Effects of adding some essential oils (mint, thyme and rosemary) to palm oils used in pre-frying process

In this study, Agria type finger potato samples (n=27) grown in Afyon region were subjected to pre-frying (180° C and 40 - 50 sec) in palm oil (containing olein and stearin fractions and imported from Malaysia). Palm samples oil used per-frying process were divided into four groups: control (without volatile oils), those containing rosemary, thyme and mint essential oils (produced by hydrodistillation method) in certain proportions (% 0,25, % 0,50 and % 1,00) The selected essential oils are a natural antioxidant source and are found in high amounts in the flora of Turkey. It is possible to easily provide these oils as a domestic and cheap economic source. It is aimed to increase the number of uses of palm oil in pre-frying processes with the addition of essential oil. All palm oil samples used in pre-frying (control and other oils with added volatile oil) were used until the total polar substance amount (TPM) values reached the official maximum limit of % 25 during pre-frying. Some physico-chemical analyses (% TPM, Lovibond color values, refractive index, free fatty acid amount [FFA], acid number, peroxide number [PS] and specific absorbance values absorbed at UV [232 and 270 nm] and fatty acid profile with GC capillary column method) were performed at certain stages (3rd, 8th and last) in all oil samples. According to TPM values, while the final pre-frying stage was the 13th for the control, this value increased for samples with added essential oil (14th - 19th). A remarkable changes was determined in the values of LRS (R: 0,9 –3,6; Y:7,6 – 20), refractive index [RI] (1,46721 – 1,.47473), FFA ( 0,13 – 0,88%), AS (1,3 – 8,8 mg KOH/ g oil ), PS (3,18 – 54,23 meqO2/kg.oil) – 2,591) in the palm oil samples with the thermal treatment time/number and essential oil addition. PS values of palm oil samples increased continuously with frying time and number except for decreases in 16th and 17th samples containing %0,50 and % 1,00 peppermint essential oil. In all palm oil samples, the values of major fatty acids palmitic acid [C16:0] (% 46,55–53,56), stearic acid [C18:0] (% 3,64–8,20) and SFA (% 52,40–60,41) together with some minor fatty acid isomers such as caprylic (C8:0) and capric (C10:0) [Short-chain saturated fatty acids], lauric (C12:0), myristic (C14:0), palmitoleic acid (C16:1), behenic (C22:0) and lignoceric (C24:0) increased relatively with pre-frying, while oleic [C18:1 omega 9, MUFA] (% 36,55–33,63), linoleic [C18:2, omega 9 and essential fatty acid, PUFA] (% 36,55–33,63) increased. MUFA (% 36,81 – 35,85), PUFA (% 10,74 – 5,12) values of (10,54 – 5,07) and linolenic [C18:3, omega 3 and essential fatty acid, PUFA] (% 0,20 – 0,05) acids were found to decrease with heat treatment. This situation was also confirmed by the quantitative analysis of omega (3,6 and 9) fatty acids. Trans fatty acids were not determined in palm oil samples. In addition, MUFA/PUFA, linoleic/linolenic (52,19 – 103,39), oleic/linoleic, palmitic/linoleic (4,42 – 10,53), linoleic/linolenic and TOSI values calculated based on fatty acids increased as essential oil addition to palm oil samples, while iodine number (52,65 – 39,89), Ox Succ and Cox parameters tended to decrease. Characterization of palm oil samples according to fatty acid profile during heat treatment was carried out by multiple data (chemometric) analysis (PCA). In the light of the research findings, it was concluded that rosemary EO (essential oil) was more effective than thyme EO, and the thyme EO was more effective than the mint EO in terms of preserving oxidative stability in palm oils during pre-frying.