Lipid Oxidation in Food - American Chemical Society

Chapter 15

Sensory Evaluation of Lipid Oxidation in Foods Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 2, 2016 | http://pubs.acs.org Publication Date: August 5, 1992 | doi: 10.1021/bk-1992-0500.ch015

G. V . Civille and C . A . Dus Sensory Spectrum, Inc., 24 Washington Avenue, Chatham, N J 07928

Traditionally, some sensory terms describing lipid oxidation have been common across food products. In many cases, however, researchers also have developed terminology specific to a given food type. Many of these descriptive terms evolved from the sources or reasons for the oxidation rather than a description of the result in the product. This paper examines a common approach to describing flavor notes generated by lipid oxidation across several food products in terms of both the typical characteristics for both fresh samples and aged samples. Meat, peanuts and vegetable oils are used as examples to illustrate the use of common lexicons and common sensory methods to measure responses to lipid oxidation in fresh, aging and aged products. Food scientists, lipid chemists and sensory analysts have long been interested in finding appropriate words to describe the sensory characteristics of lipid based foodstuffs. The quality of the terminology selected and used may be viewed differently by food scientists than sensory scientists. Food scientists might be content with words which describe the apparent cause of the flavor. Sensory analysts, however, are often more interested in descriptions of the perceived flavor note or characteristics. To the product developer or research chemist, terms such as "rancid," "oxidized," "warmed-over" and "light-struck" describe apparent reasons for the "off-notes." For the sensory analyst these terms suggest the occurrence of specific chemical reactions or probable causes, they do not provide an accurate description of the flavor perception itself. The development of lexicons and methodologies which detect off-flavors caused by oxidation has resulted in terminology that describes sensory characteristics which describe perceptions rather than causes.

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© 1992 American Chemical Society In Lipid Oxidation in Food; St. Angelo, Allen J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

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LIPID OXIDATION IN FOOD

Sensory Evaluation of Lipid-Oxidation Off-Flavors: The Past

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 2, 2016 | http://pubs.acs.org Publication Date: August 5, 1992 | doi: 10.1021/bk-1992-0500.ch015

The terminology and methodology developed for specific product types, such as meats, peanuts and vegetable oils, have been lexicons and methodologies which predominantly focus on the occurrence of off-flavors in each category of products. Meat and Poultiy. Warmed-Over Flavor or W O F is a general term used to describe off-flavor in reheated meat which has been precooked and refrigerated. In food service situations, such as institutional cafeterias or airlines, where the foods, including meats, are cooked ahead and refrigerated and reheated before serving, the presence of "warmed-over" flavor in the meat is regarded as a defect. Meat and poultry research at university and government laboratories has sought to identify the causes, chemical and physical conditions and potential means to reduce or eliminate "warmed-over" flavor. W O F describes the cause of a combination of changes in flavor attributes within a given meat or poultry product. Investigators, aware of this deficiency have tried to develop expanded terminology to describe the individual sensations that are perceived. Table I illustrates some researchers' choices of terms for description of meat flavor.

Table I. Descriptors Used in Some Investigations of Warmed-Over Flavor For Beef Jacobson & Koehler (1970)

Harris & Lindsay (1972)

Joseph et. al. (1980)

Bland Sweet Rich Meaty Sulfury Gizzard-Like Musty Stale "old" Rancid

Greasy Sulfur Liver-Giblet Warmed-Over Stale Rancid

Sour Bitter Metallic Sweet Putrid Salty Rancid Other off-flavor

a

a

a

a

a

a

a

These quality descriptors were highest in intensity in meats having W O F or were used most frequently by panelists describing meat with this flavor. SOURCE: Reproduced with permission from ref. 1. Copyright 1987 Academic.

These researchers used different flavor descriptors (musty, stale, rancid and warmed-over) to describe the effects of reheating precooked meat. O f these off-notes related to reheating, only musty describes a sensory characteristic, whereas stale, rancid and warmed-over describe the process suspected of producing off-notes or flavors.

In Lipid Oxidation in Food; St. Angelo, Allen J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

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It should be noted that these earlier meat lists did include a few terms to describe the full flavor of fresh or "on" meat and poultry flavor. Peanuts. As with meats, the peanut industry has used several terms to describe peanut flavor which included descriptors of flavor sensations, such as roasted peanut, nutty and green, as well as descriptors for the sources suspected to contribute to off-flavors, such as rancid, stale and oxidized, shown in Table II. The C L E R (Critical Laboratory Evaluation Roast) Method uses a quality measurement which originally combined intensity and hedonic responses on a single continuum (2). The updated method includes specific flavor changes in a supplemental comments section only (3).

Table II Descriptors Used in Some Investigations of Peanut Flavor Oupadissakoon & Young (1984)

Syarief et.al. (1985)

Holaday (1971)

Aroma Flavor Aftertaste Astringent Bite Bitter Burnt Chemical Earthy Green Nutty Oil Rancid Roasted Peanut Sour Stale Sweet

Roasted Peanut Fruity Mold Bitter Sour Over/Under Roast Earthy Oxidized Petroleum

Off-Flavor Low Level Off-Flavor Low Peanut Flavor Good Peanut Flavor

S O U R C E : Adapted from ref. 2, 4-5.

The Edible Oil Industry. The flavor of a high quality oil is generally described as bland. It is when the quality of the oil is suspect and off-flavors are prevalent that chemists and food scientists use more descriptive terminology. A s the oil deteriorates, flavor volatile compounds are created at each stage which impart different flavor notes that encompass nutty and beany to rancid and fishy. The terms are divided into terms that refer to a specific characteristic (corny, nutty, fishy) and terms that describe the suspected degrading process (reverted, rancid, oxidized). The A O C S (American O i l Chemists Society) Flavor Quality Scale,



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shown in Table III, combined intensity and quality into one scale having each grade associated with a specific flavor description.


Table III. AOCS Flavor Quality Scale a

Flavor Grade

Description of Flavor

10 (Excellent) 9 (Good) 8 7 (Fair) 6 5 (Poor) 4 3 2 1 (Repulsive)

Completely bland Trace of Flavor but not recognizable Nutty, sweet, buttery, corny Beany, hydrogenated, popcorn, bacony Oxidized, musty, weedy, burnt, grassy Raw, reverted, rubbery, watermelon, bitter Rancid, painty Fishy, buggy Intensive objectionable flavors

Flavor intensity at presented concentration rated slight. SOURCE: Reproduced with permission from ref. 6. Copyright 1985 American Oil Chemists' Society. The original A O C S scale is difficult to use since it requires the integration of quality and intensity of both appropriate and off-notes. The original A O C S Flavor Quality Scale has since been revised to incorporate separate ballots for grading and flavor intensity. The terms used to describe oxidized oil not only include terms that refer to a specific flavor sensation, but continue to include terms that are process orientated. The descriptors are so divided in Table I V .

Table IV. A Partial List of Terms Used to Describe Oxidized Oil Flavor Related Terms

Process Oriented Terms

Buttery Nutty Beany Grassy Watermelon Painty Fishy

Hydrogenated Oxidized Reverted Light-Struck Rancid

S O U R C E : Adapted from ref. 7.


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Across these three food categories, (meats, peanuts and oils) certain flavor descriptors are common for describing lipid oxidation: stale, rancid, oxidized, fresh and off-flavor. Within each category, other terms have been used specifically to describe some forms of lipid oxidation: meats - warmed-over and musty, peanuts - cardboard and soapy, and oils - fishy, reverted and light-struck.


Sensory Evaluation of Lipid Oxidation Off-Flavors: Recent Development The recent focus on improved descriptive terminology has resulted in complete lexicons for product categories. The American Society of Testing Materials Committee E18 has a task group dedicated to the development of precise descriptive terminology. The use of descriptive analysis methodology has allowed for more complete lexicons and more precise intensity measurements. The prescribed characteristics of a complete lexicon are as follows: terminology must be orthogonal, based on underlying structure, based on a broad reference set, precisely defined and primary, rather than integrated (7). Descriptive Analysis. Descriptive analysis methods involve the detection and the description of both the qualitative and quantitative sensory aspects of a product by a trained panel (8). In the terminology development stage, one descriptive analysis method, the Spectrum Method, provides a wide array of flavor references for training panelists. Processing variables, ingredient variables and examples of off-flavors are presented to the panelists in order to develop a list of terms that completely characterize the product's sensory attributes. Intensity references (both general and product specific) are also presented to the panelists, thus insuring quantitative and qualitative analytical sensory data which is both valid and reliable. The development of standard lexicons, standard rating scales, standard methods for preparation and presentation of products and standard panel training all contribute to a uniform analytical sensory technique. The focus in the past investigations of lipid oxidation has been to describe the "off-notes" and/or quantify them in some way to indicate the quality of the food in question. Only some research in lipid oxidation attempted to describe and quantify the flavor of the fresh product. Current sensory and food science research in these food categories and others involving lipid oxidation have focused on the full descriptions of the "on-flavors" as well as the off-notes, which include those resulting from oxidation. On-flavor incorporates those flavor characteristics which describe the fresh meat, peanuts or oil. The most current terms for lipid oxidation flavors describe the characteristics (cardboard, painty) rather than the suspected cause or process (stale, rancid or oxidized). The Meat Industry: Warmed-Over Flavor. The phenomenon of W O F is complex and, despite recent developments (9), its formation is not yet completely understood. Analytical chemists, engaged in solving this mystery, need terminology to describe the flavor notes that arise as W O F develops.


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Table V shows a beef lexicon developed by a panel of meat flavor experts convened by the Monell Chemical Senses Center. To create a complete list, the panelists were initially presented with a variety of meats (beef, pork, turkey and chicken), cooking procedures, storage times and reheating procedures. The beef flavor descriptors which were the focus of the research were defined clearly and reference samples were developed for each descriptor (10).


Table V. Beef Flavor Descriptions Attribute

Definition

Cooked Beef Lean

The aromatic associated with cooked beef muscle meat. The aromatic associated with cooked beef fat. The aromatic associated with grilled

Cooked Beef Fat Browned or broiled beef. Serum/Bloody Grainy/Cowy

Cardboard

Oxidized/Rancid/Painty

Fishy

Sweet Sour Salty Bitter

The aromatic associated with raw beef lean. The aromatic associated with cow meat and/or beef in which grain feed character is detectable. The aromatic associated with slightly stale beef (refrigerated for a few days only) and associated with wet cardboard and stale oils and fats. The aromatic associated with rancid oil and fat (distinctly like linseed oil). The aromatic associated with some rancid fats and oils (similar to old fish). Tastes on the tongue associated with sugars. Tastes on the tongue associated with acids. Tastes on the tongue associated with sodium ions. Tastes on the tongue associated with bitter agents such as caffeine, quinine, etc.

SOURCE: Reproduced with permission from ref. 10. Copyright 1986 Dial Technical Center. These terms, in conjunction with intensity ratings, allow the researcher to track not only the development of off-flavors, but also the decrease of on-flavors. Table V I shows the differences between a fresh, frozen beef patty


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and a beef patty which was stored for 5 days then reheated. Note that the intensity of the off-notes cardboard and oxid/rancid/painty increased and the intensity of the cooked beef lean and cooked beef fat notes decreased. Table V I . Comparison of Fresh Control Baked Beef Patty with Stored Steamed And Baked Patty


Control Cooked Beef Lean Cooked Beef Fat (fresh) Browned Serum/Bloody Grainy/Cowy Cardboard Oxid/Rancid/Painty Fishy Sweet Sour Salty Bitter

6 4 4 3 2 1 0 0 3 1 2 0

SOURCE: Reproduced with permission from ref. 10. Technical Center.

Reheated 4 1 1 2 1 4 3 0 2 3 2 0 Copyright 1986 Dial

A similar approach was developed for chicken. Table VTI indicates the differences between fresh cooked chicken patties and patties stored for 3 days. Table VII. A Comparison Between Fresh Cooked Chicken Patties And Patties Stored For Three Days

Chickeny Meaty Brothy Liver/Organy Browned Burned Cardboard Warmed-Over Rancid/Painty Sweet Bitter Metallic

Fresh Cooked

Stored 3 Days

53.3 54.2 35.6 27.2 16.7 7.3 7.7 9.5 5.5 22.3 8.3 10.5

28.6 32.9 9.3 14.1 33.8 31.7 35.6 54.3 46.1 5.6 23.6 19.5

S O U R C E : Adapted from ref 11.


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Table VIE. Lexicon of Peanut Flavor Descriptors Attribute

Definition

Roasted Peanutty

The aromatic associated with medium-roast peanuts (about 3-4 on USDA color chips) and having fragrant character such as methyl pyrazine. The aromatic associated with dark-roasted peanuts (about 1-2 on USDA color chips) and having legume-like character. The aromatic associated with dark roasted peanuts (4+ on USDA color chips) and having very browned toasted character. The aromatics associated with sweet material such as caramel, vanilla, molasses, fruit. The aromatics associated with base peanut character (absence of fragrant top notes) and related to dry wood, peanut hulls and skins. The aromatics associated with somewhat oxidized fats and oils and reminiscent of cardboard. The aromatic associated with linseed oil and oil based paint. The aromatic associated with very dark roast, burnt starches and carbohydrates, (burnt toast or espresso coffee). The aromatic associated with uncooked vegetables/grass/twigs, cis-2-hexanal. The aromatic associated with wet dirt and mulch. The aromatic associated with raw grain (bran, starch, corn, sorghum). The aromatic associated with trimethylamine, cod liver oil and old


Raw Bean/Peanutty

Dark Roasted Peanut

Sweet Aromatic Woody/Hulls/Skins

Cardboard Painty Burnt Green Earthy Grainy Fishy

fish.

Chemical/Plastic Skunky/Mercaptan Sweet Sour Salty Bitter Astringent Metallic

The aromatics associated with plastic and burnt plastics. The aromatic associated with sulfur compounds, such as mercaptan, which exhibit skunk-like character. The taste on the tongue associated with sugars. The taste on the tongue associated with acids. The taste on the tongue associated with sodium ions. The taste on the tongue associated with bitter agents such as caffeine or quinine. The chemical feeling factor on the tongue, described as puckering/dry and associated with tannins or alum. The chemical feeling factor on the tongue described as flat, metallic and associated with iron and copper.

SOURCE: Reproduced with permission from ref. 12. Copyright 1988 Dial Technical Center.



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The Peanut Industry. The peanut industry, like the meat industry, sought to develop a comprehensive flavor lexicon. The U S D A - A R S - S R R C and the Monell Chemical Senses Center assembled a panel of peanut experts to develop a complete peanut lexicon (22). The panel, presented with peanut paste samples that represented different roast levels as well as a variety of flavors resulting from different growing and handling conditions, developed terms to encompass the treatment variables. Terminology was also developed to describe the flavor notes generated when the oils oxidize. The complex lexicon is presented in Table VIII and is currently being used in research studies to investigate the development of flavor changes in peanuts. In Table IX, a comparison of fresh and oxidized peanut pastes made from the same peanut source, demonstrates the decrease in the "fresh/on" peanut characteristics (roasted peanutty, sweet aromatic and sweet) as well as the increase in the cardboard and painty terms. This system allows for tracking the relative decrease in fresh notes and the increases in the two flavor characteristics which describe the effects of oxidation (cardboard and painty).

Table IX. Comparison of Fresh Peanut Paste and Oxidized Peanut Paste Attribute

Fresh

Roasted Peanutty Raw Bean/Peanut Dark Roasted Peanut Sweet Aromatic Woody/Hulls/Skin Cardboard Painty Sweet Bitter Astringency

6.1 1.7 2.1 3.5 1.2 0 0 2.9 1.2 1.6

Oxidized 2.7 1.4 1.3 1.3 2.1 3.4 4.7 1.4 2.0 2.0

S O U R C E : Adapted from ref. 12. The Vegetable Oil Industry. Through the efforts of the sensory analysts who work with vegetable oils, new studies are being conducted to develop effective sensory methodology. The A S T M E18 task group on edible oils is responding to the needs of the oil industry, which has used the A O C S quality method for so long, while providing better qualification and quantitative description of the oil description of the oil flavors. Table X includes both an overall quality rating and the intensity ratings for individual descriptors. Unlike the descriptors for meat and peanuts, the rancid and painty notes for oil description have not yet been combined. The use, however, of the on-flavor descriptors with intensity allows for characterization of the unique properties of oils from different seed sources.


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Table X. Flavor Quality and Descriptive Analysis of Fresh Aged Low Erucic Acid Rapeseed Oil (Canola)

Overall Quality Buttery Nutty Toasted Waxy Painty Rancid Metallic Fishy Sulfur (vegetable)

O-Time

Aged 8 Days, 60 C

8.2 3.1 2.3 1.2 1.3 0 0 0 0 0

4.5 0 0 0 3.6 7.4 5.4 3.2 2.1 1.7

S O U R C E : Warner, K., U S D A - A R S - N O R T H . R E G . R E S . C N T R . , unpublished data

CONCLUSION The contribution of sensory analysis to the development of descriptors, definitions, and reference for the use in food analysis have special application to lipid oxidation in foods. Other research with coffee, nuts, fish, milk products, cereals and grains has been undertaken and continues to develop new descriptors for describing the on-flavor of fresh product and the flavors of lipid oxidation. The move toward a more unified approach to documenting flavor gives researchers high quality analytical sensory tools that can be used to study treatments which cause or retard lipid oxidation in foods.

Literature Cited

1. 2. 3

4. 5.

Melton, S.L., Davidson, PM. and Mount, J.R. In Warmed-Over Flavor of Meat; A.J. St. Angelo and M.E. Bailey., Eds.; Academic Press: Orlando, FL, 1987; pp 141-164. Holaday, C.E. J. Amer. Peanut Res. Educ. Soc. 1971, 3 (II), 239-241. Fletcher, M.M. In Peanut Quality - Its Assurance and Maintenance the Farm to End Product; H. Ahmed and H.E. Pattee., Eds.; Tech. Bull. 874; Agric. Ex.Stat., Inst. Food and Agric. Sci., Univ. of Florida, Gainsville. 1987; pp 60-72. Oupadissakoon, C. and Young, CT. J. Food Sci., 1984, 49, 52-58. Syarief, H., Hamann, D.D., Giesbrecht, F.G., Young, C.T. and Monroe, R.J. J. Food Sci. 1985, 50, 631-638.


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8. 9. 10. 11. 12.

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Warner, K. In Flavor Chemistry of Fats and Oils; D.B. Minn and T.H. Smouse, Eds.; American Oil Chemist's Society: Champaign,IL,1985, pp 207-222. Civille, G.V. and Lawless, H.L. J. Sensory Studies, 1986, 1 (3/4), 203-206. Meilgaard, M., Civille, G.V. and Carr, B.T. Sensory Evaluation Techniques. CRC Press: Boca Raton, FL, 1991, pp 187-199. Spanier, A.M., Vercellotti, J.R. and James, C. J. FoodSci.,in press. Johnsen, P.B. and Civille, G.V. J. Sensory Studies, 1986, 1, 99-104. Lyon, B.G., Lyon, C.E., Ang, C.Y.W. and Young, L.L. Poultry Sci., 1988, 67, 736-742. Johnsen, P.B., Civille, G.V., Vercellotti, J., Sanders, T.H. and Dus, C.A. J. Sensory Studies, 1988, 3, 9-18.

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Lipid Oxidation in Food - American Chemical Society

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