Changes in dielectric constant as a measure of frying oil deterioration

Abstract

A 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.

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

“…As the number of polar molecules increases, the DEC of the oil increases. DEC of frying oils have been reported to increase linearly during deep frying (9) and have high correlations with TPC (10,11). These results are in agreement with those of the present study.…”

“…However, it should be noted that different types of oils show different DEC variations during frying. For example, nonhydrogenated vegetable oils show greater changes in DEC than animal fats, and the DEC of animal fat is more variable than that of hydrogenated oils (9). Furthermore, oils of the same type, but differing fatty acid profiles, like the three high-oleic canola oils in this study, can also show different DEC variations during frying.…”

Frying Performance of No‐trans, Low‐Linolenic Acid Soybean Oils

“…The greatest changes in CDA content occurred at the beginning of the frying period: after day 5 the evolution in the CDA content was much slower. A previous study showed the same trend in CDA development during the initial stages of frying [18]. All the oils had reached their maximum levels of CDA by day 6.…”

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

“…Peroxides were present at reduced concentrations after the first day of heating (Tables 1-4), as expected owing to the rapid decomposition of peroxides that occurs at temperatures greater than 100°C (9,19). PV determination is best used as an indicator of oxidation at storage temperatures well below 100°C (9).…”