharide degrading enzymes were monitored. The differences in fibre yield, fineness and strength are presented.