ENYMOLOGIC CHARACTERIZATION OF GARLIC FRUCTAN EXOHYDROLASE

Abstract

Fructans represent over 75% of the dry mass of garlic (Allium sativum L.). Understanding the enzymologic characteristics of garlic fructan exohydrolase (FEH) can provide theoretical basis on garlic germination inhibition and mass production of high-quality garlic fructans. In this study, we isolated and localized FEH by ammonium sulfate fractional precipitation, analyzed the fructan enzymolysis products by thin-layer chromatography (TLC) and ion chromatography, and determined FEH activity by measuring changes of reducing sugars via 3,5-dinitrosalicylic acid assay. We further characterized the hydrolysis site of FEH and effects of temperature, pH level, ionic strength and substrate concentration on its activity. Results showed that FEH was present in the 0–20% ammonium sulfate fraction. Analysis of the hydrolysis product by both TLC and ion chromatography suggested that FEH was an excision enzyme. The optimum conditions for FEH activity were 45C, pH 5.5, ionic strength of 1.5 M (sodium chloride) and substrate concentration of 4 mg/mL. PRACTICAL APPLICATIONS During garlic storage, quality degradation such as shrinkage, softening, drying and decreased crispiness often occurs. These deteriorations might be related to garlic fructan exohydrolase (FEH), because FEH could hydrolyze storage carbohydrates (fructan) to produce monosaccharide for energy metabolism. Thus, to keep the high quality of garlic during storage, the key is to control the activity of garlic FEH. We studied the activity of the enzyme. Results obtained from this study will provide foundation for FEH research and insights for manufacturing homogeneous-quality garlic fructan products.