利用核磁共振及其成像技术研究鸡蛋的腐败过程

应用核磁共振(NMR)和磁共振成像(MRI)技术研究室温和冷藏(4℃)储藏条件下鸡蛋的腐败过程.测定不同储藏时间的鸡蛋的失水率和磁共振弛豫特性,分析腐败过程中失水率、弛豫特性、储藏时间与理化指标之间的相关性;通过磁共振成像技术观测鸡蛋的内部结构,了解蛋白高度的变化和蛋清中水分的迁移过程.结果表明:冷藏鸡蛋的货架期明显长于室温储藏;室温储藏鸡蛋的失水率为16.41%,冷藏鸡蛋的失水率为10.51%,两者差异显著.此外,鸡蛋的各项理化指标和弛豫特性的相关性显著,因此可以用该技术来预测鸡蛋的货架期.     

草莓保存过程中的质构与理化性质变化研究

主要探讨草莓在存放过程中各种质量指标的变化。定时测定了草莓在常温存放过程中穿刺强度、剪切功、还原糖含量、酸度、Vc、色泽、失重等因素的变化,分析了各个指标之间的相关性及与成熟度或者新鲜度的关系。结果显示,草莓在常温存放过程中,水分损失和Vc的损失呈线性变化,总糖和总酸变化不显著,还原糖在存放前期轻微上升,后期几乎不变化,穿刺力与剪切功都呈现对数下降态势,色泽变化前期呈现指数上升趋势,48h后就色泽几乎完全改变。     

不同保藏方式对龙眼贮藏过程中感官与理化品质的影响

研究不同保藏方式对龙眼贮藏过程中感官与理化品质的影响。分别对龙眼进行抽真空包装和充氮气包装,设置常温和低温(4℃)两种贮藏条件,通过测定贮藏过程中龙眼的感官品质和理化指标(可滴定酸度、还原糖含量、水分含量、维生素C含量)的变化来比较不同保藏方式下龙眼的品质变化。结果表明:真空包装和充氮气包装均可延缓贮藏过程中龙眼感官品质的劣变;低温贮藏能有效抑制贮藏过程中龙眼各理化指标的褪变,延长其货架期; 4℃、真空保藏方式下贮藏的龙眼的总体品质最优,展现出优良的感官和理化指标。     

核磁共振技术(NMR)研究脐橙的储藏过程

本实验采用低场核磁共振技术研究不同处理方法脐橙在储藏过程中水分的变化以及水分的迁移行为,同时结合理化分析,探讨脐橙储藏过程中磁共振参数与脐橙品质变化的相关性。实验结果发现,果蜡处理的脐橙在四种方法中具有最高的T2弛豫时间,2,4-D处理的变化较缓。从T2数据结合理化性质分析可得,空白清水处理的样品货价期最短,其它方法处理的脐橙有较长的货架期;大分子物质降解为小分子物质,果皮失去持水能力,自由水分的生成大于自由水分的消耗是脐橙腐败的主要影响因素。     

核磁共振技术在脐橙保藏和质量评估中的应用

采用低场核磁共振技术研究脐橙储藏过程中水分的状态、变化以及水分的迁移.利用Carr-Purcell-Mei-boom-Gill(CPMG)序列采集样品的核磁共振受激回波信号,采用多重指数衰减模型对收集的信号数据进行分析并计算组织中不同水分自旋-自旋弛豫时间.探讨脐橙在储藏过程中品质变化与核磁共振弛豫参数变化的相关性.发现在脐橙的后成熟期、稳定期和腐烂期,对应的自旋-自旋弛豫时间变化呈现一个上升-稳定-急速下降的过程,且在脐橙腐烂前出现了一个自旋-自旋驰豫时间急剧下降的过程.该方法可以作为脐橙质量评估的有效手段,对于脐橙的质量评估和保藏方法的评估等具有指导意义.     

超声协同钙浸渍液对采后草莓理化特性及水分迁移规律的影响

研究通过超声波协同钙浸渍液处理采后草莓果实,考察超声波处理时间、功率密度、温度对草莓果实理化品质的影响。研究结果表明:在超声波处理时间20 min,功率密度0.12 W/cm~3,温度20℃时,草莓硬度达到最大值12.2 N,显著高于新鲜果实的硬度10.8 N;且草莓的失水率最低为1.7%;随着超声波处理温度的增加草莓果实失水率显著下降;通过低场核磁技术从微观角度研究超声波协同处理技术对采后草莓果实中水分分布规律的影响,结果表明:草莓失水过程中水分从果芯向着果皮迁移,且失水率越大,果实硬度越小,果皮含水量越高,核磁成像中果皮亮度越高;草莓果实中水分分布的变化与其硬度和失水率存在密切关系。     

草莓液态与固态糖渍过程中的水分分布与迁移规律

采用低场核磁共振技术研究了固态渗透(solid osmotic dehydration, SSD)和液态渗透(liquid osmotic dehydration, LOD)过程中草莓水分的流失规律。结果表明,在糖渍72 h的过程中,2种糖渍方式下草莓水分含量均逐渐降低;在渗糖72 h时,SSD和LOD处理的草莓水分含量分别由91.83%下降至74.56%、79.90%。2种渗透方式的弛豫时间T₂₂与T₂₃值均伴随着渗透过程而变小,表示SSD和LOD都使得草莓中不易流动水和自由水的流动性减小;同时峰面积A₂₂值均逐渐减小,表示2种渗透方式均减少了不易流动水的水分含量。然而在LOD处理过程中,草莓中自由水峰面积在渗透过程中呈下降趋势,但下降不显著(P>0.05),同时弛豫时间T₂₁峰位置逐渐右移,表示随着渗透时间的延长,草莓中结合水的流动性增强;相反,在SSD处理中,草莓中自由水峰面积在渗透72 h后显著下降(P<0.05),相比0 h,下降幅度达55.35%,并伴随着渗透时间的延长,草莓...     

热处理对袋装草莓果保鲜效果的影响

研究了袋装草莓果经 40℃热处理后在室温 ( 2 2± 2 )℃贮藏过程中呼吸强度和化学成分的变化。结果表明 ,热处理可降低草莓果贮藏期间的腐烂率和减少抗坏血酸、还原糖和有机酸含量的损失。以热处理 3 0min的效果最明显 ,且对草莓呼吸的刺激作用最小     

冰温保藏技术在生鲜肉保藏中的应用

生鲜肉营养丰富,但在加工、运输和储存过程中易受微生物和外界环境的影响发生腐败变质,因此保鲜方式极其重要。冰温保藏较传统冷藏技术可更加有效地延长产品的货架期,同时也不会因冻结而造成产品品质下降,因此近年来在生鲜肉的保藏逐渐受到关注。目前对冰温保藏技术在生鲜肉的应用还缺乏全面的综述,因此,本文以冰温保藏技术为研究对象,阐述了其原理以及在禽肉、畜肉、水产品保鲜中的应用研究进展,论述了冰温保藏技术在生鲜肉保藏中的应用前景,介绍了冰温保藏技术与真空、气调和生物保鲜剂相结合的保藏方式在生鲜肉中的应用研究进展,为冰温保藏技术能更好地应用于生鲜肉中提供一些思路和研究方向,以期为冰温保藏技术的推广应用提供参考。     

魔芋葡甘聚糖/壳聚糖复合涂膜对草莓采后贮藏品质的影响

针对草莓贮藏保鲜时间短的问题,选取魔芋葡甘聚糖(KGM)为主要材料,以壳聚糖(CTS)为复配材料,研究KGM/CTS复合膜不同配比(1:2、1:1、3:2、2:1、5:2)对草莓采后贮藏效果及品质(腐败率、失重率、硬度、总酸、可溶性固形物、Vc)的影响。研究结果表明,KGM/CTS复合膜的最佳配比为3:2,其比例能一定程度上降低草莓的腐败率和失重率,同时可以减少草莓内部营养成分的损失,如可溶性固形物、有机酸、Vc等。     

核磁共振研究膳食纤维面包制作过程的水分迁移行为

利用核磁共振测定三种不同配方面包在制作过程(和面、发酵、醒发和焙烤)中质子的自旋-自旋弛豫时间(T2),面团中流动性不同的水分,表现出不同的弛豫时间。实验表明,在面包制作过程中,其束缚相和自由相的迁移行为不同,此外140MPa处理的膳食纤维具有强持水性,添加至面包中可改善其储藏性。     

Effect of physical properties on the stability of Lactobacillus bulgaricus in a freeze-dried galacto-oligosaccharides matrix

The ability of galacto-oligosaccharides (GOS) to protect Lactobacillus delbrueckii subsp. bulgaricus upon freeze drying was analyzed on the basis of their capacity to form glassy structures. Glass transition temperatures (T(g)) of a GOS matrix at various relative humidities (RH) were determined by DSC. Survival of L. bulgaricus in a glassy GOS matrix was investigated after freezing, freeze drying, equilibration at different RHs and storage at different temperatures. At 32 °C, a drastic viability loss was observed. At 20 °C, the survival was affected by the water content, having the samples stored at lower RHs, the highest survival percentages. At 4°C, no decay in the cells count was observed after 45 days of storage. The correlation between molecular mobility [as measured by Proton nuclear magnetic resonance (1H NMR)] and loss of viability explained the efficiency of GOS as cryoprotectants. The preservation of microorganisms was improved at low molecular mobility and this condition was obtained at low water contents and low storage temperatures. These results are important in the developing of new functional foods containing pre and probiotics.     

柠檬烯复合液对草莓采后保鲜效果的影响

用柠檬烯复合溶液浸泡草莓3min,研究柠檬烯复合液对草莓贮藏期间各项营养指标的影响。结果表明,与对照相比,各处理均能明显减缓草莓果实中维生素C、可滴定酸和可溶性固形物含量的下降,抑制草莓的失水和腐烂,对草莓有较好的保鲜效果。     

Bound and free water determination by pulsed nuclear magnetic resonance.

In the present paper the analysis of the transverse magnetization decay curves of water is discussed. Whenever the spin-echo decay curve of water does not show a single exponential behaviour and the apparent relaxation rates of bound and free component vary with the moisture content, an exchange process must be hypothesized. A method for obtaining the amount of bound and free water, in the presence of exchange, is reported. If the described procedure is applied, the amount of bound water as determined by pulsed nuclear magnetic resonance (NMR) is in good agreement with the amount of unfreezable water as determined by other techniques.     

Investigation on moisture migration,microstructure and quality changes of fresh-cut apple during storage

Moisture migration of fresh-cut apple during 4 °C storage was monitored by low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI). Three water components were identified in apple tissue by LF-NMR T₂ relaxation, corresponding to water in cell wall, cytoplasm and vacuole. The relaxation results also revealed that the moisture migrated from the vacuole to cytoplasm and the mobility of water in vacuole decreased with the extension of storage time. T₂ weighted images of MRI indicated that high density of water appeared at the edge of the fresh-cut apple in the later stage of storage. Breakdown of cell walls and intracellular network were observed by cryo scanning electron microscope (cryo-SEM). Moreover, storage process also led to the decrease in moisture content, browning and softening of fresh-cut apple. In addition, good prediction models have been developed for quality indicators using partial least squares regression based on Carr–Purcell–Meiboom–Gill decay data.     

草莓保鲜剂的开发研究

目的 探讨不同类型保鲜剂对草莓采摘后的保鲜效果。方法 将草莓置于蒸馏水、生姜提取液、甘草-壳聚糖溶液中浸泡1 min, 探讨保鲜剂对草莓感官、营养、生化指标等的影响。结果 与对照组相比, 2种保鲜剂都能显著抑制草莓失重、腐烂, 也能延缓维生素C和可滴定酸含量下降, 抑制超氧化物歧化酶和过氧化物酶活性损失, 但甘草-壳聚糖保鲜效果更好。贮藏6 d后, 甘草-壳聚糖组比空白对照组可滴定酸含量高72.90%, 维生素C含量高93.79%, 过氧化物酶活性高233.01%, 超氧化物歧化酶活性高187.47%。结论 甘草-壳聚糖作为保鲜剂, 能有效地延长草莓贮藏期。     

The effects of soy on freezable bread dough: a magnetic resonance study

Hygroscopic soy ingredients were hypothesised to slow the rate of water migration in unleavened bread dough during frozen storage. Thawed soy (18% dry weight) and wheat dough samples were assessed using non-destructive nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) for up to 8 wks frozen storage time. MRI suggested a spatially homogeneous, net increase in proton mobility with frozen storage and, with solution state proton NMR, distinct "free" and "bound" states were discerned. T(2) relaxation times of the majority proton population suggested increased mobility with frozen storage time, and statistical difference from the fresh sample was seen later for the soy samples than the wheat samples. As seen by (13)C-solid state NMR, the crystallinity of the starch was not affected by either soy addition or frozen storage. In conclusion, addition of soy to bakery products led to slightly enhanced preservation of "fresh" characteristics of the dough during frozen storage.     

奥尔良鸡腿排冻藏期间的品质变化

以奥尔良鸡腿排为研究对象,每30 d对奥尔良鸡腿排的色泽、质构特性、剪切力、解冻损失率、蒸煮损失 率、pH值、总挥发性盐基氮（total volatile basic nitrogen,TVB-N）含量、硫代巴比妥酸反应物（thiobarbituric acid reactive substance,TBARs）值进行测定,并结合低场核磁共振（low field nuclear magnetic resonance,LF-NMR）技 术对其水分状态进行测定,研究奥尔良鸡腿排在240 d冻藏期间的品质变化。结果表明：奥尔良鸡腿排的理化指标 受冻藏时间影响显著（P＜0.05）,随着冻藏时间的延长,奥尔良鸡腿排的pH值不断增加,TBARs值呈上升趋势, TVB-N含量不断上升,菌落总数的变化趋势为先下降后上升;色泽指标中的亮度值及红度值呈降低趋势,而黄度值 呈升高趋势;质构指标中的硬度、咀嚼性、黏结性和剪切力呈上升趋势,而弹性逐渐下降;蒸煮损失率和解冻损失 率逐渐增大;横向弛豫时间T23峰面积（自由水含量）减小,T21峰面积（结合水含量）几乎不变,T22峰面积（不易 流动水含量）略有减小;磁共振成像结果表明,肉质表面氢质子发生明显迁移,与水分变化分析结果一致。     

Electrostatic and Conventional Spraying of Alginate-Based Edible Coating with Natural Antimicrobials for Preserving Fresh Strawberry Quality

Microbial contamination and mold growth are common causes of strawberry deterioration during storage. The growing need for extending shelf-life while enhancing the overall quality of perishable fruits has generated increasing interest in the development of novel preservation technologies. This study used electrostatic spraying (ES) technology as an innovative and efficient technique for the application of edible alginate coating enriched with carvacrol and methyl cinnamate (natural antimicrobials) on fresh strawberries. The efficiency of the electrostatic technology was compared to non-electrostatic (conventional) spray (NES) technology in terms of transfer efficiency and coating evenness. Furthermore, physicochemical and textural parameters (such as weight loss, visible decay, firmness, surface color, total soluble phenolic content, and antioxidant capacity) of ES and NES coated fruits were studied and compared to uncoated controls. ES technology demonstrated higher transfer efficiency and evenness than NES, which led to a significant reduction of visible decay over uncoated controls. The delay in microbial spoilage by ES (11 days) was greater than by NES (10 days) and uncoated strawberries (7 days). ES coating significantly inhibited strawberry decay with only 5.6 % of infected fruits, compared to 16.6 and 8.3 % for control and NES fruits after 13 days of storage, respectively. At the end of 13 days of storage, ES coating demonstrated superior performance on strawberry firmness, color retention, and weight loss reduction. Additionally, no differences were observed between uncoated and coated fruits with regard to their antioxidant and total soluble phenolics.     

核磁共振技术研究馒头水分的迁移变化

利用NMR(nuclear magnetic resonance)技术和质构分析法(texture profile analysis)从分子水平上探讨水分在馒头储藏过程中的迁移情况。通过对馒头的硬度和NMR 参数之间进行相关分析,发现它们之间具有显著相关性(p<0.01)。实验结果表明：储藏期间馒头的硬度指标与其水分存在状态的变化密切相关,水分迁移运动是导致馒头老化的重要原因,馒头心部的老化变硬比表层老化变硬滞后。