carbohydrates 1h
Carbohydrates are usually defined as polyhydroxy aldehydes and ketones or substances that hydrolyze to yield polyhydroxy aldehydes and ketones. Q&#
Monosaccharides are classified according to (1) the number of carbon atoms present in the molecule and (2) whether they contain an aldehyde or keto group, thus a monosaccharide containing six carbon atoms is called hexose; a monosaccharide containing an aldehyde group is called aldose; and one containing a keto is called a ketose. V`s8
The most important representatives of monosacchrides are glucose, arabinose, galactose, mannose, ribose, and fructose. Glucose is usually used as a carbon source for fermentation. Because the glucose in refined form such as crystalline form or as syrup form is more expensive, glucose in fermentation medium is mostly produced by direct enzymatic conversion of starch. b.a|?\
The oligosaccharides can be classified into disaccharides and trisaccharides. The most important representatives of disaccharides are sucrose (from beet or cane), lactose, maltose and cellobiose. The most important representatives of trisaccharides are raffinose which occurs in sugar beet. 8>H.Xe
Sucrose is available for use in fermentation processes either in crystalline form or in crude form as raw juice or molasses (a by-product of sugar manufacture). The sucrose contained in molasses is obviously cheaper, but the compositions of molasses varies GREatly with sources (cane or beet), quality of the crop and the nature of the sugar refining process. The molasses should be pretreated before being used as a raw material for fermentation medium. B:>
Lactose is present in whey (a by-product of cheese making that arise following the separation of curds, the solidified casein and butter fat) at a concentration of 4%-5% and whole whey or deproteinized whey is used as a cheap source of carbohydrate in some alcohol production process. 1Rw,
Polysaccharides are constructed from monosaccharide unit and their derivatives, and have ten to several thousand units. D-glucose is the most common unit. They are insoluble and nonreducing. The most important representatives are starch, glycogens, and cellulose. }E5(2{
Starch is the most important carbohydrate used on fermentation processes. It is from plants such as corn, rice, wheat, potatoes and cassava. Blb
The extent of starch hydrolysis required varies with fermentation process and depends on considerations as to whether or not the microbial strain to be used produces amylase whether product synthesis is subject to catabolite repression. For citric acid production, because the A. niger has the ability to synthesize glucoamylase (or amyloglucosidase: an enzyme that catalyzes the removal of one glucose molecule at a time from the terminal end of dextrins, breaking 1,4 links), the starch slurry is gelatinized by cooking at high temperature, then the gelatinized starch is liquefied and dextrinized by thermostable amylase, and the saccharification step is not necessary. The soluble dextrin hydrolysate is used as a raw material for fermentation medium.~
碳水化合物(&=qC
碳水化合物通常的定义是多羟基的醛和酮或者水解产生多羟基的醛和酮的物质。:w)MJ
单糖的分类按照（1）分子中碳原子的数目（2）是否含有一个醛基或酮基，因此一个单糖含有6个碳原子叫做己糖；一个单糖含有醛基叫醛糖；含有酮基叫酮糖。c{
最有代表性的单糖是葡萄糖、阿拉伯糖、半乳糖、甘露糖、核糖和果糖。葡萄糖通常是发酵的碳源。因为葡萄糖有晶体结构或糖浆结构的精巧结构使它更昂贵，葡萄糖在发酵培养基中是主要的产物，通过直接糖化酶转化淀粉得到。w{, 'u
低聚糖可一分为二糖和三糖。二糖最重要的代表是蔗糖（来自于甜菜或甘蔗），乳糖，麦芽糖和纤维二糖。三糖最重要的代表是来自于甜菜糖中的蜜三糖。?z2
蔗糖可在发酵过程中被利用，包括晶体结构、天然糖浆、糖蜜（食糖加工的副产品）。糖蜜含有的蔗糖明显便宜，但是糖蜜的成分根据来源的不同变化很大（甘蔗或甜菜），收获农产品的质量和糖精炼工艺的种类。在用于发酵培养基时，糖蜜应该象其他原料一样在作为发酵培养基使用前进行预处理。;XaZ
乳糖是从乳清中得到的（干酪加工的副产品，发生在以下的情况，从凝乳中分离出来，凝固的酪蛋白和黄油脂肪），浓度4-5%，乳清或脱去蛋白质的乳清在一些酒精加工过程中是廉价的碳水化合物来源。A
多糖是由单糖单位构建成和他们的衍生物，有十到几十个单位。D-葡萄糖是最常见的单位。它不溶解。最典型的代表是淀粉、糖原和纤维素。?`af,
淀粉是用于发酵过程最重要的碳水化合物。它从植物中得到，像玉米、稻子、小麦、马铃薯和木薯。."*
