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Tracking flax dew retting by infrared vibrational spectroscopy combined with a powerful multivariate statistical analysis
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International audience. Natural fibers are of great interest for the industrial sector, particularly those from flax (Linum usitatissimum L.). Before the industrial process, flax stems have to undergo ‘dew retting’. Under-retting and over-retting can result in fibers with lower industrial value and this process is currently empirical. In this study, we aimed to accurately monitor the flax dew retting by determining FT-IR spectra of uprooted stems after 1-, 6-, 20- and 25 days. As FTIR was usually performed after retting, it is original. With both one-way anova (‘a priori’ approach’) and a multivariate analysis (‘without a priori’ approach), we pinpoint significant markers of the retting progression. But the ‘without a priori’ approach reveals more significant markers. The early retting step was suported by peaks corresponding to esterified and alkyl-esterified pectins (1734 cm−1), other pectin (1335 cm−1) and aromatics (1508 cm−1). Degradation of the epidermis and the middle lamella from cortical parenchyma are taking place early. This is a prerequisite for fungus hyphae or bacteria colonization. The final retting step showed significant contributions from cellulose/hemicellulose peak (1317; 1427 cm−1), crystalline cellulose (1371 cm−1) and, OH- (3270 cm−1). This suggests almost complete outer tissue disorganization as well as the beginning of the release of bast fibers from bundles. Identifying specific peaks related to the end of the retting will help to build a predictive model. This will constitute a valuable tool to parameter a handheld device for helping farmers to determine the optimal retting point to harvest flax stems ensuring maximum fiber quality.
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