目的:探究4℃冷藏过程中鲈鱼肌肉品质的变化。方法:测定4℃冷藏过程中鲈鱼肌肉pH值、菌落总数、总挥发性盐基氮(total volatile base nitrogen,TVB-N)含量、K值和质构等指标,综合评价鲈鱼生理生化品质的变化,采用Masson染色和免疫组化...目的:探究4℃冷藏过程中鲈鱼肌肉品质的变化。方法:测定4℃冷藏过程中鲈鱼肌肉pH值、菌落总数、总挥发性盐基氮(total volatile base nitrogen,TVB-N)含量、K值和质构等指标,综合评价鲈鱼生理生化品质的变化,采用Masson染色和免疫组化分析评价组织形态学变化,利用酶解荧光肽底物测定特异性酶解胶原蛋白的基质金属蛋白酶(matrix metalloproteinases,MMPs)活力变化。结果:鲈鱼在贮藏期间pH值呈先下降后升高趋势,菌落总数、TVB-N含量和K值随贮藏时间的延长而增加,并在第8天超过临界值。十二烷基硫酸钠-聚丙烯酰胺凝胶电泳分析结果显示,贮藏至6 d鲈鱼肌肉蛋白组成没有明显变化,而在第8天肌球蛋白重链降解明显。Masson染色和I型胶原免疫组化分析结果显示,随贮藏时间的延长,肌内膜逐渐被降解,至第12天,肌膜I型胶原蛋白和肌纤维之间出现明显间隙。MMPs活力随贮藏时间的延长而明显增加,而鱼肉硬度不断下降。结论:鱼类冷藏期间肌肉的软化与胶原蛋白分解密切相关,而MMPs对I型胶原蛋白的降解可能是鱼死后肌肉软化的主要原因。展开更多
Abalones reveal unique taste after processing,mainly because of their abundant free amino acids(FAAs)and nucleotides.FAAs are nutrition components that can contribute to the unique taste.However,which factor(s)is resp...Abalones reveal unique taste after processing,mainly because of their abundant free amino acids(FAAs)and nucleotides.FAAs are nutrition components that can contribute to the unique taste.However,which factor(s)is responsible for the accumulation of FAAs still need further studies.To analyze the production of FAAs,we studied the variation of FAAs during 7 days of storage at 4℃.The content of taste-active amino acids,including Asp,Glu,Ser,and Gly increased by 1.7-fold,2.0-fold,3.0-fold,and 8.4-fold,respectively.The relative activity of cathepsin L and aminopeptidase(AP)increased significantly during the cold storage period.To identify AP in abalone and its function in mediating the production of FAAs,an aminopeptidase with wide substrate specificity was then extracted and purified from abalone muscle to homogeneity.Purified AP with a molecular mass of 100 kDa exhibited its maximum activity at 30℃,pH 7.5,and was further confirmed by LC-MS.Bestatin specifically inhibited the activity of AP,and metalloproteinase inhibitors EDTA,EGTA and 1,10-phenanthroline also suppressed its activity to different degrees.Based on its highest activity to substrate Leu-MCA and its peptide sequences,the purified enzyme was identified as leucine aminopeptidase(LAP).Our present study indicated the essential role of AP for FAAs accumulation during cold storage of abalone.展开更多
为探究干燥方式对蛋清蛋白(egg white protein,EWP)功能特性的影响及其内在机理,分别通过喷雾干燥与真空冷冻干燥制备蛋清蛋白粉,并对其蛋白结构、理化性质与功能特性进行研究。结果表明,与蛋清液(EWPC)相比,喷雾干燥使蛋清蛋白(EWP-P)...为探究干燥方式对蛋清蛋白(egg white protein,EWP)功能特性的影响及其内在机理,分别通过喷雾干燥与真空冷冻干燥制备蛋清蛋白粉,并对其蛋白结构、理化性质与功能特性进行研究。结果表明,与蛋清液(EWPC)相比,喷雾干燥使蛋清蛋白(EWP-P)的内源性荧光强度降低,表面疏水性和表面游离巯基含量增大。傅里叶变换红外光谱分析显示,EWP-P的α-螺旋、β-折叠和β-转角分别为16.30%、25.72%和40.23%,冷冻干燥蛋清蛋白(EWP-D)分别为20.43%、24.32%和35.69%。不同pH下,EWP-D的溶解度均高于EWP-P,表面张力小于EWP-P。此外,EWP-P的接触角为99.62°,高于EWP-D(接触角为65.97°),表明喷雾干燥能显著提高蛋白的疏水性(P<0.05)。EWP-D在不同pH下的乳化性、乳化稳定性以及起泡性均大于EWP-P,但起泡稳定性更小,这与EWP-D较高的溶解性与较低的表明疏水性有关。荧光倒置显微镜及激光共聚焦扫描显微镜分析表明EWP-D乳液的微粒更小,分布更均匀,其稳定性高于EWP-P。综上,喷雾干燥蛋清蛋白的β-折叠结构较多,表面游离巯基含量和表面疏水性较高,具有较好的凝胶性;冷冻干燥蛋清蛋白的表面疏水性较小,且表面张力小、溶解度大,具有更好的乳化能力与起泡性。展开更多
以蓝圆鲹(Decapterus maruadsi)分离蛋白为原料,采用碱性蛋白酶对其进行限制性酶解,研究水解度(degree of hydrolysis,DH)对分离蛋白酶解产物溶解性、持油力、乳化性与起泡性等功能特性的影响。结果表明,碱性蛋白酶酶解产物的相对分子...以蓝圆鲹(Decapterus maruadsi)分离蛋白为原料,采用碱性蛋白酶对其进行限制性酶解,研究水解度(degree of hydrolysis,DH)对分离蛋白酶解产物溶解性、持油力、乳化性与起泡性等功能特性的影响。结果表明,碱性蛋白酶酶解产物的相对分子质量显著下降。酶解可有效提高分离蛋白的溶解性,其溶解度随DH增加而增加。与对照组相比,分离蛋白经酶解后,产物乳化性与起泡性均显著提高,并呈现先升高后降低的趋势。不同DH酶解产物在pH值为4.0时的乳化性和起泡性最低;当pH值为10.0时,DH5(DH=5%)的乳化性最高((100.9±0.7)m2/g);当pH值为7.0时,DH5起泡性最高((227.3±3.8)%)。除DH20外,其他组的持油力均有显著提高,其中DH5的持油力最高,达3.50 g/g(油/蛋白)。结果表明,一定程度的水解可以显著提高蓝圆鲹分离蛋白的功能特性。本研究为鱼蛋白在食品蛋白配料中的应用提供了一定理论参考。展开更多
文摘为了探究太平洋牡蛎(Crassostrea gigas)在0℃和4℃冷藏过程中的品质变化,首先对牡蛎不同组织(闭壳肌、外套膜、鳃和内脏团)在冷藏过程中的表观变化进行观察,利用十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(sodium dodecyl sulphate-polyacrylamide gel electrophoresis,SDS-PAGE)分析冷藏过程中各组织中全蛋白的变化,进一步通过Western blotting鉴定闭壳肌中肌球蛋白重链(myosin heavy chain,MHC)、肌动蛋白、副肌球蛋白(paramyosin,PM)和原肌球蛋白(tropomyosin,TM)的降解情况,采用荧光光谱分析闭壳肌冷藏过程中内源性丝氨酸蛋白酶和组织蛋白酶B的活力变化,以闭壳肌的pH、K值和质构特性等为评价指标,分析其在冷藏过程中品质的变化。结果显示,随着冷藏时间延长,闭壳肌由紧实变得绵软,表观变化最明显。Western blotting结果显示,在0℃和4℃冷藏过程中,闭壳肌中MHC分别在第3天和第1天开始降解,表明低温有利于降低蛋白酶解速率;但是,肌动蛋白、PM和TM无明显变化。闭壳肌中丝氨酸蛋白酶和组织蛋白酶B活力在冷藏过程中总体呈现先升高后降低的趋势。在0、4℃冷藏过程中,pH值从初始的6.79开始呈现下降趋势,至第11天时分别为6.52、5.84;K值分别在第9天和第5天超过二级鲜度范围(40%);闭壳肌硬度和咀嚼性均在第1天达到峰值,随后逐渐下降,弹性呈现下降趋势;闭壳肌中MHC的降解最为明显,并与牡蛎品质劣化密切相关。研究可为牡蛎冷藏保鲜提供理论参考。
基金supported by the National Key R&D Program of China(No.2018YFD0901004)the National Natural Science Foundation of China(No.31772049).
文摘Abalones reveal unique taste after processing,mainly because of their abundant free amino acids(FAAs)and nucleotides.FAAs are nutrition components that can contribute to the unique taste.However,which factor(s)is responsible for the accumulation of FAAs still need further studies.To analyze the production of FAAs,we studied the variation of FAAs during 7 days of storage at 4℃.The content of taste-active amino acids,including Asp,Glu,Ser,and Gly increased by 1.7-fold,2.0-fold,3.0-fold,and 8.4-fold,respectively.The relative activity of cathepsin L and aminopeptidase(AP)increased significantly during the cold storage period.To identify AP in abalone and its function in mediating the production of FAAs,an aminopeptidase with wide substrate specificity was then extracted and purified from abalone muscle to homogeneity.Purified AP with a molecular mass of 100 kDa exhibited its maximum activity at 30℃,pH 7.5,and was further confirmed by LC-MS.Bestatin specifically inhibited the activity of AP,and metalloproteinase inhibitors EDTA,EGTA and 1,10-phenanthroline also suppressed its activity to different degrees.Based on its highest activity to substrate Leu-MCA and its peptide sequences,the purified enzyme was identified as leucine aminopeptidase(LAP).Our present study indicated the essential role of AP for FAAs accumulation during cold storage of abalone.
文摘为探究干燥方式对蛋清蛋白(egg white protein,EWP)功能特性的影响及其内在机理,分别通过喷雾干燥与真空冷冻干燥制备蛋清蛋白粉,并对其蛋白结构、理化性质与功能特性进行研究。结果表明,与蛋清液(EWPC)相比,喷雾干燥使蛋清蛋白(EWP-P)的内源性荧光强度降低,表面疏水性和表面游离巯基含量增大。傅里叶变换红外光谱分析显示,EWP-P的α-螺旋、β-折叠和β-转角分别为16.30%、25.72%和40.23%,冷冻干燥蛋清蛋白(EWP-D)分别为20.43%、24.32%和35.69%。不同pH下,EWP-D的溶解度均高于EWP-P,表面张力小于EWP-P。此外,EWP-P的接触角为99.62°,高于EWP-D(接触角为65.97°),表明喷雾干燥能显著提高蛋白的疏水性(P<0.05)。EWP-D在不同pH下的乳化性、乳化稳定性以及起泡性均大于EWP-P,但起泡稳定性更小,这与EWP-D较高的溶解性与较低的表明疏水性有关。荧光倒置显微镜及激光共聚焦扫描显微镜分析表明EWP-D乳液的微粒更小,分布更均匀,其稳定性高于EWP-P。综上,喷雾干燥蛋清蛋白的β-折叠结构较多,表面游离巯基含量和表面疏水性较高,具有较好的凝胶性;冷冻干燥蛋清蛋白的表面疏水性较小,且表面张力小、溶解度大,具有更好的乳化能力与起泡性。
文摘以蓝圆鲹(Decapterus maruadsi)分离蛋白为原料,采用碱性蛋白酶对其进行限制性酶解,研究水解度(degree of hydrolysis,DH)对分离蛋白酶解产物溶解性、持油力、乳化性与起泡性等功能特性的影响。结果表明,碱性蛋白酶酶解产物的相对分子质量显著下降。酶解可有效提高分离蛋白的溶解性,其溶解度随DH增加而增加。与对照组相比,分离蛋白经酶解后,产物乳化性与起泡性均显著提高,并呈现先升高后降低的趋势。不同DH酶解产物在pH值为4.0时的乳化性和起泡性最低;当pH值为10.0时,DH5(DH=5%)的乳化性最高((100.9±0.7)m2/g);当pH值为7.0时,DH5起泡性最高((227.3±3.8)%)。除DH20外,其他组的持油力均有显著提高,其中DH5的持油力最高,达3.50 g/g(油/蛋白)。结果表明,一定程度的水解可以显著提高蓝圆鲹分离蛋白的功能特性。本研究为鱼蛋白在食品蛋白配料中的应用提供了一定理论参考。
