Understanding resistant-starch formation during drying high-amylose maize kernels.

Area of Science:

• Food Science and Technology
• Biochemistry
• Nutritional Science

Background:

• Growing interest in high-amylose maize (HAM) for low glycemic index (GI) food applications.
• Understanding resistant starch formation is crucial for optimizing HAM properties.
• Drying conditions significantly impact starch structure and functionality.

Purpose of the Study:

• To investigate the formation of resistant starch in HAM kernels during various drying processes.
• To correlate drying temperatures with changes in HAM flour's physicochemical properties and enzymatic digestibility.

Main Methods:

• High-amylose maize kernels with 28.2% moisture were subjected to sun drying (~30°C) or hot-air drying (50°C, 70°C, 90°C, 110°C).
• Enzymatic digestibility, swelling power, solubility, viscosity, gelatinization properties, and relative crystallinity of milled HAM flours were analyzed.
• Microscopic techniques (light and scanning electron microscopy) were used to observe starch granule aggregation.

Main Results:

• Enzymatic digestibility of HAM flour decreased significantly from 63.6% to 41.1% with increasing drying temperatures (30°C to 110°C).
• Higher drying temperatures (110°C) led to decreased swelling power, solubility, and viscosity, but increased gelatinization temperatures, enthalpy, and relative crystallinity.
• Microscopy revealed increased starch granule aggregation at higher drying temperatures, with aggregates persisting after enzymatic hydrolysis.

Conclusions:

• Increased drying temperatures promote the formation of ordered structures within starch granules and starch aggregation in HAM flour.
• These structural changes result in enhanced enzymatic resistance, making HAM flour more suitable for low GI food development.
• The study highlights the critical role of drying temperature in tailoring HAM properties for functional food ingredients.