Oxidative stability of avocado oil

This study is concerned with the extent of oxidative deterioration and oil stability as determined by measuring peroxide and conjugable oxidation products (COP) values and AOM time of refined bleached avocado oil in comparison with refined soybean and olive oil. The formation of peroxides in avocado oil exposed to daylight at room temperature is similar to that of soybean oil but greater than that of olive oil. No differences were found in peroxide formation, oxodiene values and COP values between the tested oil stored in the dark, at 60 C and at room temperature. The COP ratio in oils stored at 60 C is similar for avocado and olive oil, but differs from that of soybean oil. The AOM stability time both for refined avocado and soybean oil was approximately 14 hr, and for refined olive oil was 15 hr. The extent of oxidative stability of crude avocado oil was determined by measuring peroxide value compared with crude olive oil. Crude avocado oil is very sensitive to oxidation when exposed to daylight and fluorescent light, in contrast to its stability in the dark at room temperature. The chlorophyll content in crude avocado oil is reduced rapidly on exposure to daylight and fluorescent light.     

Dry extrusion as an aid to mechanical expelling of oil from soybeans

A new concept is described for mechanical extraction of oil from soybeans, using dry extrusion as a pretreatment. It was found that coarsely ground whole soybeans at 10 to 14% moisture could be extrusion cooked so that the extrudate emerges from the die in a semi-fluid state. The dwell time within the extruder was less than 30 seconds, and the temperature was raised to about 135 C. The semi-fluid extrudate was immediately pressed in a continuous screw press to obtain high quality oil and press cake. Extrusion prior to expelling greatly increased the throughput of the expeller over the rated capacity. An oil recovery of 70% was obtained in single pass expelling using pilot model expellers. Higher recovery rates can be expected with commercial scale expellers. The high temperature-short time extrusion cooking process eliminates the prolonged heating and holding of raw material in conventional expelling. Under the experimental conditions, press cake with 50% protein, 6% residual oil and 90% inactivation of trypsin inhibitors was obtained. The low fat cake was easily ground in a hammer mill without the usual problems associated with milling of whole beans. The expelled oil was remarkably stable with an AOM stability of 15 hr, which is comparable to refined deodorized oil according to NSPA specifications. The new procedure offers potential for producing natural soybean oil and food grade low fat soy flour by a relatively low cost operation. It may be adopted as an improvement to existing conventional expelling operations in less developed countries or as a commercial or on-farm operation for producing value added products from soybeans within the U.S.     

Effect of fatty acid composition of oils on flavor and stability of fried foods

Effects of fatty acid composition of frying oils on intensities of fried-food flavor and off-flavors in potato chips and french-fried potatoes were determined. Commercially processed cottonseed oil (CSO) and high-oleic sunflower oil (HOSUN) were blended to produce oils with 12 to 55% linoleic acid and 16 to 78% oleic acid. Analytical sensory panels evaluated french-fried potatoes and pilot plant-processed potato chips. Initially, both foods prepared in CSO (16% oleic/55% linoleic acid) had the highest intensities of fried-food flavor; however, this positive flavor decreased with decreasing levels of linoleic acid. 2,4-Decadienal in potato chips also decreased with decreasing linoleic acid in the oils. Frying oil stability, measured by total polar compounds (TPC), and oxidative stability of potato chips, measured by volatile compounds, showed that HOSUN (78% oleic acid) produced the lowest levels of TPC and the lowest levels of hexanal and pentanal, indicating greater frying oil stability and oxidative stability of the food. However, fresh potato chips fried in HOSUN had the lowest intensities of fried-food flavor and lowest overall flavor quality. Fried-food flavor intensity was the best indicator of overall flavor quality in fresh potato chips. Volatile compounds, TPC, and oxidative stability index directly varied with increasing oleic acid, and were therefore not directly indicative of flavor quality. No oil analysis predicted flavor stability of aged potato chips. Compositions of 16 to 42% oleic acid and 37 to 55% linoleic acid produced fresh fried-food with moderate fried food flavor intensity, good overall flavor quality, and low to moderate TPC levels (chips only). However, in aged food or food fried in deteriorated oil, compositions of 42 to 63% oleic and 23 to 37% linoleic provided the best flavor stability.     

Effect of heat treatments on the volatile composition of coconut oil

Fresh coconut oil was heated under different conditions for 48 hr at 180 C. The heat treatments included heating in vacuo, heating in air and heating in air and water. The samples were distilled under high vacuum and the volatiles thus obtained were analyzed by combined gas chromatography-mass spectrometry. In all heated samples, a series of n-alkanes and I-alkenes, n-alkanals, methyl alkanones, alkenals, gamma-and delta-lactones, methyl and ethyl esters and free fatty acids were identified. The relative amounts of these compounds varied with the type of heat treatment to which the coconut oil was subjected.     

Evidence of an Enzymatic Source of Off Flavors in “Lipoxygenase-Null” Soybeans

The utilization of soybean products as food ingredients and foods is often limited by their beany-grassy flavor. Eliminating seed lipoxygenase (LOX) isozymes 1, 2 and 3 reduces the amounts of volatile off-flavor compounds in stored soybeans and soy products significantly, but they are not completely eliminated. The present work presents evidence that lipoxygenase-null (LOX-null) soybeans contain a LOX-like enzyme that is responsible for the off-flavors in LOX-null soybeans. Volatiles production in triple LOX-null soybeans was terminated by heat treatment, which suggests an enzymatic cause to the off-flavors. The source is LOX-like in that the volatile compounds produced are similar to LOX-generated products of polyunsaturated fatty acids. Oxygen was consumed when a LOX-null protein solution was incubated with crude soybean oil suggesting that the enzyme catalyzed oxygen consuming reactions. The generation of flavor compounds was inhibited by the typical LOX inhibitors propyl gallate and nordihydroguaiaretic acid (NDGA). The enzyme appears to be more active with phosphatidylcholine than with other lipid substrates. The cause of the off-flavors in LOX-null beans appears to have enzyme-like characteristics. This is the first report of the initial characterization of this LOX-like enzyme.     

椰子油单乙醇酰胺丙氧基醚的合成研究

以椰子油单乙醇酰胺、环氧丙烷为原料,进行开环聚合反应合成椰子油单乙醇酰胺丙氧基醚,考察了椰子油单乙醇酰胺丙氧基醚合成的条件,实验表明,在催化剂氢氧化钾用量为反应物总物质的量的0.5%,反应物椰子油单乙醇酰胺与环氧丙烷物质的量比为1：2,反应温度145℃,反应时间3h的条件下,环氧丙烷的转化率可达99.9%。经测试,椰子油单乙醇酰胺丙氧基醚与椰子油单乙醇酰胺的稳泡性能相近,具有黏度低,水溶性好的特点。     

A comparison of several analytical techniques for prediction of relative stability of fats and oils to oxidation

Three analytical methods proposed by various workers for predicting the relative stability of fats and oils to oxidation have been compared on a series of samples. The Eckey Oxygen Absorption, the modification of the A.S.T.M. Oxygen Bomb (4), and the Active Oxygen Method (AOM) were applied to combinations of animal and vegetable fats and oils, with and without added monoglycerides and antioxidants. The results indicate that the Eckey Oxygen Absorption and modified ASTM Oxygen Bomb methods are more precise than the AOM method, and more in keeping with the experience in the fat and oil field in relation to actual performance stability than the AOM. Experimental relationships of these factors and methods to shelf life storage studies measured organoleptically will be the subject of a later paper.     

Chemical Properties of Virgin Coconut Oil

A study on the commercial virgin coconut oil (VCO) available in the Malaysian and Indonesian market was conducted. The paper reported the chemical characteristics and fatty acid composition of VCO. There was no significant difference in lauric acid content (46.64–48.03%) among VCO samples. The major triacylglycerols obtained for the oils were LaLaLa, LaLaM, CLaLa, LaMM and CCLa (La, lauric; C, capric; M, myristic). Iodine value ranged from 4.47 to 8.55, indicative of only few unsaturated bond presence. Saponification value ranged from 250.07 to 260.67 mg KOH/g oil. The low peroxide value (0.21–0.57 mequiv oxygen/kg) signified its high oxidative stability, while anisidine value ranged from 0.16 to 0.19. Free fatty acid content of 0.15–0.25 was fairly low, showing that VCO samples were of good quality. All chemical compositions were within the limit of Codex standard for edible coconut oil. Total phenolic contents of VCO samples (7.78–29.18 mg GAE/100 g oil) were significantly higher than refined, bleached and deodorized (RBD) coconut oil (6.14 mg GAE/100 g oil). These results suggest that VCO is as good as RBD coconut oil in chemical properties with the added benefit of being higher in phenolic content.     

Molecular Finger Printing of Nutra-Coconut Oil with Improved Health Protective Phytoceuticals and its Efficacy as Frying Medium

Coconut oil is rich in medium chain triglycerides but lacks polyunsaturated fatty acids (PUFA) and bio‐active phytoceuticals. In the present work nutra‐coconut oil was prepared by blending coconut oil and flaxseed oil (70:30) and adding 3000 ppm of flaxseed cake concentrate using ethanol, methanol and 20 % aqueous ethanol. The concentrate prepared from flaxseed was from ethanol as it gave maximum yield. The different bio‐active molecules in flaxseed concentrate observed are polyphenols (39.04 %), tocopherols (4.37 %), ferulic acid (0.17 mg g^?1), p‐coumaric acid (2.24 mg g^?1), chlorogenic acid (16.11 mg g^?1), gallic acid (8.58 mg g^?1), sinapic acid (0.64 mg g^?1) and secoisolariresinol (30.13 mg g^?1). The nutra‐coconut oil was found to have polyphenols (2.86 %), tocopherols (442.96 ppm) and antiradical activity (94 %). The PUFA content was found to increase in nutra‐coconut oil significantly (p < 0.05) (2–22 %). The FT‐IR spectra of nutra‐coconut oil revealed that the peak at 3009 and 1651 cm^?1 was associated with the presence of unsaturated fatty acids. There was no significant (p > 0.05) difference observed in sensory attributes of snack food fried using coconut oil and nutra‐coconut oil indicating that the later could be used as a frying medium and useful for food processing industries.     

Processing for industrial fatty acids - II

Fatty acids are produced industrially from tallow, palm oil, palm stearin, palm kernel oil and coconut oil. The current and future supply situations of these raw materials and market economics favor palm stearin and palm kernel oil as major raw materials for fatty acids. The Malaysian oleochemical industry has adopted high-temperature and high-pressure “splitting” of triglycerides. Variations in product yields occurring in the processing of tallow and palm stearin and of coconut oil and palm kernel oil are indicated. Developments on the enzymic hydrolysis of triglycerides to fatty acids have been made, particularly in Japan. Enzymic hydrolysis at low temperature has the advantage of energy conservation compared to the high-temperature and pressure-splitting process. But enzymic hydrolysis is only applicable to triglycerides of low titre, such as palm kernel oil.     

Oxidative stability during storage of structured lipids produced from fish oil and caprylic acid

Structured lipids produced by enzymatic or chemical methods for different applications have been receiving considerable attention. The oxidative stability of a randomized structured lipid (RFO), produced by chemical interesterification from fish oil (FO) and tricaprylin, and a specific structured lipid (SFO), produced by enzymatic interesterification from the same oil and caprylic acid, was compared with the stability of FO. Oils were stored at 2°C for 11 wk followed by storage at 20°C for 6 wk. In addition, the antioxidative effect of adding the metal chelators EDTA or citric acid to SFO was investigated. FO contained the largest amount of PUFA and RFO the lowest. However, SFO had a higher PV initially and during storage at 2°C, whereas the PV of FO was highest during storage at 20°C. The level of volatile oxidation products was highest in SFO during the entire storage period, and off-flavors were more pronounced in SFO. The lower oxidative stability of SFO was probably related to the initially lower quality (regarding oxidation products), which is apparently a result of the long production procedure required. Addition of metal chelators did not reduce the oxidation of the SFO.     

Effects of minor components on the crystallization of coconut oil

Variations in the crystallization behavior of fats have important consequences for the processing of fatty foods. This paper is concerned with the changes in the crystallization of coconut oil due to refining, and the effects of diacylglycerols, free fatty acids and phospholipids on oil crystallization. The changes in coconut oil crystallization due to changes in oil composition have been studied by pulsed nuclear magnetic resonance spectroscopy. Bleaching or neutralization of crude coconut oil caused a dramatic reduction in the induction time before the onset of detectable crystallization at 15°C. The addition of oleic and lauric acid caused a large increase in the induction time of refined coconut oil whereas palmitic acid had a smaller effect. However, the changes in coconut oil crystallization during refining are not completely explained by the removal of free fatty acids. Dilaurin retarded the nucleation of coconut oil whereas diolein did not have any significant effect. Phosphatidylcholine also retarded the nucleation of coconut oil at 15°C, but this effect is not significant in practice for coconut oil because of the low levels of phospholipids present in the crude oil.     

The solubility of water in edible oils and fats above 100 C

The solubilities of water in rapeseed and coconut oils have been determined at temperatures between 90 and 160 C. Oil samples were equilibrated with water vapor under conditions of constant temperature and humidity. The equilibrium water content was determined by means of the Karl Fischer titration method. Solubility was found to be independent of the type of oil when expressed in terms of the mole fraction, in agreement with previous work at temperatures below 100 C. An equation is given relating solubility and temperature between 0–250 C.     

Oil stability: A DSC alternative for the active oxygen method

A differential scanning calorimeter was used to measure the keeping time of commercial fats. The method described is rapid and simple. The stability of oils which would require 14 days in the AOM (AOCS) procedure can be deteremined in less than 4 hr by the differential scanning calorimeter technique. Although a good correlation was found with keeping times determined by the AOM method, the spread in AOM hours calculated from the calorimetric data was too great to suggest replacement of the AOM method by this new one.     

Die Weiterentwicklung der Codex Alimentarius Standards für Öle und Fette

Further Development of Codex Alimentarius Standards for Oils and Fats Further development of Codex Alimentarius standards for oils and fats, which was discussed at the 7th meeting of the Codex Committee in London, is reported. Limits of fatty acid composition of individual oils and fats, problems of solvent residues as well as the development of new standards for lowerucic rapeseed oil, low calorie spreads, coconut oil, palm oil and palm kernel oil were discussed at the above meeting. It has already been realized that the Recommended Standards have a significant impact both on harmonization work within the European Community and international development of food legislation.     

Survey of soybean oil and meal qualities produced by different processes

Soybean oil and meal produced by extruding-expelling (E-E) are believed to have unique characteristics compared with products produced by solvent extraction (SE). A survey was conducted to compare quality characteristics of the oils and meals produced from different types of soybean processing methods. Soybean oil and meal samples were collected three different times within a 1-yr period from 13 E-E mills, 8 SE plants, and 1 continuous screwpress (SP) plant. Properties of oil and meal varied considerably between different types of plants and among plants of the same type and sampling times. In general, settled crude E-E and SP oils had significantly greater peroxide values than those of SE oils. E-E oils contained less free fatty acid and phosphorus than did SE and SP oils. The oxidative stability (AOM) of E-E oil was less than that of SE oil, and that of SP oil was intermediate. E-E and SP meals had higher oil and lower protein and moisture contents than those of SE meals. Protein dispersibility indices were lower for E-E and SP meals. Protein solubilities in KOH were similar for E-E and SE meal, but higher than that of SP meal (62%). Rumen bypass protein values were higher for the SP meal.     

Iodine values of acidulated coconut oil soapstock

Summary Analyses and comparisons of a number of representative samples have shown that acidulated coconut oil soapstock may have an iodine value as much as 100% greater than that of the corresponding refined oil without any contamination being involved. Exactly what the spread between any given soapstock and oil will be apparently depends on the free fatty acid content of the original crude oil and the relative efficiency of the refining process. It was found that, for coconut soapstocks produced by standard laboratory refining tests, the relation between free fatty acid content and iodine value spread can be represented by the formula I.V. Spread=9.5–759 FFA. The efficiency of the refining process affects results insofar as it reduces the entrainment of neutral oil. Removing all of the neutral oil from four laboratory-produced soapstocks prior to acidulation raised the iodine value approximately two units in all cases. The practical significance of these results is obvious. A refiner processing high grade crude coconut oil of 9.5, iodine value by a highly efficient refining procedure cannot be expected to produce an acidulated soapstock of less than about 18.0 in iodine value. With higher free fatty acid crude oil and less efficient refining procedures lower iodine values are possible, but since soapstock is of minor economic value compared to refined oil, the trend will always be toward better grade crude oils and more efficient refining processes.     

VACCUM DRYING CHARACTERISTICS OF COCONUT

The drying characteristics of shredded coconut under vacuum and at atmospheric pressure have been studied. It was found that a decrease in the absolute pressure within the drying compartment retarded the drying rate of coconut. A model for drying of coconut is proposed on the assumption that the surface of coconut is partially covered with layers of moisture and oil. It was found that oil seepage to surface was responsible for lower drying rates at low absolute vacuum pressures within the dryer.     

Determination of Iodine Value in Hydrogenated Oils: Comparison of Titration and Gas Chromatography with Flame‐Ionization Detection Methodologies

The United States Food and Drug Administration (FDA) recently issued its final determination that partially hydrogenated oils (PHO) are no longer generally recognized as safe (GRAS) for any use in human food. Consequently, the discrimination between PHO and fully hydrogenated oils (FHO), which is achieved by the iodine value (IV), has become an important regulatory issue. This study compared American Oil Chemists’ Society (AOCS) and International Organization for Standardization (ISO) titration and gas chromatography with flame‐ionization detection (GC‐FID) methodologies for the determination of IV in seven samples of hydrogenated oil, namely coconut, cottonseed (n = 2), palm kernel, palm stearine, and soybean (n = 2) oils. Titrations produced statistically higher IV determinations than those achieved by GC‐FID, for all samples except the FH coconut oil. The unsaponifiable matter content of the hydrogenated oils, which varied from 0.15% to 0.47% of total fat, likely contributed modest increases to the IV by titration. Both methodologies were prone to issues at low IV (~4), with titrations showing greater variability, and GC‐FID being susceptible to incomplete separation, identification, and quantification of all unsaturated fatty acids. The variability observed with titrations could be minimized by careful execution of the titration protocol. Although both approaches successfully discriminated PHO and FHO in the test materials, at low IV (~4), titration is the most accurate method for determining the IV, and the only approach that has been validated in oils with a very low IV (<1).     

Characteristics of Laboratory-Processed: Cucurbita foetidissima Seed Oil

The effects of variations in laboratory processing on the quality of the seed oil of the buffalo gourd, Cucurbita foetidissima, were determined. Conditions found most effective were: triple refining at 65 C for 15 min using 16°Be and 20°Be NaOH at 80% of maximum and 20°Be NaOH at the maximum; bleaching at 105 C for 30 min by a mixture of activated bleaching earth (3%) and activated carbon (0.3%); and deodorization with 5% steam at 210 C for 120 min. Processed oil showed these analytical values: carotenoids (3.6 mg/kg), free fatty acids (0.28%), peroxide (0.2 meq/kg), conjugated unsaturated fatty acids (1.59%). Oxidative stability test (AOM) conditions gave peroxide values of 100 in 4.9 hr and 141 in 8 hr. The triglyceride fatty acid composition was 11.9% palmitic, 3.5% stearic, 22.0% oleic and 61.0% linoleic acid.