Bài giảng Phụ gia thực phẩm: Phụ gia chống oxi hóa (p1) - ThS. Đặng Bùi Khuê

Bài giảng này trình bày các nội dung liên quan đến phụ gia chống oxi hóa. Các nội dung được trình bày trong chương này gồm có: Types of Rancidity, Initiation Reactions, Propagation Reactions (Primary Reactions), Termination Reactions, Definitions of Antioxidants and Antioxidant Types,...và các nội dung liên quan khác.
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Bài giảng Phụ gia thực phẩm: Phụ gia chống oxi hóa (p1) - ThS. Đặng Bùi KhuêPhụgiachốngoxihóa ThS.Đặng BùiKhuê• Types of Rancidity• 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• Mechanis m of Oxidative Rancidity• three main phases – initiation – Propagatio n – 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• 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• Mechanism of Action of Antioxidants – (2) alkoxy free radical formed during the decomposition of Hydroperoxides – (3,4) free antioxidant radicals react• Mechanism of Action of Antioxidants – (5) free antioxidant radicals react with another antioxidant free radical – (6) free antioxidant radical is con-• Mechanism of Action of Antioxidants – (7) Free antioxidant radical can also react with some labile compounds, such as terpenes, which form free Someantioxidant s• 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• 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′- isopropylidenediphenoldivinylbenzene 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 Butylated Hydroxyanisole 3-tert-butyl-4-methoxoyphenol 2-tert-butyl-4-methoxyphenol ...