Abstract

Natural antioxidants are used as food ingredients because these are safer than synthetic antioxidants. Antioxidant effects of some meal acetone extracts were tested in stabilizing refined cotton oil (RCO). Here, we have explored the antioxidant potential of meal extracts (sesame and sunflower). RCO was mixed with both meal extracts at different concentrations and kept at 50°C, for their assessment with synthetic antioxidants used as positive controls; propyl gallate (PG) and tert-butyl hydroquinone (TBHQ) at a concentration of 200 ppm. The result showed that both meal extracts could lower the values of various parameters of oil such as total oxidation, conjugated diene (CD), p-anisidine, and peroxide value when the results were analyzed after 120 days of their storage. Seasme meal extract displayed better result in comparision to sunflower meal extract as it showed lower CD value at 500 ppm (34.46±0.02) in comparison to sunflower extract at 500 ppm (42.6±0.04).

1. Introduction

Consumption of polyunsaturated vegetable oils is significantly increasing nowdays. As per the OECD-FAO Agricultural Outlook per capita consumption of vegetable oil is around 19-19.80 kg per person per annum over the last five years ¹. The increase in the consumpstion of vegetable oils is responsible for the consequences related to higher rate of lipid oxidation ². However, the main associated concern currently is rancidity caused mainly because of storing crude and refined vegetable oil. The rancidity is further responsible for the low class of oil owing to multiple bonds in the principal unsaturated fatty acids ³. Oxidation of oils and fats is a series of chemical reactions that is the major cause of oil deterioration and responsible for generating free radicals. Oxidation leads to rancidity with off flavors, smells, and discoloration. During the first stage, lipid oxidation of unsaturated fatty acid oxidizes to produce the primary oxidation product (peroxides, free fatty acids, and conjugated dienes) ⁴. The primary product then oxidizes to secondary products (such as carbonyls, aldehydes, and trienes) which further oxidize into tertiary products (alkyl furans, aldol adducts). This process not only affects the nutritional quality but also generates potential toxic compounds by reacting with reactive oxygen species (ROS). These compounds could be unhealthy for human beings and can be one of the major cause of disease such as early ageing and cancer ⁵.

Free radicals can be an atom or molecules owning unpaired electrons. Free radicals and ROS are extremely reactive elements generated in the body’s cells due to metabolic processes ^{6, 7}. Free radicals and ROS are extremely reactive in nature and can rapidly reacts with neighboring molecules through a variety of reactions ⁸. Because of these, there is a damaging impact on DNA and proteins. This impact could either be reversible damage or irreversible ⁹. These free radicals can be blocked for their harmful effect using antioxidants, which hinder lipids oxidation by interfering with any stage of oxidative chain reactions i.e. the initiation or propagation ¹⁰. Out of two antioxidants, the first one is preventive antioxidant, which is responsible for the lower rate of chain initiation through the deactivation of active species. The other antioxidant (chain-breaking), is responsible for the removal of oxygen radicals during chain propagating and thus forming a stable product which in turn helps in reducing lipid oxidation ¹¹.

An antioxidant is defined as a substance that is present in low concentrations and significantly inhibits oxidation ¹². Several food antioxidants are used to protect the oxidation of oxidizable fats ¹³. Similarly, some antioxidants are used to retard the oxidation reaction taking place in oils. At the present time, to extend the storage stability several synthetic antioxidants are explored as food additives, some of them are Tertiary Butylated Hydroxy Quinone (TBHQ), and Propyl Gallate (PG) ¹⁴. However, these synthetic antioxidants are associated with health concerns. Therefore, there is an urgent need to develop natural antioxidants, which can be explored as replacement for synthetic antioxidants. Various plant extracts offer unique applications in the food industry for health and wellness.

Therefore, the objective of this research is to examine the antioxidant potential of naturally occurring meal extracts such as sesame and sunflower in the oxidation of refined cotton oil. The results of both extracts were compared with synthetic antioxidants, PG, and TBHQ to see the antioxidant potency of meal extracts of sesame and sunflower.

2. Materials and Methods

All the materials related to the study such as meals, and cotton seeds acquired from the nearby market in Hisar, Haryana. The other basic step of the current study such as sample preparation of the meals, extraction of cotton oil, and refining of oils was performed as per earlier reported literature ¹⁵. A commercial sample of sesame and sunflower meal were dried and then ground into a fine powder. 100 grams of the samples defatted with hexane (3 times × 500 ml) at room temperature. The defatted residue was washed with distill water (3 times × 500 ml) and dried at 50°C. 10 grams of the above residue was extracted with 150 ml acetone by Soxhlet method for 8 h. Extracts were filtered, solvent removed (in a rotary evaporator below 40°C), weighed and the residue was redissolved in 100 ml of acetone to give an antioxidant solution of known concentration and stored in refrigerator for further use. The seeds of cotton were ground to powder. Oil was extracted by Soxhlet method using petroleum ether (60-80°C) for 8 h. Solvent extraction processes include basically three steps: preparation, extraction, and desolventizing.

The meal acetone extracts which are considered for this study were sesame and sunflower. These extracts were used at various concentrations of 2000, 1000, and 500 ppm and added to refined cotton oil. To compare the results, we have also performed experiments with synthetic antioxidants such as TBHQ and PG at a concentration of 200 ppm. One control experiment without the addition of any antioxidants was also carried out. All experiments are performed in duplicate. The oil samples were then stored in an incubator at 50°C for 120 days to accelerate the deterioration of the oil. Required quantity of the oils were withdrawn at day 20, day 40, day 60, day 80, day 100 and day 120 and studied for the oxidative quality indices ¹⁵.

The analytical procedure related to the quality of oil such as total oxidation, conjugated diene, p-anisidine, and peroxide value is done using reported literature methods ^{16, 17}.

3. Results and Discussion

Natural antioxidants not only protect from harmful diseases but also prevent oxidative deterioration of lipid food during processing and storage ¹⁸. Figure 1 depicts the effect of incubating temperature (50°C) on the peroxide value of refined cotton oil. The peroxide value of the oil samples increased with storage time and it may be due to autooxidation, thermal polymerization, and hydrolysis of fatty acids which occurred in oil during prolonged storage ¹⁹. Upon 120 days of storage at 50°C, the peroxide value of the control RCO sample raised to 223.59±2.5 meq/kg from the initial value of 1.5±0.05 meq/kg. However the addition of antioxidants viz. TBHQ 200 ppm, PG 200 ppm, and sesame and sunflower meal acetone extracts at the same concentrations of 2000, 1000 and 500 ppm have been found to improve the oil quality. Better result were noted for both sesame and sunflower meal extracts at a concentration of 500 ppm. The effectiveness of sesame and sunflower meal extracts in retarding oil deterioration was retained all over the storage period. Among meal extracts, sesame meal extract had a better stabilization effect than sunflower meal extract and also better than PG 200 ppm. The sample containing TBHQ exhibited maximum oil stability. Overall, result presents that sesame meal extract could be used as antioxidant over synthetic one’s, but need to be validated with more experimental results as presented in the subsequent section.

The formation of conjugated dienes in oil samples was monitored during a storage period of 120 days in refined cotton oil. During the early stage of storage, the double bond of polyunsaturated fatty acid dislayed an absorbtion at 234 nm wavelength in UV-visible sprectrum due to migration in the molecule which led to the formation of a conjugated system. The ability of both meal extracts to prevent the formation of CD over the oxidation period is shown in Figure 2. Lower CD value is needed for overpowering the oxidation of the oil by the extract. There was a lower rate of formation of the CD for extracts as compared to control samples, but it was higher when compared to the oil sample. The initial CD value of oil was 3.2±0.05 (% as dienoic acid). The CD values of RCO with control (60.21±0.01), TBHQ 200ppm (24.55±0.03), PG 200ppm (40.81±0.01), sesame extract at 2000 (38.71±0.05), 1000 (36.62±0.03), 500 ppm (34.46±0.02) and sunflower extract at 2000 (49.89±0.04), 1000 (45.77±0.04) and 500 ppm (42.6±0.04) after the end of 120 days at 50°C. The inhibitory effect of TBHQ 200 ppm against CD formation was maximum, followed by sesame meal extract, PG 200 ppm, and sunflower meal extracts. Here, the promising result were shown by sesame extract, although it was not better as compared to TBHQ but could be useful as it is not a synthetic antioxidants.

AV values of oil samples containing different levels of natural as well as synthetic antioxidants during accelerated storage at 50°C are shown in Table 1. AV value was considerably less during the first 20 days of storage but after that, a pronounced increase was seen in AV values. The highest AV values were found in the case of the control sample containing no additives. The initial AV value of RCO was 1.12±0.02. The AV value of RCO with control, TBHQ 200ppm, PG 200ppm, sesame and sunflower meal acetone extracts at the same concentrations of 2000, 1000 and 500 ppm were 202.19±1.1, 112.43±0.3, 168.09±0.8, 165.44±0.7, 162.57±0.5, 158.66±0.8, 183.5±0.9, 175.28±0.7 and 170.37±0.9, respectively, after the end of 120 days at 50°C. During the 120 days of the study, it was observed that the higher concentration of extracts showed more effectiveness in lowering the reduction of AV of RCO as compared to oil samples. These observations were in accordance with that reported by Chatha et al ²⁰. In their study, the authors reported that the supplementation of canola oil with wheat bran extract is responsible for the strong inhibition of anisidine values for a complete storage period. During storage of RCO, sesame meal extracts were more effective than PG (200 ppm) while sunflower extracts were less effective in reducing the AV of RCO. Overall, the result has indicated the effectiveness of TBHQ in preserving RCO. These differences in the antioxidant properties could be because of the different chemical compositions of the elements. In total, more stable the phenoxy radicals better storage stability of oils with the reduced rate of oxidation reactions ²¹.

Table 2 shows TOTOX of RCO stored with different elements such as TBHQ (200 ppm), PG (200 ppm), and sesame and sunflower meal extracts at concentrations of 500, 1000, and 2000 ppm. It is observed that RCO containing the extracts of TBHQ (200 ppm), PG (200 ppm), and sesame and sunflower meal had three months incubation period during which there is no noticeable change in TOTOX value as compared to the control sample. The control sample reached 649.37±2.9 from an initial value of 4.12±0.03. RCO treated with TBHQ 200 ppm, PG 200 ppm, and sesame and sunflower meal extracts at the same varying concentrations of 2000, 1000 and 500 ppm had the following values 325.27±1.8, 465.33±1.8, 459.3±2.6, 445.51±1.3, 435.46±1.1, 520.24±2.6, 493.96±3.0 and 480.83±2.0, respectively, after the end of 120 days. There was a huge difference in the TOTOX value of all the elemental extract compared to the control sample. The elemental extracts for antioxidant effect in RCO followed the order: TBHQ > sesame > PG > sunflower. During incubation, TBHQ maintained the lowest TOTOX value. Again the promising result were shown by sesame meal extract motivating for further exploration of the same with new experiments which could provide us the better insight about the use of meal extract over synthetic antioxidant.

4. Conclusion

In this study, we have explored meal extracts of sesame and sunflower at concentrations of 2000, 1000, and 500 ppm. These extracts were added to refined cotton oil and analyzed for different parameters of oil stability in terms of total oxidation, conjugated diene, p-anisidine, and peroxide value. Both these extracts successfully lowered the values of all the concerned parameters in comparison to control under similar conditions. Here, the better results were displayed by sesame meal extract over sunflower meal extract. Overall, the present study highlights the importance of seed meals as effective antioxidants, which are often discarded as by-products.

Acknowledgments

Anjani is thankful to the University Grant Commission, New Delhi, India for providing a junior research fellowship (JRF) during the period of this work.

Highlights

• The stability of refined cotton oil was studied concerning different oxidative indices.

• Sesame and sunflower meal acetone extract was used as natural antioxidants.

• The study was conducted at 50°C for 120 days.

• Natural antioxidants are comparably as effective as synthetic antioxidants.

References