HTM*2700 Introductory Foods
HTM*2700 Introductory Foods Monday Lecture Sept 16th /2013 Dispersion Systems à Liquid / Liquid Dispersion System à Emulsions Emulsions: special sub-‐group of liquid/ liquid dispersion systems. Always contains 2 immiscible liquids. (etc vinegar and oil, oil and water)
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Liquids which are not capable of staying mixed together, by themselves, for any length of time.
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One immiscible liquid is dispersed in the other immiscible liquid.
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Oil is always dispersed in vinegar or water
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2 Types : -‐ Temporary
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-‐ Permanent
Types of Emulsions 1) Temporary Emulsions e.g.) vinaigrette dressings (oil, vinegar and seasonings) -‐ oil is temporary dispersed in vinegar -‐ the 2 immiscible liquids separate upon standing. 2) Permanent of Emulsions e.g.) mayonnaise -‐ Contains an emulsifier (egg) -‐ Emulsifiers keep one immiscible liquid dispersed in another immiscible liquid permanently. -‐ In mayonnaise, oil is dispersed phase and vinegar is continuous phase. Egg yolk contains emulsifier LECITHIN Emulsifier •
Has an affinity for both phases of an emulsion
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Most common emulsifier is lecithin in egg yolks
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Has a hydrophilic end and a hydrophobic end
HYDRO = Water PHOBIC = Fear of PHILIC = Loving/ liking In mayonnaise the 2 ends of the lecithin emulsifier in egg yolk will orient themselves as follows: -‐
Hydrophobic (water fearing) end towards the oil
-‐
Hydrophilic (water loving) end towards the vinegar
Course Pack p.21A Parenchyma Cell diagram Cell Wall is composed of: 1). Cellulose: -‐ main constituent -‐ complex carbohydrate which is a polymer of glucose -‐ source of fibre in the diet à Beta linkage cannot be broken by humans 2). Hemicellulose -‐ cellulose is embedded in hemicellulose -‐ complex carbohydrate which is a polymer of xylose -‐ breaks down in alkaline conditions -‐ will be a factor when talking about vegetables Effect of cooking on cellulose and hemicellulose •
heat and water together cause softening
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texture changes from hard or film or crisp to softer or less firm or less crisp
•
Cellulose and Hemicellulose become softer ( do NOT break down)
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Acid slows down softening process, allowing fruits/vegetables to remain firmness longer.
-‐ Alkaline conditions cause hemicellulose ONLY to break down -‐ Results in mushy, slimy vegetables e.g.) Guelph water has PH = 8.0 Cell Wall is also composed of 3.) Pectic Substances •
Complex carbohydrates which are polymers of galacturonic acid
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Also found in the spaces between cells (intercellular spaces), and found in the cell wall
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3 pectic substances: Protopectic, pectin and pectin acid.
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Protopectin is cement (glue) between cells, allowing a fruit to maintain its shape.
During ripening OR Cooking of fruit (heat + acid): Protopectin àPectin à Pectin Acid •
Glue or cement like substance
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Called solubilization of protopectin
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Results in a loss of fruit shape
Effect of Cooking on Pectic Substances Acid (added or naturally occurring organic acids) spreads up rate of protopectin solubilization Fruit loses shape faster Sugar slows down protopectin solubilization by forming hydrogen bonds with protopectin Fruit retains shape longer Fruit: •
High proportion of pectic substances
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Low in cellulose and hemicellulose
Vegetables (Next week) •
High in cellulose and hemicellulose
•
Low in pectic substances
Cooking Fresh Fruit H2O only (hypotonic medium) e.g. apple sauce 1). Softening – cellulose and hemicellulose absorb water so the apple will change its texture form, crispy to soften. 2). Loss of shape – protopectin solubilizers, organic acids in fruit speed this process H2O and sugar (hypertonic solution) e.g. apple compote 1). Softening: cellulose and hemicellulose absorb water 2). Retention of shape: -‐ sugar hydrogen bonds to protopectin -‐ sugar slows solubilization of protopectin. Friday Lecture Sept, 20th/2013 Oxidative Enzymatic Browning Mitochondria: contains the 1) Enzyme (E) polyphenoloxidase **Course pack, Fruit Summary Notes, pp. 38 & 39 (Reaction formula, SàPàMelanins) Enzyme •
Organic catalyst which speeds up the rate of a chemical reaction
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Composed mainly of protein
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Denatured by heat ( & acid, which means we have to make PH very low)
•
Functions within narrow pH and temperature range
Polyphenoloxidase •
Optimum pH = 7.0
•
Decreased activity at pH
•
Liquids which are not capable of staying mixed together, by themselves, for any length of time.
•
One immiscible liquid is dispersed in the other immiscible liquid.
•
Oil is always dispersed in vinegar or water
•
2 Types : -‐ Temporary
•
-‐ Permanent
Types of Emulsions 1) Temporary Emulsions e.g.) vinaigrette dressings (oil, vinegar and seasonings) -‐ oil is temporary dispersed in vinegar -‐ the 2 immiscible liquids separate upon standing. 2) Permanent of Emulsions e.g.) mayonnaise -‐ Contains an emulsifier (egg) -‐ Emulsifiers keep one immiscible liquid dispersed in another immiscible liquid permanently. -‐ In mayonnaise, oil is dispersed phase and vinegar is continuous phase. Egg yolk contains emulsifier LECITHIN Emulsifier •
Has an affinity for both phases of an emulsion
•
Most common emulsifier is lecithin in egg yolks
•
Has a hydrophilic end and a hydrophobic end
HYDRO = Water PHOBIC = Fear of PHILIC = Loving/ liking In mayonnaise the 2 ends of the lecithin emulsifier in egg yolk will orient themselves as follows: -‐
Hydrophobic (water fearing) end towards the oil
-‐
Hydrophilic (water loving) end towards the vinegar
Course Pack p.21A Parenchyma Cell diagram Cell Wall is composed of: 1). Cellulose: -‐ main constituent -‐ complex carbohydrate which is a polymer of glucose -‐ source of fibre in the diet à Beta linkage cannot be broken by humans 2). Hemicellulose -‐ cellulose is embedded in hemicellulose -‐ complex carbohydrate which is a polymer of xylose -‐ breaks down in alkaline conditions -‐ will be a factor when talking about vegetables Effect of cooking on cellulose and hemicellulose •
heat and water together cause softening
•
texture changes from hard or film or crisp to softer or less firm or less crisp
•
Cellulose and Hemicellulose become softer ( do NOT break down)
•
Acid slows down softening process, allowing fruits/vegetables to remain firmness longer.
-‐ Alkaline conditions cause hemicellulose ONLY to break down -‐ Results in mushy, slimy vegetables e.g.) Guelph water has PH = 8.0 Cell Wall is also composed of 3.) Pectic Substances •
Complex carbohydrates which are polymers of galacturonic acid
•
Also found in the spaces between cells (intercellular spaces), and found in the cell wall
•
3 pectic substances: Protopectic, pectin and pectin acid.
•
Protopectin is cement (glue) between cells, allowing a fruit to maintain its shape.
During ripening OR Cooking of fruit (heat + acid): Protopectin àPectin à Pectin Acid •
Glue or cement like substance
•
Called solubilization of protopectin
•
Results in a loss of fruit shape
Effect of Cooking on Pectic Substances Acid (added or naturally occurring organic acids) spreads up rate of protopectin solubilization Fruit loses shape faster Sugar slows down protopectin solubilization by forming hydrogen bonds with protopectin Fruit retains shape longer Fruit: •
High proportion of pectic substances
•
Low in cellulose and hemicellulose
Vegetables (Next week) •
High in cellulose and hemicellulose
•
Low in pectic substances
Cooking Fresh Fruit H2O only (hypotonic medium) e.g. apple sauce 1). Softening – cellulose and hemicellulose absorb water so the apple will change its texture form, crispy to soften. 2). Loss of shape – protopectin solubilizers, organic acids in fruit speed this process H2O and sugar (hypertonic solution) e.g. apple compote 1). Softening: cellulose and hemicellulose absorb water 2). Retention of shape: -‐ sugar hydrogen bonds to protopectin -‐ sugar slows solubilization of protopectin. Friday Lecture Sept, 20th/2013 Oxidative Enzymatic Browning Mitochondria: contains the 1) Enzyme (E) polyphenoloxidase **Course pack, Fruit Summary Notes, pp. 38 & 39 (Reaction formula, SàPàMelanins) Enzyme •
Organic catalyst which speeds up the rate of a chemical reaction
•
Composed mainly of protein
•
Denatured by heat ( & acid, which means we have to make PH very low)
•
Functions within narrow pH and temperature range
Polyphenoloxidase •
Optimum pH = 7.0
•
Decreased activity at pH
