One of the major reasons for people's aloofness from soy foods in many countries, especially where fermented soy products are not in vogue, is the flatulence experienced on consumption. Raffinose and stachyose are the two flatulence-inducing sugars, which constitute about 0.5% and 4% of the total soybean seed on a dry weight basis, respectively. Both raffinose and stachyose are the galactosyl derivatives of sucrose. Raffinose is one unit of galactose attached to a sucrose moiety with a 1^6 glycosidic linkage; stachyose is one unit of galactose attached to raffinose with the same glycosidic linkage. Therefore, they are collectively referred to as raffinosaccharides or raffinose family oligosaccharides (RFOs). The RFOs remain undigested in the upper intestine as Homo sapiens lack the a 1^6 glycosidase required for degradation of a 1^6 galactosidic linkage. They then pass on to the lower intestinal tract where they are metabolized by intestinal microflora, leading to the production of CO2, hydrogen and methane. These gases cause abdominal discomfort. Unlike some of the other undesirable components such as trypsin inhibitor and lipoxygenases in soybean, the RFOs are not heat labile; however, they can be reduced to an extent by soaking or boiling through leaching.
The RFO content in soy meal impacts the efficiency of the poultry and swine industries as animals fed on soybean meal attain satiety early, and the weight of the animal, which is economically important, is not realized to the maximum genetic potential. The RFOs reduce the metabolizable energy of the animal feed. It has been shown that a complete removal of raffinose and stachyose from the animal feed can improve the metaboli-zable energy in animals by 12% (Graham et al., 2002). Therefore, genetic reduction or elimination of RFOs is one of the prime plant breeding objectives. A substantial reduction in RFOs has been achieved in mutants LR28 and LR33 using N-nitroso-N-methyl urea (Sebastian et al., 2000), with a total RFO concentration of 1.37% and 0.88%, respectively, in the seed. Molecular characterization of LR28 and LR33 has shown mutations at the raffinose synthase and myoinosito1-p synthase levels of the RFO pathway, respectively (Hitz et al., 2002). Combining the two mutations through conventional plant breeding approaches has led to a breeding line with 0.24% raffinose and 0.47% stachyose.
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