石斛花鼓风干燥机理和感官品质变化规律

基于远红外鼓风干燥和低频核磁共振探索霍山石斛花和铁皮石斛花干燥过程,构建适合干燥不同种类石斛花的基础参数模型,并使用质构分析仪研究石斛干花的感官品质变化规律。结果表明:远红外鼓风干燥仪干制后的霍山石斛花和铁皮石斛花,通过低频核磁共振发现,干品水分含量均是结合水,干品泡制后的复水性佳;利用干燥动力学模型所得数据与试验数据的相关系数平方高于0.99,相关性很好;经质构仪测定,随着干燥次数增加,硬度和脆性也增加,干制品品质提高,延长了贮存期。     

基于LF-NMR的香芋微波真空干燥中水分扩散特性研究

为了研究香芋片微波真空干燥过程中水分扩散特性,采用微波真空干燥箱在1.5、2.0和2.5 W/g 3个微波强度下对香芋片进行了干燥试验,利用低场核磁共振技术测定了香芋片微波真空干燥过程中水分迁移及分布情况。结果表明,香芋片微波真空干燥过程主要为降速阶段,3种微波强度下平均干燥速率为0.149、0.185和0.224 g/(g·min);有效水分扩散系数为7.30×10-9、9.46×10-9、1.14×10-8m~2/s。NMR T2谱显示,香芋中存在结合水、不易流动水和自由水3种状态,其横向弛豫时间分别为T21 (2.31～9.32 ms),T22 (10.72～49.77ms)和T23 (57.22～705.48 ms)。干燥过程中,MVD香芋内自由水含量显著降低(p0.05),不易流动水所占比例呈现先增加后下降的趋势,结合水含量变化不显著(p0.05),所占比例逐步上升。MRI检测表明,MVD香芋内外同时失水,且微波强度越高,弛豫信号消失的越快。该研究揭示了微波真空干燥中香芋内水分扩散规律,即微波强度越高,样品内水分扩散速率及不同组分水分之间的转化越迅速。该研究为香芋的微波真空干燥产业化生产提供理论依据。     

低场核磁结合电子鼻判定复合保鲜剂对冷藏虹鳟鱼片品质变化的影响

以质构、pH值、硫代巴比妥酸(TBA)值、挥发性盐基氮(TVB-N)值及菌落总数为评价指标,同时采用低场核磁共振(LF-NMR)及电子鼻技术对鱼片贮藏期间的水分和挥发性成分变化进行检测,研究复合保鲜剂(壳聚糖、茶多酚及柠檬汁)对虹鳟鱼片贮藏期间品质的影响。结果表明,复合保鲜剂组能较好地维持鱼片质构特性,同时可延缓鱼片TBA值、TVB-N值及菌落总数的增加。低场核磁测得两组鱼片贮藏期间T21幅值逐渐降低,在贮藏后期(12~14d),保鲜剂组鱼片自由水比例显著低于对照组(P0.05),且两组鱼片自由水比例与初期比较均增加。电子鼻PCA分析及LDA分析均可较好地区分贮藏期间鱼片的品质变化,LA分析发现引起鱼片新鲜度变化的主要成分为氮氧化合物、无机硫化物、芳香成分物质和乙醇等,而PCA分析结果表明对照组鱼片第6天开始发生腐败变质,保鲜剂组鱼片第10天开始趋于腐败。综上表明,低场核磁及电子鼻检测结果与理化指标结果具有一致性。     

Characterisation of moisture migration of shiitake mushroom (Lentinula edodes) during storage and its relationship to quality deterioration

Water is a critical factor influencing the quality of mushrooms. This paper investigated the moisture migration of shiitake mushroom during storage using low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) and its relationship to quality deterioration. Three water components assigned as water in different cell compartments of cell wall, cytoplasm and vacuole were observed in shiitake mushroom matrix. As the prolonging of storage time, the right shift of immobilised water and left shift of free water led to the merge of these two peaks at the end of storage. The increase in peak area of water in cytoplasm and decrease in the peak area of water in vacuole indicated evident moisture migration from vacuole to cytoplasm. MRI images showed heterogeneous water distribution in shiitake mushroom, and the water migrated from centre to surface, then evaporated to the environment. Besides, the moisture migration might be related to the weight loss and textural softening of shiitake mushroom.     

Effect of ripening with Penicillium roqueforti on texture,microstructure, water distribution and volatiles of chicken breast meat

In this study, the influence of ripening with Penicillium roqueforti on texture, microstructure, protein structure, water mobility and volatile flavour compounds of chicken breast meat was investigated. Scanning electron microscopy (SEM) and transmission electron microscope (TEM) images showed that the granule formed and chicken myofibril fractured after ripening. Reduction in α-helix and increases in β-sheet structure content accompanied by decrease in hardness and springiness and increase in gumminess were found in ripened chicken breast meat. Low field nuclear magnetic resonance (LF-NMR) revealed that increasing intra-myofibrillar water and decreasing extra-myofibrillar water resulted in the higher water-holding capacity after ripening with P. roqueforti. In addition, chicken breast meat ripened with P. roqueforti contained more volatile flavour compounds, in particular aldehydes.     

Changes in physicochemical properties and myofibrillar protein properties in grass carp salted by brining and injection

The aim of this study was to investigate the changes in physicochemical properties and myofibrillar protein properties of grass carp meat during brining and brine injection at 4 °C. The time reached equilibrium was 7 h in brining group and 5 h by injection, where the salt content was about 1.76%. The water content, water holding capacity and yield in injection group (86.59%, 9.18% and 110%, respectively) were higher than brining group (84.76%, 11.47%, and 108%, respectively) at equilibrium point significantly (P < 0.05). This was attributed to the more swollen filament lattices and disordered protein structure in injection group (P < 0.05). The myofibrillar protein structure was compared, including sulphydryl content, surface hydrophobicity, solubility, sodium dodecyl sulphate polyacrylamide gel electrophoresis pattern and secondary structure. The injection group presented the better quality of salted fish meat in shorter time.     

LF-NMR to explore water migration and water–protein interaction of lamb meat being air-dried at 35°C

To decrease the drying time and energy consuming, water migration and water–protein interactions of lamb meat being air-dried at 35°C were investigated. Low-field nuclear magnetic resonance T_2b indicated the water–protein interactions changed during air-drying. Area of T₂₁ (intramyofibrillar water) decreased, meanwhile the area of T₂₂ (extra-myofibrillar water) increased when the moisture content decreased from 55 to 45%, indicating the water migrated from myofibril to extramyofibril. Drying rate (the rate of water migration from meat to air) could be predicted by the area of T₂ populations, and the correlation coefficient was 0.990. Change of water binding and hydration in myofibrils was evident by the increase in hydrophobicity and decrease in solubility of myofibrillar protein. Differential scanning calorimetry showed denaturation of myosin in dried meat which might result in water migration from myofibril to extramyofibril space. In conclusion, water–protein interactions changed, and then influenced the drying rate during drying.     

面条蒸制过程中水分迁移及糊化特性

运用低场核磁共振、核磁成像、快速黏度分析和光学显微镜研究蒸制过程中面条的水分分布、迁移、糊化特性及微观结构的变化。对水分含量、弛豫时间（T2）、质子密度（M2）和糊化特性进行相关性分析。结果表明：面条中的水分主要以弱结合水的形式存在。在蒸制过程中,水分由面条外部向内部迁移,总水分、弱结合水和深层结合水含量整体呈现先增加后稳定的趋势,深层结合水增长趋势缓慢;弱结合水自由度逐渐增大。面条峰值黏度、衰减值随蒸制时间延长呈下降趋势。观察面条微观结构发现,蒸制使面条淀粉糊化,体积变大,表层淀粉糊化程度高于内层。相关性分析结果表明,水分含量与T22、M22和M总呈极显著正相关（P＜0.01）;水分含量、T22、M22及M总均与峰值黏度、衰减值、最终黏度呈显著负相关（P＜0.05）或极显著负相关（P＜0.01）。     

一种基于LF-NMR技术的不同含水量猪肉检测方法研究

研究了一种基于低场核磁共振技术的不同含水量猪肉检测方法。选择猪背部最长肌于宰后5 h内注射肉质量分数分别为0%、8.72%、14.23%和17.03%的蒸馏水,于注水后0、12 h和24 h测定肉色（L*、a*和b*）、低场核磁共振横向弛豫时间（T2）。结果表明,随着注水量的增加,低场核磁共振中T2中第2个峰（T21）的峰时间（t21）增大、峰面积（A21）减小、峰面积比（P21）减小以及色差中的亮度值（L*）增大,其他指标变化相对较小。因此,建议利用t21、A21、P21、L*这4 项指标组合,检测不同含水量的猪肉。     

新采收玉米籽粒中水分状态对淀粉热特性的影响

以2 种中国东北地区玉米郑单958（Zd958）和先玉335（Xy335）为研究对象,采用低场强核磁共振技术（low field nuclear magnetic resonance,LF-NMR）和差示扫描量热技术分析新玉米采后60?d内籽粒水分迁移和分布变化,及其对淀粉热特性影响。结果表明,东北新采收玉米采后水分T2弛豫时间和水分分布呈显著变化（P＜0.05）,2?种玉米淀粉凝胶焓值在40?d达到最高分别为18.54?J/g和15.06?J/g,结合水弛豫时间T21与籽粒水分含量呈极显著相关（P＜0.01）,结合水相对面积A21与籽粒水分含量呈极显著负相关（P＜0.01）,A21与凝胶吸热焓值（?H）呈显著相关（P＜0.05）,表明水分迁移和分布是影响淀粉分子晶体结构变化原因之一,利用LF-NMR技术可以有效分析采后籽粒内部水分动态变化,及其对淀粉功能特性影响。