| Vaccinium Bracteatum Thunb.(VBT), a traditional Chinese herbal medicine, is widely grown throughout China, which has great development prospects. The VBTL extraction(main component was VBTL pigment) was extracted and purified in this research, and its properties were analyzed. The mechanism of the interaction between VBTL pigment and rice protein/starch were also investigated.Firstly, the process for extracting Vaccinium Bracteatum Thunb. Leaf pigment(VBTL pigment) was optimized as following: the ratio of leaves to water 1:30(m:V), p H 5.0, temperature 50 ℃, extraction time 2 h and extraction number twice. Meanwhile, the purification process by using AB-8 macroporous resin was also optimized: p H 5.0, flow rate 2 ml/min, sample concentration 4.00 mg/m L, a two-step elution method by using 60% ethanol and ethyl acetate, respectively. The VBTL pigment collected by this process was the best purified and best dyed and it contains 61.97% polyphenol.Secondly, the properties of VBTL pigment were studied. The UV absorption spectra and infrared absorption spectra showed typical absorption peaks of polyphenols. VBTL pigment was solvable in water and common organic reagents, but was insoluble in petroleum ether. The colourity of VBTL pigment was 80.90. The research in antioxidant activity of VBTL pigment showed that DPPH and ABTS radical scavenging capacity was 4.92 and 1.39 times than gallic acid, respectively. The stability tests showed thatthe condition of light exposure and alkaline could result in a decrease in VBTL pigment stability. But VBTL pigment had certain heat resistance and was stable in weak acid. Meanwhile, VBTL pigment could coexisted with several common metal ions and additives except Cu2+, Fe3+, H2O2, Na2SO3 and sodium benzoate.Thirdly, the interaction between VBTL pigment and rice protein was investigated. It was found that temperature, time and protein structures could affect the interaction significantly. The protein adsorption isotherm showed that temperature and interaction time could improved the adsorption significantly. The color analysis showed that L* and b* value were significantly decreased after the dyeing process, while a* value was disordered. The surface hydrophobicity showed that the hydrophobic index was decreased significantly after interaction and built hydrophobic interaction between VBTL pigment and rice protein. The FT-IR analysis showed that VBTL pigment caused more intense changes of protein secondary structures and built hydrogen bonds. The interaction between different types of rice protein and VBTL pigment was also investigated and showed the structure changes could influence the main interaction. The main interaction between glutenin/ globulin and VBTL pigment was hydrophobic bonds and that between albumin and VBTL pigment was hydrogen bonds. At the same time, the function properties of rice protein after dyeing was investigated. The solubility was increased and oil-holding capacity was decreased after dyeing. The water-holding capacity was increased at p H<8.0, while was opposite at p H>8.0. The foaming capacity, emulsifying capacity and emulsion stability were increased significantly and foam stability was decreased after dyeing.Fourthly, the interaction between VBTL pigment and rice starch was investigated. The gelatinization temperature and enthalpy were decreased by adding VBTL pigment, which inhibited starch retrogradation. The peak viscosity, trough viscosity and breakdown were enhanced, while final viscosity and setback were weakened. VBTL pigment caused significant changes of starch gel properties and led to the reducing of hardness, adhesiveness and gumminess. The color of starch became black by adding VBTL pigment and caused the decreased of L*. Scanning electron microscopy revealed that VBTL pigment could cause looser gel structrues of dried rice starch gels.Finally, dyeing mechanism of VBTL pigment and rice protein was described. The mechanism and the theory of pigment-protein interaction was studied using molecular model of atomic level and the kinetic and thermodynamic process were inveatigated. The theoretical basis was provided by the study above. |
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