Characteristics of the emulsion stabilized by polysaccharide conjugates alkali-extracted from green tea residue and its protective effect on catechins

Abstract

Alkali-extracted tea polysaccharide conjugates, termed TPC-A, are obtained from the residue derived from tea after water extraction. Oil-in-water emulsions stabilized by different concentrations of TPC-A (0.5 wt%, 1.0 wt %, 1.5 wt %, 2.0 wt %, and 3.0 wt%) were prepared using medium chain triglycerides (MCT). The optimal concentrations of TPC-A were 2.0 wt % and 3.0 wt %. We investigated the effects of the storage time of 10 days, pH 2.0–10.0, and metal ions (Na+ and Ca2+) on the emulsion stabilized using 2.0 wt % TPC-A at 25 ℃. During the 10-day storage period, the mean particle diameter (MPD) (d32) of the emulsion stabilized using 2.0 wt % TPC-A slightly increased from 0.31 μm to 0.37 μm, and the absolute value of the zeta potential increased from 44.9 mV to 41.4 mV. Under neutral or alkaline conditions, the emulsion stabilized using TPC-A had the MPD (d32) of less than 0.30 μm and the absolute value of the zeta potential ranging from 40.52 to 41.53 mV. The MPD (d32) of the emulsion in different Na+ concentrations from 0 mmol/L to 500 mmol/L, increased from 0.30 μm to 2.80 μm, and their absolute value of zeta potential decreased from 41.0 mV to 37.7 mV. The emulsion stabilized using TPC-A had a favorable protective effect on EGCG and EGC, and the retention rates of EGCG and EGC during the 10 days were 7 and 6 times higher than those without TPC-A emulsion protection, respectively. TPC-A extracted from tea residue, which is abundantly available and cheap, can be used as a natural emulsifier, in order to develop a milky food or beverage products with excellent health benefits.