Food Oil Sensor Research Articles

Determination of total polar parts with new methods for the quality survey of frying fats and oils

During the frying process the fat undergoes several chemical and physical changes caused by heat, water and atmospheric oxygen. With prolonged heating time the accumulation of deterioration products leads to organoleptic failures and a decrease of the nutritive value. For the quality control of frying fats or oils the determination of total polar parts by preparative column chromatography is an approved standard method. Many attempts were undertaken to replace this time and chemical consuming method. To substitute for the determination of polar components by column chromatography the measurement of dielectric properties with a food oil sensor, nuclear magnetic resonance spectroscopy (NMR) and near infrared spectroscopy (NIR) proved to be suitable.

Effect of vacuum frying on the oxidative stability of oils

AbstractThe purpose of this study was to evaluate frying oil quality with different assessment methods during vacuum frying of carrot slices. In six consecutive days, palm oil, lard, and soybean oil were fried under vacuum at 105°C for 20 min each hour in an 8‐h shift. Peroxide value, acid value, carbonyl value, total polar components, dielectric constant (Food Oil Sensor reading), viscosity, and fatty acid composition were used to evaluate the quality of these oils. Results showed that palm oil and lard possess greater thermal stability than soybean oil. The decrease in C18:2/C16:0 ratio was greater for soybean oil than the other two oils. Of the assessment methods used, peroxide value, carbonyl value, total polar components, and dielectric constant all showed good correlation with frying time and between each other. Viscosity was suitable to assess vacuum‐fried lard and soybean oil, but not palm oil. The measurement of dielectric constant, on the other hand, appeared to be unsuitable to assess vacuum‐fried soybean oil.

Heated fat‐based oil substitutes, oleic and linoleic acid‐esterified propoxylated glycerol

AbstractFour oils [triolein, trilinolein, oleic acid‐esterified propoxylated glycerol (EPG‐08 oleate), and linoleic acid‐esterified propoxylated glycerol (EPG‐08 linoleate)], each without added antioxidants, were heated for 12 h/d at approximately 190°C in a small deep‐fat fryer until the polymer concentration exceeded 20%, as determined by high‐performance size‐exclusion chromatography. Increases in the free fatty acid content, total acid value, food oil sensor value, and p‐anisidine value during heating indicated that significant thermal oxidation had occurred in each oil. Capillary supercritical fluid chromatography (SFC) was used to determine the substrate concentration of each oil after each heating interval. The average, apparent first‐order reaction rate constant (as determined by SFC) for trilinolein was 0.0348±0.0034 h−1, while the rate for EPG‐08 linoleate was 0.0253±0.0032 h−1. The average apparent reaction rate constant for triolein was 0.0256±0.0011 h−1, while the rate for EPG‐08 oleate was 0.0252±0.0008 h−1. Triolein contained >20% polymer after 60 h of heating, EPG‐08 oleate contained >20% polymer after 36 h of heating, and both trilinolein and EPG‐08 linoleate contained >20% polymer after 24 h of heating.

Review of stability measurements for frying oils and fried food flavor

AbstractMeasurements 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.

Nonvolatile components produced in triolein during deep‐fat frying

AbstractTriolein was heated at 190°C (375°F) in a deep‐fat fryer for 12 h/day until high‐performance size‐exclusion chromatography indicated polymer formation had exceeded 20%. Increases in the free fatty acid, total acid value, food oil sensor andp‐anisidine values upon heating indicated that thermal oxidation and degradation of triolein had occurred. After the initial sample (day 0), the peroxide values decreased to very low values. The amount of polymeric triacylglycerol material increased during heating. Linear regression analysis of percent polymer vs. heating time indicated that the sample would contain ≥20% polymers after 51.1 h of heating. Capillary supercritical fluid chromatography (SFC) was used to determine the percentage of triolein remaining after 12, 24, 36, 48 and 60 h of heating, which was 68.6, 53.9, 35.9, 33.0 and 19.0%, respectively. The average reaction rate constant (apparent first‐order) for the change in triolein concentration, SFC, during heating was 0.0256±0.0011 h−1.

Survey of quality of used frying oils from restaurants

AbstractCommercial frying practices and frying conditions at 62 restaurants or fast‐food outlets were investigated and the quality of their discarded frying oils was evaluated by several standard laboratory methods: total polar components (TPC), free fatty acids (%FFA), p‐anisidine and peroxide values, color, viscosity, C18:2/C16:0, absorbance at 232 and 268 nm, and five quick test methods (Foodoil sensor, Oxifrit (RAU‐Test), Fritest, Veri‐Fry‐TAM 150, and Veri‐Fry‐FFA 500). Frying techniques varied from primitive traditional practice at traditional shops to modern sophisticated frying procedures at some franchise restaurants. Discarded oils appeared to be heat‐damaged to a varying extent according to the degree of quality control applied by the corresponding restaurants. Test methods were shown to possess different statistical correlations. Highly significant correlations were found between TPC and Foodoil sensor (c.f=0.93) and between Oxifrit and Fritest (c.f=0.94), each of which were also correlated relatively well to the TPC. Peroxide value followed by %FFA did not significantly (p<0.05) correlate with the TPC. Significant linear relationships (p⊕0.05) were found between the TPC and each of the other indicators but %FFA and peroxide value.

A comparative study of analytical methods for evaluation of soybean oil quality

This study is focused on the improvement of soybean oil stability by addition of additives and blending with more stable oils. The methods for evaluation of oil deterioration include changes in dielectric constant (DC), total polar (TP) compounds, refractive index (RF), fritest (FT), acid value (AV), iodine value (IV), anisidine value (AnV), carbonyl value (COV), viscosity and color. Statistically significant correlations were obtained between changes in DC and increase in the TP compounds, RF, FT, AV, AnV, COV and the decrease in the IV, respectively. Food oil sensor reading of 4 as a measure of changes in DC of oil has been suggested as the criterion of low oil quality. Consequently, the cut‐off level for straight and blended soybean oils were thereby identified by using the above parameters.

Quality assessment of industrial prefried french fries

An industrial production of prefried french fries using palm oil as a frying medium was studied over a period of 12 days. Samples of oils and french fries were withdrawn once a day. The quality of both the oil and the french fries was assessed using two types of tests. Some tests, such as the determination of free fatty acid (FFA) and the determination of thiobarbituric acid value (TBA), oxifritest and Food Oil Sensor correspond to what was used by a quality control laboratory. More elaborate techniques such as the determination of polar components, polymers and cyclic fatty acid monomers (CFAM) were also used. Only small increases of FFA, TBA, polar components and polymers were observed. However, in the case of palm oil, which contains a high percentage of diglycerides, it is more reliable to determine the quality of the oil using the amount of polymers instead of polar components which may include some diglycerides. Thus a high “polar components” value (up to 20–25%) would not necessarily reflect an altered sample. The maximum amount of CFAM detected was 0.1% and they did not seem to be preferentially adsorbed on the french fries. These results, along with the sensory evaluations, showed that the french fries obtained in these production conditions were of good quality as far as the fat was concerned.

A technique for monitoring the quality of used frying oils

AbstractThe objective of this work was to develop a practical method for monitoring the quality of oils during the frying process. A special effort was made to find a technique that would not be affected by dilution, since replenishment with fresh oil to varying degrees is a frequent necessity. Nine analytical methods, i.e., measurements of viscosity, polymers, change in dielectric constant, polar compounds, dimers, free fatty acids, smoke point, carbonyls and cyclic monomers, as well as certain combinations of these measurements were evaluated. Since each single method was influenced by replenishment with fresh oil, combinations of two methods were studied in an attempt to produce a single value unaffected by dilution. The ratio polymer/FOS (polymers according to Peled's technique of methylation and extraction and change in dielectric constant by Foodoil Sensor readings) proved not only to be adequate for monitoring the quality of the used oil, but also was affected minimally by replenishment.

Changes in physical and chemical properties of shortenings used for commercial deep‐fat frying

AbstractThis study evaluated some of the changes that occur in shortenings used for commercial deep‐fat frying in fast‐service restaurants. Foods cooked in partially hydrogenated soybean oil were battered chicken parts and french fries. Sixty‐five samples of fresh and used shortenings were collected from nine restaurants on three occasions over a three‐month period. Frying periods varied from 0 to 300 hr, and most samples were taken just before the used fat was discarded. For fresh shortenings, percentages of polar materials, free fatty acids (FFA), materials not eluted by gas chromatography, and fatty acid profiles differed only slightly. For used samples, there were marked variations in these analyses and in increases of dielectric constant measurements. Frying times were highly correlated with increases in dielectric constant, polar materials and FFA. The greatest change in fatty acid profiles occurred intrans‐C18 monoenes which decreased from over 40% to as low as 13%. Due to lipid exchange with chicken fat, both oleic and linoleic acids increased in the shortenings with hours of use, whereas stearic acid decreased. There were high correlations, among increases in dielectric constant, percentages of polar materials and FFA, demonstrating that each of these methods could predict degradation of the shortening. However, the increase in dielectric constant, as measured by a Foodoil Sensor (FOS), was the most convenient for quality control in restaurant situations. In most cases, used shortening was discarded before 100 hr of frying time; and only a few of these samples had FOS readings near 4.0, FFA over 1.00%, or percentages of polar materials over 27%. These values have been suggested as discard criteria. However, a number of samples used between 100 and 300 hr exceeded these limits. There is a need to specify suitable limits, related to quality and health factors, to determine at what point a cooking fat should be discarded.

A comparative study of analytical methods for quality evaluation of frying fat

AbstractFour quick‐test methods (the Foodoil sensor, RAU‐Test, Fritest® and Spot test) and two ordinary laboratory methods (the free fatty acids and GLC determination of triglycerid dimers) were compared to a standard method (column chromatographic determination of polar compounds). One hundred samples collected from fast food shops and restaurants were included in the investigation. The Foodoil sensor showed the highest correlation to the standard method (c. f.=0.94). The RAU‐Test, Fritest® and Spot test were also well correlated to the standard method. It was easier to compare the colour of the reaction mixtures to the colour scale of the RAU‐Test than to that of the Fritest®. The amount of free fatty acids were found to be an unreliable indicator of deteriorated frying fat. The triglyceride dimers could not be quantified, but assessment by visual comparison of the peak pattern in the chromatogram corresponded well with the results of the standard method.

Changes in dielectric constant as a measure of frying oil deterioration

AbstractA soybean oil, a hydrogenated vegetable frying shortening and an animal‐vegetable shortening were heated at 190 C for 8 hours each day for 4 days with and without the frying of potatoes. Samples were taken periodically and analyzed for various changes normally used to measure frying oil deterioration. The changes in the dielectric constant were determined with a patented instrument called the Food Oil Sensor. This instrument is standardized with 3. sample of the fresh oil, and it then measures the change in the electric capacitance of the heated oil samples. The dielectric constant of all three shortenings increased linearly with heating time. The greatest change occurred in the soybean oil sample and the smallest change in the hydrogenated vegetable shortening. For each shortening the increase was somewhat greater during frying than during heating without frying. Statistically significant correlations were obtained between instrument readings and increase in the total polar materials, the color, the peroxide values, the diene content, and the free fatty acids and the decrease in the iodine values.