Cereal Chem. 70:463-470   |  VIEW ARTICLE

Structure of Tapioca Pearls Compared to Starch Noodles from Mung Beans.

A. Xu and P. A. Seib. Copyright 1993 by the American Association of Cereal Chemists, Inc. 

Commercial tapioca pearls contain approximately 60% gelatinized starch, as determined by differential scanning calorimetry and glucoamylase digestibility. Exhaustive digestions showed that 2, 5, and 6% of cooked tapioca pearls were resistant to alpha-amylase, acid (1M HCl at 35 C), and to a combination of isoamylase and beta-amylase, respectively, whereas digestion of cooked starch noodles from mung bean gave 12, 16, and 26%, respectively, of resistant residues. All the resistant residues gave the B-polymorphic X-ray pattern typical of retrograded starch. At 75% moisture, the alpha-amylase-resistant residue did not melt below 147 C, whereas the acid-resistant residue melted at 128 C (Tp), and the isoamylase and beta- amylase-resistant residue melted at 92 C (Tp). Size-exclusion chromatography showed that the alpha- amylase-resistant residues contained unit chains with a peak at a number-average degree of polymerization (DP[n]) of 33-37, and the acid-resistant residues contained chains with a peak at DP[n] 25-26. The isoamylase and beta-amylase-resistant fractions were composed mainly of long linear chains, supporting the hypothesis that, in cooked mung bean starch noodles and tapioca pearls, micelles of retrograded amylose formed a structural network that resisted disintegration during cooking.