Noticeable quantitative differences were found in the content of free and bound phenolic acids in flours obtained from soybeans, cottonseed, peanuts, rapeseed, white mustard, flax and sesame seeds. Independently of the type of seeds used to produce flour, the highest amounts of acids were liberated from ester bonds. These acids were especially abundant in flour made from rape and white mustard seeds. Phenolic compounds identified in these flours were predominated by sinapic and p-hydroxybenzoic acids and in the other flours by other phenolic acids.
Phenolic compounds present in the oilseeds are considered as components responsible for the colour, taste and flavour of protein preparates [lo]. For instance, it has been found that bitter taste of rapeseed flour is closely connected with the presence of sinapins [l]. CLANDININ [2] and AUSTIN et al. [l] did not note any negative effect of sinapine on animals organism, but studies by RACKIS et al. showed that sinapine in poultry feeds affected colour, taste and flavour of the eggs. Moreover, gray colour of sunflower isolates has been ascribed to the presence of chlorogenic acid [lo]. It has also been found that specific off flavour during heating of soybean flour is caused by the formation of 4-vinylguaiacol and 4-vinylphenol, for which phenolic acids p-coumaric and ferulic constitute the precursors .
The objective of this work was to identify and estimate the content of free phenolic acids and phenolic acids occurring in complexes in the flours obtained from oilseeds. Soybean, cottonseed, peanut, white mustard, flax and sesame flours were studied. The method used in course of our studies did not allow for an analysis of phenolic acids in sunflower flour, so phenolic compounds in this flour will be discussed in a separate paper.
Material and methods
Rapeseed (vr. Gorczanski), soybean (vr. Ajma) and white mustard were obtained from the Institute of Plant Breeding and Acclimatization, Poznan, Poland, whereas cottonseed