H. J. Dutton

The flavor problem of soybean oil. VIII. Linolenic acid

SummaryCircumstantial evidence has long pointed to linolenic acid as the unstable precursor of “reversion” flavors in soybean oil. Direct evidence has now been obtained from two sources: a) A qualitative study of the flavors after storage of soybean oil in which the linolenic acid content has been significantly lowered by furfural extraction, and b) organoleptic identification studies of stored soybean oil, stored cottonseed oil, and a cottonseed oil into whose glyceride structure linolenic acid has been introduced with the use of an interesterification catalyst. It is concluded that linolenic acid is an unstable precursor of “fishy-painty-grassy-melony” flavors in soybean oil.

Chromatographic separation ofcis andtrans fatty esters by argentation with a macroreticular exchange resin

Methyl oleate and methyl elaidate, as well as other monoenecis andtrans isomers of fatty esters, can be separated quickly and conveniently by a preparative chromatographic procedure in which a silver-saturated ion-exchange resin is used. Separations are based on differences in stabilites of the silver-olefin complexes. Recoveries of better than 95% were made, and puretrans andcis monoene fractions were collected. This method can be used to separate saturates fromcis andtrans monoenes. Thecis,trans,cis,cis, andtrans,trans-9-12-octadecadienoates were separated. Whilecis,trans andtrans,trans dienes were cluted separately, thecis,cis diene isomer remained on the column.

Hydrogenation of linolenate. II. Hydrazine reduction

Observations by Aylward and Rao that hydrazine is a reducing agent for a number of unsaturated fatty acids were extended. The hydrazine reaction on linolenic acid was followed by periodic sampling until methyl esters prepared from the reduced acids had an iodine value of 162. These esters were shown by countercurrent distribution to consist of 26% triene, 43% diene, 26% monoene, and 5% stearate and by infrared analysis to contain notrans bonds.Oxidation of the separated monoene and diene fractions by permanganate-periodate mixtures and gas chromatography of the dibasic acids showed that the double bonds were in the original 9, 12, and 15 positions and that the double bonds farthest from the carboxyl were reduced at a slightly faster rate. Gas chromatography of the monoene fraction indicated three components that were identified in the order of elution from the column as 9, 12, and 15 monoenes; in the diene fraction three components were identified in the order of elution as 9,12; 9,15; and 12,15 dienes. After alkali isomerization of this diene fraction, the conjugated material was reacted with maleic anhydride; the unreacted 9,15 diene isomer was separated by distillation.

“Zerotrans” margarines: Preparation, structure, and properties of interesterified soybean oil-Soy trisaturate blends

Abstract and SummarThe sodium methoxide-catalyzed random interesterification of liquid soybean oil-soy trisaturate blends was explored as a possible route to zerotrans margarine oils. Lipase hydrolysis of the rearranged fats showed that with 0.2% catalyst, interesterification is complete within 30 min at 75-80 C. The glyceride structures of natural and randomized soybean oil-soy trisaturate blends are presented, and relationships between their structure and physical properties are discussed. Organoleptic evaluations showed that randomization of the glyceride structure had no adverse effects on flavor and oxidative stability. Flavor evaluations made against a commercially hardened tub margarine oil showed that interesterified oil had comparable initial and aged flavor scores. X-ray diffraction studies demonstrated that randomized soybean oil-soy trisaturate blends possess the beta-prime crystal structure desirable for use in margarine production. Dilatometric data indicate that random interesterification of 20% by weight of soy trisaturate into the glyceride structure of soybean oil provides a product having a solid fat index suitable for use in a soft tub margarine.

Preparation of pure fatty acid methyl esters by countercurrent distribution

SummaryAcetonitrile-pentane-hexane makes a desirable solvent system for preparation of pure methyl esters because of its immiscibility, selectivity toward unsaturation, low boiling point, stability, and ease of recovery. Since separated esters are removed from the apparatus dissolved in the pentane-hexane layer, successive batches may be fractionated without removing the acetonitrile layer from the instrument. Applications have been illustrated for the preparation of methyl linolenate from an 85% linolenate concentrate, methyl linoleate from safflower esters, and methyl arachidonate from pig liver lipids.This procedure provides a source of “natural” fatty acids with the double bond configuration unchanged, in contrast to those from the conventional bromination-debromination process. Automation of the process is completed by use of a recording refractometer which monitors concentration of solutions issuing from the extractor. Resolutions to be anticipated with lesser numbers of extraction tubes than 200 are calculated for an equal mixture of linoleate and linolenate.

Glyceride structure of vegetable oils by countercurrent distribution. I. Linseed oil

Corn oil has been fractionated in a 200-tube countereurrent distribution apparatus. Although this technique gives no information about the positional isomers of the glycerides, the fatty acid composition of the fractions and the amounts of the more unsaturated triglycerides are in agreement with an essentially random pattern.

The flavor problem of soybean oil. IV. Structure of compounds counteracting the effect of prooxidant metals

SummaryA study has been made of the effectiveness of various polycarboxylic acids and polyhydric alcohols in improving the stability of soybean oil. Certain observations have been made regarding the structural groups required and the possible mechanism of reaction. Since salts and esters of organic acids are inactive, free carboxyl groups are required. Among the four carbon atom dicarboxylic acids activity increases with the number of hydroxyl groups. Within the polyalcohols activity increases with the increase in number of hydroxyl groups. Steric immobility and loss of hydroxyl groups by dehydration reduces activity. Evidence is presented which attributes to citric acid and certain polyhydric alcohols the role of metal scavenger. For example, it has been demonstrated that the addition of citric acid and sorbitol to soybean oil containing prooxidant metallic salts effectively increases the oxidative and flavor stability of the oil. By using a sample of treated soybean oil with no detectable tocopherols, in order to eliminate synergistic effects of citric acid, it has been shown that the prooxidant effect of iron stearate is counteracted by the presence of citric acid. The demonstration that polyhydric alcohols increase the flavor and oxidative stability is compatible with their known metal complexing properties. Evidence is presented which indicates a relationship between flavor stability and oxidative stability.

Analysis of fat acid oxidation products by countercurrent distribution methods. V. Low-temperature decomposition of methyl linoleate hydroperoxide

Methylcis, trans diene conjugated linoleate hydroperoxide isolated by counterenrrent distritbution from 4°C, auatoxidation of methyl linoleate was stored in atmospheres of oxygen and of nitrogen at 4°C. in darkenss. Besides manometric changes, infrared and ultraviolet characteristics, peroxide value, diene conjugation, and molecular weights were followed on samples removed at various periods of storage up to 53 days. These same analyses were obtained on fractions obtained by counter-current distributions.Evidence for the reaction that occurs on storage in oxygen may be summarized thus: 1 mole oxygen absorbed by linoleate hydroperoxides destroys 1 molecis, trans diene conjugation, 1/2 mole peroxide group, and 1 mole linoleate hydroperoxide; dimers of varying polarities, scission acids, and isolatedrans bonds are formed.Since to volume changes were observed in the nitrogen storage of methyl linoleate hydroperoxide, changes in chemical and physical characteristics can only be related to time of storage. Storage in nitrogen at 4°C, destroys diene conjugation, peroxides, and linoleate hydroperoxide and produces dimers of varying polaritics, seission neids, and isolatedrans bonds. Destruction of diene conjugation was one-fourth as rapid in a nitrogen atmosphere as in oxygen. While differences in reactions and products were observed between oxygen and nitrogen storage, particularly in rates and in countereurrent distribution patterns, the similarity of products from oxygen and nitrogen storage is remarkable. One methyl linoleate hydroperoxide is formed regardless of storage atmosphere, dimirization and attendant destruction of double bonds and peroxides proceed.

Volatile components from tristearin heated in air

Tristearin was heated to 192 C in air, and its volatile oxidation products were collected directly on a cooled (−60 C) gas liquid chromatography column. Subsequently, the volatile products were separated by temperature programing up to 250 C and identified by mass spectrometry. Methyl ketones and aldehydes were the major degradation products along with minor amounts of monobasic acids, n-hydrocarbons, primary alcohols, and γ-lactones. Qualitative results indicated all the fatty acid methylene carbon atoms are susceptible to oxidation. Quantities of aldehydes and ketones were found to be in excess of their taste threshold concentrations, suggesting thermally oxidized saturated fatty acids may be precursors of some odors and flavors associated with heated lipids.

The flavor problem of soybean oil. III. A four-sample, glass laboratory deodorizer

SummaryA glass laboratory deodorizer has been described which permits the simultaneous deodorization of four samples under nearly identical conditions of time, temperature, pressure and rate of steam flow. The design includes provision for measuring and controlling the steam flow, for preventing bumping, for “breaking” the vacuum, and for heating and cooling the deodorizer. Successful deodorizations have been made in relatively short periods of time. Upon deodorization of the same alkali-refined bleached oil in each of the four flasks no difference has been found either in the initial quality or in the stability of the samples.