Comparitive study of monocarbonyl compounds formed during deep frying in different fats

Fresh commercial corn oil, fresh commercial lard, and hydrogenated vegetable shortening were analyzed for carbonyl compounds before and after deep frying. The frying was carried out in an apparatus with a capacity for 2000 g of oil designed to quantitatively trap the volatile materials evolved during frying and which would ordinarily escape into the atmosphere. The trapped distillate was also subjected to carbonyl analysis. Analysis of the fats and distillates showed a carbonyl pattern in essential agreement with the classical autoxidation mechanism for the different fats, i.e., the typical alkanals, alk-2-enals, and alk-2,4-dienals. The pattern correlated generally with the fatty acid composition of the fats. Comparison of the concentrations of the monocarbonyl compounds in the fats before and after frying, and in their distillates, indicated that the deodorization process which accompanies frying is effective in preventing the accumulation of the more volatile compounds formed. The less volatile products, mainly deca-2,4-dienal, were not efficiently removed. Accordingly, it was observed that the oils containing higher proportions of linoleic acid contained more residual monocarbonyl compounds after frying. Scientific Article No. A-1124, Contribution No. 3570 of the Maryland Agricultural Experiment Station.     

Carbonyls in oxidizing fat. V. The composition of neutral volatile monocarbonyl compounds from autoxidized oleate,linoleate, linolenate esters,and fats

The steam volatile monocarbonyl compounds in mildly autoxidized esters of oleic, linoleic, linolenic acids, and animal and vegetable fats were quantitatively estimated. The major aldehydes in oleate and linoleate were those that might be expected from the scission of reported monomeric hydroperoxide isomers. The predominance of hept-2,4-dienal and propanal in linolenate suggested that the major monomeric hydroperoxides were 12-and 16-hydroperoxy conjugated dienoic isomers. The number of minor aldehydes increased with degree of unsaturation of the fatty acid. The amounts of monocarbonyl compounds in the fats examined generally agreed with their average fatty acid composition. Appreciable amounts of heptanal in lamb and beef fat and heptanal and decanal in butterfat, under the conditions of oxidation, could not have come from the three unsaturated acids. Heating at 165°C. in all samples increased the proportions of the most unsaturated major aldehydes.     

Carbonyls in oxidizing fat. VII. A comparison of methods of isolating monocarbonyl compounds

Comparison of quantitative methods for the isolation of aldehydes from lard oxidized at 23C showed an extreme sensitivity of precursors to isolation conditions. Differences existed in the quantity and class compositions of the monocarbonyl compounds isolated. Acid conditions caused considerable breakdown of alkanal and alk-2-enal precursors. Steam distillation (100C) released alkanals, alk-2-enals, and alk-2,4-dienals. The mild Girard T method apparently produced a small amt of alk-2-enals from precursors, but except in the initial stages isolated the lowest amounts of aldehydes. Complete evaluation of the method for isolation of free aldehydes was not possible because alkanals were released from precursors during the vacuum distillation procedure (50C). The Schwartz (dilute phosphoric acid), Girard T, and vacuum distillation methods isolated similar amounts of alk-2,4-dienals. Curious changes in relationships, possibly indicative of oxidation stages, were observed as autoxidation progressed.     

Determination of monoglycerides in crude oils and fats

The periodate oxidation method was adapted for the determination of small amounts of monolycerides present in natural oils and fats. The modification consisted in enriching the monoglycerides by extraction with 90% acetic acid saturated with boric acid in order to eliminate interfering substances prior to the reaction with periodate. A multifold concentration of monoglycerides originally present was achieved. This reduced the error of the standard periodate method to a minimum. Crude oils, such as soybean, rice bran, coconut, and palm, analyzed by the modified method showed monoglyceride contents considerably lower than those obtained by direct reaction of periodate with these oils.     

Determination of dimethylpolysiloxanes in fats and oils1

A direct aspiration, flame atomic absorption method has been developed for the determination of dimethylpolysiloxanes (DMPS) in fats and oils. The detection limit of the method is approximately 1 ppm with a standard deviation for samples containing 1–10 ppm DMPS of 0.3. The technique is reasonably rapid, requires a minimum of sample preparation, and is applicable to the analysis of both hydrogenated and nonhydrogenated products. Presented at a symposium of the North Central Section, March 28, 1979.     

Determination of sorbitan tristearate in vegetable oils and fats

A new method for analysis of Sorbitan Tristearate (STS) in vegetable oils and fats has been developed. The method is based on isolation and hydrolysis of STS compounds in a silica cartridge. The polyalcohols are eluted from the silica cartridge and the final separation and quantitation are done by high-performance liquid chromatography and refractive index detection. Linearity, precision, and recovery satisfy general demands on quantitative methods. The detection limit and the quantitation limit are well below the concentrations normally used to attain functional effects of STS in vegetable oils and fats.     

Determination and occurrence of oxofatty acids in fats and oils

A relatively simple method is detailed for the routine isolation and estimation of oxofatty acids (OFA) in lipids. The lipid in cyclohexane is transmethylated in a two-phase, 3.5 min procedure, and the carbonyls in the methyl ester fraction are derivatized with 2,4-dinitrophenylhydrazine (DNPH) in the presence of monochloroacetic acid (MCA). The derivatives are fractionated on alumina, and the OFA fraction is obtained and evaluated spectrophotometrically. A large variety of animal, plant, and marine lipids contained OFA ranging from <1 to >50 μmoles/g. Data also show that (a) OFA are formed in naturally oxidizing fats and oils, and (b) strongly acidic conditions can cause elaboration of OFA in hydroperoxidized fats and oils.     

Determination of ultratrace metals in hydrogenated vegetable oils and fats

Ultratrace levels of nickel, chromium, copper and iron occurring in hydrogenated vegetable oil products were estimated by dispersion of the samples in 4 methyl-2-pentanone and atomic absorption analysis by the graphite furnace technique. The principal goals in establishing the analytical methods were improved sensitivity to metals at low levels and applicability to limited amounts of products. Using reproducibility and linearity of response as criteria, optimum oil concentration in solvent and instrument parameters were established. For a series of commercial products, the method of standard addi-tions was adopted to correct for matrix differences between the products and salad oil-based standards. The range for the metals was determined in five cooking oils: Ni, 29–207 ppb; Cr, 1–5 ppb; Cu, 13–37 ppb; and Fe, 138–301 ppb; in recovered oils from five margarines: Ni, 34–70 ppb; Cr, 2–12 ppb; Cu, 26–58 ppb; and Fe, 239–540 ppb; and in five solid shortenings: Ni, 592–2772 ppb; Cr, 8–35 ppb; Cu, 26–108 ppb.     

Use of labeled compounds to study the mechanism of flavor formation in oxidizing fats

2-¹⁴C-Hexanal,trans, trans-5-¹⁴C-2,4-decadienal, 4-¹⁴C-1-octen-3-ol, 4-¹⁴C-1-octen-3-one and 1-¹⁴C-1-pentanol were synthesized and added to freshly deodorized soybean oil in concentrations ranging from 7–125 ppm. The soybean oil was oxidized, and the fate of the labeled compounds was followed. Hexanal was converted to hexanoic acid especially at 50 C or higher. The 2,4-decadienal was converted to 2,4-decadienoic acid at room temperature, and heptenal, 2-octanal, 2-nonanal, glyoxal and malonaldehyde were found among the labeled products. 1-Octen-3-ol was converted to 1-octen-3-one at room temperature, but the 1-octen-3-one formed a stable end product that produced no other labeled compounds. 1-Pentanol was converted to pentanoic acid at 50 C or higher. One of 13 papers presented in the symposium “Flavor Research in Fats and Fat Bearing Foods,” AOCS Meeting, Atlantic City, October 1971. Journal Paper No. J-7082 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50010. Project 1856.     

Determination of BHA,BHT and TBHQ in edible fats and oils

A method is described for the rapid analysis of the phenolic antioxidants BHA, BHT and TBHQ in edible fats and oils. The procedure is based on gel permeation chromatography with UV detection, and requires no preliminary isolation of the antioxidants from the matrix. Detection limits with the instrumentation used in this study were<1 ppm for BHA and BHT, and ca. 20 ppm for TBHQ.     

Determination of monoglyceride in fats and oils by oxidation with periodic acid

Summary A method based upon oxidation of monoglyceride by periodic acid has been developed for the determination of monoglyceride in fats and oils. The reaction and conditions that influence the determination have been described and discussed. This paper was presented at the Chicago meeting of the American Oil Chemists’ Society, October 25–27, 1944.     

A study of the antioxidant effectiveness of several compounds on vegetable fats and oils

Summary 1. A number of compounds and combinations of compounds have been examined for antioxidant properties. 2. The most effective single compound was gallic acid, although NDGA, ascorbic acid and ascorbyl palmitate each about doubled the keeping time of any given vegetable fat or oil. 3. Amino acids were negative with the exception of methionine. 4. NDGA in combination with either citric acid or phosphoric acid showed marked synergism. These combinations were very effective antioxidants. The work described in this paper was carried out under a contract, recommended by the Committee on Medical Research, between the Office of Scientific Research and Development and the University of Pittsburgh. Contribution No. 519 from the Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania.     

Winterization of oils and fats

The process of winterization consists of fractional crystallization of oils and fats followed by the separation of solids to make high quality salad oils. To design a winterization process, the rate of cooling of oil, the temperature of crystallization and the mobility of triglyceride molecules in the oil mass are crucial. These variables play a significant role both in separating the solid fats as distinct crystals and facilitating their filtration from the oil. Thus, the main emphasis in this paper is on the effect of the above variables on the performance of the winterization process. Presented at the AOCS short course held April 21–23 1980, Lake Kiamesha, NY.