Michael G. Legendre

Lipid oxidation in foods

This review discusses the basic chemical reactions that affect food flavor quality. Although there are many reactions that can lead to the deterioration of quality in foods, this review focuses on lipid oxidation and how it adversely affects flavor principles. It also presents technological advances for studying the basic mechanism of lipid oxidation, for measuring its intensity, and for retaining food quality. The food commodities that provide the subject matter for this review include vegetable oils, legumes, cereal grains, eggs, beef, lamb, poultry, seafoods, and catfish. The methodologies for assessing food quality form a multidisciplinary approach that includes primarily instrumental analysis by direct gas chromatography, chemical analysis by the TBA test, and sensory analysis by quantitative descriptive determinations. The author hopes that the information presented in this review is applicable to food commodities not discussed.

Novel technique for the analysis of volatiles in aqueous and nonaqueous systems

A simple, efficient, external inlet assembly is described for analyzing volatile components in raw and processed foods by direct gas chromatography and mass spectrometry. The device comprises three sections: a sample inlet, a condenser, and a six-port rotary valve. The versatility and effectiveness of this assembly is demonstrated by the analysis and identification of volatiles from diverse food products as salad oils, vinegar, and corn-soy food blends. The procedure is rapid, efficient, and offers the following desirable features: it is compatible with all commonly used chromatographs and can accomodate samples of different size; sample volatiles are obtained without use of prior enrichment techniques, at ambient or elevated temperatures; uniform heating enhances volatiles elution, thereby improving sensitivity; moisture and air are removed to facilitate mass spectral analysis; the closed nature of the system minimizes loss of low molecular weight volatiles during elution, thus producing a highly reliable pro-file of volatiles.

Analysis of vegetable oils for flavor quality by direct gas chromatography

Abstract and SummaryRecently, a direct gas Chromatographic method for examining volatiles in vegetable oils was reported [Dupuy et al., JAOCS 50:340 (1973); and Dupuy et al., Ibid. 53:628 (1976)]. The procedure stimulated the development of instrumental techniques for determining odor and flavor characteristics of vegetable oils. This symposium paper describes modifications of the original direct gas Chromatographie procedure that substantially enhance its sensitivity and applicability. Profiles of volatiles for several experimental oils obtained by the modified system are presented, together with mass spectral data characterizing significant flavor-related peaks. Regression analysis of the instrumental data, with oil flavor scores, indicates that reliable flavor characteristics of high- and low-quality vegetable oils may be obtained rapidly and efficiently by instrumentation.

Identification of lipoxygenase-linoleate decomposition products by direct gas chromatography-mass spectrometry

Lipoxygenase, prepared from Virginia-type peanuts, was used to catalyze the oxidation of linoleic acid and methyl linoleate to form the C−9 and C−13 hydroperoxides. These reactions were monitored by rapid unconventional direct gas chromatography-mass spectroscopy. An aliquot of the enzymatic reaction mixture, without prior extraction or chemical modification, was secured directly into the heated (40–70 C) or nonheated (room temperature) injection system. When the reaction mixture was analyzed at room temperature, only hexanal was found. At elevated temperatures, five major and several minor components were identified. The predominant compounds identified were pentane, hexanal, 2-pentylfuran,trans-2,cis-4-decadienal, andtrans-2,trans-4-decadienal. These products originate from decomposition of either the C−9 or C−13 hydroperoxides generated by peanut lipoxygenase.

Direct sampling capillary gas chromatography of volatiles in vegetable oils

Direct sampling gas chromatography used for determining volatiles and, indirectly, the flavor of vegetable oils, has been improved by a capillary column in place of the usual packed columns. Data on two good vegetable oils from a supermarket, and on one of these samples after intentional deterioration, are presented. Use of the capillary column provides a more efficient technique to differentiate between the better oils than did the previously used packed columns.

Analysis of flavor quality and residual solvent of soy protein products

A simple, direct, gas Chromatographic technique is described for eluting and resolving residual solvent and flavor-related volatile components from soy products such as flour and protein isolates. No prior enrichment of volatiles is necessary. A sample, together with a small amount of water, is secured in a glass liner and placed in the heated injection port of a gas Chromatograph. The volatiles are rapidly steam distilled from the sample by the heat, moisture, and flow of carrier gas and are adsorbed on the chromatographic column in situ. Residual solvent and other volatiles adsorbed on the column are resolved by temperature-programmed gas chromatography and identified by combined gas chromatography-mass spectrometry. The correlation between taste panel flavor score and concentration of volatile components is significant at the 1% level.

Analysis of neutral volatiles of mayonnaise by direct gas chromatography and mass spectrometry

Simple procedures have been developed for analyzing neutral volatiles from mayonnaise by direct gas chromatography and combined direct gas chromatography-mass spectrometry. For gas Chromatographic analysis, a glass liner containing glass wool coated with alkali in the lower quarter and plain glass wool in the remaining space is placed in the heated inlet of a gas Chromatograph, and mayonnaise and water are injected onto the plain packing. Neutral volatiles eluted from the mayonnaise by the combined action of water, carrier gas, and heat collect on the cool column of the gas Chromatograph, but acetic acid is trapped by the alkaline glass wool and thus does not interfere with the analysis. After removal of the liner with the spent sample, the temperature of the column oven is programmed to resolve the volatiles. For mass spectrometric analysis, neutral volatiles are passed directly from a Chromatograph inlet to a second inlet liner containing a porous polymer that traps most organic compounds but has low affinity for water. These neutral organic volatiles are desorbed from the porous polymer in the inlet of a Chromatograph interfaced with a mass spectrometer for analysis. This procedure allows components resolved by the gas Chromatograph to be identified by mass spectrometry without interference from either water or acetic acid. A total of 21 neutral volatile compounds was identified in mayonnaise.

Analysis of trace volatiles in food and beverage products involving removal at a mild temperature under vacuum

Abstract A simple approach for the detection and identification of volatiles in food and beverage products involving removal at mild temperatures under vacuum is presented. Volatiles are stripped from the sample between 30 and 60°C and adsorbed onto a Tenax-GC trap at 8 psi. The GC oven is cooled to −30°C for several minutes. Then the moisture-free volatiles are desorbed directly onto the cold capillary GC column and resolution is accomplished by temperature programming. This approach minimizes thermal decomposition and permits the detection and identification of trace volatiles in foods and beverages down to the parts-per-billion level by GC-MS.

Rapid Instrumental Analysis of Lipid Oxidation Products

The oxidation of unsaturated fatty acids initially involves the formation of their hydroperoxides. Once these products are formed, they can be decomposed or further oxidized to secondary products such as alcohols, acids, ketones, and aldehydes that are capable of reacting with other constituents of food such as amino acids, proteins, enzymes, and vitamins. These reactions can have an adverse affect on the nutritive value and quality of their respective foods. Additionally, as witnessed in other chapters of this book, the free radicals generated by the oxidative mechanisms have been implicated in reactions that can lead to pathological changes in animal and human tissue.

Rapid instrumental technique for the analysis of volatiles in salad dressing

A simple, rapid, efficient procedure for analyzing the volatile components in salad dressings is described. A unique inlet system, used in conjunction with gas chromatography and mass spectrometry, provides an objective, tangible profile of volatiles characteristic of the product. The individual components may be identified to qualify more effectively the odor and flavor quality of the specimen.