food chemistry - weebly
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Food Chemistry
Tuesday, February 28, 2012
Distinguish between a food and a nutrient.
• Food: “Any substance, whether processed, semi- processed or raw, which is intended for human consumption, and includes drink, chewing gum and any substance which has been used in the manufacture, preparation or treatment of ‘food’, but does not include cosmetics or tobacco substances used only as drugs.” (Codex Alimentarius (FAO/WHO) definition 2005)
• Nutrient: Any substance obtained from food and used by the body to provide energy, regulate growth, maintenance and repair of the body’s tissues.
• Proteins, lipids, carbohydrates, vitamins, minerals and water are considered nutrients.
Tuesday, February 28, 2012
Describe the chemical composition of lipids (fats and oils), carbohydrates and proteins.
• Fats and oils are tri-esters (triglycerides) formed from three long-chain fatty acid (carboxylic acid) molecules and one glycerol molecule.
• The simplest carbohydrates are monosaccharides.
• They contain one carbonyl group (C=O) and at least two hydroxyl (–OH) groups, and have the empirical formula CH2O. Monosaccharides are the building blocks of disaccharides and polysaccharides.
• Proteins are made up of 2-amino acids.
Tuesday, February 28, 2012
Fats and oils
Tuesday, February 28, 2012
Monosaccharides (sugars)• one carbonyl group (C=O or aldehyde) and at least two hydroxyl (–OH)
groups
Tuesday, February 28, 2012
Proteins are made up of 2-amino acids
Tuesday, February 28, 2012
Describe the difference in structure between saturated and unsaturated (mono- and poly-unsaturated) fatty acids.• Saturated compounds are "saturated" with hydrogen. Unsaturated compounds
have double bonds (C=C) between carbon atoms. Saturated compounds have single bonds (C-C) between the carbon atoms, and the other bond is bound to hydrogen atoms (for example =CH-CH=, -CH2-CH2-, etc.).
Tuesday, February 28, 2012
Predict the degree of crystallization (solidi"cation) and melting point of fats and oils from their structure, and explain the relevance of this property in the home and in industry.
• Unsaturated fats have a lower melting point and are more likely to be liquid. Saturated fats have a higher melting point and are more likely to be solid.
• Solid fats are more likely to be crystalline, more saturated and/or have longer fatty acid hydrocarbon chains. Mono-unsaturated (olive, canola and peanut) and poly-unsaturated fats (safflower, sunflower, corn, fish, linoleic and linolenic) are liquids, and saturated fats (palm, coconut, lard, butter and shortening) are solids at room temperature.
• The melting point of fatty acids increases with increasing relative molecular mass and increasing degree of saturation. Fats and oils are chosen for cooking on the basis of their melting temperature. For example, cocoa butter melts at close to body temperature, and fats chosen for cake-making melt over a wide range of temperatures.
• Cis fatty acids (the hydrogen atoms are on the same side of the carbon–carbon double bond) have lower melting points than trans fatty acids (the hydrogen atoms are on opposite sides of the carbon–carbon double bond).
Tuesday, February 28, 2012
Deduce the stability of fats and oils from their structure.
• Saturated fats are more stable than unsaturated fats. The carbon–carbon double bonds in unsaturated fats react with oxygen (auto-oxidation), hydrogen (hydrogenation), light (photo-oxidation) and enzymes/heat/water (hydrolysis).
Tuesday, February 28, 2012
Describe the process of hydrogenation of unsaturated fats.
• The addition of hydrogen to the carbon–carbon double bond of a fatty acid in the presence of heat (140–225oC), pressure and a finely divided metal catalyst (Zn, Cu, Ni) increases the amount of saturation, which can be partial or full.
• Hydrogenation of unsaturated fatty acids is widely practiced to give saturated fatty acids, which are less prone toward rancidification. Since the saturated fatty acids are higher melting than the unsaturated relatives, the process is called hardening. This technology is used to convert vegetable oils into margarine.
Tuesday, February 28, 2012
Discuss the advantages and disadvantages of hydrogenating fats and oils.
• Advantages:
• make the melting point of an unsaturated fat more like that of a saturated fat
• less reactive (to oxidation)
• harder
• Disadvantages:
• unsaturated fats are healthier
• trans fats can form
• trans fatty acids are hard to metabolize, accumulate in fatty tissue, are difficult to excrete from the body, increases LDL cholesterol and are a low-quality energy source.
Tuesday, February 28, 2012
Shelf life:
• A food reaches its shelf life when it no longer maintains the expected quality desired by the consumer because of changes in flavour, smell, texture and appearance (colour, mass) or because of microbial spoilage.
Tuesday, February 28, 2012
Discuss the factors that affect the shelf life and quality of food.
• Product quality is often mathematically modeled around a parameter (concentration of a chemical compound, a microbiological index, or moisture content).
• water content: dry foods become vulnerable to microbial spoilage if they take on moisture
• Chemical Change (pH) , can affect taste and colour changes (When bacteria breaks down the food, acids and other waste products are created in the process.[1] While the bacteria itself may or may not be harmful, the waste products may be unpleasant to taste or may even be harmful to one's health.)
• Light
• Temperature: effects rate of spoilage (chemical reactions double their rate for each temperature increase of 10 degrees Celsius (°C))
• Air: effect oxidation
Tuesday, February 28, 2012
Describe the rancidity of fats.
• Rancidification is the chemical decomposition of fats, oils and other lipids
• When these processes occur in food, undesirable odors and flavors can result. In some cases, however, the flavors can be desirable (as in aged cheeses).
• Rancidity is the perception of flavours in lipids, those that our senses perceive as off because they have a disagreeable smell, taste, texture or appearance.
• Hydrolytic rancidity occurs when water splits fatty acid chains away from the glycerol backbone in triglycerides (fats).
• Oxidative rancidity is associated with the degradation by oxygen in the air.
• Microbial rancidity refers to a process in which microorganisms, such as bacteria, use their enzymes such as lipases to break down fat.
Tuesday, February 28, 2012
Compare the processes of hydrolytic and oxidative rancidity in lipids.
• Hydrolytic rancidity: The breaking down of a lipid into its component fatty acids and glycerol. It takes place more rapidly in the presence of enzymes (lipase), heat and moisture. In deep frying, water present in food and high temperatures increase the rate of hydrolysis.
Tuesday, February 28, 2012
oxidative rancidity
• Oxidative rancidity: The fatty acid chains are oxidized, typically by the addition of oxygen across the carbon–carbon double bond of the unsaturated fatty acid.
• Oily fish (such as herring and mackerel) contain a high proportion of unsaturated fatty acids and are prone to oxidative rancidity. The process can be catalysed by light (photo-oxidation) and enzymes. Details of the free-radical chain mechanism will not be assessed.
Tuesday, February 28, 2012
Tuesday, February 28, 2012
Describe ways to minimize the rate ofrancidity and prolong the shelf life offood.
• low temperature
• low light
• low moisture
• inert gas in packaging
• minimizes air in packaging
• low permeability in packaging
• sodium sulfite, sodium hydrogensulfite, citric acid
• sodium/potassium nitrite
• sodium benzoate and benzoic acid
• sorbic acid, propanoic acid, calicum propanoate and sodium propanoate
• ethanoic and benzoic acid
Tuesday, February 28, 2012
Describe the traditional methodsused by different cultures to extendthe shelf life of foods.
• fermentation
• The primary benefit of fermentation is the conversion of sugars and other carbohydrates, e.g., converting juice into wine, grains into beer, carbohydrates into carbon dioxide toleaven bread, and sugars in vegetables into preservative organic acids.
Tuesday, February 28, 2012
Preserving• Preserving fruit, by turning it into jam, for
example, involves boiling (to reduce the fruitʼs moisture content and to kill bacteria, yeasts, etc.), sugaring (to prevent their re-growth) and sealing within an airtight jar (to prevent recontamination).
Tuesday, February 28, 2012
Salting• Salting is used because most
bacteria, fungi and other potentially pathogenic organisms cannot survive in a highly salty environment, due to the hypertonic nature of salt.
• Any living cell in such an environment will become dehydrated through osmosis and die or become temporarily inactivated.
Tuesday, February 28, 2012
Smoking• A number of wood smoke compounds
act as preservatives. Phenol and other phenolic compounds in wood smoke are both antioxidants, which slow rancidification of animal fats, and antimicrobials, which slow bacterial growth.
• Other antimicrobials in wood smoke include formaldehyde, acetic acid, and other organic acids, which give wood smoke a low pH—about 2.5. Some of these compounds are toxic to people as well, and may have health effects in the quantities found in cooking applications.
Tuesday, February 28, 2012
Antioxidant
• A substance that delays the onset or slows the rate of oxidation. It is used to extend the shelf life of food.
Tuesday, February 28, 2012
List examples of common naturallyoccurring antioxidants and theirsources.
• Vitamin C (green leafy vegetables, citrus)
• Vitamin E (nuts, seeds, green leafy vegetables)
• Beta Carotene (carrots, broccoli)
• Selenium (fish, red meat, eggs)
Tuesday, February 28, 2012
Compare the structural features of themajor synthetic antioxidants in food.
• 2- and 3-tert-butyl-4- hydroxyanisole (BHA)
• 3,5-di-tert-butyl-4-hydroxytoluene (BHT)
• propyl gallate (PG)
• 2,4,5-trihydroxybutyrophenone (THBP)
• tertbutylhydroquinone(TBHQ).
Vitamin C
Tuesday, February 28, 2012
Discuss the advantages anddisadvantages associated with naturaland synthetic antioxidants.
• Natural occurring Vitamin C reduces free radicals, which reduces cancer and heart disease risk.
• Perceived safety risk from synthetic compounds.
• Synthetic compounds can be more effective.
Tuesday, February 28, 2012
List some antioxidants found in thetraditional foods of different culturesthat may have health bene"ts.
• Examples include green tea, turmeric, oregano,blueberries, cranberries and dark chocolate, which have been linked to lowering LDL cholesterol and blood sugar levels, reducing high blood pressure and preventing cancerous cell development.
Tuesday, February 28, 2012