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Abstract Citric acid-esterified rice starch was synthesized using a one-step reactive extrusion method. The structure, physicochemical properties, and digestibility of the esterified starch were then measured. An in vitro digestion study indicated that esterification significantly increased the level of resistant starch (RS) in the samples. Fourier transform infrared spectroscopy (FT-IR) confirmed esterification had occurred between the citric acid and starch, with a new peak appearing at around 1730 cm−1. X-ray diffraction indicated that esterification caused a decrease in the degree of crystallinity in the starch. The swelling power and solubility of starch citrate were both lower than unmodified starch. Turbidity measurements suggested there was a slower rate of reassociation in starch citrates during storage. These results suggest that citric acid esterification promoted cross-linking within the starch that significantly reduced its digestibility. This simple method may be useful for the creation of healthier starchy foods. Graphical abstract Image 1 Highlights • One-step extrusion was developed as a means to produce starch citrate. • Citric acid esterification increased the resistant starch content of rice starch. • Physiochemical and structural analysis indicated the formation of a cross-linked structure in starch citrate. • This method may be suitable for commercial production of healthier starchy foods. [ABSTRACT FROM AUTHOR]

The rate and extent of starch hydrolysis in the digestive tract impacts blood glucose levels, which may influence an individual's susceptibility to diabetes and obesity. Strategies for decreasing starch digestibility are therefore useful for developing healthier foods. β-amylase is an exo -hydrolase that specifically cleaves α-1,4 glycosidic linkages of gelatinized starches. In this study, starch granules were disrupted by extrusion under different feed moisture conditions, and then subjected to β-amylolysis. The degree of starch gelatinization increased with increasing feed moisture content during extrusion, leading to faster β-amylolysis. The hydrolysis of in vitro starch digestion study was reduced for extruded samples treated with β-amylase, which was attributed to an increase in resistant starch (RS) after β-amylase treatment. Indeed, X-ray diffraction (XRD) indicated that the crystalline structure in the extruded starch was either partially or fully lost after β-amylase treatment. Similarly, Fourier transform infrared (FTIR) analysis indicated there was a higher level of amorphous regions in the starch after β-amylase treatment. Overall, our results suggest that enzymatic treatment of extruded starch with β-amylolysis reduces the ratio of crystalline-to-amorphous regions, which increases the level of resistant starch, thereby slowing down digestion. These results have important implications for the development of healthier starch-based foods. [ABSTRACT FROM AUTHOR]

Food extrusion has evolved over the past decades and is now a unique research area. Starch is a primary ingredient of raw materials that are widely used in food extrusion. Extrusion is a thermomechanical process that can break the bonds of starch, leading to starch gelatinization, melting, and degradation. This article reviews the effects of extrusion on structure (crystallinity, morphology, molecular weight) and physico‐chemical properties (expansion ratio, water absorption index, water soluble index, texture, pasting property, and digestion) of starch. In addition, some applications of extruded starches are described. This review is of significance as it provides an overview of the effects of extrusion on starch properties and indicates the potential of extrusion applications in the food industry. Starches are the primary raw materials widely used in extrusion processing. Extrusion is a thermo‐mechanical process that significantly changes the morphology and fine structure of the starches, thereby giving new physicochemical properties to the starches. The properties of starches after extrusion may be varied with the processing parameters. In this review, the applications of extruded starches are also introduced. [ABSTRACT FROM AUTHOR]