Abstract Four 2,5-dicholorobenzoate monomers were prepared by chlorination and esterification and then polymerized to ester substituted poly( p -phenylene)s through Ni/Zn catalyzed coupling reaction. The thermal stability and pyrolysis behavior of ester substituted poly( p -phenylene)s were investigated through TGA method. The possible mechanism of thermal modification of the polymers was proposed that included de-esterification, dehydration and decarboxylation, and finally de-anhydridization. Only pyrolysis of esters substituted poly( p -phenylene)s containing two neighboring carboxyl groups may result in the formation of the corresponding anhydride.
Tianyou Cui,Yujing Tang,Mengqian Zhao,Yang Hu,Mingjie Jin,Xuwei Long
This investigation developed a novel strategy for efficiently preparing glucolipids (GLs) by chemically modifying crude sophorolipids. Running this strategy, crude sophorolipids were effectively transformed into GLs through deglycosylation and de-esterification, with a yield of 54.1%. The acquired GLs were then purified via stepwise extractions, and 66.2% of GLs with 95% purity was recovered. GLs are more hydrophobic and present a stronger surface activity than acidic sophorolipids (ASLs). More importantly, these GLs displayed a superior antimicrobial activity to that of ASLs against the tested Gram-positive food pathogens, with a minimum inhibitory concentration of 32–64 mg/L, except against E. coli . This activity of GLs is pH-dependent and especially more powerful under acidic conditions. The mechanism involved is possibly associated with the more efficient adsorption of GLs, as demonstrated by the hydrophobicity of the cell membrane. These GLs could be used as antimicrobial agents for food preservation and health in the food industry.
The amidation of pectin by amino acids has been widely applied due to its safety and excellent gelling properties. This study systematically examined the effects of pH on the gelling properties of lysine-amidated pectin during amidation and gelation . Pectin was amidated over the range of pH 4–10, and the amidated pectin obtained at pH 10 showed the highest degree of amidation (DA, 27.0 %) due to the de-esterification, electrostatic attraction, and the stretching state of pectin. Moreover, it also exhibited the best gelling properties due to its greater numbers of calcium-binding regions (carboxyl groups) and hydrogen bond donors (amide groups). During gelation, the gel strength of CP (Lys 10) at pH 3–10 first increased and then decreased, with the highest gel strength at pH 8, which was due to the deprotonation of carboxyl groups, protonation of amino groups, and β-elimination. These results show that pH plays a key role in both amidation and gelation, with distinct mechanisms, and would provide a basis for the preparation of amidated pectins with excellent gelling properties. This will facilitate their application in the food industry.
Chao Tang,Zhaojuan Shi,Jun Wu,Tingting Zhu,Qingmei Zeng,Chuanxun Yuan,Risheng Jin
Summary This study examined the effects of different degree of esterification (DE) on the stability of high internal phase Pickering emulsions (HIPPEs) fabricated using pectin-whey protein isolate complexes. The modified pectin with different DE was prepared using the alkali de-esterification method with high methoxyl pectin (HMP). The impact of DE on the conformational changes of pectin and whey protein isolate (WPI) during the complexes formation was examined using Fourier transform infrared spectroscopy (FTIR) and fluorescence spectroscopy. Citrus pectin (CP)–WPI complexes and camellia oil were used to create an emulsion with a self-supporting structure of 75% internal phase volume. The thermal, centrifugal, storage and freeze–thaw stabilities of CP–WPI stabilised HIPPEs with different DE were evaluated and the results revealed that the low methoxyl pectin (LMP) produced via alkali de-esterification altered the charge density of pectin. Compared with the untreated pectin, the electrostatic interaction between CP–WPI complexes was enhanced and the stability of CP–WPI stabilised HIPPEs was improved. The study will help to better understand the interaction between CP and WPI, enhance the efficiency of the pectin–protein delivery system and improve the utilisation rate of citrus pectin, which has important guiding significance.
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