The Studies Of The Molecular Structure And Functional Properties Of Rapeseed Protein Treated By Dry-heating

The objective of this experiment was to research the effects of dry-heating on the molecular structure and functional properties of rapeseed protein, and to provider basic data for the efficient utilization of rapeseed protein. The rapeseed protein was treated with80℃and100℃respectively for15min,30min,60min,90min and120min. The effects of dry-heating treatment on the protein molecular structure were detected by methods of polyacrylamide gel electrophoresis, surface hydrophobicity, near infrared spectrum, Sulphur and disulfide bond content, amino content and scanning electron microscope. The effects of dry-heating treatment on the protein solubility, emulsification and emulsion stability, and oil absorption and protein digestion rate were also discussed. The conclusions were as followed.(1) The extraction of rapeseed protein by methods of alkaline solution and isoelectric precipitation was studied. The results show that:the rapeseed protein had higher extraction yield from pH10to pH12, all above80%. The isoelectric point area of rapeseed protein was wide, from pH4to pH6. The rapeseed protein in this experiment was obtained with the alkaline solution pH10and precipitation pH6. The purity of rapeseed protein was73.05%,and the molecular weight was concentrated between2kDa-16kDa,16kDa-35kDa and50kDa-70kDa.(2) The differential scanning calorimetry (DSC) show that:the thermal stability of2S albumin was worse than that of12S globulin. When heated, the2S albumin was more easily denaturized.With different heat treatment temperature and heat treatment time, the molecular structure of rapeseed protein got great changes. Thermal decomposition of the protein was detected by polyacrlamide gel electrophoresis, near infrared spectrum, disulfide bond content andscanning electron microscopy. But new aggregates were formed with the degree of heat treatment, making the surface hydrophobicity of protein declined firstly and then increased. The change of amino content reflected the heat treatment made rapeseed protein Involved in mallard reaction, which had a great impact on the content of free amino and lysine, greatly reducing the nutritional value of rapeseed protein.(3) With the change of the molecular structure of rapeseed protein, its functional properties changed too. Emulsification rise first and then decreased; Oil-absorbing first decreased and then increased, showing the same trend of the change of surface hydrophobicity. Due to the formation of aggregates, the solubility of rapeseed protein damaged a lot. After heat treatment90min and120min by100℃, the solubility of rapeseed protein from pH2to pH10was all lower than10%. So, the higher the temperature and the longer the processing time, the worse the solubility of rapeseed protein. Studies also shown that moderate heat treatment can improve the rapeseed protein digestibility of pepsin and trypsin; Excessive heat treatment might decrease the protein digestion rate because of the formation of large aggregates.(4) The functional properties of2S albumin,12S globulin and rapeseed protein with80℃heat-treatment were analyzed. The results show that:rapeseed protein components had a significant impact on its functional property, such as oil absorption, emulsification, emulsifying stability and protein solubility. The protein solubility, emulsification and emulsifying stability of albumin were significantly better than that of the rapeseed protein and globulin. The study also showed:the functional properties of rapeseed protein components could be improved with proper heat-treatment parameters.