Determination of vitamin B6 content in brown beans (Phaseolus vulgaris L) from Öland : the influence of cultivar, year of cultivation, geographical area and type of fertilizer

Abstract: Legumes are nutritious and contribute to a sustainable food production system. In Sweden, brown beans (Phaseolus vulgaris L) are cultivated on Öland. Vitamin B6 is one of many nutrients found in brown beans and it works as a coenzyme in the metabolism in the human body. Vitamin B6 consist of pyridoxal (PL), pyridoxine (PN) and pyridoxamine (PM) and their phosphorylated forms PL-5-phosphate, PN-5-phosphate and PM-5-phosphate. Pyridoxine is in plants glycosylated (pyridoxine-5--D-glucoside) to 5-80 percent and this form has a reduced bioavailability in hu-mans. The aim of this study was to determine the content of vitamin B6 in brown beans from Öland and to find factors which influence the content. Consideration was taken to the factors cultivars, year of cultivation, geographical areas, and dif-ferent types of fertilizer. The total-, free-, glycosylated vitamin B6 as well as the water content were determined. In total 25 samples were analysed with HPLC with fluorescence detector. The content of vitamin B6 in brown beans was 0.32  0.02 mg/100g and on average 49 percent was glycosylated. There was no difference in the content of vitamin B6 between cultivars, geographical areas or types of fertiliz-er, but there was a difference between years. Vitamin B6 was higher 2008 com-pared to 2009. Glycosylated vitamin B6 was higher 2008 and 2010 compared to 2009 meanwhile there was no significant difference in free PN (all vitamers except glycosylated PN). The meteorological weather conditions were less beneficial for the beans 2008 and 2010 compared to 2009. Thereby, during less beneficial mete-orological weather conditions, the content of vitamin B6 increased by increased content of glycosylated pyridoxine. The water content was significantly higher in Katja compared to Karin, indicating on better water holding capacity (WHC). For Katja, there was a significant difference between years and water content. The chemical composition between cultivars and in cultivars between years (affected by weather) must be elucidated for an explanation of the difference in WHC.