During heat treatment, fat is subjected to hydrolysis, oxidation and polymerization that results in quality deterioration with respect to sensory quality and nutritive value. Though, synthetic antioxidants are widely used to stabilize heating oils, concern for safety has shifted the focus to replace them with safer natural counterparts. The present study was undertaken to study the quality changes in groundnut and cottonseed oils with and without added pomegranate peel phenolic extracts (PPPE) during heating in a model system. Experimental samples included two levels of PPPE (250, 500 ppm) added to groundnut and cottonseed oils. Oil samples were heated at a temperature 180±5ÚC for upto 24 hrs in batches of 4 hrs. Oil samples were analyzed for various quality parameters. Peroxide value of control oil increased continuously with time of heating. But the variations of peroxide value in antioxidant added oils did not steadily increase. Thiobarbiutric acid value increased higher in control oil compared to antioxidant added oil. Iodine value and total antioxidant capacity decreased maximum in control oils and minimum in antioxidant added oils. Maximum increased in viscosity was observed for control oil compared to PPPE added oils. Fatty acid composition was also affected by the varying heating time, but the addition of PPPE protects the changes and fatty acid composition. All the quality parameters were affected at higher level by heat treatment in cottonseed oil compared to groundnut oil. In conclusion, PPPE showed good antioxidant capacity and could be used as natural antioxidant to improve the stability and safety of edible oils.
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Keywords: Pomegranate, peel, antioxidants, frying and stability
Lipid peroxidation is responsible for the quality deterioration of vegetable oils, fats and other food systems. Due to these changes, consumers do not accept oxidized products and industries suffer from economic losses. The oil industry has to pay special attention in this context, as oils, fats and fatty foods suffer stability problems. Due to cost-effectiveness of synthetic antioxidants, use of natural antioxidants is increasing now days. The search for cheap and abundant sources of natural antioxidants is attracting worldwide interest. Pomegranate peels are waste products of the pomegranate industries. Use of such materials can reduce the product loss with minimum cost.
In recent time, the demand and consumption of fried foods has increased throughout the world due to their pleasant sensory attributes.
Oils are rich sources of unsaturated fatty acids, hence, more susceptible against oxidative damage (Yoshida et al. 1990). During storage and heat treatment, fat is subjected to hydrolysis, oxidation and polymerization that results in quality deterioration with respect to sensory quality and nutritive value (Che Man et al. 1999). The hydrolysis of lipids, which contain short chain fatty acids, result in the formation of unpleasant taste and aroma, whereas the presence of long chain fatty acids does not cause any detectable changes in sensory features of the product. Free fatty acids (FFAs), which appear as a result of hydrolysis, can further undergo oxidation reaction. In the presence of oxygen, peroxides and hydroperoxides are formed. These primary products are rapidly decomposed to form a variety of secondary products, such as aldehydes, ketones, alcohols, hydrocarbons and polymers among others (White 1991; Boyd et al. 1992; Hamilton 1994; Takeoka 1996).
During the course of heating, fats and oils are partially converted into volatile products, nonvolatile oxidized derivatives and dimeric, polymeric and cyclic substances. Various chemical reactions take place which are responsible for thermal deterioration, like formation of peroxides, decomposition of peroxides to carbomyles, epoxy hydroxyl fatty acid and polymerization of partially oxidized fats (Murray et al. 2000). All these reactions result into degenerative changes, to cause increased anisidine value, peroxide value, viscosity, refractive index, free fatty acids and 2-thiobarbituric acid (TBA) value and decreased in iodine value and antioxidant capacity of oil (Nawar 1977). Due to these changes, consumers do not accept oxidized products and industries suffer from economic losses. The oil industry has to pay special attention in this context as oil, fat and fatty foods suffer stability problems (Wu and Nawar 1986).
There is growing interest among food scientist to identify antioxidants that are safe and natural origin. Thus natural antioxidants have become the focus of intensive researches. Several sources of natural antioxidants have been investigated, including plants and microorganisms. Plant are rich source of natural antioxidants of which the best known as tocopherols, carotenoids, vitamin C and different phenolics (Vichi et al., 2001).
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With increased knowledge on the toxicology of food additives many synthetic antioxidants previously permitted for use in foods are either banned as their use is restricted. With the limitation of such antioxidants, attention is now focused on the use of the naturally occurring antioxidant substances for stabilizing oils. Recently, it has been focused on the addition of polyphenols to food and biological systems, due to their well known abilities to scavenge free radicals, i.e. antioxidant power (Steinberg, 1992).
The pomegranate (panica granatum L.) is one of the oldest edible fruits and is widely grown in many tropical and subtropical countries (Salaheddin and Kader, 1984). Pomegranate juice and peel contain substantial amounts of polyphenols such as, ellagic acid and gallic acid (Loren et al., 2005). It has the preparation of tinctures, cosmetic, therapeutic formula and food recipes (Finkel and Holbrook., 2000). In this regard pomegranate peel is a good source of antioxidants (Singh et al., 2001).
In view of the above, the present study was planned to evaluate the effect of high temperature on oil stability at varying period of time and also to evaluate the effect of pomegranate peel phenolic compounds on oil stability at high temperature.
Antioxidant potential of Pomegranate peel polyphenols in two different plant oils heated in a model system.
Materials and Methods
Procurement of raw material and preparation of dried pomegranate peel
The oil selected in this experiment included groundnut oil and cottonseed oil which were purchased from a local market of V.V.Nagar. Pomegranate peel was collected from various fruit juice centre. Pomegranate peel was washed thoroughly with a tap water. Then the excess moisture of pomegranate peel was removed using a filter paper. It was dried in an oven at 60ËšC for 24 hrs. The dried peel was coarsely crushed in pestle and mortar after that, it was ground in a grinder and the fine powder was passed through a 400 mesh size sieve and then it was packed and stored at -20ËšC until extraction was done.
10 gm of dried pomegranate peel was extracted with 50 ml of methanol on shaker (New Brunswick scientific, USA) at 120 rpm for 30 minutes. The content was centrifuge (Remi Research Centrifuge R-24) for 15 min at 4000 rpm and was filtered through Whatman filter paper No. 42 to remove fine particles. The residue was reextracted using 25 ml of methanol, twice. Then the filtrates were pooled and concentrated to make total phenol concentration to 500 mg of total phenol per ml, and the extract was stored in a freezer at -20ËšC.
Estimation of total phenolic compound
Total phenolic compound were determined based on assay original developed by Chandler and Dodds (1983) using folin ciocalteu phenol reagent. Standard series of known concentration of gallic acid was prepared and final volume was made to 2 ml with 95% methanol and there after treated in the same way as sample. For blank, 2 ml of 95% methanol was taken and there after treated in same way as sample.
Addition of pomegranate peel phenolic extraction (PPPE)
Appropriate amount of PPPE obtained was added at a concentration of 250 ppm and 500 ppm to 250 ml of oil and was heated at 60ËšC on a magnetic stirrer for proper mixing of PPPE with oil. These are considered as experimental oils.
Thermal treatment to oils
100 ml of above properly mixed samples were taken individually in 250 ml beaker and was placed in an oven at 180ËšC ± 5ÚC temperature for varying period of time (0 hrs, 4 hrs, 8 hrs, 12 hrs, 16 hrs, 20 hrs and 24 hrs). Control samples (oil) were also placed in same manner to compare the efficacy of natural antioxidants.
Analysis of Physico-chemical characteristics of oil
Peroxide value was determined according to the method given by AOCS, 1973. TBA value was measured by the method given in IUPAC pure and applied chem., (1989). Anisidine value was measured according to . The totax value was calculated using the following formula: 2 - Peroxide Value + Anisidine value. Viscosity was measured using a Brookfield viscometer at 25ËšC.
Fatty acid composition
To determine the fatty acid composition of the fat, gas liquid chromatography (GC) was used. Fatty acid methyl esters (FAMEs) were prepared as per the method of Christie (1982). About 1-2 drops of oil was taken in a clean screw capped tube and 5 ml of 0.5 N methanolic sodium methoxide was added. Tube was capped and heated in a boiling water bath for 10 minutes. After cooling, 0.5 ml of Boron Trifluoride (14% BF3) was added, again heated in similar manner for 5 minutes for complete methylation and that tube was allowed to cool at room temperature. Spectroscopic grade hexane (2 ml) was added to the tube, mixed on cyclomixer. Fatty acid analysis was performed using gas chromatography GC (Model: MS auto system XL, Perkin-Elmer) equipped with a hydrogen flame ionization detection using a 250mn (ID)´25 M (length) capillary column substrate with BP 225. Column was operated with programming from initial temperature of 65ÚC, which was increased to 220ÚC@10ÚC per minutes. Injector temperature was 250ÚC while detector temperature was 300ÚC using 1:50 split injection with a hydrogen carrier gas flow rate of 45 ml/minute while air flow rate of 450 ml/minute through the column. Total analysis time taken for all individual FAMEs was about 30 minutes. Methyl esters were identified and quantified by comparing the retention time and peak of the unknowns with those of the fatty acid methyl ester standards.
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All results were presented as means ± S.D. difference between variables were tested for significance by using a one ways analysis of variance procedure, Duncan, using a level of significance p<0.05 (SPSS for windows 10.0). Correlation analysis was performed using MS-EXCEL.
Results and discussion
Peroxide value (PV)
Peroxide value is conventionally used as measure of oxidative deterioration of oil, fat and fatty food (Kochhar et al., 2000). High peroxide values are definite indication of rancid fat, but moderate values may be the result of depletion of peroxides after reaching high concentration. The mean values of peroxide value of groundnut oil and cottonseed oil heated at 180ËšC for varying period of time with and without PPPE are summarized in table no.1.
The PV was increased significantly in both the type of oils till 8 hrs of heating in control oils as well as oils added with 250 and 500 ppm PPPE. The increased in PV was higher in cottonseed oil (423.8 % and 660 % at 4 hrs and 8 hrs respectively) compared to groundnut oil. These results agreed with Yoshida et al., (1991) who reported that the effect of fatty acid on peroxide accumulation in the oils during microwave heating. This increased in PV suggest that free radicals are accepted by polyunsatureated fatty acid in this oil but in the presence of (O2) oxygen, this lead to rapid accumulation of hydroperoxides.
The similar results were also reported by Parinitha and Saraswathi (1977) who reported that oils had a highly significant increase in peroxide value. Nirmala et al. (1996) reported increase in the peroxide value during storage of edible oils. Susheelamma et al. (2002) reported a continuous increase of PV during three successive frying of model dough in all investigated samples of oils and blends.
After reaching the maximum values, the peroxide value was decreased significantly for 12 to 24 hrs of time interval. Che Man et al., (1999) reported a decrease in the PV of oil sample after an initial increase. A significant decrease of PVs after reaching maximum values confirm that peroxides which are formed in the early stages of oxidation are unstable components and are highly susceptible to further changes that results in the formation of secondary products of oxidation (Orthoefer and Coopper, 1996). The oils added with PPPE at 250 and 500 ppm levels showed similar trend but the changes were minimum compared to control oil. The PPPEs at both the concentrations, controlled the PV significantly, revealing good antioxidant efficacy in stabilizing of both the oils. The similar results were also reported by Yasoubi et al., (2007) who reported the antioxidative property of pomegranate peel extract in soyabeans oil indicated by lower PV during heating at 600C. Sagir et al., (2006) reported the antioxidant activity of different solvent extract of rice bran in sunflower oil indicated by lower peroxide value during accelerated storage of sunflower oil. Ahindra Nag (2000) reported a sharp rise in peroxide value with increasing temperature. With the addition of antioxidant, the peroxide value remained nearly constant with increasing temperature when they used capsicum powder as an antioxidant to stabilize flax seed oil. They showed that incorporation of oil soluble capsicum extract moderates the rate of oxidation to such as a degree that almost no rise in peroxide value.
Iodine value (IV)
The mean values of Iodine value of the groundnut oil and cottonseed oil heated at 1800C for varying period of time with and without PPPE are summarized in table no. 2.
The iodine value was decreased significantly in both the type of oils upon 4 hrs of heating in control oils as well as oils added with 250 and 500 ppm PPPE.
The % change at this time of heating was minimum in groundnut oil added with 500 ppm. Further the Iodine value showed decreasing trend till the 24 hours of heating in both the type of oils.
The present study showed decreased in iodine value but when compared with both oils sample, not much significantly difference was seen. These observations are in accordance with the results obtained by Menlick (1957) who reported decreased linolenic acid content in heated oil and he also reported an inversely relation between iodine value and heating. The decrease in iodine value might be due to formation of dimers, polymers and peroxides at double bond. He also reported higher decreased in iodine value in mustered oil as it contained more amount of PUFA compared to groundnut oil and cottonseed oil.
Sultana and Sen, (1979) reported that the deteriorative changes during heating of groundnut oil vanaspati and safflower oil. Results showed that deceased in Iodine value as the heating time increase. Parvatham et al., (1994) reported decreased iodine number after 6 hrs heating of palm oil.
The decreased in iodine value was low in added of PPPE added samples than control samples, and it is -4.2 % and -15.9 % in groundnut oil and cottonseed oil respectively, at 24 hours of the heating. The PPPEs at both the concentrations 250 and 500 ppm, control the iodine value significantly and these results are also in accordance with the Weng and Wang (2006) who have been reported the effectiveness of antioxidants 1,1-Di-(2',5'-Dihydroxy-4'-Tert-Butylphenyl) ethane: a novel antioxidant on iodine value during frying experiment conducted at 180ËšC upto 81 hrs. They also reported that the change of iodine value can also be at indicator of the effectiveness of the antioxidant used and, PPPE showed significant protection against decrease in iodine value of both the oils at 2 different levels confirmed the antioxidant property.
P-anisidine value (AV)
The mean values of P-anisinde value of groundnut and cottonseed oil heated at 180ËšC for varying period of time with and without PPPE are summarized in table no. 3.
The P-anisidine value was 6.33 to 8.55 for groundnut oil and 22.48 to 31.80 for cottonseed oil at 0 hrs (initial value). The P-anisidine value was increased significantly in both the type of oils upon 4 hrs of heating in control oils as well as oils treated with 250 and 500 ppm PPPE. The % change at this time of heating was lower in groundnut oil compared to cottonseed oil. Further, the AV showed significant increasing trend till the 24 hrs of heating in both the type of oils. The present study shown the relative increase in the P-anisidine value of control oils as well as PPPEs treated oils. The similar results were also reported by Parvatham et al., (1994). They reported increasing in P-anisidine value after 6 hours heating of palm oil. Lee et al., (2004) reported increased AV value in fried products during frying in soyabeans oil.
Choe et al., (2005) have been showed as the lipid oxidation goes on, unstable primary oxidation products of lipids are often decomposed and produce many volatile compounds such as aldehydes and the newly formed aldehydes in heating oils could cause relatively increase AV value.
At the every time period of heating methanolic extraction of pomegranate peel showed protecting effect on AV value by preventing the formation of newly aldehydes compounds. This may be related to the observation of Warner (2002) who suggested less production of aldehydes from oxidized lipids which can contribute to the flavour stability of the fried product during storage, because most aldehydes formed by decomposition of oxidized lipids cause off flavour.
PPPE showed significant protection against increasing AV value of both the oils at two different levels, confirmed their antioxidant property by increasing the rate to extend the induction period of lipid oxidation and decreasing decomposition of the oxidized lipids. The similar results are also reported by Saddiq et al., (2005) who reported the antioxidant activity of 80% methanolic extract of rice bran was the most effective by lowest rise in p-anisidine values of sunflower oil during accelerated storage.
Thiobarbituric acid (TBA)
TBA value measures the formation of secondary oxidation products, mainly malonaldehye, which may contribute to an off-flavour in oxidizing oil Rossel (1994). The mean values of TBA value of groundnut oil and cottonseed oil heated at 180ËšC for varying period of time with and without PPPE are summarized in table no.4.
The TBA value was 3.05 to 3.83 for groundnut oil and 5.75 to 7.00 for cottonseed oil at 0 hrs. TBA value increased significantly in groundnut oil upon 4 hrs of heating in control oil as well as experimental oils added with 250 and 500 ppm PPPE i.e. (5.28, 4.28 and 3.48 respectively). The % change at this time of heating was lower in groundnut oil compared to cottonseed oil and also in experimental oils treated with 250 and 500 ppm PPPE. TBA value showed significantly increasing trend till the 24 hrs of heating of control as well as experimental groundnut oil. The similar results were also reported by Pravatham et al., (1994) who reported increased TBA value after 6 ours hating of palm oil.
The TBA value was increased significantly in cottonseed oils till 16 hrs of heating in control oil as well as oil added with 250 and 500 ppm PPPE and it was 18.05, 15.50 and 14.27 respectively. These may be related to the observation of Kishida et al (1993) who compared the results of oxygen consumption with the content of TBA reactive substances (TBARS) and with the content of melonaldehyde (MDA) specifically determined in oleic, linoleic and linolenic acids. They found that TBARS are a good indicator of lipid oxidation only in the early phase of the reaction when the O2 consumed by the oleic acid was about 700 mmol/L, the level of TBARS reached at maximum. After reaching maximum level the TBA value was decreased in cottonseed oil significantly at 20 hrs and 24 hrs of the heating period but the decreasing level high in control oil compared to PPPE added oil.
During entire period of heating TBA values showed minimum increase in oils added with PPPE which prevent the oxidation process in unsaturated fatty acids and oxidative rancidity. As a result, there is decease in the formation of secondary oxidation products i.e. aldehydes or carbonyls, which may contribute to off-flavour of oxidizing oils. These observation in accordance with the results obtained by Yasoubi et al., (2007) who reported the antioxidant property of pomegranate peel extract in soyabean oil indicated by lower the TBA value, during heating at 600C. Ahindara Nag (2000) reported capsicum powder used as an antioxidant to stabilized flax seed oil, which prevent increased in TBA values.
Total antioxidant capacity (TAC)
The total antioxidant capacity of control as well as experimental oils is shown in table no. 5. The TAC of control oil at 0 hrs was 66.80 % to 83.18 % in groundnut oil and 64.20 % to 78.72 % in cottonseed oil was significantly higher in experimental oils, in which PPPE was added, these could be due to the addition of pomegranate peel phenolic extract and it was not a concentration dependent. The total antioxidant capacity was decreased significantly as the time of heating increases in both groundnut oil as well as cottonseed oil. The decrease in TAC was 17.83 % in groundnut oil and 13.77 % in cottonseed oil at 24 hrs of the heating.
These results were in accordance with the Warner and Knowltan (1997). They reported the loss of antioxidant activity, after longer heating times at high temperature which may be due to various chemical reactions occurring during oxidation, leading to the formation of hydroperioxids, hydrolysis, polymerization and chemical decomposition, which lead to deterioration in oils and fats giving rancidity.
Addition of PPPE showed significant protective effect on total antioxidant capacity by preventing lipid peroxidation so the percentage change was lower compared to their respective control oils but it was not a concentration dependent. The similar results were reported by Yasoubi et al., (2007). They reported the pomegranate peel extract possessed a relatively high antioxidant activity in soybean oil during heating at 60ËšC and it might be considered as a rich source of natural antioxidant.
Anwar et al., (2000) reported phenolic antioxidants which inhibit lipid peroxidation so it did not interrupt oil and fat deterioration. Weng and Wang (2006) reported the effectiveness of DHPE as an antioxidant was evaluated in soybean oil, lard and emulsion systems showed that at 63±10C in both oil, DHPE showed good antioxidant activity. Iqbal and Bhanger (2005) reported that the methonolic extraction of garlic extract significantly increased antioxidant capacity at all the concentration, revealing an increase in oxidative stability of the treated sunflower oil. Sagir et al., (2006) reported that the methoanolic extraction of rice bran extract was significant and most effective to enhance the oxidative stability of sunflower oil in terms of increased antioxidant capacity.
Totax value (TV)
The mean values of Totax value of groundnut oil and cottonseed oil heated at 1800C for varying period of time, with and without PPPE are summarized in table no.6.
The Totax value was 12.85 to 15.23 for groundnut oil and 24.13 to 33.90 for cottonseed oil at 0 hrs. The totax value was increased significantly in both type of oils as well as oil treated with 250 and 500 ppm PPPE. Graphical presentation of percentage change in totax value is shown in figure no. 6.
The totax value showed significantly increasing trend till the 24 hrs of heating in both the type of control as well as experimental oils. The similar results were reported by Parvatham et al., (1994). They reported that the totax value increased in the palm oil after 6 hrs of heating. Nirmala et al., (1996) reported the increased totax value during storage of the edible samples.
During entire period of heating time, methanolic extraction of pomegranate peel showed protective effect on totax value by preventing the lipid oxidation process as a result the formation of hydroperoxides, aldehydes, malonaldehyde decreases. These results are supported by Che Man et al., (1999). They reported that the α-tocopherol was more effective in reducing anisidine and totax values in refined, bleached and deodorized (RBD) palmolein during frying.
The colour values of control oil as well as experimental oils are shown in table no. 7. The mean value of colour of control oil at the 0 hrs was 0.04 for groundnut oil and 0.06 for cottonseed oil and it was found significantly higher in PPPE added oils and they were concentration dependent. The colour values were significantly increased in both control as well as experimental oils, as the time of heating increases. The colour value increased significantly as the heating time increases and these may be due to the increased rate of polymerization due to unsaturation in the triglycerides. The results are similar in accordance with the Parvatham et al., (1994). They showed that colour of crude palm oil changed after 6 hrs of heating. Hidaka et al., (1991) showed that the brown colour developed in oil which used in vacuum frying. Vegammai and Gouri (1995) have been shown the colour of the oil darker after repeated heating. Khatoon and Krishona (1998) reported extensive polymerization of the sunflower oil during continuous heating in an open pan.
The mean values of viscosity of control as well as experimental oils are shown in table no. 8. The viscosity of control oil at the 0 hrs was 54.89 CP in groundnut oil and 49.94 CP in cottonseed oil and it was increased as the time of heating increases in both the type of oils. The increased in viscosity at the24 hrs of heating was 57.11 CP in groundnut oil and 64.76 CP in cottonseed oil and it was significantly different.
The significant increase in viscosity of oils during heating can be attributed to the formation of cyclic compounds and non volatile decomposition products eventually produced during thermal heating. These reactions are temperature dependent. The similar results were also reported by Khatoon and Krishana (1998). They reported increased viscosity of sunflower oil at 180ËšC for 8 hrs of heating. Shyu et al., (1998) showed viscosity change in palm oil during frying.
Addition of PPPE showed significant protective effect on viscosity. The percentage change was lower in experimental oils compared to control oils. The viscosity of antioxidant added oils were found to be lower than those of the control oil, because the antioxidants may help in delaying the formation of polymers during heating.
Fatty acid composition:
The relative percentage of C14, C16, C18:1 and C18:2 were 0.21%, 14.39%, 47.83% and 37.47% respectively in groundnut oil and was remain approximately same in the PPPE added oils at two different level. In cottonseed oil, the relative percentage of fatty acid were found to be 0.65%, 24.69%, 3.22%, 18.38% and 50.49% for C14, C16, C16:1, C18:1 and C18:2 respectively. These fatty acid composition of cottonseed oil were also remained unchanged in response to the addition of PPPE at two different levels. These results are similar as reported by Meyer (2002).
When both the oils were heated at 180ËšC ± 5ÚC for varying period of time showed slight decreased in a sum of saturated fatty acid at every stage of heating. In case of MUFA, it was decreased in groundnut oil due to a heat treatment. In cottonseed oil it was found unchanged. The PUFA showed decreasing trend due to the heating process.
The decreasing in MUFA and PUFA is due to the rate of fatty acid break down is related to the number of double bond in the carbon chain of the molecule. As the number of double bonds increases, the rate of oxidation increased (Yoshida et al., 1992).
The oils added with two different level of PPPE showed a good antioxidant property and as protected against the oxidation process at the double bond of fatty acid. This is confirmed by the results obtain for the ratio of SFA to PUFA (s/p) as mentioned in table no. 9(a) and 9(b). These results are similar as reported by Chung et al., (2006). They reported that the fatty acid composition of the products fried in soybean oil containing different amounts of sesame oil and they showed minimum loss of linolenic acid in soybean oil which was added with more amount of sesame oil. A graph of fatty acid composition depicted in Figure 1.
Correlation coefficients of heating time with quality characteristics of control groundnut and cottonseed oil have shown in table no. 10 (a).
The correlation coefficient data of control groundnut oil and cottonseed oil have shown a good relationship between heating time and various quality characteristics. Heating time was negatively and significantly correlated with iodine value and total antioxidant capacity whereas, insignificantly correlated with peroxide value. It has shown negative relationship with peroxide value with groundnut oil but positive relationship with cottonseed oil. Heating time has shown positive and significant relationship with anisidine value, thiobarbituric acid value and totax value.
Table no. 10(b) and 10(c) showed a correlation coefficient of heating time with quality characteristics of PPPE that is (250 ppm and 500 ppm) added groundnut oil and cottonseed oil.
These data showed similar trend as it was observed in control groundnut oil and cottonseed oil. When the relationship between iodine value with anisidine value, thiobarbiutric acid value, total antioxidant capacity and totax value was observed, it has shown a strong protective effect of PPPE in stabilization of the oil.
From the above it can be inferred that peroxide values of all PPPE added oils were lower than control oil. Similarly, higher (500 ppm) level of PPPE added resulted in lower peroxide value than the low level (250 ppm) PPPE. The peroxide value of all PPPE added oils peaked at around 8 hrs of heating and thereafter remained more or less constant.