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     

Steam blanching effect on polyphenoloxidase,peroxidase and colour of mango (Mangifera indica L.) slices

The heat stability of peroxidase (POD) and polyphenoloxidase (PPO) was investigated in mango (Mangifera indica L.) slices, and the relative colour was studied after different steam blanching times. There was complete inactivation after 5 min for POD and 7 min for PPO. Steam blanching of 3 min gave residual activity of 2.85% and 8.33% for PPO and POD, respectively, and when compared with samples blanched for 5 min had no effect on colour over 20 days of storage. Correlation was found between activities of PPO, POD and colour change over 20 days. After 7 min steam blanching the browning index was stable but less than at 3 and 5 min because non-enzymic browning had occurred. This research suggests that yellowness (b) and lightness (L) values contribute positively to the browning index (BI), compared to redness (a).     

漂烫对真空油炸银杏果品质的影响

以大佛指银杏果为原料,研究漂烫温度和时间对银杏果POD酶失活时间、水分含量、淀粉糊化度,以及对真空油炸银杏果微观结构、质构、脂肪含量、色泽和感官品质的影响。结果表明:随着漂烫温度和时间的增大,POD酶失活时间逐渐缩短,而银杏果中淀粉糊化度和水分含量逐渐升高;漂烫时间越长真空油炸银杏果的脆性和色泽越好,但真空油炸银杏果的脂肪含量越高;100℃漂烫5min时银杏果真空油炸后能形成多孔状,且感官评分最高。综合考虑,采用100℃条件下对银杏果进行漂烫5min处理。     

基于BP神经网络的葡萄气体射流冲击干燥含水率预测

为实现葡萄气体射流冲击干燥过程中含水率的预测,本文探究了不同烫漂前处理时间(30、60、90和120 s)和干燥温度(55、60、65和70℃)对葡萄干燥时间和干燥速率的影响,建立了输入层为烫漂时间、干燥温度和干燥时间,隐藏层节点数为7,输出层为葡萄含水率,结构为"3-7-1"的BP神经网络模型。结果表明:烫漂预处理时间和干燥温度均对葡萄干燥速率有影响,增加烫漂时间和提高干燥温度能够有效的缩短葡萄干燥时间,提高干燥效率。采用Levenberg-Marquardt(LM)算法为训练函数,选择tansig-purelin为网络传递函数,经过有限次训练得到的BP神经网络模型,其预测值与实测值之间的决定系数R~2为0.9915,均方根误差RMSE为0.03376,预测快速且准确,为葡萄在干燥过程中的含水率在线预测提供理论依据和技术支持。     

蕨菜护色工艺条件优化

以凉山州新鲜蕨菜为原料,研究烫漂、护色工艺条件对蕨菜质量的影响。试验结果表明,最佳烫漂工艺条件是温度90℃,时间4 min,NaCl浓度0.5%;最佳护色工艺条件研究结果是:pH 4,Cu(COOH)2浓度300 mg/kg,时间25 min。     

脱水甘蓝护色工艺的优化

甘蓝在干燥过程中叶绿素含量降低,产品感官品质下降。采用正交试验方法优化脱水甘蓝护色工艺,以期提高脱水甘蓝的感官品质。正交试验以叶绿素残留率为指标,优化最佳护色工艺。结果显示,采用浓度为1%的Na2CO3溶液浸泡15min,100℃热烫1.5min,脱水甘蓝叶绿素保存率为52.3%,此时过氧化物酶相对酶活小于5%,可以有效保持甘蓝的原有颜色。     

切分及烹调对叶类蔬菜品质的影响

以芥菜、菜心、生菜等为主要原材料,研究切分方式与烹调方式对叶类蔬菜中维生素C、叶绿素和亚硝酸盐含量的影响,以明确加工条件对叶类蔬菜品质的影响。结果表明,切分后烫漂,叶类蔬菜中维生素C较新鲜蔬菜下降超过40%,亚硝酸盐含量下降超过45%,叶绿素下降不明显,且随细胞液的流失有明显上升趋势;油炒、烫漂和汽蒸三种烹饪方式对叶类蔬菜中叶绿素、维生素C、亚硝酸盐影响的研究表明,汽蒸加工可以保留叶类蔬菜中60~67%的维生素C,可降低40~70%的亚硝酸盐含量,而对叶绿素含量影响不大,是一种较理想的营养烹饪方式。本论文的研究成果具备良好的理论与实践意义,对减少叶类蔬菜烹饪加工过程中营养成分的损失、有害物质的产生、提高叶类蔬菜烹饪品质起到良好的方法借鉴。     

蒸汽烫漂结合真空微波干燥工艺对龙牙百合粉品质的影响

为拓展药食同源植物资源龙牙百合的应用,研究高品质龙牙百合粉的制备方法,本实验拟考察不同的护色工艺和干燥工艺组合对龙牙百合粉产品质量的影响。以新鲜龙牙百合为原料,分别考察护色工艺（蒸汽烫漂和热水烫漂）和干燥工艺（常压热风干燥和真空微波干燥）的不同组合对龙牙百合粉感官品质、化学质量指标及抗氧化能力等功能品质的影响。结果表明,与传统工艺（热水烫漂结合常压热风干燥）比较,蒸汽烫漂结合真空微波干燥的工艺组合使龙牙百合粉产品总多糖、总黄酮和总多酚含量分别提高了24%、19%和37%。采用真空微波干燥制备的百合粉其体外抗氧化能力均强于热风干燥产品,其中蒸汽烫漂结合真空微波干燥工艺组合制备的百合粉体外抗氧化能力最强,其总还原能力、DPPH·和·OH清除能力的IC₅₀分别为17.24、12.00和10.21 mg/mL,显著低于传统工艺产品的IC₅₀值42.38、18.77和16.56 mg/mL。蒸汽烫漂结合真空微波干燥工艺组合制备的龙牙百合粉产品综合品质明显优于其他考察的工艺组合,可作为高品质百合粉的工艺选项之一。