5.5 - Processing of Fats and Oils

Question 1

what is the first step in the processing of fats and oils? what’s the point?

Answer 1

heat treatment: aid in knocking out enzymes (lipase/lipoxygenase) that cause deteriorative reactions (lipolysis/autoxidation)

Question 2

what happens as a result of tissue disruption?

Answer 2

lipids are exposed to oxygen and other reactive agents such that a multitude of reactions occur

Question 3

what are the 2 enzymes that catalyze deteriorative reactions in fats and oils?

Answer 3

1) lipase - catalyzes lipolysis

2) lipoxygenase - catalyzes direct oxidation of polyunsat. fatty acid chains

Question 4

what is lipolysis?

Answer 4

hydrolysis of ester linkage between glycerol and fatty acid on TG molecule

Question 5

what group does lipoxygenase target on a fatty acid?

Answer 5

cis,cis-1,4-pentadiene groups (e.g. linoleic and linolenic)

Question 6

After heating/crushing, what are the 3 ways oils are obtained from plant sources?

Answer 6

1) hydraulic pressing
2) expelling
3) solvent extraction

Question 7

describe hydraulic pressing

Answer 7

• 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

Question 8

describe expelling

Answer 8

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

Question 9

describe solvent extraction

Answer 9

• 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

Question 10

what is rendering?

Answer 10

• 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

Question 11

what’s an oil like just after extraction? (what does it look like)

Answer 11

dark brown, smelly liquid with lots of particulates

Question 12

what happens to the press cake after exraction?

Answer 12

it’s desolventized and usually sold as animal feed

Question 13

why is freshly extracted oil dark?

Answer 13

presence of lipid-soluble pigments like carotenoids and chlorophyll and pheophytin

Question 14

what are some undesirable components of extracted oils? (5)

Answer 14

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)

Question 15

what are some processes used to clean up oil extract? list them in the correct order.

Answer 15

1) settling and degumming
2) refining
3) bleaching
4) deodorization

Question 16

describe settling and degumming

Answer 16

• 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

Question 17

describe refining (of oil)

Answer 17

• 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

Question 18

regarding settling/degumming and refining, what’s done these days?

Answer 18

these processes are carried out simultaneously and combined with centrifugation, which removes 99.9% of moisture and particulates from oil

Question 19

describe bleaching of oils

Answer 19

• 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

Question 20

describe deodorization

Answer 20

• 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

Question 21

what are the 3 types of olive oils?

Answer 21

1) virgin - only physical means, no chemical treatment
2) refined - chemically treated
3) olive pomace oil - oil was extracted using solvents (hexane) and heat

Question 22

what are some other processes that oils can undergo?

Answer 22

1) winterization
2) hydrogenation
3) interesterification

Question 23

describe winterization

Answer 23

• 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)