The object of the present invention is to provide a dispersion stabilizer that can minimize coagulated precipitation of a protein under acidic conditions, especially in the pH range of around pH 5 which is closer to neutrality than the range around the isoelectric point of the protein. It is possible to stabilize dispersion of protein particles around pH 5, and thus prepare an acidic protein food, by using a legume seed polysaccharide esterified with a succinic acid derivative having a hydrocarbon chain bonded to the 2-position carbon of succinic acid or succinic acid. The hydrocarbon chain of the succinic acid derivative preferably has 2 to 18 carbon atoms, and is most preferably an octenyl group. The esterified legume seed polysaccharides also have high emulsifying ability.
