Volatile lipid oxidation products.

Publisher Summary This chapter presents the ubiquitous nature and pervasiveness of lipid oxidation ex vivo in foods and in vivo , and demonstrates that oxidation generally has deleterious results in both systems. This dramatizes the need for more effective strategies for controlling lipid oxidation, both in food materials and in tissues in vivo . The chapter discusses the existing practices using antioxidants, chelators, enzyme inactivation, and anoxic and low-temperature storage conditions. The oxidative degradation of the unsaturated fatty acid components of food lipids may be beneficial in some foods in generating low levels of desirable flavorful carbonyl compounds. However, in general, oxidation causes deleterious changes in flavor, taste, color, texture, and possibly safety of foods. The polyunsaturated fatty acids (PUFA)—particularly the trienoic, pentaenoic, and hexaenoic PUFA commonly found in oilseeds and seafoods—render these foods, which are particularly sensitive to oxidative changes which limit their self-life.

Oxidation of polyunsaturated fatty acids: mechanisms, products, and inhibition with emphasis on fish.

Occurrence and Characteristics of Oils and Fats

Summary
Kinetic variations in lipid oxidation in various parts of mackerel stored at −15, −30 and −40°C were studied by measuring the changes of POV and of TBA molar values as a function of time. Oxidation developed in the skin sample (subcutaneous fat) was found to be eight times faster in TBA change than in the white and dark muscles from mackerel held at −15°C for two months. This rapid development of rancidity in the skin was effectively inhibited by lowering the frozen storage temperature to −40°C, where relatively the degree of lipid oxidation in the dark muscle was found to be of the same order of magnitude. the in vitro rate of autoxidation at 60° C for the lipids extracted from skin and the fillet muscle also showed an unusual difference which indicated that unknown pro−oxidative substances in mackerel skin were fat solvent extractable. the activity of the unknown compounds in the skin was also temperature dependent even in the frozen state, but could be effectively mitigated by lowering temperature to −40°C. Lipid hydrolysis in mackerel was also retarded completely when the fish were stored at −40° C. the comparative compositions of fatty acids and volatile carbonyls were determined in head, skin, white and dark muscle, and suggested an active non-specific oxidation system in the skin fat.

Differential lipid oxidation in various parts of frozen mackerel

Aquatic taste and odor (T/O) is rarely produced by toxic contaminants or pathogens; nevertheless, it has major negative impacts on the public and the drinking-water industry. Consumers use T/O as a primary measure of drinking water safety, yet this criterion is poorly understood, and its origins and triggers often go untraced. Much surface-water T/O is produced by the increased production of volatile organic compounds (VOCs) by algae. These chemicals can be symptomatic of short-term problems with source, treatment, or distribution systems. At a broader level, they can signify fundamental changes in aquatic ecosystems induced by human activity. T/O varies in chemistry, intensity, and production patterns among different algal taxa, and is often linked with excessive algal growth and/or the invasion of noxious species. Some VOCs may signal the presence of potentially toxic algae and/or other associated water quality issues. Traditionally, T/O has been linked with the widespread eutrophication of many surface waters; however, there has been a recent growth in the number of T/O events reported in oligo-mesotrophic systems, for example, the Glenmore Reservoir (Calgary AB) and the Laurentian Great Lakes. From a management and public perspective, therefore, it is vitally important to monitor T/O, and to continue to work toward a better understanding of the proximal and the ultimate causes-which VOCs and algae species are involved. In the short term, odor events could be anticipated and water treatment optimized. In the long term, this approach would contribute toward more a robust management of this resource through remedial or preventative measures.

Aquatic taste and odor: a primary signal of drinking-water integrity.

A possible decomposition product of oils containing unsaturated fatty acids with the double bond pattern ω3,6,9 or ω3,6,9, etc., is 2-trans,4-cis,7-cis-decatrienal. It has therefore been investigated whether this trienal is present in strongly autoxidized linolenic acid, soybean, linseed and fish oils. Via a degassing technique the carbonyls from the samples of oils heated in a closed system under nitrogen were collected and separated as their 2,4-dinitrophenylhydrazones (DNPHs) by thin layer chromatography (TLC). The presence of 2-trans,4-cis,7-cis-decatrienal in the samples was positively established by TLC, UV absorption and mass spectroscopy of its DNPH. All analytical data established the complete identity of the isolated DNPH with a synthesized 2,4,7-decatrienal-DNPH. The free aldehyde obtained on hydrolysis of the alkatrienal-DNPH in question had the same flavor as authentic 2-trans,4-cis,7-cis-decatrienal, having a fish or rather a whale oil flavor.

P. W. Meijboom

Papers

2‐trans,4‐cis,7‐cis‐Decatrienal, the fishy off‐flavor occurring in strongly autoxidized oils containing linolenic acid or ω 3,6,9, etc., fatty acids