Microfiltration of high concentration black tea streams for haze removal using polymeric membranes

Abstract

Black tea used for RTD beverages suffers from an inherent haze problem affecting the appeal of products in terms of colour and appearance; the affect also diminishes health giving properties. Microfiltration of black tea streams up to 10.0 wt.% has been carried out in an attempt to remove this haze by way of a feasibility study for a unit operation to replace current alkali solubilisation methods which can be damaging to the product. The three commercial polysulfone membranes tested show superior haze removal in tea when filtered at ambient temperature, with turbidity values of below 5 NTU being recorded for all membranes over all processing conditions tested. In addition, haze reoccurrence has been slowed following membrane filtration, with turbidity values generally remaining below 50 NTU after 4 weeks of cold storage. At the cross flow velocities used for experimentation (0.5-1.5 ms-1), fluxes were below what would be classified as acceptable for industrial applications although flux improvements were shown to be apparent for elevated tangential velocity and transmembrane pressure (4.0 bar) with membrane resistance during filtration dominated by concentration polarisation; a result of the high solids load in the feed. There is a loss of polyphenolics and colour in the permeate product although a trade-off between haze and stability over time and levels of key polyphenolics (responsible for colour and flavour) was expected. The rejection coefficients for polyphenolic species was much greater compared to total solids rejection for all operating conditions. Tea permeate appearance showed strong dependency with operating conditions, which shows the potential for tailoring of tea appearance, a useful capability in terms of maintaining product consistency given the natural variability, a result of growing conditions and other factors. Overall the potential for microfiltration of black tea has been shown to be effective in removing haze with this article highlighting the research efforts required to make this process a scalable industrial practice.

Membrane fouling mechanisms and permeate flux decline model in soy sauce microfiltration

“…However, the increasing trend became slow when CFV increase from 0.30 m/s to 0.47 m/s. Similar phenomenon was found in black tea, apple juice and titanium white waste acid clarification (Argyle & Bird, ; Vladisavljevic et al, ; Zhao et al, ).…”

“…In this work, the optimized TMP was about 0.12 MPa and higher pressure resulted in severe membrane fouling. apple juice and titanium white waste acid clarification (Argyle & Bird, 2014;Vladisavljevic et al, 2003;Zhao et al, 2003).…”

The effect of ethanol pre-treatment upon the mechanical, structural and surface modification of ultrafiltration membranes

“…This assumes that any modification occurring on the surface also occurs inside the pores. Argyle et al [9] showed that the through-pore negative zeta potential decreased upon ethanol treatment of PSU membranes. This indicated that the effect may arise due to a thin film of alcohol remaining on pore walls, resulting in a shielding of the true pore surface charge and consequently a reduction in the streaming potential value.…”

Manufacturing of Low Haze Instant Tea Extracts Using Sri Lankan Broken Mixed Fannings (BMF) as Raw Materials

“…Instant tea suffers from an inherent haze problem or tea cream formation which causes the loss of transparency, colour, taste and cup quality (Powell et al, 1993) which reduces consumer preference and affects physical and sensory attributes and biological activities (Youngmok & Stephen, 2012). The complexation of polyphenols by the association of their galloyl groups with limited solubility is said to be the cause for the tea cream formation (Argyle & Bird, 2015). Studies have shown that phenolic acids, tea catechins, and flavanol glycosides are involved in tea creaming and potassium and calcium ions activated the process.…”