淀粉糊化溫度的測定

1、Methods for measuring temperature of gelatinization and examples淀粉糊化溫度的測定方法及實(shí)例 Methods for measuring temperature of gelatinization and examples糊化測定方法實(shí)例定義影響因素過程DSC熱分析法電導(dǎo)率法Ohmic heating 布拉班德粘度儀(BV)快速粘度分析儀（RVA）蓮藕淀粉糊化溫度的測定電導(dǎo)率法淀粉糊化溫度測定及其影響因素的研究Determination of starch gelatinization temperature by ohmic h

2、eating大米糊化特性曲線探討1.用RVA儀分析玉米淀粉的糊化特性定義：淀粉在常溫下不溶于水，但當(dāng)水溫至53以上時(shí)，淀粉的物理性能發(fā)生明顯變化。淀粉在高溫下溶脹、分裂形成均勻糊狀溶液的特性，稱為淀粉的糊化 。淀粉糊化過程是淀粉顆粒結(jié)晶區(qū)熔化，分子水解，顆粒不可逆潤脹過程，糊化后淀粉水體系直接表現(xiàn)為粘度增加。根據(jù)淀粉顆粒吸水膨脹、粘度增大、偏光特性改變，其糊化過程可分為淀粉乳中水分子被淀粉粒無定形區(qū)極性基團(tuán)吸附并加熱到初始糊化前的可逆潤脹階段，及繼續(xù)加熱達(dá)到糊化起始溫度后的不可逆潤脹階段。淀粉顆粒體積膨脹到一定程度出現(xiàn)破裂，淀粉分子最后穩(wěn)定形成網(wǎng)狀含水膠體?？赡嫖A段不可逆吸水階段顆粒解體階

3、段影響因素： A 淀粉的種類和顆粒大小； B 食品中的含水量； C 添加物：高濃度糖降低淀粉的糊化，脂類物質(zhì)能與淀粉形成復(fù)合物降低糊化程度，提高糊化溫度，食鹽有時(shí)會使糊化溫度提高，有時(shí)會使糊化溫度降低； D 酸度：在 pH 4-7 的范圍內(nèi)酸度對糊化的影響不明顯，當(dāng) pH 大于10.0，降低酸度會加速糊化 糊化糊化溫度測定方法 DSC法法 電導(dǎo)率法電導(dǎo)率法 歐姆加熱法歐姆加熱法 BV法法 RVA法法蓮藕淀粉糊化溫度的測定大米糊化特性曲線探討利用歐姆加熱測定淀粉糊化溫度電導(dǎo)率法淀粉糊化溫度測定及其影響因素的研究用RVA儀分析玉米淀粉的糊化特性 DSC熱分析法蓮藕淀粉制備流程 新鮮蓮藕去皮切塊 用

4、 1%Nacl 和 0.2NaHSO3 的水溶液浸泡 30min 勻漿反復(fù)幾次加水過濾,濾液靜置后傾去上清液,取沉淀 粉碎機(jī)粉碎后經(jīng)膠體磨打漿 粗淀粉 反復(fù)水洗后 40烘干 用石油醚在索氏抽提器中抽提脫脂，用 1%Nacl 洗三次，然后用 0.01mol/l NaOH 洗一次脫蛋白，蒸餾水洗三次后 40烘干 純蓮藕淀粉 3 試驗(yàn)方法 3. 1 偏光十字消失法 取淀粉試樣0. 5g, 加50mL蒸餾水, 混勻, 在一定溫度下保溫5min, 取一滴淀粉漿(或糊)于載玻片上,在偏光顯微鏡下分別記錄視野內(nèi)淀粉粒偏光十字2% 消失和98% 消失時(shí)的溫度并測定不同溫度下的粒徑, 重復(fù)測定三次, 取平均值。

5、 淀 粉 試 樣0.5g+50ml蒸 餾 水 取 一 滴 淀 粉 漿 于 載 玻 片 上 混 勻 ， 在 一 定 溫 度 下 保 存在 偏 光 顯 微 鏡 下 分 別 記 錄 視 野 內(nèi) 淀 粉 粒 偏 光 十 字2% 消 失 和98% 消 失 時(shí) 的 溫 度 并 測 定 不 同 溫 度 下的 粒 徑 重 復(fù) 測 定 三 次 , 取 平 均 值 從圖中可以清楚的看到原始淀粉和淀粉在糊化過程中淀粉顆粒的變化。偏光十字法測定蓮藕淀粉的糊化溫度為63. 8 71. 8。 3. 2 動(dòng)態(tài)流變儀法稱取蓮藕淀粉4. 8g, 加入80mL蒸餾水, 攪拌均勻后上樣進(jìn)行流變特性測試。將稱取好的淀粉乳放置在載物臺

6、上, 啟動(dòng)儀器使平板進(jìn)入設(shè)置間隙, 刮去平板外多余淀粉乳, 加上蓋板, 并加上液體石蠟防止水分蒸發(fā)。采用動(dòng)態(tài)振蕩程序, 設(shè)置三個(gè)溫度掃描步驟: 從20e 升溫到100 使淀粉體系糊化, 然后從100 降溫至20 使凝膠形成, 最后再從20e 升溫到100 考察凝膠的破壞情況, 升降溫速率均為5 /min。淀粉試樣 4.5g+80ml 蒸餾水 淀粉乳 攪拌混勻，進(jìn)行流變特性測試 放置在載物臺上, 啟動(dòng)儀器使平板進(jìn)入設(shè)置間隙, 刮去平板外多余淀粉乳, 加上蓋板, 并加上液體石蠟防止水分蒸發(fā) 采用動(dòng)態(tài)振蕩程序, 設(shè)置三個(gè)溫度掃描步驟: 從 20e 升溫到 100 使淀粉體系糊化, 然后從 100 降

7、溫至 20 使凝膠形成, 最后再從 20e 升溫到 100 考察凝膠的破壞情況, 升降溫速率均為 5 /min 模具選用直徑為30mm 的平板, 狹縫間隙設(shè)置為1. 0mm, 形變?yōu)?%, 角頻率為5 rad / s。它通過測定凝膠體的耗能模量G”和儲能模量G以及二者的比值tg來反應(yīng)凝膠體的彈性和黏性的變化。儲能模量G對應(yīng)著凝膠體的剛度和彈性,耗能模量G”對應(yīng)凝膠體的黏度和流動(dòng), 二者比值則tg反應(yīng)凝膠體中彈性組分和黏性組分的比值。圖2是在蓮藕淀粉升溫糊化、降溫冷卻和重新升溫時(shí), 體系的耗能模量G”變化圖。結(jié)論：結(jié)論：從圖2中可以看出在升溫糊化階段, 隨著溫度的升高, 到達(dá)一定溫度時(shí), 淀粉體

8、系耗模量顯著升高, 到達(dá)一定高度后又開始快速下降。這可從淀粉的糊化過程來合理解釋: 隨著溫度的升高, 淀粉粒吸水膨脹, 到達(dá)糊化溫度時(shí), 淀粉粒大量吸水膨脹, 直鏈分子從淀粉粒中滲析出來形成凝膠包裹淀粉粒。淀粉體系黏度和流動(dòng)性顯著增加, G”值升高; 隨著溫度的進(jìn)一步升高, 膨脹的淀粉粒間的碰撞加劇, 部分淀粉粒破裂, 同時(shí)直鏈的鏈的遷移能力增強(qiáng), 凝膠網(wǎng)絡(luò)中的部分氫鍵斷裂。 動(dòng)態(tài)流變儀法測得糊化溫度為60. 1 66. 2 。這與偏光十字消失法測得的糊化溫度相比范圍偏小。耗能模量的變化在降溫和再升溫過程中基本可逆, 說明蓮藕淀粉相當(dāng)穩(wěn)定, 短時(shí)間內(nèi)不會出現(xiàn)回生老化現(xiàn)象。 3.3 DSC法方法

9、是制備6% ( W /V)淀粉乳, 上樣測試。將樣品放在DSC的加熱器上, 同時(shí)用一空鋁盒作對照, 從室溫附近的溫度開始, 加熱速度10K /MIN, 測試范圍30 100 。結(jié)果以吸熱曲線表示, 曲線上的吸熱峰是計(jì)算糊化溫度和反應(yīng)熱的依據(jù)。從峰的形成到結(jié)束可以得到起始溫度、峰值溫度和結(jié)束溫度, 峰的面積則表示糊化所需的熱焓( J/G) 。備注：先測出淀粉的水份。如W，稱取質(zhì)量為6/(1-w)克的淀粉樣品，加水為100-6/(1-w)克，攪拌均勻就是所求的淀粉乳 3.3 DSC法淀粉糊化時(shí)伴隨的能量變化在DSC 分析圖譜上表現(xiàn)為吸熱峰。ZOBEL認(rèn)為, 淀粉在糊化過程中同時(shí)伴有玻璃化轉(zhuǎn)變和晶體

10、的崩解過程。6% 蓮藕淀粉乳的DSC 圖譜見圖3, 熱特性參數(shù)見表1。在過量水分下加熱淀粉乳, 所有淀粉顆粒均能吸水膨脹, 因此DSC 圖譜只出現(xiàn)一個(gè)峰, 即淀粉的糊化峰。淀粉的糊化溫度為63. 5 74. 7, 這與偏光十字消失法測得的糊化溫度相比大一些, 其原因是一小部分淀粉顆粒發(fā)生變化時(shí), 雖沒有引起淀粉出現(xiàn)糊化, 卻有吸熱現(xiàn)象發(fā)生。電導(dǎo)率法1 材料與方法1.1 實(shí)驗(yàn)材料和設(shè)備實(shí)驗(yàn)所用淀粉(質(zhì)量等級: 一級)均為市售。在130 烘箱中加熱淀粉4 H 測得水分含量。實(shí)驗(yàn)用水為蒸餾水。玉米淀粉: GB/8885, 水分含量11.77%, 北京京南食品有限公司; NACL、KCL: 分析純,

11、北京化學(xué)試劑廠。Q10 型差示掃描量熱分析儀: TA INSTRUMENTS;SR8001 型電子天平A: 精度0.001 G, METERTOLEDO; FA1004 型電子天平B: 精度0.0001 G, 上海天平儀器廠; HP34970A 數(shù)據(jù)采集器: 接入三個(gè)通道, 美國惠普公司; S21- I 磁力攪拌器; TDGC- 5 變壓器: 220 V/110、V20 A/8 A, 北京華興電源設(shè)備廠; 圓筒型加熱槽: =45 MM 長L=90 MM V=143.07ML, 自制; 方型加熱槽: 寬B=105 MM 長L=100 MM高HMAX=100 MM, 自制; CS020G 電流傳感

12、器: 201; PT100 溫度傳感器: 長8 MM。通電加熱測得溫度、電壓和電流的數(shù)據(jù), 通過計(jì)算得到某一溫度下的電導(dǎo)率, 進(jìn)一步得到電導(dǎo)率對溫度T 的微分d/dT 隨溫度T 的變化曲線d/dT- T。在這個(gè)曲線上確定淀粉糊化溫度的具體步驟為: 作出淀粉糊化前和糊化后d/dT 的值對應(yīng)的兩條常數(shù)線, 在峰的起始邊作切線, 該切線與糊化前d/dT 常數(shù)線的交點(diǎn), 即為糊化開始溫度To; 峰值溫度為d/dT- T 曲線在糊化溫度范圍內(nèi)的最低點(diǎn)所對應(yīng)的溫度Tp; 在峰的終了邊作切線, 該切線與糊化后d/dT 常數(shù)線的交點(diǎn), 即為糊化終了溫度Tc。2.原理及步驟配制好試樣裝入加熱槽, 施加一定電壓的

13、交流電, 采集溫度、電壓和電流的數(shù)據(jù), 利用公式(1)計(jì)算出電導(dǎo)率值。=Il/UA (1)式中: 為電導(dǎo)率, s/m;I為電流, A;l為兩極板間距離, m;U為電壓, V;A為極板有效面積, 。3.結(jié)論DSC 曲線和d/dT- T 曲線得出的糊化特性比用d/dT- T 曲線得出的糊化峰值溫度是72.56。在高的升溫速率10.94/min 時(shí), DSC 確定的糊化峰值溫度74.76, 略高于電導(dǎo)率得出的糊峰值溫度; 在低的升溫速率1 /min 時(shí), DSC 確定的糊化峰值溫度為70.44 , 略低于電導(dǎo)率得出的糊化峰值溫度。電導(dǎo)率法測得的糊化溫度值在兩次DSC 測得的糊化溫度范圍之間, 具有很

14、好的代表性。所以,測定電導(dǎo)率的方法得到的d/dT- T 曲線, 可以用來確定淀粉的糊化溫度。備注：利用差示掃描量熱分析儀(DSC)進(jìn)行測定。取上述試樣13 mg, 從室溫加熱到120 , 升溫速率和通電加熱的升溫速率相同, 定為10.94 /min。讀取糊化峰值溫度。把升溫速率調(diào)為1 /min, 其余同上, 進(jìn)行實(shí)驗(yàn)。歐姆加熱法（歐姆加熱法（ 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淀粉粘度計(jì)法(BV法）1 材料材料1.1 材料1.1.1 紫金糯, 屬晚糯, 畝產(chǎn)4 75 5 0 公斤, 江蘇地區(qū)糯稻主要品種;1.1.2 龍晴4 號, 屬早熟釉稻, 畝產(chǎn)30 0 一3 50 公斤, 由江蘇省農(nóng)科院選育而成。外觀紫黑色, 別名紫香糯;1.1.3 武復(fù)粳, 屬中熟晚粳, 畝產(chǎn)5 0 公斤,