Isolation and characterisation of tropomyosin from shrimp (Penaeus vannamei Boone) and its association property at high ionic strength.

Shrimps are important and highly demanded seafood, but they have been reported as a cause of food hypersensitive reaction. The major allergen of shrimp is tropomyosin (TM). However, so far, there has been few report on such purification procedure. In this study, we developed a strategy for the purification of TM from shrimp (Penaeus vannamei Boone). Subsequently, we demonstrated that the apparent MW of this protein is about 66 kDa, and this protein naturally contains two subunits (38.5 and 36.6 kDa) with a ratio of 1 to 1. Interestingly, different from other known TMs from vertebrates, shrimp TM can self-assemble into nanofibres at high ionic strength induced by ATP. These findings help to understand the structure and polymerisation property of TM from shrimps.

The interaction of phenolic acids with Fe(III) in the presence of citrate as studied by isothermal titration calorimetry.

Under physiological conditions, exogenous chelators such as polyphenols might interact with non-protein bound ferric complexes, such as Fe(III)-citrate. Additionally, Fe(III) and citrate are widely distributed in various fruits and vegetables which are also rich in phenolic acids. In this study, we focus on the interaction between phenolic acids (gallic acid, methyl gallate and protocatechuic acid) and Fe(III) in the presence of excessive citrate by isothermal titration calorimetry (ITC) for thermodynamic studies, and stopped-flow absorption spectrometry for fast kinetic studies. Results reveal that all of these three phenolic acids can bind to the Fe(III) with the same stoichiometry (3:1). Moreover, the binding constants of these three compounds with Fe(III) are greatly dependent on ligand structure, and are much higher than that of Fe(III)-citrate. Based on their stoichiometry and superhigh binding constants, it is most likely that these three phenolic acids can displace the citrate to bind with one iron(III) ion to form a stable octahedral geometric structure, albeit at different rates. These findings shed light on the interaction between phenolic acids and Fe(III) in the presence of citrate under either physiological conditions or in a food system.

Encapsulation of ß-carotene within ferritin nanocages greatly increases its water-solubility and thermal stability.

Carotenoids may play a number of potential health benefits for human. However, their use in food industry is limited mostly because of their poor water-solubility and low thermal stability. Ferritins are widely distributed in nature with a shell-like structure which offers a great opportunity to improve the water-solubility and thermal stability of the carotenoids by encapsulation. In this work, recombinant human H-chain ferritin (rHuHF) was prepared and used to encapsulate ß-carotene, a typical compound among carotenoids, by taking advantage of the reversible dissociation and reassembly characteristic of apoferritin in different pH environments. Results from high-performance liquid chromatography (HPLC), UV/Vis spectroscopy and transmission electron microscope (TEM) indicated that ß-carotene molecules were successfully encapsulated within protein cages with a ß-carotene/protein molar ratio of 12.4-1. Upon such encapsulation, these ß-carotene-containing apoferritin nanocomposites were water-soluble. Interestingly, the thermal stability of the ß-carotene encapsulated within apoferritin nanocages was markedly improved as compared to free ß-carotene. These new properties might be favourable to the utilisation of ß-carotene in food industry.