Physical and chemical properties of trans-free fats produced by chemical interesterification of vegetable oil blends

Fat blends, formulated by mixing a highly saturated fat (palm stearin or fully hydrogenated soybean oil) with a native vegetable oil (soybean oil) in different ratios from 10:90 to 75:25 (wt%), were subjected to chemical interesterification reactions on laboratory scale (0.2% sodium methoxide catalyst, time=90 min, temperature=90°C). Starting and interesterified blends were investigated for triglyceride composition, solid fat content, free fatty acid content, and trans fatty acid (TFA) levels. Obtained values were compared to those of low- and high-trans commercial food fats. The interesterified blends with 30–50% of hard stock had plasticity curves in the range of commercial shortenings and stick-type margarines, while interesterified blends with 20% hard stock were suitable for use in soft tubtype margarines. Confectionery fat basestocks could be prepared from interesterified fat blends with 40% palm stearin or 25% fully hydrogenated soybean oil. TFA levels of interesterified blends were low (0.1%) compared to 1.3–12.1% in commercial food fats. Presented at the 88th AOCS Annual Meeting and Expo, May 11–14, 1997, Seattle, Washington.     

Physical properties of interesterified fat blends

Fat blends, formulated by mixing fully hydrogenated soybean oil with nine different commonly used vegetable oils in a ratio of 1:1 (w/w), were subjected to interesterification (also commonly referred to as rearrangement or randomization) with sodium methoxide catalyst. Fatty acid composition and triacylglycerol molecular species of each fat blend and the interesterified product were determined and correlated with the following physical properties: melting, crystallization characteristics and solid fat content. The differences in the endothermic and exothermic peak temperatures, total heat of fusion and crystallization (β and β′ crystalline content) and solid fat content among the fat blends clearly showed the effect of the composition of each oil on the physical properties. Oils that contained a considerable amount of palmitic acid had a favorable influence on the crystallization and polymorphic form of interesterified fat blends.     

The influence of chemical interesterification on the physicochemical properties of complex fat systems. 3. Rheology and fractality of the crystal network

Chemically interesterified and noninteresterified lard-canola oil (LCO) and palm oil-soybean oil blends ranging from 100% hardstock to 50%:50% hardstock/vegetable oil (w/w) were evaluated for hardness index (HI) using cone penetrometry and viscoelastic properties, such as shear storage modulus G′, using controlled-stress rheometry. The HI and G′ of palm oil decreased upon addition of soybean oil, and chemical interesterification did not affect the HI or G′ of palm oil or palm oil-soybean oil blends. The HI and G′ of lard decreased upon addition of canola oil, while chemical interesterification led to increases in both the HI and G′ of lard and LCO blends. All these effects were nonsolid fat content-related, since solid fat content did not change substantially upon chemical interesterification. The microstructure of the fat crystal network in lard and palm oil was quantified rheologically using fractal analysis. Chemical interesterification did not affect the fractal dimension of the fat crystal networks in palm oil or lard (2.82 and 2.88, respectively). The rheological properties of the macroscopic systems were not affected by the spatial distribution of mass within their fat crystal networks. Moreover, our results suggest that the increases in G′ observed in lard upon chemical interesterification are potentially due to changes in the properties of the particles which make up the network (crystal habit).     

Suitability of hydrogenated soybean oils for prefrying of deep-frozen french fries

The suitability of hydrogenated soybean oils (fats) for prefrying of deep-frozen french fries has been investigated in a frying and storage experiment with five hydrogenated oils, of which four were commercially available and one was experimentally prepared. Three frying oils were hydrogenated soybean fats (0% C18:2 and C18:3), one was a partly hydrogenated soybean oil (25% C18:2; 0% C18:3) and one a hydrogenated palm fat (0% C18:2). An intermittent frying and heating procedure was used. Prefried french fries were stored deep-frozen at ?18 to ?20 C for a period of one year. Although differences in hydrolysis and oxidation during frying were observed, the five hydrogenated frying oils were quite stable. During the storage period, hydrolytic and oxidative changes in the oil phase of prefried french fries were not detected, regardless of the frying oil used. Only slight changes in sensory quality could be detected in all french fry samples stored for one year at ?18 to ?20 C. Some differences in odor and taste of finish-fried french fries observed initially were not observed after prolonged storage. Thus, it has been concluded that hydrogenated soybean oils, including a partly hydrogenated one, are suitable for prefrying french fries and for long-term storage of deep-frozen products.     

The influence of chemical interesterification on physicochemical properties of complex fat systems 1. Melting and crystallization

The effects of blending palm oil (PO) with soybean oil (SBO) and lard with canola oil, and subsequent chemical interesterification (CIE), on their melting and crystallization behavior were investigated. Lard underwent larger CIE-induced changes in triacylglycerol (TAG) composition than palm oil. Within 30 min to 1 h of CIE, changes in TAG profile appeared complete for both lard and PO. PO had a solid fat content (SFC) of ∼68% at 0°C, which diminished by ∼30% between 10 and 20°C. Dilution with SBO gradually lowered the initial SFC. CIE linearized the melting profile of all palm oil-soybean oil (POSBO) blends between 5 and 40°C. Lard SFC followed an entirely different trend. The melting behavior of lard and lard-canola oil (LCO) blends in the 0–40°C range was linear. CIE led to more abrupt melting for all LCO blends. Both systems displayed monotectic behavior. CIE increased the DP of POSBO blends with ≥80% PO in the blend and lowered that of blends with ≤70% PO. All CIE LCO blends had a slightly lower DP vis-à-vis their noninteresterified counterparts.     

Polymorphic behavior of some fully hydrogenated oils and their mixtures with liquid oil

Fully hydrogenated soybean oil, beef fat, rapeseed oil, a rapeseed, palm and soybean oil blend, cottonseed oil and palm oil were characterized by fatty acid composition, glyceride carbon number and partial glyceride content, as well as melting and crystallization properties. The latter were established by differential scanning calorimetry. Polymorphic behavior was analyzed by X-ray diffraction of the products in the flake or granulated form and when freshly crystallized from a melt. The hard fats were dissolved in canola oil at levels of 20, 50 and 80% and crystallized from the melt. Palm oil had the lowest crystallization temperature and the lowest melting temperature; rapessed had the highest crystallization temperature and soybean the highest melting temperature. All of the hard fats crystallized initially in the =00 form. When diluted with canola oil, only palm oil was able to maintain β′ stability.     

Changes in the characteristics and composition of oils during deep-fat frying

Refined, bleached, and deodorized soybean oil and vanaspati (partially hydrogenated vegetable oil blend consisting of peanut, cottonseed, nigerseed, palm, rapeseed, mustard, rice bran, soybean, sunflower, corn, safflower, sesame oil, etc., in varying proportions) were used for deep-fat frying potato chips at 170, 180, and 190°C. Refractive index, specific gravity, color, viscosity, saponification value, and free fatty acids of soybean oil increased with frying temperature, whereas the iodine value decreased. The same trend was observed in vanaspati, but less markedly than in soybean oil, indicating a lesser degree of deterioration. Iodine values of soybean oil and vanaspati decreased from their initial values of 129.8 and 74.7 to 96.2 and 59.6, respectively, after 70 h of frying. Polyunsaturated fatty acids decreased in direct proportion to frying time and temperature. Losses were highest in soybean oil with a 79% decrease in trienoic acids and a 60% decrease in dienoic acids. Levels of nonurea adduct-forming esters were proportional to the losses of unsaturated fatty acids. Butylated hydroxyanisole and tertiary butylhydroquinone did not affect deterioration of soybean oil at frying temperatures.     

Analysis of thermally abused soybean oils for cyclic monomers

Cyclic monomers derived from the intramolecular condensation of the C₁₈ polyunsaturated fatty acids have been reported to elicit toxic responses when fed to laboratory animals at low dietary levels. This study was undertaken to quantitate the cyclic monomers formed by thermal oxidation induced during deep fat frying to assess the potential toxicity of commonly used vegetable oils. Two separate experiments were designed to study the effects of unsaturation and both intermittent and continuous heating on cyclic monomer formation. Both lightly hydrogenated soybean oil (iodine value [IV]=107) and refined, bleached and deodorized soybean oil were studied. The heated oil sustained substantial chemical and physical alterations, as indicated by IV decreases from 10–15 units, increases in free fatty acids of 5–10-fold and in noneluted material of 18–21%. Selected samples were completely hydrogenated and analyzed for cyclic monomers by gas chromatography. Under chromatographic conditions sufficiently sensitive to detect a cyclic monomer standard at less than 0.5% by weight, no cyclic monomers were detected in any of the heated oil samples. However, after concentration by low temperature crystallization of the hydrogenated samples to remove a major portion of the saturated components interfering in cyclic monomer resolution, about 0.3–0.6% cyclic acids, as well as 0.4–0.9% polar materials, were detected in the heated soybean oils. Components appearing in the gas chromatogram with the same retention time as those in a cyclic monomer standard were further identified by gas chromatography-mass spectrometry as disubstituted cyclic C-18 acids.     

Effect of ascorbyl palmitate on the quality of frying fats for deep frying operations

The addition of 0.02% ascorbyl palmitate (AP) reduced color development of frying fat (animal fat/vegetable oil [A-V] shortening) and vegetable oil (partially hydrogenated soybean [V-S] oil) in simulation studies. It also reduced peroxide values, development of conjugated diene hydroperoxides (CDHP) and their subsequent degradation to volatile compounds, such as decanal and 2,-4 decadienal, indicating that AP has the ability to inhibit thermal oxidation/degradation of frying fats and oils. A commercial french fry fat had lower CDHP values compared to A-V fat in simulated studies, and fried chicken oil had lower CDHP values than the V-S oil. Peanut oil had higher thermal stability than the other fats and oils.     

Review of stability measurements for frying oils and fried food flavor

Measurements of degradation in frying oils based on oil physical properties and volatile and nonvolatile decomposition products were reviewed. Rapid methods by means of test kits were also considered. Factors that affect the analysis of total polar components (TPC) in frying oils were examined. Relationships between TPC, free fatty acid (FFA) content, Food Oil Sensor readings (FOS), color change (ΔE), oil fry life and fried-food flavor were evaluated. Flavor scores for codfish, fried in fresh and discarded commercial frying oil blends, were dependent upon individuals in the consumer panel (n=77). Part (n=29) of the panel preferred the flavor of fresh fat; others (n=24) didn't; the rest (n=24) had no preference. FFA, FOS and TPC were analyzed in two soybean oils and in palm olein during a four-day period in which french fries were fried. Flavor score and volatiles of potatoes fried on days 1 and 4 in each oil were also determined. TPC, FFA and FOS significantly increased (P<0.05) in all oils during the frying period. TPC and FFA were highest in the used palm olein, and flavor of potatoes fried in palm olein on day 1 was less desirable than those fried in the soybean oils. Potatoes fried in day-1 oils had significantly higher concentrations (P<0.10) of several pyrazines and aldehydes than those fried in day-4 oils. Presented at the 84th Annual Meeting of the American Oil Chemists' Society, Anaheim, California, April 25–29, 1993.     

Environmentally Friendly Determination of Quality Parameters of Biodiesel/Diesel Blends Using Fourier Transform Infrared Spectra

Multivariate calibration models based on data from mid‐infrared spectroscopy of biodiesel/diesel blends were obtained. The blends were prepared from diesel oil and esters of soybean oil, waste cooking oil, and hydrogenated vegetable oil in proportions ranging from 0 to 100 % biodiesel. The results showed that the multivariate regression models with interval partial least squares (iPLS), backward interval partial least squares (biPLS), and synergy interval partial least squares (siPLS) were able to determine the fractions of the infrared spectrum that contain the relevant information for estimating the values of physicochemical properties, flash point, specific gravity, and cetane number, which are used in quality control of the blends. In the best models, the values of determination coefficients were greater than 0.9500, proving their efficiency as an alternative to traditional analytical methods.     

Formulation of zero-<Emphasis Type="Italic">trans</Emphasis> acid shortenings and margarines and other food fats with products of the oil palm

The fruit of the oil palm yields two types of oil. The flesh yields 20–22% of palm oil (C16∶0 44%, C18∶1 39%, C18∶2 10%). This represents about 90% of the total oil yield. The other 10%, obtained from the kernel, is a lauric acid oil similar to coconut oil. Palm oil is semisolid, and a large part of the annual Malaysian production of about 14 million tonnes is fractionated to give palm olein, which is widely used for industrial frying, and palm stearin, a valuable hard stock. Various grades of the latter are available. Formulae have been developed by straight blending and by interesterification of palm oil and palm kernel oil to produce shortenings and margarines using hydrogenated fats to give the consistency required. Products that include these formulations are cake shortenings, vanaspati (for the Indian subcontinent), soft and brick margarines, pastry margarines, and reduced fat spreads. Other food uses of palm products in vegetable-fat ice cream and cheese, salad oils, as a peanut butter stabilizer, and in confectioners fats are discussed briefly here.     

Physical Properties of <Emphasis Type="Italic">trans</Emphasis>-Free Bakery Shortening Produced by Lipase-Catalyzed Interesterification

Lipase-catalyzed interesterified solid fat was produced with fully hydrogenated soybean oil (FHSBO), and rapeseed oil (RSO) and palm stearin (PS) in a weight ratio of 15:20:65, 15:40:45 and 15:50:35. The interesterified fats contained palmitic (27.8–44.6%), stearic (15.6–16.2%), oleic (27.5–36.5%) and linoleic acids (8.0–13.5%). After interesterification of the blends, the physical properties of the products changed and showed lower melting points and solid fat contents, different melting and crystallization behaviors as well as the formation of more stable crystals. The produced interesterified fats (FHSBO:RSO:PS 15:20:65, 15:40:45 and 15:50:35 blends) contained desirable crystal polymorphism (β′ form) as determined by X-ray diffraction spectroscopy, a long plastic range with solid fat content of 51–63% at 10 °C to 4–12% at 40 °C, and melting points of 39 (15:50:35), 42 (15:50:45) and 45 °C (15:20:65). However, a reduction in tocopherols (α and γ) content and a reduced oxidative stability were observed in the interesterified fats. The physical properties of the interesterifed fats were influenced by the amount of PS, resulting in more hardness and higher solid fat contents for 15:20:65 than 15:40:45 and 15:50:35 blends. The present study suggested that the produced interesterified fats containing trans-free fatty acids could be used as alternatives to hydrogenated types of bakery shortenings.     

Random interesterification of fat blends with alkali catalysts

Random interestification of fat blends, composed from vegetable oil and fully hydrogenated vegetable oil, catalyzed by sodium hydroxide and sodium methoxide, has been investigated. Sodium methoxide was used as a reference catalyst to evaluate the influence and the catalytic efficiency of NaOH on interesterification. Sodium hydroxide was found to be a suitable catalyst for this purpose. The choice of methods suitable for the investigation of interesterification reactions and characterization of the initial fat blends and their interesterified products is described. The randomization was followed by the changes in the triacylglycerol (TAG) composition of the fat blends determined by HPLC and high temperature GLC. This triacylglycerol composition of the original blends and the randomized products with the physical properties such as melting behaviour, crystallization and solid fat content were compared. The results show that the randomization of vegetable oil - fully hydrogenated vegetable oil fat blends in various ratios can be used to produce fats with desired physical and nutritional properties.     

Chemical composition and physical properties of soft (tub) margarines sold in Malaysia

Seven samples of domestic and imported Malaysian tub margarines were analyzed for their fatty acid and triglyceride (carbon number) composition, solid fat content, dropping and softening points, crystallization temperature, polymorphic form, color, and textural attributes. Domestic margarines were formulated from palm oil or palm olein and palm kernel oil with a liquid oil but no hydrogenated oils. Two imported products contained hydrogenated palm oil product, which resulted in a high level of β′ crystals, whereas the domestic nonhydrogenated products contained more β than β′ crystals. Crystal habit was related to the fatty acid and triglyceride composition of the high-melting glycerides. Domestic products were firmer in texture, probably because they were formulated to be sold in a tropical climate.     

Oxidative stability of blends and interesterified blends of soybean oil and palm olein

Improvement of oxidative stability of soybean oil by blending with a more stable oil was investigated. Autoxidation of blends and interesterified blends (9∶1, 8∶2, 7∶3 and 1∶1, w/w) of soybean oil and palm olein was studied with respect to fatty acid composition, fatty acid location and triacylglycerol composition. Rates of formation of triacylglycerol hydroproxides, peroxide value and volatiles were evaluated. The fatty acid composition of soybean oil was changed by blending. Linolenic and linoleic acids decreased and oleic acid increased. The triacylglycerol composition of blends and interesterified blends was different from that of soybean oil. Relative to soybean oil, LnLL, LLL, LLO, LLP, LOO and LLS triacylglycerols were lowered and POO, POP and PLP were higher in blends and interesterified blends (where Ln, L, O, P and S represent linolenic, linoleic, oleic, palmitic and stearic acids, respectively). Interesterification of the blends leads to a decrease in POO and POP and an increase in LOP. Linoleic acid concentration at triacylglycerol carbon-2 was decreased by blending and interesterification. Rates of change for peroxide value and oxidation product formation confirmed the improvement of soybean oil stability by blending and interesterification. But, blends were more stable than interesterified blends. Also, the formation of hexanal, the major volatile of linoleate hydroperoxides of soybean oil, was decreased by blending and interesterification.     

Low-linolenic acid soybean oil—Alternatives to frying oils

Oil was hexane-extracted from soybeans that had been modified by hybridization breeding for low-linolenic acid (18∶3) content. Extracted crude oils were processed to finished edible oils by laboratory simulations of commercial oil processing procedures. Oils from three germplasm lines N83-375 (5.5% 18∶3), N89-2009 (2.9% 18∶3) and N85-2176 (1.9% 18∶3) were compared to commercial unhydrogenated soybean salad oil with 6.2% 18∶3 and two hydrogenated soybean frying oils, HSBOI (4.1% 18∶3) and HSBOII (<0.2% 18∶3). Low-18∶3 oils produced by hybridization showed significantly lower room odor intensity scores than the commercial soybean salad oil and the commercial frying oils. The N85-2176 oil with an 18∶3 content below 2.0% showed no fishy odor after 10 h at 190°C and lower burnt and acrid odors after 20 h of use when compared to the commercial oils. Flavor quality of potatoes fried with the N85-2176 oil at 190°C after 10 and 20 h was good, and significantly better at both time periods than that of potatoes fried in the unhydrogenated oil or in the hydrogenated oils. Flavor quality scores of potatoes fried in the N89-2009 oil (2.9% 18∶3) after 10 and 20 h was good and equal to that of potatoes fried in the HSBOI oil (4.1% 18∶3). Fishy flavors, perceived with potatoes fried in the low-18∶3 oils, were significantly lower than those reported for potatoes fried in the unhydrogenated control oil, and the potatoes lacked the hydrogenated flavors of potatoes fried in hydrogenated oils. These results indicate that oils with lowered linolenic acid content produced by hybridization breeding of soybeans are potential alternatives to hydrogenated frying oils.     

Effects of fresh and used hydrogenated soybean oil on reproduction and teratology in rats

Groups of 25 pairs of two generations of male and female rats were fed diets containing 15% of either fresh hydrogenated soybean oil (iodine value, 107), a similar fat used 56 hr for deep frying or an unhydrogenated mixture of fats and oils with a fatty acid composition similar to the hydrogenated soybean oil. The first two litters of each generation were permitted to be born naturally. During the third pregnancy of each generation, one-half of the females were sacrificed on day 13 of gestation and inspected for early embryonic death. The remaining females were sacrificed on day 21 of gestation, and the fetuses were examined for either skeletal or softtissue abnormalities. There was no evidence of any deleterious effects on the reproductive parameters nor any teratogenic effects due to either hydrogenated soybean oil, a similar oil used for frying foods for 56 hr or an unhydrogenated mixture of fats and oils.     

Effects of fresh and used hydrogenated soybean oil on reproduction and teratology in rats

Groups of 25 pairs of two generations of male and female rats were fed diets containing 15% of either fresh hydrogenated soybean oil (iodine value, 107), a similar fat used 56 hr for deep frying or an unhydrogenated mixture of fats and oils with a fatty acid composition similar to the hydrogenated soybean oil. The first two litters of each generation were permitted to be born naturally. During the third pregnancy of each generation, one-half of the females were sacrificed on day 13 of gestation and inspected for early embryonic death. The remaining females were sacrificed on day 21 of gestation, and the fetuses were examined for either skeletal or softtissue abnormalities. There was no evidence of any deleterious effects on the reproductive parameters nor any teratogenic effects due to either hydrogenated soybean oil, a similar oil used for frying foods for 56 hr or an unhydrogenated mixture of fats and oils.     

Palm oil and palm kernel oil in food products

Cocoa butter equivalent (CBE) formulation, especially the compatibility of palm oil based CBE with cocoa butter, is of special interest to chocolate manufacturers. Traditionally palm oil is fractionated to obtain high-melting stearin and olein with a clear point of around 25 C, the latter serving as cooking oil. Recently, palm oil has been fractionated to recover an intermediate fraction known as palm mid-fraction (PMF), which is suitable for CBE formulations. Generally, production of PMF is based on a three-step procedure. However, a dry fractionation system, which includes selective crystallization and removal of liquid olein by means of a hydraulic press, has been developed. Iodine value, solid content (SFI) at different temperatures, cooling curves (Shukoff 0°) and triglyceride/fatty acid composition determination confirmed effectiveness of the procedure followed. A direct relationship between yield, quality of PMF and crystallization temperature during fractionation has been achieved. Yield of 60% for olein of IV 64–67 has been achieved. Yield of 30% for PMF of IV 36–38 and 10% for high melting stearin of IV of 20–22 are also being achieved. High-melting stearin may be used in oleochemical applications, soaps, food emulsifiers and other industrial applications such as lubricating oil. Olein fraction, especially after flash hydrogenation thereby reducing the IV to 62/64, has excellent frying and cooking oil characteristics. Palm olein is also suitable as dietary fat and in infant formulation. Studies on interesterification of high-melting stearin with olein showed possibilities to formulate hardstocks for margarine and spread formulations, even without using hydrogenated fat components. Palm kernel and coconut fats or fractions or derived products are used for confectionery products as partial CB replacers and as ice cream fats and coatings. Coconut oil also serves as a starting material for the production of medium-chain triglycerides.