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1、Chapter 7 Starch processing7.1 Starch Composition7.2 Starch properties7.3 Starch Isolation7.4 Modified starch7.5 Starch hydrolysates7.1 Starch Composition Amylose.Linear alpha-1,4 glucose chainlf.DP:180-320,MW106.Branch approximately every 200 glucose units Amylopectin.Linear alpha-1,4 chain with an
2、 alpha-1,6 branch approximately every 20 glucose units.MW108 Amylose:amylopectin 1:3 Waxy starches all amylopectin High amylose mutants up to 70%amyloseAmylose Linear component of starch Contains 1,4-alpha-glucosidic bonds Molecular weight:less than 0.5 million Can form coils which will trap iodine
3、and turn blueAmylopectin Branched component of starch Contains 1,4-alpha-glucosidic as well as 1,6-alpha-glucosidic bonds Molecular weight:50-500 million Limited coiling causes purplish-red color when iodine addedStarch Granule Amylopectin forms in concentric circles with amyose dispersed in between
4、 Held together by hydrogen bonds The granule swells when heated in waterStarch GranuleStarch Granules(SG)Amylopectin-responsible for semi-crystalline growth ringSG contain growth rings of alternating amorphous and semi-crystalline layers Unheated starch granule Heated starch granule 由于淀粉具有不溶于冷水和比重大于
5、水两个基本由于淀粉具有不溶于冷水和比重大于水两个基本特征特征，这是淀粉得以制取的根本原因这是淀粉得以制取的根本原因。由于制取淀粉的过程中需要大量用水由于制取淀粉的过程中需要大量用水，故有故有“水水磨法磨法”之称之称（wet-milled）。Amaranth（苋菜籽）starch(Bar:1 m)Arrowroot（竹芋）starch(Bar:20 m)Buckwheat（荞麦）starch(Bar:5 m)Cassavaks:vstarch(Bar:10 m)Corn starch(Bar:10 m)Oat starch(Bar:5 m)Potato starch(Bar:50 m)Rice
6、starch(Bar:2 m)Kidney bean starch(Bar:20 m)7.2 Starch properties7.2.1.Gelatinization,Pasting and Gelation When starch is heated in water Hydrogen bonds break,allowing water to enter the granule and the granule swells Amylose migrates out of the granule H-bonding between water and amylopectin increas
7、es Reduced free water changes the viscosity of the starch mixture,thickening itGelatinization and Pasting“Starch gelatinisation is the collapse(disruption of molecular order)within the starch granule,manifested in irreversible changes in properties such as granular swelling,native crystalline meltin
8、g,loss of birefringence and starch solubilisation.”Gelatinization and Pasting“Pasting is the phenomenon following gelatinisation in the dissociation of starch.It involves granular swelling,exudation渗出渗出 of molecular components from the granule;and eventually the total disruption of the granules.”Raw
9、,uncooked starch granulesheated in waterSwelling is evidentNotice loss of amylose from the granulesGelatinization and pasting are completeSome granules have collapsed.Now we start to cool.GelationNotice areas of association.These arecalled junction zones.This picture is not yet complete as we havent
10、 accounted for the water in the system.waterwaterwaterwaterwaterwaterThis is a starch gelEffect of continuous heating in excess water Results in formation of starch paste due to:further granule swelling beyond reversible point additional leaching of soluble compounds total disruption of granulesVisc
11、osity and Type of StarchGelation As a starch paste cools,a gel is formed Free amylose molecules lose energy as the temperature decreases and form hydrogen bonds The bonds create a network that holds the swelled granules in placePaste and gel Paste Granule swelling and disruption of granules produce
12、Viscousmass(paste)Consisting of a continuous phase of solubilised amylose and or amylopectin and a discontinuous phase of granule remnants(granule ghosts and fragments)Cooling of a hot-starch paste partially reassociate resulting in a viscoelastic,firm,rigid precipitate or gel,process called retrogr
13、adation.Gel continuous,3-dimensional network of connected molecules or particles entrapping a large volume of a continuous liquid phase,much as does a sponge In many food products,the gel network consists of polymer molecules or fibrilsformed from polymer molecules joined in junction zones by hydrog
14、en bonding,hydrophobic associations,ionic cross bridges,entanglements,or covalent bonds,and the liquid phase is an aqueous solution of low-mw solutes and portions of polymer chains.7.2.2.Retrogradation Solubilised starch polymer and remaining insoluble granular fragment tend to re-associate after he
15、ating.The re-associating is termed“Retrogradation”.Retrogradation has been defined as follows:7.2.2.Retrogradation“Retrogradation is a process which occurs when starch chains start to re-associate into an ordered structure.In its initial phase,two or more starch chains may form a simple junction poi
16、nt,which then may develop into more extensively ordered regions.Ultimately,under favourable conditions,a crystalline order appears.”Generally,amylose-containing starches show greater retrogradation.Factors relating to retrogradation include:Temperature 4 Moisture content 20-60%Amount of branching Hi
17、gh amylopectin starches-e.g.,waxy maize shows no retrogradation when frozenHydrogen bonding between OH groups in amylose in gelatinised starches during coolingWater forced out of gel structure(syneresis)&Starch insolubilized.Amylopectin also plays a role in retrogradation over time.Short-term retrog
18、radation is largely associated with amylose(which reaches a limit in 2 days),whereas long-term retrogradation is thought to involved amylopectin(reaching a limit is 40 days)Factors relating to retrogradation include:7.3 Starch Isolation Starch can be extracted using various processes,depending on th
19、e plant source and end use of the starch.Wet milling processing is widely used in cereal starch production.The purpose of wet milling is to separate the kernel(grain)into its constituent chemical components.Figure 7.1 presents the major procedures for extracting starches from cereal grains and tuber
20、s.7.3 Starch Isolation7.3.1 Cereal starch isolation As shown in the schematic,the major steps of cereal starch isolation include steeping,milling,and separation.Steeping is the first critical processing step in wet milling.It usually involves using an aqueous solution of sulfur dioxide and lactic ac
21、id at certain pH and temperature for certain periods of time.This unit operation is carried out for about 40 hours.7.3.1 Cereal starch isolation The main purposes of the steeping process are to loosen the granules in the packed cell structure.7.3.1 Cereal starch isolation To isolate starch with mini
22、mum damage and maximum purity;To reduce or inhibit the activity of undesirable microorganisms.7.3.1 Cereal starch isolation After steeping,the softened grain is degerminated by coarse grinding粗磨粗磨.A hydroclone水力旋流器水力旋流器separator is used to separate the germs which are less dense and contain high lev
23、els of oil.7.3.1 Cereal starch isolation The remaining materials are reground to liberate most of the remaining starch and other components.Starch can be separated from other components by centrifugation,based on density difference between starch and other components such as protein.7.3.1 Cereal sta
24、rch isolation Drying:The purified starch milk is dewatered by means of a thickening filter in order to reach a dry solid content suitable for the following drying.Drying is operated by dosing the starch into the dryer at controlled temperature maintained by an air conditioning unit.The dry starch is
25、 then separated by the air stream and stored and packed.flash dryer气流干燥器气流干燥器7.3.2 7.3.2 Tuber starch isolation Starch granules are unevenly distributed in the cell walls of tubers.They can be liberated from tuber by disruption of the cell walls.This is done during tuber disintegration by a cylindri
26、cal drum containing rotary saw blades on its circumference or a juice extractor for extraction at a small scale.Starch can be purified by washing,sedimentation,and centrifugation.7.3.2 7.3.2 Tuber starch isolation Potato starch Due to the tissue structure of potatoes and the fact that starch is depo
27、sited loosely in the fruit water of potato cells the process of starch production is relatively simple.7.3.2 7.3.2 Tuber starch isolation Starch isolation begins,in principle,with disintegration of the storage parenchyma 贮贮藏薄壁组织藏薄壁组织 of the tuber followed either by immediate removal of the concentra
28、ted potato juice and subsequent washing out of starch or in other concepts by extracting the cell content with different amounts of water.7.3.2 7.3.2 Tuber starch isolation Disintegration is limited by the fact that the greater part of cell wall tissue residues should remain at a size separable by w
29、et sieving mill starch streams.From the resulting diluted suspensions the starch gets rid of impurities,like fibre and protein residues as well as minerals,by a combination of concentration and washing steps.7.3.2 7.3.2 Tuber starch isolation Counter-current washing with soft fresh water in a multic
30、yclone多级旋风分离器多级旋风分离器station or nozzle 喷嘴喷嘴separators followed by conventional concentration and dewatering systems produces a starch cake,which is dried in the moving bed of a heated air stream to a moisture content of less than 20%in a flash dryer气流干燥器气流干燥器.7.3.3 7.3.3 The isolation of starches fro
31、m legume seeds豆类淀粉豆类淀粉The isolation of starches from legume seeds is difficult due to the presence of insoluble flocculent絮凝的絮凝的protein and fine fiber,which decreases sedimentation and co-settles with the starch to give a brownish deposit.Legume starches are isolated using aqueous techniques as well
32、 as pin milling and air classification.目前国内外豆类淀粉生产的方法有三种。即酸浆法、离心目前国内外豆类淀粉生产的方法有三种。即酸浆法、离心分离法和旋流分离法。分离法和旋流分离法。酸浆法是生产绿豆酸浆法是生产绿豆、豌豆淀粉及粉丝的传统工艺豌豆淀粉及粉丝的传统工艺。采用的酸浆是通过自然发酵得到的采用的酸浆是通过自然发酵得到的，受气候影响很大受气候影响很大，而而且操作较为繁琐且操作较为繁琐，经验性强经验性强，不适合机械化连续生产不适合机械化连续生产，此此法豆类的蛋白质不利于综合利用法豆类的蛋白质不利于综合利用，为了克服上述缺点为了克服上述缺点，可可采用离心分离
33、法采用离心分离法。原料豆原料豆清理清理浸泡浸泡破碎破碎浮选分离浮选分离磨浆磨浆筛分筛分离离心分离心分离洗涤洗涤离心分离离心分离脱水脱水干燥干燥绿豆淀粉的生产工艺流程绿豆淀粉的生产工艺流程7.4 7.4 Modified starch变性淀粉变性淀粉 7.4.1.Definition Native starches have many disadvantages for industrial applications such as insolubility in cold water,loss of viscosity,and thickening power aftercooking.The
34、 functionality of starch can be modified through physical,chemical,and biotechnological means to stabilize starch granules during processing and make starch suitable for many food and industrial applications.7.4.2 Principle可能是淀粉大分子结构中的苷键和羟基的改变可能是淀粉大分子结构中的苷键和羟基的改变。苷键苷键断裂使淀粉聚合度降低断裂使淀粉聚合度降低，大分子降解大分子降解，
35、而位于葡萄糖而位于葡萄糖残基的伯残基的伯、仲碳原子上的羟基具有通常的伯仲碳原子上的羟基具有通常的伯、仲醇基仲醇基的氧化的氧化、酯化酯化、醚化反应能力醚化反应能力，故可制得相应衍生物故可制得相应衍生物。变性淀粉只能改变其部分性质变性淀粉只能改变其部分性质，不能改变其全部性质不能改变其全部性质，否则就不是变性而是失性了否则就不是变性而是失性了。一般高温一般高温、辐射辐射、氧化剂氧化剂、淀粉酶和交联剂等淀粉酶和交联剂等，都可都可用来制作变性淀粉用来制作变性淀粉。7.4.3 Classification7.4.3 Classification 变性淀粉的分类一般是根据处理方式来进行变性淀粉的分类一般是
36、根据处理方式来进行。(1 1)物理变性物理变性 预糊化预糊化(-化化)淀粉淀粉、-射线射线、超高频辐射处理淀粉超高频辐射处理淀粉、机机械研磨处理淀粉械研磨处理淀粉、湿热处理淀粉等湿热处理淀粉等。(2 2)化学变性化学变性 用各种化学试剂处理得到的变性淀粉用各种化学试剂处理得到的变性淀粉。其中有两大类；一其中有两大类；一类是使淀粉分子量下降类是使淀粉分子量下降，如酸解淀粉如酸解淀粉、氧化淀粉等；另一氧化淀粉等；另一类是使淀粉分子量增加类是使淀粉分子量增加，如交联淀粉如交联淀粉、酯化淀粉酯化淀粉、醚化淀醚化淀粉粉、接枝淀粉等接枝淀粉等。(3)(3)酶法变性酶法变性(生物改性生物改性)各种酶处理淀粉
37、。各种酶处理淀粉。如环状糊精、麦芽糊精、直链淀粉等。如环状糊精、麦芽糊精、直链淀粉等。(4)(4)复合变性复合变性 采用两种以上处理方法得到的变性淀粉。采用两种以上处理方法得到的变性淀粉。如氧化交联淀粉、交联酯化淀粉等。采用复合变如氧化交联淀粉、交联酯化淀粉等。采用复合变性得到的变性淀粉具有两种变性淀粉的各自优点。性得到的变性淀粉具有两种变性淀粉的各自优点。变性淀粉还可按生产工艺路线进行分类：变性淀粉还可按生产工艺路线进行分类：有干法有干法(如磷酸酯淀粉如磷酸酯淀粉、酸解淀粉酸解淀粉、阳离子淀粉阳离子淀粉、氨基甲氨基甲酸酯淀粉等酸酯淀粉等)；湿法湿法 有机溶剂法有机溶剂法(如羧基淀粉制备一般采
38、用乙醇作溶剂如羧基淀粉制备一般采用乙醇作溶剂)挤压法挤压法 滚筒干燥法滚筒干燥法(如天然淀粉或变性淀粉为原料生产预糊化淀如天然淀粉或变性淀粉为原料生产预糊化淀粉粉)等等。7.4.4 Parameters of modification7.4.4 Parameters of modification 浓度浓度 干法生产一般水分控制在干法生产一般水分控制在525%范围内；范围内；湿法生产淀粉乳含量一般为湿法生产淀粉乳含量一般为3540%（干基干基）。温度温度 按淀粉的品种以及变性要求不同而不同按淀粉的品种以及变性要求不同而不同 一般为一般为2060，反应温度一般低于淀粉的糊化温度反应温度一般低于淀
39、粉的糊化温度（糊糊精精、酶法除外酶法除外）。pH值值 除酸水解外，除酸水解外，pH值控制在值控制在712范围。范围。在反应过程中为避免在反应过程中为避免O2对淀粉产生的降解作用，可对淀粉产生的降解作用，可考虑通入考虑通入N2。试剂用量试剂用量 取决于取代度（取决于取代度（DS）要求和残留量等卫生指标。）要求和残留量等卫生指标。反应介质反应介质 生产低取代度的产品用水作为反应介质生产低取代度的产品用水作为反应介质，成本低；成本低；高取度的产品用有机溶剂作为反应介质高取度的产品用有机溶剂作为反应介质，但成本高但成本高。另外可添加少量盐另外可添加少量盐（如如NaCl、Na2SO4等等），其作用主要其
40、作用主要为：为：避免淀粉糊化；避免试剂分解避免淀粉糊化；避免试剂分解，如如POCl3；遇水分解；遇水分解，加入加入NaCl可避免其在水中分解；可避免其在水中分解；盐可以破坏水化层盐可以破坏水化层，使试剂容易进去使试剂容易进去，从而提高反应效率从而提高反应效率。产品提纯产品提纯 干法改性干法改性，一般不提纯；但用于食品的产品必须经一般不提纯；但用于食品的产品必须经过洗涤过洗涤，使产品残留试剂符合食品卫生质量指标；使产品残留试剂符合食品卫生质量指标；湿法改性湿法改性，根据产品质量要求根据产品质量要求，反应完毕用水或溶反应完毕用水或溶剂洗涤剂洗涤2或或3次次。干燥干燥 脱水后的淀粉水分含量一般在脱水
41、后的淀粉水分含量一般在40%左右左右，高水分含高水分含量的淀粉不便于储藏和运输量的淀粉不便于储藏和运输，因此在它们作为最终因此在它们作为最终产品之前必须进行干燥产品之前必须进行干燥，使水分含量降到安全水分使水分含量降到安全水分以下以下。目前一般工业生产采用气流干燥；目前一般工业生产采用气流干燥；中小型工厂也有采用烘房干燥或带式干燥机干燥中小型工厂也有采用烘房干燥或带式干燥机干燥。7.4.5 淀粉变性程度的衡量淀粉变性程度的衡量酶法糊精评价指标为酶法糊精评价指标为DE值值，即还原糖含量占总固形物的比即还原糖含量占总固形物的比例例，DE值越高值越高，酶解程度越高；酶解程度越高；其他变性淀粉用取代度
42、其他变性淀粉用取代度DS或摩尔取代度或摩尔取代度MS来表示来表示，DS或或MS值越大值越大，表示变性程度越高表示变性程度越高。DS是指每个是指每个D-吡喃葡萄糖残基吡喃葡萄糖残基（AGU）中羟基被取代的中羟基被取代的平均数量平均数量。淀粉中大多数淀粉中大多数D-吡喃葡萄糖残基上有吡喃葡萄糖残基上有3个可被取个可被取代的羟基代的羟基，所以所以DS的最大值为的最大值为3，其计算公式如下：其计算公式如下：wMwwDSr)1(100162Degree of substitution(DS)Indicates the average number of etherified hydroxyl group
43、s in a glucose unit.DS equals the number of hydroxyl groups replaced by the substituent in every anhydroglucose unit in the chain.As an anhydroglucose unit has three hydroxyl groups available for conversion,the maximum obtainable degree of substitution DS=3.7.4.6 7.4.6 变性淀粉的生产方法变性淀粉的生产方法 变性淀粉生产的方法主要
44、有湿法变性淀粉生产的方法主要有湿法、干法干法、滚筒干燥法和挤滚筒干燥法和挤压法等几种压法等几种，其中最主要的生产方法还是湿法其中最主要的生产方法还是湿法。湿法也称浆法湿法也称浆法，将淀粉分散在水或其他液体介质中将淀粉分散在水或其他液体介质中，配成配成一定浓度的悬浮液一定浓度的悬浮液，在一定的温度条件下与化学试剂进行在一定的温度条件下与化学试剂进行氧化氧化、酸化酸化、酯化酯化、醚化醚化、交联等反应交联等反应，生成变性淀粉生成变性淀粉。如果采用的分散介质不是水如果采用的分散介质不是水，而是有机溶剂而是有机溶剂，或含水的混或含水的混合溶剂时合溶剂时，为了区别水又称为溶剂法为了区别水又称为溶剂法。大多
45、数变性淀粉都可采用湿法生产大多数变性淀粉都可采用湿法生产。7.5 7.5 Starch hydrolysates淀粉制糖淀粉制糖 淀粉糖是以淀粉为原料淀粉糖是以淀粉为原料，通过酸或酶的催化水解反通过酸或酶的催化水解反应生产的糖品的总称应生产的糖品的总称，是淀粉深加工的主要产品是淀粉深加工的主要产品。The hydrolysis of starch to sweeteners by mineral acid was discovered in 1811.Enzymes are employed to produce starch from syrups with a preponderance
46、of maltose or glucose and to isomerize some of the glucose in high-glucose syrups to fructose,so as to enhance sweetness.7.5.1Types of Starch hydrolysates 淀淀粉糖的种类与性质粉糖的种类与性质 General classifications of sweeteners are as follows 1.Corn syrup(glucose syrup):The purified,concentrated aqueous solution of
47、 nutritive saccharides obtained from edible starch and having a DE of 20 or more.2.Dried corn syrup(dried glucose syrup):Corn syrup from which the water has been partially removed.7.5.1Types of Starch hydrolysates 3.Dextrose monohydrate:Purified and crystallized D-glucose,containing one molecule of
48、water of crystallization.4.Dextrose anhydrous:Purified and crystallized D-glucose without water of crystallization.7.5.1Types of Starch hydrolysates 5.Maltodextrin:A purified,concentrated aqueous solution of nutritive saccharides obtained from edible starch or the dried product derived from said sol
49、ution and having a DE of less than 20.6.HFCS(High-fructose corn syrup):A purified,concentrated aqueous solution of nutritive saccharides obtained from edible starch and having a portion of the glucose isomerized to fructose.7.5.1Types of Starch hydrolysates 淀粉糖工业常用葡萄糖值淀粉糖工业常用葡萄糖值(dextrose equivalent
50、)简称简称DE值值(糖化液中还原性糖全部当做葡萄糖计算，占干物糖化液中还原性糖全部当做葡萄糖计算，占干物质的百分率称葡萄糖值质的百分率称葡萄糖值)来表示淀粉水解的程度。来表示淀粉水解的程度。DE of a product of hydrolysis is its reducing poweras a%of reducing power of pure dextrose(D-glucose)7.5.2 7.5.2 Production methodsStarch,gelatinized by heat,may be hydrolyzed by acid,enzyme,or by a combin