STRUCTURE OF TAPIOCA PEARLS COMPARED TO STARCH NOODLES FROM MUNG BEANS

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 cooke d tapioca pearls were resistant to alpha-amylase, acid (IM HCI at 35-d egrees-C), and to a combination of isoamylase and beta-amylase, respec tively, whereas digestion of cooked starch noodles from mung bean gave 12, 16, and 26%, respectively, of resistant residues. All the resista nt residues gave the B-polymorphic X-ray pattern typical of retrograde d starch. At 75% moisture, the alpha-amylase-resistant residue did not melt below 147-degrees-C, whereas the acid-resistant residue melted a t 128-degrees-C (T(p)), and the isoamylase and beta-amylase-resistant residue melted at 92-degrees-C (T(p)). Size-exclusion chromatography s howed that the a-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 8-amylase-resistant fractions were composed mainly of long linear chains, supporting the hypothesis that, in cook ed mung bean starch noodles and tapioca pearls, micelles of retrograde d amylose formed a structural network that resisted disintegration dur ing cooking.