Dietary fibers fractionated from gardenia (Gardenia jasminoides Ellis) husk: structure and in vitro hypoglycemic effect.

ABSTRACT

BACKGROUND: Gardenia (Gardenia jasminoides Ellis) husk rich in dietary fiber is a byproduct of fructus processing, and commonly discarded as waste. The husk was fractionated by sequential extraction into four fractions water-soluble fiber (W-SF), acid-soluble fiber (Ac-SF), alkali-soluble fiber (Al-SF) and insoluble residue fiber (IRF). The aim of this study was to investigate the differences in structure and in vitro hypoglycemic effect of these fibers. RESULTS: Monosaccharide composition and Fourier transform infrared spectra showed that the major component might be pectin for W-SF and Ac-SF, xylan as well as pectin for Al-SF and cellulose for IRF. These fibers offered excellent water-holding capacity and swelling capacity, except that IRF was only slightly swellable in water. W-SF exhibited significantly higher capacities to adsorb glucose (2.408 mmol g-1 at a glucose concentration of 200 mmol L-1 ) and inhibit α-amylase activity (29.48-49.45% inhibition rate at a concentration of 4-8 mg mL-1 ), probably caused by the higher viscosity and hydration properties; while Ac-SF, Al-SF and IRF (especially Al-SF) were more effective in retarding the glucose diffusion across a dialysis membrane (34.97-41.67% at 20-30 min), which might be attributed to particle size and specific surface area. All the fibers could quench the intrinsic fluorescence of α-amylase to some degree. CONCLUSIONS: Dietary fiber from gardenia husk, especially W-SF, can be used as a potential hypoglycemic ingredient in diabetic functional foods. © 2020 Society of Chemical Industry.