Abstract
Sunflower extraction meal (SEM) is an economically interesting protein source. During alkaline extraction of proteins, the presence of chlorogenic acid (CQA) in the meal gives rise to the formation of o-quinones. Reactions with nucleophiles present in proteins can lead to green discoloration. Although such reactions have been known for a long time, there is a lack of information on the chemical nature of the reaction products. SEM and model systems consisting of amino acids and CQA were subjected to alkaline treatment and, for comparison, to oxidation of CQA by polyphenoloxidase (PPO). Several green trihydroxy benzacridine (TBA) derivatives were tentatively identified in all samples by UHPLC-DAD-MS/MS. Surprisingly, in alkaline-treated samples of particular amino acids as well as in SEM, the same six TBA isomers were detected. In contrast, the enzymatically oxidized samples resulted in only three TBA derivatives. Contrary to previous findings, neither peptide nor amino acid residues were attached to the resultant benzacridine core. The results indicate that the formation of TBA derivatives is caused by the reaction between CQA quinones and free NH2 groups. Further research is necessary to elucidate the structure of the addition products for a comprehensive evaluation of food and feed safety aspects.
Highlights
Sunflower (Helianthus annuus L.) seeds are considered a promising source of proteins
It was expected that such a comparatively simple were tested for their reactivity towards alkaline and enzymatically generated CQA quinone and to system would allow conclusions to be drawn as to the situation in the intact protein
Contrary to the formation of trihydroxy benzacridine (TBA) derivatives reported by Namiki et al and other groups, neither peptide nor amino acid residues were attached to the resultant benzacridine core, except for model systems containing β-alanine or lysine
Summary
Sunflower (Helianthus annuus L.) seeds are considered a promising source of proteins Except for their low lysine content, sunflower proteins match the FAO (Food and Agriculture Organization) reference protein patterns in terms of amino acid composition and are low in antinutritive compounds. Discoloration whereas as a result of in mechanically processed plants, CQA can interact with each other due toisthe ruptured the reaction of quinones and proteins hasand longproteins been realized, only little information available on the cell structure. Such interactions have been shown to alter the physicochemical properties of chemical nature of the reaction products. SEM and model systems were subjected to alkaline treatment to investigate reactions between SEM protein and chlorogenic acid quinone
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