Application of α-amylase-assisted extraction of longan seed polysaccharides in preparation of chromium-free tanning agents

The present study examined the effect of α-amylase on complex carbohydrates in longan seeds and assessed the feasibility of using these carbohydrates as tanning agents. Enzymatic and hot-water extracts were purified and analyzed for their structural components and physicochemical properties. Enzymatic extraction with ultrasonic assistance yielded higher levels of bioactive components in longan seed polysaccharides (LSPs) than the non-enzymatic method. Dialdehyde longan seed polysaccharides (DLSPs) were prepared using LSPs and NaIO 4 . The effects of different NaIO 4 concentrations on molecular size, aldehyde content, other chemical compositions, structural characteristics, and tanning performance of DLSPs were evaluated. Increasing NaIO 4 concentrations decreased total sugars, polyphenols, and saponins, while raising protein content. The oxidant broke glycosidic bonds and oxidized o -dihydroxyl groups, forming reactive aldehyde groups. The DLSP-tanned leather exhibited a shrinkage temperature of 76.4 °C and tensile strength of 17.03 MPa. The tanning performance and bioactivity of DLSPs stem from lower molecular weight and high aldehyde and hydroxyl content. These polysaccharide samples exhibited good permeability and cross-linking reactivity within the collagen fiber network. Therefore, DLSPs are a promising new type of chromium-free tanning agents.