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Membrane Processing of Black Tea Extracts.

IR@CSIR-CFTRI

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Relation http://ir.cftri.com/11348/
 
Title Membrane Processing of Black Tea Extracts.
 
Creator Chandini, S. Kumar
 
Subject 16 Enzyme Chemistry
08 Tea
 
Description 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.
Membrane 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. UF (500 kDa) and MF (200 and 450 nm)
membranes resulted in greater retention of original colour, besides higher and
polyphenols-to-pectin ratios in the clarified extract. Accordingly, subsequent
studies were planned with these membranes at various higher feed
concentrations to improve the recovery and productivity under diafiltration (DF)
mode of operation. Increase in feed concentration affected the recovery. DF
was effective in improving solids recovery including polyphenols and theaflavins
but suggested a limit (100-150%) so that elimination of hostile components such
as pectins is not dropped below 50%. Assessment of primary quality criteria,
turbidity and tea cream contents as well as PPS (polyphenols-in-permeated
solids) supported processing at low feed concentrations. Solids and polyphenols
recoveries obtained with 0.6% feed concentration and MF-450 membrane
combination were unmatched with any other combination employed. The study
asserted that MF is preferred over UF membranes for clarification of tea extracts.
Further, the antioxidant potential (DPPH) of reject stream of membrane process
was comparable to the original tea solids of the crude extract, despite significant
differences in their phenolic contents owing to contributions from other nonphenolic
tea components. The results suggested that the final retentate stream
containing a substantial amount of tea solids (~24%) could be used as a tea
conserve in functional foods. The study revealed that membrane clarification of
tea extracts offers the possibility of reducing tea cream formation and haze in
RTD tea beverages and improve its stability during refrigerated storage while
retaining most of the natural quality characteristics of tea.
 
Contributor Subramanian, R.
 
Date 2011
 
Type Thesis
NonPeerReviewed
 
Format application/pdf
 
Language en
 
Rights —
 
Identifier http://ir.cftri.com/11348/1/Chandini.pdf
Chandini, S. Kumar (2011) Membrane Processing of Black Tea Extracts. PhD thesis, University of Mysore.