Abstract:

Freshly harvested old tea leaves were pretreated for the removals of lipid and water-soluble substances such as polyphenols, sugars and amino acids before sequential hydrolysis with amylase followed by papain for production of waterinsoluble dietary fiber (IDF). To maximize IDF yield, papain hydrolysis parameters such as enzyme dosage, pH, hydrolysis temperature and time and material/liquid ratio were investigated by single factor and orthogonal array design methods. Results showed that the effects of the parameters on IDF yield decreased in the following order: pH＞hydrolysis time＞enzyme dosage ＞hydrolysis temperature＞material/liquid ratio. A maximum IDF yield of up to 94.12% was obtained through the extraction for 2 h at 65 ℃, pH 4.0 and a material/liquid ratio of 1:10 using an enzyme dosage of 0.004 g/g. The IDF obtained was good in water holding capacity, swelling capacity, water binding capacity, oil holding capacity, cation exchange capacity and cholesterol and sodium cholate adsorption capacity, thereby providing an excellent IDF resource.

Key words: tea, water-insoluble dietary fiber, enzymatic method, extraction, physicochemical properties