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 7-1actones. 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.
AND SUMMARYThe sodium rnethoxide-catalyzed random interesterification of liquid soybean oil-soy trisaturate blends was explored as a possible route to zero trans 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. Initial flavors Metallic, grassy, painty Buttery Buttery Buttery, rancid Storage flavors Rancid, palnty, grassy Rancid, grassy, buttery Rancid, buttery, beany Rancid, buttery Triene, % 7.5 7.5 7.5 4.4 a** Denotes significance at 1% confidence level, + denotes no statistical significance. Values in parentheses are peroxide values at time of tasting. bLiquid soybean oil (90%), 10% soy trisaturate by weight; simple mixture and interesterified samples contained no antioxidants or metal scavengers. CLiquid soybean (90%), 10% soy trisaturate by weight, sample treated with 0.01% citric acid and 0.076% Tenox 6 during deodorization. dCommerciai tub margarine oil, sample treated with 0.01% citric acid and 0.076% Tenox 6 during deodorization. eAOM = active oxygen method.
Summary Circumstantial 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.
Pure trilinolein and mixtures of trilinolein‐tristearin, trilinolein‐triolein, and trilinolein‐triolein‐tristearin were heated to 192 C in air. Volatiles were collected, separated, and identified by gas chromatography‐mass spectrometry. Major volatiles observed from each heated sample produced compounds unique to the autoxidation‐decomposition of the trilinolein component and included: pentane, acrolein, pentanal, 1‐pentanol, hexanal, 2‐ and/or 3‐hexenal, 2‐heptenal, 2‐octenal, 2,4‐decadienal, and 4,5‐epoxydec‐2‐enal. When samples containing both trilinolein and triolein were heated, volatiles were produced that could be ascribed to each triglyceride. However, heated mixtures containing tristearin produced no observable volatiles that could be related to the oxidized saturated triglyceride. Minor volatiles identified from the heated trilinolein and its mixtures included; aliphatic acids, saturated and unsaturated aldehydes, primary and secondary alcohols, gamma lactones, furans, hydrocarbons, and methyl ketones.
AND SUMMARYIn a continuing study to identify volatile odor constituents and their precursors from heated soybean oil, the following model triglycerides were heated to 192 C in air for I0 min: (a) pure triolein, (b) a mixture of triolein (25%)-tristearin, and (c) a randomly esterified triglyceride composed of oleic (25%) and stearic acids. Each model system produced the same major compounds which were identified as heptane, octane, heptanal, octanal, nonanal, 2-decenal, and 2-undecenal. These seven compounds apparently are unique to the oxidation of the oleate fatty acid in each triglyceride sample. Minor volatile compounds from oxidized triolein included saturated and unsaturated aldehydes and n-hydrocarbons and saturated primary alcohols, methyl ketones, gamma lactones, and monobasic acids. Incorporation of stearic acid in the triglycerides noticeably increased the amounts of saturated minor compounds and the range of their carbon chain lengths. Decomposition products characteristic of the oxidation of stearate were apparent among decomposition products associated with the oxidation of oleate.
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