Advances in the Formation and Control Methods of Undesirable Flavors in Fish

Abstract

Undesirable flavor formation in fish is a dynamic biological process, decreasing the overall flavor quality of fish products and impeding the sale of fresh fish. This review extensively summarizes chemical compounds contributing to undesirable flavors and their sources or formation. Specifically, hexanal, heptanal, nonanal, 1-octen-3-ol, 1-penten-3-ol, (E,E)-2,4-heptadienal, (E,E)-2,4-decadienal, trimethylamine, dimethyl sulfide, 2-methyl-butanol, etc., are characteristic compounds causing off-odors. These volatile compounds are mainly generated via enzymatic reactions, lipid autoxidation, environmentally derived reactions, and microbial actions. A brief description of progress in existing deodorization methods for controlling undesirable flavors in fish, e.g., proper fermenting, defatting, appropriate use of food additives, and packaging, is also presented. Lastly, we propose a developmental method regarding the multifunctional natural active substances made available during fish processing or packaging, which hold great potential in controlling undesirable flavors in fish due to their safety and efficiency in deodorization.

Keywords: deodorization; lipid oxidation; microorganism; natural active substances; undesirable flavor.

Figure 1

Freshness assessment of iced−stored sardine with emphasis on odor development according to EU grading and QIM (the EU grade is the European Union grade; the QIM score is the Quality Index Method score). The EU freshness grading distinguishes four categories of fish, from E (very fresh state), A, and B to C (not admitted). The QIM uses many weighted parameters (e.g., appearance, eyes, cover, and gills) with a scoring system from 0 to 4 demerit points for each parameter; it gives a total score of zero to very fresh fish and returns an increasingly larger result as fish deteriorates [26].

Figure 2

Proposed mechanism for biochemical reactions of eicosapentaenoic acid.

Figure 3

Enzymatic degradation of cysteine and methionine, generating DMS.

Figure 4

(a) Biosynthesis of MIB via methylation of geranyldiphosphate (GPP) and cyclization of (E) −−2−−geranyldiphosphate; (b) biosynthesis of GSM via 1,2−−hydride shift, loss of hydroxypropyl moiety, and capture of water.