Introduction to Fructose
Did you know apple, cherry, grape, guava, mango, litchi, sugar cane and even honey all have one thing in common? Do you know what is it? Well, the answer is they all contain the same kind of sugar which is Fructose. Fructose is also called fruit sugar or levulose. The word ‘fructose’ is made up of the Latin word ‘Fructus’ which means ‘fruit’ and ‘ose’ which means sugar. ‘ose’ is a generic chemical suffix for sugars. Fructose was discovered by French Chemist Augustine – Pierre Dubrunfaut in 1847 while the name fructose was coined by English Chemist William Allen Miller in 1857. Fructose or fruit sugar is naturally found in fruits, honey, flowers, berries, and most root vegetables. It is a simpler sugar than glucose and sucrose. So, it is easier to digest but only the liver can digest fructose sugar. Overconsumption of fructose leads to overwork pressure on the liver. In this condition, the liver starts converting fructose into fat which leads to obesity. Apart from this, overconsumption of fructose can be a key driver of many diseases like type diabetes, heart disease and liver failure.
What is Fructose?
Fructose is simple ketonic monosaccharide sugar found in many plants, flowers, and fruits. It is a fruit sugar which is one of the three dietary monosaccharides along with glucose and galactose that is absorbed into the blood directly during digestion. monosaccharides are the simplest form of sugar and the basic unit of carbohydrates. So, fructose is the simplest sugars and easier to digest than other sugars. In pure form, it is sweet, white, odorless, and crystalline solid. It is more soluble in water than other sugars. Commonly it is found in fruits such as mango, litchi, cherry, guava, and vegetables such as carrot, radish, beetroot and sugarcane etc. Commercially, it is derived from sugar cane, maize, and sugar beets.
Structure of Fructose
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.
Cyclic Form of Fructose
Fructose contains six carbons atoms, twelve hydrogen atoms and six oxygen atoms. It has a ketone functional group at carbon number 2. Thus, it is a ketohexose. It is obtained along with glucose. The molecular formula of fructose is C6H12O6.
Physical Properties of Fructose
Fructose is an important ketohexose that is obtained by hydrolysis of disaccharide sucrose. Physical properties of fructose are listed below –
Its molar mass is 180.156 g.mol-1.
Its melting point is 103 0C.
It is the most soluble sugar in water.
It is sweet in taste. This is the reason it is used in beverages and foods as a sweetening agent. It is low cost and sweetest of all naturally occurring carbohydrates. As we increase the temperature, its relative sweetness decreases.
It is a white crystalline solid at room temperature.
It is an odorless sugar.
It is sticky.
It has great hygroscopicity, ie; the ability to absorb moisture from surrounding elements. It quickly takes in moisture and slowly releases out compared to other sugars.
It has great humectant, ie; moisture withholding. It can also retain the moisture absorbed.
Chemical Properties of Fructose
It is very important to know all chemical aspects of fructose as it is extensively used in food products and part of our daily diet. The chemical properties of fructose are listed below –
Fructose can be fermented anaerobically by yeast and bacteria. Yeast converts sugar to ethanol and carbon dioxide.
It shows Maillard reaction. As it can exist in open-chain form for a greater extent so the initial stage of the Maillard reaction occurs more rapidly.
It has the potential to form mutagenic compounds.
After dehydration, fructose gives hydroxymethylfurfural (“HMF”).
Preparation of Fructose
It can be prepared by hydrolysis of sucrose in presence of invertase or dilute sulfuric acid. It is a laboratory method of preparation of fructose. The reaction is given below –
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Now fructose is separated from glucose by crystallization using alcohol. As glucose is only sparingly soluble in alcohol so it gets separated first in the form of crystals. Commercial production of fructose is done by using glucose. An aqueous solution of glucose is prepared which is then converted into D – glucosone. Now by chemical hydrogenation process D – glucosone is converted into pure fructose.
Different Types of fructose
There are majorly two divisions in fructose. (i) Crystalline fructose and (ii) High Fructose Corn Syrup (HFCS). Let’s take a deeper look at them.
Crystalline fructose
It consists of only the fructose components ie; 100 percent. It is considered one of the best natural sweeteners. Crystalline fructose improves the texture and consistency of cakes and other baked products. It also provides a visually appealing brown colour to the eatables.
High fructose corn syrup
Generally, sucrose and HFCS contain an equal amount of glucose and fructose. The component ratio of HFCS is usually 55%-45% for fructose and glucose respectively. But variations might come. It is mainly made up of corn starch. Fructose is formed as a result of corn starch processing. The ingredient is first extracted after which enzyme action takes place. This results in the conversion of glucose into fructose. HFCS is commercially used in baked items, canned items, packet soups, ice-creams etc.
Applications of Fructose
Fructose has various applications. A few of them are listed below –
As it can be converted into hydroxymethylfurfural (“HMF”) so it can be used as diesel fuel additives and diesel fuel itself.
Large scale applications of fructose involve its use as a sweetener. It is used in many foods as a sweetening agent. It is a low-calorie sweetener that enhances its value as a sweetening agent.
It is used in plastics as well.
It is used to increase the shelf life of foods like nutrition bars and cookies.
Corn syrup is produced by using fructose.
It is used in infant feeding formulas.
It is used as a food for diabetics.
It has a low glycemic index and results in a moderate release of insulin to the bloodstream relative to glucose and fructose.
It is used in stevia.
It is used in many beverages and baked goods etc.
Potential Health Effects of Fructose
Overconsumption of fructose causes many adverse effects on human health. A few of them are listed below –
It causes weight gain. Due to obesity, hypertension is caused.
High fructose corn syrup (HFCS) may cause Alzheimer’s and memory loss. Such corn syrups appear for more than 40% of the caloric sweeteners and are symbols of unhealthy foods. HFCS causes the deposition of beta-amyloid that is associated with Alzheimer’s’. It also increases the central neuronal insulin resistance that in turn elevates dementia.
It elevates bad cholesterol levels in the body.
It causes type – II diabetes.
Overconsumption creates a lot of work pressure on the liver and that may cause damage to the liver.
It can cause cardiovascular disorders.
It is extremely addictive and can cause damage to the immune system as well.
Although fructose is a low-calorie sugar when compared to glucose and sucrose, it has many benefits over them as stated above. It also has many adverse health effects when consumed in large amounts. So, we need to consume fructose added food products in limited and required amounts.
This is all about Fructose, if you are looking for solutions to NCERT Textbook problems based on this topic, then log on to the Vedantu website or download Vedantu Learning App. By doing so, you will be able to access free PDFs of NCERT Solutions as well as Revision notes, Mock Tests and much more.
FAQs on Fructose
1. What are the different types of plant foods containing fructose?
The different types of plant foods that contain natural fructose are :
Vegetables - Red beetroot, carrot, red pepper, onion, sweet potato, yam, sugar cane etc.
Fruits - Apple, fig, apricot, banana, grapes, navel orange, pineapple, peach, pear plum etc.
Apple and pear contain way higher concentrations of the component and it does not go well with the enterocytes of the small intestine, especially in children. This creates a higher concentration of fructose solute in the small intestine creating osmotic diarrhoea. Therefore, paediatricians always keep these fruits in low priority when it comes to the recommendation of foods for children.
2. Is fructolysis related to fructose?
Yes. It refers to the metabolism of fructose from dietary sources. The fructose molecules are broken into smaller units and are either oxidised to release energy or used for some other activity. In fructolysis, the enzyme fructokinase initially produces fructose 1-phosphate, which is split by aldolase B to produce the trioses dihydroxyacetone phosphate (DHAP) and glyceraldehyde. (52) Unlike glycolysis, in fructolysis, the triose glyceraldehyde lacks a phosphate group.
3. What is HFI?
Hereditary fructose intolerance is a condition in which an individual is insufficient with the proteins breaking down the fructose. It happens when an enzyme called aldolase B is absent in a persons’ body. Consumption of food containing fructose by such people can lead to dangerous chemical changes in their bodies. As a result, unnecessary substances get accumulated in the liver and cause problems. This disease can be passed down to generations. There is a 25% chance for children to inherit it if both the parents have HFI.
4. Is fructose bad for diabetic patients?
Fructose can be considered as a sweet alternative for patients with a sweet tooth. However, the amount of intake should be watched carefully. Fructose gives lower postprandial glucose in patients with very moderate diabetes mellitus which are non-insulin-dependent. Many clinical studies prove that fructose has made visible changes in diabetic patients. It has also contributed to improving their metabolic management. Patients who seem vulnerable to hypertriglyceridemia should avoid high fructose as it can give bad effects. However, since there are not many traces about any long-term research regarding this topic, it is always advisable to have controlled natural intake of not just fructose, but any kind of less healthy food.
5. What happens if fructose is not digested properly?
Improper digestion of fructose is caused due to malabsorption. Sometimes, the small intestine does not wholly absorb fructose. The unabsorbed fructose is transported to the large intestine, where its fermentation by colonic flora takes place. The colonic flora produces hydrogen, carbon dioxide, organic acids etc. The H2 gets dissolved into the blood and is then taken to the lungs. The organic acids produced as a result of unabsorbed fructose causes several gastric and stomach problems like diarrhoea, stomach pain, bloating etc.
