A process for producing a natural sweetening enhancer composition comprising at least an Rebaudioside C (RC) extract, said process comprises the steps of preparing a saccharide mother liquor comprising an RC mass content of at least 15%; preparing feed liquid from about 8-25 mg/L of the mother liquor; flowing feed liquid through a porous adsorption column, having a pore size of between about 0.001 to 0,.2 micron, and at a flow rate of between 25 to 35 L/m2h and at a pH of between 6 to 8; eluting RC extract with alcohol, said RC extract having a mass concentration of at least 10%; fractionally collecting eluate based on chromatographic critical point for RC extract; concentrating the RC extract and drying the extract so formed. Another process for preparing a crude RC extract which comprises the steps of preparing a saccharide mother liquor into a feedstock solution with a mass concentration of about 0.5-1%; passing the solution through an ultrafiltration membrane device at a flow rate of 25-35 L/m2h, with a molecular weight cut-off at about 5500-6500 DA and at a pH of between about 6.5-7.5, collecting and then concentrating the RC filtrate from about 55°C to 65°C„ drying solid and liquid fractions obtained from the concentrate separately to provide a crude RC extract. Extracts obtained from processes above are further refined by crystallization from water-alcohols (e.g. ethanol and methanol)-acetone mixed solvents to provide a crystalline solid comprising high content of RC.