【作者】 Ernest Ekow Abano；

【导师】 马海乐；

【作者基本信息】 江苏大学 ， Food Science and Engineering， 2013， 博士

【摘要】 干燥是农产品收获后保藏的最古老和最常见的方法之一。目前使用的干燥方式有很多,如热风干燥、真空微波干燥、红外干燥等,研究的重点集中在干燥工艺参数的优化及设备的研发上,而针对各种干燥方法的干燥动力学过程及其对产品品质影响的对比性研究较少。因此本研究进行了热风干燥、真空微波干燥和红外干燥三种干燥方式对番茄片的干燥动力学和品质影响的对比性研究。首先,本研究采用电热干燥方法对番茄片进行干燥处理,研究不同干燥温度(50℃、60℃、70℃和80℃)对干燥动力学参数和产品品质的影响,其中考察的产品品质指标包括非酶褐变指数、番茄红素含量、颜色和气味的变化。研究结果显示：随着干燥温度从50℃增加到80℃,干燥时间从1140min缩短到540min。在80℃下干燥后番茄片的非酶促褐化指数由新鲜番茄的0.051升高到1.40。在50℃、60℃、70℃和80℃下干燥后,番茄红素含量均显著增加(P<0.05),由新鲜番茄的11.46mg/100g(干基含量)分别上升至61.23mg/100g、59.10mg/100g、60.88mg/100g和65.28mg/100g(干基含量)。所有干燥样品的颜色值介于51.81°和61.95°之间,颜色均为黄色,由此推断干燥过程中样品均发生了褐变反应。采用电子鼻系统检测发现所有干燥样品的气味与新鲜番茄相比均有所下降；采用4个常见的干燥模型进行实验数据拟合,研究结果显示Page模型是预测番茄片电热干燥动力学过程的最佳模型。有效水分扩散系数随着干燥温度的增加而增加,在50℃、60℃、70℃和80℃下,分别为5.13×10-10m2s-1、6.45×10-10m2s-1、8.44×10-10m2s-1和10.26×10-10m2s-1,得出干燥活化能为22.28KJ/mol。其次,本研究采用真空微波干燥方法对番茄片进行干燥处理,研究不同微波功率(200W、300W、500W和700W)和不同真空度(0.04MPa、0.05MPa和0.06MPa)对干燥动力学参数和产品品质的影响,其中考察的产品品质指标包括非酶褐变指数、Vc含量、番茄红素含量、颜色和气味的变化。研究结果显示：随着微波功率从200W增加到700W,干燥速率不断提高,干燥时间从84min缩短到14min。非酶褐变指数随微波功率的增加而增加。在干燥实验中,Vc含量均显著降低(P<0.05),从新鲜番茄的2.744±0.29mg/g下降到最低值1.87±±0.13mg/g,与新鲜番茄相比,番茄干的Vc含量下降最大值为32%,样品在200W和0.06MPa的干燥条件下具有最大的Vc保留率。番茄红素含量均显著增加(P<0.05),在700W和0.04MPa下干燥后由新鲜番茄的11.46mg/100g(干基含量)上升至25.44mg/100g(干基含量)。观察发现,所有干燥样品的亮度和黄色度与新鲜番茄相比均有所增加,但是红色度有略微的减小。所有干燥样品的气味与新鲜番茄相比均有所下降,气味指标比新鲜番茄减少了18.99%-20.80%；采用13个常见的干燥模型进行实验数据拟合,研究结果显示Midilli模型是预测番茄片真空微波干燥动力学过程的最佳模型。有效水分扩散系数随着微波功率的增加而增加,在200W、300W、500W和700W下,分别为7.22×10-9m2s-1、9.10×10-9m2s-1、14.99×10-9m2s-1和25.19×10-9m2s-1。再次,本研究采用风机辅助的热风干燥方法对番茄片进行干燥处理,通过响应面优化实验研究热风温度(40～60℃)、风速(1～2m/s)和样品厚度(7～11mm)对产品品质的影响。研究确定的最佳热风干燥条件为：温度44℃、风速2m/s、样品厚度7.72mm。在此最佳条件下,干燥时间为527±76min,番茄红素含量为62.7±4.3mg/100g(干基含量),Vc含量为3.07±0.14mg/g(干基含量),亮度值为62.92±2.18,红色度值与黄色度值的比例为0.78±0.05,非酶褐变指数为0.55±0.06。最后,本研究采用催化式红外干燥方法对番茄片进行干燥处理,考察了样品厚度(7mm、mm、11mm)和红外辐射距离(38cm、44cm、50cm、56cm)对产品品质的影响。建立了随辐照距离(红外辐射板与样品之间的距离)与样品厚度之间的干燥动力学模型。随着番茄片厚度的减小和辐射距离的缩短番茄的水分有效扩散率增加,并呈现三次多项式的关系。只有催化式红外干燥番茄片干燥速率呈现下降趋势,而没有干燥速率稳定期。相对远红外干燥的样品与新鲜番茄相比,58.3%的干制品的风味有所提升,增加值为3.0%-36.6%之间,而41.7%的干制品风味有所下降,减少值为3.1%-14.1%。通过对薄层干燥模型与干燥数据进行拟合,Midilli模型能够最好的预测干燥过程中的水分变化。研究结果表明,真空微波和远红外辐射干燥是一种高效的干燥方法,其能够很好的保持产品颜色和维生素C含量,有效防止产品发生褐变,以及增加番茄红素的保留率。在真空微波干燥番茄过程中,应避免较高的微波功率(例700W)。本研究能够为工业化生产高品质产品提供有效信息及最优干燥条件。更多还原

【Abstract】 Drying is one of the oldest and commonest methods of preserving agricultural produce after harvest. The study investigated the influence of hot air, microwave-vacuum, and far-infrared catalytic drying on drying kinetics and quality of dried tomato slices. In the first study, a conventional hot air dryer was used to investigate the effect of four temperatures (50,60,70, and80℃) on the drying kinetics and quality changes in the lycopene content, non-enzymatic browning, colour and flavour of dried tomatoes. As expected, the drying time reduced from1140mins to540mins as the air temperature increased from50to80℃. The non-enzymatic browning increased with temperature from0.051in the fresh tomatoes to1.40after drying at80℃. The lycopene levels of the fresh tomatoes significantly (p=0.05) increased from11.46mg/100g dry matter to61.23,59.10,60.88, and65.28mg/100g dry matter when dried at50,60,70, and80℃respectively. Eleven out of the twelve sensors used in the electronic nose system indicated flavour degradation of all dried samples compared with the fresh tomatoes. The values of the hue angles recorded for the dried tomatoes ranged between51.81°and61.95°, revealing that the dried tomatoes were yellow hued, thus indicating less browning. The drying characteristics curves were evaluated against the Page, Henderson and Pabis, and the Logarithmic mathematical models but the Page model best described the drying of tomato slices. The effective moisture diffusivity coefficient increased with increasing air temperature and was5.13×10-10m2s-1,6.45×10-10m2s-1,8.44×10-10m2s-1, and10.26×10-10m2s-1at respective air temperatures of50,60,70, and80℃with activation energy for moisture removal of22.28KJ/mol.In the second study, a microwave-vacuum dryer was used to investigate the influence of four microwave powers (200,300,500,700W) and three vacuum pressures (0.04,0.05and0.06MPa) on drying kinetics and quality of dried tomato slices. The results showed that increase in microwave-vacuum drying conditions increased drying rates and resulted in decreased drying time from84to14min. The non-enzymatic browning index increased with microwave power whereas the overall flavour degradation was between18.99and20.80%. The brightness and the yellowness of the dried tomatoes generally increased but there was a slight reduction in redness when compared with the fresh. The effective moisture diffusivity increased with microwave power and was7.22×10-9m2s-1,9.10×10-9m2s-1,14.99×10-9m2s-1, and25.19×10-9m2s-1at respective microwave powers of200,300,500, and700W.Among the thirteen thin layer drying models that were used to fit the experimental data, the Midilli et al model gave the highest correlation coefficient, lowest residual sum of squares, root mean square error, and reduced chi-square, thus indicating that the model of Middilli et al best described the micro wave-vacuum drying of tomato slices. The highest ascorbic acid retention occurred in the samples dried at200W and0.06MPa, with a significant decrease (p<0.05) from an initial average value of2.74±0.29mg/g to1.87±0.13mg/g dry matter, representing a decrease of about32%in relation to the fresh tomato. On the other hand, the average lycopene content of the dried tomatoes significantly (p<0.05) increased from11.46mg/100g dry matter to a maximum value of25.44mg/100g dry matter after microwave-vacuum drying at700W and0.04MPa.In the third study, another hot air dryer assisted with a blower was used to dry tomato slices. In this study, the response surface method was used to investigate the results of experiment designed with the Box-Behken approach to make known the effects of air temperature, air velocity, and sample thickness, on drying time, lycopene content, ascorbic acid content, non-enzymatic browning, and colour of dried tomato slices. Three levels of temperature (40to60℃), air velocity (1.0to2.0m/s) and sample thickness (7to11mm) were used for the experiment. The desirability index technique was used to predict the ideal drying condition. At the best conditions of44℃air temperature,2.0m/s air velocity, and7.72mm sample thickness, drying time was527±76min, lycopene content was62.7±4.3mg/100g dry matter, ascorbic acid content was3.07±0.14mg/g dry matter, brightness value was62.92±2.18, ratio of redness to yellowness was,0.78±0.05, and the non-enzymatic browning index was0.55±0.06absorbance unit.In the fourth study, a catalytic far-infrared radiation (FIR) dryer was designed by us and used co dry the tomato slices. The three-level factorial response surface method was used to investigate the effects of distance between FIR emitter and the surface of tomato slices, and sample thickness on drying time, non-enzymatic browning, colour brightness, ratio of redness to yellowness, ascorbic acid content, and lycopene content of the dried tomato slices. Three levels of distance (38to50cm), sample thickness (7to11mm) were used for the experiment. The desirability index technique was used to determine the ideal drying conditions that yield minimum drying time and nonenzymatic browning and maximum brightness colour, redness to yellowness ratio, lycopene content, and ascorbic acid of drying of tomato slices. At the best conditions of40.29cm distance and9.04mm sample thickness, the drying time was108±4min, the non-enzymatic browning index was0.338±0.12Abs unit, the brightness colour was40.43±2.29, the ratio of redness to yellowness was0.92±0.13, the ascorbic acid content was3.76±0.27mg/g dry matter, and the lycopene content was72.34±19.87mg/100g dry matter. The second part of the fourth study investigated the effect of four levels of distances (i.e.38,44,50to56cm) and three-levels of sample thickness (7,9,11mm) on the drying kinetics and flavour of dried tomatoes. The drying kinetics was dependent on the distance between FIR emitters and the heat-irradiated surface, and thickness of the samples as well. The effective moisture diffusivity from the tomatoes increased and correlated to a third order polynomial relationship with decreasing sample thickness and distance between FIR emitter and surface of tomatoes. Only the falling drying rate period was observed with catalytic FIR drying of tomato slices without the constant drying rate period. Relativity’s of far-infrared energy dried samples to the fresh tomatoes revealed that,58.3%of the dried products had flavour enhancement between3.0to36.6%whereas41.7%had flavour degradation between3.1and14.1%. Among the thin-layer drying models fitted to the FIR drying data, the Midilli et al model gave the best fit. These results demonstrate that microwave-vacuum and FIR should be considered as efficient drying methods for tomato with respect to colour and ascorbic acid preservation, minimization of brown pigment formation and increment in lycopene content. Higher microwave powers (i.e.700W) should be avoided in microwave-vacuum drying of tomatoes. The study thus provides useful information for optimization of drying conditions for industrial processing of quality products.更多还原