椰麸组分蛋白的氨基酸组成、结构与乳化性分析

Analysis of Amino Acid Composition, Structure and Emulsion Properties of Coconut Cake Protein Fractions

为提高椰子加工副产物的利用,本研究从椰麸中依次提取4种组分蛋白,包括清蛋白、球蛋白、谷蛋白-1和谷蛋白-2。分析这4种组分蛋白的氨基酸组成,并利用SDS-PAGE技术分析其亚基组成和分子量。同时分析其表面疏水性,并研究不同离子强度对椰麸各组分蛋白的乳化性和乳化稳定性的影响。结果表明,椰麸蛋白质中清单白、球蛋白、谷蛋白-1和谷蛋白-2的含量分别为(8.84±1.16)、(54.35±3.69)、(20.49±1.11)、(6.14±1.42)g/100 g。各组分蛋白都富含精氨酸与谷氨酸,必需氨基酸的含量都比FAO/WHO的推荐值要高,而且氨基酸的配比合理。在4种椰麸组分蛋白中,椰麸清蛋白的生物效价最高(58.63)。SDS-PAGE分析表明,清蛋白、球蛋白、谷蛋白-1的亚基组成差异较大,分子量范围约为17.7~53.3 kDa。谷蛋白-1中酸性亚基含量为46.1%,而谷蛋白-2中碱性亚基的含量为27.5%,这是二者不同溶解性的主要原因之一。谷蛋白-2由10条亚基组成,分子量范围为18.8~119.2 kDa,是5种椰麸组分蛋白中分子量分布最广的。椰麸球蛋白和谷蛋白-2的表面疏水性显著高于清蛋白和谷蛋白-1(P<0.05)。此外,椰麸球蛋白表现出最高的乳化性(127.3 m^(2)/g)和乳化稳定性(98.13%),其次为谷蛋白-2和清蛋白,而谷蛋白-1的乳化性最低(11.79 m^(2)/g)。在离子强度为0 mol/L时,椰麸球蛋白、谷蛋白-2和清蛋白的乳化性都显著大于大豆分离蛋白。椰麸球蛋白、谷蛋白-2和清蛋白的乳化稳定性无显著性差异,但都高于大豆分离蛋白(P<0.05)。当离子强度为0~0.4 mol/L时,随着离子强度增大,球蛋白的乳化性和乳化稳定性提高,清蛋白和谷蛋白-2的乳化性反而降低。本研究结果为椰子蛋白质的精深加工与利用提供了理论基础。

To improve the utilization of coconut processing byproduct,four protein fractions including albumin,globulin,gluten-1 and gluten-2 were separately extracted from coconut cake.The amino acid composition of the protein fractions was analyzed.The subunit composition and molecular weight of the fractions were analyzed by SDS-PAGE.The hy-drophobicity of coconut cake albumin,globulin,gluten-1 and gluten-2 were determined.The effects of different ionic strength on emulsifying capacity and emulsion stability of the protein fractions were studied,too.The content of coconut cake albumin,globulin,glutelin-1 and glutelin-2 was(8.84±1.16),(54.35±3.69),(20.49±1.11)and(6.14±1.42)g/100 g,respectively.The protein fractions are all rich in arginine and glutamic acid.In addition,the essential amino acid content of the protein fractions was relatively high than that recommended by FAO/WHO.The essential amino acid composition was reasonable.The albumin showed the highest biological value(58.63)among the four coconut cake protein fractions.This indicates that albumin has the highest nutritional value.Results of the SDS-PAGE analysis showed that there was significant difference in subunit composition among coconut cake albumin,globulin and gluten-1.The molecular weight was ranged from 17.7 to 53.3 kDa.Acid subunit composition of glutlelin-1 was 46.1%,in contrast the content of basic subunits in glutelin-2 was 27.5%,which was one of the main reasons why glutelin-1 and glutelin-2 has different solution.Glutelin-2 was composed of ten subunits with a molecular weight range of 18.8‒119.2 kDa,which is the widest range among coconut cake protein fractions.The hydrophobicity of globulin and glutelin-2 was higher than that of albumin and glutelin-1(P<0.05).In addition,at the same ionic strength,the globulin showed the highest emulsifying capacity(127.3 m^(2)/g)and emulsion stability(98.13%)among the fractions,following which was the glutelin-2 and albumin,whereas glutelin-1 exhibited the lowest emulsifying capacity(11.79 m^(2)/g).There was no significant difference on emul-sion stability among coconut cake globulin,glutelin-2 and albumin.But the emulsion stability of globulin,glutelin-2 and albumin was higher than that of soybean protein isolate(P<0.05).When ionic strength was from 0 to 0.4 mol/L,the emulsifying capacity and emulsion stability of globulin were improved as ionic strength increased.In contrast,the emulsifying capacity of albumin and glugelin-2 was reduced as ionic strength increased.This study would provide a theory basis for the further application of coconut cake protein.