Resistant Starch Contents of Starch Isolated from Black Longan Seeds

A large quantity of longan fruits (Dimocarpus longan Lour.) produced annually are processed into many products, one of which is black longan, from which the dried, dark-brown meat has been used medicinally in traditional medicine, while the starch-containing seeds are discarded. In this study, starch samples (BLGSs) were isolated from seeds of black longan fruits prepared using varied conditions. The in vitro digestibility was determined in comparison with those extracted from fresh (FLGS) and dried (DLGS) seeds. Scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy were employed to evaluate the starch properties. The results showed that the yields of FLGS, DLGS, and BLGSs were 20%, 23%, and 16–22% w/w, respectively. SEM images showed starch granules of mixed shapes, with sizes up to 15 µm in all samples. XRD patterns confirmed an A-type crystallinity for FLGS and DLGS, with strong refraction peaks at 2θ = 15°, 17°, 18°, and 23°, while BLGSs also showed detectable peaks at 2θ = 10° and 21°, which suggested V-type structures. Thermal properties corroborated the changes by showing increases in peak gelatinization temperature (T_p) and enthalpy energy (ΔH) in BLGSs. The paste viscosity of BLGSs (5% w/w) decreased by 20–58% from that of FLGS. The FTIR peak ratio at 1045/1022 and 1022/995 cm⁻¹ also indicated an increase in ordered structure in BLGSs compared to FLGS. The significant increase in the amounts of slowly digestible starch (SDS) and resistant starch (RS) in BLGSs compared to FLGS, especially at a prolonged incubation time of 20 (4.2×) and 30 days (4.1×), was proposed to be due to the heat-induced formation of starch inclusion with other components inside the seed during the black longan production process. Thus, black longan seed could be a new source of starch, with increased RS content, for potential use in the food and related industries.     

Mathematical modelling for equilibrium configurations of concentric gold nanoparticles

Nanotechnology is a promising research area, and it is believed that the unique properties of molecules at the nano-scale will benefit mankind especially in the medical exploration. Here we utilize an applied mathematical modelling to investigate spherical and cylindrical concentric structures of gold nanoparticles, with the aim of maximising the free space for which to improve amount of drug or gene to bind on the nanoparticle surfaces and deliver to the target cells. The energy between two gold molecules is modelled by the 6–12 Lennard-Jones potential function, and the total potential between two layers for such particles is calculated using the continuous approximation. On minimising the energy function, the radii for five layers for the concentric sphere and likewise for the cylinder are presented. Further, the equilibrium spacing between any two layers is predicted to lie in the range 2.94–2.96 Å, for both concentric structures. There are at present no experimental or simulation results for comparison with the theoretical equilibrium configurations for concentric gold nanoparticles predicted by this study.