Factors affecting the deterioration of stored flaxseed including the potential of insect infestation

Abstract

Flaxseed (Linum usitatissimum L. 'McGregor') stored at 10, 20, 30, 40, and 50 °C and 35, 50, 60, and 70% relative humidity (RH) for up to 12 mo deteriorated in quality in < 1–3 mo at the two highest temperatures, although the seed was stored "dry" (≤ 10% moisture content, MC). Initial fatty acid values (FAV) of 41.1 mg KOH 100 g −1 dry seed (0.51% free fatty acids in oil) rarely increased more than 1.5-fold over 12 mo at 10 or 20 °C and up to 10% MC, or at 30 °C and 7 to 8% MC. Using FAV as a storage quality-loss criterion, flaxseed at 8–9% MC could be stored for 6 mo at 30 °C, 1–2 mo at 40 °C, or a few weeks at 50 °C with less than a 1.5-fold increase. A twofold increase in FAV was correlated to a discoloured or charred appearance of seeds and a rapid loss in seed germination. Seed germination did not decrease during 12 mo at 10 or 20 °C and 70% RH, or at 30 °C and 60% RH. The fungi Aspergillus glaucus group, A. candidus Link, and Penicillium spp. infected seed at some temperatures and relative humidities with low frequency by 6 mo, and A. flavus Link also occurred at 12 mo. Visible microflora were absent after 6 mo on seed at 40 and 50 °C. The beetles Oryzaephilus mercator (Fauvel), O. surinamensis L., Tribolium castaneum (Herbst), and T. confusum J. duVal survived and produced some larvae on both whole and ground flaxseed in 2 mo. McGregor was slightly more suitable for insect reproduction than NorMan or NorLin. Five other insect species could not survive. Extensive infestation of flaxseed by stored-product insects is unlikely. Key words: Flaxseed, storage, free fatty acids, germination, microflora, insects