加热对鸡胸肉肌原纤维蛋白结构与凝胶特性的影响

Influence of Heating on Structure and Gel Properties of Myofibrillar Proteins from Chicken Breast Muscle

【目的】研究加热温度对肌原纤维蛋白二级结构和凝胶特性的影响,并探讨肌原纤维蛋白二级结构与凝胶特性之间的内在关系。【方法】将活AA鸡20只(40日龄)屠宰,取鸡胸肉在-18℃下储存,用于提取鸡胸肉肌原纤维蛋白。用圆二色谱(CD)研究加热过程中肌原纤维蛋白二级结构(α-螺旋,β-折叠,β-转角和无规则卷曲)的变化;使用流变仪测定加热温度对肌原纤维蛋白的流变性质参数储能模量G’和相位角正切值(Tanδ)的影响;将肌原纤维蛋白在不同温度下制备成凝胶,运用质构仪研究成胶温度对凝胶硬度和弹性的影响;用低场核磁共振仪(NMR)测定不同加热温度下成胶的肌原纤维蛋白凝胶的弛豫时间T2,以此研究不同温度下制得凝胶的水分布特性。利用SPSS17.0对所得的数据进行相关性分析等处理,以便阐明加热温度与肌原纤维蛋白二级结构及其凝胶特性的关系。【结果】加热温度显著影响肌原纤维蛋白的二级结构。随着加热温度升高,肌原纤维蛋白二级结构中α-螺旋含量逐渐降低。在30℃时α-螺旋含量为95.77%,加热温度在30—40℃以及70—80℃之间时α-螺旋含量变化很小,在40—70℃之间显著下降(P<0.05),到80℃时下降到45.05%。β-折叠含量在30—45℃之间随温度上升缓慢增加,在40—70℃之间显著增加(P<0.05),超过70℃后含量仅略有增加;在30—80℃加热范围内,β-折叠含量从0.20%增加到12.65%。α-螺旋含量降低代表蛋白质分子展开程度增加,而β-折叠含量增加代表蛋白质分子间聚集程度增加。加热温度影响肌原纤维蛋白的流变性、质构特性和水分布特性。G’开始增加时的温度为42℃,表明肌原纤维蛋白在此温度下开始胶凝。在42—50℃之间,G’迅速增加到峰值177 Pa,之后G’迅速下降(50—55℃),在55—75℃范围内G’再次快速增加;肌原纤维蛋白凝胶硬度在40—75℃内随温度上升而显著增大,在75℃时硬度达到最大值51.4 g。凝胶弹性在55℃达到弹性最大值0.754;在NMR图谱中T2有3个峰,其中T22表示不可移动水,肌原纤维蛋白成胶温度在40—60℃内的凝胶T22值随加热温度上升从403.7 ms降到265.6 ms,即T22向快弛豫方向移动,表明随着温度的升高,水分子移动性降低。经相关性分析发现,加热温度、β-折叠含量与凝胶G’和凝胶硬度呈极显著正相关(P<0.01),相关系数均高于0.849,说明加热引起了蛋白质分子展开、聚集、并导致蛋白质分子胶凝、凝胶的G’及硬度显著变化。α-螺旋、β-折叠含量与凝胶的弹性和T22之间相关性不显著(P>0.05)。综合分析加热温度对α-螺旋含量、β-折叠含量和G’的影响,发现加热温度超过40℃时,加热同时导致肌原纤维分子展开、分子间聚集和胶凝;并发现展开后的肌原纤维蛋白分子部分重排成β-折叠结构是导致凝胶G’增加的关键因素;分析加热温度对β-折叠含量和凝胶硬度的影响,发现β-折叠结构含量增加也是导致凝胶硬度增加的关键因素。【结论】肌原纤维蛋白从30℃加热到80℃时,其α-螺旋含量显著下降,β-折叠含量显著提高,加热引起蛋白质二级结构发生重大变化,肌原纤维蛋白在42℃开始胶凝。凝胶硬度在75℃时达最大值51.4 g。加热温度、β-折叠含量与凝胶的G’和硬度呈极显著正相关,加热过程中β-折叠含量增加是导致凝胶G’和硬度增加的关键。

ObjectiveThis study was designed to investigate the influence of heating on myofibrillar proteins（MP） secondary structure and gel properties, and to reveal the relationship between MP secondary structure and gel properties.[Method]Forty-day-old commercial AA broilers were slaughtered. The breast muscle was stored at-18℃ before MP was extracted. The MP secondary structure was measured using a circular dichroism spectra to determine the content ofα-helix,β-sheet,β-turn and random coil during heating. The values of G＇ and Tanδ were continuously measured using a rheometer during heating. The influence of heating temperature on textural properties of MP gel prepared under different temperatures was measured using a textural analyzer. Spin-spin relaxation time （T2） of the gels prepared under different temperatures was measured using a NMR Analyzer in order to investigate the water distribution of gels. SPSS17.0 software was used to analyze the data such as correlation analysis so as to illustrate the relationship between the heating temperature and protein structure and gel properties. [Result] Heating temperature influenced significantly MP secondary structure. Theα-helix content declined from 95.77%to 45.05%as temperature increased from 30℃ to 80℃. Theα-helix content declined slightly as temperature increased from 30℃ to 40℃ and from 70℃ to 80℃, declined abruptly between 40℃ and 70℃ （P〈0.05）. The β-sheet content increased from 0.20% to 12.65% as temperature increased from 30℃ to 80℃. The decline inα-helix content indicates the unfolding of a protein molecule. The increase inβ-sheet content indicates the aggregation of unfolding protein molecules. Heating temperature influenced rheological properties, textural properties and water distribution of MP. G＇ values began to increase at about 42℃ indicating the starting of protein gelling. G’ values showed a sharp increase between 42℃ and 50℃ （177 Pa） with a subsequent decrease between 50℃ and 55℃ and a final increase between 55℃and 75℃. Hardness values of MP gel increased as the temperature of the gel prepared rose from 40℃ to 75℃ and reached the maximum value of 51.4 g at 75℃. Springiness values reached the maximum value of 0.754 at 55℃. T2 curves of MP gel usually contained 3 peaks and T22 means immobile water. T22 values of the gels decreased from 403.7 ms to 265.6 ms as the gel preparing temperature rose from 40℃ to 60℃, which indicated that water mobility decreased as temperature rose from 40℃ to 60℃. Heating temperature andβ-sheet content showed a significant positive relationship to G＇ and hardness of gel （P〈0.01）, and the correlation coefficients were all over 0.849. The correlation analysis indicated that heating caused MP molecules unfolding, aggregating, gelling, and led to significant change of G＇ and hardness of MP gel. α-Helix and β-sheet, which didn＇t show a significant relationship to springiness and T22 of the MP gel. It was found that heating led to MP molecules unfolding, aggregating, gelling simultaneously at temperature over 40℃ by analyzing the influence of heating temperature on α-helix, β-sheet content and G’. The unfolding MP molecules rearranging toβ-sheet was the key factor for the increase of G’ values. The unfolding MP molecules rearranging toβ-sheet was also the key factor for the increase of hardness values by analyzing the influence of heating temperature onβ-sheet content and hardness values of MP gel.[Conclusion]Theα-helix content declined andβ-sheet content increased as temperature increased from 30℃ to 80℃. Heating led to significant changes of protein secondary structure. G＇ values began to increase and the values of Tanδbegan to decrease at about 42℃, which indicated the starting of protein gelling. Gel hardness values reached the maximum 51.4 g at 75℃. Heating temperature andβ-sheet content showed a significant positive relationship to G＇ and hardness of the gel. The increase ofβ-sheet content was the key factor for the increase of G’ and hardness values of the MP gel.