The pectin content as a measure of the retting and rettability of flax

Abstract

Field retting of flax is very weather-dependent. This often causes unfavourable variations in fibre characteristics and hampers valuable applications. The few studies directed to the control of field retting suggest that a sensitive method is needed to determine the initial rettability of flax and to monitor the degree of retting during field retting. The degradation of pectin is the key process in retting. We related retting directly to the pectin content of the stems and determined the rettability of flax stems as the rate of degradation of pectin during controlled water retting. The initial pectin content of 25–30 g/kg of stem decreased to 7–10 g/kg (on initial DM base) when retting was completed in field retting or in water retting. Water retting of flax that had previously been subjected to partial or total field retting resulted in a similar final pectin content. This suggests that the same pectin fraction remains after these two processes. Plant density did not affect the initial pectin content nor the rate of retting. The pectin content of the stems decreased during flowering and seed ripening. Pectin degradation was faster with flax harvested during flowering, whereas mature flax retted slower. Rettability was not related to the pectin content. Lignification probably limits microbial attack and differences in rettability may be better understood by applying the findings of the extensive literature on forage digestibility and biodegradability of litter. Crushing the stems did not accelerate field retting. However, drying the flax before laying it out resulted in more homogeneous retting and a lower final pectin content. The pectin content of partially and fully retted flax was related to the fibre properties after scutching. The relationship between pectin content and tensile strength appeared to be complex and the relationship between pectin content and the fineness of the fibres was also unclear. A close linear relationship was found between the pectin content and fibre cleanness as determined with a Shirley Analyser.