Consequence of Commercial Fish Frying on Some Quality Parameters of Oil with Special Reference to Trans Fat

Abstract

In the present study, the quality of frying oil, as affected by commercial pan fish frying, was investigated. The quality of fresh frying oil, null replenishment (NR) oil, and discarded frying oil were evaluated by drawing out the oil samples from the fryer at the initial stage, just before the addition of new frying oil for level make-up and used oil of the last frying cycle, respectively. The parameters used to assess the quality were the fatty acid composition including trans fatty acid (TFA), free fatty acid, and peroxide values of frying oil. Gas chromatography-mass spectroscopy (GC-MS) was used to examine fatty acids profiles of the frying oils. Trans fatty acid in fresh oils varied from 2.5%–3.8% (except oil-6, which contained 13%), whereas NR oils and discarded oils contained 5.6%–14.8% and 7.3%–20.8% trans fatty acids, correspondingly. Free fatty acid in fresh, NR, and discarded oils were 0.12%–0.24%, 0.22%–1.74%, and 0.80%–3.39%, respectively. Peroxide value in fresh, NR, and discarded oils were determined to be 1.15–3.93, 2.71–7.51, and 2.84–14.68 meq of O₂ /kg oil. It was observed that commercial fryers were not using the proper oil for frying. Furthermore, the last frying cycle just before discarding the oil may be dangerous for the health of consumers due to their significant level of TFA, free fatty acid, and peroxide values.

Keywords:

• Trans fatty acids (TFA)
• Free fatty acids
• Peroxide value
• Commercial fish frying
• GC-MS

INTRODUCTION

Frying is the cooking of foods in hot oil and is a highly versatile process, which has been used since antiquity for the frying of many materials in different types of oils. It involves heat and mass transfer which includes complex interactions between the material and the frying medium.[1] It is a common domestic practice and is also used in the food industry due to the significant sale of many fried foods. The quality of frying oil has an important role to the quality of fried foods. Repetitive use of oil at high temperature in the presence of moisture and air causes thermal degradation of oil.[2,3] This result to change in the fatty acids composition and formation of trans fatty acids.[4,5] In technologically advanced countries, food sources are either trans free or to a limited level due to the strict rules and regulations and application of the latest methodological industrial process to control trans formation.[6] While in Pakistan and in some other developing countries where there is no standards with regard to trans fat, commercial fryers are not using the proper oils for foods frying.

The interest in trans fatty acids has increased in the past few years, because of the relation between trans fatty acid intake and the risk of cardiovascular disease;[7,8] and it could also be associated with chronic respiratory disease, neural degenerative diseases, and cancer.[9] Trans fatty acids are also positively associated with the markers of systemic inflammation in women, particularly the C-reactive protein.[10] More recent studies have suggested that higher intakes of trans fat could induce endothelial dysfunction.[11] However, heat treatments, such as the frying process, have produced diverse amounts of trans-fatty acid depending on the oils used.[12–15 15 The fatty acid composition of the frying oil is an important factor affecting fried food flavor and its stability. However, most trans-fatty acids in these foods have been considered to come from the oil used and not from the process itself.[16] The scientific awareness about the nutritional quality and health implication of trans fatty acid (TFA) are the highly effective issues. Vast parts of the population in many countries, including Pakistan, still consume fried foods in the diet because of their customary eating habits and lifestyle. A few preliminary studies have been reported on trans fatty acid (TFA) contents in hydrogenated fats, butters, and margarines.[17–20 20 The present study deals with the quality changes regarding the alteration of fatty acid composition including trans fatty acids, free fatty acid, and peroxide values in commercial pan fish frying.

MATERIALS AND METHODS

All reagents, chemicals, and solvents used were from E. Merck (Darmstadt, Germany). Trans and cis fatty acid methyl esters (FAMEs) standards (GLC 481-B and 607) were purchased from Nu-Check Prep, Inc. (Elysian, MN, USA). A set of fresh, null replenishment (NR) (just before the addition of new frying oil for level make-up) and discarded oils (used oil of last frying cycle) from each vendor were collected from six fish commercial pan fryers, food street, Hyderabad, Pakistan. Domestic stainless steel, gas-heated uncovered deep fat fryers with 5 to 6 kg oil capacities were used by the commercial fryers. Frying oil samples were taken from two stages: null replenishment (NR) and discarded oil (oil from last frying cycle after frequent replenishment). The NR and discarded oil include, on average, 17 and 57 frying cycles, respectively. Each frying cycle contained 2.5 kg of fish in 5.0 L oil and frying time was restricted to 27 min. Frying temperatures were found to be very high (∼230°C), measured at the time of sampling. The usage of oil, fish and time for frying cycles were just estimated by the kitchen personnel, although there is a doubt about the accuracy of the information provided. A fresh oil sample was taken before the start of frying, null replenishment (NR) and discarded oil samples were also collected from each vendor for analysis. The samples were flushed with nitrogen to retard oxidation and stored frozen at −18°C in caped vials until further analysis.

Peroxide value, expressed in milliequivalents of active oxygen per kilogram of oil (meq/kg), was determined as follows: a mixture of oil and chloroform/acetic acid was left to react with a solution of potassium iodide in darkness; the free iodine was then titrated with a sodium thiosulfate solution using AOCS Official Method Cd 8–53.[21] Free fatty acid content as % of oleic acid, was determined by the titration of a solution of oil dissolved in hot neutral ethanol with sodium hydroxide in the presence of phenolphthalein indicator using AOCS Official Method Ca 5a-40.[21]

For the determination of fatty acid profile of fresh and used commercial oil samples, FAMEs were prepared using standard IUPAC method 2.301.[22] According to the standard procedure the 200 mg of the oil samples were taken in the 50-ml conical flask containing 4 ml of 0.5 N solution of sodium hydroxide and 5 ml of methanolic solution of BF₃. After reflux for 15 min, the extracted methyl esters with hexane were injected in to GC-MS. The GC-MS analysis of FAME was carried out using an Agilent Technologies gas chromatograph (GC-6890 N, Little Fall, NY, USA) equipped with an Agilent autosampler 7683-B injector (Agilent Technologies, Little Fall, NY, USA) and MS-5975 inert XL Mass selective detector (Restek Corp., Benner Circle, Bellefonte, USA). Analytical separation was achieved using a Rt-2560 Biscyanopropylsiloxane capillary column (100 m × 0.25 mm i.d. × 0.25 micron film thickness) for the separation of fatty acid methyl esters. The initial temperature of 140°C was maintained for 2 min, raised to 230°C at the rate of 4°C/min, and kept at 230°C for 5 min. The split ratio was 1:50, and helium was used as a carrier gas with the flow rate of 0.8 ml/min. The injector and detector temperatures were 240°C and 260°C, respectively. The mass spectrometer was operated in the electron impact mode at 70 eV; with an ion source temperature of 230°C, a quadrupole temperature of 150°C, and a translating line temperature of 270°C. The mass scan ranged from 50–550 m/z with an Em voltage, 1035 V.

Peak identification of the fatty acids methyl esters in the analyzed frying oil samples were identified by the similarities of their mass spectra stored in the installed NIST and Wiley libraries. For the quantitative analysis only those methyl esters were included whose matching percentage of their mass spectra were above 97% and quoted as relative percentage with respect to all methyl esters. Each sample was analyzed in triplicate and the data obtained were put into the OriginPro 7.5 program (OriginPro 7.5 SRO, OriginLab Corp., Northampton, MA, USA) and reported as mean ± standard deviation.

RESULTS AND DISCUSSION

The fatty acid profile of six fresh frying oils is shown in Table 1. The major saturated fatty acids (SFA) were palmitic and stearic acid. The highest amount of palmitic acid was found in oil-6 (38.9%), whereas the lowest was found in oil-3 (3.4%). Stearic acid ranged from 2.0–4.7% in oil-3 and oil-2, respectively. Other saturated fatty acids like lauric, myristic, and arachidic acids were present of less than 1% in all fresh frying oil samples except sample-5 which contained 1.3% myristic acid. Among the mono unsaturated fatty acids (MUFA) the key contributor was oleic acid in all samples, and it was found in the range of (21.0%–60.1%), the highest amount of oleic acid was determined in sample-3 and lesser amount in oil-5. Among the PUFA, linoleic acid was found in the range of 11.75%–58.5%, the highest amount of linoleic acid was determined in oil-2 and lowest amount contained in oil-6. The level of linolenic acid was found in the range of 0.8%–9.5%. Among the trans fatty acids, elaidic acid was predominant and present in the range of 2.3%–11.5%, whereas low levels of trans fatty acid (18:2) were determined in all samples except frying oil sample-5.

Table 1 Fatty acid profiles (Mean ± SD) of fresh commercial frying oil samples (%)

Samples	C12:0	C14:0	C16:0	C18:0	C18:1c	C18:1t	C18:2c	C18:2t	C18:3	C20:0
Fresh oil-1	0.1 ± 0.0	0.1 ± 0.0	10.2 ± 0.5	3.9 ± 0.2	23.6 ± 1.2	3.0 ± 0.1	51.6 ± 2.5	0.4 ± 0.0	6.9 ± 0.3	0.2 ± 0.0
Fresh oil-2	—	—	6.9 ± 0.3	4.7 ± 0.2	26.4 ± 1.2	2.3 ± 0.1	58.5 ± 2.6	0.2 ± 0.0	0.9 ± 0.1	0.1 ± 0.0
Fresh oil-3	—	0.1 ± 0.0	3.4 ± 0.1	2.0 ± 0.1	60.1 ± 2.5	2.9 ± 0.01	21.8 ± 1.1	0.1 ± 0.0	9.5 ± 0.1	0.1 ± 0.0
Fresh oil-4	—	0.4 ± 0.01	14.6 ± 0.7	3.2 ± 0.2	24.1 ± 1.2	2.8 ± 0.1	52.2 ± 2.5	1.0 ± 0.0	1.3 ± 0.1	0.4 ± 0.0
Fresh oil-5	—	1.3 ± 0.05	20.5 ± 0.5	3.6 ± 0.1	21.0 ± 1.0	2.7 ± 0.1	50.1 ± 2.4	—	0.8 ± 0.0	—
Fresh oil-6	0.2 ± 0.0	0.9 ± 0.04	38.9 ± 1.5	4.5 ± 0.2	30.8 ± 1.3	11.5 ± 0.5	11.7 ± 0.5	1.5 ± 0.0	—	—

Data represented in Table 2 corresponds to the fatty acid profiles of null replenishment (NR) and discarded frying oil samples. The changes in the amount of fatty acids were observed during commercial frying due to oxidative degradation that leads to decrease in the total unsaturated fatty acids and increase in the saturated fatty acids like the reported study.[23] The alteration in the level of fatty acid including trans fatty acid during frying process may be due to the repetitive use of oils at the high temperature and exchange of fatty acids between the fried food and the oil.[5,24,25]. In the present study, a significant amount of trans fatty acids were found in the all discarded frying oils. Table 2 shows that the range of elaidic acid (C 18:1 t) in a null replenishment (NR) and discarded frying oil samples from 4.9–13.1% and 7.3–18.4%. Out of 6 samples, five samples (1, 2, 3, 4, and 6) contained linoelaidic acid (C18:2 Δ9 Δ12 t-t) in the range of 0.1%–1.7% and 1.4%–2.7% for null replenishment (NR) and discarded frying oils, respectively. The highest amount of trans fatty acid was observed in sample-6 discarded frying oil (20.8%). Which clearly indicates that the last frying cycle just before discarding is very dangerous to the health of consumers. The levels of trans fatty acids in the discarded frying oil samples were significantly higher than in null replenishment (NR). Which may be due to repeated use of frying oils at elevated temperature, and lengthened frying period.[24,25] Among the unsaturated fatty acid, oleic acid (C18:1 cis-9) was the major mono unsaturated fatty acid. Oleic acid is considered to be responsible for lowering LDL cholesterol levels. In null replenishment (NR) and discarded frying oil samples, oleic acid was found in the range of 15.4%–58.2% and 11.1%–54.9%, correspondingly. Polyunsaturated fatty acids (PUFA) have beneficial effects on both normal health and chronic diseases, such as regulation of lipid levels;[26] cardiovascular;[27] and immuno functions.[28] The range of cis C18:2 and cis C18:3 in null replenishment (NR) and discarded frying oil samples were found at 10.2%–55.1%, 0.6%–7.8%, 7.6%–48.7%, and 0.2–5.2%, respectively. The losses in unsaturated fatty acids during frying indicated thermal degradation during the frying process.[29]

Table 2 Fatty acid profiles (Mean ± SD) of null replenishment (NR) and discarded commercial frying oil samples (%)

Samples	C12:0	C14:0	C16:0	C18:0	C18:1c	C18:1t	C18:2c	C18:2t	C18:3	C20:0
Frying oil-1
NR	0.1 ± 0.0	0.2 ± 0.0	14.1 ± 0.6	4.8 ± 0.2	20.6 ± 0.8	5.9 ± 0.2	48.0 ± 2.1	0.9 ± 0.0	5.2 ± 0.2	0.2 ± 0.0
Discarded	0.1 ± 0.0	0.2 ± 0.0	20.6 ± 0.8	6.3 ± 0.3	18.4 ± 0.6	11.8 ± 0.5	38.4 ± 1.8	1.4 ± 0.1	2.1 ± 0.1	0.7 ± 0.0
Frying oil-2
NR	—	—	7.6 ± 0.3	5.4 ± 0.2	25.0 ± 0.7	5.4 ± 0.2	55.1 ± 2.1	0.3 ± 0.0	0.7 ± 0.0	0.5 ± 0.0
Discarded	—	—	10.8 ± 0.5	6.9 ± 0.3	22.1 ± 0.5	8.0 ± 0.3	48.7 ± 1.5	2.4 ± 0.1	0.4 ± 0.0	0.7 ± 0.0
Frying oil-3
NR	—	0.3 ± 0.0	5.7 ± 0.2	3.2 ± 0.2	58.2 ± 2.2	6.7 ± 0.3	17.5 ± 0.6	0.1 ± 0.0	7.8 ± 0.3	0.5 ± 0.0
Discarded	—	0.5 ± 0.0	8.2 ± 0.3	6.3 ± 0.2	54.9 ± 2.3	13.0 ± 0.5	9.5 ± 0.3	1.6 ± 0.1	5.2 ± 0.2	0.8 ± 0.0
Frying oil-4
NR	—	0.4 ± 0.0	16.3 ± 0.6	5.4 ± 0.2	21.6 ± 0.9	4.9 ± 0.2	48.3 ± 1.6	1.4 ± 0.1	1.1 ± 0.1	0.6 ± 0.0
Discarded	—	0.7 ± 0.1	19.7 ± 0.8	9.3 ± 0.4	17.6 ± 0.8	11.8 ± 0.5	36.7 ± 1.4	2.7 ± 0.2	0.6 ± 0.0	0.9 ± 0.0
Frying oil-5
NR	—	1.8 ± 0.1	26.9 ± 1.2	5.2 ± 0.2	15.4 ± 0.5	5.6 ± 0.2	44.5 ± 1.9	—	0.6 ± 0.0	—
Discarded	—	2.7 ± 0.2	32.1 ± 1.5	8.4 ± 0.4	11.1 ± 0.4	7.3 ± 0.3	38.2 ± 1.5	—	0.2 ± 0.0	—
Frying oil-6
NR	0.3 ± 0.0	1.1 ± 0.1	41.7 ± 1.9	7.5 ± 0.3	24.4 ± 1.2	13.1 ± 0.6	10.2 ± 0.4	1.7 ± 0.1	—	—
Discarded	0.8 ± 0.1	1.7 ± 0.1	44.3 ± 1.9	10.1 ± 0.5	14.7 ± 0.5	18.4 ± 0.8	7.6 ± 0.3	2.4 ± 0.1	—	—

Data represented in Table 3 shows the main fatty acid groups (%) and their ratio present in fresh, null replenishment (NR) and discarded commercial frying oils. In the six fresh oil samples, the mean value of total saturated fatty acids was 20.05%, and in null replenishment (NR) the mean value was 24.97%. Upon more frying, this value was further increased in the discarded frying oil up to 32.13%. The mean values of PUFA in the fresh, null replenishment (NR) and discarded oils were determined 44.75%, 40.40%, and 33.01%, respectively. The significant decreases >25% was observed in the poly unsaturated fatty acids, and results supported the previous study.[30] The ratio of saturated/unsaturated FA shows the relation between two major FA groups of the frying oil composition. This value varies in fresh oil samples from 0.10 to 0.80 with a mean value of 0.32. As frying time increases the saturated/unsaturated FA ratio of null replenishment (NR) and discarded frying oil also increases from 0.10 to 1.0 and 0.20 to 1.20, respectively, with a mean value of 0.38 and 0.55. The discarded frying oil samples comprise a larger mean value ratio, which indicates a high proportion of saturated FA produced during the frying.

Table 3 Main fatty acid groups (%) and their ratio of fresh, null replenishment (NR) and discarded commercial frying oil samples

Samples	Σ SFA	Σ UFA	Cis MUFA	Trans MUFA	Σ MUFA	Cis PUFA C18:2	Trans PUFA C18:2	Cis PUFA C18:3	Σ PUFA	Σ TFA	Cis PUFA/ SFA	SFA/ UFA	Trans/ cis	C18:2/ C16:0
Frying oil-1
Fresh	14.5	85.5	23.6	3.0	26.6	51.6	0.4	6.9	58.9	3.4	4.0	0.2	0.04	5.1
NR	19.4	80.6	20.6	5.9	26.5	48.0	0.9	5.2	54.1	6.8	2.7	0.2	0.09	3.4
Discarded	27.9	72.1	18.4	11.8	30.2	38.4	1.4	2.1	41.9	13.2	1.5	0.4	0.22	1.9
Frying oil-2
Fresh	11.7	88.3	26.4	2.3	28.7	58.5	0.2	0.9	59.6	2.5	5.1	0.1	0.03	8.5
NR	13.5	86.5	25.0	5.4	30.4	55.1	0.3	0.7	56.1	5.7	4.1	0.2	0.07	7.3
Discarded	18.4	81.6	22.1	8.0	30.1	48.7	2.4	0.4	51.5	10.4	2.7	0.2	0.15	4.3
Frying oil-3
Fresh	5.6	94.4	60.1	2.9	63.0	21.8	0.1	9.5	31.4	3.0	5.6	0.1	0.03	6.4
NR	9.7	90.3	58.2	6.7	64.9	17.5	0.1	7.8	25.4	6.8	2.6	0.1	0.08	3.1
Discarded	15.8	84.2	54.9	13.0	67.9	9.5	1.6	5.2	16.3	14.6	0.9	0.2	0.21	1.2
Frying oil-4
Fresh	18.6	81.4	24.1	2.8	26.9	52.2	1.0	1.3	54.5	3.8	2.9	0.2	0.05	3.6
NR	22.7	77.3	21.6	4.9	26.5	48.3	1.4	1.1	50.8	6.3	2.2	0.3	0.09	3.0
Discarded	30.6	69.4	17.6	11.8	29.4	36.7	2.7	0.6	40.0	14.5	1.2	0.4	0.26	1.9
Frying oil-5
Fresh	25.4	74.6	21.0	2.7	23.7	50.1	—	0.8	50.9	2.7	2.0	0.3	0.04	2.4
NR	33.9	66.1	15.4	5.6	21.0	44.5	—	0.6	45.1	5.6	1.3	0.5	0.09	1.7
Discarded	43.2	56.8	11.1	7.3	18.4	38.2	—	0.2	38.4	7.3	0.9	0.8	0.15	1.2
Frying oil-6
Fresh	44.5	55.5	30.8	11.5	42.3	11.7	1.5	—	13.2	13.0	0.3	0.8	0.31	0.3
NR	50.6	49.4	24.4	13.1	37.5	10.2	1.7	—	10.9	14.8	0.2	1.0	0.43	0.2
Discarded	56.9	43.1	14.7	18.4	33.1	7.6	2.4	—	10.0	20.8	0.1	1.3	0.93	0.2

The percentage of total trans fatty acids in fresh, null replenishment (NR) and discarded oil was determined in the range of 2.5%–13.0%, 5.6%–14.8%, and 7.3%–20.8% with a mean value of 4.73%, 7.67%, and 13.47%, respectively. The mean value of trans level in the discarded oil was much higher than fresh and null replenishment (NR). The ratio of trans-FA/cis-FA expresses the degree of conversion of the cis-forms to trans-forms and also higher ratio indicates the greater conversion of cis fatty acids to trans fatty acids during frying of the oils. The ratio varies between 0.03%–0.31%, 0.07%–0.43%, and 0.15%– 0.93% with a mean value of 0.08%, 0.14%, and 0.32% for fresh, null replenishment (NR) and discarded oils, respectively. The highest ratio 0.93 was found in discarded frying oil sample-6 while lowest 0.15 in the discarded frying oil sample-2 and sample-5.

The minimal cis PUFA/SFA ratio 0.45 is recommended by the British Department of Health UK.[31] In this study, the comparatively higher cis PUFA/SFA ratio was found as 5.6–0.9 in frying oil-3 and lowest 0.3–0.1 in frying oil-6 (because this oil contains a greater amount of saturated fatty acids), which is very much lower than the recommended. It was observed that as frying time increases, this ratio decreases gradually. A lower value is not considered to be good for the health, in relation to cardiovascular disease.[32] As reported in the literature changes took place in the fatty acid composition of oils during frying, in particular the decrease in linoleic to palmitic acid ratio, considered to be valid indicator of the level of deterioration.[33,34] The result of present study also support the reported fact as the negative correlation (r = −0.82446) was observed between linoleic to palmitic acid ratio and the frying stages, i.e., fresh, null replenishment and discarded oil of six commercial fish pan fryers, which is clearly shown in Figure 1. Furthermore, it is obvious from Figure 1 that with the increase of frying period from null replenishment to discarded frying oil, the linoleic to palmitic acid ratio decreased that lie in the straight line for all six samples. A maximum drop in the ratio was observed in frying oil sample-3 (81.25%) while it was lowest in the frying oil sample-6 (33.33%). This ratio indicated that frying oil-6 was more stable while frying oil-3 was least stable as compared to other analyzed frying oil samples.

Figure 1 Vertical drop line plot of linoleic to palmitic ratio of fresh, null replenishment (NR) and discarded frying oils of six fish commercial fryers (color figure available online).

The repetitive use of oil at frying temperature and due to the presence of moisture of food materials, results in the production of free fatty acids and peroxides. These both are the most frequently determined quality parameters and are important to impart sensory quality characteristics on frying oils and as well as on fried foods. Table 4 shows the mean values of free fatty acids (FFA) and peroxide values of fresh, null replenishment (NR) and discarded commercial frying oil samples. Similar to previous studies,[29,35] the increased trend in the level of FFA was observed with the increase of frying cycles. The FFA of fresh frying oil samples were ranged from 0.12%–0.24%, whereas null replenishment (NR) and discarded frying oil samples were determined in the range of 0.22%–1.74% and 0.80%–3.39%, respectively. The higher value of FFA in discarded frying oil-6 may be due to the higher initial concentration of FFA (0.80%) in fresh oil.

Table 4 Free fatty acids and peroxide value (Mean ±SD) of fresh, null replenishment (NR) and discarded commercial frying oil samples

Samples	FFA (%)	Peroxide value (meq/kg)
Frying oil-1
Fresh	0.16 ± 0.0	2.50 ± 0.0
NR	0.73 ± 0.0	4.03 ± 0.1
Discarded	2.17 ± 0.1	7.69 ± 0.3
Frying oil-2
Fresh	0.14 ± 0.0	2.01 ± 0.1
NR	0.56 ± 0.1	3.40 ± 0.1
Discarded	2.09 ± 0.0	3.24 ± 0.3
Frying oil-3
Fresh	0.19 ± 0.0	3.11 ± 0.1
NR	0.94 ± 0.0	4.33 ± 0.3
Discarded	2.86 ± 0.1	8.94 ± 0.5
Frying oil-4
Fresh	0.13 ± 0.1	1.90 ± 0.1
NR	0.37 ± 0.0	3.01 ± 0.1
Discarded	2.01 ± 0.2	2.84 ± 0.2
Frying oil-5
Fresh	0.12 ± 0.1	1.15 ± 0.1
NR	0.22 ± 0.0	2.71 ± 0.1
Discarded	0.80 ± 0.2	6.94 ± 0.3
Frying oil-6
Fresh	0.24 ± 0.0	3.93 ± 0.1
NR	1.74 ± 0.4	7.51 ± 0.3
Discarded	3.39 ± 0.3	14.68 ± 0.4

The relationships between trans fatty acids and free fatty acids were evaluated by using OriginPro 7.5 software. A linear relation between the both parameters was obtained. The value found for the coefficient of correlation was 0.88204 with the following regression equation and regression results as shown in Figure 2:

Figure 2 TFA versus FFA of fresh, null replenishment (NR) and discarded frying oil samples (color figure available online).

The PV of fresh frying oil samples were ranged from 1.15–3.93, whereas null replenishment (NR) and discarded frying oil samples were determined in the range of 2.71–7.51 and 2.84–14.68 meq of O₂/Kg of oil, respectively. The results have shown that an increase in PV occurred during the initial stage of frying in all analyzed samples, while haphazard change has been observed from null replenishment frying to discarded oil. The highest PV 14.68 meq of O₂/Kg of oil was observed in the discarded oil of sample-6. Usually in freshly processed edible oil the FFA and PV values are less than 0.1% and 1%, respectively. The slightly higher value of FFA and PV in fresh frying oil shows that food vendors purchase cheaper unbranded oil and store for many days in open drums where the quality of oil is further deteriorated.

CONCLUSION

The results of the present research work indicated that the commercial fish pan fryers are not using proper oil for frying. Therefore, use of proper frying oils with a minimum level of trans fat and linolenic acid (<2.0%) is very necessary for the health point of view. Proper oils could be used for a longer time for cost-effective frying. A side benefit would be to the pollution problem created by the discarded frying oil. Especially last cycle of frying just before discarding the frying oil provided the significant level of trans fat, free fatty acids, and peroxide values and revealed to be dangerous for the health of consumers. The data of the study is very important for the three major players, who can play an important role to control the quality of frying oil, i.e., oil industries, standard and quality control authorities, and consumers.

ACKNOWLEDGMENTS

The National Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Pakistan is thankfully acknowledged for providing the financial support.