Structural and Physicochemical Properties of Longan Kernel Starch by Enzyme-assisted Alkali Extraction

Objective: To clarify the structure and physicochemical properties of longan kernel starch extracted by enzyme-assisted alkali method. Methods: Using longan kernel as raw material and alkaline protease as enzymatic hydrolysis agent, the longan kernel starch was extracted. The chemical composition, particle size, morphology, crystal structure, transparency, solubility and swelling power, thermodynamic properties and gelatinizing properties of starch were studied. Results: 100 g longan kernel starch contained 82.64 g starch, 0.68 g crude fat, 0.46 g crude protein and 1.06 g ash, and its amylose content was 36.37%. Its particles were mostly elliptic or irregular polygon, and their average size was 11.21 μm. The starch had type A crystalline structure and higher short-range order degree. In addition, 1% (w/v) longan kernel starch paste had 4% transparency. Its solubility and swelling power increased with the increase of temperature, being 11.26% and 15.93% at 90 ℃, respectively. Longan kernel starch had high gelatinization initial temperature (70.4 ℃), peak temperature (75.9 ℃), conclusion temperature (82.1 ℃) and enthalpy change (13.7 J/g). Its hot paste stability was poor while its cold paste stability was better. Conclusion: Longan kernel starch by enzyme-assisted alkali extraction had high amylose content and its protein content decreased obviously. In addition, it had small granules, and it was not easily gelatinized.