Transfer of heat and moisture during oven baking of potatoes

Potatoes were baked for up to 60 min in a conventional fan‐assisted oven. Temperature profiles within the potato tubers were determined both by direct measurement and by following the inward progress of starch gelatinisation, which occurs at 65 °C. Temperature profiles with time were S‐shaped and about 30 min was needed for the centre to reach 100 °C. From the nature of the temperature profiles, long potato tubers will cook faster than round tubers of the same weight, and a varietal ‘shape factor’ was defined to quantify this effect. The slow temperature rise, compared to other forms of cooking, was due to evaporative cooling. Moisture loss was linear with time after an initial lag and reached 15–20% of the mass of the potato after 1 h of cooking. Approximately half of the moisture was lost from the outermost layer of the potato under the periderm, leaving behind a dried layer of flesh that appeared to restrict water transport and, unlike any other part of the potato, could exceed 100 °C. This has consequences for the thermal development of flavour compounds as well as for perceived texture. © 2002 Society of Chemical Industry     

Transfer of heat and moisture during microwave baking of potatoes

Microwave baking of potatoes comprised two phases. In the first phase the internal temperature of the potatoes rose to approximately 100 °C with little loss of water vapour. The uniformity of internal heating during this phase was assessed by identifying gelatinised starch. Starch gelatinisation began near the outer surface after 1.5 min of cooking and was complete by 2.5 min. During the second cooking phase the thermal energy absorbed was used to evaporate water. When immersion in boiling water was substituted for this second phase of microwave cooking, it took significantly longer for the internal texture to soften adequately for the potatoes to be considered cooked. This suggests that microwave cooking influences texture independently of the thermal profile of the cooking process. Damage by escaping steam is suggested as a mechanism. © 2002 Society of Chemical Industry     

果胶协同干热变性对甘薯淀粉分子结构的影响

本文利用扫描电镜、紫外光谱、粒度分析仪等分析手段研究果胶浓度、干热温度和干热时间对甘薯淀粉分子结构的影响。结果表明:经过不同时间干热处理,淀粉与果胶共混的颗粒随着时间的延长而形成小团块且逐渐增多、变大;甘薯淀粉与果胶共混干热后,添加不同浓度果胶的淀粉分子链间的聚合度减小(由未添加果胶的620~626 nm降低到浓度为0.05%的603~608 nm),随着温度的增加和时间的延长可使淀粉分子间的聚合度增大,紫外光谱的最大吸收波长均发生蓝移现象;淀粉颗粒中位径、大颗粒体积分数随着果胶浓度、温度、时间的增加而增大,在干热时间为3 h时淀粉颗粒的中位径最大(为15.47μm),大颗粒体积分数最大可达到6.27%,比在1 h时的大颗粒体积分数高出1.81%;淀粉与果胶共混物的直链淀粉的溶出量随着果胶浓度(0.01%~0.04%)、干热温度和干热时间(1~4 h)的增加而得到更好的抑制。果胶协同干热处理对开发新型甘薯变性淀粉具有重要意义。      

DPPH法研究不同品种甘薯抗性淀粉抗氧化性

该实验采取DPPH方法研究不同品种甘薯抗性淀粉在浓度、温度、离子等因素影响下抗氧化性。结果表明:不同品种甘薯抗性淀粉抗氧化性具有明显差别,在最佳浓度条件下,苏薯八号、日本黄薯、京薯六号、香蕉薯、金海二号、水果薯、美国黑薯、德国黑薯、花心薯抗性淀粉对DPPH自由基抑制率分别为:84.0%、91.4%、83.7%、78.1%、78.3%、78.3%、83.7%、98.2%、68.2%;在最佳温度条件下,苏薯八号、日本黄薯、京薯六号、香蕉薯、金海二号、水果薯、美国黑薯、德国黑薯、花心薯抗性淀粉对DPPH自由基抑制率分别为:62.3%、63.9%、58.8%、62.6%、67.7%、69.0%、79.1%、75.2%、60.6%;与Vc抗氧化性比较,德国黑薯抗氧化性最强,为Vc1.03倍。     

精制甘薯淀粉的生产技术

采用去皮工艺,控制沉降的温度和pH值,在破碎的同时加入0.005％抗坏血酸和0.005％亚酸酸钠,生产出精制甘薯淀粉,其白度达到88.80。     

甘薯果胶纯化工艺研究

采用活性炭法、硅藻土法、超滤膜等对甘薯果胶进行脱色处理,并采用蛋白酶水解除去提取液中蛋白质。结果表明,活性炭用量2.0%,温度50℃,脱色时间为40min效果较好;超滤膜法脱色得率为85%~92%,工艺简便,成本较低。脱色同时还可以去除其他小分子物质,并且适合工业化连续生产。      

酶法水解甘薯提取三种紫甘薯色素

甘薯俗称地瓜,是我国四大主要粮食作物之一,具有丰富营养价值,是我国人民喜爱的粮、菜兼用,物美价廉大众食品。自19世纪中期第一个人工合成有机色素问世以来,合成色素被大量应用于食品工业中,此后,由于合成色素安全性受到质疑,并确认部分合成色素具有潜在致畸、致癌及其它毒副作用,人们便把注意力转向天然色素。甘薯经冷冻、打浆、加酶、离心、浓缩、酒精沉淀等过程可得到甘薯色素,最适酶解条件为:α-淀粉酶添加量200U/mL,温度40℃,pH5,酶解时间20min;果胶酶和纤维素酶添加会破坏紫甘薯色素,碱性条件下紫甘薯色素会分解;酶法水解三种紫甘薯色素提取率分别为:美国黑薯1.25%,德国黑薯0.82%,花心薯1.09%。     

Methods for the preparation of cell walls from potatoes

A group of new methods is described for preparing cell walls from potatoes and processed potato products. Starting from raw domestic potatoes, starch is degraded enzymatically after a very brief 100 °C gelatinisation step conducted after homogenisation to minimise the time required for heat transfer. Protein is removed by detergent and phenol extraction. This procedure (method 1) gave cell wall preparations containing <5% starch, with minimal degradation of wall polysaccharides. It did not, however, remove starch efficiently from industrial potatoes in which the starch content is much higher. A different procedure, method 2, was used in this case. In method 2 a 20 min starch gelatinisation step was used but the temperature was restricted to 70 °C and the pH to 4.0, with the aim of protecting pectins from depolymerisation. Method 2 and method 1A, which is a hybrid procedure involving the starch gelatinisation step from method 2 and other steps from method 1, gave low‐starch cell walls from industrial as well as domestic potatoes. These methods are suitable for a range of potato types and potato products and are either more efficient or more convenient than previous procedures for cell wall isolation. © 2002 Society of Chemical Industry     

干制过程中甘薯粉条老化规律研究

目的 保持干燥温度恒定为60℃,探究干燥过程粉条中水分对淀粉老化的影响规律。方法 将新鲜制备的甘薯粉条在相同温度不同相对湿度条件下干燥至相同水分含量,以及在相同干燥条件下干燥至相同水分含量后恒定在该水分含量及温度条件下保持不同时间,对上述样品的结晶特性、短程有序度、热特性等进行测定和分析,研究水分变化对甘薯粉条老化特性的影响。结果 干燥温度恒定,淀粉老化受热风相对湿度影响,这主要在于影响了粉条中水分蒸发速度;随着粉条水分含量减小,粉条中淀粉相对结晶度及短程有序度增加。当保持干燥条件不变时,粉条具有较高的老化速度的水分含量区间在25%～40%,对应的水分活度值为0.7～0.9。结论 粉条干燥过程中淀粉老化具有水分依赖性,通过控制水分含量可对淀粉老化进行调控。     

Effects of low‐temperature blanching on tissue firmness and cell wall strengthening during sweet potato flour processing

Free starch rate has been one of the most important criterions to evaluate the quality of sweet potato flour. Low‐temperature blanching (LTB) of sweet potatoes before steam cooking has shown significant increase in tissue firmness and cell wall strengthening. This research indicated that pectin methylesterase (PME) activity decreased by 87.8% after 30 min of blanching in water at 60 °C, while polygalacturonase (PG) and β‐amylase activity decreased 69.4% and 7.44%, respectively, under the same condition. Both PME and β‐amylase played important roles in tissue firmness. Further studies of tissue firmness and methyl esterification showed that the combination of LTB and Ca²⁺ could increase the activity of PME and significantly enhance the pectin gel hardness to strengthen the cell walls and decrease free starch rate from 12.83% to 7.28%.     

甘薯淀粉性质的研究

研究了甘薯淀粉的理化性质,结果表明:其颗粒粒径的平均值为5~31mm,结晶结构属C型,直链淀粉含量18.5%,糊化温度为60.8~78.5℃。甘薯淀粉的透明度为42%,凝胶强度为98g。     

酶法水解不同品种甘薯制备甘薯多糖

甘薯经酶解、高温糊化、离心分离、酒精沉淀等工艺制备甘薯多糖。研究结果表明,经酶解后甘薯液在30℃、甘薯液酒精度达81.2度时沉淀,甘薯多糖沉淀最多。在此条件下,不同品种甘薯多糖制备率分别为:苏薯8号0.87%;日本黄薯0.73%;京薯6号1.88%;香蕉薯1.77%;金海2号1.58%;水果薯2.57%;美国黑薯2.41%;德国黑薯3.59%;花心薯1.24%。其中德国黑薯甘薯多糖制备率最高,是宜于制备甘薯多糖品种。     

食用交联甘薯淀粉制备与性质研究

以甘薯淀粉为原料,三偏磷酸钠为交联剂,对甘薯淀粉进行变性,制备食品用交联甘薯淀粉。以交联淀粉峰值粘度和结合磷含量为指标,以三偏磷酸钠用量、反应pH、温度、时间和硫酸钠用量为因素研究交联反应最优工艺;并研究系列食用交联甘薯淀粉粘度、溶解度、膨胀度、透明度、凝沉性、冻融稳定性等理化性质及形态学和结构性质,为其在食品中应用提供理论依据。     

熟化甘薯热风干燥特性及数学模型研究

利用热风干燥试验台对熟化甘薯的热风干燥特性进行研究,探讨不同干燥温度、热风风速、铺料密度对干燥速率的影响,其影响因素大小依序为：干燥温度＞干燥风速＞铺料密度.利用3种不同干燥速率模型对实验数据进行拟合,发现甘薯热风干燥符合Page方程,即,模型拟合F值为1 102.35,呈极显著.     

三种紫甘薯色素性质及稳定性研究

紫甘薯美国黑薯、花心薯和德国黑薯水溶性色素吸收最大吸收波长分别为538.5nm、525nm和532nm。三种紫甘薯色素在酸性条件下呈深红色,性质稳定,通过对三种紫甘薯色素稳定性研究发现,pH对色素稳定性有很大影响,在pH为3时温度和光照对色素基本不产生影响,三种紫甘薯色素有良好耐热性和耐光性。     

甘薯交联抗性淀粉热力学性质与消化性研究

根据膨胀度、糊化度及差示扫描量热仪(DSC)测得热力学参数,综合分析甘薯交联抗性淀粉和原淀粉热力学性质,并采用Jenkins提出In–vitro模型测定淀粉体外消化性。结果表明:在同一温度下,甘薯交联抗性淀粉膨胀度和糊化度均较原淀粉低,且交联剂用量越高,淀粉膨胀度和糊化度越小;DSC测试结果显示,甘薯交联抗性淀粉相转变温度To、Tp、Tc随交联剂用量增加而升高,Tc–To和△H均比原淀粉低。In–vitro消化模拟实验表明,甘薯交联抗性淀粉消化性比原淀粉低,并随交联剂含量增加,消化产物量减少,消化速度降低。     

红薯淀粉水凝胶制备及吸水特性研究

以红薯淀粉为原料,以4-二甲基氨基吡啶为催化剂,于水相中经过醋酸酐酯化处理制备红薯淀粉水凝胶。确定了制备红薯淀粉水凝胶的最佳工艺条件,红外光谱确认在淀粉中引入了羧甲基。红薯淀粉水凝胶吸水性增强,黏度增大,糊透明度得到改善,说明红薯淀粉水凝胶具有优良吸水特性。     

提取工艺对甘薯果胶物化特性影响的研究

分别以盐酸和磷酸氢二钠为提取剂从甘薯渣中提取果胶,经乙醇沉淀和冷冻干燥得到甘薯果胶。研究酸法、盐法2种工艺对甘薯果胶物化特性的影响。结果表明:盐提果胶纯度为(81.5±9.3)%,溶解度(99.8±1.6)%,黏度为(22±4.6)%,酯化度为(58.2±3.5)%,胶凝度为(146.1±3.5)%。盐提果胶物化特性优于酸提果胶,与苹果果胶相似,盐提果胶的纯度高,水溶性较好,适合食品工业应用。研究对甘薯果胶的工业化生产具有理论及实践意义。     

甘薯渣去除淀粉工艺研究

甘薯渣中淀粉的存在严重影响了提取果胶的纯度,因此,开发和利用薯渣中的果胶资源,必须除去甘薯渣中的淀粉。甘薯渣中淀粉去除的最佳工艺为固液比为1∶15,甘薯渣醪液pH6.0,经高温α-淀粉酶在90℃酶解30min;然后调整pH至4.5,依次加入糖化酶、普鲁兰酶,在60℃保温酶解180min,淀粉转化率较高,达到94.22%±3.43%。根据电镜图片可知,去除淀粉效果较好。因此,甘薯渣可以采用高温α-淀粉酶、糖化酶和普鲁兰酶复合酶制剂去除淀粉。研究对甘薯果胶开发中去除甘薯渣中淀粉的工艺具有理论及实践意义。      

糖醇对甘薯淀粉理化性质的影响

以甘薯淀粉为原料,研究不同添加量的麦芽糖醇、赤藓糖醇和木糖醇对甘薯淀粉溶胀度和可溶指数、糊化特性及淀粉凝胶质构特性的影响。结果表明:3种糖醇均明显降低了甘薯淀粉的溶胀度和溶解性,且随着添加量的增多,降低越明显;糊化温度随添加量的增多显著性升高;当麦芽糖醇和木糖醇的添加量与淀粉比值均为1∶1时,峰值黏度显著升高至最大值,添加量继续增多,淀粉糊的峰值黏度显著性降低;糖醇的添加量与淀粉比值小于4∶1时,随着木糖醇添加量增多,回生值升高,而赤藓糖醇的添加量对回生值没有显著性影响;随着糖醇添加量的增多,淀粉凝胶硬度增加越明显,麦芽糖醇和木糖醇对于凝胶弹性、内聚性和恢复性降低越明显。