Fructose is a simple sugar, also called “fruit sugar”. Fructose is a monosaccharide like glucose and is found in all types of fruits hence, the name fruit sugar. Fructose has four calories per gram. Fructose also occurs in various foods such as honey, sugar cane, corn, etc.

In this article, we will learn about Fructose, its structure, preparation, properties, uses, and comparison between glucose and fructose.

What is Fructose?

Fructose is a simple ketonic monosaccharide, a simple sugar, found naturally in various foods. It is a key component of sucrose, commonly known as table sugar, and is responsible for the sweetness of many fruits and vegetables. Fructose is the simplest sugar and easier to digest than other sugars.

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Fructose Formula

Chemical Formula of Fructose is C₆H₁₂O₆

Discovery of Fructose

French chemist named Augustin-Pierre Dubrunfaut was the first to discover fructose in the year 1847. It is called fruit sugar because it is found in various fruits. For commercial purposes it is derived from corn, sugar cane, and sugar beets,

Structure of Fructose

The structure of fructose is cyclic or chair-like. There are a few deviations to the general structure of fructose, but its overall form is largely identical to that of glucose. The functional group of fructose is ketone, and the ring closure starts at the second carbon position.

This causes fructose to form an intramolecular hemiacetal or to ascend to a 5-membered ring. The carbon at the second position mixes with the OH at the fifth carbon.

There are four carbons and one oxygen in the five-membered ring. In essence, there are two configurations of -CH₂OH and -OH groups as well as a creation of chiral carbon. Fructose essentially exhibits stereoisomerism.

Ring Structure of Fructose

Fructose is a levorotatory monosaccharide, which means it rotates the plane-polarised light in the left direction. The chemical composition of fructose is C₆H₁₂O₆ but shows different bonding from glucose. Fructose is a hexose, however, it exists as a 5-member hemiketal ring. The hemiketal ring helps with a long metabolic pathway and high reactivity in comparison to glucose.

Formation of Ring Closure Structure of Fructose (Hemiketal Synthesis)

Ether is formed when the carbon atoms in the alcohol oxygen are bonded together using the electrons present in the oxygen.

A new OH bond is formed when the hydrogen is moved to the carbonyl oxygen, giving fructose’s keto structure a ring like structure.

The carbon, which is the center of the hemiketal functional group, is referred to as anomeric carbon. The hemiketal group has both an ether oxygen and an alcohol group which is attached to two other carbons. Crystalline fructose possesses a ring structure. It is a 6 – carbon polyhydroxy ketone.

It gains stability by hemiketal and internal hydrogen bonding. In this form it is called D – fructopyranose while in its water solution fructose occurs as an equilibrium mixture of 70% fructopyranose and 22% fructofuranose and 7% three other forms including its acyclic structures.

Preparation of Fructose

Commercial production of fructose is done by using glucose. An aqueous solution of glucose is prepared which is converted into D – glucosone and then by chemical hydrogenation process D – glucosone is converted into pure fructose.

• From Sucrose: Fructose is obtained from sucrose by heating with dilute H₂SO₄ or with the enzyme invertase.

• From Insulin: Fructose is prepared commercially by hydrolysis of Inulin (a polysaccharide) in an acidic medium_.

Comparison of Alpha and Beta Structure of Fructose

Alpha and Beta fructose are two stereoisomers of the sugar fructose, differing in the spatial arrangement of functional groups around a chiral center.

Chirality in Fructose

• Alpha Fructose: In alpha fructose, the hydroxyl group (-OH) at the chiral center (C₃) is oriented downward.
• Beta Fructose: In beta fructose, the hydroxyl group at the chiral center (C₃) is oriented upward.

Nature of Fructose

• Alpha Fructose: Found naturally in some fruits and foods.
• Beta Fructose: Also found naturally in certain fruits and foods.

Properties of Fructose

Some of the properties of fructose are as follows,

• Fructose is a white crystalline compound.
• Fructose melts at a temperature of 102⁰C.
• Fructose absorbs moisture rapidly and slowly it forms Hydroxymethylfurfural as comparison to other sugars.
• It can be fermented anaerobically using yeast or bacteria, by which they are converted into ethanol and carbon dioxide.

Physical Properties of Fructose

Fructose is a monosaccharide, a simple sugar, and it possesses various physical properties that contribute to its characteristics. Here are some key physical properties of fructose:

• State: Fructose is typically found as a white, crystalline solid. In solution, it forms a clear, colorless liquid.
• Solubility: Highly soluble in water. Forms a clear solution when mixed with water.
• Melting Point: The melting point of fructose is around 103 to 105 degrees Celsius.
• Sweetness: Fructose is sweeter than glucose and sucrose (table sugar).
• Optical Activity: Fructose is optically active due to its chiral center at Carbon 3 (C₃). It can exist in two stereoisomeric forms: alpha and beta fructose.
• Crystalline Structure: In its solid state, fructose forms a crystalline structure. The crystalline form is influenced by factors such as temperature and concentration during the crystallization process.

Chemical Properties of Fructose

Fructose exhibits various chemical properties that are essential for understanding its behavior in biochemical processes and its interactions in different contexts. Some key chemical properties of fructose are:

Reducing Sugar: Fructose is a reducing sugar, meaning it has the ability to reduce other substances by donating electrons during chemical reactions. This property is due to the presence of a carbonyl group in its structure.

Reaction with Alkaline Solutions: Fructose reacts with alkaline solutions, undergoing a process known as alkaline degradation. This reaction results in the formation of brown products and is associated with the caramelization of sugars.

Maillard Reaction: Participates in the Maillard reaction, a chemical reaction between amino acids and reducing sugars, which is responsible for the browning of foods during cooking.

Acetylation: Fructose can undergo acetylation reactions, where acetyl groups are added to the molecule under specific conditions.

Isomerization: Under certain conditions, fructose can undergo isomerization, converting between its two stereoisomeric forms: alpha and beta fructose. The isomerization process can be influenced by factors such as temperature and pH.

Difference between Glucose and Fructose

The difference between Glucose and Fructose are listed below

Read more about Glucose and Fructose.

Types of Fructose

It is mainly of two types i.e. Crystalline Fructose and High Fructose Corn Syrup (HFCS).

• Crystalline Fructose: It contain only the fructose components i.e. 100 % . It is considered as one of the best natural sweeteners. This Crystalline fructose improves the texture and consistency of cakes and other baked products and also provides a visually appealing brown colour to the eatables.

• High-Fructose Corn Syrup (HFCS): HFCS is a sweetener used in many processed foods and beverages. It is produced by enzymatic isomerization of glucose (usually derived from corn starch) to fructose. The most common forms of HFCS are HFCS-55 (55% fructose and 45% glucose) and HFCS-42 (42% fructose and 58% glucose).

Fructose as Reducing Sugar

Fructose is also known as Reducing Sugar and for a sugar to be considered as Reducing Sugar it should fulfill following points:

A sugar considered as reducing sugar which can be can be oxidized by a weak oxidizing agent such as Tollen’s reagent (capable of oxidizing aldehydes, not alcohol) under a basic aqueous solution.

Fructose doesn’t contain any aldehyde group but it can reduce such reagents. This is due to the reason that the reagents are basic solutions, hence fructose can be isomerized to different aldoses( glucose and mannose).

Uses of Fructose

Application of Fructose are as follows-

1. It can be used as diesel fuel additives and diesel fuel as it can be converted into Hydroxymethylfurfural.
2. Fructose is mainly used use as a sweetener and is used in many foods as a sweetening agent. It is a low-calorie sweetener
3. It is used in plastics as well.
4. It is used to increase the shelf life of foods like nutrition bars and cookies.
5. In medical applications, fructose may be used in certain formulations, such as liquid medications or solutions, for its sweetening properties.
6. It is used as a food for diabetics.
7. It is used in many beverages and baked goods etc.
8. Some sports and energy products, such as energy bars and gels, may contain fructose as a source of quick-release energy.

Health Effects of Fructose

Overconsumption of fructose may lead to many side effects on human health.

• Weight Gain: High consumption of fructose may lead to weight gain and obesity which is due to its effects on appetite regulation and metabolism.

• Liver Health (Fatty Liver Disease): High intake of fructose, mainly in the form of added sugars, which is the cause of non-alcoholic fatty liver disease (NAFLD).

• Cardiovascular Health (Blood Pressure): High consumption of added sugars, including fructose, may lead to high blood pressure, which is a risk factor for cardiovascular disease.

• Metabolic Effects (Insulin Resistance): High intake of fructose, especially in the form of added sugars, is linked with insulin resistance, which contribute to the development of type 2 diabetes.

• High fructose corn syrup (HFCS) may cause Alzheimer’s and memory loss.

Read More,

• Sucrose
• Glucose
• Carbohydartes

Sample Questions on Fructose

Some questions on fructose are answered below,

Question 1 : What is Fructose Used for?

Fructose is a simple ketonic monosaccharide, a simple sugar, found naturally in various foods. Fructose in its pure form has been used as a sweetener. It is found in various foods, particularly in fruits, honey, and certain vegetables.

Question 2: What are Properties of Fructose?

Fructose has a lower melting point compared with other sugars such as glucose, which has a melting point of 146°C. The molar mass of fructose compound is 180.16 g/mol and density of 1.69 g/cm .

Question 3: What happens if Fructose is not digested properly?

If Fructose is not digested properly then it can lead to various digestive issues and discomfort.

Question 4: What are Health Effects of Consuming Fructose?

Excessive intake of added fructose, especially in the form of added sugars, has been associated with health issues such as insulin resistance, obesity, and fatty liver disease.

Question 5: Is Fructose Safe for individuals with Diabetes?

Fructose is generally considered safe for individuals with diabetes when used in moderate amounts from natural sources .However, it’s important to monitor overall sugar intake, especially from added sugars.

Fructose – Frequently Asked Questions

What is difference between Glucose and Fructose?

Glucose is a 6-membered ring, whereas fructose is a 5-membered ring compound. Another important difference is glucose is aldohexose, whereas fructose is ketohexose.

Is Fructose a Reducing Sugar or Not?

Fructose is a Reducing Sugar as for a sugar to be considered as reducing sugar it can be oxidized by a weak oxidizing agent such as Tollen’s Reagent (capable of oxidizing aldehydes, not alcohol) under a basic aqueous solution.

What are Some Common Sources of Fructose?

Common sources of fructose include fruits (apples, pears, and watermelon), honey, and some vegetables. Additionally, high-fructose corn syrup (HFCS) is a major source of added fructose in processed foods and beverages.

What is Fructose Malabsorption?

Fructose malabsorption is a condition where the small intestine has difficulty in absorbing fructose efficiently. It can lead to gastrointestinal symptoms such as bloating, gas, and diarrhea.

Is Fructose a Good or Bad Sugar?

In limited quantity fructose is good for our health but in excess it causes several types of problems in human body.

Which Food Contain Fructose?

Fructose is found naturally in various fruits, vegetables and honey.