Presentation on theme: "Food Biotechnology Dr. Kamal E. M"— Presentation transcript:
1 Food Biotechnology Dr. Kamal E. M Food Biotechnology Dr. Kamal E. M. Elkahlout Food Biochemistry 6 Chemical properties of food
2 Pigments Contributions Natural substances in cells and tissues of plants and animals that impart colourContributionsColors help insect to get attracted to flowers which helps in the pollination
3 Color and appearance are major quality attributes of foods Because of our ability to easily perceive these factors as first evaluated by consumers when purchasing foodConsumers relates colors of food to qualityRedness in meat: freshnessGreen pawpaw : immatureOrange pawpaw : ripe
4 Color also influence flavour perception Red drinks: strawberry, cherry flavorGreen drinks: lime flavorColors such as carotenoids, riboflavin, etc are not only colors but are nutrientsthus colors have multiple effects on consumersMany food pigments are unstable during processing and storage, thus need careful preparation
5 Categories of natural pigments 1. tetrapyrrole compoundsinclude chlorophyll, blood pigments (myoglobin and haemoglobin)2. isoprenoid derivativescarotenoids3. benzopyran derivatesanothocyanins and flavonoids4. artefactsmelanoidins, caramels.
6 Tetrapyrrole Pigments Chlorophyll-major pigment in green plants and algae for photosynthesisOccurs in different formsChlorophyll amost abundant form in naturehas a methyl group at the R positiontotal resonance and the methyl (CH3) group result in a pigment color of blue-greenChlorophyll bR group is an aldehyde (C=OH) groupgives a yellowish green color
8 Chlorophyll degradation In heated vegetables chlorophyll is degraded by change in pHAcidic pH(3)-chlorophyll is unstableBasic pH(9)-chlorophyll is stableMg2+ atom is easily displaced by 2 hydrogen ionsresult in formation of olive-brown pheophytin a and breaction is irreversable in aqueous solutionProlonged heating further degrade pheophytin into Pyropheophytin which has an olive drab color
9 To avoid degradationlessen the action of heat through the use of high temperature short-time thermal treatmentsby raising the pH of the medium (by the use of baking soda) which this results in the formation of chlorophyllin that has an unrealistic bright color and the texture of the vegetable is extremely mushyMushiness can be prevented by the addition of calcium acetate or any other calcium salt whish will prevent breakdown of the hemicellulose in the alkaline medium
10 ISOPRENOID DERIVATIVES CarotenoidsPigments are responsible formost of yellow and orange coloursHave antioxidant activity-prevent lipid perioxidation
11 Stability during processing Quite stable during storage and handlingThere is a little change in content during freezingBlanching influence levels due to inactivation of lipoxygenase, which catalyse oxidative decomposition of carotenoids and enhance efficiency of extraction of pigments compared to raw sampleVery high tempt yield fragmentation products that are volatileAir dehydration exposes to oxygen causing extensive degradationExposure to light aggravates degradation
12 Benzopyran derivatesFlavonoids and anthocyanins
13 Flavonoids Polyphenolic compounds in fruits and vegetables In fresh plants present in the form of glycosidesIn processed foods present in aglycones form
15 Compounds Food sources Cyanidin Peonidin Pelargonidin Pelphinidin apple fruit skin, blackberry, elderberry fruits, red cabbage, strawberry, rhubarb, black currant, corn, plum, raspberry, red onionPeonidinpeony flowers, cherry, cranberry, sweet potato, plum, strawberry fruit, pomegranate flowersPelargonidinpelagonium flowersPelphinidindelphinium flowers, hydrangea flowers, bluebell flowersPetunidinMalvidinpetunia flowers, cherries, berries, grape skins, cyclamen flowersGrapes, pine bark
16 Stability Is relatively unstable Stable in acidic conditions Stability is affected bySubstituents of the aglyconePelargonidin, cyanidin or delphinidin are less stablePetunidin and malvidin are more stableTemperatureOxygen conc
17 Artefacts melanoidins, caramels. These are products of a physical process resulting in a chemicals processresult of enzymatic or non-enzymatic browning
18 Enzyme ActivityEnzymes are biological catalysts which is an agent affecting the velocity of a chemical reaction without appearing among the final products of the reaction.They operate at a temperature of approximately 37°C and pH close to neutrality.Use of enzymes in food industry-malted barley in brewingyeast in the production of alcoholic beveragesIn bread and cheese making
19 Factors Affecting the Rate of Enzyme Catalyzed Reactions Effect of Enzyme Concentration –the rate of reaction depends on the concentration of enzyme
20 Effect of Substrate Concentration -reaction speed is proportional to substrate concentration only at low concentrations of the substrate and is independent of it at high concentration.
21 Effect of Temperature -Enzyme activity proceeds very slowly at low temperatures As the temperature increases, the rate of the enzyme- catalyzed reaction increasessince enzymes are proteins, thermal denaturation of the apoenzyme sets in as temperature increases, resulting in inactivation of the enzyme.For most enzymes optimum activity is between 30-40°C
22 Effect of pH -The activity of an enzyme depends on the pH of the reaction medium Most enzymes are active in the pH range from 4.5 to 8.0. There are exceptions: pepsin has a pH optimum of 1.8 and arginase around 10.At extremes of acidity and alkalinity the denaturation of the protein takes place with a concomitant loss of enzyme activity
23 Flavor and aromatic compounds in food Appearance of a food is important, but it is the flavor that ultimately determines the quality and acceptability of foods. No matter how safe, nutritious, inexpensive and colorful a food may be, if the flavor is undesirable it is rejected .is a sensory phenomenon depending upon taste, odour or aroma, appearance, temperature—sensation of heat and cold, and texture or “mouthfeel” affecting the sense of touchThe Sensation of TasteThe sense of taste refers to the ability of the taste organs to perceive and recognizeThe four basic tastes → sweet, sour, salty and bitter
24 Saltiness is produced by inorganic salts. Substances with TasteSaltiness is produced by inorganic salts.Sodium chloride is the only compound that gives a pure salty taste.Other salts have additional tastes, e.g. some iodides and bromides are bitter and some inorganic salts of lead and beryllium are sweet.Sweetness is stimulated by a number of organic compounds. Aliphatic hydroxy compounds, such as carbohydrates, are sweet substances. Diverse compounds, such as saccharin, peptides and cyclamates, are also sweet.
25 Sourness is caused by proton donors Sourness is caused by proton donors. This does not, however, entirely account for sourness; at the same pH, acetic acid tastes more sour than hydrochloric acid. Aliphatic long chain fatty acids are more sour than short chain acids.One group of bitter substances are alkaloids like quinine, strychnine and nicotine.Caffeine, a constituent of coffee and tea, is bitter. Phenolic compounds like tannin and some flavonoid compounds contribute to bitterness and astringency.
26 The Smell SensationOdour or smell plays a prominent role in most flavours. One can experience thousands of odour sensations.Like taste, smell is recognized by receptor cells called olfactory cells
27 pH and acidityorganic and inorganic acids occur in foods and serve a variety of rolescontribution of sour tasteacids have the power of intensifying and modifying the taste perception of other flavor agentsAcids and acid salts are used as chemical leavening agents to impart a characteristic porous, cellular structure to baked foods.Acids act as microbial inhibitors in food preservation (e.g., benzoic acid).They also help achieve the sterilization of fruits and vegetables under less severe thermal conditions.Acids are also important in the setting of pectin gels, in defoaming and bringing about emulsification.Acids induce coagulation of milk proteins in the production of cheese and other dairy products.
28 Alkaline agentsare used to neutralize excess acid in the production of butter from fermented milk. The reduction of acidity improves churning efficiency and retards the development of oxidative off-flavours.substances like sodium carbonate and bicarbonate are used, along with acids, for the production of carbon dioxide during baking.are also used for the enhancement of colour and flavour of foods. For example, treatment of ripe olives with dilute sodium hydroxide solution aids the removal of the bitter principal and development of dark colour.Use of sodium bicarbonate during cocoa processing produces dark chocolate.Strong bases are employed for peeling a number of fruits and vegetables.
29 Tutorial1. What are the most frequently employed techniques of enzyme inhibition in food?Explain using graph the effect of Enzyme Concentration?Discuss the 4 major flavor sensations perceived by tongue4. What are some of the functions of Acids and Bases in Foods?5. How does pH change affect chlorophyll?6. As a food technologist what will you do to preserve the color of garden peas and maintain its texture as well?7. What is metmyoglobin? When is it formed?8. What conditions degrade carotenoids?9. How does temperature affect the property of enzymes?10. Pigments in fruits and vegetables contribute to appreciation of food. Food preservation and processing try to maintain as close as possible the original color of the raw materials. Name the pigments that you have studied and describe how they are degraded during food processing
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