Comparative study of physical methods for lipid oxidation measurement in oils

For the determination of lipid oxidation in oils, electrical, optical, spectroscopic and extraction methods were investigated using rice bran oil and doubly-fractionated palm olein as model systems. The oxidized polar components and dielectric constant of rice bran oil increased very similarly with those of double-fractionated palm olein. In the case of rice bran oil, all of the test methods were shown to possess good statistical correlations. Polar components, dielectric constant, refractive index and polymer content showed relatively better correlations. It was shown that diene and triene content determined by spectroscopic methods was not suitable for more saturated oils such as palm olein.     

The Effect of Type of Oil and Degree of Degradation on Glycidyl Esters Content During the Frying of French Fries

The aim of the study was to determine the effect of oil degradation on the content of glycidyl esters (GEs) in oils used for the frying of French fries. As frying media, refined oils such as rapeseed, palm, palm olein and blend were used. French fries were fried for 40 h in oils heated to 180 °C in 30‐min cycles. After every 8 h of frying, fresh oil and samples were analyzed for acid and anisidine values, color, refractive index, fatty acid composition, and content and composition of the polar fraction. GEs were determined by LC–MS. Hydrolysis and polymerization occurred most intensively in palm olein, while oxidation was reported for rapeseed oil. The degradation of oil caused increased changes in the RI of frying oils. Losses of mono‐ and polyunsaturated fatty acids were observed in all samples, with the largest share in blend. The highest content of GE found in fresh oil was in palm olein (25 mg kg^?1) and the lowest content of GE was found in rapeseed oil (0.8 mg kg^?1). The palm oil, palm olein and blend were dominated by GEs of palmitic and oleic acids, while rapeseed oil was dominated by GE of oleic acid. With increasing frying time, the content of GEs decreased with losses from 47 % in rapeseed oil to 78 % in palm oil after finishing frying.     

Chemical and physical analyses and sensory evaluation of six deep-frying oils

The performance of three high-oleic canola oils with different levels of linolenic acid [low-linolenic canola (LLC), medium-linolenic canola (MLC), and high-linolenic canola (HLC)], a medium-high-oleic sunflower oil, a commercial palm olein and a commercial, partially hydrogenated canola oil, was monitored by chemical and physical analyses and sensory evaluation during two 80-h deep-frying trials with potato chips. Linolenic acid content was a critical factor in the deep-frying performance of the high-oleic canola oils and was inversely related to both the sensory ranking of the food fried in the oils and the oxidative stability of the oils (as measured by color index, free fatty acid content, and total polar compounds). LLC and sunflower oil were ranked the best of the six oils in sensory evaluation, although LLC performed significantly better than sunflower oil in color index, free fatty acid content, and total polar compounds. MLC was as good as palm olein in sensory evaluation, but was better than palm olein in oxidative stability. Partially hydrogenated canola oil received the lowest scores in sensory evaluation. High-oleic canola oil (Monola) with 2.5% linolenic acid was found to be very well suited for deep frying.     

Effect of Saturated/Unsaturated Fatty Acid Ratio on Physicochemical Properties of Palm Olein–Olive Oil Blend

Although blending polyunsaturated oil with more saturated or monounsaturated oils has been studied extensively, there is no similar information regarding the partial replacement of palm olein with olive oil (OO). Therefore the main objective of this study was to investigate the effects of OO partial replacement (0, 25, 50, 75, 90 and 100% w/w) on the chemical stability of palm olein oil (POO). The physicochemical properties of oil samples namely iodine value, peroxide value (PV), anisidine value, TOTOX value (total oxidation value, TV), free fatty acid (FFA), cloud point, color and viscosity were considered as response variables. Significant differences among the oil blend properties were determined at the significance level of P < 0.05. Apart from FFA, all the response variables were significantly influenced by type and concentration of oils. The oil blend containing 10% POO and 90% OO showed the highest TV (6.10); whereas the blend containing 90% POO and 10% OO exhibited the least TV (2.41). This study indicated that the chemical stability of oil blend significantly (P < 0.05) increased with increasing the proportion of polyunsaturated/monounsaturated fatty acid.     

Frying Quality Characteristics of French Fries Prepared in Refined Olive Oil and Palm Olein

The objective of this study was to compare two oils with different polyunsaturated/saturated (P/S) fatty acid ratios, refined olive oil (P/S 0.75) and palm olein (P/S 0.25), in frying French fries. The chemical qualities of the oil residues extracted from the French fries were assayed for five consecutive batches fried at 1-h intervals. The levels of total polar compounds, free fatty acids, p-anisidine value and phytosterol oxidation products (POPs) were elevated in French fries fried in both oils. The level of total polar compounds increased from 4.6 in fresh refined olive oil to 7.3% in final batches of French fries. The corresponding figures for palm olein were 9.8–13.8%. The level of free fatty acid in fresh refined olive oil increased from 0.06 to 0.11% in final products. These figures for palm olein were 0.04–0.13%. The p-anisidine value increased from 3.7 to 32.8 and 2.5 to 53.4 in fresh oils and in final batches of French fries in refined olive oil and palm olein, respectively. The total amount of POPs in fresh refined olive oil increased from 5.1 to 9.6 μg/g oil in final products. These figures were 1.9 to 5.3 μg/g oil for palm olein.     

Palmöl und Palmkernöl

Palm Oil and Palm Kernel Oil Adulteration of palm oil with palm stearin can be recognized by examining the ration of the triglycerides PPP to MOP, which lies in pure palm oil between 3.5 and 4.5 and is elevated in the case of adulteration. The content of palmitic acid and the solid fat content are additional indications. Adulteration of coconut and palm kernal oils with palm kernel olein is best recognized by measuring the iodine number (which is max. 11 for coconut oil and 19 for palm kernel oil) and also by the content of stearic, oleic and linoleic acids, the sum of which should not exceed 11.5% for coconut oil and 22% for palm kernel oil respectively. The content of triglycerides with carbon number 46 to 54 may additionally be used.     

Composition of oil

International trade in palm oil has increased considerably over the last ten years, and so too has the trade in processed palm oil products, especially palm fractions. It is important to establish reliable purity criteria for palm oil, not only because of the commercial need to verify oil authenticity, but also to comply with foodstuff labelling legislation in many countries. Palm kernel and coconut oils both contain about 47% lauric acid. This gives the oils close similarities in physical and chemical properties. The oils do differ, however, and it is important to be able to distinguish between them. Purity problems can arise as a result of commingling of oils with one another, or as a result of fractionation perhaps coupled with subsequent blending. A research program jointly funded by the (U.K.) Ministry of Agriculture, Fisheries and Foods, the Federation of Oils, Fats & Seeds Associations Ltd (FOSFA International), and the Leatherhead Food RA, was established to study purity characteristics of the major edible vegetable oils. Forty-seven samples of crude palm oil were obtained from reliable sources, often plantation managers, together with five samples of palm olein and eight samples of palm stearin. Fifty-four palm kernel and 23 coconut oils were obtained in the laboratory from seed samples of known geographical origins and authenticities. These oil samples were analyzed for fatty acid, triglyceride, sterol and tocopherol compositions; the melting properties were also determined, and in the case of palm oil the compositions of the acids at the triglyceride 2-positions were measured. Compositional ranges will be presented for the different geographical production areas in each case and related to existing data, e.g., of PORIM and Codex. An initial statistical analysis of the results has shown that a combination of values from the carbon number analysis differentiates palm kernel and coconut oils, and can be used to decide on the proportion of each in a blend. In the case of palm oil samples suspected to be contaminated with palm fractions, it was found useful to plot melting point against iodine value, and to compute the product of the C48 triglyceride content and the palmitic acid enrichment factor.     

<Emphasis Type="Italic">cis</Emphasis>-, <Emphasis Type="Italic">trans</Emphasis>- and Saturated Fatty Acids in Selected Hydrogenated and Refined Vegetable Oils in the Indian Market

The fatty acid composition of 27 samples of commercial hydrogenated vegetable oils and 23 samples of refined oils such as sunflower oil, rice bran oil, soybean oil and RBD palmolein marketed in India were analyzed. Total cis, trans unsaturated fatty acids (TFA) and saturated fatty acids (SFA) were determined. Out of the 27 hydrogenated fats, 11 % had TFA about 1 % where as 11 % had more than 5 % TFA with an average value of about 13.1 %. The 18:1 trans isomers, elaidic acid was the major trans contributor found to have an average value of about 10.8 % among the fats. The unsaturated fatty acids like cis-oleic acid, linoleic acid and α-linolenic acid were in the range of 21.8–40.2, 1.9–12.2, 0.0–0.7 % respectively. Out of the samples, eight fats had fatty acid profiles of low TFA (less than 10 %) and high polyunsaturated fatty acids (PUFA) such as linoleic and α-linolenic acid. They had a maximum TFA content of 7.3 % and PUFA of 11.7 %. Among the samples of refined oils, rice bran oil (5.8 %) and sunflower oil (4.4 %) had the maximum TFA content. RBD palmolein and rice bran oils had maximum saturated fatty acids content of 45.1 and 24.4 % respectively. RBD palmolein had a high monounsaturated fatty acids (MUFA) content of about 43.4 %, sunflower oil had a high linoleic acid content of about 56.1 % and soybean oil had a high α-linolenic acid content of about 5.3 %.     

Palmöle und Palmöl-Fraktionen und ihre analytische Differenzierung

Palm Oils and Palm Oil Fractions and their Analytical Differentiation Due to the increasing production of palm oils and the correlating production of palm oil fractions there is a need to differentiate analytically between palm oils and palm oil fractions. The analytical differentiation of these products on the one hand and the detection of unwanted additions and mixtures on the other hand is intended to be achieved. Palm oils of different origin and palm oil fractions, fractionated by different procedures, were examined in this context. The composition of total fatty acids, fatty acids in 2-position of the triglycerides, slip point, iodine value, composition of triglycerides by gaschromatography as well as saturated triglycerides were determined. The slip point, which can easily be determined, and the palmitic acid content in 2-position of t he triglycerides proved to be most suitable for the analytical practice.     

Production of High Oleic Palm Oils on a Pilot Scale

Refined, bleached and deodorized palm olein (RBD POo) with an iodine value (IV) of 62 was chemically interesterified with methyl oleate (MO) at a ratio of 50:50 (w/w). The reaction was carried out at 110 °C in the presence of sodium methoxide as a catalyst using a 100-kg pilot scale reactor. Randomization between 15 and 30 min resulted in less free fatty acid (FFA) formation and higher oleic content in the interesterified product as compared to longer reaction time of 60–90 min. Sodium methoxide-catalyzed ester interchange increased the oleic content of the interesterified product to more than 57% from its initial content of 45%. The product obtained also has an IV of more than 75. The interesterified oil was then subjected to dry fractionation in a 200-kg De Smet jacketed crystallizer at 8 °C to further enhance the oleic content of the liquid olein fraction. The resulted olein had an improved cloud point and higher IV of 81. The solid stearin had a slightly higher IV and oleic content as compared to normal palm stearin. The solid fat content was comparable to normal palm oil. The pilot scale study has proven a successful conversion of laboratory findings to a larger scale production and gave the most realistic information for possible commercialization.     

Isolation and Evaluation of Stearin and Olein Fractions from Rice Bran Oil Fatty Acid Distillate by Detergent Fractionation and Conversion into Neutral Glycerides by Autocatalytic Esterification Reaction

Detergent fractionation (Lanza process) offers a valuable separation process for edible oils that contain varying amounts of saturated and unsaturated fatty acids. The rice bran oil fatty acid distillate (RBOFAD), obtained as a major byproduct of rice bran oil deacidification refining process, was fractionated by detergent solution into a fatty acid mixture as follows: low-melting (19.00 °C) fraction of fatty acids as olein fraction (44.50 g/100 g) and high-melting (49.00 °C) fatty acids as stearin fraction (37.15 g/100 g). A high amount of palmitic acid (42.75 wt%) is present in stearin fraction, while oleic acid is higher (48.21 wt%) in the olein fraction. The stearin and olein fractions of RBOFAD with very high content of free fatty acids are converted into neutral glycerides by autocatalytic esterification reaction with a theoretical amount of glycerol at high temperatures (130–230 °C) and at a reduced pressure (30 mmHg). Acid value, peroxide value, saponification value, and unsaponifiable matters are important analytical parameters to identity for quality assurance. These neutral glyceride-rich stearin and olein fractions, along with unsaponifiable matters, can be used as nutritionally and functionally superior quality food ingredients in margarine and in baked goods as shortenings.     

Biological modification of oil composition

Prospects for modification of palm oil composition through oil palm breeding, tissue culture and enzyme-catalyzed transesterification are reviewed. Present emphasis in oil modification is toward greater unsaturation. The greatest prospect for this area lies in the interspecific hybridization ofE. oleifera andE. guineensis. The target recommended is for a hybrid oil of iodine value above 72 having a palmitic acid content below 25% and an oleic acid content above 60%. It is noted that the variability of linoleic acid in the oil palm is limited regardless of species. The greatest contribution towards unsaturation, therefore, lies mainly in oleic acid. Tissue culture is seen as a potential propagating tool for selecting progenies of important crosses from the hybridization ofE. oleifera andE. guineensis, while enzyme-catalyzed transesterification using a 1,3 specific lipase offers the possibility of enhancing the level of linoleic acid in palm oil. Besides breeding for unsaturation, production of palms giving oils of specific fatty acid or triglyceride types also may be possible ultimately.     

Fractionation studies of palm oil by density gradient

The paper describes a method of fractionating vegetable, animal and fish oils, and in particular palm oil. The method involves addition of a medium comprising two common solvents to the semisolid oils. On centrifugation, the olein and stearin are separated by the medium in the middle. Thirteen media made up from binary combinations of nine solvents, viz. water, propylene glycol, glycerine, methanol, ethanol,n-propanol, isopropanol (IPA), acetone and butanone, are found to be effective in olein-stearin separation. However, only the water/IPA and water/methanol systems have been studied in detail. The aqueous IPA provides a higher yield of olein than water/ methanol but intersolubility between oil and medium is also greater. The fractionation process can be carried out at any suitable temperature. Fractionation of the special prime bleached (SPB) palm oil at 16 C yields an olein with a cloud point of 4.8 C. Some hybrid palm oils produce a large quantity of low cloud point olein which can be bleached readily. The process can be extended to include degumming and neutralization by using an alkaline medium for centrifugation. The olein fractions obtained have been found to be free of phosphatides and the free fatty acids reduced to as low as 0.02%. Metal-scavenging agents have also been added to the medium in an attempt to remove copper and iron. The development of this process into a continuous one has been demonstrated on the AlfaLaval LAPX 202 Separator. Fractionation of crude palm oil using a density gradient provides seven fractions of different characteristics. The iodine values vary from 37.5 to 57.4 and the unsaturated fatty acids range from 32.7% to 51.2%. Triglyceride analysis by carbon numbers shows great differences in the C₄₈ and C₅₂ constituents of the fractions. aThe volume ratio of oil to medium in each case was 1:1. The separation involved the oil and wax.     

Efficacy of the antioxidants BHA and BHT in palm olein during heating and frying

The effectiveness of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in retarding the deterioration of RBD palm olein during static heating (180 C) and frying operations was assessed by determining the peroxide, anisidine, acid and iodine values; absorbances at 232 and 268 nm; and the fatty acid composition of the oil. During static heating of the oil, BHA was found to be a more effective antioxidant than BHT whereas, during intermittent frying of potato chips, both the antioxidants were relatively ineffective in retarding the deterioration of the oil. The loss of BHT from the oil during static heating exceeded that of BHA. On the other hand, when potato chips were fried in the oil periodically, a higher loss of BHA was observed.     

Studies on the nutritional and physiological effects of thermally oxidized oils

Summary The present results indicated that the thermal oxidation products from the polyunsaturated fatty acids, primarily linoleic acid, are responsible for much of the loss of nutritional value in thermally oxidized edible oils. Oils which have a high linoleic acid content are more likely to undergo thermal oxidative damage than those with lower linoleic contents. Also the ratio of linoleic acid to total unsaturation has some effect on the nutritive stability of the oil when it has been thermally oxidized. An oil with a high iodine value but with a low linoleic acid value appears to be more stable to thermal oxidation than an oil with an iodine value one half as great but with most of the unsaturation in the oil caused by linoleic acid. The products formed during thermal oxidation which cause the loss of nutritional value are those which do not form urea-inclusion compounds. They are probably polymeric in nature, but thermally oxidized oils also contain carboxylic acids and carbonyl groups which might cause some of the nutritional loss observed when thermally oxidized oils are fed. The rate ofin vitro hydrolysis of the thermally oxidized corn oil by pancreatic lipase, also the rate of absorption from the intestine of the male rats, were found to be decreased. However the percentage of absorption in 24 hrs. was the same with both fresh and thermally oxidized oil. The liver-body weight ratio of rats fed a diet containing the thermally oxidized oil were found to be significantly larger than the liver-body weight ratio in animals fed diets containing fresh oil. However the livers of animals fed the thermally oxidized oil diets did not differ in lipide percentage or total solid content, and histopathological investigations did not show any abnormal conditions.     

Palm olein quality parameter changes during industrial production of potato chips

New legislation introduced in South Africa for the quality of used frying oils has resulted in the need to identify quicker, more suitable methods that correlate well with results from two official methods, namely, total polymerized glycerides and total polar components. Oil and product samples were taken at regular intervals during a commercial frying process in palm olein. Oil samples were analyzed for a number of different quality parameters viz. tocopherol content, dielectric constant, total polymerized glycerides, total polar components, tertiary butylhydroquinone (TBHQ) content, anisidine value, Rancimat induction period, and free fatty acid content, and the results statistically compared to results from official methods. Oil was expressed from product stored under accelerated conditions and analyzed for the same quality parameters. Fried product was also subjected to sensory evaluation to measure the degree of oil deterioration and sensory preference. The frying trial was successfully executed with refined, bleached, and deodorized palm olein and the frying oil used to a free fatty acid (FFA) content of 0.41%. Oil and product sampling were done at different FFA value levels. Frying oil quality was verified at the onset of the trial and at regular intervals. The frying oil total polar component value increased to approximately half of the limit set by the official regulation. This point was reached mainly due to the high starting value of the fresh oil. Frying oil total polymerized glycerides increased from below 1% to 2.1%. This increase is negligible when compared to the general trend for polyunsaturated oils. The alternative laboratory methods used for predicting oil quality can be rated as follows: total tocopherol content >dielectric constant >FFA >TBHQ content >anisidine value >Rancimat induction period. The first three methods correlated well with total polar component levels and it is recommended that the dielectric constant and FFA measurements be applied for monitoring oil condition during frying. It is possible that viscosity changes could be used for the monitoring of polyunsaturated frying oils. Evaluation of oil extracted from product revealed a negligible effect of non-oil components on oil quality parameters. The same was observed when product was stored at −10°C and at 37°C.     

Preparation of diacylglycerol‐enriched palm olein by phospholipase A1‐catalyzed partial hydrolysis

Partial hydrolysis of palm olein catalyzed by phospholipase A₁ (Lecitase Ultra) in a solvent‐free system was carried out to produce diacylglycerol (DAG)‐enriched palm olein (DEPO). Four reaction parameters, namely, reaction time (2–10 h), water content (20–60 wt‐% of the oil mass), enzyme load (10–50 U/g of the oil mass), and reaction temperature (30–60 °C), were investigated. The optimal conditions for partial hydrolysis of palm olein catalyzed by Lecitase Ultra were obtained by an orthogonal experiment as follows: 45 °C reaction temperature, 44 wt‐% water content, 8 h reaction time, and an enzyme load of 34 U/g. The upper oil layer of the reaction mixture with an acid value of 54.26 ± 0.86 mg KOH/g was first molecularly distilled at 150 °C to yield a DEPO with 35.51 wt‐% of DAG. The DEPO was distilled again at 250 °C to obtain a DAG oil with 74.52 wt‐% of DAG. The composition of the acylglycerols of palm olein and the DEPO were analyzed and identified by high‐performance liquid chromatography (HPLC) and HPLC/electrospray ionization/mass spectrometry. The released fatty acids from the partial hydrolysis of palm olein catalyzed by phospholipase A₁ showed a higher saturated fatty acid content than that of the raw material.     

Fatty acid compositions of corn oils in relation to oil contents of the kernels

Summary The fatty acid compositions of 13 oils from corns having oil contents over the range of 1.6 to 11.5% oil, d.b., were determined either by a spectrophotometric technique applied to the whole oil or by the methyl ester fractional distillation technique. Linear relationships between iodine values and fatty acid compositions, between oil contents of the corns and iodine values, and between oil contents and fatty acid compositions were determined. An increase in oil content of the corn is accompanied by a decrease in iodine value and linoleic acid content of the oil and by an increase in oleic acid and saturated acids.     

Effect of oil replenishment during deep-fat frying of frozen foods in sunflower oil and high-oleic acid sunflower oil

Frying stability of sunflower oil (SO) with 23% oleic acid and 61% linoleic acid, and of high-oleic acid sunflower oil (HOSO) with 74% oleic acid and 13% linoleic acid was studied during 20 discontinuous deep-fat fryings of various frozen foods, with or without frequent replenishment of the used oil with fresh oil. Alterations of both oils were measured by column, gas-liquid and high-performance size-exclusion chromatography. Total polar content and compounds, related to thermoxidative changes, and diacylglycerides, related to hydrolytic changes, increased in all oils during frying but reached higher levels in SO than in HOSO. Nevertheless, the increased levels of diacylglycerides observed may result from the frozen potatoes prefried in palm oil. Oleic acid in HOSO and linoleic acid in SO significantly decreased, but the fatty acid modifications that occurred during the repeated fryings were not only related to thermoxidative alteration but also to interactions between the bath oil and the fat in the fried products. Data from this study also indicated that HOSO performed more satisfactorily than SO in repeated fryings of frozen foods. Moreover, frequent addition of fresh oil throughout the deep-frying process minimized thermoxidative and hydrolytic changes in the frying oils and extended the frying life of the oils.     

Clarity of blends of double-fractionated palm olein with low-erucic acid rapeseed oil

Double-fractionated palm olein (DfPOo) fractions with iodine values (IV) of 60 and 65 were each blended with low-erucic acid rapeseed (LEAR) oil in various proportions. Clarities of the blends at different temperatures were determined. Maximum levels of DfPOo-IV60 and DfPOo-IV65 in blends that remained clear at 20°C for at least 120 d were 40 and 80%, respectively. At 15°C, the maximum levels were 10 and 40%, and at 10°C, 10 and 20%, respectively. At 5°C, only a blend of 10% DfPOo-IV65 in LEAR remained clear for 120 d. Maximum levels of DfPOo-IV60 and DfPOo-IV65 in blends that passed the cold test were 30% for both palm oleins. Maximum levels of the palm oleins in blends with LEAR were higher than those of blends with soybean oil. Cloud points were lower in palm olein/LEAR blends than those of palm olein/soybean oil blends, probably because LEAR contains less saturated fatty acids than soybean oil.