【作者】 陈丰；

【导师】 郑宝东；

【作者基本信息】 福建农林大学 ， 农产品加工及贮藏工程， 2010， 硕士

【摘要】 莲子干制工艺是莲子加工产业最重要的研究方向。本文将微波真空干燥技术应用于莲子干制加工,较为系统地研究了莲子微波真空干燥特性、品质学特性,并在此基础上通过二次正交旋转组合设计试验,结合响应面法确定莲子微波真空干燥工艺的最优参数组合。通过试验研究结果如下:1.莲子微波真空干燥特性的研究莲子微波真空干燥原料选择条件:二、三级成熟度鲜莲(果皮呈浅褐色或褐黄色),不需进行异Vc钠护色处理的鲜莲。将微波真空干燥应用于莲子干燥,能显著提高干燥速度,降低干燥温度,改善产品品质。微波功率、微波间歇比对莲子微波真空干燥影响较大,分别表现为:微波功率越高,微波间歇比越大,干燥速度越大,干燥用时越短。真空度对莲子微波真空干燥影响不显著,但仍然表现为真空度越高,干燥用时越短。整个干燥过程分为加速期和降速期两个阶段,无明显恒速期。加速期短,微波功率越高、真空度越大、微波间歇比越大降速期越短。干燥过程中,莲子的中心温度和表面温度基本相同,干燥温度远低于单纯微波干燥。2.莲子微波真空干燥品质学的研究通过观察微波真空干制莲子切片电镜扫描图可知,莲子内部细胞呈现有规则的层叠排列结构,细胞间有大量大小不一的孔隙;部分淀粉糊化,仍有部分淀粉颗粒完整存在;在其内部形成独有旋流冲刷“溶洞”现象,便于干燥时水分排出,也有助于干莲复水后保持原有形态。对干燥过程中PPO活性的研究可知,干燥至2min时,PPO活性基本丧失,微波真空干燥能在短时间内控制酶促褐变对外观品质的影响。通过微波真空干燥对莲子收缩率、复水率影响的研究得知,增大微波功率、真空度、间歇比,收缩率降低,复水率增加,在-0.08MPa时复水能力最强。但微波功率高达4kW或真空度为-0.09 MPa时,则反之。通过微波真空干燥对莲子色泽影响的研究得知,微波功率、真空度、间歇比越大,莲子的色泽白度值越大。当微波功率为3 kW时,WH相当接近于鲜莲的白度值,但当功率高达4 kW时,WH反而变小;当真空度到达-0.09 MPa时,WH基本接近于鲜莲的白度。3.莲子微波真空干燥工艺优化的研究通过二次正交旋转组合设计试验方案,分别建立微波功率X1、真空度X2、间歇比X3和干燥时间Y1、收缩率Y2、复水率Y3、色泽白度Y4之间的动态数学模型为: Y1=14.08696-3.687769X1-2.020287X2-2.316503X3-1.6875X1X2+1.1875X1X3 Y2= 39.08823-2.97355X2-1.98288X3+4.19479X12 +2.15833X22 +1.65098X32 Y3=154.3661+2.214661X1-0.604753X2+1.780317X3-1.577267X12-1.665654X22- 0.4X2X3-1.488879X32 Y4= 67.82598+1.666092X2-3.704279X22-2.735536X32运用响应面法对工艺参数进行优化,并综合考虑各指标重要性及生产成本等因素,得到莲子微波真空干燥工艺的最优参数组合为:微波功率3 kW,真空度-0.086 MPa,间歇比3.5(94s-on/26-off)。更多还原

【Abstract】 Drying technology is played the most important roles in lotus-seed processing industry. The microwave-vacuum drying (MVD) technology was applied to lotus-seed drying; the drying and quality characteristics of lotus-seed were systematically studied in this paper. On the basis, quadratic rotation-orthogonal combination design was used for experimental design, combined with response surface methodology to determine the optimal procedure parameters of lotus-seed drying. The results as following:1. Studied on the drying characteristics of MVD lotus-seedConditions of raw material: Fresh lotus-seed, at second or third stage maturity, with no color protection.The MVD was resulted in substantial saving of processing time, lower of drying temperature, and improved quality of lotus-seed. The effects of microwave power, on/off ratio were significant: the higher the power and the on/off ratio were, the bigger the drying rate was, the shorter the drying time was; The vacuum was higher, then the drying time was shorter, but the effect was inconspicuousness.Two drying periods, namely accelerated drying and decelerated drying were found in MVD lotus-seed, with no significant constant drying period. The accelerated drying period was short, and when the microwave power, vacuum and on/off ratio were higher, the decelerated drying period was shorter. In MVD lotus-seed, the central and surface temperatures were basically similar, and far lower than microwave drying simply.2. Studied on the quality of MVD lotus-seedThe results of electrical microscope slice showed that the cells were single regularly stacked, and a mass of pores were existed in intercellular. The starch was partly gelatinized, and still some starch granules integrated existed. The unique phenomenon“cave”was formed, easy for water migration and good quality keeping when rehydration.The results of PPO activity research showed that PPO activity was inhibited within 2 min. That means the effect of enzymatic browning could be effectively controlled by MVD in a short time.The results of shrinkage and rehydration research showed that lower shrinkage and higher rehydration could be achieved by increasing microwave power, vacuum pressure and on/off ratio. But when the power reached 4 kW, the shrinkage rage was no longer lower and the rage got lower. While vacuum pressure was -0.08MPa, the rehydration was the biggest, but when it reached -0.09 MPa, the rehydration rage was no longer bigger.The results of color research showed that higher WH could be achieved by increasing microwave power, vacuum pressure and on/off ratio. When microwave power was at 3 kW, WH was quite close to the fresh, but it reached 4 kW, WH got lower. When the vacuum pressure was -0.09 MPa, WH was quite similar to the fresh.3. Studied on the process optimization of MVD lotus-seedThe quadratic rotation-orthogonal combination design was used for experimental design, and the dynamic mathematical model was established as follows:(microwave powerX1, vacuum pressureX2, on/off ratioX3, drying time Y1, shrinkage Y2, rehydration Y3, whiteness Y4) Y1=14.08696-3.687769X1-2.020287X2-2.316503X3-1.6875X1X2+1.1875X1X3 Y2= 39.08823-2.97355X2-1.98288X3+4.19479X12 +2.15833X22 +1.65098X32 Y3=154.3661+2.214661X1-0.604753X2+1.780317X3-1.577267X12-1.665654X22- 0.4X2X3-1.488879X32 Y4= 67.82598+1.666092X2-3.704279X22-2.735536X32The response surface methodology and weight value analysis was used to determine the optimal procedure parameters of MVD lotus-seed. When comprehensively considering the costs and the quality of MVD lotus-seed, the optimal parameters of microwave power, vacuum pressure and on/off ratio should be kept at 3 kW, -0.086 MPa, 3.5 (94s-on/26-off).更多还原