PRINCIPLE OF FOOD

• Chemical property of food compositions: CARBOHYDRATES

  
• Simple carbohydrates


  Consist of either one basic sugar unit or a few of these small units linked together
• Complex carbohydrates


  Consist of thousands of basic sugar unit linked together to form very large molecule
• Chemical classification of carbohydrates

  • Simple carbohydrates
  • Sugars
  • Oligosaccharides
  • Polysaccharides
  • Starch
  • Non-starch eg. Cellulose, Pectin

  
• Simple carbohydrates

  • Monosaccharides
  • Disaccharides
• Monosaccharides

  • Glucose
  • Fructose
  • Galactose
• Glucose

  The most widely distributed monosaccharide, found in fruits & vegetables, starch, syrup, honey, circulates in the blood stream
• Fructose


  The sweetest of all the common sugars, found in many fruits & honey, very soluble, not easily crystallised, 1.3 to 1.7 times sweeter than sucrose
• Galactose

  Generally not found free in nature, a basic unit of lactose, a derivative (galacturonic acid) is the basic unit of pectic substance
• Disaccharides

  • Sucrose
  • Maltose
  • Lactose
• Sucrose

  Table sugar, widely used in crystallised form for food preparation, produced from sugar cane or sugar beets
• Sucrose is made up of glucose and fructose linked by a glycosidic bond
• Invert syrup

  Sucrose splitting into glucose and fructose, important during the formation of candies and jellies, formed by water, acid, heat, or enzyme invertase/sucrase
• Maltose


  One of the products of hydrolysis when the complex carbohydrate starch is broken, found in germinating or sprouting grains, corn syrup
• Maltose is made up of two glucose units linked by a glycosidic bond
• Lactose


  Found naturally mainly in milk and milk products, also called "milk sugar"
• Lactose is made up of glucose and galactose linked by a glycosidic bond
• Relative sweetness of sugars

  Sucrose = 100, Lactose = 16, Galactose = 32, Maltose = 32, Glucose = 74, Fructose = 173
• Carbonyl group (-C=O)


  Reactive group, contributes to Maillard browning and reducing activity
• Alcohol/hydroxyl group (-OH)


  Contributes to solubility
• Reducing sugars


  Sugars with a structure that allows electron exchange, act as reducing agents, include all common monosaccharides and some disaccharides
• Oxidation and reduction involve the exchange of electrons between molecules
• Oligosaccharides


  Carbohydrate molecules containing a few monosaccharide units, not digested by humans and may be broken down by intestinal bacteria

  
• Prebiotics


  Substances that promote the growth of good bacteria (Acidophilus, Bifidobacterium) and retard the growth of bad bacteria
• Sources of prebiotics


  • banana, garlic, honey, barley, onion, wheat, tomato, rye, brown sugar, asparagus, artichokes
• Inulin


  A fructo-oligosaccharide that functions as a prebiotic and soluble dietary fibre, occurs naturally in plants like onion and asparagus, can provide thickening, mimic creaminess, and act as a sugar replacer
• Polysaccharides


  Complex carbohydrates containing a large number of sugar units linked together by glycosidic linkages, with a degree of polymerization up to 60,000 units
• Major food polysaccharides


  • Starch
  • Cellulose
  • Pectin
• Starch


  The energy storage molecule of plants, composed of amylose (linear) and amylopectin (highly branched) polymers, the ratio of which contributes to sensorial properties

  
• Starch granules are composed of a mixture of amylose and amylopectin
• Modified starches


  Chemically modified to produce physical changes that contribute to preferred properties in food applications, including pregelatinized, cold water-swelling, stabilized, and acid-modified starches
• Cellulose


  A major structural component of plant cell walls, insoluble in water but can be converted to water-soluble gums, serves as dietary fibre
• Cellulose has a flat, ribbon-like structure where the monomers are turned upside down and associated through hydrogen bonding
• Pectin


  A polysaccharide that acts as a glue among plant cells, plays an important role in fruit texture, can be metabolized during ripening causing softening
• Pectin is widely used as a gelling agent, thickener, and stabilizer in food products
• Cellulose


  • Units in the chain are turned upside down
  • Associates with each other through hydrogen bonding and form polycrystalline, fibrous bundles
  • Insoluble in water but can be converted into water-soluble gums (through modifications) such as CMC, MC
  • Usually serves as dietary fibre because of indigestibility and does not contribute energy or significant nourishment through human digestive system
• Non-starch polysaccharide: Pectin


  • Cannot be metabolised by human
  • Acts as glue among cells in plant tissue
  • Plays important roles in texture of food product particularly, fruits
  • Can be metabolised during ripening of fruits causing softening in texture
• Pectin


  • Polysaccharide that is widely used as gelling agents, thickeners, and stabilisers
  • Naturally from plant tissue constituents
  • Common types: Low-methoxyl pectins (form gel without the need for sugar or acid), High-methoxyl pectins (form gel with the presence of sugar and acid, commonly used for jellies)
• Major Functional Properties of Carbohydrates in Food

  • Heat associated browning reactions (Maillard reaction, Caramelisation)
  • Crystallisation

  
• Maillard reaction


  • Reducing sugar + amino acids → melanoidins
  • Found in baked products, dried egg whites, instant mashed potatoes, development of chocolate flavour, roast beef flavour, cooked meat flavour
  • Favoured by high sugar (reducing sugar) & protein content, high temperature, high pH, low water content