| Jackfruit seed is one of the main by-products in the jackfruit industry chain.The consumption patterns of fresh food and dried fruit processing make the jackfruit industry produce a large number of by-products.If these by-products are directly discarded,they will not only reduce the overall economic benefits of the jackfruit industry,but also cause certain pollution to the environment.Studies have shown that jackfruit seed contains a large amount of starch and protein,and jackfruit seed starch has good physicochemical properties,which conforms to the national standard for the quality of industrial starch,and is a new resource to be developed.However,there are few studies on the protein of jackfruit seed which is another main component of jackfruit seed.In order to further improve the utilization value of jackfruit seeds,it is necessary to conduct in-depth research on its properties and structure,and explore its applicable fields.In this paper,Osborne method and alkali dissolving and acid precipitating method were used to extract the protein from the jackfruit seed,and the proteins from jackfruit seed were determined and compared with each other in terms of physicochemical properties,functional properties and structure.The major contents and results were as follows:(1)The physicochemical properties of protein fractions and protein isolate extracted by Osborne method and alkali dissolving and acid precipitating method were investigated.The specific results were as follows:the purity of albumin 83.26%,globulin 85.05%,glutelin 76.76%,and protein isolates 83.32%,and the rates were:16.7%,26.1%,14.2%,and 45.0%,respectively.The isoelectric points of the four kinds of jackfruit seed proteins were all in the acidic environment:albumin pH 4.93,globulin pH 4.65,gluten pH 2.44,and protein isolate pH 4.17.The results of amino acid composition analysis showed that the 9 essential amino acids in jackfruit seed protein,except histidine,basically meets the FAO/WHO/UNO recommended standard for adults/children,and the content was close to or even higher than soybean protein.In terms of surface hydrophobicity,glutelin has the highest surface hydrophobicity,followed by protein isolate,globulin and albumin.(2)The effects of different pH on the protein functional properties of jackfruit seeds were investigated,and the best emulsifying protein isolate was selected as emulsifier to explore the unstable mechanism of the emulsion preparation.The specific results were as follows:proteins solubility of jackfruit seeds presented a "U"shape,and the highest albumin and globulin solubility was higher than 90%,while glutelin was the lowest and the highest was only 18.64%.In terms of foaming ability,glutelin has the highest foaming ability at pH 3 and higher foam stability in acidic environments.The gel properties of jackfruit seed proteins was poor,among which albumin has the best gel property,but the minimum gel concentration is only 11%.The result indicate that jackfruit seed protein may not be suitable to be used as a gel agent in the food industry.The emulsification of jackfruit seed proteins was pH dependent and close,but the protein isolate had the best emulsifying stability The potential of the emulsion prepared by protein isolate increased with the pH value,but the absolute value of the potential was low,and there was no significant change in the emulsion potential after 24 h storage.The results of emulsion creaming index and micromorphology showed that the emulsion prepared with jackfruit seed protein isolate as emulsifier was the most unstable at pH 3,the most stable at pH 7,the creaming index was the lowest,and the oil droplets had smaller particle size.The study on the mechanism of emulsion formation and destabilizing shows that the emulsion is unstable due to the presence of a competing protein or a change in the conformation of the protein(3)The structural characteristics of jackfruit seed protein were investigated.The measurement results were as follows:the molecular weight distribution range of the jackfruit seed proteins was mainly between 10 kDa-34 kDa,and the major subunits were similar in composition.Under reduction conditions,many new bands of jackfruit seed proteins appeared between 10 kDa-20 kDa,indicating the presence of disulfide bonds in jackfruit seed proteins.At pH 3,the protein of jackfruit seed had the lowest fluorescence intensity,indicating that under the pH condition,jackfruit seed may undergo a certain degree of degeneration,leading to more tyrosine residues and tryptophan residues exposed to the hydrophilic environment,causing a certain fluorescence quenching.The results of circular dichroism determination showed that the secondary structure of jackfruit seed protein was mainly ?-sheet and random coil,and the content of ?-sheet structure increased with the increase of pH except for glutelin.The micromorphology of albumin was mainly large flakes and a small number of spheres and rods globulin was globular aggregates of different sizes and a single globular structure,glutelin showed the morphology of large irregular clumps,and protein isolates included three types of flakes,spheres and clumps. |
PDF Full Text Request