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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
Antioxidants and Functional Components in Aquatic Foods compiles for the first time the past and present research done on pro and antioxidants in aquatic animals. The book addresses an area of extreme importance for aquatic foods, since lipid oxidation leads to such a large number of quality problems. Many of these problems are also seen in other muscle based foods, but are exaggerated in aquatic foods, so the book's contents will be of great use and interest to other fields. Written by top researchers in the field, the book offers not only general overviews of lipid oxidation in aquatic foods and aquatic food pro and antioxidant systems, but also covers specifics and gives the latest information on the key pro and anti-oxidants derived from aquatic foods as well as some of the most recent and innovative means to control lipid oxidations in aquatic foods and food systems with fish oils. Coverage includes the latest research on the effects aquatic foods have on oxidative stress in the human body, an area of great interest recently. Additionally, a chapter is devoted to the latest techniques to measure antioxidative potential of aquatic foods, an area still in development and one very important to the antioxidant research community. Antioxidants and Functional Components in Aquatic Foods will be of great interest to the food science, medical, biochemical and pharmaceutical fields for professionals who deal with aquatic food products, muscle foods products (beef, pork, poultry etc), lipid oxidation, and pro-oxidant and antioxidant systems.
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CONTENTS
Cover
Title page
Copyright page
List of Contributors
Preface
1 Oxidation in aquatic foods and analysis methods
1.1 Introduction
1.2 Analysis of lipid oxidation
1.3 Conclusions
References
2 Protein oxidation in aquatic foods
2.1 Introduction
2.2 Mechanisms involved in protein oxidation
2.3 Impact of protein oxidation on aquatic food
2.4 Case studies
2.5 Conclusions and perspectives
References
3 Influence of processing on lipids and lipid oxidation in aquatic foods
3.1 Effect of freezing on lipid oxidation
3.2 Effect of salting and drying on lipid oxidation
3.3 Effect of fermentation on lipid oxidation
3.4 Effect of smoking on lipid oxidation
3.5 Effect of high-pressure processing on lipid oxidation
3.6 Effect of irradiation on lipid oxidation
3.7 Effect of microwave processing on lipid oxidation
3.8 Effect of modified atmospheres on lipid oxidation
3.9 Effect of the pH shift extraction method on lipid oxidation
3.10 Effect of canning on lipid oxidation
References
4 Strategies to minimize lipid oxidation of aquatic food products post harvest
4.1 Introduction
4.2 Lipid oxidation and quality deterioration in post-harvest aquatic food products
4.3 Post-harvest control of oxidative deterioration in aquatic food products
4.4 Conclusions and prospects
References
5 Antioxidative strategies to minimize oxidation in formulated food systems containing fish oils and omega-3 fatty acids
5.1 Introduction
5.2 The lipid oxidation process
5.3 Factors affecting lipid oxidation in omega-3-enriched foods
5.4 Introduction to antioxidants
5.5 Antioxidant effects in different omega-3-enriched food products
5.6 Other strategies to protect omega-3 products against oxidation
5.7 Conclusions
References
6 Methods for assessing the antioxidative activity of aquatic food compounds
6.1 Background
6.2 Oxidation and antioxidants
6.3 Methods for determining antioxidant activity
References
7 Influence of fish consumption and some of its individual constituents on oxidative stress in cells, animals, and humans
7.1 Introduction
7.2 What is oxidative stress?
7.3 Why is oxidative stress of importance and how does it link to diet?
7.4 How is oxidative stress measured?
7.5 Do components in fish affect oxidative stress?
7.6 Effects of fish intake on biomarkers used to evaluate oxidative stress
7.7 Methodological considerations
7.8 Conclusion and need for future studies
References
8 Marine antioxidants
8.1 Introduction
8.2 Chain-breaking antioxidants
8.3 Antioxidants and their beneficial health effects
8.4 Seaweeds as a rich source of antioxidants
8.5 Algal polyphenols
8.6 Marine carotenoids
8.7 Antioxidant activity of carotenoids
8.8 Astaxanthin and fucoxanthin
8.9 Conclusions
References
9 Fish protein hydrolysates
9.1 Introduction
9.2 Source of fish protein hydrolysates
9.3 Production of fish protein hydrolysate
9.4 Properties of hydrolysate
9.5 Applications of fish protein hydrolysates
References
10 Antioxidant properties of marine macroalgae
10.1 Introduction
10.2 Antioxidant properties of algal polyphenols
10.3 Antioxidant activity of algal sulfated polysaccharides
10.4 Antioxidant activities of fucoxanthin
10.5 Antioxidant activities of sterols from marine algae
10.6 Antioxidant activities of peptides derived from marine algae
10.7 Antioxidant activity of mycosporine-like amino acids
10.8 Concluding remarks
References
Supplemental Images
Index
End User License Agreement
List of Tables
Chapter 01
Table 1.1 Overview of the main methods used to monitor lipid oxidation products and potential predictors of lipid oxidation
Table 1.2 Important pro-oxidants present in fish tissues (Underland, 1997. Reproduced with permission of the International Institute of Refridgeration.)
Table 1.3 Important inhibitors of lipid oxidation located in fish muscle. (adapted from Jonsdottir et al. 2008)
Chapter 02
Table 2.1 Amino acids susceptible to oxidation and some of their most common oxidation products
Table 2.2 Protein carbonyls measured for nine rainbow trout immediately after killing and after storage for 48 hours on ice (from Baron et al. 2007)
Table 2.3 Proteins identified as oxidized in fish muscle after storage at −20 °C for 22 months using immunoblotting and LC-MS/MS sequencing (modified from Kjærsgaard et al. 2006)
Table 2.4 Protein carbonyls in rainbow trout fed fish oil and stored at −20 °C measured at the beginning of the storage period (T0) and after 22 months (T22) (from Baron et al. 2009)
Chapter 04
Table 4.1 Fatty acid content (mg/g oil) of minced bigeye tuna (Thunnus obesus) and Pacific mackerel (Scomber japonicus) meats before and after ice storage
Chapter 05
Table 5.1 Summary of the effects of different antioxidants in omega-3-enriched mayonnaise and dressing
Table 5.2 Summary of effects of antioxidants in different omega-3-enriched dairy products
Table 5.3 Summary of effects of individual antioxidants in different omega-3 enriched foods
Chapter 06
Table 6.1 Examples of aquatic compounds and antioxidative activities obtained by various antioxidative assays
Table 6.2 Comparison of HAT- and SET-based assays
Chapter 07
Table 7.1 Human studies assessing markers for oxidative stress in relation to fish oil intake
Table 7.2 Human studies assessing markers for oxidative stress in relation to fish intake
Chapter 09
Table 9.1 FPH produced from fish muscle with different pretreatments
Table 9.2 Fish proteases used for FPH production
Table 9.3 Commercial proteases used for FPH production
Table 9.4 Antioxidant peptides from FPH
Table 9.5 ACE inhibiting peptides from FPH
List of Illustrations
Chapter 01
Figure 1.1 Autoxidation of polyunsaturated fatty acids. LH; AH.
Figure 1.2 An example of the progress of lipid oxidation and breakdown of lipid oxidation products as assessed by different methods. Oxygen uptake is with Oxipress or an oxygen electrode. The primary products are measured as peroxide values (PVs). Measurement of free fatty acids (FFA) gives the acid value. Secondary products (e.g., aldehydes) are measured by the thiobarbituric acid (TBA) test, and sensory evaluation and gas chromatography (GC). Tertiary products are polymers, which can be measured with fluorescence, colorimetric and sensory evaluation. Rosa Jonsdottir, Matis-Icelandic Food Research. Reproduced with permission of Rosa Jonsdottir.
Figure 1.3 Chemical reaction steps in the conjugable oxidation products assay. Shahidi & Wanasundra, 2002.
Figure 1.4 Reaction of 2-thiobarbituric acid (TBA) and malonaldehyde (MA).
Figure 1.5 Reaction of lipid oxidation products and amines.
Chapter 02
Figure 2.1 Mechanism for metal-catalyzed protein oxidation leading to the formation of carbonyl groups on protein.
Figure 2.2 Loading plot from the principal component analysis performed on the data set obtained from the chemical analysis of frozen trout for the entire storage period. The arrow indicates increasing oxidative stability. (Modified from Baron et al. 2009.)
Figure 2.3 A, SDS-PAGE of herring muscle; B, immunoblot against myosin heavy chain; C, texture profile analysis with solid bars representing the first compression and empty bars representing the second compression. F/0 represents fresh herring and the numbers (2, 85, 151 and 371) represent days of ripening.
Chapter 04
Figure 4.1 The involvement of singlet oxygen in lipid oxidation.
Figure 4.2 Non-heme iron form participates in the production of reactive oxygen species.
Figure 4.3 The impacts of lipid oxidation on the quality of aquatic food products.
Figure 4.4 Changes in the contents of total lipid hydroperoxides (HPO) in ordinary and dark muscles in ice storage: (a) yellowtail (Seriola quinqueradiata), (b) amberjack (Seriola purpurascens), (c) Japanese butterfish (Hyperoglyphe japonicus), (d) Pacific saury (Cololabis saira), (e) Japanese Spanish mackerel (Scomberromorus niphonius), (f) chub mackerel (Scomber japonicus). Error bars present as mean ± SD (n = 3).
Figure 4.5 Correlation between total lipid hydroperoxide (HPO) content and metmyoglobin concentration in total myoglobin of minced bigeye tuna meat in ice storage. Error bars present as mean ± SD (n = 3).
Figure 4.6 Three possible tautomeric structures for L-ergothioneine.
Figure 4.7 Effect of mushroom extract on the total lipid hydroperoxides (HPO) formation (a) and the residual amount of oxygen absorbed (b) of cod liver oil in water emulsion. Error bars present as mean ± SD (n = 5).
Figure 4.8 Changes in total lipid hydroperoxides (a) and thiobarbituric acid reactive substances (b) of minced bigeye tuna meats with added different antioxidants: ×, 15 mg of mushroom ergothioneine added to 100 g meat; , 500 ppm of α-tocopherol added to 100 g of meat; , 500 ppm of ascorbic acid sodium salt added to 100 g meat; , control with 5 mL of distilled water added to 100 g of meat. Error bars present as mean ± SD (n = 3). Values with different superscript letters represent significant differences (p < 0.05).
Figure 4.9 Changes in visual color (a) and regression models correlation (b) loadings based on total lipid hydroperoxides content (HPO), metmyoglobin concentration in total myoglobin (metMb), and r and g values of minced bigeye tuna meats with added different amounts of mushroom ergothioneine.
Figure 4.10 Proposed mechanism for delaying oxidation of lipid and myoglobin in minced bigeye tuna meat by adding ergothioneine in mushroom extract. Mb (Fe
2+
), deoxymyoglobin; MbO
2
(Fe
2+
), oxymyoglobin; Mb (Fe
3+
), metmyoglobin; Mb (Fe = O)
2+
, ferrylmyoglobin; •Mb (Fe = O)
2+
, perferrylmyoglobin; ESH, ergothioneine; ESSE, ergothioneine disulfide.
Chapter 06
Figure 6.1 An overview representing the diversity of bioactive compounds obtained from aquatic organisms.
Figure 6.2 The frequency of publications per year on aquatic antioxidants for the last two decades when searched for the topic “aquatic antioxidants” within Web of Science® on 15 January 2013 (www.webofknowledge.com). Results were refined to timeframes of 5 years except for 2010–2012 (2 years). The number of hits was divided by five to calculate the average number of publications per year. For 2010–2012 two was used for the calculation.
Figure 6.3 The principle of the ORAC assay. ROS generated from the thermal decomposition of AAPH over time quench the signal from fluorescent probe fluorescein. The loss of fluorescence generates a curve and the area under the sample curve is subtracted from the area under the blank curve. This net area under the curve data is compared to the standard curve generated by different concentrations of Trolox®.
Figure 6.4 Signal curve of different concentrations of Trolox® compared to blank. The top right-hand side shows the linear standard curve from the calculated net area under the signal curve versus Trolox® concentrations in μM (Hamaguchi et al., unpublished data).
Figure 6.5 Effect on cellular ROS level induced by AAPH in HepG2 cells by brown seaweed extract at 0.05, 0.025, and 0.005 mg/ml and Trolox® at 50 μM sample concentration. The blank consisted of cells exposed to only the DCFH-DA probe. The control consisted of cells with the DCFH-DA probe and the AAPH peroxyl radical initiator but in the absence of brown seaweed. Values shown are the mean ± standard deviation of three replicates. (a) Fluorescence intensity versus time. (b) Cellular ROS generation as percentages of the DCF fluorescence intensity compared to that of control cells at certain time point (60 min) (Sveinsdóttir et al., unpublished data).
Chapter 08
Figure 8.1 Lipid oxidation mechanism.
Figure 8.2 Inhibition of lipid oxidation by antioxidants.
Figure 8.3 Chemical structures of phlorotannins.
Figure 8.4 Structures of some selected marine carotenoids.
Figure 8.5 Possible molecular mechanism of fucoxanthin activities.
Chapter 09
Figure 9.1 Enzymatic hydrolysis of proteins by endo- and exopeptidases.
Figure 9.2 A scheme for FPH production.
Figure 9.3 Phospholipid membrane removal from fish muscle protein prior to hydrolysis.
Figure 9.4 The acid or alkaline solubilization process used to prepare fish protein isolate.
Figure 9.5 Bioactivities of fish protein-derived peptides. (Chibuike et al. 2011. Reproduced with permission of Wiley.)
Chapter 10
Figure 10.1 Chemical structures of common brown algal phlorotannins.
Figure 10.2 PCA bi-plot of total phenolic content (TPC) and antioxidant activities (AA) (DPPH, ORAC and ferrous ion-chelating activity) of water (WE) and 70% acetone extracts (AE) from selected Icelandic seaweeds: F. ves, F. vesiculosus; F. ser, F. serratus; A. nod, A. nodosum; L. hyp, L. hyperborea; A. esc, A. esculenta; S. lat, S. latissima; L. dig, L. digitata; U. lac, U. lactuca; P. pal, P. palmata; C. cri, C. crispus. Brown seaweeds are indicated by italics, red seaweeds by underline, green seaweeds in bold.
Figure 10.3 Chemical structure of fucoxanthin and its metabolites fucoxanthinol and halocynthiaxanthin.
Figure 10.4 Chemical structures of common sterols from marine algae.
Figure 10.5 Chemical structures of some typical mycosporine-like amino acids found in different marine organisms.
Guide
Cover
Table of Contents
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Antioxidants and Functional Components in Aquatic Foods
Edited by
Hordur G. Kristinsson
Matis Ltd, Reykjavik, Iceland
This edition first published 2014 © 2014 by John Wiley & Sons, Ltd
Registered officeJohn Wiley & Sons, Ltd, The Atrium, Southern Gate, Chichester, West Sussex,PO19 8SQ, UK
Editorial offices9600 Garsington Road, Oxford, OX4 2DQ, UKThe Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK111 River Street, Hoboken, NJ 07030-5774, USA
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Cover image: Fresh Rainbow trout and fish oil capsules © Shutterstock/tab62Underwater background © iStock/NastcoCover design by Andy Meaden
List of Contributors
Niklas AnderssonDivision of Life Sciences/Food Science, Department of Chemical and Biological Engineering, Chalmers University of Technology, Gothenburg, Sweden
Hilma Eidsdottir BakkenDivision of Biotechnology and Biomolecules, Matis Ltd, Saudarkrokur, Iceland
Huynh Nguyen Duy BaoFaculty of Food Technology, Nha Trang University, Vietnam
Caroline P. BaronNational Food Institute, Technical University of Denmark, Kgs. Lyngby, Denmark
Soottawat BenjakulDepartment of Food Technology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai, Songkhla, Thailand
K. H. Sabeena FarvinSection for Aquatic Lipids and Oxidation, National Institute of Aquatic Resources, Technical University of Denmark, Kgs. Lyngby, Denmark
Britt GabrielssonDivision of Life Sciences/Food Science, Department of Chemical and Biological Engineering, Chalmers University of Technology, Gothenburg, Sweden
Sigrun M. HalldorsdottirDivision of Biotechnology and Biomolecules, Matis Ltd, Reykjavik, Iceland
Patricia Y. HamaguchiDivision of Biotechnology and Biomolecules, Matis Ltd, Saudarkrokur, Iceland
Anna Frisenfeldt HornSection for Aquatic Lipids and Oxidation, National Institute of Aquatic Resources, Technical University of Denmark, Kgs. Lyngby, Denmark
Charlotte JacobsenSection for Aquatic Lipids and Oxidation, National Institute of Aquatic Resources, Technical University of Denmark, Kgs. Lyngby, Denmark
Rosa JonsdottirDivision of Biotechnology and Biomolecules, Matis Ltd, Reykjavik, Iceland
Magnea G. KarlsdottirDivision of Biotechnology and Biomolecules, Matis Ltd, Reykjavik, Iceland
Hordur G. KristinssonDivision of Biotechnology and Biomolecules, Matis Ltd, Reykjavik, IcelandDepartment of Food Science and Human Nutrition, University of Florida, Gainesville, Florida, USA
Kazuo MiyashitaFaculty of Fisheries Sciences, Hokkaido University, Hakodate, Japan
Nina Skall NielsenSection for Aquatic Lipids and Oxidation, National Institute of Aquatic Resources, Technical University of Denmark, Kgs. Lyngby, Denmark
Gudrun OlafsdottirSchool of Engineering and Natural Sciences, University of Iceland, Reykjavik, Iceland
Toshiaki OhshimaDepartment of Food Science and Technology, Tokyo University of Marine Science and Technology, Japan
Holly T. PettyDepartment of Food Science and Human Nutrition, University of Florida, Gainesville, Florida, USA
Sivakumar RaghavanDepartment of Food Science and Human Nutrition, University of Florida, Gainesville, Florida, USA
Theeraphol SenphanDepartment of Food Technology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai, Songkhla, Thailand
Ann-Dorit Moltke SørensenSection for Aquatic Lipids and Oxidation, National Institute of Aquatic Resources, Technical University of Denmark, Kgs. Lyngby, Denmark
Holmfridur SveinsdottirDivision of Biotechnology and Biomolecules, Matis Ltd, Saudarkrokur, Iceland
Ingrid UndelandDivision of Life Sciences/Food Science, Department of Chemical and Biological Engineering, Chalmers University of Technology, Gothenburg, Sweden
Tao WangSchool of Food Science and Technology, Dalian Polytechnic University, Dalian, ChinaCenter for Excellence in Post-Harvest Technologies, North Carolina A&T State University, Kannapolis, NC, USA
Suthasinee YarnpakdeeDepartment of Food Technology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai, Songkhla, Thailand
Preface
The consumption and popularity of fish and other aquatic animals in the world continues to grow. One of the reasons for this is the health benefits of seafood, which traditionally have been linked to the beneficial fatty acid profile and content of many fish (i.e. omega-3 fatty acids). Recent research, however, points to many more compounds that can have beneficial health effects. Aquatic animals, particularly fish, have long been known to be very susceptible to lipid oxidation, which leads to off-odors/flavors, reduced nutritional value, undesirable appearance and loss of quality. Omega-3 fatty acids are particularly prone to oxidation and if oxidized they lose their nutritional value. It is therefore important to understand the processes behind oxidation and how we can delay it. Only relatively recently have food scientists truly started to understand the role, function, and magnitude of different endogenous pro-oxidants. Also, we have in recent years started to understand better the natural antioxidative systems found in fish muscle and made the discovery that they are particularly potent and may even have the potential to be developed into ingredients for other food products. This goes beyond just fish, as there are many other aquatic animals that contain interesting and highly functional compounds that can find uses in the food, pharmaceutical and feed industries, including marine algae.
This book, written by leading experts in the field, provides comprehensive coverage of the oxidative processes associated with aquatic foods, antioxidant mechanisms and procedures, the influence of processing on oxidation, and the health effects of consuming aquatic foods and their components. It also gives an overview of various natural antioxidants found in aquatic animals, or that can be extracted from them, in addition to techniques for analysing their activity.
1Oxidation in aquatic foods and analysis methods
Magnea G. Karlsdottir1, Holly T. Petty2, and Hordur G. Kristinsson1,2
1 Division of Biotechnology and Biomolecules, Matis Ltd, Reykjavik, Iceland
2 Department of Food Science and Human Nutrition, University of Florida, Gainesville, Florida, USA
1.1 Introduction
Lipid oxidation in muscle food is one of the major deteriorative reactions causing a loss in quality during storage. Marine lipids are natural and good sources of polyunsaturated omega-3 fatty acids (PUFAs), which have been reported to have beneficial health effects. However, because of the high amount of PUFAs (Ackman 1980; Shewfelt 1981; Gandemer 1999), along with highly active pro-oxidants (Hultin 1994), marine lipids are highly vulnerable towards oxidation. Lipid oxidation is therefore one of the primary causes of deterioration of fish muscle during storage (Ackman 1980) and negatively affects color (Wasasundara and Shahidi 1994), odor and flavor (Bateman et al. 1953), protein functionality and conformation (Gutteridge 1988), and the overall nutritional content of fish muscle (Pearson et al. 1983; Gray 1987).
Lipid oxidation can be divided into three types of initiation reactions, including non-enzymatic and enzymatic reactions. Non-enzymatic mechanisms include autoxidation (free radical mechanism) and photogenic oxidation (singlet oxygen mediated). Enzymatic mechanisms include actions by lipoxygenase and cyclooxygenase. Lipid oxidation most commonly occurs by a free radical mechanism involving the formation of a reactive peroxyl radical (Erickson 2002).
The autoxidation mechanism occurs when the unsaturated fatty acids are exposed to oxygen and undergo an autocatalytic chain reaction (Figure 1.1). This mechanism is deemed to be the primary cause of lipid oxidation in post-mortem fish (Erickson 2002) and is historically referred to as lipid peroxidation (Mead 1976). The process has three main phases: initiation, propagation, and termination.
Figure 1.1 Autoxidation of polyunsaturated fatty acids. LH; AH.
Initiation begins with hydrogen abstraction from an unsaturated fatty acid, particularly those having a pentadiene structure (Erickson 2002). The lipid radical (L∙) then reacts with molecular oxygen, resulting in peroxyl radical (LOO∙). Propagation is the phase in which the peroxyl radical (LOO∙) abstracts hydrogen from neighboring lipid molecules, thereby forming more lipid radicals and lipid hydroperoxide (LOOH) molecules. Lipid hydroperoxides cannot be detected through sensory analysis, which is the reason why peroxides do not correlate with “off-flavor”. The degradation of these lipid hydroperoxides, due to metal catalysts, results in unfavorable secondary intermediates of shorter chain length: ketones, aldehydes, alcohols, and small alkanes. The secondary products give rise to off-aromas, flavors, and yellow color in fish (Khayat and Schwall 1983). Termination occurs when a radical reaction is quenched by a reaction with another radical or antioxidant. It is important to note that these reactions occur simultaneously and that the mechanism of lipid oxidations can become quite complex (Huss 1995).
1.2 Analysis of lipid oxidation
Several methods have been developed to measure different compounds as they form or degrade during lipid oxidation (Figure 1.2). Since the system is dynamic, it is recommended that two or more methods are used to obtain a more complete understanding of lipid oxidation. In order to follow the lipid oxidation process, reactants, intermediates, and final products can be measured. Many of these compounds are unstable and they are often variously affected by the presence of pro-oxidants, antioxidants, and oxygen. Also, since various food systems have different compositions, the pattern of intermediates and products formed differs greatly. It is therefore recommended that more than one stage of the oxidation process is monitored since using only one method might give rise to results that are difficult to interpret and highly misleading (Undeland 1997).
Figure 1.2 An example of the progress of lipid oxidation and breakdown of lipid oxidation products as assessed by different methods. Oxygen uptake is with Oxipress or an oxygen electrode. The primary products are measured as peroxide values (PVs). Measurement of free fatty acids (FFA) gives the acid value. Secondary products (e.g., aldehydes) are measured by the thiobarbituric acid (TBA) test, and sensory evaluation and gas chromatography (GC). Tertiary products are polymers, which can be measured with fluorescence, colorimetric and sensory evaluation. Rosa Jonsdottir, Matis-Icelandic Food Research. Reproduced with permission of Rosa Jonsdottir.
The available methods for monitoring and evaluate lipid oxidation in foods can be divided into few groups based on what they measure: oxygen consumption, loss of initial substrates, formation of free radicals, and formation of primary, secondary, and tertiary oxidation products. Table 1.1 summarizes the main methods that have been employed in laboratories and the industry for the measurement of various lipid oxidation parameters.
Table 1.1 Overview of the main methods used to monitor lipid oxidation products and potential predictors of lipid oxidation
Methods
Advantages
Disadvantages
References
Oxygen consumption
Good correlation with rancidity shelf-life test
Useful in simple lipid systems
Eriksson and Svensson 1970; Halliwell and Gutteridge 1985; German
et al
. 1986; Undeland 1997; Pike 2003
Pro-oxidants
e.g., metals and heme protein
May be used as predictors of lipid oxidation
The function and relevance of each pro-oxidant largely depends on its concentration and close surrounding
The presence of other compounds may enhance or inhibit the catalytic effect
Hultin 1988; Decker
et al
. 1989; Harris and Tall 1989; Decker and Hultin 1992; Schaich 1992; Hultin 1994; Undeland 1997; Lauritzsen
et al
. 1999; Lauridsen
et al
. 2000; Thanonkaew
et al
. 2006
Loss of antioxidants
e.g., α-tocopherol
Can be used as a chemical marker of lipid oxidation
These compounds may also be consumed by protein oxidation
Have to be carefully evaluated
Deng
et al
. 1978; Banda and Hultin 1983; Philippy 1984; Erickson 1993a,b; Brannan and Erickson 1996; Watanabe
et al
. 1996
Iodine value
Measure of degree of unsaturation
Can be used as an indication of lipid oxidation since there is a decline in unsaturation during oxidation
Not a rapid method
Lipid extraction needed
Hudson and Gordon 1999; Pike 2003
Fatty acid composition
May be used as an indicator of lipid oxidation
May correlate with PV and TBARS
Not a rapid method
Lipid extraction and esterification of fatty acids needed before GC analysis
Species dependant
Shono and Toyomitzu 1971; Beltran and Moral 1990; Polvi
et al
. 1991; Xing
et al
. 1993; Verma
et al
. 1995; Castrillón
et al
. 1996; Milo and Grosch 1996; Aubourg
et al
. 1997; Undeland 1997; Frankel 1998; Sarma
et al
. 2000; Aranda
et al
. 2006
Electron spin resonance
Sensitive to the detection of free radicals (intermediate)
Highly sophisticated way of measuring intermediates
Radicals not detectable at low concentration
Halliwell and Gutteridge 1985; Halliwell and Chirico 1993; Undeland 1997; Carlsen
et al
. 2001; Andersen and Rinnan 2002
Peroxide value
Sensitive and simple method
Most common measurement of primary oxidation in fish
Small sample amounts needed
Lipid hydroperoxides can also be analyzed in more specific ways using HPCL
Misleading results: a low value may represent either the beginning of or advanced oxidation
Poor correlation with sensory evaluation
Hazardous solvents used
Need to extract lipid from the samples
Wheeler 1932; Lea 1946; Asakawa and Matsushita 1978; Gray 1978; Akasaka
et al
. 1987; Yamamoto and Ames 1987; Francisco and Munch 1989; Ohshima
et al
. 1996; Undeland 1997; Yasuda and Narita 1997; Pike 2003; Chotimarkorn
et al
. 2006
Conjugated dienes and trienes
Useful for monitoring the early stages of oxidation
Rapid and simple method
Fairly unspecific method
The magnitude of the changes in absorption is not easily related to the extent of oxidation in the advanced stage
At 268 nm, other oxidation products are also absorbing, in addition to the trienes
Gray 1978; Brown and Snyder 1982; Madhavi
et al
. 1996; Undeland 1997; Pike 2003
Anisidine value
Sensitive and simple method
Gives good information about lipid oxidation
Correlates well with the amount of total volatile substances
Does not measure the concentration of specific compounds (no unit; measure group of chemicals)
The absorption depends on the substrate combination and the value is only comparable within the same oil type
Need to extract lipids from the sample
White 1995; Doleschall
et al
. 2002; Guillén and Cabo 2002; Pike 2003; van der Merwe
et al
. 2004
TBA value
Sensitive method
Lipid extraction is not required
Many modifications of the test have been developed
Correlates well with sensory evaluation
Other compounds can react with TBA
A measure of a transient product of oxidation
Marcuse and Johansson 1973; Gray 1978; Ke and Woyewoda 1979; Robbles-Martinez
et al
. 1982; Pokorny
et al
. 1985; Shahidi
et al
. 1985, 1987; Tomas and Fumes 1987; Harris and Tall 1989; Schmedes and Holmer 1989; Undeland 1997; Pike 2003
Fluorescence spectroscopy
Sensitive technique for lipid oxidation
Correlates with TBARS, FFA and TVB
Comparable with sensory analysis and GC
Non-specific to the vast amount of different oxidation products
A new approach
Pokorny
et al
. 1974; Erickson 1993a; Aubourg
et al
. 1997, 1998; Undeland 1997; Frankel 1998; Undeland
et al
. 1998; Aubourg 1999; Wold
et al
. 2002; Veberg
et al
. 2006
Fluorescent image analysis
Potential for on-line/at-line determination of lipid oxidation
Quantification at low concentration, high analysis speed and rapid sample preparation
May be used for direct determination of lipid hydroperoxides in fish muscle, without the need for extraction of lipid
Non-specific to the vast amount of different oxidation products
A new approach
Akasaka
et al
. 1987; Francisco and Munch 1989; Aubourg
et al
. 1997, 1998; Undeland 1997; Frankel 1998; Aubourg 1999; Chotimarkorn
et al
. 2006; Veberg
et al
. 2006
Volatile organic compounds
Lipid extraction is not required
May correlate well with sensory determination of lipid oxidation
The quantity of other volatile compounds resulting from lipid oxidation can be obtained simultaneously and may enhance the characterization of lipid oxidation in various food commodities
McGill
et al
. 1974; Undeland 1997; Pike 2003; Olafsdottir and Jonsdottir 2009
Sensory analysis
Best method to monitor quality changes in fish caused by lipid oxidation
Costly method
Poor reproducibility, depends on level of panelist training and skill
Requires large samples
Frankel 1998; Coppin and Pike 2001; Macfarlane
et al
. 2001; Broadbent and Pike 2003; Timm Heinrich
et al
. 2003; Rustad 2010
Near-intrared spectroscopy
Fast and non-destructive method
Simultaneous determination of multiple components per measurement
Can provide real-time information from the process stream
A secondary method, depends on less-precise reference methods
Need to develop appropriate multivariate calibration approaches to build accurate model systems before it can be used for routine analysis
Li
et al
. 2000; Yildiz
et al
. 2001; Gerde
et al
. 2007; Roggo
et al
. 2007; Poon 2009
PV, peroxide value; TBARS, thiobarbituric acid reactive substances; GC, gas chromatography, TBA, thiobarbituric acid; FFA, free fatty acids; TVB, total volatile basic nitrogen
1.2.1 Reactants and initiation of lipid oxidation
1.2.1.1 Oxygen consumption
The major reactants in lipid oxidation are oxygen and unsaturated fatty acids, but exposure of lipids to atmospheric oxygen results in unstable intermediates (Erickson 2002). Inasmuch as lipid oxidation results in the uptake of oxygen from the surroundings, measuring the time required for the onset of the rapid disappearance of oxygen in a closed system provides a means of determining oxidative stability (Pike 2003). Oxygen consumption can also be measured by electrochemical detection of changes in oxygen concentration and can be useful in simple lipid systems (Eriksson and Svensson 1970; Halliwell and Gutteridge 1985). This technique has been used to analyze the activity of lipoxygenases isolated from fish (German et al. 1986), for example, but the analysis of the graphical data obtained creates a bottleneck for it.
1.2.1.2 Pro-oxidants
There are many compounds that are naturally present in fish muscle and can serve as pro-oxidants by interfering with the reactants at different stages of the oxidation process (Hultin 1988). They could therefore serve as predictors of lipid oxidation. These compounds are in nature both enzymatic and non-enzymatic (Table 1.2), such as transition metals, heme proteins, reducing agents, peroxidases, and lipoxygenases (Harris and Tall 1989; Hultin 1994).
Table 1.2 Important pro-oxidants present in fish tissues (Underland, 1997. Reproduced with permission of the International Institute of Refridgeration.)
Low molecular weight metals
Reducing systems
Heme protein
Enzymes
Iron
Superoxide
Myoglobin
Lipoxygenases
Copper
Ascorbate
Hemoglobin
Cyclooxygenase
Mitochondial systems
Cytochromes
Peroxidases
Microsomal systems
Transitional metals and heme proteins have been reported as one of the major pro-oxidants in muscle foods (Decker and Hultin 1992) and are thought to play a key role in the initiation of the autoxidation process. It has been reported that the detrimental effects of transitional metals and heme proteins are greater than effects due to lipoxygenase, mainly because of longer-lasting pro-oxidative activity (Medina et al. 1999). Both Fe and Cu are known to promote oxidative reactions (Walling 1975), resulting in highly reactive hydroxyl radicals that cause oxidative damage to lipid membranes (Decker et al. 1989; Lauritzsen et al. 1999; Lauridsen et al. 2000). Thanonkaew et al. (2006) studied the effects of various metal ions (Fe, Cu, and Cd) at various concentrations on lipid oxidation, discolorations, and physicochemical properties of muscle protein in cuttlefish subjected to multiple freeze–thaw cycles. The rate of thiobarbituric acid reactive substances (TBARS) increases varied depending on concentration, type, and valency of the metal ion. Fe(II) induced lipid oxidation most effectively and its pro-oxidative effect was in a concentration-dependent manner, while Cu(I), Cu(II), and Cd(II) showed negligible effects on lipid oxidation.
Detection of different pro-oxidants could be a valuable way to predict lipid oxidation, but the relevance and function of each pro-oxidant largely depends on its close surroundings and its concentration.
1.2.1.3 Antioxidants
Antioxidants have the potential to act as chemical markers of lipid oxidation (Table 1.3). Following the dynamics of antioxidants degradation has been suggested as a convenient way to predict when the exponential phase of lipid oxidation would start, given that the various antioxidants deteriorate at different times (Buettner 1993). Loss of antioxidants could therefore serve as an early indicator of lipid oxidation, and this method has gained more and more attention (Deng et al. 1978; Banda and Hultin 1983; Philippy 1984; Erickson 1993a,b; Watanabe et al. 1996). It is known that α-tocopherol may decrease significantly during cold and frozen storage of fatty fish such as sardine, trout, and mackerel (Pozo et al. 1988; Ackman and Timmins 1995), leaner fish like saithe (Dulavik et al. 1998), and channel catfish (Brannan and Erickson 1996). The study by Erickson (1993a) showed that following the decrease in α-tocopherol level was the best way to distinguish between farm-raised and hybrid striped bass during the induction period of the lipid oxidation process in comparison with TBARS, volatiles, dienes, fluorescence, and ascorbic acid. According to earlier studies, aqueous antioxidants appear to be more sensitive predictors of early oxidation changes in muscle since they seems to be consumed faster than their lipid-soluble counterparts. In channel catfish, antioxidants decreased in the following order at −6 °C: glutathione > ascorbic acid > α-tocopherol > γ-tocopherol (Brannan and Erickson 1996). However, before using antioxidants as predictors of lipid oxidation, the correlation between their degradation and the formation of lipid oxidation products should be carefully evaluated since these compounds can also be consumed by protein oxidation (Srinivasan and Hultin 1994; Undeland 1997).
Table 1.3 Important inhibitors of lipid oxidation located in fish muscle. (adapted from Jonsdottir et al. 2008)
Inhibitor/antioxidant
Lipophilic antioxidants
Hydrophilic antioxidants
– Phenol compounds
– Phenol compounds
– α-tocopherol
– Glutathione
– Carotenoids
– Ascorbate (vitamin C)
Antioxidants enzymes
– Peptide, polyamine
– Superoxide dismutase
– Free amino acids (histidine)
– Glutathione peroxidase
– Urea
– Q-10 (ubiquinone)
1.2.1.4 Iodine value
The iodine value is a measure of the degree of unsaturation, that is, the number of carbon–carbon double bonds in relation to the amount of fat or oil. The higher the amount of unsaturation, the more iodine is absorbed, therefore the higher the iodine value and the greater the degree of unsaturation. The iodine value can be used as an index of lipid oxidation since there is a reduction in unsaturation during oxidation (Hudson and Gordon 1999). This method is not rapid, however, and requires lipid extraction of muscle samples.
1.2.1.5 Fatty acid composition
The fatty acid composition, or fatty acid profile, of food products is determined by quantifying the kind and amount of fatty acids that are present, usually by extracting the lipids and analyzing them using gas chromatography (GC). Changes in fatty acid composition provide an indirect measure of the extent of lipid oxidation. Initiation of lipid oxidation in fish is generally associated with PUFAs in the phospholipids of muscle cell membranes, which are known to be more susceptible to oxidation than triacylglycerols in fat deposits. Studies are rather conflicting, however, concerning the use of fatty acid loss as an indicator of lipid oxidation. Considerable loss of PUFAs has been found after storage of jack mackerel light muscle and carp at 5 °C (Shono and Toyomitzu 1971). Castrillón et al. (1996) also found a link between a drop in the C22:6/C16:0 ratio and the rate of peroxide value (PV) and TBARS increase in frozen sardines. In contrast, no consistent pattern of change in omega-3 fatty acids was found in frozen sardines (Beltran and Moral 1990), in frozen and iced cod and mackerel (Xing et al. 1993) or in Atlantic salmon (Polvi et al. 1991).
1.2.2 Intermediate products of lipid oxidation
Free radicals are important short-lived intermediates involved in the initial steps of lipid oxidation. The level of oxidation can be measured directly by detecting the formation of radicals, but methods based on this detection provide a good indication of initiation of lipid oxidation (Carlsen et al. 2001; Andersen and Skibsted 2002). Electron spin resonance (ESR) spectrometry is the only analytical technique that can specifically detect free radicals involved in autoxidation and related processes (Holley and Cheeseman 1993; Sharma and Buettner 1993; Milic et al. 1998). This method has been used to detect the formation of lipid radicals during oxidation in biological systems as well as the presence of superoxide and hydroxyl radicals (Halliwell and Gutteridge 1985; Halliwell and Chirico 1993). It can be rather difficult to quantify these radicals at low concentration, however, due to their short lifetimes.
1.2.3 Lipid oxidation products (primary, secondary, and tertiary)
1.2.3.1 Peroxide value
The most common method of measuring primary oxidation products in muscle foods and oils is PV (Gray 1978; Pike 2003). The PV represents the total hydroperoxide and peroxide oxygen content of lipids or lipid-containing material, and is one of the most common quality indicators of fats and oils (Ruiz et al. 2001; Antolovich et al. 2002). A number of methods have been developed for determination of PV, but the iodometric (Wheeler 1932; Lea 1946; Asakawa and Matsushita 1978) and ferric thiocyanate (Santha and Decker Eric 1994) methods are the most frequently used. Lipid hydroperoxides can also be analyzed in a more specific way using HPCL (Yamamoto and Ames 1987; Ohshima et al. 1996; Yasuda and Narita 1997).
The iodometric method is based on the ability of hydroperoxide to produce iodine (I2) from potassium iodide by a titration process using sodium thiosulfate (Na2S2O3). The chemical reactions involved in this method are given below, where ROOH is lipid hydroperoxide and ROOR is lipid peroxide:
Potential limitations of this method are well recognized and include poor sensitivity and selectivity, absorption of iodine at unsaturation sites of fatty acids leading to low results, liberation of iodine from potassium iodide by oxygen present in the solution to be titrated, and variation in the reactivity of different peroxides. This method also fails to adequately measure low PV because of difficulties in determination of the titration end point. For determination in foodstuffs, a disadvantage of this technique is the large amount of sample required, leading both to a significant amount of waste and difficulty in obtaining sufficient quantities from foods low in fat. Despite several disadvantages, the iodometric method still remains the standard procedure.
The ferric thiocyanate method is a colorimetric method based on the ability of hydroperoxide to oxidase ferrous ion (Fe2+) to ferric ion (Fe3+) and has been widely accepted. This technique is simple, reproducible and more sensitive than the standard iodometric method and can detect very low peroxide concentrations. The small sample size requirement is also an advantage, making this method convenient for studying a large number of samples.
The unstable and intermediate nature of peroxides and their sensitivity to temperature makes PV an approximate indicator of the state of oxidation, but particularly in the early stage of oxidation it serves as a good tool for the measurement of degree of oxidation. The PV method, however, generally shows little correlation with sensory evaluation as the lipid hydroperoxides are odor and flavorless, and as such it is not a useful practical method for detecting rancidity levels in aquatic foods as they are perceived by people.
1.2.3.2 Conjugated dienes and trienes
Double bonds in polyunsaturated lipids are changed from non-conjugated to conjugated bonds on oxidation. Primary products containing conjugated double bonds can be measured with simple spectrometry at 234 (dienes) and 268 nm (trienes) (Figure 1.3). This is a rapid method and useful for monitoring the early stage of oxidation, but at the same time it is a rather unspecific method (Gray 1978). High background absorbance originating from the native lipid interferes with that arising from the conjugated diene structure at 234 nm. At 268 nm, other oxidation products are also absorbing in addition to the triens, such as ethylenic di-ketones and oxo-dienes (Brown and Snyder 1982; Pike 2003).
Figure 1.3 Chemical reaction steps in the conjugable oxidation products assay. Shahidi & Wanasundra, 2002.
Reproduced with permission of Taylor and Francis.
This method can often not be performed directly on muscle samples because many other interfering substances are present (Madhavi et al. 1996), such as heme proteins, carotenoids, and chlorophylls, which absorb strongly in the UV region. Extraction of lipids into organic solvents before analysis is therefore a common approach to this problem.
1.2.3.3 p-anisidine value and totox value
The p-ansidine value determines the amount of α- and β-unsaturated aldehydes (principally 2-alkenal and 2,4-alkadienals), which are secondary oxidation products, in fats and oils. The aldehydes react with p-ansidine to form chromogen, resulting in yellowish products that absorb at 350 nm. Since colored products from unsaturated aldehydes are more strongly absorbed at this wavelength, the method is more sensitive to unsaturated aldehydes compared to the saturated aldehydes. The method correlates well with the amount of total volatile substances (Doleschall et al. 2002) and has been shown to be a reliable indicator of lipid oxidation in oils and fatty foods (van der Merwe et al. 2004). However, studies have shown that the p-ansidine value is only comparable within the same oil type due to variation of the initial value among oil sources (White 1995; Guillén and Cabo 2002).
The Totox value indicates the total oxidation of a sample using both the peroxide (primary oxidation product) and p-ansidine (secondary oxidation product) values:
Since the PV measures hydorperoxide (which increases and then decreases) and the p-ansidine value measures aldehydes (decay products of hyroperoxides which continually increase), the Totox value usually rises continually during the course of lipid oxidation (Pike 2003). The main disadvantage of the Totox value is its lack of scientific basis because it combines variables with different dimensions (Shahidi and Wanasundra 2002).
1.2.3.4 Thiobarbituric acid test
The thiobarbituric acid (2-thiobarbituric acid; TBA) test measures a secondary product of lipid oxidation, in particular malonaldehyde (Gray 1978), and is one of the most commonly used methods of detecting rancidity in some foods and oxidation products in biological systems (Frankel 1998). It is a colorimetric method based on the absorbance at 530–535 nm of the pink color formed between TBA and oxidation products of polyunsaturated lipids, in particular malonaldehyde (or malonaldehyde-type products) (Figure 1.4). This reaction is not specific to malonaldehyde, and results are often reported as TBARS. The tissue samples may be reacted directly with TBA or on a tissue distillate to eliminate interfering substances. One advantage of this method, therefore, is that the lipid does not have to be extracted from the tissue (Harris and Tall 1989; Undeland 1997).
Figure 1.4 Reaction of 2-thiobarbituric acid (TBA) and malonaldehyde (MA).
There are a few limitations when using the TBA test for evaluation of the oxidative state of foods and biological systems due to their chemical complexity. Components such as protein and sugar degradation products, amino acids, and nucleic acids interfere with the formation of the TBA color complex. Many modifications of the test have therefore been developed (Marcuse and Johansson 1973; Ke and Woyewoda 1979; Robbles-Martinez et al. 1982; Pokorny et al. 1985; Shahidi et al. 1985, 1987; Tomas and Fumes 1987; Schmedes and Holmer 1989).
Despite its limitations, the TBA test, with minor modifications, is frequently used to measure lipid oxidation in a wide range of food products (Pike 2003). The test provides a good means of evaluating the relative oxidative state of food systems, especially on a comparative basis (Shahidi and Wanasundra 2002).
1.2.3.5 Fluorescence spectroscopy
The formation of tertiary lipid oxidation products can be followed using fluorescence spectroscopy. Hydroperoxides (primary oxidation products) and aldehydes such as malonaldehyde (secondary oxidation products) can interact with proteins, phospholipids, and nucleic acids, forming Schiff bases (Figure 1.5). This reaction can lead to the formation of chromophores, which are brown-colored compounds (Frankel 1998). The fluorescent compounds formed from lipids are the result of the oxidation of phospholipids or are formed from oxidized fatty acids in the presence of phospholipids (Rustad 2010).
Figure 1.5 Reaction of lipid oxidation products and amines.
Fluorescence spectroscopy has been demonstrated to yield good indices of lipid oxidation in biological materials such as fish (Aubourg et al. 1998). Formation of both aqueous and lipid-soluble fluorescence has been followed in fish (Pokorny et al. 1974; Erickson 1993a; Undeland et al. 1998; Aubourg and Medina 1999; Aubourg et al. 2007). Evaluations of organic fluorescence have been proved to be better than aqueous fluorescence in monitoring the initiation and propagation phases of lipid oxidation in minced bass (Erickson 1993a). Fluorescence with excitation/emission settings of 327/415 and 393/463 nm have been demonstrated to be a more effective index of changes in fish quality than other commonly used methods (Aubourg and Medina 1999), and correlate well with TBARS after frozen storage and TVB-N after chilled storage (Aubourg and Medina 1997).
Front-face fluorescence is a relatively new approach in which intact samples are measured. This method has been shown to be a sensitive technique with regard to lipid oxidation and comparable with sensory analysis and gas chromatography (Wold et al. 2002). It is therefore one of few methods with an on-line/at-line potential for determination of lipid oxidation.
The fluorescence techniques are very sensitive and are 10–100 times more sensitive for the detection of malonaldehyde compared to the TBA method. However, the fluorescence technique is not specific since it evaluates a complex mixture resulting from interactions of oxidized lipids, phospholipids, malonaldehyde, and unsaturated aldehydes with proteins, peptides, amino acids, nucleic acids, and DNA (Frankel 1998).
1.2.3.6 Volatile organic compounds
Most secondary lipid oxidation products are volatile and can be responsible for the off-flavors and odors of oxidized oils and fats. Volatile compounds are therefore highly related to flavor, quality, and oxidative stability. Oxidative processes occurring during the storage of fish result in the accumulation of aldehydes, which contribute to the development of rancid cold-store flavors such as hexanal, cis-4-heptenal, 2,4-heptadienal, and 2,4,7-decadienal (McGill et al. 1974). Studies by Olafsdottir and Jonsdottir (2009) on the development of volatile compounds in chilled cod fillets showed that oxidatively formed, lipid-derived saturated aldehydes such as hexanal, heptanal, and decanal were detected in the fillets throughout the storage time. These oxidation products contributed to the overall characteristic fish-like odors of chilled cod fillets in combination with other carbonyls (3-hydroxy-2-butanone, 3-methyl-butanal, 2-butanone, 3-pentanone, and 6-methyl-5-heptene-2-one). Aldehydes generally have low odor thresholds therefore their impact was greater than that of alcohols and ketones, although their overall levels were lower (Olafsdottir and Jonsdottir 2009).
Headspace gas chromatographic methods are excellent tools for determining the volatile oxidation products that are directly responsible for or serve as markers of the flavor development in oxidized lipids. Beside correlation with flavor scores from sensory analyses, these GC analyses also provide a sensitive method of detecting low levels of oxidation in various oils and food lipids. The most common GC method for detecting and quantifying volatile oxidation products is static headspace analysis. Samples are held in a closed container until the volatile compounds diffuse and vaporize into the gas phase, and reach or approach equilibrium. An aliquot of the gas phase headspace is then injected directly into the gas chromatograph. This method is rapid and complex food systems can be analyzed directly without manipulations or extraction. The main disadvantage of the static headspace method is the difficulty of reaching complete equilibrium with viscous and semi-solid samples. Solid-phase microextraction (SPME) is an absorption technique that has gained extensive acceptance in the analysis of volatile compounds. This technique is rapid and has vanquished the difficulties experienced with traditional headspace methods. Volatile compounds are absorbed onto fused silica fiber and directly desorbed into the gas chromatograph.
1.2.4 Other methods of monitoring lipid oxidation
1.2.4.1 Near-infrared spectroscopy
Near-infrared (NIR) spectroscopy has become the alternative quality control method to traditional chemical and sensory methods in the food industry because of its advantages over other analytical techniques. It is used routinely for the compositional, functional, and sensory analysis of food ingredients, process intermediates, and final products. NIR spectroscopy has several advantages compared with traditional analytical methods. It is fast, non-destructive, and requires little or no sample preparation. It is also economic and environmentally friendly because no reagents are required, labor requirements are low, and no chemical wastes are produced. One of the strengths of NIR spectroscopy is that it can provide simultaneous determination of multiple components per measurement with a remote sampling capability and hence can provide real-time information from the process stream.
NIR spectroscopy has been successfully used to enhance or replace classical methods in the determination of PV, conjugated dienes, and p-anisidine value in fats and oils (Li et al. 2000; Yildiz et al. 2001; Gerde et al. 2007; Poon 2009).
The major limitation of NIR spectroscopy in food analysis is its dependence on less-precise reference methods (Roggo et al. 2007), and it cannot therefore not be considered a primary method. The main challenge of utilizing NIR technology for the determination of lipid oxidation is to develop appropriate multivariate calibration approaches to build accurate model systems so that it can be used for routine analysis.
1.2.4.2 Sensory analysis
The most powerful way of evaluating rancid odor and flavor is sensory analysis by trained panel. Sensory evaluation is defined as “the scientific discipline used to evoke, measure, analyze and interpret human reactions to characteristic of food perceived through the sense of sight, smell, taste, touch and hearing” (Huss 1995). Sensory analysis of lipid oxidation has been demonstrated by many researchers (e.g., Coppin and Pike 2001; Broadbent and Pike 2003; Timm Heinrich et al. 2003). Typical terms generally used to describe the oxidized flavor in foods include painty, cardboard, fishy, oily, and nutty. The flavor perceived as rancid flavor depends also on the composition of the product.
Fish is known to be rich in long-chain omega-3 fatty acids. Lipid oxidation products from these fatty acids are known to have a great impact on odor and flavor, even at very low concentration. The detection of these low levels is not easy with general oxidation measurements methods. The primary oxidation product is hydroperoxides, which can degrade further into secondary oxidation products. These compounds are generally volatile products that are responsible for off-flavors and odor in, for example, fish oils. Frankel (1998) reported that sensory panels can detect off-flavors in oils with PVs lower than 1 meq/kg. This has been supported by the study of Macfarlane et al. (2001), which showed that freshly refined fish oil samples with PVs lower than 1 meq/kg had a strong fishy taste.
The main limitations of sensory analysis are its cost and the requirement for a well-trained taste and odor panel. Even though sensory methods can give conclusive information, it can be difficult to compare data from different panels using different vocabularies to describe sensory attributes or data from the same panel analyzed at different times. Sensory methods also require a considerable number of samples, and the use of other chemical methods is recommended to support and complement the sensory data (Frankel 1998; Rustad 2010).
1.3 Conclusions
There are several methods that exist for the analysis of lipid oxidation in aquatic food products, among which formation of oxidation products is the most commonly used. The diversity and abundance of methods used to assess lipid oxidation reflect the complexity of this issue and confirm the fact that multiple methods should be applied to get the maximum information available. Each method has both advantages and disadvantages, therefore is it of great importance to select the most appropriate method depending on the system under investigation and the state of the oxidation.
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