ARS | Publication request: Glucosylation of Raffinose via Alternansucrase Acceptor Reactions

Submitted to: Carbohydrate Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 22, 2009
Publication Date: September 21, 2009
Citation: Cote, G.L., Dunlap, C.A., Vermillion, K. 2009. Glucosylation of raffinose via alternansucrase acceptor reactions. Carbohydrate Research. 344:1951-1959.

Interpretive Summary: We have developed a method that uses a food-grade bacterial enzyme to modify carbohydrates from cottonseed meal or soybeans and convert them to new carbohydrates with potential applications in food and feed. Raffinose is a carbohydrate that occurs in the seeds of many agricultural crops, including soy and cotton. It is found in soy whey, a co-product of soy protein production, and can also be extracted in good yields from cottonseed meal, the residue remaining after the oil has been pressed out of the seeds. Although raffinose can enhance the growth of beneficial bacteria in the large intestine, it also causes gas production in the intestine when high raffinose foods such as beans are eaten. This new process modifies raffinose to give novel carbohydrates that show promise as prebiotics, which enhance the growth of beneficial bacteria. This process could be used in the production of valuable food and feed additives from soy whey or cottonseed meal.

Technical Abstract: The glucansucrase known as alternansucrase [EC 2.4.1.140] can transfer glucosyl units from sucrose to raffinose to give good yields of oligosaccharides, which may serve as prebiotics. The main products were the tetrasaccharides a-D-Glcp-(1-3)-a-D-Galp-(1-6)-a-D-Glcp-(1-2)-ß-D-Fruf and a-D-Glcp-(1-4)-a-D-Galp-(1-6)-a-D-Glcp-(1-2)-ß-D-Fruf in ratios ranging from 4:1 to 9:1, along with lesser amounts of a-D-Glcp-(1-6)-a-D-Galp-(1-6)-a-D-Glcp-(1-2)-ß-D-Fruf. Ten unusual pentasaccharide structures were isolated. Three of these arose from glucosylation of the major tetrasaccharide product, two each from the minor tetrasaccharides, and three were the result of glucosylations of the fructose acceptor products leucrose or isomaltulose. The major pentasaccharide product arose from glucosylation of the major tetrasaccharide at position 4 of the fructofuranosyl unit, to give a subunit structure analogous to that of maltulose. A number of hexasaccharides and higher oligosaccharides were also produced. Unlike alternansucrase, dextransucrase [EC 2.4.1.5] gave only a single tetrasaccharide product in low yield, and no significant amounts of higher oligosaccharides. The tetrasaccharide structure from dextransucrase was found to be a-D-Glcp-(1-4)-a-D-Galp-(1-6)-a-D-Glcp-(1-2)-ß-D-Fruf, which is at odds with the previously published structure.