【作者】 吴本刚；

【导师】 潘忠礼； 马海乐；

【作者基本信息】 江苏大学 ， 食品科学， 2014， 博士

【摘要】 我国是农业大国,果蔬产量巨大,居世界首位。新鲜果蔬货架期短,极易腐烂,多数在本地以低价销售。胡萝卜富含维生素和纤维素,是人类消费最多的蔬菜之一。然而,胡萝卜营养成分及外观品质的保存是目前面临的一个挑战。脱水技术是能够延长果蔬货架期,很好保留其营养成分的有效处理方法。我国利用热水烫漂、热风干燥技术生产了大量的脱水胡萝卜片用于出口和本国消费。但是此技术方法存在许多的缺点,包括能源利用效率低、处理时间长、产品品质恶化和引起一系列环境问题等。因此,该行业迫切需要一种低能耗,并保证产品质量的杀青和干燥技术的出现。本研究以新鲜胡萝卜为原料,对催化式红外干法杀青、催化式红外干燥、热风干燥、以及催化式红外干法杀青-红外热风顺序联合干燥进行了研究。建立了一种生产高品质脱水胡萝卜片的新技术。对催化式红外干法杀青同步脱水过程中,过氧化物酶钝化动力学模型、水分干燥动力学模型和颜色变化动力学模型进行了研究。首先对新鲜胡萝卜直接催化红外和热风干燥处理进行研究。主要考察催化式红外和热风干燥处理参数和物料特性对干燥过程及产品质量的影响。考察催化式红外处理高度(26、32和38cm)和胡萝卜片厚度(3、5和7mm)对干燥速率、干燥时间、产品表面颜色和复水性的影响。对胡萝卜催化式红外干燥和热风干燥进行了比较研究。分别对两种干燥方法的不同胡萝卜片厚度(3、5和7mm)和处理温度(60、70和80℃)进行了比较研究。对催化式红外干燥研究结果显示：红外处理高度越低、胡萝卜片越薄,干燥速率越大、所需干燥时间越短。在红外处理高度为32cm,胡萝卜片厚度为3和5mm,有较高的干燥速率,且得到较高质量的产品。对催化式红外和热风干燥比较研究结果显示：在水分含量达到16%-30%之前,催化式红外干燥具有较高的干燥速率,较短的干燥时间和较高的水分有效扩散系数。催化式红外干燥和热风干燥的有效扩散系数分别为2.38-10.30×10-9m2s-1和1.43-5.50×10-9m2s-1。催化式红外干燥所需总干燥时间比热风干燥缩短60%左右。胡萝卜片在60和70℃催化式红外干燥得到的产品比热风干燥具有更高的复水性。通过对两种干燥方法比较得出,催化式红外干燥在处理温度为70℃,胡萝卜片厚度为3-5mm时,有较高的干燥速率和较好的产品质量。由此得出,催化式红外干燥应用于生产干燥胡萝卜片的前期阶段,热风干燥用于干燥后期。对八种干燥模型进行拟合,得到适合催化式红外和热风干燥胡萝卜片的动力学模型。通过决定系数(R2)和均方根误差(RMSE)得出：Midilli模型(MR=aexp(-ktn)+bt)能够很好的拟合催化式红外和热风干燥两种模式的干燥曲线。将两种干燥方法的处理参数对模型系数进行拟合,分别建立催化式红外和热风干燥胡萝卜片的干燥模型方程,两模型能够很好的预测两种干燥过程中水分变化情况。计算水分有效扩散系数和活化能,通过水分扩散过程从机理上证明催化式红外干燥比热风干燥具有更高的干燥效率。对催化式红外干法杀青胡萝卜片进行研究。考察不同工艺参数对胡萝卜片品质的影响。工艺参数包括：胡萝卜片表面温度(85、90和95℃)、胡萝卜片厚度(3、5和7mm)和处理时间(0-30min)。通过对产品过氧化物酶(POD)残留量、水分减少量、干燥速率、产品表面颜色变化和维生素C保留率等指标,确定最优处理条件。结果表明,胡萝卜片表面温度越高、厚度越薄,POD酶的失活速率和水分减少越快。当POD残留量达到10%时,不同处理条件下胡萝卜片的水分减少量为40.2%-88.8%之间,颜色变化值为3.17-5.13,维生素C保留率为56.92%～77.34%。因此,红外干法杀青技术在达到杀青目的的同时,能够去除部分水分,起到干燥的作用,并且可以得到高品质的胡萝卜片。通过产品质量指标得出最优工艺条件为：胡萝卜片表面温度为90℃,胡萝卜片厚度为3-5mm。基于催化式红外干法杀青试验数据,对干法杀青过程中,POD酶钝化动力学、水分干燥动力学和颜色变化动力学模型进行研究。结果表明,两阶段模型能够很好的描述POD酶的灭活过程,并且与模型假设POD酶有两种同工酶,热稳定型同工酶(ER)和热不稳定型同工酶(EL),每一种同工酶符合一级动力学方程相吻合。通过对模型参数的分析与试验测量值的比较,对POD酶灭活机理进行了探讨。Midilli模型(MR=aexp(-ktn)+bt)能够很好的描述杀青过程中水分变化过程。将Middili模型的系数(a、k、n和b)对处理温度(T)和胡萝卜片厚度(H)进行线性回归,得到Midilli模型方程表达式如下：MR=(1.01+5.95×10-5T-7.70×10-4H)exp(-(-1.07×10-3+4.16×10-4T-3.16×10-3H)t(1.47-1.22×10-3T+1.17×10-3H))+(-2.42×10-3-9.16×10-5T+1.77×10-3H)t。此模型方程能够很好的预测胡萝卜红外干法杀青同步脱水过程中水分变化值(R2大于0.9996,RMSE值在0.0017～0.0065之间)。通过对水分有效扩散系数和活化能的计算与分析,从机理上对水分干燥过程进行了阐述。五阶多项式模型(△E=at5+bt4+ct3+dt2+et+f)能够很好的描述胡萝卜干法杀青过程中颜色变化情况。将五阶动力学模型系数(a. b、c、d、e和f)对处理温度(T)和胡萝卜厚度(H)进行线性回归,得到产品颜色变化数学模型方程表达式如下：△E=(-3.66×10-4+4.37×10-6T-1.55×10-6H)t5+(1.46×10-2-1.81×10-4T+1.45×10-4H)t4+(-0.16+2.30×10-3T-4.54×10-3H)t3+(0.14-7.27×10-3T1+5.30×10-2H)t2+(3.77-1.51×10-2T-0.18H)t+(-4.05+4.23×10-2r+4.64×10-2H)。通过此动力学模型的建立,可以为处理终点值的判定做出依据,保证产品的质量,对实际生产操作和控制有非常重要的意义。基于前文对胡萝卜片催化式红外杀青、干燥以及热风干燥结论,考察了两种杀青方法、四种干燥方法对胡萝卜片品质的影响,建立了一种催化式红外干法杀青-红外热风顺序联合干燥的新技术。杀青方法为：90℃红外干法杀青,90℃热水烫漂。干燥方法为：红外杀青后,70℃红外单一干燥、70℃热风单一干燥、红外热风顺序联合干燥；热水烫漂后,70℃热风干燥。杀青效果考察指标包括POD酶活残留量、产品表面颜色变化、维生素C保留率和水分减少量。脱水胡萝卜片质量指标包括维生素C保留率、复水性、颜色变化、收缩性和硬度等。杀青结果显示,90℃红外干法杀青15min,能够得到较合理的POD酶活残留量和水分去除量,并且产品质量较高。干燥结果显示,红外杀青-红外干燥和红外杀青-红外热风顺序联合干燥拥有更高的干燥速率和更少的干燥时间。而红外杀青-红外热风顺序干燥可得到更高品质的产品。通过对红外杀青-红外热风顺序联合干燥转换点的优化得出,胡萝卜最佳处理方式为：90℃红外干法杀青15min,然后70℃进行红外干燥至水分含量为30%-40%,最后阶段转换为70℃热风干燥至终点。以上研究结果表明：催化式红外干法杀青-红外热风顺序联合干燥是一种能够生产高品质胡萝卜片,具有高效、节能和环保等优势的新技术。更多还原

【Abstract】 China is the largest country in production fruits and vegetables. Due to the short shelf life and highly perishable, the majority of fresh fruits and vegetables were saled at low prices at local market. Carrot is one of the most demanded vegetables for human nutrition due to its high vitamin and fiber content. However, there is a challenge to retain the nutritional quality and appearance of fresh carrot. Drying is an effective method to improve the shelf life and retain the nutritional quality of carrot. China produces a large amount of dried carrot slices using hot water blanching and hot air drying for export and domestic consumption. But this method has many disadvantages, including low energy efficiency, long processing time, quality deterioration and environmental problems. The industry is very interested in new blanching and drying technologies for the application to lower production cost and improve the product quality.This study investigated the blanching and drying characteristics of carrot slices under catalytic infrared (CIR) dry-blanching, catalytic infrared drying, hot air (HA) drying and sequential infrared (IR) radiation heating and hot air (HA) drying. A POD inactivation kinetic model, a drying kinetic model and a surface color change kinetic model were successfully developed for describing the dry-blanching and dehydration process of carrot.First, it investigated the drying characteristics and models of carrot slices under catalytic infrared (CIR) heating. Carrot slices with thicknesses of3,5and7mm were dried at radiation distance of26,32and38cm. A two-factor factorial experiment design was conducted to determine the influence of drying parameters on drying rate, time required, surface color change and rehydration ratio. It was observed that the drying rate increased and the times required decreased quite significantly as radiation distance decreased and/or the slice thickness decreased. The best processing parameters for CIR drying with higher drying rates and the best dried carrot quality were radiation distance of32cm, and slice thickness of3-5mm. The obtained correlation coefficient (R2) and root mean square error (RMSE) values indicated that the Midilli model (MR=aexp(-ktn)+bt) was the best for predicting the moisture ratio change kinetics of carrot slices for CIR drying processes. Based on this conclusion, the CIR can be used to drying of carrots.It investigated the drying and quality characteristics of carrot slices under catalytic infrared (CIR) and hot air (HA) heating. Carrot slices with thicknesses of3,5and7mm were dried at temperatures of60,70and80℃with both methods. CIR had higher drying rates, shorter drying times and greater effective diffusivities than HA before the moisture contents reached the range of16%-30%on a wet basis. The total drying times required by CIR to reach the final moisture content was60%less than HA. The effective diffusivities were in the range of2.38-10.30×10-9m2s-1for CIR drying and1.43-5.50×10-9m2s-1for HA drying. Results revealed that carrot slices dried with CIR, particularly at60and70℃, had better rehydration characteristics the samples dried with HA. Thickness had a significant impact on overall color change of carrot slices. The obtained correlation coefficient (R2) and root mean square error (RMSE) values indicated that the Midilli model was the best for predicting the moisture ratio change kinetics of carrot slices for both drying processes. Based on this conclusion, it is highly recommended that the CIR is used in the early stage drying of carrots.It investigated the effects of various processing parameters on carrot slices exposed to infrared (IR) radiation heating for achieving simultaneous infrared dry-blanching and dehydration (SIRDBD). The investigated parameters were product surface temperature, slice thickness and processing time. A three-factor factorial design was conducted to determine the influence of processing parameters on moisture reduction, drying rate, residual peroxidase (POD) activities, surface color change and vitamin C retention. High surface temperature and/or thin slices had faster inactivation of enzymes and quicker moisture removal compared to the low surface temperature and/or thick slices. The process which produced1log reduction in POD activity has resulted in moisture reduction from40.2%to88.8%, overall color change (△E) from3.17to5.13and retention of vitamin C from56.92%to77.34%compared to control. It was concluded that SIRDBD could be used as an alternative to produce high quality blanched and partially dehydrated fruits and vegetables.Based on the data of infrared dry-blanching and dehydration, a POD inactivation kinetic model, a drying kinetic model and a surface color change kinetic model were developed for describing the dry-blanching and dehydration process of carrot. A biphasic model performed well for describing the POD inactivation behavior during the treatment. To apply this mathematical model, it is assumed that only two types of isozymes are present, where, one is heat resistant (ER) and the other is heat labile (EL). In addition, each fraction of the enzyme is assumed to follow first-order kinetics mathematically. Based on the model parameters, the mechanism of POD inactivation was discussed. A Midilli model (MR=aexp(-ktn)+bt) performed well for describing drying behavior during the treatment. The constants and coefficients (a, k, n and b) of the Midilli model were regressed with processing variables including slice thickness (H) and target surface temperature (T) by linear type of equation. MR=(1.01+5.95×10-5,T-7.70×10-4H)exp(-(-1.07×10-3+4.16×10-4T-3.16R10-3H)t(1.47-1.22×10-3T+117×10-3H))+(-2.42×10-3-9.16×10-5T+1.77×10-3H)t. The obtained empirical drying equation demonstrated good predictability with a strong correlation between predicted and experimental values (R2>0.9996,0.0017<RMSE<0.0065). The effective moisture diffusivity and the activation energy represent mass transport of moisture. A quantic model (△E=at5+bt4+ct3+dt2+et+f) fit well for describing the surface color change during the process. The constants and coefficients (a, b, c, d, e and f) of the Quintic model were regressed with processing variables including slice thickness (H) and target surface temperature (7) by linear type of equation.△E=(-3.66×10-4+4.37×10-6T-1.55×10-6H)t5+(1.46×10-2-1.81×10-4T+1.45×10-4H)t4+(-0.16+2.30×10-3T-4.54×10-3H)t3+(0.14-7.27×10-3T1+5.30×10-2H)t2+(3.77-1.51×10-2T-0.18H)t+(-4.05+4.23×10-2r+4.64×10-2H).The blanching and drying characteristics of carrot slices processed with a sequential infrared (IR) radiation heating and hot air (HA) drying were investigated. Carrot slices with5mm thickness were blanched using IR heating and water at90℃. The characteristics of blanched carrot slices, including peroxidase (POD) activities, vitamin C, color and moisture reduction, were evaluated. The IR blanched carrots were dried by separated infrared drying (IRB-IRD), separated hot air drying (IRB-HAD) and sequential infrared and hot air drying (IRB-SIRHAD). Water blanched carrots were dried by hot air (WB-HAD) as control. The drying temperatures were at70℃for both IR. and HA drying. The quality characteristics of dried carrot slices, including vitamin C, rehydration, color, shrinkage and hardness, were evaluated. The blanching results showed that the IR. dry-blanching for15min resulted in a reasonably residual POD activities and moisture reduction, the lower surface color change and higher retention of vitamin C. The drying results showed that IRB-IRD and IRB-SIRHAD have higher drying rate and less drying time. The quality of dried carrots results showed that IRB-SIRHAD can get high-quality carrots. It has been concluded that the best processing method was carrot slices blanched using IR at90℃for15min, then dried using IR drying at70℃until the moisture content (MC) reached30%-40%, and then followed by HA drying at70℃in the latter stage.更多还原