THE PECTIN CONTENT AS A MEASURE OF THE RETTING AND RETTABILITY OF FLAX

Field retting of flax is very weather-dependent. This often causes unf avourable variations in fibre characteristics and hampers valuable app lications. The few studies directed to the control of field retting su ggest that a sensitive method is needed to determine the initial retta bility of flax and to monitor the degree of retting during field retti ng. The degradation of pectin is the key process in retting. We relate d retting directly to the pectin content of the stems and determined t he rettability of flax stems as the rate of degradation of pectin duri ng 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 c ompleted in field retting or in water retting. Water retting of flax t hat had previously been subjected to partial or total field retting re sulted in a similar final pectin content. This suggests that the same pectin fraction remains after these two processes. Plant density did n ot affect the initial pectin content nor the rate of retting. The pect in content of the stems decreased during flowering and seed ripening. Pectin degradation was faster with flax harvested during flowering, wh ereas mature flax retted slower. Rettability was not related to the pe ctin content. Lignification probably limits microbial attack and diffe rences in rettability may be better understood by applying the finding s of the extensive literature on forage digestibility and biodegradabi lity of litter. Crushing the stems did not accelerate field retting. H owever, drying the flax before laying it out resulted in more homogene ous retting and a lower final pectin content. The pectin content of pa rtially and fully retted flax was related to the fibre properties afte r scutching. The relationship between pectin content and tensile stren gth appeared to be complex and the relationship between pectin content and the fineness of the fibres was also unclear. A close linear relat ionship was found between the pectin content and fibre cleanness as de termined with a Shirley Analyser.