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关键词：: 剪切螺杆挤压设计

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摘要

目前膨化食品越来越受到人们的欢迎，而挤压技术在膨化食品中的应用也更加广泛。

在挤压机内的面团类食品中的水分由于处于压力之下成液态，然后从模板孔挤出时，过热的水分突然处于常压下，压力突然降低，水分蒸发成水蒸汽，产生伸张的和膨胀，这样使这种产品产生一种低密度轻质的状态。

挤压技术作为食品工业中一项非常重要的技术得到更大的发展，现代食品工业用的螺杆挤压机集混合、融合、蒸煮、改性反映、调质、组织化、成型、膨化等多种功能于一身，体现出有利于自动控制、便于灵活转产以及节能、节劳力、节省生产场地等优点。

单螺杆挤压机的结构简单、易于加工制造、成本低廉，广泛用于加工各种膨化小吃食品，本设计中设计一台单螺杆挤压机，其特点是高转速，高剪切率，外部无加热和冷却装置，而是利用其高剪切率产生的摩擦热来加热熔融原料使食品原料得到蒸煮熟化，从而生产出松脆可口的膨化谷物食品。设计将从挤压机的传动系统，挤压系统，喂料系统等进行完整的设计。

关键词：膨化食品；挤压技术；单螺杆挤压机

Abstract

At present puffs food more and more to receive people's welcome.

The extrusion technology in puffs in food the application to be also more widespread.In extruder pasta class food moisture content because is in under the pressure to become the liquid state,Then when squeezes out from the template hole, the superheat moisture content suddenly is in under the atmospheric pressure, the pressure reduces suddenly,The pressure reduces suddenly, the moisture evaporation steam, produces promotes and the inflation, like this causes this product to have one kind of low density light quality condition.

The extrusion technology took in the food industry an extremely important technology obtains a bigger development,Modern food industrial used screw rod extruder have the mix, the fusion, the steam boiling, the modification reflected, the quenching and tempering, the organization, the formation, puff and so on many kinds of functions,manifests is advantageous to the automatic control, is advantageous for produces a different product nimbly as well as the energy conservation, the festival labor force, saves produces merits and so on location.

The single screw extruder structure simple, easy to process the manufacture, the cost is inexpensive, widely uses in processing each kind to puff snack food,In the design designs a single screw rod extruder, its characteristic is the high speed, high cutting rate, the outside does not have the heating and the cooling system, but is uses the friction heat which its high cutting rate produces to heat up the fusing raw material enable food raw material to obtain the steam boiling curing, thus produces the pine crisply delicious to puff grain food.

The design from the extruder transmission system, the extrusion system, will feed the material system and so on to carry on the integrity the design.

Keyword: euffs food extrusion technology single screw extruder

摘要III

AbstractIV

目录V

1 绪论1

1.1 挤压技术介绍1

1.1.1 挤压技术在食品生产中的应用1

1.1.2 挤压技术在食品生产中的发展状况1

1.1.3 挤压机生产膨化食品1

1.1.4 挤压膨化原理2

1.2 意义、目的、研究范围2

1.3 本课题在国内外的发展概况及存在的问题2

1.4 本课题研究内容5

2 单螺杆挤压机整体设计方案6

2.1挤压机的主要部件6

2.1.1挤压机的供料部件6

2.1.2螺杆6

2.1.3机筒6

2.1.4模头及模板6

2.1.5其他7

2.2挤压机的驱动装置7

2.2.1 电动机的选用7

2.2.2 传动比分配8

3 挤压机零部件设计与计算9

3.1 螺杆的设计9

3.1.1 螺杆的结构9

3.1.2 螺杆各部分参数9

3.2 机筒结构设计12

3.3 带轮结构设计与计算12

4 螺杆和机筒强度计算及配合要求16

4.1 螺杆强度计算16

4.1.1 螺杆材料选取16

4.1.2 螺杆校核计算16

4.2 机筒强度校核18

5 轴承布置与校核计算20

5.1 径向轴承20

5.2 推力轴承21

5.3 键的强度校核21

5.4 螺杆的生产能力计算22

6 加料系统设计23

6.1 螺旋直径和转速的确定23

6.2 螺旋主要结构参数确定23

6.3 电机选用24

6.4 润滑油的选用24

6.4.1 齿轮传动的润滑24

6.4.2 滚动轴承的润滑25

7 挤压机操作系统24

7.1 安装24

7.1.1 挤压机的安装基础24

7.1.2 调整挤压机水平24

7.1.3 机筒的安装24

7.1.4 螺杆的装拆24

7.1.5 模头的安装24

7.2 挤压加工系统的操作与维护26

7.2.1 开车前的准备工作26

7.2.2 开车操作26

7.2.3 运转中的检查27

7.2.4 停机27

7.2.5 维护保养27

8 总结与展望29

8.1 总结29

8.2 展望29

致谢30

参考文献31

1 绪论

1.1 挤压技术介绍

1.1.1 挤压技术在食品生产中的应用

本世纪30年代，挤压技术开始应用于食品加工，它具有集输送，混炼，剪切，加热，加压等多种化工单元操作于一体的高温短时加工的特点，因此在食品加工领域的应用范围越来越广泛。除了谷物及植物组织蛋白挤压食品以外，从糖果制造到酪蛋白生产，从固体脂肪到风味成分的开发，及至饲料宠物食品加工制造都用到食品挤压机。

螺杆挤压机能将一系列的化工基本单元过程集中在挤压机中进行，螺杆挤出已连续生产代替间歇生产，必然有较高的生产率和较低的能耗，也已实现自动化，同时螺杆的搅拌作用业提高了混合质量这些因数加在一起，避让降低生产成本。挤压加工技术作为一种经济实用的新型加工方法广泛应用于食品生产中，并得到迅速的发展。加工谷物食品的工艺一般须经粉碎、混合、成型、烘烤或油炸、杀菌干燥等生产工序，每道工序都要有不同的设备，较长的生产线，较大的占地面积，高强度的劳动力，所需设备较多。通过挤压技术对谷物食品进行加工，初步混合原料后，就可用一台挤压机完成混合、熟化、粉碎、杀菌、余干燥、成型等工艺，制成膨化、组织化产品或制成不膨化食品，这些产品在再经油炸或微波、烘干、调味后即可上世，只要简单根据更换挤压磨具，并可以很方便的改变产品的造型。相对于传统工艺，挤压加工改变了谷物食品的加工工艺，大大减短了加工工艺过程，丰富了谷物样式，减低了产品的生产成本，减少了设备的占地面积，降低了生产劳动强度，同时改变了产品的形态和味道，使得产品质量得到了提高。

1.1.2 挤压技术在食品生产中的发展状况

上世纪30年代，人们首次把挤压机用于方便食品谷物的生产中;到四十年代末期挤压机的应用在食品领域进一步扩大;50年代初的蒸煮挤压机已经基本上取代了当时的饼干赔烤60年代至今挤压机的技术以及理论得到了飞速发展，对挤压机的结构设计、工艺参数、挤压过程机理进行研究，通过对挤压机理的探讨，进一步研究各种谷物以及蛋白类食物在挤压过程中发生的一系列变化，以及挤压食品的营养与吸收问题;现阶段随着控制技术的发展、新材料的发现与应用挤压技术得到更大的发展，生产能力越来越大，通过对挤压过程的精确控制，生产出的产品愈加符合人们的期望。

采用挤压技术加工食品在我国已有悠久的历史，但直到70年代还停留在爆米花的手工业状态．从70年代中期开始，尤其是近十几年来，我国用挤压方法生产食品得到了很大的发展，随着任命生活水平的提高以及饮食结构的变化，挤压食品的品种和产量日益增多。

1.1.3 挤压机生产膨化食品

本世纪30年代，挤压技术开始应用于高温短时食品加工，它具有集输送，混炼，剪切，加热，加压等多种化工单元操作于一体的特点，因此范围越来越广泛地运用于食品加工领域。食品挤压机可以加工谷物和植物组织蛋白挤压食品，可以进行糖果制造到奶酪蛋白生产，可以进行固体脂肪到风味成分的开发，以及宠物饲料食品加工。

现在国内外的各大生产膨化食品的公司企业一般都是用挤压法生产膨化食品，挤压加工概括的说是将食品物料置于挤压机的高压和适当的温度的状态下，然后突然释放到常压，使物料和各种调味料、香料达到充分渗透、混合和输出的过程。所以用蒸煮挤压法生产可以取得更好的混合效果，原料利用率高，营养损失小，生产出的膨化食品口感，香味的持久力都比传统的加工方法好。

总的来说，用挤压法生产膨化食品是现今的发展趋势。

1.1.4 挤压膨化原理

物料中含有一定的水分,物料在挤压机套筒内受到螺杆的推动作用和卸料模具或套筒内节流装置的反向阻滞作用以及加热作用。使得物料处于高达3~ 8MPa 的高压和200 e 左右的高温状态之下。压力超过了挤压温度下的饱和蒸汽压, 使得挤出机套筒内物料中的水分不会沸腾蒸发, 物料呈现出熔融状态。一旦物料从模头挤出, 压力将骤降为常压, 物料中水分瞬间蒸发, 温度降至80e左右, 从而使物料变成多孔结构形状的膨胀食品。

1.2 意义、目的、研究范围

食品挤压技术具有加工范围广、生产效率高、产品质量好、加工过程无污染等特点。单螺杆挤压机的结构简单、易加工制造、成本低廉，广泛用于加工各种膨化小吃食品。本课题的任务是设计一台高转速、高剪切率的单螺杆挤压机，其外部无外加热装置，而是利用高剪切率产生的摩擦热来加热熔融原料并使食品原料得到蒸煮熟化，从而生产出松脆可口的膨化谷物食品。

1.3 本课题在国内外的发展概况及存在的问题

直接膨化休闲食品是一类消费非常广泛的食品，它们是由所使用的挤压机类型特点而被称为玉米果，现在这类食品已被称为直接膨化食品，通常，直接膨化的食品在高剪切蒸煮积压机上生产的，此类产品是由于产品从挤压机模板处出来产生直接膨化而得名的，并且除了干燥外不需要进一步的加工处理。一些直接膨化的休闲食品的典型代表的玉米卷（焙烤的或油炸的）、洋葱圈、马铃薯条和近来的立体休闲食品。

直接膨化休闲食品的膨化过程是由加热物料使温度超过100摄氏度而产生的，在挤压机内面团中的水分由于面团是处于压力之下故呈液态，然后当面团从模板孔中挤出挤压机时，过热的水分突然处于常压下，压力迅速的降低，水分蒸发成水蒸汽，产生伸张的和膨胀是淀粉基质赋予了这种产品一种低是密度和轻的质地，整体密度降到50~160g/L范围内。这类产品的形状和大小是由模板设计、挤压物的粘弹性以及切割方式决定的，用于生产着类产品的设备可以是简单的夹套式挤压机到双螺杆挤压机。夹套式挤压机用于生产诸如玉米卷和大米膨化物等产品，若对配料要求高和生产率高，则应使用较复杂的单螺杆和双螺杆挤压机。生产率一般为：夹套式挤压机50~200kg/h,有较长套筒的单螺杆挤压机100~600kg/h，双螺杆挤压机150~1000kg/h。

挤压技术作为食品工业中得一项重要技术并得到更大的发展。它能将食品原料直接挤压成型得到我们需要的产品。现代食品工业用的螺杆挤压机集混合、融和、蒸煮、改性反应、调质、组织化、成型、膨化等多种功能于一身，体现出有利于自动控制、便于灵活转产以及节能、节劳力、节省生产场地等优点。同时，挤压技术生产婴儿食品、制品的性状发生改变，产品的速溶性、冲调性提高，产品极易消化，且提高了氨基酸的含量。

目前挤压技术还可以生产膨化小食品及夹心食品汤料、面包干、人造蛋白肉等。本设计就是生产挤压膨化食品。

物料经过挤压后又如下特点：

（1）成分损失少，有利于人体的吸收。

（2）用途广。

（3）生产率高，从进料到成品仅需20-40s。

（4）成本低。

（5）维护方便。

基于以上几点，挤压技术可以为现代生产提供巨大的支持。

随着食品工业的迅速发展，螺杆挤压机被广泛的应用于食品加工当中，特别是单螺杆挤压机在各方面都取得了长足的发展。现在单螺杆挤压机朝着高效能、高速、自动化和辅助配套连续生产方向发展。在螺杆设计方面，除增大螺杆的直径，螺杆的长径比，也研制了各种新型高效的螺杆，同时采用了计算机设计螺杆，并对自动控制提出了要求，使得产品的质量更加稳定，生产产品的水平更上一层楼。

多段组件螺杆的单螺杆挤压机，是由Wenger公司（1964年）创新设计和研制开发的成功机型。螺杆采用若干个可拆卸的单个组件，个个螺杆组件彼此连接安装在转轴上，转轴通过联轴套管与传动齿轮箱装配。第一段称为定量供料螺杆，它将原料进行混合挤压，将其运送至下一区段的螺杆组件，在中间区段的螺杆，其节距变得更短，产生更大的混合作用和挤压作用，接着物料被混合并运送到的三区段产生更大的剪切作用。随着剪切力和压力的增大，产生揉合作用，挤压料转变成为塑性物质。接着物料被推送到第四区段，该区的物料将受到更加大的剪切作用和发热，继而物料的温度升高和熟化。

在一定的产量条件下，单螺杆挤压机比双螺杆挤压机便宜1.5-2.5倍，因为结构比较简单，但是对一个挤压机系统来讲，它要对物料进行干燥等一些额外的要求，也会增加产品的成本。

进行综合的比较，对能耗进行分析，由于单螺杆挤压机广泛的采用蒸汽或电加热以及用水来调节以提供蒸煮加工所需的热量，所需热能由机械能提供的将减少。在双螺杆挤压过程中，较多的热量是由输入的机械能提供的，其他的一些热量则是由夹套传递过来的。相对来说单螺杆索要的热量消耗要经济一些。单摞杆挤出物的水分很高，相关的能耗使蒸煮的能耗得到补偿。，所以总的能耗并不是很低。另外干燥机的效率只有40%，相比之下，双螺杆挤压机的优点就是它有很多的能力来处理低水分的物料。除了低水分挤压会导致配料的过度破坏和产品的负影响外他们两者的能耗差别不是太大。

总的而言，单螺杆挤压机有它不足之处，但是它也有不可替代的优点。主要是单螺杆挤压机结构简单，制造成本低，加工的产品为各种膨化食品、速溶谷物粉、锅巴类小食品，苏释方便米粥。还有就是其操作维修方便。设备在使用一段时间后，可以更换易损件。

从结构上来看，单螺杆挤压机比双螺杆挤压机简单，操作上的限制也少。双螺杆挤压机的齿轮传动相对复杂，两根轴必须同向旋转，两轴之间狭窄的空间给设计带来很大的困难，特别是推力轴承的放置就有很大的问题。而且，双螺杆的扭力、压力和比单螺杆挤压机小的止推力限制，过度的负担将导致过度的损坏而增加维修费用。

由于单、双螺杆的不同特点，他们在食品加工中各自起着他们的作用。例如，在宠物食品的蒸煮和成型加工中，单螺杆挤压机是经济而有效的方法。在需要良好的控制以及操作灵活的蒸煮反应时，选择双螺杆挤压机会更合适。物料在单螺杆挤压机中向前输送的原理与双螺杆挤压机的有些不同。在双螺杆挤压机中，根据螺杆的旋转方向，啮合程度和螺纹参数的不同，双螺杆可以分为同向旋转和异乡旋转、啮合与非啮合等多种类型。目前发展的主流类型是同向旋转、完全啮合梯形螺纹的双螺杆挤压机。在双螺杆挤压机中，；螺杆和机筒之间扭曲了近于闭合的C形空间，由喂料机构进入的物料充满这个空间并被流畅的推送向前，当物料的体积与空隙的体积相等时，继续送入的物料将会产生压力，表面看来这是与单螺杆挤压机一样，具备了物料和螺杆共转的条件。但是，对于双螺杆挤压机而言，在C形开口出总有另一螺杆的螺旋齿齿板旋转着，即一根螺杆的螺旋齿板对另一根螺杆C形空间中的物料起着挡板的作用。因此物料不会和螺杆一起共转，机筒内部就可以做成光滑的表面，可避免不必要的摩擦，降低运转所需要的能量，同时还可以把螺杆和机筒的间隙做小，减少物料沿缝隙逆向的漏流，机对高水分、高油分的食品原料也不易发生逆流和漏流。提高承载压力的范围，甚至还可以进行更高温度的处理。

在单螺杆挤压机中，物料基本上紧密围绕在螺杆周围，形成螺旋状的连续带状物料。因此，根据螺杆螺母相似的关系，在物料与螺杆的摩擦力大于机筒与物料的摩擦力时，物料将和螺杆一起旋转，这就不可能实现物料的输送。在模头附近高压或高湿的情况下，返压力易使物料逆流，物料的水分、油分越高，这种趋势就越显著。因此，单螺杆挤压机为了解决或避免这些问题会在螺杆采取一些措施。比如增加螺杆的头数，就是螺杆旋转一周对物料的作用次数。头数越多，螺杆对物料的推动能力越强。多头的螺杆适用于粘性较高的物料。不过随着头数的增多，螺杆和机筒之间的空间就会更少，物料输送的绝对量也就降低了。所以没有必要从进料口到模头的螺旋头数都保持一致，可以选择各种螺杆的放置形式以适应各个区段的物料的变化情况。

为避免物料跟随螺杆一起旋转，可以采用一些方法。在物料上就是降低物料的水分和油分，减少物料与机筒的的润滑作用。同时，应将物料的分布控制在某个范围之内，即当物料充满螺杆与机筒的空间时，应使后继物料的传输比例降低，物料各粒子得以分散，从而降低物料在螺杆之间的紧密程度。实际上，食品物料一般多是不定型，不均匀，高水分，高油分，多成分的物料，因此，还没有成熟的方法解决这些难题。不过如果采用自动化控制，会在一定程度上解决问题。单螺杆挤压机和双螺杆挤压机的不同之处见表1.1。

表1.1 单、双螺杆挤压机的比较

机型

项目单螺杆挤压机双螺杆挤压机

物料移动方式摩擦滑移具有一定的正向输送

加工能力受物料成分的限制在一定范围内不受限制

物料允许水分10％～30％（最大40％）5％～95％

物料的热分布不均匀均匀

剪切力强弱

逆流产生程度高低

续表1.1

加工产品种类少多

耐久性大比单螺杆稍差

本课题中的单螺杆食品挤压机，能有效而稳定的长期工作，既能保证食品质量，减少对原材料的浪费，又能增加产量，提高劳动生产率，降低食品成本。应用这种食品挤压成型机，减少了人身与食品物料的直接接触和病菌传播机会。这种成型机具有结构简单，操作容易，清洗维修方便等特点，适合于在餐厅以及各个超市使用单螺杆挤压机优于双螺杆挤压机最主要的一点是其结构简单，价格便宜，因此在食品工业领域有着广泛地应用，只有当单螺杆挤压机在生产中不能得到完全令人满意的效果时才改用双螺杆挤压机。螺杆挤压机在膨化食品挤压应用广泛。目前，美国、日本及西欧等国家对挤压膨化的理论研究越来越完善，应用领域越来越广阔，各种各样的挤压食品遍步超市货架。美国生产的大型挤压膨化机生产能力已达每小时几吨至十几吨，有关挤压膨化和设备的专利已达百余项，挤压产品遍及世界各地，由于食品工业日新月异的发展，挤压设备的不断改进，挤压理论的不断完善，挤压食品在消费者中的地位也越来越重要。

1.4 本课题研究内容

在单螺杆挤压机中，大部分能量在机筒上传导。这些能量既有通过机筒外热的传导，也有由于螺杆本身的剪切作用所产生的机械能。其中机械能的大小是由螺杆转速和螺杆结构所决定的，这是因为剪切率与螺杆转速成正比，而对于一台确定的挤压机，螺杆结构一般是预先确定的，修改的可能性很小。对于大型单螺杆挤压机，热交换及其输送产量和压力的增加都将变得更加困难，因为挤压机的尺寸越大，物料的表面积与体积之比就越小。

本设计名为自热式单螺杆挤压机，即是用螺杆本身的剪切作用所产生的机械能而产生的热量来加热物料，而不需要在外部通过加热装置进行预热物料处理。

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内容简介：: 编号无锡太湖学院毕业设计（论文）相关资料题目：高剪切式单螺杆挤压机设计信机系机械工程及自动化专业学号： 0923202学生姓名：沈川指导教师：戴宁（职称：副教授） 2013年5月25日目录一、毕业设计（论文）开题报告二、毕业设计（论文）外文资料翻译及原文三、学生“毕业论文（论文）计划、进度、检查及落实表”四、实习鉴定表无锡太湖学院毕业设计（论文）开题报告题目：高剪切式单螺杆挤压机设计信机系机械工程及自动化专业学号： 0923202 学生姓名：沈川指导教师：戴宁（职称：副教授） 2012年11月25日课题来源自拟题目科学依据（包括课题的科学意义；国内外研究概况、水平和发展趋势；应用前景等）（1）课题科学意义挤压机是挤压加工技术的关键. 挤压加工技术作为一种经济实用的新型加工方法广泛应用于食品生产中, 并得到迅速发展. 挤压加工主要由一台挤压机一步完成原料的混炼、熟化、破碎、杀菌、预干燥、成型等工艺, 制成膨化、组织化产品或制成不膨化的产品. 只要简单地更换挤压模具, 便可以很方便地改变产品的造型。（2）挤压机的研究状况及其发展前景. 近十年来，挤压机行业发展迅速，CAD/CAM的电脑软件应用，数控切割机，电火花机床，加工中心等电脑控制机床的运用普遍运用于挤压模具的制造，极大满足了挤压制品的复杂程度，表面质量，尺寸精度。同时，用于冷挤和热挤的工具材料越来越多，满足了挤压工具的多样性选择。材料的热处理也越来越规范，提高了挤压工具的使用寿命。连续挤压因其连续性、投资小，见效快的优点广泛被小型企业采用。连续挤压主要运用在铝及铝合金挤压管材，简单界面的挤压制品生产。挤压技术作为食品工业中得一项重要技术并得到更大的发展。它能将食品原料直接挤压成型得到我们需要的产品。现代食品工业用的螺杆挤压机集混合、融和、蒸煮、改性反应、调质、组织化、成型、膨化等多种功能于一身，体现出有利于自动控制、便于灵活转产以及节能、节劳力、节省生产场地等优点。同时，挤压技术生产婴儿食品、制品的性状发生改变，产品的速溶性、冲调性提高，产品极易消化，且提高了氨基酸的含量。研究内容高剪切式单螺杆挤压机在食品工业中的应用及工作原理高剪切式单螺杆挤压机的总体结构高剪切式单螺杆挤压机的主要参数计算高剪切式单螺杆挤压机的传动系统及挤压部件设计拟采取的研究方法、技术路线、实验方案及可行性分析（1）实验方案掌握高剪切式单螺杆挤压机的工作原理，通过对其结构及特点的研究了解挤压机的结构，从而进行对挤压部件的研究和设计。（2）研究方法通过学习了解挤压机的结构参数，对挤压部件的参数进行计算及确定，按照挤压机的结构进行装配图及挤压部件零件图的绘制。研究计划及预期成果研究计划：2012年10月12日-2012年12月31日：按照任务书要求查阅论文相关参考资料，完成毕业设计开题报告书。2013年1月1日-2013年1月27日：学习并翻译一篇与毕业设计相关的英文材料。2013年1月28日-2013年3月3日：毕业实习。2013年3月4日-2013年3月17日：单螺杆挤压机的主要参数计算与确定。2013年3月18日-2013年4月14日：高剪切式单螺杆挤压机的总体结构设计。2013年4月15日-2013年4月28日：零件图及三维画图设计。2013年4月29日-2013年5月21日：毕业论文撰写和修改工作。预期成果：了解挤压机的工作原理,内部结构以及高剪切式单螺杆挤压机的优缺点,熟练绘制挤压机的装配图,传动系统及挤压部件的零件图。特色或创新之处单螺杆挤压机在食品工业中操作更简单。高剪切式单螺杆挤压机结构简单、易操作、装拆方便。已具备的条件和尚需解决的问题设计方案思路已经非常明确，已经具备机械设计的知识。研究问题的能力尚需加强，结构设计能力尚需加强。指导教师意见指导教师签名：年月日教研室（学科组、研究所）意见教研室主任签名：年月日系意见主管领导签名：年月日英文原文Ability of a very low-cost extruder to produce instantinfant flours at a small scale in VietnamC. Mouqueta,*, B. Salvignolb, N. Van Hoanb, J. Monvoisc, S. TrechedaUR106, Nutrition, limentation Societes, IRD, BP 182, Ouagadougou 01, Burkina FasobGRET, 269 Kim Ma Street, Hanoi, Viet NamcGRET, 213 rue La Fayette, 75010 Paris, FrancedUR106, IRD, BP64501, F34 394 Montpellier cedex FranceReceived 25 July 2002; received in revised form 18 November 2002; accepted 21 November 2002Abstract Extrusion cooking is a useful process for the production of instant infant flours, as it allows gelatinisation and partial dextrinisation of starch, as well as reduction of the activity of some antinutritional factors. But existing extrusion equipment is not suited to the context of developing countries as it requires considerable financial investment and the production capacity (minimum300 kg/h) is too high. The aim of our study was to improve traditional extruders with low production capacity (about 30 kg/h) manufactured in Vietnam and to test their performance in the production of infant flours. Several blends made with rice, sesame and/or soybean have been extruded with the modified equipment that we name very low-cost extruder. In the case of blends containing soybean, starch gelatinisation was not complete, and decreased with an increase in the lipid content of the blend. The rate of trypsin inhibitor destruction evolved in a similar way. Adding water before extrusion, or extruding the blends twice was not effective in increasing the rates of starch gelatinisation or trypsin inhibitor destruction. However, the very low-cost extruder proved its ability to process the ricesesame blend that had a lipid content of less than 6 g/100 g DM, and low initial water content around 10%, wet basis (wb). In this case, extrusion led to total starch gelatinisation and the extent of starch dextrinisation, which was measured by comparing the viscosity of gruels prepared from crude and corresponding extruded blends, was sufficient to prepare gruels with substantially increased energy density. With the addition of roasted soybean flour, sugar, milk powder, vitamins and minerals, this blend could provide a nutritious instant flour usable as complementary food for infants and young children.# 2003 Elsevier Science Ltd. All rights reserved.Keywords: Extrusion cooking; Instant flour; Complementary food; Gelatinisation; Dextrinisation; Trypsin inhibitor destruction1. Introduction Extrusion cooking is one of several different processes used to produce infant flours. This particular process has many advantages that have been extensively reviewed (Bjo rck & Asp, 1983; Camire, Camire, & Krumhar, 1990; Harper & Jansen, 1985). From a nutritional point of view, extrusion cooking allows inactivation of certain antinutritional factors like trypsin inhibitor factors thus increasing protein digestibility. The high temperature generated during processing ensures satisfactory hygienic quality, and in general results in starch gelatinisation, thus leading to an instant flour. If not truly instant, the flour is at least pre-cooked, and the subsequent time required to cook the gruel is considerably reduced. During extrusion cooking, raw materials also undergo high shear, thus allowing partial starch hydrolysis (Colonna, Doublier, Melcion, De Monredon, & Mercier, 1984). The extent of hydrolysis determines the energy density at which it will be possible to prepare a gruel of semi-liquid consistency that is acceptable to infants. At a given consistency, the more important the starch is hydrolyzed, the higher the gruel energy densitywill be. In spite of these advantages, the adoption of extrusion cooking processing for the production of infant flour in developing countries is still limited. Only a few industrial units produce extruded flour at a large scale mainly in response to the need of international or non-govern- 0308-8146/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0308-8146(02)00545-9 Food Chemistry 82 (2003) 249255 /locate/foodchem *Tel.: +226-30-67-37; fax: +226-31-03-85. E-mail address: claire.mouquetird.bf (C. Mouquet). mental organisations for emergency supplies. The main reason for this is that most extruders are designed for large-scale production, thus requiring very high investment and technical knowledge. Even the so-called low-cost extruders, or dry extruders that were developed for the production of complementary foods at the beginning of the 1980s by the university of Colorado (Harper, 1995; Harper & Jansen, 1985; Said, 2000), are too costly and their production capacity is too high (about 55,000 dollars for a machine with a production capacity of 1 ton per hour), and are thus not affordable for developing countries. The development of a small simple machine, with a small production capacity (about 30 kg/h) is therefore of great potential interest. The Vietnamese context is particularly well suited for the development of the production of infant flour by extrusion cooking for several reasons. 1. In rural areas and particularly in the plains, mothers prepare a thermos of boiled hot water each morning in order to have a supply of safe drinking water available during the day, and this water could easily be used for the preparation of a gruel with an instant flour 2. A rudimentary extrusion cooking process has been used for many years in the countryside; simple extruders with very small production capacity already exist and are used for the production of snacks or cassava noodles sold in the street. These machines were probably originally designed in the United States at the end of the nineteenth century for the extrusion of plastic. 3. These small extruders are now manufactured locally in small mechanical workshops, and it is also easy and cheap to construct spare parts locally for the maintenance of the machines. Occasional attempts have been made to produce instant infant flours using these rudimentary localextruders but these efforts have not continued, firstly because their impact on nutritional quality of infant flours was not satisfactory, and secondly because the machines were not sturdy and often broke down during production. Taking the features of this specific context into account, we modified the rudimentary type of local extruder to improve their ability to produce infant flour, as well as their sturdiness. These improved extruders with limited production capacity were named very low-cost extruders in reference to the low-cost extruders that Harper and Jansen already developed for the production of nutritious precooked foods for developing countries (Harper &Jansen,1985). The objective of this study was to test the performance of these improved very low-cost extruders and, in particular, to evaluate the instant character of the flour, the extent of starch dextrinisation and the residual trypsin inhibitor activity of extruded blends.2. Materials and methods 2.1. Extrusion cooking equipment The very low-cost extruder we used is a simple single- screw autogenous extruder manufactured in Vietnam by a small enterprise named Mechanical Workshop no. 14700, (Phan Chu Trinh Street, Da nang City) according plans that we furnished (see photo in Fig. 1). The drive motor has a power of 10.5 kW. The barrel length is 200 mm with a length/diameter ratio of 5 and has a central cylindrical die of 5 mm in diameter and 9 mm in length. The rotating speed of the screw is high (500 rpm), thus allowing high shear. The design of the screw was modified (constant pitch and gradual decrease in the flight depth), to allow a progressive increase in friction forces and consequently in the temperature inside the barrel. The screw diameter is 40 mm and the root diameter increases gradually from 33 to 38 mm (see photo in Fig. 2) The extruder barrel wall has reverse helical grooves to enhance forward conveyance of the product. To ensure a regular feeding rate, the extruder is equipped with a motorised feeding screw that allows feeding rates from 5 to 39 kg/h. Residence time is between 4 and 20 s, which is very short in comparison to other extruders but longer than the residence time observed in rudimentary Vietnamese extruders.2.2. Raw materials The raw materials used to prepare composite flours were the cheapest and the most easily available on the Vietnamese market. The basic cereal was polished rice. Soybean and sesame were added to increase lipid and protein contents. All raw materials were bought locally. Soybean was dried in an oven to reach a dry matter content above 92%, wet basis (wb), before being dehulled in an abrasive disk huller equipped with a cyclone to remove hulls and straws. After dehulling, the abrasive disks were brought closer and the soybean passed a second time in the machine to be roughly ground to a size of about 2 mm. Different infant flour formulas (flours A, B, C and D) were calculated to achieve the minimum protein and lipid contents of respectively, 12 and 8 g/100 g DM required for complementary foods, after addition of a premix to the extruded blends (Table 1). The premixC. Mouquet et al. / Food Chemistry 82 (2003) 249255Fig. 1. The very low-cost extrusion-cooker used for experiments (designed and manufactured in Vietnam). 1. Feeding hopper; 2. screw and barrel;3. central cylindrical die; 4. control panel (amperage, temperature, feeding screw On/Off, extruder On/Off); 5. feeding screw speed variator.Fig. 2. Main spare parts of the very low-cost extrusion-cooker. 1. Barrel; 2. screw with gradual decrease in the flight depth and constant pitch; 3. cylindrical die of 5 mm in diameter and 9 mm in length.Table 1Formulas and calculated protein and lipid contents of final composite floursComposition (g/100 g dry matter) Nutrient content of final flour (g/100 g DM) Ingredients blended Ingredients added Lipid Protein before extrusion after extrusion Rice Soybean Sesame Roasted soybean Premix Flour A 49.9 21.7 5.7 0.0 22.7 10.03 15.45 Flour B 50.2 27.1 0.0 0.0 22.7 8.05 16.63 Flour C 50.2 24.7 2.3 0.0 22.7 8.82 16.70 Flour D 52.4 0.0 4.9 20.0 22.7 10.12 16.33 Calculated from Souci et al. (2000).Premix prepared by blending sugar (66%), milk powder (22%), salt (4%), vitamins and minerals (7%) and vanilla aroma (1%).Total N content multiplied by 5.80, 5.30, 5.71 and 6.38 for rice, soybean, sesame and milk powder, respectively. (sugar 66%, milk powder 22%, salt 4%, aroma 1%, vitamins and minerals 7%, wt.) was added in order to meet recommendations for vitamin and mineral contents and confer suitable organoleptic characteristics to the flours. For blend D, the formula was calculated taking into account the addition of roasted soybean flour bought on the local market after extrusion to achieve requiredprotein and lipid contents. The formula calculations were made with data from food composition tables (Souci, Fachman, & Kraut, 2000). Extrusion cooking experiments were performed on rice alone and on the different blends of rice, soybean and/or sesame used for the preparation of flours A, B, C and D (Table 2). After extrusion, all extrudates were ground (particle size 500 mm) before biochemical analysis.C. Mouquet et al. / Food Chemistry 82 (2003) 249255Table 2Composition and calculated lipid and protein contents of rice and blends before extrusion Composition (g/100 g DM) Nutrient contenta (g/100 g DM) Rice Soybean Sesame Lipid Proteinb Rice 100.0 0.0 0.0 0.71 7.84 Blend A 64.5 8.1 7.4 11.18 18.25 Blend B 65.0 35.0 0.0 8.61 19.78 Blend C 65.0 32.0 3.0 9.60 19.09 Blend D 91.4 0.0 8.6 5.47 8.82 Calculated from Souci et al. (2000). Total N content multiplied by 5.80, 5.30 and 5.71 for rice, soybean and sesame, respectively.2.3. Starch gelatinisation rate Total starch content of composite flours was determined by the enzymatic method of Batey (1982). Analyses were made in duplicate and both values are given. The extent of starch gelatinisation during extrusion cooking was determined in duplicate by a method based on the evaluation of amyloglucosidase hydrolysis susceptibility (Chiang & Johnson, 1977; Kainuma, Matsunaga, Itagawa, & Kobayashi, 1981). The gelatinisation rate is the ratio of starch fraction susceptible to amyloglucosidase hydrolysis and total starch (minimum, maximum and mean values are given).2.4. Preparation of gruels Crude and extruded blend were ground and the flours obtained were used for the preparation of gruels with different dry matter contents using: 1. A cooking procedure comprising mixing flour with cold demineralised water into a slurry and cooking on a hot plate (300 C) with continuous stirring for 5 min once the mixture started to boil.2. An instant procedure comprising adding demineralised water heated to 75 C to the flourand stirring vigorously. After preparation, gruels were allowed to cool to 45 C before viscosity measurements. Dry matter contents of the gruels were determined by oven drying at 105 C to constant weight.2.5. Apparent viscosity measurements Apparent viscosity measurements were performed on gruels with a Haake viscometer VT550 with SV-DIN coaxial cylinders driven by a PC computer with the Rheowin 2.67 software. We applied the measurement procedure proposed by Mouquet and Treche (2001), i.e. shear rate of 83 s1, shear time of 10 min and measurement temperature of 45.00.5 C.2.6. Procedure used to check the instant character of extruded blends To our knowledge, the term instant, which usually describes dehydrated precooked food usable after the simple addition of hot water, is not accurately defined from a biochemical point of view. As starch becomes easier to digest when it is completely gelatinised and swollen, we chose to evaluate the instant character by comparing apparent viscosity of gruels prepared by the instant and the cooking procedures with the same dry matter content. Two scenarios can be expected: if the apparent viscosity of the gruel prepared with the instant procedure is equal or slightly higher than the viscosity of the gruel prepared with the cooking procedure, then the flour can be considered as instant. If it is lower, it implies that part of the flour starch is not totally precooked during the extrusion cooking stage and will continue to swell during the cooking of the gruel, thus leading to an increase in viscosity.2.7. Trypsin inhibitor activity Trypsin inhibitor activity (TIA) was determined induplicate by the method of Kakade, Rackis, MacGhee, and Puski (1974), modified by Smith, Van Megen, Twaalfhoven, and Hitchcock (1980), and both values, expressed in trypsin inhibitor units (TIU) per 100 g DM, are given. The percentage of trypsin inhibitor destroyed during extrusion cooking were calculated from the ratio between TIA before and after extrusion, and mean, minimum and maximum values are given.3. Results and discussion3.1. Effect of very low-cost extruder on starch gelatinisation rate The main characteristics of the different extruded blends are given in Table 3. In all cases, we observed an increase in dry matter content after extrusion cooking. This increase is due to water loss by instant vaporisation at the exit of the die. For extruded rice and blend D only, the gelatinisation rate exceeded 90%, from which we estimated that gelatinisation rate had reached a satisfactory level. For extruded blends A, B and C, the gelatinisation rate after extrusion cooking ranged from 56 to 83%. The remaining native and, thus, non-digestible starch content was non negligible, and we consequently considered that the corresponding flours could not be used as instant flours, even though they appeared to be precooked.C. Mouquet et al. / Food Chemistry 82 (2003) 249255Table 3Effects of processing with the very low-cost extruder on the starch gelatinisation rate and the trypsin inhibitor activity of rice and different blendsBlend used for Dry matter Total starch Gelatinised Gelatinisation Trypsin inhibitor activity TI destroyed TIdestroyed (%) extrusion cooking content content starch content rate(%)c (g/100g, wb) (g/100g DM) (g/100g DM) TIU/g DM TIU/g DM of soybean Rice Before ECa 86.0 91.993.9 10.811.5 12 (1112) eRice After EC 90.5 85.087.8 93 (9196)A Before EC 88.9 55.557.3 9.410.9 18 (1620) 12,21312,246 44,25044,490eA After EC 90.4 30.333.3 57 (5360) 57666091 20,89022,066 52 (5053)B Before EC 90.1 61.265.9 10.612.7 18 (1621) 13,51813,900 37,65538,719eB After EC 95.5 51.153.8 83 (7887) 31403491 95489924 76 (7478)C Before EC 90.6 56.358.5 10.511.3 19 (1820) 13,39413,774 40,83641,994eC After EC 95.4 44.046.6 79 (7583) 23802574 67778327 82 (8183)eC After EC 89.9 35.639.0 65 (6169) 60416625 18,41820,198 53 (5156)eC After EC 92.0 45.846.0 80 (7882) 19722112 60146438 85 (8486)eC After EC 90.8 44.344.4 77 (7679) 21672292 66086990 84 (8384)D Before EC 88.7 84.486.3 19.321.7 24 (2325) eD After EC 92.7 82.384.9 98 (95100) wb, wet basis; DM, dry matter; TIU, trypsin inhibitor units; TI, trypsin inhibitor; EC, extrusion cooking; eRice, extruded rice; eA, extruded blend A,. . .Analyses were made in duplicate and both values are given. For ratios, mean values calculated from analyses results are given (minimum and maximum values in parentheses). eCa, the blend C was added with water (10ml/100g) before extrusion cooking, lowering the initial dry matter content of the blend to 81.8 g/100 g DM. eCb, the blend B was extruded a first time, then sesame and water (10 ml/100 g, wb) were added and the blend extruded a second time. eCc, the blend C was extruded twice, with addition of water (15 ml/100 g, wb) between the two treatments. To check this, the apparent viscosity of gruels prepared at different concentrations with the flours obtained from extruded blends according to the two different procedures (instant and cooking) were compared. The viscous behaviour of gruels prepared with the flour of the crude blend was also determined. Results obtained with rice, and with blends A and D are presented in Fig. 3. The curves of apparent viscosity of gruels obtained with the flour of the extruded blend D (Fig. 3c) were almost superimposed for the two gruel preparation procedures indicating that this procedure had no major effect on its consistency. This confirms that flour D can be sold and used as instant flour. However, in the case of the flour of the extruded blend A (Fig. 3b), the viscositycurve of gruels prepared by the instant procedure was very far from those of gruels prepared by boiling for 5 min, indicating that a starch fraction that had not gelatinised during the extrusion cooking treatment, gelatinised and swelled during gruel preparation, leading to a much more viscous gruel at the same concentration. The viscous behaviour of those gruels was very close to that of gruels prepared with the corresponding flour of crude blend and we concluded that the extrusion cooking treatment had had very little effect on starch in this case. In the case of the extruded rice flour (Fig. 3a) surprisingly, gruels cooked by boiling for 5 min were thinner at the same concentration, than those prepared by the addition of hot water. This can be explained by a partial solubilisation of swollen granules of starch during the cooking of the gruel that resulted in reduced viscosity. Thus, while extruded rice or blend D resulted in flours that can be considered instant, the persistence of a non gelatinised fraction of starch in blend A after extrusion cooking led us to conclude that the processing with very low-cost extruders was not appropriate for this blend.3.2. Effect of very low-cost extruder on starch dextrinisation The results presented in Fig. 3 can also be used to evaluate the intensity of starch dextrinisation during the extrusion cooking process. Partial starch dextrinisation is desirable because it reduces swelling during gruel preparation, thus allowing an appropriate semi-fluid consistency to be maintained at a higher concentration, i.e. higher energy density. To achieve this, we measured the gain in dry matter content between gruels prepared at the same apparent viscosity with crude flours according to the cooking procedure and with flours of extruded blends according to the instant procedure when starch gelatinisation was complete (extruded rice and blend D), or according to the cooking procedure when starch gelatinisation was only partial (extruded blend A). At the apparent viscosity value of 1.5 Pa.s, which corresponds to a thick but spoonable gruel(Mouquet & Treche, 2001), the increases in dry matter content of gruels due to the extrusion cooking treatment for rice and blend D were 5.7 and 4.3 g/100 g of gruel, respectively (Fig. 3a and c). This increase was limited to 1.2 g/100 g of gruel for extruded blend A, demonstrat-ing once again the less drastic effect of the extrusion cooking treatment (Fig. 3b).C. Mouquet et al. / Food Chemistry 82 (2003) 249255Fig. 3. Effect of the concentration on the apparent viscosity of gruels prepared with rice and experimental blends according to different procedures. + Crude flour, boiling 5 min; extruded flour, addition of water at 75 C; extruded flour, boiling 5 min.Fig. 4. Influence of the initial lipid content of the blend on the percentages of trypsin inhibitor destruction and starch gelatinisation during processing in very low-cost extruder (mean, minimum and maximum values).3.3. Effect of very low-cost extruder on the reduction of trypsin inhibitor activity The TIA of crude grains of soybean bought on the local market is very high, about 40,000 TIU/g DM of soybean (Table 3). After extrusion cooking, we observed a reduction in TIA that took place in a similar way to the gelatinisation rate as a function of the composition of the blend (Fig. 4). The lipid content of the blends seemed to be one of the main factors affecting the severity of the extrusion cooking treatment. It is indeed well known that lipids, by lubricating the screw and the internal surface of the barrel, decrease friction forces and thus reduce the maximum temperature inside the extruder. In our experiments, until it reached 6 g/100 g DM, the lipid content of the blends appeared to have no effect on starch gelatinisation. Beyond this value, the starch gelatinisation rate started to decrease, resulting in reduced efficiency of the extrusion cooking treatment. We also observed a simultaneous decrease in trypsin inhibitor destruction rates, as lipid content increased. These results are consistent with the threshold value of 7 g/100 g DM previously mentioned for lipid content under which it becomes difficult to transform mechanical energy into heat with a single-screw extruder and without steam injection (Huber, 2000). To increase the efficiency of the extrusion cooking process, we tried several combinations of treatment: 1. We increased the initial water content of blend C (trial Ca) from 9.5 to 18.2 by water spraying to favour starch gelatinisation assuming that the gelatinisation temperature decreases with increasing initial water content of the blend (Lelievre, 1973), 2. We attempted to amplify the effects of extrusion cooking by repeating the treatment: in trial Cb, we first extruded blend B (rice and soybean) and then added sesame to obtain blend C for the second extrusion. In trial Cc, we twice extruded the complete blend C (rice, soybean and sesame). We had to add water to the blends between the two extrusion cooking treatments, because after the first extrusion cooking treatment, the dry matter content was more than 95%, and there was a risk of damage to the extruder. The quantity of water added was calculated to reachan initial dry matter content of about 90%, close to the values of initial blends. The effects of these combined or modified treatments on starch gelatinisation and trypsin inhibitor destruction rates are given in Table 3. The results of trial Ca show that the addition of water to the initial blend had a strong negative effect on the efficiency of the extrusion cooking treatment probably due to a marked decrease in the maximum temperature reached inside the barrel (maximum temperature measuredon the external side of the barrel near the die was 156 C without water addition, and decreased to 108 C when water was added before extrusion). The percentages of gelatinised starch and destroyed trypsin inhibitor fell from 79 and 82% respectively, without the addition of water, to 65 and 53%. The very low-cost extruder is not equipped with a steam injection system to balance the reduction of the friction forces due to the smoothing effect of the water. For trials Cb and Cc,the second extrusion cooking treatment had no beneficial effects on the gelatinisation rate and allowed an increase of only a few percent in the trypsin inhibitor destruction rate, which was not sufficient to justify performing the second extrusion cooking operation in commercial production.4. Conclusion The results of our experiments showed that the kind of very low-cost extruders with a small production capacity that we improved in Vietnam is suitable to process blends with low water content (around 10%, wb) and low lipid content (below 6%, db). In these conditions, the ricesesame blend extruded with this equipment resulted in total starch gelatinisation, which is required if the flour is to be sold as instant flour. Starch was also partially dextrinised during the treatment, thus allowing the preparation of gruels of higher energy density. After extrusion, the addition of roasted soybean flour and premix allowed the appropriate macro and micronutrient balance required for a complete infant flour to be achieved.ReferencesBatey, I. L. (1982). Starch analysis using thermostable a-amylase. Starch, 4, 125128.Bjo rck, I., & Asp, N. (1983). The effects of extrusion cooking on nutritional valuea literature review. Journal of Food Engineering, 2, 281308.Camire, M., Camire, A., & Krumhar, K. (1990). Chemical and nutritional changes in foods during extrusion. Critical Reviews in Food Science and Nutrition, 29(1), 3556.Chiang, C. J., & Johnson, J. A. (1977). Measurement of total and gelatinized starch by glucoamylase and o-toluidine reagent. Cereal Chemistry, 54(3), 429435.Colonna, P., Doublier, J. L., Melcion, J. P., De Monredon, F., & Mercier, C. (1984). Extrusion cooking and drum drying of wheat starch. I. Physical and macromolecular modifications. Cereal Chemistry, 61(6), 538544.Harper, J. (1995). Low-cost extrusion: possibilities for Africa. The South-African Journal of Food Science and Nutrition, 7, 142147.Harper, J., & Jansen, G. (1985). Production of nutritious precooked foods in developing countries by low-cost extrusion technology. Food Reviews International, 1(1), 2797.Huber, G. R. (2000). Twin-screw extruders. In M. N. Riaz (Ed.), Extruders in food applications (pp. 81114). Texas: Technomic publishing Co.Kainuma, K., Matsunaga, F., Itagawa, M., & Kobayashi, S. (1981). New enzyme system b-amylasepullulanase to determine the degree of gelatinization and retrogradation of starch or starch products. Journal of Japanese Society on Starch Science, 28(4), 235240.Kakade, M. L., Rackis, J. J., MacGhee, J. E., & Puski, G. (1974). Determination of trypsin inhibitor activity of soy products: a collaborative analysis of an improved procedure. Cereal Chemistry, 51, 376382.Lelievre, J. (1973). Starch gelatinization. Journal of Applied Polymer Science, 18, 293296.Mouquet, C., & Treche, S. (2001). Viscosity of gruels for infants: a comparison of measurement procedures. International Journal of Food Sciences and Nutrition, 52, 389400.Said, N. W. (2000). Dry extruders. In M. N. Riaz (Ed.), Extruders in food applications (pp. 5162). Texas: Technomic publishing Co.Smith, C., Van-Megen, W., Twaalfhoven, L., & Hitchcock, C. (1980). The determination of trypsin inhibitor levels in foodstuffs. Journal of the Science of Food and Agriculture, 31, 341350.Souci, S., Fachman, W., & Kraut, H. (2000). Food composition and nutrition tables (6th ed). London: Medpharm Scientific Publisher &CRC Press.中文译文越南小规模婴儿粉“低成本挤压机”的生产效能C. Mouqueta,*, B. Salvignolb, N. Van Hoanb, J. Monvoisc, S. TrechedaUR106, Nutrition, limentation Societes, IRD, BP 182, Ouagadougou 01, Burkina FasobGRET, 269 Kim Ma Street, Hanoi, VietNamcGRET, 213 rue La Fayette, 75010 Paris, FrancedUR106, IRD, BP64501, F34 394 Montpellier cedex France2002年7月25日：初稿 2002年11月8日：校稿 2002年11月21日：发布摘要挤压蒸煮是一种生产即时婴儿米粉有效的方法，因为它可使淀粉糊化和部分糊精化，并且使一些抗营养因子的活性降低。但是，现有的挤出设备不适合于发展中国家，因为它需要大量的财政投资，并且生产能力（最小范围内300公斤/小时）过高。我们研究的目的在于改善越南传统挤出机生产能力低（约30公斤/小时）的问题，以及测试其在生产婴儿粉时的效能。我们把这种可以混合大米、芝麻和/或大豆挤压的设备叫做“低成本挤压机”。在混合物中含大豆的情况下，淀粉不能完全糊化，并且糊化程度还随着混合物中脂肪含量的增加而减少。胰蛋酶抑制剂的破坏率以类似的方式发展。挤压前加入水，或挤压两次不能有效的提高淀粉的糊化率或胰蛋白酶抑制剂的破坏率。然而，事实证明“低成本挤压机”能够处理低初始含水量10左右，湿基（wb），脂肪含量少于6g/100gDM。在这种情况下，挤压会导致淀粉的整体糊化和淀粉的糊精化程度加深。通过测量挤压前准备稀糊化混合物与挤压后混合物的粘滞度的对比，就可以知道稀糊化所需要的能量密度。随着烤熟的大豆粉、奶粉、维生素以及矿物质的加入，这种混合物所含有的营养可以在婴幼儿辅助食品中使用。 #2003 Elsevier科学有限公司保留所有权利。关键词：挤压蒸煮，即时面粉;补充食品，糊化;糊精化;胰蛋白酶抑制破坏剂。1 引言挤压蒸煮是婴儿米粉生产的几个不同过程之一。这种特殊的过程拥因有许多优势而被广泛采用。 (Bjo rck & Asp, 1983; Camire, Camire, &Krumhar, 1990; Harper & Jansen, 1985).从营养角度上来说，挤压蒸煮可以灭活某些抗营养因子如胰蛋白酶，而这可以增加蛋白质的消化率。挤压过程中的高温环境，可以保证卫生要求，并使得淀粉基本糊化，从而生产出速溶粉。如果没能真正的速溶化，但此时，混合物已经预热，可以大大减少其稀糊化所需时间。挤压蒸煮过程中，原料还经过高剪切过程，从而使淀粉部分降解。(Colonna, Doublier, Melcion, De

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