5.5 - Processing of Fats and Oils Flashcards
what is the first step in the processing of fats and oils? what’s the point?
heat treatment: aid in knocking out enzymes (lipase/lipoxygenase) that cause deteriorative reactions (lipolysis/autoxidation)
what happens as a result of tissue disruption?
lipids are exposed to oxygen and other reactive agents such that a multitude of reactions occur
what are the 2 enzymes that catalyze deteriorative reactions in fats and oils?
1) lipase - catalyzes lipolysis
2) lipoxygenase - catalyzes direct oxidation of polyunsat. fatty acid chains
what is lipolysis?
hydrolysis of ester linkage between glycerol and fatty acid on TG molecule
what group does lipoxygenase target on a fatty acid?
cis,cis-1,4-pentadiene groups (e.g. linoleic and linolenic)
After heating/crushing, what are the 3 ways oils are obtained from plant sources?
1) hydraulic pressing
2) expelling
3) solvent extraction
describe hydraulic pressing
- use of screw press to apply pressure and crush the seed to force out oil from the crush
- slow and inefficient
- oil quality is poor due to time, which allows enzymes (lipases and lipoxygenases) to act
- used for virgin olive oil to develop flavors
describe expelling
mechanical version of hydraulic pressing (continuous process)
- archimedes screw in a barrel which tapers toward the end - pressure is increased and the oil is squeezed out
- high throughput
- meal/press cake contains significant levels of oil
- usually followed by solvent extraction
describe solvent extraction
- organic solvent (hexane) is used to extract residual from oilseed cake produced by expelling operation
- $$$ for equipment (solvent recovery system)
- very efficient, but rare due to cost
what is rendering?
- taking ground meat/fish and placing into a pressurized vessel and heated with steam under pressure –> lipids melt and are released from tissue
- fat is skimmed off then further processed
what’s an oil like just after extraction? (what does it look like)
dark brown, smelly liquid with lots of particulates
what happens to the press cake after exraction?
it’s desolventized and usually sold as animal feed
why is freshly extracted oil dark?
presence of lipid-soluble pigments like carotenoids and chlorophyll and pheophytin
what are some undesirable components of extracted oils? (5)
1) free fatty acids (from lipases)
2) oxidative breakdown products (from enzymes and attack by oxygen)
3) phospholipids (naturally present in oil)
4) free and complexed metal ions (Mg2+ in chlorphyll)
5) flavor components (fishy and paintlike)
what are some processes used to clean up oil extract? list them in the correct order.
1) settling and degumming
2) refining
3) bleaching
4) deodorization
describe settling and degumming
- vigorous mixing of oil with water, allowed to stand in conical tank for some time
- carbs, proteinaceous extraneous matter, and P-lipids hydrate and associate themselves w/aqueous phase
- aqueous layer separates from oil, carrying cellular debris, carbohydrates, and P-lipids
- time expensive (can lead to continued deteriorating)
- this is accelerated with steam injection and constant centrifugation
describe refining (of oil)
- removal of free fatty acids from oil
- involves treatment of oil with DILUTE ALKALI (NaOH) to convert FAs into soap
- soap is removed from aq phase
- alkali must be carefully measured to ensure no excess to avoid saponification of the oil
regarding settling/degumming and refining, what’s done these days?
these processes are carried out simultaneously and combined with centrifugation, which removes 99.9% of moisture and particulates from oil
describe bleaching of oils
- removes colored materials from oil (carotenoids, chlorophyll, and pheophytin)
- note: most color compounds are slightly more polar than TGs
- dry bentonite absorbs these slightly polar compounds in the absence of moisture
- activated charcoal can also absorb
- leaves a clear pale, yellow oil
describe deodorization
- removes volatile compounds that give undesirable off-flavors
- removed by STEAM STRIPPING, which involves spraying the oil into an evacuated chambe containing superheated steam flowing counter-current to the oil droplets
- volatiles are acarried away with steam, leaving a bland clear oil
what are the 3 types of olive oils?
1) virgin - only physical means, no chemical treatment
2) refined - chemically treated
3) olive pomace oil - oil was extracted using solvents (hexane) and heat
what are some other processes that oils can undergo?
1) winterization
2) hydrogenation
3) interesterification
describe winterization
- produces salad oils from oils not suitable for this purpose
- fractional crystallization is carried out to remove more saturated TGs
- carried out with cottonseed oil and palm oil (palm stearin or palm fat)
