Foodchem Lecture 7
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What is the usual organic solvent used to extract residual oil from the oilseed cake produced by the expelling/extrusion operation?
When is solvent extraction a good idea?
Although solvent extraction is very efficient, it is only advantageous when economies of scale are involved (so large volumes are required to make it economical
Where are most of the crushing/solvent extraction plants in Canada?
There are relatively few in Canada, most in the prairies where most of the oilseed production takes place
When is rendering to obtain oils done?
It is carried out for animal and fish sources on tissue and carcass by-products
How much moisture does animal tissue contain vs. oilseeds?
60-80% vs. 12% in oilseeds
Why is hexane a bad solvent for rendering?
It is hydrophobic and therefore immiscible with water so it cannot be used
What are the steps in rendering?
- 1. Material rendered is usually waste by-products from meat fish processing operations
- 2. Ground meat/fish is placed into large pressurized vessels
- 3. Heated with steam under pressure where the tissue is cooked and disrupted, lipids melt and are released to float to surface
- 4. Fat is skimmed off and is ready for further processing
- 5. This is also used as feedstock for biodiesel - Rothsay - 2.5 billion kg of food waste
What are the steps in lipid extraction?
- 1. Heat, crush, expel, and solvent extract
- 2. The residual "press cake" is desolventized and is usually sold as animal feed (bulk)
- 3. Some of the press cake may be further processed to obtain soybean protein for human consumption (relatively minor amounts)
- 4. Resulting extracted oil is dark brown (due to lipid-soluble materials like carotenoids, chlorophyll, pheophytin) and smelly with a lot of particulate material in it (particulate made up of proteins and carbs)
What are some of the other components present in the oil resulting from soybean extraction?
- Free fatty acids: released by the action of lipase
- Hydroperoxides: and their breakdown products formed by enzymatic action of lipoxygenase and attacked by oxygen during crushing
- Phospholipids (Lecithins): may be naturally present in the oil in significant quantities- especially in soybeans
- Metal Ions: Free and complexed
- Flavor Components: oil would not be particularly appetixing tastin anywhere from 'plant-like' to 'fishy'
What is settling and drumming?
Vigorously mixing the oil with water and allowing it to stand in a conical tank for some time
What is the purpose of settling and drumming?
Carbohydrates, proteinaceous extraneous matter and phosphoipids will hydrate over time and tend to associate themselves with the aqueous phase- the aqueous layer would eventually seperate carrying with it the cellular debris, carbohydrates and phospholipids
Why is settling and drumming not used anymore?
Becaused of the long times required and the fact that the oil can continue to deteriorate while standing
How is the settling and drumming process done today?
Live steam injection is used to hydrate the colloids and phospholipids, which in conjunction with centrifugation serparate the hydrated colloids and water formed to make it a continuous process
What does refining do to the oil?
Removes free fatty acids from the oil
How is refining done?
Involves the treatment of the oil with dilute alkali, so as to convert the free fatty acids into soap- the soap formed is removed with the aqueous phase
Why must the free fatty acid content be carefully measured for the refining process?
The alkali used has to be carefully measure to ensure there is no excess NaOH so as to avoid saponification of the oil- thus the need to accurately assess the FFA content
How do moderrn processing systems combine settling degumming and refining into a single operation?
Use steam injection along with dilute base combined with centrifugation
What is added to the oil in order to bleach it and why?
Dry bentonite or activated charcoal are added because they are capable of absorbing slightly polar compounds in the basence of moisture
What is the last group of contaminants left?
How are odoriferous compounds removed from the oil?
Removed by steam stripping- spraying the oil into an evacuated chamber with superheated steam flowing counter-current to oil droplets
What happens to residual hydroperoxides during steam stripping?
Residual hydroperoxides decompose at these high temperatures- some cis-trans isomerization occurs
What are the four steps that the oils goes through after extraction?
What are three additional/supplementary processes?
What is a 'salad oil'?
A salad oil, but definition, does not cloud under refrigerator conditions- caused by selective precipitation of longer chain, more saturated glycerides
What is winderization used for?
Winterization is a process used to produce 'salad oils' from oils not suitable for this purpose
Why is winterization necessary (not just for esthetics)?
Fat crystallization will break an emulsion
What machine is used for winterization?
Scraped surface heat exchanger
What is a byproduct of fractional crystallization?
It is a means of obtaining harder fractions which can be blended with softer fractions to obtain plastic fats without resorting to hydrogenation
What is fractional crystallization?
Fractional crystallization is a common means of separating out more saturated constituents from more unsaturated oils
Why is hydrogenation used?
- Hydrogenation is used to change the physical and chemical properties of fats and oils by reducing their overall degree ofunsaturation
- It is a common means by which to convert an oil into a plastic at, or to reduce the susceptibiity of an oil to autoxidation
Wht is hydrogenation?
Addition of hydrogen across the double bond of unsaturated fatty acids in triglycerides
How is hydrogenation done?
Apply hydrogen at high tempertures/pressures in conjunction with a catalyst (usually nickel)
What is the rate of hydrogenation a function of?
- Form and concentration of the catalyst
- Temperature and pressure
- Degree of agitation of the oil
What reactions can occur as a side effect of hydrogenation?
- Isomerization of the natural cis form of the fatty acid to the trans form
- Conversion of unconjugated double bonds to conjugated double bonds or mixed bonding system
What is selectivity with reference to hydrogenation?
Refers to hydrogenating higher polyunsaturated FAs preferentially
What is the end product of the hydrogenation of linolenic acid?
In the end the properties of the resulting fat are a function of all the changes ocurring aside from the formation of saturated fatty acids. The formation of cis/trans fatty acid combinations and permutations and the additional 'wandering' of the double bonds
What is the only way to eliminate the trans product with hydrogenation?
Only if we hydrogenate completely can we avoid trans in the product, but the fat will be as hard as a rock and is very difficult to work with
What is the main use of hydrogenation?
Main use of hydrogenation is to convert oils into fats, usually for margarine/shortening production and to stabilize highly unsaturated oils to autoxidation or a combination thereof
How does one overcome the graininess of lard?
What is interesterification?
Randomizing the fatty acid distribution- exchange of fatty acids on the glycerol backbone, using heat and a catalyst such as tin, lead, zinc or alkali earth metals
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