RESUMEN
AIMS: To increase yield of starch conversion to large-ring cyclodextrins (LR-CDs) by amylomaltase from Corynebacterium glutamicum (CgAM). METHODS AND RESULTS: In this work, LR-CDs produced from pea, tapioca, corn, potato, rice and glutinous-rice starch by the recombinant CgAM were analysed by High-Performance Anion-Exchange Chromatography Using Pulsed Amperometric Detection (HPAEC-PAD). Among these, pea starch gave the highest yield of LR-CDs. Pretreatment of pea starch with isoamylase prior to incubation with CgAM resulted in the increase in LR-CD products by 20%. Surprisingly, CgAM converted starch into LR-CDs within a wide pH range (pH 5·5-9·0). LR-CD syntheses at alkaline pH or at a long incubation time favoured low-degree of polymerization (DP) products (CD22-CD32). Addition of 5-15% dimethyl sulfoxide (DMSO) promoted the synthesis of medium-DP species (CD33-CD43) by 10-25%. CONCLUSIONS: Pretreatment of pea starch with isoamylase could enhance the yield of LR-CDs. The ratio of LR-CD products depends on pH, incubation time and addition of organic solvents such as DMSO. SIGNIFICANCE AND IMPACT OF THE STUDY: LR-CD yield can be increased by thorough optimization of starch types, starch concentrations, enzyme activities, pH and incubation times. This study is the first report of the effect of organic solvents on LR-CD production by amylomaltase.