Food Structure


Comparisons using scanning electron microscopy (SEM) were made among seeds of the isogenic bean strains, 'Nep - 2' and 'San Fernando' and 'Sanilac', a navy bean cultivar, to ascertain interrelationships between seed microstructure and water absorption characteristics. During a 90 min soaking period 1:1 (v /v) tap and distilled water, 'San Fernando' hydrated at the s lowest rate and imbibed water at only 60% and 78% of the percentages of water imbibed by 'Sanilac' and 'Nep-2', respec tively. Among the three bean genotypes, 'Sanilac' hydrated the most rapidly and imbibed the most water (5 2.9% ). 'Nep - 2' was intermediate between 'Sanilac' and 'San Fernando' for water imbibition. The interpretation of SEM micrographs for 'Sanilac', 'Nep- 2' and 'San Fernando' provided evidence for an association between microstructure and the water imbibition patterns observed. 'Sanilac' had an open and heart - shaped micropyle and prominent seed coat pores. The quality of these structures as observed by SEM favored rapid water uptake- by 'Sanilac'. On the other hand, 'San Fernando' had an occluded micropyle and lacked seed coat pores. 'Nep - 2' had a partially opened micropyle and a few prominent seed coat pores. The seed coat palisade cell layer was thicker in 'San Fernando' than the palisade layer thickness in the other two genotypes. Starch granules in 'San Fernando' viewed from SEM cross sections of cotyledons appeared smaller and more tightly enveloped by the protein matrix than the starch granules for 'Nep - 2' or ' Sanilac'. 'Nep - 2' tended to resemble a "hybrid" between 'San Fernando' and 'Sanilac' for microstructure of the seed. The microstructural differences observed between 'San Fernando' and 'Nep-2' are associated with the mutational induction of white seed coat ('Nep - 2') by treating black seeds of 'San Fernando' with ethyl methane sulfonate. Manifold effects associated with an alternate state (e.g. , white) of the major seed coat color locus in otherwise isogenic strains of beans are due to genetic linkage or pleiotropy.

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