Food Chem Lecture 8
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Food Chem Lecture 8
Food Chem lecture
Food Chem lecture 8
What happens if an interesterification reaction is carried to completion?
If carried to completion, there will be a complte randomixation of the fatty acids on the glycoerides- which can significantly change the physical properties of the fat/oil
What happens if the interesterification reaction is carried out at lower temperatures?
If the reaction is carried out a lower temperatures, the more saturated long chain glycerides will fractionally crystallize out
What does interesterification allow?
Interesterification allows one to change physical properties without forming trans atty acids (eg. becel)
What is interesterification used for?
Interesterification is used extensively to remove the graininess from lard and to change the characteristics of other fats and oils to provide properties other thna those naturally present
What is the unique property of cocoa butter?
Has a relatively sharp melting point at body temperature- expensive product
Can be imitated in part by proper modification of other fats and oils, so that they can be used as extenders (dilute) and reduce the need for the more expensive cocoa butter component
What are monoglycerides used for?
Interesterification is also used to manufacture monoglycerides which are used extensively as emulsifiers
How are monoglycerides produced?
Triglycerides interestrified with excess glycerol produces predominantly monoglycerides
How are monoglycerides seperated from residual di- and triglycerides?
Why are monoglycerides excellent emulsifiers?
Have both hydrophilic (2-OH from glycerol) and hydrophobic (fatty acid chain) groups
Why do fats not have a sharp melting point?
They are a complex mixture of trilgycerides, each triglyceride having its own melting point
The fat melting point is a composite of all individual melting points of the glycerides- leads to a broad melting range
Why are fats not 'solid' at room temperature?
Fats are actually oil trapped in a crystalline matrix- hence a plastic fat
How does one determine the spreadable properties of a plastic fat?
Its plastic or spreadable properties depend on the solid to liquid ratio of the system
What are crystals held together by?
Van der Waals forces
What is the 'plastic range' of a fat?
When a fat can be deformed readily, it is said to be in its 'plastic range', which is a function of the triglyceride fatty acid composition and distribution
What are the more common polymorphic forms of fats?
How does one form alpha crystals in a fat?
Melt a fat first and cool it quickly- the majority of the glycerides will crystallize into the alpha form, which are predominantly thin, lead like crystals
What happens if the holding tmperature rises above the temperature of stability for the alpha crystal form?
It will spontabeously start to change to another crystalline form
How does one produce a beta prime crystalline structure?
re-melt and cool the far more slowly to provide more time for molecular arrangement and the beta prime crystals will be formed
How does one produce beta crystals?
Re-melt and cool very slowly and very dense, large beta crystals are produced
Why are beta crystals undesirable?
Beta crystals are undesirable because they induce graininess (detected organleptically) and reduce functionality
Why is the knowledge of the solid fat content of fats as a function of temperature important?
Such information is required for blending and obtaining consistent textural and functional characteristics for a fat
how is the solid fat content commonly measured?
The measurement of the solid fat content is commonly determined by dilatometry or NMR
What is dilatomentry?
Based on the measurement of specific volume (the inverse of density) per unit temperature
Fat is simply placed in a reservoir, which a capillary attached (dilatometer) and the expansion of fat is measured as the temperature is changed in specific, defined increments
What are the three general regions of a dilatometry curve?
1. Solid fat undergoing thermal expansion of the solid
2. Representing expansion of solid and progressive dilation due to a change in state to a liquid
3. Representing the epansion of the liquid only
What is the term for dilametric determination of solids in fats?
Solid Fat Index
What is NMR?
NMR (Nuclear Magnetic Resonance) is the probing of the fat using radio waves and magnetic field- the radio waves causing the hydrogen in liquid fat molecules to resonate
What is measurement by NMR termed?
Solid Fat Content- the amount of resonance generated is propertional to the liquid portion of the fat
What do shortenings do?
Have the capability to reduce the elasticity of a dugh to make pastry more tender/flaky
Which fats have a greater shortening power?
Fats with higher levels of unsaturated atty acids have greated shortening power- often prepared by hydrogenation of vegetable oils
What is a natural shortening?
Lard is a natural shortening- its quality dependent on the dominant crystal form and its solid fat content
What problem does untreated lard have?
Lard sufferes from graininess which can be interesterified to overcome the graininess problem
How can one control the plasticity of shortening?
Shortening plasticity can also be varied by varying the amo0unt of nitrogen incorporated into the at, which also whitens it
What are margarines?
Far and oil bends which have extensively replaced butter
Water (~20%) in oil (W/O) emulsion, with some milk solids
How is margarine made?
Fed into a cooled scraped surface heat exchanged, which partially solidifies the material
Product is the tempered to crystallize (beta-prime) in a manner which gives good consistency
What is often incorporated into margarines and why?
Hydrogenated cottonseed oil is often incorporated into margarines because of its preference for crystallizing into the beta prime form
What is an enrobing fat?
Has narrow melting point range and contains about 80% di-saturated triglycerides
What is the advantage of enrobing fats?
They solidify rapidly, enabling them to be used as enrobing fats but they melt at body temperature- desirable
How does one produce cheaper enrobing fats?
Selective interesterification, hydrogenation and or blending of other fats can be used to produce cheaper enrobing fats
What is the most expensive enrobing fat?
Why can one not completely cut fats out of their diet?
Lipids are an integral constituent of tissue and cell memebranes and hence they are required in adequate amounts
Which types of fats have been implicated as a contributing factor to arterioclerosis?
Saturated and trans fats
What are the fat soluble vitamins?
A, D, E and K
What is satiety?
The feeling of fullness
How does frying work?
Allows high temperatures to be reached, driving moisture out of the product and allowing desirable browning and flacor development reactions to take place
Why are fats incorporated into baked products?
To shorten texture- reduces the interaction of the wheat proteins to produce a desirable crumbly texture required for cakes and cookies
Why are mono/di-glyceride emulsifiers important in the formulation of salad dressings?
Stabilize the emulsion formed by their polar/non-polar moieties
What are phospholipid by-products used for?
Used extensively as emulsifiers, as food/pan release agents and anti-spattering agents
How do emulsifiers work?
Reduce the interfacial tension between oil and water by bridging the two phases by having both hydrophilic and hydrophobic moieties within its molecular structure
What are the properties of an emulsion?
Becomes viscous, opaque and the fatty sensation associated with oil is masked
Why do frying oils seem to not go rancid as fast?
Because the peroxides which form break down quickly and the breakdown prducts are volatilized and lost at elevated frying temperatures
Which products tend to accumulate in frying oils?
Products accumulating tend to be predominantly fatty acids (hydrolysis and polymerization products
How does fatty acid accumulation affect frying oils?
Fatty acid accumulation lowers the smoke point over time- changes the frying characteristics of the material being cooked, but do not represent a health hazard per se
How do polymers affect frying oils?
High levels of polymers manifest themselves by increasing the oil viscosity- higher polymers are known to be toxic to rats
What other changes occur in high temperature oils?
Decrease in the iodine value and conversion of the cis to trans isomers
Why is there generally no health hazard associated with frying oils?
Because there is usually a constant replenishment of the oil due to its absorption by foods being fried
What happens when fatty foods are friend?
When fatty foods such as chicken, fish, and port and fried, the fat level will increase and has to be monitored
Why are medium chain triglycerides sold for clinical, health food/athletic markets?
Absorbed more readily- these FFAs are taken from lumen directly to the blood system rather than going via the lymphatic system
What are medium chain triglycerides used for clinically?
Used for treatment of fat malabsorption in premature infants and for intravenous feeding
What is olestra?
A fat replacer- all the properties of an oil, but not digestible