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編號
無錫太湖學(xué)院
畢業(yè)設(shè)計（論文）
相關(guān)資料
題目： 絞龍式和面機(jī)設(shè)計
信機(jī) 系 機(jī)械工程及自動化專業(yè)
學(xué) 號： 0923223
學(xué)生姓名： 徐 斌
指導(dǎo)教師： 戴 寧（職稱：副教授 ）
（職稱： ）
2013年5月25日
目 錄
一、畢業(yè)設(shè)計（論文）開題報告
二、畢業(yè)設(shè)計（論文）外文資料翻譯及原文
三、學(xué)生“畢業(yè)論文（論文）計劃、進(jìn)度、檢查及落實表”
四、實習(xí)鑒定表
無錫太湖學(xué)院
畢業(yè)設(shè)計（論文）
開題報告
題目： 絞龍式和面機(jī)設(shè)計
信機(jī) 系 機(jī)械工程及自動化 專業(yè)
學(xué) 號： 0923223
學(xué)生姓名： 徐 斌
指導(dǎo)教師： 戴 寧 （職稱：副教授 ）
（職稱： ）
2012年11月25日
課題來源
自擬課題
科學(xué)依據(jù)（包括課題的科學(xué)意義；國內(nèi)外研究概況、水平和發(fā)展趨勢；應(yīng)用前景等）
（1）課題科學(xué)意義
和面機(jī)又稱調(diào)粉機(jī)，是面食加工的主要設(shè)備，它主要用于將小麥粉與水按1：0.38—0.45的比例，根據(jù)用戶加工工藝要求（有時加食油、食堂、及其他食物和食物添加劑）混合制成面團(tuán)，廣泛適用于食堂、飯店及面食加工單位的面食加工。
隨著市場份額的發(fā)展，手工和面的產(chǎn)量已跟不上人們的日常需求，和面機(jī)也應(yīng)運(yùn)而生。和面機(jī)操作方便，自動化程度高，不僅節(jié)省了人力，還省事省力，真正的做到了化勞力為動力的要求。和面機(jī)的產(chǎn)生使得面粉事業(yè)得到了更一步的發(fā)展。
和面機(jī)模擬手工和面的原理，使面筋網(wǎng)絡(luò)快速形成，使得蛋白組織結(jié)構(gòu)均衡，使面的的產(chǎn)量大大高于手工和面，且生產(chǎn)出來的面品，口感光滑，透明度高，彈性好。
單軸式和面機(jī)的特點：1、均采用齒輪減速傳動結(jié)構(gòu)，具有結(jié)構(gòu)簡單，緊湊，操作方便，不需復(fù)雜的維修，使用壽命長等優(yōu)點。2、面斗采用不銹鋼材料和特殊的表面處理，絕對符合衛(wèi)生標(biāo)準(zhǔn)。3、運(yùn)轉(zhuǎn)應(yīng)平穩(wěn)，無異響。
（2）和面機(jī)的研究狀況及其發(fā)展前景
隨著食品行業(yè)的日益發(fā)展壯大，生產(chǎn)設(shè)備產(chǎn)能變大的要求變得日益強(qiáng)烈。和面機(jī)是大多數(shù)食品行業(yè)必備的生產(chǎn)設(shè)備，且一般處在生產(chǎn)流程的上游，和面機(jī)的產(chǎn)能，穩(wěn)定性，對整個生產(chǎn)線來說就顯得非常重要。如果單純靠增加設(shè)備的數(shù)量，產(chǎn)能雖然可以上去，但是不但設(shè)備的費用回大大增加，人力成本和故障率也會增加。
為了很好的解決以上問題，于是大型和面機(jī)誕生了。大型和面機(jī)自動化程度高，機(jī)器故障率低，一個人可以輕松看護(hù)兩臺大型和面機(jī)，其產(chǎn)量可以滿足大中型食品企業(yè)的需求。
研究內(nèi)容
1、熟練掌握和面機(jī)的工作原理與結(jié)構(gòu)；
2、熟悉單軸式和面機(jī)中和面過程的運(yùn)動攪拌器結(jié)構(gòu)設(shè)計與受力分析；
3、熟練掌握單軸式和面機(jī)各參數(shù)的設(shè)計和各傳動的結(jié)構(gòu)的設(shè)計；
擬采取的研究方法、技術(shù)路線、實驗方案及可行性分析
研究方法：
1、根據(jù)課題所確定的和面機(jī)種類，用途及生產(chǎn)能力確定和面機(jī)的主要構(gòu)件（例如槳葉，容器）機(jī)構(gòu)形式和尺寸參數(shù)，運(yùn)動參數(shù)及動力參數(shù)（電機(jī)功率）。
2、根據(jù)和面機(jī)主要構(gòu)件的形式，性質(zhì)及運(yùn)動參數(shù)，擬定整機(jī)的機(jī)械傳動鏈和傳動系統(tǒng)圖。計算并確定各級傳動的傳動比，皮帶轉(zhuǎn)動，齒輪轉(zhuǎn)動等傳動構(gòu)件的結(jié)構(gòu)參數(shù)及尺寸，擬定機(jī)器的結(jié)構(gòu)方案圖。
3、根據(jù)結(jié)構(gòu)方案圖，在正式圖紙上擬定傳動構(gòu)件及執(zhí)行構(gòu)件的位置，然后依次進(jìn)行執(zhí)行構(gòu)件及傳動系統(tǒng)設(shè)計機(jī)體，操縱機(jī)構(gòu)設(shè)計，密封及潤滑的結(jié)構(gòu)設(shè)計。
研究計劃及預(yù)期成果
研究計劃：
2012年10月12日-2012年12月31日：按照任務(wù)書要求查閱論文相關(guān)參考資料，完
成畢業(yè)設(shè)計開題報告書。
2013年1月1日-2013年1月27日：學(xué)習(xí)并翻譯一篇與畢業(yè)設(shè)計相關(guān)的英文材料。
2013年1月28日-2013年3月3日：畢業(yè)實習(xí)。
2013年3月4日-2013年3月17日：單軸式和面機(jī)的主要參數(shù)計算與確定。
2013年3月18日-2013年4月14日：單軸式和面機(jī)總體結(jié)構(gòu)設(shè)計。
2013年4月15日-2013年4月28日：部件圖和零件圖設(shè)計。
2013年4月29日-2013年5月21日：畢業(yè)論文撰寫和修改工作。
預(yù)期成果：
根據(jù)提供的主要構(gòu)件參數(shù)而計算出的傳動構(gòu)件的參數(shù)，尺寸及機(jī)體等是合理的，可以進(jìn)行正常的生產(chǎn)組裝，最終達(dá)到和面機(jī)的工作要求。
特色或創(chuàng)新之處
造型優(yōu)美，占地面積小，機(jī)器操作噪音小。故障率低，使用壽命長。
已具備的條件和尚需解決的問題
1、 設(shè)計方案思路已經(jīng)非常明確，已經(jīng)具備使用CAD制圖的能力和了解和面機(jī)原理結(jié)構(gòu)等知識。
2、使用CAD制圖能力尚需加強(qiáng)，結(jié)構(gòu)設(shè)計能力尚需加強(qiáng)。
指導(dǎo)教師意見
指導(dǎo)教師簽名：
年 月 日
教研室（學(xué)科組、研究所）意見
教研室主任簽名：
年 月 日
系意見
主管領(lǐng)導(dǎo)簽名：
年 月 日
Dough thermo-mechanical properties: influence of
sodium chloride, mixing time and equipment
A. Angioloni*, M. Dalla Rosa
Abstract
Thermo-mechanical properties of doughs prepared from common wheat flour were investigated under different kneading conditions and with different amounts of sodium chloride. Dynamic mechanical thermal analysis showed that high-speed mixing and the addition of salt to dough slowed heat-induced reactions such as starch gelatinisation and protein coagulation. The effect of dough mixing technology was more significant than the amount of sodium chloride in modifying dough rheological characteristics. q 2004 Elsevier Ltd. All rights reserved.
Keywords: Dough; Mixing; Sodium chloride; Thermo-mechanical properties; Starch gelatinization
1. Introduction
The first step in a baking process is mixing the dough; how the mixing is performed and the ingredients are incorporated and dispersed largely determine the final quality of the baked product (Aamodt et al., 2003; Basaran and Go¨cmen, 2003). The production of wheat dough is a process in which raw materials (mainly flour, water, salt and yeast) are mixed and subjected to a large range of strain situations. Dough is a complex mixture of starch, protein, fat and salt. Mixing has three important functions: (i) it blends the ingredients into a macroscopically homogeneous mass, (ii) it develops the dough into a three-dimensional viscoelastic structure with gas-retaining properties and (iii) it incorporates air which will form nuclei for gas bubbles that grow during dough fermentation (Bloksma, 1990; Collado and Leyn, 2000; Dobraszczyk and Morgenstern, 2003; Hoseney and Rogers, 1990; Naeem et al., 2002). Both mixing intensity and mixing energy must be above a minimum critical level to develop the dough properly, the level varying with flour and mixer type (Kilborn and Tipples, 1972; MacRitchie, 1986; Skeggs, 1985; Zheng et al., 2000). The time required for optimum dough development is positively correlated with the polymeric protein composition and the balance between protein polymers and monomers (Dobraszczyk and Morgenstern, 2003; MacRitchie, 1992; Millar, 2004). Rheological properties change during every stage of the dough making process; stress conditions are high when the dough is mixed in high-speed mixers, to become an elastic and coherent mass. Mixing speed and energy (work input) must be higher than a certain value to develop the gluten network and to produce a suitable breadmaking dough. On the other hand, an optimal mixing time has been related to optimum breadmaking performance which varies depending on mixer type and ingredients (Dobraszczyk and Morgenstern, 2003; Mani et al., 1992). For example, kneading doughs to reach optimum development using elongational flow in sheeting, required only 10–15% of the energy generally imparted by conventional high speed shear mixers, suggesting that much higher rates of work input can be achieved due to the improved strain hardening of dough under extension (Dobraszczyk and Morgenstern, 2003; Kilborn and Tipples, 1974; Millar, 2004) Starch, the major component of wheat flour, making upabout 80% of its dry weight, influences dough rheological properties, especially upon heating in the presence of water when starch gelatinises (Li and Yeh, 2001). The gelatinization process includes a number of changes: absorption of water and swelling of the granules, change in size and shape of the granules, loss of birefringence and X-ray diffraction pattern, leaching of amylose from the granules into the solvent and the formation of a paste (Atwell et al., 1988). At reduced water contents, such as in dough, the changes resulting from gelatinisation are strongly dependent on the amount of water available (Eliasson, 1983; Seetharaman et al., 2004). The increase in viscosity due to starch gelatinisation has been suggested to modify structural properties of dough.
In addition, the presence of sodium chloride is known to affect dough properties; salt toughens the protein and helps in conditioning the dough by improving its tolerance to mixing; the addition of salt produced a more stable and stiff dough (Galal et al., 1978; Shiu and Yeh, 2001). Moreover it is known that when salt is added to the dough, heat-induced reactions such as starch gelatinisation and protein coagulation, are slowed.
The aim of the present work was to analyse the effects of increasing sodium chloride concentration and different kneading conditions on several dough thermo-mechanical properties, using a dynamical stress-strain controlled rheometer.
2. Materials and methods
Commercial wheat flour was from Mulino Pivetti (Italy), sodium chloride, from Carlo Erba (Italy). AACC (2000) methods were used to determine moisture (44-19), ash (08-01), protein (46-10) and gluten (38-12) in the flour and its Alveograph characteristics. Dough samples with 50% moisture were prepared in accordance with Alveograph method AACC 54-30A (2000), using two different mixers and mixing times. In the first (sample A) the Alveograph mixer was used with standard conditions (250 g of flour was mixed with water for 7 min to form the dough). In the second (sample M) a prototype mixer was used where the ingredients were kneaded for only 15 s but at high-speed (1500 rpm). In this way high amounts of energy were transferred to the dough. The prototype mixer had a parallelpiped shape (12!8!12 cm) with two vertical arms operated by a 1.5 kW motor (Gamar s.r.l., VE-Italy). Sodium chloride, 0–4.5%, dry basis (d.b.) was added, for each different kneading condition and mixer type (Table 1). Before rheological analysis all doughs were rested for 30 min at room temperature in a plastic container. Doughtemperatures at the end of kneading were 26–28 8C for sample A and w35 8C for sample M; although the use of prototype mixer rapidly Thermomechanical tests were made using a controlled stress-strain rheometer (MCR 300, Physica/Anton Paar; Messtechnik, Ostfildern, Germany), using parallel-plate geometry (25 mm plate diameter, 2 mm plate gap). The upper, serrated 25 mm plate was lowered until the thickness of sample was 2 mm and excess was trimmed off. The exposed surface was covered with a thin layer of mineral oil to prevent moisture loss during testing. The sample was
rested another 15 min in the rheometer, before each measurement, allowing relaxation of stresses induced during sample loading to relax. All measurements were performed at a heating rate of 0.8 8C/min at fixed frequency of 1 Hz with the oscillation amplitude small enough to ensure linear viscoelasticity.
The data are reported as means of measurements made on three samples, where each sample was obtained from a separately prepared batch of dough for each formulation and for the different mixers used. Significant differences in storage modulus (G0) at 1Hz were determined by Least Significant Difference analysis with P%0.05. All statistical analyses were performed with the Stat Soft Version 6.
3. Results and discussion
3.1. Flour chemical and physical properties
The chemical composition and rheological properties of the flour are shown in Table 2. Analysis of Alveograph data categorises the flour used as weak, and as seen by the P/L ratio, the gluten is richer in gliadins than in glutenins The resistance of a gluten dough to extension decreases and extensibility increases with an increasing gliadin to glutenin ratio (Grasberger et al., 2003; Kim et al., 1988;
Uthayakumuran et al., 2000).
3.2. Thermo-mechanical properties of doughs
The same amounts of salt (0, 2.5, 3.5, 4.5% d.b.) were added to both samples (A; M) to check the effect of salt and different kneading conditions on sample behaviour during dynamic mechanical thermal analysis. This measurement simulates the physicochemical changes that take place during thermal treatment of dough. Figs. 1 and 2 show the effect of salt addition on the storage modulus (G0) during an oscillatory temperature ramp. Below 55 8C, G0, for both samples, gradually decreased as temperature increased, indicating softening of the dough. Thereafter, the storage modulus increased from 55–60 to 80 8C and then slowly decreased. The abrupt increase can be attributed to the gelatinization of starch; the swelling and distortion of starch granules during gelatinization were responsible for the rapid increase of G0 not only by their action as a filler in the gluten network, but also by promoting effective cross-linking in the system (Dreese et al., 1988). The glutenin fraction of gluten has been found to be more sensitive to heat than the gliadin fraction; on heating up to 75 8C glutenin proteins unfolds and disulphide/sulphydryl interchange reactions are promoted, thus increasing the molecular size of the aggregates
(Dreese et al., 1988; Peressini et al., 1999). The increase of storage modulus during heating has been reported (He and Hoseney, 1991) to be proportional to the starch content of the dough; indicating the physicochemical changes in heated dough are essentially due to changes in the starch fraction.
For both samples the transition temperature range of salted dough appeared to be shifted to higher values than doughs made without salt (Figs. 1 and 2) as reported previously by Dreese et al. (1988) and Peressini et al. (1999). Moreover, a comparison of the slopes obtained from the linear regressions over the temperature range (55–70 8C) where the G0 increased, showed that, in all cases, the slopes for salted dough were significantly lower than for unsalted doughs (Figs. 1(a) and 2(a) and Table 3).
The effect of sodium chloride in delaying the starch gelatinization has been reported (Chiotelli et al., 2002; Galal et al., 1978; Peressini et al., 1999; Preston, 1989) and different explanations for this phenomenon proposed. When salt is added to dough, it lowers water activity and increases the energy necessary for chemical and physical reactions involving water (Kim and Cornillon, 2001; Seetharaman et al., 2004).
Table 4 compares the slopes obtained from linear regressions at the different kneading conditions (in the temperature range from 55 to 70 8C) with respect to starch gelatinization. For each salt concentration it can be seen that the slopes sample M are lower that those for sample A, consequently the type of mixing seems to be relevant to the delay phenomenon.
The doughs prepared using short time and high-speed mixing conditions, sample M, where high energies were transferred to the dough, were probably less hydrated and developed than sample A, therefore for starch gelatinization, for which water is indispensable, requires higher energy. The dough structure created in these kneading conditions could decrease the capability of water being effectively involved in starch granule swelling and therefore the gelatinization process is delayed.
氯化鈉、混合時間及設(shè)備對面團(tuán)的熱力學(xué)特性的影響
摘要：
在不同揉捏條件和加入不同數(shù)量氯化鈉條件下對麥粉的熱力學(xué)性能進(jìn)行了測試。強(qiáng)有力的熱力學(xué)報告表明：高速混合及加入食鹽會緩慢熱誘導(dǎo)淀粉糊化和蛋白質(zhì)凝結(jié)等反應(yīng)。生面團(tuán)混合工藝對面團(tuán)流變特性的影響比相當(dāng)數(shù)量的氯化鈉更顯著一些。
關(guān)鍵字：生面團(tuán)、混合、氯化鈉、熱力學(xué)性能、淀粉糊化
1.引言
在一個烘焙過程中第一步是混合面粉。混合過程如何進(jìn)行、各成分如何進(jìn)行合并分解很大程度上決定了烘焙產(chǎn)品的最終質(zhì)量（阿莫特等，2003;巴薩蘭與格茲曼，2003）。小麥面團(tuán)的制作是將各天然原料（主要是面粉、水、食鹽和酵母粉）混合并進(jìn)行一系列的張緊操作。生面團(tuán)是由淀粉、蛋白質(zhì)、脂肪和食鹽等組成的復(fù)雜混合物?；旌线^程有三個重要作用：1、使各組成成分混合成宏觀上同質(zhì)的物質(zhì)；2、使面團(tuán)變成內(nèi)含氣體的三維有粘彈性結(jié)構(gòu)的物質(zhì)；3、包含在面團(tuán)發(fā)酵時為氣泡變大提供核心的空氣（布蘭克，1990；克拉多及萊納，2000；多布羅斯科克及摩根斯頓，2003；侯賽因及羅杰斯，1990；納伊姆等，2002）。混合的強(qiáng)度和能量都要大于正常加工面團(tuán)所需水平的最小值，這一水平是隨面粉和混合器類型變化的（基爾伯恩及提普爾斯，1986；斯凱格斯，1985；曾等，2000）。生面團(tuán)生長所需最佳時間絕對跟聚合的蛋白質(zhì)合成物，以及蛋白質(zhì)高分子材料和單體之間的平衡有關(guān)(多布羅斯科克及摩根斯頓，2003；麥克里奇，1992；米勒，2004)。在生面團(tuán)形成的每一個階段流變學(xué)性質(zhì)都會發(fā)生變化。生面團(tuán)在高速混合器中混合時，需要很高的條件才能形成有彈性、混合均勻的整體。攪拌速度、能源(工作輸入)一定要大于形成面筋狀物質(zhì)和形成適合做面包的面團(tuán)所需要的值。另一方面，最佳混合時間與由混合器決定的做面包時的最佳性能有關(guān)（多布羅斯科克及摩根士特恩，2003；馬尼，1992）。例如，要揉捏生面團(tuán)達(dá)到最適合在護(hù)墻板中伸長流動的狀態(tài)僅需要常規(guī)高速混合器所提供能量的10-15%，由于改善的生面團(tuán)張緊硬化法，能夠獲取更高比例的能力（?多布羅斯科克及摩根斯頓，2003；基爾伯恩及提普拉斯，1974；米勒，2004）。
淀粉，面粉的主要成分，占其干重的80%左右，影響生面團(tuán)的流變學(xué)性質(zhì)，特別是淀粉糊化時在暖氣設(shè)備中有水存在(李、葉，2001)。糊化過程包括一系列的變化：水分的吸收和顆粒膨脹；顆粒大小和形狀的改變；雙折射和x射線衍射樣式的損耗；顆粒中的直系淀粉進(jìn)入溶劑中；糊狀物的形成（埃利亞松，1983；塞特曼等，2004）。因淀粉糊化導(dǎo)致的粘度增加被證實會改變生面團(tuán)的結(jié)構(gòu)形式。
另外，氯化鈉的存在會影響生面團(tuán)的特性；食鹽會使蛋白質(zhì)硬化并且對改善生面團(tuán)混合時的忍耐力有幫助；加入食鹽制造出更穩(wěn)定更硬的生面團(tuán)（加拉爾等，1978；蘇、葉，2001）。再者，當(dāng)在生面團(tuán)中加入食鹽時，熱誘導(dǎo)比如淀粉糊化和蛋白質(zhì)凝結(jié)會變慢。
本文的目的是分析不同濃度的氯化鈉和不同程度的揉捏對生面團(tuán)的幾個熱力學(xué)特性的影響，使用的是一種電動的應(yīng)力-應(yīng)變控制的流變儀。
1. 原料和方法
商務(wù)小麥來自穆利諾皮韋帝(意大利)，氯化鈉來自卡洛蘇丹（意大利）。AACC（2000）方法用來確定面粉中的水分（44-19）、灰燼（08-01）、蛋白質(zhì)（46-10）和面筋（38-12）以及它的面筋拉力測定儀特性。根據(jù)面筋拉力測定儀AACC 54-30A (2000)方法，使用兩種不同的混合器和兩種不同的混合時間，準(zhǔn)備好兩個含50%水分的生面團(tuán)樣本。第一個樣本（樣本A），面筋拉力測定儀混合器在標(biāo)準(zhǔn)條件下使用（250g面粉用水混合7分鐘形成面團(tuán)），第二個樣本（樣本M）各原料在雛形混合器中僅混合15秒，但是在高速條件（1500轉(zhuǎn)/分）進(jìn)行。這樣，大量的能量被轉(zhuǎn)移到生面團(tuán)中。雛形混合器的外形尺寸是（12×8×12cm），有兩個在1.5kw功率下工作的垂直攪拌軸（gamar公司，意大利）。為每種不同的揉捏條件和混合器類型加入0-4.5干基的氯化鈉（表1）。在進(jìn)行流變學(xué)分析之前，所以的面團(tuán)都在室溫條件下置于塑料容器中30分鐘。在揉捏完之后，樣品A的溫度要在26-28℃，樣品M要在35℃，即使雛形混合器的使用會使生面團(tuán)溫度迅速升高。
表1
實驗生面團(tuán)的構(gòu)成
生面團(tuán)
面粉（g）
食鹽（%）
水
A- M
A- M
A- M
A- M
250
243.75
241.25
238.75
B- 0
C- 2.5
D- 3.5
E- 4.5
F- 143.7
G- 143.7
H- 143.7
I- 143.7
A是用面筋拉力測定儀混合器得到的面團(tuán)，M是用雛形混合器的到的面團(tuán)。加水使生面團(tuán)含水量50%
熱機(jī)械的測試用一個受控制的應(yīng)力-應(yīng)變流變儀（MCR 300，物理學(xué)/安東帕）和平行板幾何（板直徑25cm,間隙2mm）完成。在上面的直徑25mm邊緣呈鋸齒狀的平板只有在樣本厚度大于2mm并且邊緣被修剪過時才會下降。暴露的表面要覆蓋一層薄薄的礦物油以防實驗時水分散失。樣本在流變儀中放置15分鐘后讀取測量結(jié)果，在放置期間允許壓力減小。在升溫速度為0.8℃/分，頻率穩(wěn)定在1Hz振蕩幅度足夠小而不致影響線性粘彈性的情況下完成測試。
以從三個樣本獲取的測試結(jié)果為基礎(chǔ)的數(shù)據(jù)被記錄下來，這些樣本是從為每個方案和不同的混合器分別準(zhǔn)備的生面團(tuán)中獲取的。Significant貯藏系數(shù)在1Hz時的顯著不同點是由P≤0.05時最低顯著性差異分析報告決定的。所有統(tǒng)計學(xué)的分析報告都由軟件Stat Soft Version 6完成的。
1. 結(jié)果與討論
3.1面粉的化學(xué)、物理特性
面粉化學(xué)成分和流變特性如表2所示。面筋拉力測定儀數(shù)據(jù)分析報告把面粉各成分列出，以P/L比率表示，麩質(zhì)在醇溶蛋白中比谷蛋白麥中含量更多。麩質(zhì)生面團(tuán)抗延長的能力降低并且延長性隨麩朊與麥谷蛋白的比例增大而增強(qiáng)（Grasberger等，2003；吉姆等，1988；Uthayakumaran等，2000）。
表2
面粉化學(xué)成分和流變學(xué)特性
面粉
蛋白質(zhì)（%）
麩質(zhì)(%)
灰 (%)
水分（%）
面筋拉力測定儀（%）
W(×)
P(高度×1.1)（mm）
長度（mm）
P/L
11.830.15
31.100.87
0.400.01
10.80.06
1043.3
29.630.96
118.003.61
0.250.01
3.2.生面團(tuán)熱力學(xué)特性
相同數(shù)量的食鹽（0，2.5%,3.5%,4.5%）添加在兩個生面團(tuán)樣本中，以此來檢測食鹽和不同揉捏條件在動態(tài)的熱力學(xué)特性分析中對面團(tuán)的影響。不同揉捏條件這種測試模擬在生面團(tuán)熱處理中的物理化學(xué)變化。圖1和2所示為加入食鹽對貯藏系數(shù)G’隨溫度變化的影響。55℃以下，G’在兩個樣本中都隨溫度的上升逐漸下降，indicating softening of the dough.貯藏系數(shù)在55-60℃到80℃之間隨溫度上升而上升，最后緩慢下降。那些突變性的上升是由淀粉的膠凝造成的；在膠凝中淀粉顆粒的腫脹和變形是造成G’急速上漲的原因，不僅因為淀粉在麩質(zhì)網(wǎng)狀物中作為填充物的作用效果，還因為提高交聯(lián)在面團(tuán)中的影響（德里斯等，1988）。麥谷蛋白分解，二硫化物/氫硫基互換反應(yīng)加劇，因此增大了分子的大?。ǖ吕锼沟龋?988；帕諾斯尼等，1999）。據(jù)報道，在加熱時貯藏系數(shù)的上升與面團(tuán)中淀粉的含量成正比。在加熱的面團(tuán)中，物理化學(xué)變化的指標(biāo)在本質(zhì)上取決于淀粉的含量。
圖2
表3
LogG’隨溫度的線性衰減分析報告
樣本 斜率
A 0.060a 0.984
A 2.5%食鹽 0.055b 0.995
A 3.5%食鹽 0.056b 0.995
A 4.5%食鹽 0.052c 0.991
M 0.052a 0.994
M 2.5%食鹽 0.047b 0.990
M 3.5%食鹽 0.041c 0.990
M 4.5%食鹽 0.042c 0.982
據(jù)以前德里斯（1988）和帕偌斯尼（1999）等報道，對于兩個生面團(tuán)，放鹽的比沒放鹽的度變化范圍更大（圖1和2）。并且，在G’上升的55-70℃獲取的線性衰退斜率對比表明放鹽的面團(tuán)斜率明顯低于沒放鹽的生面團(tuán)斜率（圖1(a)和2（a）、表3）。
氯化鈉對延遲淀粉膠凝的作用已被證實(),并且針對此現(xiàn)象各種不同的解釋被提出。當(dāng)食鹽加入生面團(tuán)時，降低了水的活性并且因化學(xué)物理反應(yīng)而增加了能力需求(吉姆和考尼倫，2001；賽斯羅曼等，2004)。
表4
樣本 斜率
A 0.060a 0.984
M 0.060a 0.984
A 2.5%食鹽 0.055b 0.995
M 2.5%食鹽 0.047b 0.990
A 3.5%食鹽 0.056b 0.995
M 3.5%食鹽 0.041b 0.990
A 4.5%食鹽 0.052a 0.991
M 4.5%食鹽 0.042b 0.982
表4對比了在不同揉捏條件下（55-70℃范圍內(nèi)）從線性衰退中得到的斜率，淀粉膠凝也被考慮在內(nèi)。可以發(fā)現(xiàn)，在每個食鹽比例條件下樣本M的斜率比同條件下的樣本A要小，所以混合的類型看來跟延遲這一現(xiàn)象有關(guān)。
用較短時間和高速混合條件獲得的有較多能量轉(zhuǎn)移到其中的生面團(tuán)樣本M，，可能含水量和成熟度都小于樣本A，因此有水才能進(jìn)行的淀粉膠凝需要更多的能量。在這種揉捏條件下形成的生面團(tuán)結(jié)構(gòu)會降低水有效參與淀粉顆粒膨脹的能力，因此膠凝作用被延遲。
4. 結(jié)論
實驗表明G’在55-70℃之間的快速升高是由于淀粉的膠凝作用。它們還表明生面團(tuán)的淀粉膠凝和蛋白質(zhì)凝結(jié)反應(yīng)因加入食鹽這一條件被延遲，在雛形混合器高速揉捏得到的面團(tuán)效果更明顯。所以不僅是食鹽的加入會改變生面團(tuán)的熱力學(xué)特性，所用的混合工藝也會改變。這些結(jié)論是很有應(yīng)用前景的，引出了一個新的研究方向來找到一種新方法在巴氏消毒溫度條件下制造更穩(wěn)定的面團(tuán)結(jié)構(gòu)以用于長保質(zhì)期食品和配好料的烘烤產(chǎn)品，在該產(chǎn)品中部分淀粉膠凝會導(dǎo)致產(chǎn)生一種感官效果差的像塑料的產(chǎn)物。