Abstract
The NaOH-HCl- and ethanol-pretreated pomelo peel samples were prepared to apply to the batch adsorption for epigallocatechin-3-gallate (EGCG). The characteristics of peel samples were determined by Fourier transform infrared spectroscopy, scanning electron microscopy and a laser particle analyzer. The results of the physiochemical properties of the peel samples demonstrate that these peel samples have a promising adsorption capacity for EGCG, because of the increased potential binding sites on the surface compared with those of untreated peel samples. These two peel samples showed enhanced adsorption capacities of EGCG compared with that of unmodified peel in terms of the isothermal adsorption process, which could be described by both Langmuir and Freundlich models, with the theoretical maximum adsorption capacity of 77.52 and 94.34 mg g−1 for the NaOH-HCl and ethanol-treated peel samples, respectively. The adsorption kinetics demonstrated an excellent fitness to pseudo-second-order, showing that chemisorption was the rate-limiting step. The thermodynamics analysis revealed that the adsorption reaction was a spontaneous and endothermic process. This work highlights that the processed pomelo peels have outstanding adsorption capacities for EGCG, which could be promising candidates for EGCG delivering in functional food application.
Highlights
Tea catechins are a class of abundant polyphenolic compounds belonging to flavanols present in Camellia sinensis (L.), of which epigallocatechin-3-gallate (EGCG) is the most important component with the highest content and several health benefits, including anti-irradiation [1], anti-carcinogenic [2], anti-inflammatory [3], anti-oxidative [4] and anti-cardiovascular [5] features, etc
The band appeared around cm−1 in pomelo peel (PP) was attributed to the stretching vibration of the C=O bond from non-ionic carboxyl groups (-COOCH3, -COOH), which was observed in ethanol-modified peel (EP) peel, while the decrease of this band in the NaOH-HCl modified pomelo peel (NHP) peel sample implied that the phenolic acids were probably removed from the NHP after
The band peaked at 1645 cm−1 in the NHP sample could be related to C=O vibration of acid or ester, indicating alkaline treatment induced a saponification effect, resulting in a asymmetric stretching vibrations increasing of ionic carboxylic acid groups (-COO− ), while this band was shifted to 1633 cm−1 in EP with a little decrease, suggesting that the carboxylic functional group was probably esterified by ethanol [23]
Summary
Tea catechins are a class of abundant polyphenolic compounds belonging to flavanols present in Camellia sinensis (L.), of which epigallocatechin-3-gallate (EGCG) is the most important component with the highest content and several health benefits, including anti-irradiation [1], anti-carcinogenic [2], anti-inflammatory [3], anti-oxidative [4] and anti-cardiovascular [5] features, etc. The stability and bioavailability of EGCG are quite susceptible to oxidants, high temperatures and alkaline environments; the degradation or epimerization could be observed when EGCG has suffered from those adverse factors [6,7,8,9], which limits the application of EGCG in functional foods. The lipid nanoparticlulate delivery system has been used for EGCG delivering, which protected EGCG against degradation during gastrointestinal digestion, with the stability of encapsulated EGCG ranging from 80% to 90% [10]. Whey protein has been applied to the formation of the EGCG complex to stabilize the EGCG in digestion simulation, and the phenolic showed a more stable property when associated with the protein [11]. The controlled-release rate of EGCG from zein/chitosan nanoparticles in 95% ethanol fatty simulant could arrived at 32%, with a long-term protection against oxidation for Molecules 2020, 25, 4249; doi:10.3390/molecules25184249 www.mdpi.com/journal/molecules
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