Abstract
Drying is an essential pre-treatment prior to extraction of tea polyphenols from tea leaves, which is a time and energy-intensive process. In this study, pulsed electric field (PEF) was utilized to replace the conventional thermal dehydration procedure before the phenolic extraction. The influence of different PEF conditions on total polyphenol yield from fresh tea leaves combined with a solid-liquid extraction were compared. PEF treatment at 1.00 kV/cm electric field strength, 100 pulses of 100 μs pulse duration, and 5 s pulse repetition, which delivered 22 kJ/kg and induced 1.5 °C of temperature increase, was used for further study on the extraction kinetics of green tea catechins. The results indicated that compared to oven drying, PEF pre-treatment increased the extraction rate by approximately two times, without significantly altering the phenolic profiles, as revealed by using liquid chromatography combined with mass spectrometry. Scanning electron microscopy imaging revealed that PEF pre-treatment induced the formation of inhomogeneously distributed pores and protuberances on the surface of leaf tissues, which might facilitate the penetration of extraction solvent and the migration of phenolics. This study demonstrates that PEF as a time and energy efficient processing method is a promising alternative for the conventional drying process before further tea polyphenol extraction.
Highlights
It has been widely accepted that tea, derived from the leaves of Camellia sinensis, is a healthy beverage
Many studies have shown the efficiency of the application of pulsed electric field (PEF) as pre-treatment combined with organic solvent extraction for bioactive compound transfer from plant matrices (Zbinden et al 2013; Boussetta et al 2014; Jaeschke et al 2016)
Turkmen et al have highlighted the efficiency of a mixture of acetone and water (1:1) for tea polyphenol extraction (Turkmen et al 2006), and this was chosen as the extraction solvent in this study
Summary
It has been widely accepted that tea, derived from the leaves of Camellia sinensis, is a healthy beverage. Mechanical pressing or grinding is widely used to completely disrupt the cell, but it results in non-selective release of all cell components and creates large amounts of cell debris, which complicates the subsequent fractionation (Postma et al 2016). Drying is another widely used procedure for disruption of plant cells. This procedure causes breakage and collapse of cell walls and the formation of large cavities and intercellular spaces, allowing the cellular substances to be extracted (Drosou et al 2015).
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