549
disaccharides, oligosaccharides, and polysaccharides. The smallest carbohydrates are
monosaccharides such as glucose. When two molecules of monosaccharides are
linked together, they form disaccharides. The three most common forms of monosaccharides are glucose, galactose, and fructose. Glucose is the most preferred source of
energy for completion of cellular functions of the living organisms. Except during
extreme starvation conditions, our brain completely depends on glucose as preferred
source of energy. Another monosaccharide is galactose that differs from glucose only
in the position of hydroxyl group on the fourth carbon atom. This small structural
alteration causes galactose to be less stable than glucose and as a result the liver rapidly converts galactose to glucose which is then quickly utilized for energy production in cells. Fructose differs from glucose in its chemical structure, as the ring
structure of fructose contains only five carbons. Unlike glucose, fructose is not an
energy source for other cells in the body. Ribose is abundant in the nucleic acids
(RNA and DNA), and some pentoses are components of fiber. Sugar alcohols like
sorbitol, xylitol, and glycerol are industrially synthetic derivatives of monosaccharides. Due to their moderate sweetness and poor absorption sugar alcohols are often
used by the diabetic patients in place of sucrose to sweeten foods. Due to their quick
degradation by the bacteria in the mouth sugar alcohols do not cause tooth decay
(Gibney et al. 2009; Mahan and Raymond 2016; Titchenal et al. 2018). The most
common example of disaccharide is sucrose, lactose, and maltose composed of two
monosaccharide units one of which is mainly glucose. Sucrose comprising of both
glucose and fructose molecules is found in fruits and vegetables, and at high concentrations in sugar beet and sugarcane. Lactose, commonly known as milk sugar is
prevalent in dairy products such as milk, yogurt, and cheese. Maltose on the other
hand consists of two glucose molecules and is a common breakdown product of plant
starches and is rarely found in foods as a disaccharide.
Oligosaccharides consist of three to six monosaccharide units but are not frequently found in natural sources. Polysaccharides are polymer of monosaccharides
that may be branched or unbranched. Starch and cellulose are two main examples of
polysaccharides which are considered as slow releasing carbohydrates. Starch is
found in abundance in grains, legumes, and root vegetables, like potato. A plant
starch amylose, is a small linear chain containing hundreds of glucose units,
whereas, another plant starch amylopectin, is a large branched chain containing
thousands of glucose units. These two starch molecules are found together in foods
and are known as energy–storing molecules of plants. The smaller one (amylose) is
less abundant. Eating raw foods containing starches provides very little energy as
the digestive system takes longer to break them. Cooking results in degradation of
larger starch molecule to small units which are easier to breakdown and easy to
digest in the body. The starches that remain intact throughout digestion are called
resistant starches. Bacteria in the gut can breakdown some of these and may benefit
gastrointestinal health. Some of the isolated and modified starches are used widely
in the food industry as food thickeners. Polysaccharides such as starch, cellulose
and glycogen are large molecules comprising of many glucose units. Grains, milk,
fruits, and starchy vegetables are the major food sources of carbohydrates whereas,
non–starchy vegetables contain carbohydrates in lesser quantities. Carbohydrates
25 Bioavailability of Nutrients and Safety Measurements
disaccharides, oligosaccharides, and polysaccharides. The smallest carbohydrates are
monosaccharides such as glucose. When two molecules of monosaccharides are
linked together, they form disaccharides. The three most common forms of monosaccharides are glucose, galactose, and fructose. Glucose is the most preferred source of
energy for completion of cellular functions of the living organisms. Except during
extreme starvation conditions, our brain completely depends on glucose as preferred
source of energy. Another monosaccharide is galactose that differs from glucose only
in the position of hydroxyl group on the fourth carbon atom. This small structural
alteration causes galactose to be less stable than glucose and as a result the liver rapidly converts galactose to glucose which is then quickly utilized for energy production in cells. Fructose differs from glucose in its chemical structure, as the ring
structure of fructose contains only five carbons. Unlike glucose, fructose is not an
energy source for other cells in the body. Ribose is abundant in the nucleic acids
(RNA and DNA), and some pentoses are components of fiber. Sugar alcohols like
sorbitol, xylitol, and glycerol are industrially synthetic derivatives of monosaccharides. Due to their moderate sweetness and poor absorption sugar alcohols are often
used by the diabetic patients in place of sucrose to sweeten foods. Due to their quick
degradation by the bacteria in the mouth sugar alcohols do not cause tooth decay
(Gibney et al. 2009; Mahan and Raymond 2016; Titchenal et al. 2018). The most
common example of disaccharide is sucrose, lactose, and maltose composed of two
monosaccharide units one of which is mainly glucose. Sucrose comprising of both
glucose and fructose molecules is found in fruits and vegetables, and at high concentrations in sugar beet and sugarcane. Lactose, commonly known as milk sugar is
prevalent in dairy products such as milk, yogurt, and cheese. Maltose on the other
hand consists of two glucose molecules and is a common breakdown product of plant
starches and is rarely found in foods as a disaccharide.
Oligosaccharides consist of three to six monosaccharide units but are not frequently found in natural sources. Polysaccharides are polymer of monosaccharides
that may be branched or unbranched. Starch and cellulose are two main examples of
polysaccharides which are considered as slow releasing carbohydrates. Starch is
found in abundance in grains, legumes, and root vegetables, like potato. A plant
starch amylose, is a small linear chain containing hundreds of glucose units,
whereas, another plant starch amylopectin, is a large branched chain containing
thousands of glucose units. These two starch molecules are found together in foods
and are known as energy–storing molecules of plants. The smaller one (amylose) is
less abundant. Eating raw foods containing starches provides very little energy as
the digestive system takes longer to break them. Cooking results in degradation of
larger starch molecule to small units which are easier to breakdown and easy to
digest in the body. The starches that remain intact throughout digestion are called
resistant starches. Bacteria in the gut can breakdown some of these and may benefit
gastrointestinal health. Some of the isolated and modified starches are used widely
in the food industry as food thickeners. Polysaccharides such as starch, cellulose
and glycogen are large molecules comprising of many glucose units. Grains, milk,
fruits, and starchy vegetables are the major food sources of carbohydrates whereas,
non–starchy vegetables contain carbohydrates in lesser quantities. Carbohydrates
25 Bioavailability of Nutrients and Safety Measurements