Phenolic compounds in Fagopyrum sp. grains (buckwheat) : profile, bioactivity and effect of processing

University essay from SLU/Department of Molecular Sciences

Abstract: This study aimed to investigate the health benefits related to chemical com-pounds found in buckwheat cultivars. Factors influencing the presence of bioactive compounds with assumed health effects were examined. Two spe-cies of buckwheat, Fagopyrum esculentum (common buckwheat) and Fag-opyrum Tartaricum (tartary buckwheat) were evaluated. The selection of species was based on the comprehensive documented effects of these as well as their long-raging use as therapeutics in traditional medicine. Buck-wheat can be considered an optimal cultivar in sustainable food farming since it has a strong adaptability to harsh environment, making it a versatile crop which can be cultivated worldwide without using pesticides. Both buckwheat species have in previous studies been shown to contain high amounts of carbohydrates and proteins, rich in vitamins and minerals. Besides, they contain high quantities of phenolic compounds and phytoster-ols with pharmacological properties and potential to prevent the develop-ment of some chronic diseases. Additionally, buckwheat has a unique, bal-anced macro and micro nutritional composition and is free of gluten and re-lated prolamins, making it prospective as a functional food, suitable for peo-ple with coeliac disease. Crude protein has all essential amino acids and are observed to reduce serum cholesterol and cell proliferation. Extracted pro-tein could be used to develop plant-based protein products with low envi-ronmental impact. Phenols, compounds with high antioxidant activity, have been found ubiqui-tous in buckwheat and were suggested to be responsible for various health modulating effects. Hence, the emphasis in this study was to determine the Abstract plant material that contained the highest amount of phenols and other com-pounds with biological activity. The result demonstrated that the highest total phenolic content was found in F. Tartaricum (tartary buckwheat). The content was particularly high in the bran followed by the hull and the flour (9.49, 7.71, 3.06, 1.26 GA/g-1 DW, respectively). In F. esculentum the total phenolic content ranged from 0,05 (‘Novosadska’) to 0.3 g (Bosna 1 and 2) GA/g-1 DW. The concentrations obtained varied significantly in the same species depending on location and environment of cultivation. Tartary buckwheat also had a significantly higher content of free phenols compared to common buckwheat, with a co-herently higher antioxidant activity. P-hydroxybenzoic, ferulic and proto-catechuic acids were the dominant phenolic acids in tartary buckwheat, and accounted for 83–88% of the total phenolic acid content while ferulic, vanil-lic, p-coumaric and syringic acids were estimated as the major individual phenolic acids in common buckwheat.Among the flavonoids, the most abundant compounds were catechin (monomeric flavan-3-ols), rutin, orientin, vitexin and quercetin. Rutin was the major phenol in common buckwheat seeds (90,5 % of the total phenolic content). Processing of raw buckwheat somewhat altered the profile of bioactive compounds compared to the raw material. Soaking activates enzymes such as rutin 3-glucosidase which hydrolyses the glycoside rutin to quercetin. Heat treatment increases the fraction of free phenolic compounds but de-creases the ester, glycoside, and ester-bound fractions. This may enhance the antioxidant activity. Regarding absorption and bioavailability, phenols are absorbed differently depending on the chemical composition. Phenolic glycosides, polymers and esters needs to be hydrolyzed by intestinal enzyme or degraded by microbes in the colon before absorption. Quercetin glycosides, including rutin, can be transported by SGLT1. This proposes querecetin glycosides as inhibitors of glucose uptake. Many flavonoids are however rapidly metabolized in the liver into methoxy derivatives or conjugated derivatives before excretion. To conclude, buckwheat has a great potential both as a functional food and as a carrier of pharmacological compounds. It can prevent and treat diseases with high mortality rate in both first, second and third world countries. It can also be an option for drugs that is more economically, environmentally and socially sustainable.

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