Bài giảng phụ gia thực phẩm phụ gia chống oxi hóa (p1) ths đặng bùi khuê

– Lipolytic rancidity is mainly due to lipases triacylglycerol acyl hydrolases, EC 3.1.1.3, which are enzymes catalyzing the cleavage of triacylglycerols triglycerides into free fatty ac

Phụ gia chống oxi hóa

ThS Đặng Bùi Khuê

• Types of Rancidity

– Lipolytic rancidity is mainly due to lipases

(triacylglycerol acyl hydrolases, EC 3.1.1.3), which are enzymes catalyzing the cleavage of triacylglycerols (triglycerides) into free fatty acids and partial glycerol esters—monoacylglycerols (monoglycerides),

diacylglycerols (diglycerides), and glycerol

triacylglycerol

• Types of Rancidity

– Flavor reversion is a type of rancidity, typical for

soybean oil It is connected with minute absorption of oxygen by oil

• Types of Rancidity

– Ketonic rancidity, with a characteristic floral off-flavor,

is sometimes observed during the storage of foods

containing short- or medium-chain fatty acids (4–10 carbon atoms), such as those containing milk fat or coconut oil  It is caused by microbial degradation of medium-chain fatty acids into the respective alkan-2-ones or methyl ketones

methyl ketones

• Mechanism

of Oxidative Rancidity

• three main phases

– initiation – Propagation – termination

• Initiation Reactions

– polyenoic (essential) fatty acids

• methylene group adjacent to two double-bonds (-CH=CH–CH2-CH=CH-) is the primary site of

oxygen attack

• converted into the respective free radical: R-H ⇒ R* + H*

– Monoenoic fatty acids

• free radicals are formed by cleavage of a hydrogen atom on either one side of the double bond CH2-

• Initiation Reactions

– activation energy of this reaction is higher

– Most often, free radicals are formed by cleavage of a hydroperoxide molecule

• Propagation Reactions (Primary Reactions)

– forming a peroxy radical

– abstracts a hydrogen atom from another molecule of

a polyunsaturated fatty acid, forming a hydroperoxide and an alkyl free radical

– formation of a free peroxy or alkoxy radical

– polyunsaturated fatty acid is usually isomerized into a more stable conjugated dienoic system

• Termination Reactions

– recombination of two free radicals

• Definitions of Antioxidants and Antioxidant Types

• Mechanism of

Action of

Antioxidants

– (1) Antioxidants react with peroxy radicals produced

in oxidized lipids, forming a

hydroperoxide

molecule and a free radical of the antioxidant

copolymer

• Mechanism of

Action of

Antioxidants

– (5) free antioxidant radicals react with another antioxidant free radical

– (6) free antioxidant radical is con-

verted into an

antioxidant peroxy radical

compounds, such

as terpenes,

which form free radicals

Some

antioxidants

• Synthetic Antioxidants Added Directly to Food

• Anoxomer

– polymeric antioxidant that is prepared by

condensation polymerization of divinylbenzene (m-

and p-) with tert-butylhydroquinone,

tert-butyl-phenol, hydroxyanisole,p-cresol, and 4,4 -

′-isopropylidenediphenol

divinylbenzene

tert-butylhydroquinone p-cresol 4,4 -isopropylidenediphenol

′-• Anoxomer

– not less than 98.0% purity

– total monomers, dimers, and trimers below MW 500 not to exceed 1%

– phenol content not less than 3.2 meq/g and not more than 3.8 meq/g

– heavy metals, not more than 10 ppm lead, 3 ppm

arsenic or 1 ppm mercury

– in food at a level of not more than 5000 ppm

• Butylated Hydroxyanisole

– mixture of 2-tert-butyl-4-methoxyphenol and

3-tert-butyl-4-methoxoyphenol

– 3-isomer being 90% or more

– ‘‘hindered’’ phenol, and the tert-butyl group ortho or meta to the hydroxyl group serves to suppress

antioxidant activity

2-tert-butyl-4-methoxyphenol 3-tert-butyl-4-methoxoyphenol

Butylated Hydroxyanisole

• Butylated Hydroxyanisole

– strong phenolic odor (high temperatures)

– BHA effectively controls the oxidation of animal fats, but is a relatively ineffective antioxidant in most

vegetable oils

• Butylated Hydroxyanisole

– synergism with acids, BHT, propyl gallate,

hydroquinone, methionine, lecithin, thiodipropionic acid…

– AMIF-72 mixture: contains 20% BHA, 6% propyl

gallate, and 4% citric acid in propylene glycol

thiodipropionic acid lecithin

• Butylated Hydroxyanisole

– Total BHA must assay at 98.5% minimum, with a

minimum melting point of 48°C

– Food

• dehydrated potato shreds 50ppm

• active dry yeast 1000 BHA only

• beverages and desserts prepared from dry mixes (2 BHA only)

• dry breakfast cereals (50)

• Butylated Hydroxyanisole

• dry diced glazed fruit (32 BHA only)

• dry mixes for beverages and desserts (90 BHA only)

• Emulsion stabilizers for shortenings (200)

• potato flakes (50)

• potato granules (10)

• sweet potato flakes (50)

• Butylated Hydroxytoluene

– 2,6-di-tert-butyl-p-cresol; 4-methylphenol

2,6-bis(1,1-dimethylethyl)-– water-insoluble, white, crystalline solid antioxidant– more soluble in food oils and fats than is BHA

• Butylated Hydroxytoluene

– effective in animal fats

– not as effective in vegetable oils

– BHT is frequently used in combination with BHA in foods

• Butylated Hydroxytoluene

– BHT is noted for its high-temperature stability

– less effective than BHA because of the greater steric hindrance presented by two tert-butyl groups

surrounding the hydroxyl group