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義是多羥基的醛和酮或者水解產生多羥基的醛和酮的物質。:w)MJ
單糖的分類按照（1）分子中碳原子的數目（2）是否含有一個醛基或酮基，因此一個單糖含有6個碳原子叫做己糖；一個單糖含有醛基叫醛糖；含有酮基叫酮糖。c{
最有代表性的單糖是葡萄糖、阿拉伯糖、半乳糖、甘露糖、核糖和果糖。葡萄糖通常是發(fā)酵的碳源。因為葡萄糖有晶體結構或糖漿結構的精巧結構使它更昂貴，葡萄糖在發(fā)酵培養(yǎng)基中是主要的產物，通過直接糖化酶轉化淀粉得到。w{, 'u
低聚糖可一分為二糖和三糖。二糖最重要的代表是蔗糖（來自于甜菜或甘蔗），乳糖，麥芽糖和纖維二糖。三糖最重要的代表是來自于甜菜糖中的蜜三糖。?z2
蔗糖可在發(fā)酵過程中被利用，包括晶體結構、天然糖漿、糖蜜（食糖加工的副產品）。糖蜜含有的蔗糖明顯便宜，但是糖蜜的成分根據來源的不同變化很大（甘蔗或甜菜），收獲農產品的質量和糖精煉工藝的種類。在用于發(fā)酵培養(yǎng)基時，糖蜜應該象其他原料一樣在作為發(fā)酵培養(yǎng)基使用前進行預處理。;XaZ
乳糖是從乳清中得到的（干酪加工的副產品，發(fā)生在以下的情況，從凝乳中分離出來，凝固的酪蛋白和黃油脂肪），濃度4-5%，乳清或脫去蛋白質的乳清在一些酒精加工過程中是廉價的碳水化合物來源。A
多糖是由單糖單位構建成和他們的衍生物，有十到幾十個單位。D-葡萄糖是最常見的單位。它不溶解。最典型的代表是淀粉、糖原和纖維素。?`af,
淀粉是用于發(fā)酵過程最重要的碳水化合物。它從植物中得到，像玉米、稻子、小麥、馬鈴薯和木薯。."*