Physiologically meaningful moisture content determination for Brazil nut (Bertholletia excelsa Bonpl.) seeds

Abstract

Brazil nut (Bertholletia excelsa Bonpl.; Lecythidaceae) seeds are large, and the oily embryo (edible part) is covered by a thick, woody seed coat. Difficulties in seed storage may be due to desiccation sensitivity of the seeds, and prior variable results may be related to procedures for seed moisture content (MC) determination. This study first compared 3 methods of preparation of whole seeds, prior to MC determination: (i) intact seeds; (ii) chopped (<7 mm) and (iii) cut lengthwise. Drying at 105°C for 24 h was sufficient to remove free water in all three procedures, with results within tolerance limits. Secondly, seeds in equilibrium with relative humidity had a high variation in MC. This could be explained to some extent by the increased proportion of seed coat in smaller seeds, with 48% of seed weight average total. Seed coat MC was always higher than embryo MC. Linear regression revealed an increasing overestimation of embryo MC with desiccation. Considering 10% MC of the whole seed, embryo MC was 5.3% (a 1.9-fold overestimation). In this respect, it is physiologically meaningful to determine embryo MC and not whole seed MC. The approach may be applied to other species with similar seed morphology. Key words: Bertholletia excelsa, drying, Lecythidaceae, recalcitrant seeds, seed moisture content, seed testing.