基于低场核磁共振技术研究不同热风干燥工艺条件下香菇复水过程中的水分传递特性

以6种不同热风干燥工艺制备的干香菇为研究对象,利用低场核磁共振(low-field nuclear magnetic resonance,LF-NMR)与核磁共振成像(nuclear magnetic resonance imaging,MRI)技术研究干香菇复水过程中水分变化规律。结果表明,根据T2弛豫时间显示,伴随复水时间的延长,香菇体内水分的主要状态是不易流动水而并非自由水。非均匀间歇干燥(non-uniform intermittent drying,NUID)组水分信号明显强于其他各组,复水能力较强,均匀间歇干燥(uniform intermittent drying,UID)组复水能力相对较弱。因此,提升复水效率的关键在于保证干燥过程中香菇水分的均匀转移,以便复水时具有良好的保持不易流动水的能力。     

不同干燥温度对牛肉脯水分分布迁移规律的影响

借助低场核磁共振技术及其核磁共振成像技术,探讨不同热风干燥温度（50～70 ℃）在干燥时间（120～180 min）范围内牛肉脯的水分状态、水分质量分数与水分分布情况。3种干燥温度下平均干燥速率分别为 0.226 5、0.277 9、0.353 9 g/（g·min）;牛肉脯的干燥效果主要取决于其不易流动水的含量,通过在热风干燥过程中提高温度,可以明显提高肉脯的干燥速率,结合水、不易流动水和自由水的迁移也会加快;干燥过程中不易流动水在自由水和结合水之后发生变化,不同热风温度条件下的峰面积、峰比例变化趋势较为一致,温度越高曲线变化愈明显;牛肉脯水分含量与峰面积之间呈现良好的线性关系,其中70℃干燥的线性回归方程为 y=323.34x- 6 092.77（R²=0.975 0）;纵向弛豫时间T1加权成像图表明牛肉脯70 ℃热风干燥过程中氢质子密度分布相对均匀,干燥品质较高。比较3种干燥温度的差异,这可为今后肉脯品质提升、产品研发和节约能源提供理论依据。     

皱皮木瓜真空冻干工艺优化及基于LF-NMR技术的复水特性研究

目的:对皱皮木瓜片的真空冷冻条件进行优化,研究木瓜片复水过程中水分状态变化。方法:采用单因素试验结合Box-Behnken响应面法,分别以复水比和色差值为指标,考察木瓜片厚度,真空冷冻干燥机的隔板温度以及真空度3个因素对冻干工艺的影响,优化皱皮木瓜片冻干工艺;利用低场核磁共振技术比较真空冷冻干燥和热风干燥的木瓜片成品复水过程中水分状态的变化情况。结果:确定皱皮木瓜真空冷冻干燥的复水比最佳工艺条件:木瓜片厚度4 mm,隔板温度40℃,真空度2.4 mbar;色差值最优的组合为:木瓜片厚度7.45 mm,隔板温度28.37℃,真空度2.02 mbar。NMR试验表明,复水过程中进入木瓜片中的水很快转化为不易流动水,结合水和自由水变化不大,且真空冷冻干燥的木瓜片中不易流动水增加较快,说明冻干比热风干燥的木瓜片品质好。结论:本研究结果为优化的皱皮木瓜真空冷冻干燥工艺参数,低场核磁共振技术可用于表征皱皮木瓜复水过程中水分状态的变化。     

LF-NMR动态分析4种干燥方式下鱿鱼干的复水特性

以鱿鱼为研究对象,采用自然晒干、热风干燥、热泵干燥、真空冷冻干燥4种干燥技术干制鱿鱼,结合鱿鱼干的肌纤维微观结构和复水率,通过低场核磁共振(LF-NMR)动态分析鱿鱼干复水过程的水分迁移和分布,探讨干燥方式对鱿鱼干复水的影响。结果表明,4种干燥方式中,真空冷冻干燥的鱿鱼干水分含量最低,氧化程度也最低(比其它3种处理的低1.5~6.7倍)。电镜扫描图显示鱿鱼干肌纤维内部有大量疏松多孔的蜂窝状结构,且真空冷冻干燥复水最快。复水过程,部分结合水向不易流动水迁移,不易流动水含量明显增加,且占比90%以上,自由水含量也有所提升。LF-NMR分析也表明真空冷冻干燥的鱿鱼干复水效果最好,复水后可截留更多的自由水。热泵干燥的鱿鱼干复水效果与自然干燥接近,热风干燥的复水率最差。干燥方式对干制品复水效果影响明显,真空冷冻干燥和热泵干燥技术有利于水产品干制。     

超声波预处理时间对扇贝柱热泵干燥动力学及品质特性的影响

为了提高扇贝柱热泵干燥效率,改善扇贝柱干制品品质,本实验研究超声波（ultrasonic,US）预处理时间（0、10、20、30 min）对扇贝柱干燥动力学与品质特性的影响,利用低场核磁共振（low-field nuclear magnetic resonance,LF-NMR）探究扇贝柱干燥过程中水分状态分布规律。结果表明,扇贝柱干燥进程遵循降速干燥模式,干燥进程受内部水分扩散控制,US预处理提高了扇贝柱干燥速率和有效水分扩散系数。相比于CK组（除未经US预处理外,其余处理同US组）,US预处理可降低扇贝柱总色差,提高干制品韧性。干燥数学模型拟合结果表明Midilli et al.模型为描述扇贝柱热泵干燥过程的最适模型。LF-NMR分析结果表明,不易流动水决定了扇贝柱热泵干燥过程中含水率的变化;自由水和不易流动水的迁移速率随US预处理时间的延长而加快,不易流动水弛豫时间T22与含水率有很强的相关性。综上,US预处理可提高扇贝柱热泵干燥效率,并对干制品色泽、收缩率、复水比和质构特性具有一定影响,LF-NMR可预测扇贝柱干燥过程中含水率变化。本研究可为水产品尤其是扇贝柱的热泵干燥提供一定的理论依据和实践参考。     

不同干燥方式对猕猴桃果脯品质的影响

以猕猴桃果脯为试验对象,探讨热风干燥、远红外干燥和真空冷冻干燥3种不同干燥方式对其水分构成、复水性、硬度、韧性、风味和滋味等品质特性的影响。经快速水分测定仪和低场核磁共振技术检测发现,真空冷冻干燥果脯含水量显著偏低（P<0.05）,其自由水和不易流动水相对含量明显偏高;果脯复水性显著偏高（P<0.05）,果脯硬度和韧性显著高于其他两种干燥方式（P<0.05）。电子舌和电子鼻分析结果表明,真空冷冻干燥猕猴桃果脯咸味显著偏高（P<0.05）,而挥发性芳香物质含量呈现出相反的趋势（P<0.05）。经聚类分析和多元方差分析,热风干燥和远红外干燥所得猕猴桃果脯品质接近,与真空冷冻干燥的果脯品质差异显著（P<0.05）。由此可见,热风干燥和远红外干燥制备的猕猴桃果脯品质较佳。     

香菇热风微波流态化的干燥特性与机理分析

通过香菇热风微波流态化的干燥特性试验,探讨微波功率、热风功率和振动频率对香菇干燥速率的影响规律;应用低场核磁共振技术(NMR)分析香菇热风微波流态化的水分迁移变化。试验结果表明,热风微波流态化干燥香菇过程按降水速率大小分为预热、恒速和降速3个阶段。干燥速率随微波功率及热风功率的增大而明显加快,振动频率对干燥速率的影响较小。核磁共振结果显示:干燥预热阶段主要脱去自由水,恒速阶段主要是不易流动水与结合水之间的转化并脱去大量自由水,降速阶段是脱去结合水。在香菇热风微波流态化干燥过程中,提高水的流动性并延长恒速阶段干燥时间有利于提高干燥速率。     

渗透剂预处理对扇贝柱热泵干燥动力学及品质特性的影响

为提高扇贝柱热泵干燥效率,改善干制品品质,分别采用不同种类(菊糖、海藻糖、麦芽糊精和乳清分离蛋白)和质量浓度(50、100、150g/L)的渗透剂预处理扇贝柱,在温度45℃、风速2m/s条件下进行后续热泵干燥,探究不同渗透剂预处理对扇贝柱热泵干燥动力学和品质特性的影响。基于低场核磁共振(low field nuclear magnetic resonance, LF-NMR)技术,分析扇贝柱热泵干燥过程中水分状态和分布规律。结果表明:适宜质量浓度的菊糖、海藻糖、麦芽糊精和乳清分离蛋白溶液预处理可显著提高热泵干燥速率,降低色差(ΔE),提高复水效率。菊糖、海藻糖、麦芽糊精和乳清分离蛋白质量浓度分别为100、150、100、50g/L时,综合加权评分最高,复水率相比于对照组分别提高了2.98%、12.76%、11.91%和7.13%。150g/L海藻糖预处理对扇贝柱热泵干燥速率和品质特性的改善效果最优,与对照组相比,干燥时间缩短2h,ΔE降低40%,硬度降低,复水率增加22.79%,综合加权评分提高12.76%。LF-NMR结果表明:热泵干燥过程中,扇贝柱含水率的降低主要取决于不易流动水的去除;适宜质量浓度渗透剂预处理后,扇贝柱中不易流动水干燥过程中迁移速率加快,自由水峰面积占比略有增加,但总体变化不大;结合水峰面积占比呈增加趋势,而不易流动水峰面积占比显著降低;扇贝柱横向弛豫时间随干燥进行向左偏移,水分子流动性变低。综合考虑,扇贝柱热泵干燥优化预处理条件为150g/L海藻糖。     

超声及超声渗透预处理对红外辐射干燥特性研究

为探究超声及超声渗透预处理对桃片水分迁移及红外辐射干燥特性的影响,经超声及超声渗透30、60 min预处理后,进行红外辐射80℃干燥处理,采用低场核磁共振技术测定预处理后桃片横向弛豫时间T2图谱,分析水分状态及分布变化,得到干燥特性曲线,并分析水分状态及分布对干燥特性的影响。结果表明,超声降低桃片固形物含量,超声渗透明显增加固形物含量并降低水分含量;不同预处理均改变桃片内部水分状态和分布。超声后,桃片不易流动水和自由水弛豫时间增加,水分自由度增加,从而提高干燥速率,增加水分有效扩散系数;超声渗透后,桃片结合水、不易流动水及自由水弛豫时间均减小,且自由水含量明显降低,而不易流动水及结合水含量相对升高,从而降低干燥速率,减小水分有效扩散系数。该研究为超声及超声渗透预处理对红外辐射干燥水分扩散研究提供参考。     

催化式红外杀青对绿茶热风干燥的影响

以镇江金山翠芽绿茶鲜叶为原料,以蒸汽杀青为对照,研究红外杀青对茶叶品质的影响,对杀青后茶叶进行不同温度热风干燥得到茶叶成品。考察茶叶中多酚氧化酶(polyphenol oxidase,PPO)含量、VC保留率、茶多酚含量以及感官审评分等指标的变化,建立一种催化式红外杀青联合热风干燥的绿茶加工技术。最优杀青干燥工艺条件为:红外辐照距离20 cm杀青150 s,经揉捻作形后,热风干燥温度70℃、干燥40 min。实验结果建立了红外杀青过程中PPO钝化动力学模型和干燥过程中水分干燥动力学模型,可为杀青干燥过程预测提供理论参考。     

不同预处理方式对花椰菜干制品品质影响研究

为筛选适宜花椰菜干制的预处理方法,本研究通过采用沸水烫漂、蒸汽烫漂、微波加热和超声波辅助烫漂4种不同预处理方式处理新鲜花椰菜,考察干燥后其干制品收缩率、复水比、色泽、V_C、总黄酮、总酚及总硫代葡萄糖苷含量等感官和营养指标的变化情况。结果表明:不同预处理方式处理后花椰菜干燥时间均有缩短,其中沸水烫漂、蒸汽烫漂和微波加热较未处理缩短了18.18%,而超声波辅助烫漂处理后缩短了27.27%。微波加热和超声波辅助烫漂处理后花椰菜干制品的色泽变化较小,超声波辅助烫漂收缩率最小,为67.41%,微波加热复水能力较强,为3.77。不同预处理方式对花椰菜干制品营养成分影响不同,与未处理样品相比,不同烫漂方式处理后还原糖损失率为8.85%~23.96%、总糖损失率为3.74%~39.35%。微波加热花椰菜干制品可溶性蛋白和总硫代葡萄糖苷保留率分别为81.80%和31.93%,超声波辅助烫漂后花椰菜干制品V_C、总黄酮和总酚保留率分别为40.18%、83.70%和38.40%。综合比较表明:超声波辅助烫漂后花椰菜干制品感官及营养品质最佳。     

3 种预处理方式对双孢菇干制品品质的影响

研究漂烫、超声漂烫、常温超声3 种预处理方式在远红外干燥条件下对双孢菇干制品硬度、脆度、色泽、VC含量和微观结构的影响。结果表明：常温超声预处理的双孢菇干燥时间缩短,与未处理产品相比,其硬度值明显下降、脆度值显著提高。同时常温超声预处理显著提高了双孢菇干制品复水比、降低了收缩率。超声漂烫和漂烫两种预处理方式因存在高温作用,使双孢菇细胞结构遭到严重破坏,导致双孢菇干制品色泽变化明显、复水比降低、收缩率提高且VC含量降低。因此采用常温超声作为预处理方式可以提高双孢菇干制品的品质。     

亲水胶体成膜预处理对扇贝柱热泵干燥动力学与品质的影响

为提高扇贝柱热泵干燥效率,改善干制品品质,研究了低甲氧基果胶（LMP）和壳聚糖（CTS）等2种成膜预处理对扇贝柱干燥动力学与品质特性（质构、复水比、收缩率、色泽）的影响。结果表明,扇贝柱含水率随干燥时间延长而降低,扇贝柱干燥过程处于降速干燥阶段,干燥进程受内部水分扩散控制;LMP和CTS处理均提高了扇贝柱干燥速率。相比于CK,LMP和CTS成膜处理使扇贝柱有效水分扩散系数分别提高了11.08%和26.73%。相比于CK,LMP处理可降低扇贝柱收缩率、色差、硬度和韧性,提高干制品复水率;CTS处理降低了扇贝柱收缩率,提高了扇贝柱复水率、韧性和硬度,但对扇贝柱色差无影响。采用8种数学模型拟合干燥动力学数据,Midilli et al.为描述扇贝柱热泵干燥过程的最适模型。亲水胶体成膜预处理在提高扇贝柱热泵干燥效率、改善干制品品质方面具有显著效果。本研究可为水产品的热泵干燥提供一定的理论基础和实践参考。     

CONVECTIVE DRYING OF PUMPKIN: INFLUENCE OF PRETREATMENT AND DRYING TEMPERATURE

The aim of this research was to study the influence of blanching as a pretreatment on the drying rate, color and rehydration rate of pumpkin slices ( Cucurbita maxima ) dried in a convective dryer at 50, 60 and 70C.
The different pretreatments did not modify drying time. The diffusion coefficient depended on temperature and moisture content, but not on pretreatments. It varied between 1.6 and 2.9  ×  10⁻⁹ m²/s and activation energy was approximately 35.6 kJ/mol. The rehydration rate of the dried sample, which was found to be influenced by drying temperature but not by the pretreatments, reached about 2 kg water/kg dry solid in about 150 s in boiling water. Color parameters " L " and " b " were influenced by drying temperature and pretreatments. Parameter L varied between 36 and 53 and parameter b varied between 20 and 31. Samples dried at 70C without pretreatments presented color parameter values very similar to those of the fresh sample.

PRACTICAL APPLICATIONS

This work evaluates the pretreatment and drying conditions of pumpkin. Five parameters of the optimal product are considered: pretreatment time, drying time, temperature, color and rehydration rate of the product. With these results, drying of pumpkin can be carried out in industrial convective dryers and the dried product may be used in the preparation of soups, premixed foods, snacks, etc.     

Dehydration of apple slices by sequential drying pretreatments and airborne ultrasound-assisted air drying: Study on mass transfer,profiles of phenolics and organic acids and PPO activity

Pretreatments of either water blanching or NaCl immersion and airborne ultrasound-assisted air drying were combined to dehydrate apple slices. The drying time was found to be reduced by 1.6–69.0% compared with air drying without any pretreatment and sonication. Meanwhile, it was found that sequential water blanching coupled with air drying with sonication gave the shortest drying time. A modified diffusional model incorporating temperature-dependent moisture diffusivity (D_eff) could simulate the apple drying process well. Water blanching pretreatment and airborne sonication were found to lower the activation energy required for the enhancement of moisture diffusive ability, and intensify water exchange on apple surface to speed up the drying process. Both water blanching and NaCl immersion significantly increased the amounts of procyanidin B2 in dehydrated apple slices. However, airborne sonication promoted the loss of procyanidin B2 in apple slices with pretreatments during air drying. In addition, sonication had no obvious influences on apple PPO activity and individual organic acids throughout drying. Overall, the sequential NaCl immersion pretreatment (or water blanching pretreatment) and drying with airborne sonication are effective to improve the quality of dried apple slices.     

EFFECT of LOW TEMPERATURE BLANCHING, CYSTEINE-HCi, N-ACETYL-L-CYSTEINE, Na METABISULPHITE and DRYING TEMPERATURES ON the FIRMNESS and NUTRIENT CONTENT of DRIED CARROTS

Low temperature long time (LTLT) blanching (70C for 20 min) together with calcium treatment can be used to significantly improve the texture of rehydrated dried carrots when compared to high temperature short time (HTST) blanching (100C for 3 min). LTLT blanching allows pectin methyl esterase to deesterify pectin which can then react with calcium to form salt bridges. 0.3% L-cysteine-HCl was found to be most effective in preventing ascorbic acid loss and obtaining a product with the highest rehydration ability, compared to pretreatments with 0.3% N-acetyl-L-cysteine and 0.1% sodium metabisulphite. On the other hand 0.1% sodium metabisulphite was most effective in preserving the carotenoids content of dried carrots. Ascorbic acid and rehydration ability were more adversely affected by long drying time than high drying temperature, while carotenoids were more sensitive to high drying temperature than drying time. Hence, 60C drying temperature was good for ascorbic acid and rehydration ability, while 40C drying temperature was good for carotenoid and color of dried carrots.     

Pulsed electric field treatment of carrots before drying and rehydration

BACKGROUND: In this study the effects of pulsed electric field (PEF) pretreatment were evaluated during drying and rehydration of carrots. Carrots pretreated with an electric field intensity of 1 kV cm^?1 (capacitance 0.5 µF, 20 pulses) or 1.5 kV cm^?1 (capacitance 1 µF, 20 pulses) as well as blanched (100 °C, 3 min) carrots were used for the study. Following pretreatment, samples were oven dried at 70 °C and then rehydrated in distilled water (1:30 w/v) at room temperature (24 ± 1 °C). RESULTS: PEF pretreatment increased the drying rate of carrots. However, the rehydration rate of PEF‐pretreated carrots was lower than that of blanched carrots. There were no colour differences between PEF‐pretreated and blanched carrots before drying and after rehydration. In terms of texture, PEF‐pretreated carrots were firmer than blanched carrots. PEF pretreatment reduced the activity of peroxidase by 30–50%, while blanching completely inactivated the enzyme (>95%). CONCLUSIONS: Overall, the results suggest that PEF could be an effective pretreatment during drying and rehydration of carrots. Copyright © 2009 Society of Chemical Industry     

预处理方式对热风干燥玫瑰花瓣品质特性的影响

采用5%柠檬酸溶液、20%糖溶液、20%NaCl和柠檬酸混合溶液浸渍、烫漂4种处理方式处理玫瑰花瓣,以未预处理的花瓣作为对照,进行热风干燥对比试验和分析,对花瓣品质特性(色泽、总黄酮含量、总酚含量)以及微观结构等进行比较,并结合模糊数学综合评判法进行感官评定。结果表明:预处理方式对玫瑰花瓣的干燥速率有显著影响,且在含水率较高时尤其明显;微观结构有一定的差异性。其中,5%柠檬酸溶液组耗时最长,ΔE最小;20%糖溶液组复水比最低;混合溶液组色泽变化ΔE最大,总酚含量最高;烫漂组耗时最短,总黄酮含量和复水比最高。经烫漂预处理后的花瓣干燥后得到的感官评分值最高,对应的干燥时间、ΔE、复水比、总黄酮含量及总酚含量分别为120min、18.17±0.54、3.01、0.27mg/g、1.43mg/g。因此,采用烫漂预作为预处理方式可以提高食用玫瑰花瓣干制品的品质。     

酸菜微波真空冷冻干燥工艺及复水特性研究

采用微波真空冷冻干燥技术对新鲜酸菜进行脱水处理,研究微波功率、真空度和铺料层厚度对酸菜干燥特性及复水比的影响,确定最佳干燥条件,并利用低场核磁共振技术(LF-NMR)研究酸菜干制品在复水过程中的水分状态。结果表明:微波功率越大、真空度越小、铺料层厚度越小,则酸菜干燥速率越大,达干燥终点时间越短;最佳干燥工艺条件为微波功率320 W,真空度200Pa,铺料层厚度2mm,此时酸菜复水比为9.14g/g;LF-NMR表明不易流动水为复水后酸菜体内水分的主要存在形式,结合水与自由水则变化不大。     

High-Pressure and Freezing Pretreatment Effects on Drying, Rehydration, Texture and Color of Green Beans, Carrots and Potatoes

High-pressure pretreated and frozen green beans, carrot dice or potato cubes were fluidized bed dried and compared to untreated, pressure-treated or water-blanched dried samples. Drying rates varied with pre-treatments. Freezing resulted in highest drying rates. Pressure-treated and water-blanched samples retained highly acceptable colors. Freezing or hot-water blanching or high-pressure pretreatment, followed by freezing, gave good rehydration. High-pressure treatment resulted in incomplete rehydration but combined with freezing, water uptake was between 2.1 and 4.8 mL/g. Retention of cell wall structures of frozen samples during drying was presumed responsible for more efficient mass transfer. Texture measurements revealed significant effects of pretreatments. Pressure-treated samples had texture nearest that of the raw material. No major differences in color were observed.