Membrane processing of black tea extracts

Abstract

The thesis was initiated through an exhaustive review of research conducted worldwide towards application of enzymes and membrane technology in the production of ready-to-drink (RTD) black tea beverages. To begin with, the influence of extraction conditions on polyphenols content and tea cream constituents in black tea extracts was investigated, which revealed that it is desirable to optimize the extraction conditions in terms of polyphenols recovery rather than merely on extractable-solids-yield (ESY), more precisely on polyphenols content in extracted-solids (PES) with an equal focus on the important quality parameter, Theaflavins-to-thearubigins (TF/TR) ratio. However, the conditions standardized also co-extracted other tea components (proteins, calcium and pectin) responsible for various interactions leading to tea cream formation. Subsequent attempts were made using enzyme assisted extraction to enhance the recovery of polyphenols (besides ESY) and clarity using a cell-wall digesting enzyme (pectinase) and a tannin hydrolysing enzyme (tannase). The results revealed that tannase, hitherto considered only as a tannin hydrolyzing enzyme, displayed not only improvements in polyphenols recovery but also nearly a matching performance to pectinase in terms of ESY. Single enzyme treatment with only tannase could achieve similar performance to that of combined enzyme treatments, proposed earlier by several researchers. The results also revealed enzymatic extraction may be preferred over enzymatic clarification as it not only displayed reduction in tea cream and turbidity but also improved the recovery of polyphenols and ESY. newlineMembrane technology was assessed as a clarification method for black tea extract employing various microfiltration (MF) and ultrafiltration (UF) membranes with a focus on higher yield and greater retention of polyphenols.Clarity of membrane processed extracts was excellent (~4 NTU) even after 30 days of refrigerated storage.