淀粉糊化温度的测定

1、Methods for measuring temperature of gelatinization and examples淀粉糊化温度的测定方法及实例 Methods for measuring temperature of gelatinization and examples糊化测定方法实例定义影响因素过程DSC热分析法电导率法Ohmic heating 布拉班德粘度仪(BV)快速粘度分析仪（RVA）莲藕淀粉糊化温度的测定电导率法淀粉糊化温度测定及其影响因素的研究Determination of starch gelatinization temperature by ohmic h

2、eating大米糊化特性曲线探讨1.用RVA仪分析玉米淀粉的糊化特性定义：淀粉在常温下不溶于水，但当水温至53以上时，淀粉的物理性能发生明显变化。淀粉在高温下溶胀、分裂形成均匀糊状溶液的特性，称为淀粉的糊化 。淀粉糊化过程是淀粉颗粒结晶区熔化，分子水解，颗粒不可逆润胀过程，糊化后淀粉水体系直接表现为粘度增加。根据淀粉颗粒吸水膨胀、粘度增大、偏光特性改变，其糊化过程可分为淀粉乳中水分子被淀粉粒无定形区极性基团吸附并加热到初始糊化前的可逆润胀阶段，及继续加热达到糊化起始温度后的不可逆润胀阶段。淀粉颗粒体积膨胀到一定程度出现破裂，淀粉分子最后稳定形成网状含水胶体。可逆吸水阶段不可逆吸水阶段颗粒解体阶

3、段影响因素： A 淀粉的种类和颗粒大小； B 食品中的含水量； C 添加物：高浓度糖降低淀粉的糊化，脂类物质能与淀粉形成复合物降低糊化程度，提高糊化温度，食盐有时会使糊化温度提高，有时会使糊化温度降低； D 酸度：在 pH 4-7 的范围内酸度对糊化的影响不明显，当 pH 大于10.0，降低酸度会加速糊化 糊化糊化温度测定方法 DSC法法 电导率法电导率法 欧姆加热法欧姆加热法 BV法法 RVA法法莲藕淀粉糊化温度的测定大米糊化特性曲线探讨利用欧姆加热测定淀粉糊化温度电导率法淀粉糊化温度测定及其影响因素的研究用RVA仪分析玉米淀粉的糊化特性 DSC热分析法莲藕淀粉制备流程 新鲜莲藕去皮切块 用

4、 1%Nacl 和 0.2NaHSO3 的水溶液浸泡 30min 匀浆反复几次加水过滤,滤液静置后倾去上清液,取沉淀 粉碎机粉碎后经胶体磨打浆 粗淀粉 反复水洗后 40烘干 用石油醚在索氏抽提器中抽提脱脂，用 1%Nacl 洗三次，然后用 0.01mol/l NaOH 洗一次脱蛋白，蒸馏水洗三次后 40烘干 纯莲藕淀粉 3 试验方法 3. 1 偏光十字消失法 取淀粉试样0. 5g, 加50mL蒸馏水, 混匀, 在一定温度下保温5min, 取一滴淀粉浆(或糊)于载玻片上,在偏光显微镜下分别记录视野内淀粉粒偏光十字2% 消失和98% 消失时的温度并测定不同温度下的粒径, 重复测定三次, 取平均值。

5、 淀 粉 试 样0.5g+50ml蒸 馏 水 取 一 滴 淀 粉 浆 于 载 玻 片 上 混 匀 ， 在 一 定 温 度 下 保 存在 偏 光 显 微 镜 下 分 别 记 录 视 野 内 淀 粉 粒 偏 光 十 字2% 消 失 和98% 消 失 时 的 温 度 并 测 定 不 同 温 度 下的 粒 径 重 复 测 定 三 次 , 取 平 均 值 从图中可以清楚的看到原始淀粉和淀粉在糊化过程中淀粉颗粒的变化。偏光十字法测定莲藕淀粉的糊化温度为63. 8 71. 8。 3. 2 动态流变仪法称取莲藕淀粉4. 8g, 加入80mL蒸馏水, 搅拌均匀后上样进行流变特性测试。将称取好的淀粉乳放置在载物台

6、上, 启动仪器使平板进入设置间隙, 刮去平板外多余淀粉乳, 加上盖板, 并加上液体石蜡防止水分蒸发。采用动态振荡程序, 设置三个温度扫描步骤: 从20e 升温到100 使淀粉体系糊化, 然后从100 降温至20 使凝胶形成, 最后再从20e 升温到100 考察凝胶的破坏情况, 升降温速率均为5 /min。淀粉试样 4.5g+80ml 蒸馏水 淀粉乳 搅拌混匀，进行流变特性测试 放置在载物台上, 启动仪器使平板进入设置间隙, 刮去平板外多余淀粉乳, 加上盖板, 并加上液体石蜡防止水分蒸发 采用动态振荡程序, 设置三个温度扫描步骤: 从 20e 升温到 100 使淀粉体系糊化, 然后从 100 降

7、温至 20 使凝胶形成, 最后再从 20e 升温到 100 考察凝胶的破坏情况, 升降温速率均为 5 /min 模具选用直径为30mm 的平板, 狭缝间隙设置为1. 0mm, 形变为2%, 角频率为5 rad / s。它通过测定凝胶体的耗能模量G”和储能模量G以及二者的比值tg来反应凝胶体的弹性和黏性的变化。储能模量G对应着凝胶体的刚度和弹性,耗能模量G”对应凝胶体的黏度和流动, 二者比值则tg反应凝胶体中弹性组分和黏性组分的比值。图2是在莲藕淀粉升温糊化、降温冷却和重新升温时, 体系的耗能模量G”变化图。结论：结论：从图2中可以看出在升温糊化阶段, 随着温度的升高, 到达一定温度时, 淀粉体

8、系耗模量显著升高, 到达一定高度后又开始快速下降。这可从淀粉的糊化过程来合理解释: 随着温度的升高, 淀粉粒吸水膨胀, 到达糊化温度时, 淀粉粒大量吸水膨胀, 直链分子从淀粉粒中渗析出来形成凝胶包裹淀粉粒。淀粉体系黏度和流动性显著增加, G”值升高; 随着温度的进一步升高, 膨胀的淀粉粒间的碰撞加剧, 部分淀粉粒破裂, 同时直链的链的迁移能力增强, 凝胶网络中的部分氢键断裂。 动态流变仪法测得糊化温度为60. 1 66. 2 。这与偏光十字消失法测得的糊化温度相比范围偏小。耗能模量的变化在降温和再升温过程中基本可逆, 说明莲藕淀粉相当稳定, 短时间内不会出现回生老化现象。 3.3 DSC法方法

9、是制备6% ( W /V)淀粉乳, 上样测试。将样品放在DSC的加热器上, 同时用一空铝盒作对照, 从室温附近的温度开始, 加热速度10K /MIN, 测试范围30 100 。结果以吸热曲线表示, 曲线上的吸热峰是计算糊化温度和反应热的依据。从峰的形成到结束可以得到起始温度、峰值温度和结束温度, 峰的面积则表示糊化所需的热焓( J/G) 。备注：先测出淀粉的水份。如W，称取质量为6/(1-w)克的淀粉样品，加水为100-6/(1-w)克，搅拌均匀就是所求的淀粉乳 3.3 DSC法淀粉糊化时伴随的能量变化在DSC 分析图谱上表现为吸热峰。ZOBEL认为, 淀粉在糊化过程中同时伴有玻璃化转变和晶体

10、的崩解过程。6% 莲藕淀粉乳的DSC 图谱见图3, 热特性参数见表1。在过量水分下加热淀粉乳, 所有淀粉颗粒均能吸水膨胀, 因此DSC 图谱只出现一个峰, 即淀粉的糊化峰。淀粉的糊化温度为63. 5 74. 7, 这与偏光十字消失法测得的糊化温度相比大一些, 其原因是一小部分淀粉颗粒发生变化时, 虽没有引起淀粉出现糊化, 却有吸热现象发生。电导率法1 材料与方法1.1 实验材料和设备实验所用淀粉(质量等级: 一级)均为市售。在130 烘箱中加热淀粉4 H 测得水分含量。实验用水为蒸馏水。玉米淀粉: GB/8885, 水分含量11.77%, 北京京南食品有限公司; NACL、KCL: 分析纯,

11、北京化学试剂厂。Q10 型差示扫描量热分析仪: TA INSTRUMENTS;SR8001 型电子天平A: 精度0.001 G, METERTOLEDO; FA1004 型电子天平B: 精度0.0001 G, 上海天平仪器厂; HP34970A 数据采集器: 接入三个通道, 美国惠普公司; S21- I 磁力搅拌器; TDGC- 5 变压器: 220 V/110、V20 A/8 A, 北京华兴电源设备厂; 圆筒型加热槽: =45 MM 长L=90 MM V=143.07ML, 自制; 方型加热槽: 宽B=105 MM 长L=100 MM高HMAX=100 MM, 自制; CS020G 电流传感

12、器: 201; PT100 温度传感器: 长8 MM。通电加热测得温度、电压和电流的数据, 通过计算得到某一温度下的电导率, 进一步得到电导率对温度T 的微分d/dT 随温度T 的变化曲线d/dT- T。在这个曲线上确定淀粉糊化温度的具体步骤为: 作出淀粉糊化前和糊化后d/dT 的值对应的两条常数线, 在峰的起始边作切线, 该切线与糊化前d/dT 常数线的交点, 即为糊化开始温度To; 峰值温度为d/dT- T 曲线在糊化温度范围内的最低点所对应的温度Tp; 在峰的终了边作切线, 该切线与糊化后d/dT 常数线的交点, 即为糊化终了温度Tc。2.原理及步骤配制好试样装入加热槽, 施加一定电压的

13、交流电, 采集温度、电压和电流的数据, 利用公式(1)计算出电导率值。=Il/UA (1)式中: 为电导率, s/m;I为电流, A;l为两极板间距离, m;U为电压, V;A为极板有效面积, 。3.结论DSC 曲线和d/dT- T 曲线得出的糊化特性比用d/dT- T 曲线得出的糊化峰值温度是72.56。在高的升温速率10.94/min 时, DSC 确定的糊化峰值温度74.76, 略高于电导率得出的糊峰值温度; 在低的升温速率1 /min 时, DSC 确定的糊化峰值温度为70.44 , 略低于电导率得出的糊化峰值温度。电导率法测得的糊化温度值在两次DSC 测得的糊化温度范围之间, 具有很

14、好的代表性。所以,测定电导率的方法得到的d/dT- T 曲线, 可以用来确定淀粉的糊化温度。备注：利用差示扫描量热分析仪(DSC)进行测定。取上述试样13 mg, 从室温加热到120 , 升温速率和通电加热的升温速率相同, 定为10.94 /min。读取糊化峰值温度。把升温速率调为1 /min, 其余同上, 进行实验。欧姆加热法（欧姆加热法（ ohmic heating）Introduction: A method for measuring starch gelatinization temperature (T ), determined from a change in electric

15、al conductivity (r), was developed. Suspensions of native starches with different starch/water mass ratios and pre-gelatinized starches were prepared, and ohmically heated with agitation to 90 C using 100 V by AC power at 50 Hz, and a voltage gradient of 10 V/cm. The results showed that r of native

16、starch suspensions was linear with temperature (R2 0:999) except for the gelatinization range, but the linear relationship was always present for the pre-gelatinized starchwater system. It was seen that the shape of dr=dT versus T curve was essentially similar to the endothermic peak on a DSC thermo

17、gram, and the gelatinization temperature could be conveniently determined from this curve. Thus, the segment profile on this curve was called the block peak. The reason for the decrease in r of native starch suspensions in the gelatinization range was probably that the area for motion of the charged

18、 particles was reduced bythe swelling of starch granules during gelatinization.2. Materials methodsCommercial corn starch and mungbean starch (Beijing Xinghua Starch Factory, China), and potato starch (Beijing Hongdu Maolong Foods Inc., China) were employed in these studies. All samples were sifted

19、through a 100 mesh screen (Tyler standard sieve). The moisture content of the starches was determined by the official method 925.10 (AOAC, 2000). Different concentration suspensions were prepared with different starch/water mass ratios of 1/3, 1/4, 1/5 and 1/10 (w/w) by mixing the appropriate amount

20、 of water with different native starches. The weight of every sample was standardized at 590 g. In order to increase the electrical conductivity of the starch suspensions and perform the experiments, a little salt was put into the suspensions (THE MASS RATIO OF SALT TO DISTILLED WATER WAS 0.4/100).F

21、or comparing the changes in electrical conductivity of native starch suspensions with pre-gelatinized starch suspensions, pre-gelatinized mungbean starch and potato starch were prepared. The 60% w/w native starch (munbean and potato starch) suspensions were put on a stainless steel plate and heated

22、for 2 h at 120 C in an mautoclave (YMQ-L31-400 Beijing Jiangtai Medical Equipment Factory, China). To prevent retrogradation, the pre-gelatinized starches were dried in an oven dryer at 80 C for 48 h. After crushing in a mill (SK-M 10R Kyoritsu Riko Co. Ltd. Japan), the pre-gelatinized starches were

23、 also sifted through the 100 mesh screen (Tyler standard sieve), and then packaged hermeticallywith plastic bags. The mass ratio of salt to distilled water and the mass ratio of pre-gelatinized starch to distilled water were also 0.4/100 and 1/3, respectively. The weightof every sample was also stan

24、dardized at 590 g.3、Methods Their results showed that the main changes in electrical conductivity of the heated potato occurred at 4050 and 7580 4. ResultsDuring ohmic heating the relationship between the electrical conductivity and temperature of starch suspension was linear before and after starch

25、 gelatinization, but it was not linear relationship in the gelatinized temperature range. The shape and location of dr=dT T curves were similar to the endothermic peak occurring on a DSC thermogram. The section of the curve with a shape similar to a DSC endothermic peak, on the dr=dT T curve was cal

26、led a block peak. The position of the block peak was different for the different starch species, as was its area. When the concentration of starch was different, the position on the dr=dT T curve was little different but the difference in the magnitude of the block peak areas was obvious. There was

27、no block peak on the curve for pre-gelatinized starch. The magnitude of the block peak area represented the resistance of the starch system to charged particles; the larger the block peak area, the more obvious the decrease in electrical conductivity. Therefore, it was convenient to determine the gelatinization temperature on the dr=dT T curve according to the method used with a DSC thermogram.Brabender淀粉粘度计法(BV法）1 材料材料1.1 材料1.1.1 紫金糯, 属晚糯, 亩产4 75 5 0 公斤, 江苏地区糯稻主要品种;1.1.2 龙晴4 号, 属早熟釉稻, 亩产30 0 一3 50 公斤, 由江苏省农科院选育而成。外观紫黑色, 别名紫香糯;1.1.3 武复粳, 属中熟晚粳, 亩产5 0 公斤,