However, in industry, starch is important for the fermentation of ethanol to produce beer, whiskey, as well as biofuel. Also, starch has non-food uses in the industry as well. Reducing sugar refers to any sugar capable of acting as a reducing agent due to the presence of a free aldehyde or ketone group while starch refers to an odorless, tasteless, white substance, occurring widely in plant tissue such as cereals and potatoes.
Reducing sugar can be either a mono- or disaccharide, which contains a hemiacetal group with a one OH group and one O-R group attached to the same carbon while starch is a polysaccharide, consisting of numerous glucose units joined by glycosidic bonds. All monosaccharides and many disaccharides such as cellobiose , lactose, and maltose are reducing sugars while glucose polymers such as starch and starch-derivatives such as dextrin, glucose syrup, maltodextrin, etc.
Reducing sugars are either monosaccharides or disaccharides with a hemiacetal group with a free aldehyde or ketone group. Significantly, this group acts as a reducing agent, oxidizing metal salts. For instance, all monosaccharides and some disaccharides including lactose and moltose are reducing sugars. In contrast, starch is the main form of storage polysaccharide in plants.
Also, it is made up of glucose units joined by glycosidic bonds. However, it begins with a reducing sugar with a free aldehyde group. Therefore, it also has reducing properties only to a small extent. Hence, the main difference between reducing sugars and starch is their structure and properties.
Figure 2: Amylose and Amylopectin. Lastly, via Maillard reactions, carbohydrates are responsible for determining the crust color and the taste of the food such as coffee, bread, and roasted food items. There are many uses of reducing sugar in our daily life activities. In medicines, the Fehling solution has been used as a test to detect diabetes in human blood.
The relative measurement of the number of oxidizing agents reduced by the available glucose makes it easy to calculate the concentration of glucose present in the human blood or urine. Moreover, after the calculation of the exact amount of glucose present, it becomes easier to prescribe the amount of insulin that must be taken by the patients from the doctors.
In food chemistry, the levels of reducing sugar in the products such as wine, juices, and sugar cane decide their quality. Try to answer the quiz below to check what you have learned so far about reducing sugar. Reducing Sugar.
Chemistry LibreTexts. Energy Technology, 8 1 , Test for Reducing Sugars. ATP is the energy source that is typically used by an organism in its daily activities.
The name is based on its structure as it consists of an adenosine molecule and three inorganic phosphates. Read More. Skip to content Main Navigation Search. Dictionary Articles Tutorials Biology Forum. Table of Contents. Reducing Sugar biology definition : A sugar that serves as a reducing agent due to its free aldehyde or ketone functional group s in its molecular structure.
Examples are glucose , fructose , glyceraldehydes, lactose , arabinose and maltose , except for sucrose. Is glucose a reducing sugar? Is fructose a reducing sugar? All monosaccharides are reducing sugars. Glucose, fructose, and galactose are monosaccharides and are all reducing sugars.
Is maltose a reducing sugar? Is lactose a reducing sugar? Is sucrose a reducing sugar? Key differences between reducing and non-reducing sugars: Reducing sugar are the carbohydrates with free aldehyde and the ketone group while in the non-reducing sugar no such free groups are found; rather, they are available in the formation of bonds.
The non-reducing sugar form is in the acetal or the ketal form whereas the reducing forms are in the hemiketal or the hemiacetal. The reducing sugars possess mutarotation while on the other hand, the non-reducing never exhibit such rotational behaviors. The reducing sugars are mainly monosaccharides where all polysaccharides are non-reducing sugars.
The reducing sugar can reduce the capric ions of the Fehling or the Benedict solution into the cuprous ions whereas, the reduction of cupric ions into the cuprous ions is not achieved in the non-reducing sugars.
The most common examples of reducing sugar are maltose, lactose, gentiobiose, cellobiose, and melibiose while sucrose and trehalose are placed in the examples of non-reducing sugars. Quiz Choose the best answer. A reducing sugar acts as an oxidizer. A reducing sugar would have an aldehyde group. Which of the following is NOT a reducing sugar? One researcher recalls that all inductees into the U.
So it will also give a positive test for other reducing sugars. In other words, those sugars are also reducing sugars. So why does fructose give a positive test? Great question. Although fructose is a keto sugar, and ketones generally give a negative test with the Benedict, there is an exception. Likewise, some disaccharides such as maltose and lactose contain a hemiacetal.
They are also reducing sugars that give a positive Fehlings, Benedict, or Tollens test picture of lactose positive test is further below. We saw at the top of the post that hemiacetals are in equilibrium with an aldehyde or ketone.
In contrast, acetals ketals are locked in place and can only be converted back to the aldehyde or ketone with aqueous acid. The poster child for a non-reducing sugar is sucrose , a.
Sucrose is a disaccharide of glucose and fructose. See if you can find a hemiacetal in its structure, below:. This is obtained by heating glucose in acidic methanol. Sugars are able to form long chains with each other in arrangements known as polysaccharides. Common examples of polysaccharides are starch, cellulose, and glycogen.
Hemiacetals are present, but only at the termini of the polymer. Starch, for example, generally has about individual units of glucose, but only one unit the terminus has a hemiacetal.
Therefore these polysaccharides are not considered reducing sugars. For example, starch gives a negative test see below. Make sense? Quiz yourself on whether the following sugars are reducing sugars or non-reducing sugars. But if you want to go further down the rabbit hole, I invite you to read further to learn about….
One thing about all three tests is that the active reagent is not particularly bench stable and has to be freshly prepared. The purpose behind using the tartrate is that it coordinates to the copper II and helps prevent it from crashing out of solution. Once prepared, the substance to be analyzed is added, and the mixture is heated for a brief period.
The ingredients are copper II sulphate, sodium carbonate note: hydroxide is also needed! Note: in the quantitative test, potassium thiocyanate is added, which results in a colourless white precipitate. The first three lines below describe the procedure. Silver nitrate is converted to silver hydroxide, which forms silver I oxide, Ag 2 O.
Then, addition of aqueous ammonia NH 3 results in formation of the silver-ammonia complex which is the active oxidant. The sample to be tested is then added to the freshly prepared active oxidant in a basic solution. A positive test results in a beautiful mirror of silver metal being precipitated out on the reaction vessel. A variant of this procedure is used for the preparation of mirrors. Bottom line here is that adding base has the effect of increasing the concentration of the starting aldehyde.
If I am wrong, please tell me leave a comment. One of the access points for the initiation of a single-electron transfer reaction is a carbon-metal bond, which can be achieved through base-promoted formation of an enolate. That requires that the aldehyde have a proton on the alpha carbon i. Thus it would appear that the reaction needs to proceed through an enol. Hover here for a pop-up image or [ click for image of a hypothetical mechanism ].
Image sources: Benedicts solution.
0コメント