Browsing by Author "Törnroos, Tatu"

Cowpea (Vigna unguiculata) is one of the most important legumes in the world due to its high nutritional content. Its nutritional value is, however, hindered by different anti-nutrients, such as phytic acid (PA), which can lower the bioavailability of minerals and proteins. PA is a nutritionally significant compound found in many plant materials, such as cereals and legumes. PA is myo-inositol-1,2,3,4,5,6-hexakis dihydrogen phosphate (IP6) by chemical nomenclature. Measurement of PA is challenging, due to its high charges and its low content, amongst other factors. The primary aim in the thesis was to create an accurate, selective, and sensitive UPLC-QTof-ESI-MS method for quantification of PA from legumes, cereals, and other plant materials. The secondary objective was to determine PA content in raw, fermented and phytase-treated white cowpea flour and investigate the effectiveness of the processing methods on PA hydrolysis. PA content in white cowpea has been previously determined with methods lacking the capability to directly measure only PA content, without also adding in the concentration of smaller inositol phosphates (InsP) or other phosphorus containing compounds. Therefore, the presumption was that the measured PA concentration should be lower when using the selective UPLC-QTof-ESI-MS method. Besides white cowpea flour, the concentration of PA in red cowpea, wheat bran, sorghum, wheat fraction and rapeseed protein concentrate flours was also measured to investigate if the method works for other plant matrices as well. The sample preparation method consisted of two-hour extraction in 0.5 M HCl, a neutralization step, lyophilization, reconstitution with 5% MeOH and addition of adenosine 5′-monophosphate monohydrate (AMP) as internal standard. The samples were then analyzed with UPLC-QTof-ESI-MS, with electrospray ionization on negative ion mode (ESI-). The PA quantification method had excellent precision, selectivity, repeatability, and linearity (R2 = 0.991). Accuracy was good and the recovery of 100% resulted in a high level of trueness. The LoD was determined as 3.22 µg/mL but could be possibly lowered. The PA content in white cowpea flour was 5.91 mg/g dry weight. As was presumed, this result was lower than previously reported in literature. The method was also relatively suitable for the other plant samples. However, wheat fraction, rapeseed protein concentrate, and sorghum flours gave unexpected results. In the fermented sample the PA content was 3.30 mg/g and in the enzyme-treated 0.09 mg/g (or 12.4 µg/mL). However, the fermentation and enzymatic treatments did not reduce the PA concentration under the threshold of <3.3 µg/mL, where iron cation chelation still strongly takes place. The processing method could be improved by increasing the phytase dosage or increasing the reaction times to achieve higher hydrolysis of PA.