Comparison of subjective and objective methods to assess flax straw cultivars and fibre quality after dew-retting

SUMMARY Subjective and objective methods were compared for the assessment of the quality of unretted and retted straw, and the fibres obtained after dew-retting of four flax cultivars, Ariane, Evelin, Laura and Viola. Maturity of straw, degree of retting, ease of decortication after retting, divisibility, handle, cleanliness and colour were assessed as subjective factors and of these, degree of retting and handle appear to be useful for assessing quality. The samples were also analysed for physical and chemical differences using a range of objective methods. Straw quality could not be graded using height and maturity, although stem diameter and technical length could indicate quality. Changes in N, lipid and ash content, as a result of retting, were observed. The increase in the proportions of fibre fractions present in retted compared with unretted straw, due to microbial degradation of pectin, could be identified by thermal analysis. Analyses of the fibre samples to determine fineness, strength, cellulose, hemicellulose, lignin and minerals were carried out and significant differences in some of the parameters were identified. Cultivar Laura produced the best fibre. Fibre fineness, ash, lipid, caustic weight loss and fibre fractions as determined by thermal analysis were found to be important objective parameters for quality assessment. The assessment of fibre samples performed subjectively by an expert grader and by selected objective methods gave similar quality rankings.