Stephen S. Chang

Chemical reactions involved in the deep-fat frying of foods1

Deep-fat frying is one of the most commonly used procedures for the preparation and manufacture of foods in the world. During deep-fat frying, oxidative and thermal decompositions may take place with the formation of volatile and nonvolatile decomposition products, some of which in excessive amounts are harmful to human health. A limited survey of frying fats used in commercial operations indicated that some were maintained at good quality and others were overused or abused. The volatile decomposition products produced by corn oil, hydrogenated cotton-seed oil, trilinolein, and triolein, under simulated commercial frying conditions, were collected, fractionated, and identified. A total of 211 compounds were identified. The nonvolatile decomposition products produced by trilinolein, triolein, and tristearin under simulated commercial frying conditions were collected and characterized. After being treated under deep-fat frying conditions at 185 C for 74 hr, trilinolein yielded 26.3% non-urea-adduct-forming esters, triolein yielded 10.8%, and tristearin also yielded 4.2%.

Elucidation of the chemical structures of natural antioxidants isolated from rosemary

A natural antioxidant extract with activity greater than BHA and equal to BHT was isolated from rosemary leaves. The extract was separated into 7 primary fractions with liquid chromatography, using silicic acid as an adsorbent followed by gradient elution. Each fraction was rechromatographed to yield a total of 16 subfractions. Two compounds, carnosol and ursolic acid, were identified by infrared, mass and nuclear magnetic resonance spectrometry. Carnosol was shown to be one of the active antioxidant components in rosemary. Ursolic acid was not an effective antioxidant. Further fractionation of the most active antioxidant subfractions by high performance liquid chromatography and the elucidation of the chemical structures of these fractions are now in progress.

Elucidation of the chemical structure of a novel antioxidant, rosmaridiphenol, isolated from rosemary

A novel antioxidant compound has been isolated and identified from the leaves of theRosmarinus officinalis L. The compound, named rosmaridiphenol, is a diphenolic diterpene. When tested in lard, the antioxidant activity of this compound was superior to BHA. Structural elucidation of rosmaridiphenol was accomplished by infrared spectroscopy (IR), mass spectroscopy (MS),1H-NMR (nuclear magnetic resonance) and13C-NMR spectroscopy.

Natural and simulated meat flavors (with particular reference to beef)

Current information relating to the chemical composition of both natural and simulated meat flavors is presented, with particular reference to beef flavor. The origin of natural meat flavor is described in terms of the nature of the precursors and the formation pathways of volatile components contributing to meat flavor. A table listing the aroma components of natural beef is included and their relative contributions to the overall flavor is considered. The historical development of commercial meat flavorings is traced from the early spice blends and meat extracts to the thermally produced imitation meat flavors (processed meat flavorings) including “reaction products” and flavorings derived from natural meat. Some G.B. and U.S. “reaction products” patents and meat flavor contributing compounds patented since 1960 are summarized in tabular form.

The structure of rosmariquinone — A new antioxidant isolated fromRosmarinus officinalis L.

A new diterpene, named rosmariquinone, was isolated from the leaves ofRosmarinus officinalis L. The leaves were first extracted using methanol and, upon further purification, this extract yielded rosmariquinone. Structure elucidation of the antioxidant was done using IR, MS,1H-NMR and13C-NMR.

A systematic characterization of the reversion flavor of soybean oil

The volatile flavor compounds in a reverted soybean oil with a peroxide number of 4.3 meq/kg were isolated by a semicontinuous counter-current vacuum steam-distillation process, fractionated by repeated gas chromatography, and identified by infrared and mass spectrometry. A total of 71 compounds were identified, which included 19 acids, 39 nonacidic compounds, and 13 tentatively identified compounds. The acids consisted of eight normal saturated acids, nine α,β-unsaturated acids, a branch-chain acid, one hydroxy acid, two keto acids, three lactones, and one aromatic acid. The nonacidic compounds consisted of two esters, eight normal saturated aldehydes, two branched-chain aldehydes, five 2-enals, three dienals, eight ketones, eight alcohols, six hydrocarbons, and four aromatic compounds.The mechanism of formation of the identified compounds indicated that they were mostly primary or secondary autoxidation products of the hydroperoxides of the unsaturated fatty esters. Since many of the identified compounds were produced from oleic and linoleic acids, it is doubtful that linolenic acid was solely responsible for the reversion flavor.Of the compounds identified two are of unusual interest. They are 1-decyne and 2-pentyl furan. The former is the first acetylenic compound reported as the autoxidation products of unsaturated fatty esters which contained only double bonds. The latter imparts to an oil at concentrations of 5–10 ppm a beany and grassy flavor reminiscent of that of a reverted soybean oil. Since this compound is postulated as being produced by the autoxidation of linolenic acid, it is suggested that the presence of linolenic acid catalyzes the autoxidation of linoleic acid and possibly alters the decomposition pattern of its hydroperoxides.

Chemical reactions involved in the deep fat frying of foods. III. Identification of nonacidic volatile decomposition products of corn oil

Chemical identification of the volatile decomposition products (VDP) produced by fats and oils under conditions of deep fat frying is important for the elucidation of the mechanisms of thermal oxidation, for the study of their effects upon human nutrition, and for their contribution to the deep fat fried flavor of foods. The acidic VDP produced by corn oil maintained at 185C for 30 hr with periodic frying of moist cotton balls and with addition of fresh oil to replenish the oil lost due to evaporation, decomposition, and adsorption by the cotton balls were fractionated by repeated gas chromatography. The gas chromatographic fractions were identified by IR and mass spectrometry. A total of 30 acids were characterized. They consisted of 12 n-aliphatic saturated acids, seven 2-enoic acids, one 3-enoic acid, three keto acids, two hydroxy acids, four dicarboxylic acid and one aromatic acid. It is suggested that the effects of some of these acids upon human nutrition be studied.

Chemical reactions involved in deep fat frying of foods. VI. Characterization of nonvolatile decomposition products of trilinolein.

A laboratory apparatus that could be used to treat pure triglycerides under simulated deep fat frying conditions was designed and built. By the use of this apparatus, the volatile decomposition products produced during frying could be quantitatively collected at the same time. Pure trilinolein was treated in this apparatus at 185 C for 74 hr. The volatile decomposition products were collected quantitatively. Their fractionation and identification will be reported in a subsequent paper. The nonvolatile decomposition products were isolated from the treated trilinolein as the non-urea-adduct-forming methyl esters. They constituted 26.3% of the treated trilinolein and were separated into seven fractions by repeated liquid column chromatography. Chemical and physical analyses of these fractions indicated that the chemical reactions taking place under simulated deep fat frying conditions were not entirely the same as those during simple heating under air. One of the seven fractions was further purified by thin layer chromatography and then identified as a cyclic carbon to carbon linked dimer which amounted to 4.9% of the treated trilinolein. Another fraction was further purified by thin layer chromatography, followed by gas chromatography, and then identified as noncyclic hydroxy dimers formed through carbon to carbon linkages. The noncyclic dimers constituted 2.8% of the treated trilinolein. The other four fractions were depolymerized by hydroiodic acid. The depolymerization products were fractionated by thin layer chromatography and then analyzed. It was estimated that the treated trilinolein contained 8.4% of trimers formed through carbon to carbon linkages, and 4.9% of dimers and trimers joined through carbon to carbon or carbon to oxygen linkages in the same molecule and also trimers, in which all the three monomeric units were joined through carbon to oxygen linkages.

The synthesis of 2-(2-pentenyl) furans and their relationship to the reversion flavor of soybean oil

Abstractcis- andtrans-2-(2-Pentenyl)furans were synthesized and structures were confirmed by infrared, nuclear magnetic resonance and mass spectroscopy. Preliminary organoleptic evaluation of oil solutions of the compounds indicated that thecis isomer had a flavor threshold of ca. 0.25 ppm. with odor and flavor descriptions of beany, grassy and buttery at 0.50 ppm; and that thetrans isomer had a flavor threshold of ca. 0.50 ppm with odor and flavor descriptions of beany, grassy and buttery at 1 ppm and strong painty and metallic at 4 ppm. These compounds, if found in soybean oil through the autoxidation of linolenate, may contribute to the characteristic reversion flavor.

Chemical reactions involved in the deep fat frying of foods. I. A laboratory apparatus for frying under simulated restaurant conditions.

A laboratory apparatus has been designed which can be used to quantitatively collect the volatile decomposition products produced during deep fat frying under simulated restaurant conditions. In order to study the chemical reactions of frying fat without any inter-reaction with the food fried, moist cotton balls were fried in corn oil.The oil used for frying was shown to differ considerably from oil which was continuously heated. The latter had a darker color and higher viscosity. It foamed significantly while the oil used for frying did not. Furthermore, the continuously heated oil had a much lower free fatty acid content than did the oil used for frying under simulated restaurant conditions.The volatile decomposition products collected during frying of cotton balls in corn oil were separated into acidic and nonacidic compounds. Each group exhibited a definite gas chromatographic pattern after only a short period of frying. Part of the degradation products, particularly those of higher boiling points, were found to remain in the frying oil.