No abstract

Arenga pinnata starch (APS) is separated into large and small size fractions. The large granules (APS-L) show a more elongated oval shape, while the small granules (APS-S) are roughly close to a round shape. The large and small granules exhibit a Maltese cross at one end of the APS granules. Both large and small fractions show C-type crystallinity, but the APS-L display a higher crystallinity and more ordered molecular structure. In addition, APS-L have higher helices content than that of APS-S. The APS-L have higher peak viscosity, trough, and final viscosity values, breakdown value, gelatinization enthalpy, and gelatinization temperatures than that of the APS-S, but the APS-L fraction displays a lower setback value. The APS-S gel is more elastic and more solid than APS-L gel. The results indicate that granule size is significantly related to pasting, rheological, and thermal properties of the APS.

This study aims to investigate chitosan (CS) with five different molecular weight (Mw) on freeze–thaw stability of Arenga pinnata starch (APS) gel subjected to five freeze–thaw cycles (FTC). The syneresis of APS gels was reduced by adding CS and the APS gel with high Mw CS had lower syneresis duo to a higher water holding capacity (P < 0.05). The addition of CS significantly decreased the hardness and molecular ordered structure of APS gel. In addition, CS could improve the microstructural stability. The results suggested that CS could effectively improve the freeze–thaw stability of APS gel, and CS with higher Mw might have more practical utility to improve stability of APS gel.

In vitro digestibility and physicochemical properties of chitosan (CS)-modified Arenga pinnata starch (APS) after heat-moisture treatment (HMT) were evaluated. HMT would limit the enzymatic hydrolysis of APS and the digestion rate of HMT-APS-CS was further reduced with the decrease of CS molecular weight. CS and HMT inhibited the solubility (SOL) and swelling power (SP) of APS, and the inhibition effect was more obvious with the decrease in CS molecular weight. Changes in the pasting properties of the CS-modified APS indicated that the initial structure of the APS granules was destroyed with the formation of a denser structure. The increase of the relative crystallinity and the aggregation of the APS granules were related to starch cross-linking confirmed by Fourier transform infrared. The interactions between CS and APS granules after HMT greatly altered granular morphology and internal structure of APS. Therefore, the improvements of SDS and RS of HMT-APS-CS were mainly related to CS covering the surface of the APS granules, granule aggregation and HMT-induced changes in the internal structure of the starch granule.

Processing has a great influence on starch digestibility and increasing attention has been paid to the application of emerging environmentally friendly starch modification technology. Hierarchical structure and digestibility of sugar palm (Arenga pinnata) starch (APS) following high speed jet (HSJ) treatment are investigated. HSJ treatment (at 200 MPa for different processing cycles) significantly increases the rapidly digestible starch (RDS) content and decreases the slowly digestible starch and resistant starch content and significantly decreases the molecular weight of amylopectin and destroys granular structures with increasing treatment passes. The number of double helices is also reduced. The structural changes alter the digestibility of uncooked APS and transform the slowly digestible and/or resistant starch to the rapidly digestible form.