• Energy Research

Abstract The kinetics of methane hydrate decomposition was studied using a semibatch stirred-tank reactor. The decomposition was accomplished by reducing the pressure on a hydrate slurry in water to a value below the three-phase equilibrium pressure at the reactor temperature. The data were obtained at temperatures from 274 to 283 K and pressures from 0.17 to 6.97 MPa. The stirring rates were high enough to eliminate mass-transfer effects. Analysis of the data indicated that the decomposition rate was proportional to the particle surface area and to the difference in the fugacity of methane at the equilibrium pressure and the decomposition pressure. The proportionality constant showed an Arrhenius temperature dependence. An estimate of the hydrate particle diameters in the experiments permitted the development of an intrinsic model for the kinetics of hydrate decomposition.

A new strategy to concentrate phospholipids from buttermilk powder was developed using a food-grade green method based on ethanol-modified supercritical carbon dioxide (SC-CO2) extraction. The effects of extraction conditions, namely temperature (50 and 60°C), pressure (30 and 40 MPa), and ethanol concentration (10, 15, and 20%, wt/wt), on the total lipid yield and phospholipid content were investigated. The ethanol concentration had a more significant effect on the total lipid yield and phospholipid content than the temperature and pressure within the ranges studied. The highest phospholipid recovery was achieved at 60°C, 30 MPa, and 15% (wt/wt) ethanol with a total lipid yield of 6.3% (wt/wt), of which 49% (wt/wt) were phospholipids composed of dihydrosphingomyelin (5%), sphingomyelin (24%), phosphatidylethanolamine (22%), phosphatidylserine (2%), phosphatidylinositol (3%), and phosphatidylcholine (44%). The triacylglycerol compositions of extracts obtained by Folch and ethanol-modified SC-CO2 extractions were similar. A sequential pure SC-CO2 and ethanol-modified SC-CO2 extraction was carried out to separate nonpolar lipids in the first fraction, thereby concentrating phospholipids in the second fraction. This sequential extraction produced a highly concentrated phospholipid extract (76%, wt/wt). To the best of our knowledge, this is the highest phospholipid concentration reported from buttermilk powder. Thus, this phospholipid-rich extract can be used in the development of functional foods as a food-grade emulsifier with potential health-promoting effects.

This contribution proposes an enzyme-assisted eco-friendly process for the extraction of non-extractable polyphenols (NEPPs) from black tea leftover (BTLO), an underutilized tea waste. BTLO hydrolyzed with various enzyme formulations was extracted using supercritical carbon dioxide and ethanol as co-solvent (SC-CO2 + EtOH). A conventional solvent extraction (CSE) was performed using EtOH + H2O (80:20, v/v) for comparison purposes. The results revealed that hydrolysis of BTLO with 2.9% (w/w) kemzyme at 45 °C and pH 5.4 for 98 min improved the liberation of NEPPs offering 5-fold higher extract yield (g/100 g) as compared with non-treated BTLO. In vitro antioxidant evaluation and LC-MS characterization of extracts revealed the presence of phenolic acids (mainly caffeic and para-coumaric acid) of high antioxidant value. Scanning electron micrograph of the hydrolyzed BTLO samples indicated noteworthy changes in the ultrastructure of BTLO. Moreover, polyphenol extracts obtained by SC-CO2 + EtOH extraction were found to be cleaner and richer in polyphenols as compared to CSE. The devised enzyme-assisted SC-CO2 + EtOH extraction process in the present work can be explored as an effective biotechnological mean for the optimal recovery of antioxidant polyphenols. Graphical abstract Enzymatic pretreatment can effectively liberate non-extractable polyphenols (NEPPs) while hydrolyzing the cellulosic and hemicellulosic framework of black tea left overs (BTLO).