Abstract
Amylose is well known to be organized helically with six glucose per turn, allowing it to form complexes with various ligands. This interaction can be affected by the type of crystalline structure present in the starch sources. This study evaluated the effect of extrusion on the crystalline structure of starch during RS5 formation. Rice and potato starches were extruded at 100 °C and 15 rpm with 5% and 10% oleic acid (OA), then the physical, thermal, paste properties, and resistant starch content (RS) were evaluated. Potato starch extruded with 10% OA showed granules embedded in a gelatinized starch matrix. The X-ray revealed that rice (orthorhombic) and potato (hexagonal) structures remain unchanged even after extrusion. Differential scanning calorimetry (DSC) evidenced the formation of type IIa amylose-lipid complexes in OA treatments, where potato extruded with 10% OA had the highest enthalpy (0.9 J/g). Moreover, the extruded potato showed the highest pasting temperature (87.19 °C), supporting the complex formation. The RS was reduced from 15.8 (isolated) to 4.14 mg/100 mg (extruded 10% OA) in rice. For potato, RS decreased from 17 to 13 mg/100 mg (isolated and extruded 10% OA). Overall, these findings suggest a tendency in potato starch (ortho-rhombic) to interact with OA during the extrusion process, promoting a crystalline lamellae growth when extruded with 10% OA; therefore, changing their properties.
Highlights
Starch is one of the main polysaccharides in plants and has been used extensively in the food industry
This work evaluated the effect of extrusion on the crystalline structure of starch during
It is important to recall that this interaction does not produce any new crystalline structure, as has been pointed out elsewhere
Summary
Starch is one of the main polysaccharides in plants and has been used extensively in the food industry. Starch is a sub or microparticle formed by lipids, proteins, minerals, water, bonded water, amylose, and amylopectin, and pyroglycans forming orthorhombic and hexagonal crystalline structures [1]. Amylose and amylopectin are glucose polymers that differ in their branching characteristics. Amylopectin consists of D-glucose units linked by α-(1→4), branched every 20 to 22 units by glycosidic links α-(1→6), with an incidence of ~5%. Amylose is linear chains of D-glucose linked by glycosidic bonds α-(1→4), with an occasional branching α-(1→6) less than 0.5%, typically for high molecular weight amylose. Amylose is arranged in helical structures containing 6 to 8 glucose units per turn [3]. This characteristic gives amylose the ability to interact with amphiphilic or hydrophobic molecules (ligands), Polysaccharides 2021, 2, 187–201.
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