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. | Phụ gia chống oxi hóa ThS. Đặng Bùi Khuê Types of Rancidity Types of Rancidity Lipolytic rancidity is mainly due to lipases (triacylglycerol acyl hydrolases, EC ), 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-CH-CH-CH2⇒C*H-CH=CH-CH2 or CH2-CH=CH-C*H 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 . | Phụ gia chống oxi hóa ThS. Đặng Bùi Khuê Types of Rancidity Types of Rancidity Lipolytic rancidity is mainly due to lipases (triacylglycerol acyl hydrolases, EC ), 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 .
