I was wondering if it's possible to evaluate the amount of oligosaccharides (stachyose and raffinose) in soybean meal using the dinitrosalicylic method. I have dinitrosalicylic acid and alpha-galactosidase (enzyme that digests oligosaccharides), but I'm unsure if this method is applicable.
Any insight is appreciated.
2/9/23
Dear Linoy,
I don't think that DNSA would be useful for you. This reagent is used for detecting reducing sugars, i.e., sugars that have a free carbonyl that can react w/ DNSA. E.g., in the case of glucose (an aldohexose) the carbonyl is is an aldehyde at carbon 1. With fructose, the carbonyl is a keto group at carbon 2. Neither raffinose nor stachyose are reducing sugars, so they will not react w/ DNSA. I'm not sure if using alpha-galactosidase will help you. This will cleave 2 galactose residues from stachyose and 1 galactose residue from raffinose releasing sucrose. Galactose is a reducing sugar and can be detected with DNSA. However, of the total galactose quantitated, I don't think you will be able to determine what % came from raffinose and what % came from stachyose.
A better way to do this would be to use chromatography, e.g., HPLC. Raffinose is a trisaccharide (mol. wt. 504), whereas stachyose is a tetrasaccharide (mol. wt. 666). These are sufficiently different in molecular weight that they can be separated by HPLC using a molecular sieving column.
I hope this information helps you.
Bill Colonna Iowa State University, Ames, Iowa, USA [email protected]
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