Stevia rebaudiana Bertoni is a medicinal plants and commercially use as non-caloric sweetener for diabetic patient. In the present study, a protocol was developed for in vitro micropropagation using 6-benzylamino purine (BAP) and Kinetin (Kn) for the formation of multiple shoot proliferation and Indole-3-acetic acid (IAA), Indole-3-butyric acid (IBA) and 1-Naphthaleneacetic acid (NAA) for the induction of roots. Maximum shoot formation (7.82 ± 0.7 shoots per explants) was observed on a Murashige and Skoog (MS) medium supplemented with 0.5 mg L-1 BAP and 0.25 mg L-1 Kn. The maximum number of roots (30.12 ± 2.1 roots per explants) was obtained on a MS medium containing 1.0 mg L-1 IBA. The well rooted plantlets were successfully weaned and acclimatized in plant soil with survival rate of 83.3 %.

Immobilization of cross-linked tannase on pristine multiwalled carbon nanotubes (MWCNT) was successfully performed. Cross-linking of tannase molecules was made through glutaraldehyde. The immobilized tannase exhibited significantly improved pH, thermal, and recycling stability. The optimal pH for both free and immobilized tannase was observed at pH 5.0 with optimal operating temperature at 30°C. Moreover, immobilized enzyme retained greater biocatalytic activities upon 10 repeated uses compared to free enzyme in solution. Immobilization of tannase was accomplished by strong hydrophobic interaction most likely between hydrophobic amino acid moieties of the glutaraldehyde-cross-linked tannase to the MWCNT.

Summary The antioxidant activities of native‐ and tannase‐treated green tea extracts along with their major polyphenol components were investigated. The polyphenolic content and composition of the tea before and after tannase treatment were determined by liquid chromatography coupled with mass spectrometry (LC‐MS). Approximately 99% of the (−)‐epigallocatechin gallate (EGCG) and (−)‐epicatechin gallate (ECG) in green tea extract were converted by tannase to (−)‐epigallocatechin (EGC) and (−)‐epicatechin (EC), respectively, after 30 min. Biotransformed green tea exhibited a significantly higher DPPH˙ radical scavenging activities than native green tea (EC50 value of 0.024 ± 0.001 and 0.044 ± 0.001 mg mL−1, respectively). Kinetic parameters such as scavenging rate and stoichiometry were calculated. The rate of DPPH˙ radical scavenging activities for tannase‐treated green tea extract was shown to be higher than native green tea extract.

Aspergillus niger FBT1, a local extracellular strain for tannase production, was isolated from soil collected from Matang Mangrove Forest Reserve in Perak, Malaysia. This fungus strain was cultivated in an Erlenmeyer flask under a submerged fermentation system. Medium compositions play a very important role in enhancing enzyme production during fermentation. The production of tannase by A. niger FBT1 increased significantly (95%) when the medium compositions and various process parameters were optimized. Incubation for 72 hours (30EC, pH 7) in medium complemented with sodium nitrate was found optimal. Additional supplementation with tannic acid (2% w/v) as the sole carbon source strongly increased the yield of the enzyme.

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