Tolerance of coffee (Coffea spp.) seeds to ultra-low temperature exposure in relation to calorimetric properties of tissue water, lipid composition, and cooling procedure

The effect of exposure to ultra-low temperature (liquid nitrogen, LN) on vi ability of seeds desiccated to various water contents was investigated in 9 coffee species. Three groups of species could be distinguished based on se ed survival after LN exposure. In group I species, no seedling production c ould be obtained after LN exposure due to endosperm injury. In group 2 spec ies, recovery was very low or nil after rapid cooling, and only moderate af ter slow cooling. In group 3 species, very high percentages of seedling dev elopment were observed after both rapid and slow cooling. A high interspeci fic variability for the high moisture freezing limit was observed within th e species of groups 2 and 3, since it ranged from 0.14 to 0.26 g H2O g(-1) dry weight. A very highly significant correlation was found for those speci es between the unfreezable water content, as determined from DSC analysis, and the high moisture freezing limit of their seeds. No significant correla tion was found between seed lipid content, which varied from 9.8 to 34.6% d ry weight, and survival after LN exposure. However, a negative relationship was found between seed unfreezable water content and lipid content. Inters pecific differences in fatty acid composition of seed lipids resulted in a high variability in the percentage of unsaturated fatty acids, which ranged from 28.7 to 54.4% among the 9 species studied. For all species studied, a highly significant correlation was found between the percentage of unsatur ated fatty acids and the percentage of seedling recovery after rapid or slo w cooling.