Genotypic variation in nutritional composition of buckwheat grain and starch characteristics influencing resistant starch content of cooked buckwheat groats

Lu Lu

Buckwheat (Fagopyrum esculentum) is a highly nutritious pseudocereal rich in bioactive compounds including proteins, minerals, dietary fiber, phytochemicals, phenolics, and resistant starch (RS). People can capture these associated benefits by consuming buckwheat products. The lack of understanding of the nutritional composition and genetic variation among North American buckwheat cultivars requires further investigation. Cooked buckwheat exhibits a higher amount of RS than other cereals and the basis of high RS content of cooked buckwheat groats is still unclear. The objectives of this study were to determine the genetic variation of the nutritional composition of buckwheat groats and husks to facilitate selection of certain cultivars for future breeding according to their nutritional traits, and to analyze the functional properties of buckwheat starches and explore the basis of high RS content in cooked buckwheat groats. Significant (P < 0.05) genetic variation was detected in buckwheat groats for 1000- kernel weight (16.5-39.8 g), protein content (10.2-17.9%), soluble dietary fiber (SDF) (1.4-3.4%), insoluble dietary fiber (IDF) (2.3-8.6%), total dietary fiber (TDF) (3.6-10.6%), free phenolics content (4.5-17.1mg GA/g) and total phenolics content (6.8-20.7 mg GA/g). v In buckwheat husks, large genetic variation was detected in protein (3.0-6.5%), bound phenolics content (6.7-26.1mg GA/g) and total phenolic content (32.4-58.6 mg GA/g). Cooked buckwheat groats exhibited lower starch digestibility and greater RS content than raw buckwheat groats. Starch of six buckwheat cultivars exhibiting high, medium, and low RS content of cooked groats was isolated and analyzed for functional properties. Apparent and actual amylose content were 27.4% and 31.6-34.5% in high RS cultivars, 27.4-28.6% and 32.5- 33.7% in medium RS cultivars, and 21.4-25.6% and 24.5-32.0% in low RS cultivars, respectively. Amylose leaching during cooking was greater in high RS cultivars than low RS cultivars. Differential scanning calorimetry (DSC) detected cultivars of low RS content exhibited high amylose-lipid complexing. Gelatinization enthalpy of native buckwheat starch and amylopectin retrogradation showed no relationship with RS content. Starch gel hardness and syneresis, as an assessment of amylose retrogradation, exhibited positive relationships with RS content of cooked groats. Amylose content, amylose leaching capacity, amylose-lipid complexing and amylose retrogradation all appear to affect the RS content of cooked buckwheat groats.

Genotypic variation in nutritional composition of buckwheat grain and starch characteristics influencing resistant starch content of cooked buckwheat groats

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