Quantification of B6 and B1 vitamers in soybeans, soy-protein and soymilk using a targeted differential ion-mobility mass spectrometry LCMS methodology

Ethical and sustainability concerns have led many consumers to substitute milk and meat with plant-based alternatives. However, whilst traditional soy-based alternatives are rich in vitamins, most modern highly processed meat-alternatives are made from soy protein isolates or concentrates (SPI, SPC) which may be low in vitamins. Vitamin B 1 and B 6 are vital for metabolic and neurological health but since they cannot be synthesised by humans, they must be obtained from diet. These vitamins occur in plant as well as animal foods, yet several studies report insufficiency in vegetarians. Such insufficiencies could be due to plant based-alternatives being lower in vitamins than animal products or containing a higher proportion of poorly bioavailable B 6 vitamers such as pyridoxine-glucoside (PNG). However, data are currently lacking. This study therefore aimed to quantify thiamine (vitamin B 1 ), pyridoxine (PN), pyridoxamine (PM), pyridoxamine-5′-phosphate (PMP), PNG, and other B 6 vitamers in soybeans, soy-protein extracts and soymilks. Vitamers were extracted by strong-cation-exchange (SCX) chromatography and quantified using SelexION differential ion mobility LCMS. Soybeans were abundant in vitamin B 1 and B 6 , but most B 6 was present as less bioavailable PNG (5954 ng/g), with lower concentrations of PN, PM and PMP (571, 345, 243 ng/g respectively). SPCs and SPIs were low in vitamins, containing 84%–94% less B 1 and B 6 than soybeans, with levels closely linked to protein extract pH and solubility. Soymilk in contrast, showed similar vitamin levels to soybeans, except when ultraheat treated or fortified. Thus, while soybeans are rich in B 1 and B 6 , the high prevalence of less bioavailable forms and low concentrations in highly processed soy foods may limit intake.