反复冻融过程中调理狮子头脂肪氧化与低场核磁共振弛豫特性的相关性

该文研究冻融过程中调理狮子头脂肪氧化与低场核磁共振弛豫特性的相关性。利用低场核磁共振技术监测调理狮子头冻融过程中水分的存在形式及相对含量,比较冻融次数对酸价、过氧化物值及硫代巴比妥酸值(thiobarbituric acid reactive substances,TBARS)的影响,分析脂肪氧化指标与其相应低场核磁共振弛豫信号间的相关性。结果表明,随着冻融次数的增加,结合水(T21)与不易流动水(T22)弛豫时间后移,不易流动水(P22)与自由水(P23)含量不断减少;酸价和过氧化值先增后减,TBARS值不断增加。冻融次数与T23(自由水弛豫时间)、P21(结合水含量)、T22、P22和TBARS值极显著相关(P <0. 01),与过氧化值显著相关(P <0. 05); TBARS值与T22、P22极显著相关(P <0. 01); TBARS值与弛豫特性的回归模型决定系数为0. 814,回归方程拟合度较高。该实验结果为肉制品脂肪氧化的监测及科学贮藏提供理论依据。     

利用NMR研究赤藓糖醇对糙米面包贮藏期间保水性的影响

利用低场核磁共振（nuclear magnetic resonance,NMR）及成像技术,研究赤藓糖醇和蔗糖对糙米面包贮藏期间保水性的影响。通过检测面包1H NMR弛豫时间、峰面积、核磁共振成像（magnetic resonance imaging,MRI）以及水分活度,得出贮藏期间面包结合水（弛豫时间T21）相对稳定,不易流动水（弛豫时间T22）和自由水（弛豫时间T23）逐渐减少,与蔗糖面包相比,添加赤藓糖醇的面包具有高水分含量和低水分活度的特点,MRI同样体现出添加赤藓糖醇的面包具有良好的保水性。     

低场核磁共振研究冻融过程中犊牛肉品质变化

运用低场核磁共振技术,探讨反复冻融过程中犊牛肉水分分布状态。研究横向弛豫时间T2变化规律与食用品质间的关系。结果表明:随着冻融次数增加,解冻损失率变化显著,加压失水率和剪切力在3次冻融后显著增加,亮度L先增加后减小,红度a*逐渐减小,黄度b*逐渐增加。核磁共振检测到犊牛肌肉中水分有结合水、不易流动水和自由水三种状态,横向弛豫时间三个峰分别为T2b、T21、T22,其中T21与解冻次数、解冻损失率、加压失水率和亮度均显著相关(p0.05),T21可作为考察解冻犊牛肉品质的参考指标。     

不同冷藏条件下金枪鱼的水分迁移与脂肪酸变化的相关性

为了研究金枪鱼在冷藏期间的水分迁移与脂肪酸变化的相关性,采用低场核磁共振(low-field nuclear magnetic resonance,LF-NMR)技术分析金枪鱼肉组织中水分变化规律。横向弛豫时间T2分析结果表明:随着贮藏时间的延长,表征不易流动水的T21逐渐降低,表征自由水的T22逐渐升高。理化指标测定结果显示:随着贮藏时间延长,pH值先下降后上升,硫代巴比妥酸值呈上升趋势,而aw、水分含量不断下降,金枪鱼肉品质下降。相关性分析结果表明:表征强结合水的T2b与C18:0、二十碳五烯酸含量呈显著负相关(P0.05),T21与二十二碳六烯酸含量呈极显著正相关(P0.01),T22与C18:0、C18:1n9c含量分别呈极显著(P0.01)和显著(P0.05)正相关。因此,可考虑运用LF-NMR技术检测金枪鱼在冷藏期间检测脂肪酸含量的变化,从而表征其品质劣变的程度。     

微冻贮藏虾仁的水分迁移与品质变化

通过测定TVBN(total volatile basic nitrogen,TVBN)、K值、菌落总数、持水力、肌原纤维蛋白等指标变化,并结合低场核磁共振(low field nuclear magnetic resonance,NMR)和核磁共振成像技术(magnetic resonance imaging,MRI)测定水分迁移情况,以及组织切片技术,观察肌肉组织完整性等,评价虾仁的品质变化。结果表明,微冻能够明显抑制虾仁挥发性盐基总氮、K值和菌落总数的增长速度,虾仁贮藏期达24 d。低场核磁共振分析和核磁成像分析图谱的水分迁移情况与组织切片观察的肌原纤维结构变化呈正相关(P <0. 05)。第13天时,肌原纤维结构的断裂程度进一步加深,虾仁持水力随之降低,水分流失严重。在整个贮藏过程中,虾仁横向弛豫时间T21结合水含量相对稳定,T22不易流动水含量先增加后减少,T23自由水含量呈持续下降趋势。该文为虾仁微冻贮藏保鲜提供了一定的理论支撑。     

带鱼冷藏过程中品质变化与水分迁移的相关性

为了研究带鱼在冷藏期间的品质变化与水分迁移的关系,利用低场核磁共振(low-field nuclear magnetic resonance,LF-NMR)技术分析组织中水分变化规律。横向弛豫时间T_2的结果表明:随着贮藏时间的延长,不易流动水(T_(22))逐渐降低,自由水(T_(23))逐渐升高,肌原纤维内的水向外移动而大量流失,肌肉的持水能力下降、肉质逐渐劣化。这与传统理化指标的研究结果一致,且相关性分析表明,T_(22)、T_(23)与水分含量、蒸煮损失率等指标极显著相关(P0.01),与感官评分、持水力、硫代巴比妥酸值显著相关(P0.05)。因此,可考虑运用LF-NMR技术检测带鱼在冷藏期间的品质变化。     

冻融循环下鸡肉品质变化的低场核磁共振研究

运用1H低场核磁共振(LF-NMR)技术研究鸡肉反复冻融过程中的水分变化,并分析该变化与食用品质间的联系。由NMR T2弛豫测定结果可知肌肉中含有3个水群,即结合水、不易流动水和自由水,横向弛豫时间依次为T2b、T21、T22,其中T21与冻融次数显著相关(P<0.05),且与反映肌肉持水性变化的指标间高度相关。冻融后鸡肉食用品质发生显著变化,在贮运过程中需要尽可能避免这一现象。研究表明LF-NMR可用于流通过程中冻鸡肉品质的在线评价。     

利用低场核磁共振技术测定肌原纤维蛋白凝胶的保水性及其水分含量

本研究借助低场核磁共振技术研究蛋白凝胶的保水性及水分含量,并通过传统干燥法进行验证。结果表明：通过低场核磁共振测定肌原纤维蛋白凝胶的横向弛豫时间T2,研究凝胶中结合水、不易流动水和自由水3种状态水的组成及分布,自由水百分含量越高,其保水性越低,总水分含量越高;借助核磁共振成像得到凝胶中水分子氢质子密度图谱可直观反映凝胶的水分含量及空间分布情况,质子密度图灰度值越高,凝胶水分含量越高;传统干燥法的测定结果结合相关性分析表明低场核磁共振测得凝胶的不易流动水、自由水及灰度值与传统干燥法测得凝胶总水分含量相关系数分别为0.96、0.96、0.97,且均达到显著水平（p<0.05）。综上所述,低场核磁共振技术能用于研究肌原纤维蛋白凝胶的保水性及其水分含量。     

不同碱处理蛋清与蛋黄碱诱导凝胶低场NMR T_2弛豫时间分析

研究了不同碱处理对蛋清蛋黄碱诱导凝胶水分的影响,采用低场核磁共振技术测定凝胶中水分变化。结果表明,0.6%和0.7%NaOH处理组蛋清凝胶的T_2弛豫时间图上仅有2个峰,说明在凝胶体系中,存在2种水相状态:结合水和不易流动水。0.7%NaOH处理组蛋清凝胶不易流动水T_(22)为83.75±1.22 ms,显著高于0.6%NaOH处理组蛋清凝胶不易流动水T_(22)76.65±1.25 ms(p0.05):1.0%和1.2%NaOH处理组蛋黄凝胶的T_2弛豫时间图上有3个峰,说明在凝胶体系中存在3种水相状态:结合水、不易流动水和自由水。T_(21)从0.46±0.02 ms,增加到0.69±0.03 ms;T_(22)从29.62±0.86 ms增加到36.80±0.53 ms;T_(23)从198.45±4.94 ms增加到370.19±10.29 ms。说明T_2可以反映蛋清和蛋黄碱诱导凝胶的水分状态和组成。     

冰温及冷藏对鲤鱼水分迁移及质构的影响

以淡水鲤鱼为研究对象,利用低场核磁共振技术(LF-NMR)研究冰温(-2℃)及冷藏(4℃)条件对鲤鱼肌肉水分迁移的影响,并对鱼肉质构特性进行分析,考察水分迁移对鱼肉质地变化的影响。结果表明:鲤鱼在-2℃与4℃贮藏时,结合水、不易流动水以及自由水含量(pT_(21),pT_(22),pT_(23),pT_(24))的变化趋势相似,-2℃下鲤鱼肌肉各水分组分含量的变化更为稳定。冰温及冷藏条件下,T_(21)和T_(22)对应的结合水变化不大,T_(23)和T_(24)对应的不易流动水和自由水迁移明显。不易流动水的结合程度均随贮藏时间的延长而下降,-2℃贮藏下鱼肌肉自由水的结合程度变化较平缓。4℃贮藏下,鱼肉质构特征参数与贮藏时间相关度高于-2℃,即4℃下贮藏鱼肉的质地特性随贮藏时间的变化更为明显。-2℃时T_(22)对应结合水的水分活度对弹性影响较大,4℃时T_(21)对应结合水的水分活度对弹性影响较大。-2℃与4℃下鲤鱼肌肉中的不易流动水与自由水含量呈显著负相关,即不易流动水向自由水的迁移均很明显。4℃贮藏下鱼肉各水分指标间的相关度普遍高于-2℃,表明4℃贮藏下鲤鱼肌肉内部水分迁移更为剧烈。     

滚揉腌制前后鹅肉品质的变化

探讨经真空滚揉腌制以后鹅肉品质的变化,以及各个指标之间的相关性。用pH计、色差仪、压力仪、剪切力仪、低场核磁共振(NMR)、相差显微镜、透射电镜和DSC差示扫描量热仪分别测定滚揉腌制前后鹅肉的品质变化。结果显示：滚揉腌制以后鹅肉的pH值显著提高,L*值、a*值、蒸煮损失、压力损失显著降低,剪切力极显著降低,b*值差异不显著;肌纤维直径显著降低,肌节长度极显著增加;DSC测得的3个蛋白变性温度都极显著降低;NMR结果拟合后得到水有3个组分,对应的横向弛豫时间分别是T2b、T21、T22,分别对应结合水、不易流动水、自由水;滚揉腌制以后的T23消失,T21和T22都较滚揉腌制前显著增大,且T22占T2的百分比显著提高(由滚揉腌前德89.64%增大到98.25%)。多个指标之间相关性显著或极显著。滚揉腌制工艺可以显著提高鹅肉的食品品质,改善肌肉嫩度,提高保水性。     

Combination of NMR and MRI quantitation of moisture and structure changes for convection cooking of fresh chicken meat

This study demonstrates that a combination of bulk NMR and magnetic resonance imaging measurements of the T(2)-values of water protons can be used to determine the heat-induced changes in the structure and moisture content of fresh chicken meat which had been cooked in a convection oven at 200°C for a range of times. The gravimetric moisture content was also determined for both the raw and cooked meat. Multi-exponential fitting of the bulk NMR T(2) relaxation time data demonstrated three distinct water populations T(21) (39-43ms), T(22) (82-99ms) and T(23) (2-3ms) for raw meat which changed to 18-31ms (T(21)), 61-208ms (T(22)) and 3-7ms (T(23)) after the meat had been cooked. The T(1) and T(2) values obtained by MRI for cooked meat decreased progressively with increased heating time. There are highly significant correlations between the T(2) values from MRI and the T(21) values from bulk NMR measurements of cooked meat (r=0.986; p<0.01), and also between the normalised M(0) values from MRI and the gravimetric moisture content (r=0.953; p<0.01).     

低场核磁共振分析冰温牛肉中不同状态水分变化

利用低场核磁共振技术研究冰温贮藏条件下无包装与真空包装牛肉在贮藏过程中水分弛豫参数的变化规律.通过驰豫测定,结果显示新鲜牛肉中有3种不同活动状态的水分,即结合水、不易流动水和自由水,其对应的横向弛豫时间分别是T21、T22、T23.对弛豫参数与常见肉品质指标进行皮尔逊相关系数分析,揭示了两者间的相关性.结果表明:无包装牛肉自由水弛豫参数与其品质指标均有较强的相关性,而真空包装牛肉的弛豫参数与其品质指标的相关性均不强.对冰温贮藏牛肉的品质影响最大的水分是自由水,自由水的弛豫参数能够很好的用于无包装牛肉常规品质指标的研究.     

Comparative study of low-field NMR relaxation measurements and two traditional methods in the determination of water holding capacity of pork

The correlation between transverse relaxation, T(2,) and water holding capacity (WHC) determined either by Honikels bag method (Honikel, 1998) or centrifugation has been investigated in meat samples from m. longissimus dorsi (LD) 24 h post mortem from 74 pigs. Bi-exponential analysis of the transverse relaxation, T(2), showed highly significant correlations between both the two NMR time constants (T(21),T(22)) and water holding capacity determined by both Honikels bag method (r(T(21))=-0.72 and r(T(22))=0.77) and centrifugation (r(T(21))-0.50 and r(T(22))=0.75). This shows that transverse relaxation measurement is an efficient method for determination of water holding capacity in pork. Significant correlations were also found between T(21) and T(22) measured 24 h post mortem and pH measured at various time post mortem. This indicates that transverse relaxation, T(2), reflects pH-induced structural changes occurring in muscles post mortem.     

芋头添加物对金鲳鱼鱼糜凝胶的影响

研究芋头添加物对金鲳鱼鱼糜凝胶品质的影响,分析添加不同量芋头原浆和芋头淀粉时,金鲳鱼鱼糜凝胶的白度、凝胶强度、持水性、水分含量、横向弛豫时间T2的变化规律。结果表明：添加芋头原浆,金鲳鱼鱼糜凝胶的感官品质较好;添加芋头淀粉,金鲳鱼鱼糜凝胶的凝胶强度和持水力较好;芋头添加物可以降低其白度。低场核磁共振结果显示,随着芋头添加物的加入,金鲳鱼鱼糜凝胶的弛豫时间T22、T23减少,弛豫时间T21增大,峰面积S21、S22增加,峰面积S23减少,凝胶中自由水的流动性减弱。     

Development in myofibrillar water distribution of two pork qualities during 10-month freezer storage

The effects of fresh meat quality (PSE versus DFD), freezing temperature (-20°C versus -80C°) and duration of freezer storage on changes in water mobility and distribution were followed at intervals of 1-2 months during 10-month freezer storage of pork using low-field NMR T(2) relaxometry. Fresh meat quality was found to have a strong significant effect (P<0.0001) on the amount of loosely bound water (relaxation time >100ms) also after freezing, which was reflected in a significantly lower cooking yield in PSE meat compared with DFD meat (P<0.0001). While no significant changes in the cooking yield were observed with increasing length of freezer storage, NMR T(2) relaxation measurements revealed a significant increase in the amount of loosely bound water in PSE meat with increasing length of freezer storage. This finding indicates that NMR T(2) relaxation measurements are quite sensitive to freezing-induced changes in the meat structure, causing a shift in the distribution of water and possibly capable of detecting these before they are reflected in a reduced cooking yield. In addition, an interaction between fresh meat quality and effect of length of freezer storage on the amount of very mobile water easily lost as drip was observed, implying that PSE meat is more susceptible to freezer storage-induced deteriorative changes in the meat structure, causing a shift in the distribution of water, than DFD meat.     

Estimation of freezing storage time and quality changes in hake (Merluccius merluccius, L.) by low field NMR

The potential of low field NMR (LF NMR) as a fast monitoring technique to estimate the quality of hake (Merluccius merluccius) frozen stored at -10°C for up to 6months was evaluated. LF NMR clearly detected three populations of water: water strongly bound to macromolecules (T(2b)), trapped water (T(21)) and free water (T(22)). As storage time increased, and concomitant with an increase in the T(22) and a decrease in the T(21) water populations, the water holding capacity (WHC) and apparent viscosity values decreased and the shear strength increased, reflecting the characteristic loss of juiciness and tougher texture developed by hake during frozen storage. Two mathematical models were constructed: a simple regression using the biexponential analysis of the relaxation times (T(21), T(22)) and amplitudes (A(21), A(22)) and a partial least square regression (PLS) of CONTIN analysis. Both models seemed suitable to estimate the quality of the product.     

基于低场核磁共振探究解冻过程中肌原纤维水对鸡肉食用品质的影响

本研究旨在基于低场核磁共振横向弛豫时间T2分析解冻过程中肌原纤维水的分布及流动性与鸡肉食用品质间的关联性。以冷鲜鸡胸肉（宰后32 h）为对照,采用冷藏解冻、微波解冻（微波-1、微波-2）与超声解冻（180、200 W）5 种不同方式解冻中心温度为－20 ℃的冻结鸡胸肉,测定肉样T2、品质特性指标并分析它们之间的相关性。结果显示：解冻过程中肉样的T2水分分布情况发生明显变化,与对照组相比,除微波-2解冻外,其余4 组解冻肉样均发生不易流动水T22（40～50 ms）向自由水T23（100～250 ms）迁移;同时,微波-2解冻与200 W超声解冻出现强结合水水分群T20（0～0.1 ms）;相关性分析表明,T20、T21和T22峰比例与肉样的持水能力、嫩度和多汁性呈极显著正相关（P＜0.01）,与解冻损失率、蒸煮损失率呈显著（P＜0.05）或极显著（P＜0.01）负相关;剪切力与T20峰比例呈显著负相关（P＜0.05）,与T22峰比例呈极显著负相关（P＜0.01）。解冻方式对肉样的外观和风味无显著影响（P＞0.05）,微波-2解冻肉样的质地与多汁性评分最接近于对照组,整体可接受性更高;冷藏解冻与超声解冻肉样的质地与多汁性更差,整体可接受性也更低。因此,本项研究结果表明在解冻过程中肌原纤维水的迁移情况对鸡肉品质具有显著影响,并且微波-2解冻程序能够更好地抑制解冻过程中肉品质的下降。     

低场核磁结合理化指标分析低温贮藏真空包装牦牛肉的品质

本文以牦牛肉为研究对象,采用低场核磁共振(Low Field Nuclear Magnetic Resonance,LF-NMR)技术研究牦牛肉经真空包装后于4 ℃贮藏过程中水分的变化,并对其与蛋白质溶解度、挥发性盐基氮、TBARS、菌落总数及蒸煮损失的相关性进行综合分析。结果表明,随着贮藏时间的延长,TVB-N、蛋白质溶解度、TBARS的值随着时间的延长不断增加,菌落总数在第15 d时已达7.15lg cfu/g;LF-NMR测得牦牛肉的横向弛豫时间 T₂谱中出现 4个峰,在18 d的贮藏过程中T₂₁、T₂₂弛豫时间后移,结合水和自由水不断减小,且与TVB-N、蛋白质溶解度、TBARS、菌落总数之间显著或极显著相关(p<0.05或p<0.01)。通过LF-NMR技术可对真空包装的低温贮藏牦牛肉进行无损、科学的品质监测,为肉品品质变化的机理研究及科学合理贮藏牦牛肉提供实验依据。     

Physical changes of significance for early post mortem water distribution in porcine M. longissimus

The post mortem changes in water mobility and distribution were followed in porcine muscle (M. longissimus dorsi) samples using continuous low-field NMR relaxation measurements and simultaneous measurement of changes in muscle impedance as an indirect measure of membrane integrity as well as muscle contraction measurements using a rigormeter instrument. Distributed exponential fitting analysis of NMR T₂ relaxation data revealed the presence of three distinct water populations (T₂₀, T₂₁, T₂₂) within the muscle during its conversion to meat. Comparison of T₂ relaxation patterns and contraction data indicates that rigor development affects the attributes of the T₂₁ water population and thereby contributes to myofibrillar water characteristics post mortem, as the T₂₁ water population is believed to reflect inter/intra-myofibrillar water. The volume of the water population believed to reflect extra-cellular water (T₂₂) in the living muscle. Early post mortem T₂₂ decreased slightly within the first 2–3 h post mortem followed by an increase and a change in its characteristic time constant. This was ascribed to an initial muscle cell swelling followed by water being expelled from the cellular space into the extra-myofibrillar space. Comparison of changes in the T₂₂ water population and impedance characteristics within the muscle during its conversion to meat revealed close relationship between progresses in the two attributes. Obtained data strongly support that the post mortem reorganization of water is closely associated with membrane properties, which moreover was found to affect the final water-holding capacity of the meat. Finally, a model for early post mortem events leading to changes in the distribution of water within muscles is proposed.