Bài giảng Phụ gia thực phẩm - Bài: Phụ gia chống oxi hóa - Đặng Bùi Khuê

Nội dung text: Bài giảng Phụ gia thực phẩm - Bài: Phụ gia chống oxi hóa - Đặng Bùi Khuê

1. • Definitions of Antioxidants and Antioxidant Types
2. • 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
3. • Mechanism of Action of Antioxidants – (2) alkoxy free radical formed during the decomposition of Hydroperoxides – (3,4) free antioxidant radicals react with a peroxy or an alkoxy radical forming a copolymer
4. • 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
5. • Mechanism of Action of Antioxidants – (7) Free antioxidant radical can also react with some labile compounds, such as terpenes, which form free radicals
6. Some antioxidants
7. • Synthetic Antioxidants Added Directly to Food – Anoxomer – Butylated Hydroxyanisole – Butylated Hydroxytoluene – Ethoxyquin – 4-Hydroxymethyl-2,6-di-tert-butylphenol – 2-(1,1-Dimethylethyl)-1,4-Benzenediol – 2,4,5-Trihydroxybutyrophenone
8. • 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
9. • 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
10. • 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 Butylated Hydroxyanisole 3-tert-butyl-4-methoxoyphenol 2-tert-butyl-4-methoxyphenol
11. • Butylated Hydroxyanisole – The steric hindrance is probably responsible for the relative ineffectiveness of BHA in vegetable oils because the tertiary butyl group interferes with the antioxidant activity of the phenolic structure – BHA is commonly used in combination with other primary antioxidants, such as gallates gallates
12. • 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
13. • 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 lecithin thiodipropionic acid
14. • 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)
15. • 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)
16. • Butylated Hydroxytoluene – 2,6-di-tert-butyl-p-cresol; 2,6-bis(1,1-dimethylethyl)- 4-methylphenol – water-insoluble, white, crystalline solid antioxidant – more soluble in food oils and fats than is BHA
17. • Butylated Hydroxytoluene – effective in animal fats – not as effective in vegetable oils – BHT is frequently used in combination with BHA in foods
18. • 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
19. • Butylated Hydroxytoluene – A food antioxidant • Soluble in glycerides • Insoluble in water • Susceptible to loss by volatilization – Negative aspect of BHT, is that it may give a yellow coloration due to the formation of stilbenequinone in the presence of iron