Blending of different grades of olive oil with sesame oil: Impact on physicochemical properties, sensory properties and oxidative stability

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1 ORP-05 Blending of different grades of olive oil with sesame oil: Impact on physicochemical properties, sensory properties and oxidative stability Aditya Madan a*, Akash Pare b, Bhuvana S c, Durgadevi M d a Research Scholar, Indian Institute of Crop Processing Technology b Assistant Professor, Department of Primary Processing, Storage and Handling c Assistant Professor, Department of Food Safety and Quality Testing d Assistant Professor, Department of Food Product Development Indian Institute of Crop Processing Technology, Ministry of Food Processing Industries, Government of India, Pudukkottai Road, Thanjavur Tamil nadu, India *Corresponding author. (M) * address: adityamadan800@gmail.com Abstract Olive oil is known for its ability to resist oxidative deterioration because of inherent potent natural antioxidants and lower unsaturation levels. In this view, two different grades of olive oil i.e., pure olive oil (POO) and pomace olive oil (POMOO) in 20:80, 30:70 and 40:60 v/v ratios were blended with sesame oil (SO) and the impact on physicochemical properties (viscosity, colour, free fatty acid, peroxide value) and sensory attributes (appearance, aroma, stickiness) of stand-alone oils and their blends were evaluated. Apart from these, the oxidative stability as a result of blending POO and POMOO with SO was also determined. Overall, satisfactory results were obtained for physical, chemical and sensory properties of blends as compared to stand-alone oils. It was also revealed that blending of POO and POMOO with SO improved oxidative stability as the proportion of POO and POMOO increased from 20:80 to 40:60 in SO. Keywords: Blending; Olive oil; Sesame oil; Oxidative stability 1. Introduction Modern consumers are becoming more and more health conscious. To be precise, the consumption of edible oils and the nutritional aspects in foods and food products is receiving great attention. In view of this, it is essential to formulate new vegetable oil composition having improved nutritional value and storability. Oxidation of lipids is one of the major factors resulting in loss of vegetable oil quality by formation of products that have negative effects on appeal, flavour and nutritional value of food. It also increases the risk of cardiovascular disease (Chow, 1992). Some vegetable oils are not up to standards to meet consumer satisfaction in terms of their physicochemical properties or for the texture and stability of the food products. 59

2 Therefore, search for finding useful source of natural antioxidants is highly desirable because synthetic antioxidant has been questioned (Bera et al., 2004). Blending of vegetable oils and fats has emerged as an economical way of modifying the physicochemical characteristics of vegetable oils and fats besides enhancement in oxidative stability (Chu and Kung, 1997 & 1998). Blending of oils not only dilutes the effect of undesirable constituents (ex: erucic acid in mustard oil) but also brings in the advantage of micronutrients present in the blended oil. Olive oil is known for its ability to resist oxidative deterioration because of inherent gifted natural antioxidants. Olive oil has a longer shelf-life and can be blended with less stable vegetable oils to improve their stability and longevity. A consumer-friendly way of improving oxidative stability of edible oils is the addition of natural antioxidants (Abdel-Razek et al., 2011). Furthermore, if olive oil is used, chronic problems of heart and blood pressure can be curbed (Kochhar, 2000). As per the International agreement on olive oil and table olive, United Nations Treaty Collection (1987), pure olive oil (POO) marketed under name olive oil as such, consists of a blend of virgin olive oil (except lampante) and refined olive oil and having a maximum acidity, in terms of oleic acid, of 1.5 g/100 g whereas pomace olive oil (POMOO) is obtained from crude olive pomace oil by refining methods not altering the initial triacylglycerol structure and having acidity of no more than 0.5 g/100 g. Sesame oil is an edible vegetable oil derived from sesame seeds. Besides being used as a cooking oil, it is often used as a flavour enhancer in Chinese, Japanese, Middle Eastern, Korean, and Southeast Asian cuisine. The market for sesame oil is mainly located in Asia and the Middle East where the use of domestically produced sesame oil has been a tradition for centuries. Sesame seed oil also possesses antioxidative abilities due to presence of lignans such as sesamin, sesaminol, 2-episalatin and others (Kamal-Eldin et al., 1994). However, sesame seed oil is not as resistive towards oxidation as olive oil. Hassanein (2010) provided sufficient evidences on improved oxidative stability of sunflower oil, sesame seed oil and olive oils blends. Very few efforts have been made to blend olive oil to other vegetable oils for improving oxidative stability and physicochemical properties. Keeping in mind the health benefits and oxidative stability provided by olive oil and considering the regional preferences of sesame seed oil in certain parts of the world, it was aimed to blend two grades of olive oil viz. pure olive oil (POO) and pomace olive oil (POMOO) with sesame oil (SO) in ratios 20:80, 30:70 and 40:60 v/v respectively and to evaluate the influence of the same on various physicochemical properties, sensory properties and oxidative stability of oil blends. 2. Materials and methods 2.1 Materials Oil samples 60

3 Pure olive oil (POO) and pomace olive oil (POMOO) were procured from Wellkraft consulting private limited, Chennai, Tamil Nadu, India. Refined, bleached and deodourized (RBD) sesame oil (SO) was procured from local market of Thanjavur, Tamil Nadu, India Glasswares and chemicals All the necessary glasswares and chemicals were procured from local suppliers. The chemicals used for the analysis were of analytical (AR) grade. 2.2 Methods Preparation of oil blends Edible oils amounting to 250 ml were placed in 500 ml conical flask and were mixed thoroughly by using an incubator shaker (New Brunswick Scientific, Excella E24 incubator shaker series) at 40 C, speed being 70 rpm for 20 min, in order to form uniform blends. Six different blends having various proportions as shown in Table 1. Stand-alone oils of POO, POMOO, SO were considered for comparison with oil blends. Table 1 Ratio of oil blends POO/SO Oil blends (250 ml each) (v/v) POMOO/SO 20/80 20/80 30/70 30/70 40/60 40/60 POO: Pure olive oil, POMOO: Pomace olive oil, SO: Sesame oil Physicochemical analysis Physicochemical properties of edible oils play a vital role in determining the quality of any edible oil. Physicochemical parameters such as viscosity, colour, free fatty acid (FFA) and peroxide value (PV) were analysed for stand-alone oils and their blends. All the samples were analysed in triplicates. Viscosity was measured using Brookfield LV viscometer Model TC-500 (Brookfield Engineering Laboratories Stoughton, MA, USA), S61 spindle at 60 rpm speed whereas hunterlab colorimeter (HunterLab ColorFlex EZ, USA) was used for the measurement of colour values (L*, a*, b*). Chemical properties such as peroxide value (PV) and free fatty acid (FFA) content was determined according to the official method No of the Association of Official Analytical Chemist (AOAC) (1990) and IUPAC method number (1979) respectively. 61

4 Sensory evaluation One of the powerful tools for recording the sensory responses is hedonic evaluation technique which was adopted in this particular study. A nine point hedonic scale for acceptance, 1- Like extremely, 2- Like very much, 3- Like moderately, 4- Like slightly, 5- Neither like or dislike, 6- Dislike slightly, 7- Dislike moderately, 8- Dislike very much, 9- Dislike extremely, was used for the independent hedonic rating of appearance, aroma, stickiness and overall acceptability for raw oils and their blends (Ravi et al., 2005; Waghray and Gulla, 2011). Each stand-alone oil and their blends (100 ml) were presented before panellists in small identical plastic containers. The containers were blinded by appropriate coding in order to avoid bias. Sensory evaluation was carried out in a well-illuminated meeting hall. Consumers rinsed their palates with water before and between tasting and re-tasting of samples Oxidative stability Oven storage test for accelerated aging of oils, a standard methodology of American Oil Chemists' Society (Cg 5-97) (1998) was adopted for the oxidative stability study of different stand-alone oils and their blends. According to this method, oil samples were heated in an oven at 60 C for 32 days. Quality parameters such as peroxide value (PV) and free fatty acid (FFA) are then estimated, at the interval of two days, to measure oxidation levels in the individual oils and their blends Statistical Analysis All the data were tabulated and subjected to one way analysis of variance (ANOVA) for determination of significant difference (at 5% significance level) followed by Tukey s test in post-hoc analysis for determining the magnitude of significant difference between the samples, using IBM SPSS version Results and discussion 3.1. Changes in physicochemical properties Changes in viscosity and colour The changes in the viscosity of stand-alone oils and their blends can be visualized from Fig.1 (a). As the proportion of POO increases from 20% to 40% in SO, there is an increase in viscosity. This may be due to an increase in the saturation as the amount of POO is increased from 20% to 40%. In case of POMOO and its blends, 30% of POMOO in SO recorded higher viscosity values as compared to other blend ratios. On account of blending POO and POMOO with SO, the appearance of oil blends changes. These changes in colour in terms of L*, a* and b* were studied. Change in the whiteness or lightness value (L* value), as the POO and POMOO are blended with SO in 20, 30 and 40%, can be visualized from Fig.1(b1). In general, whiteness 62

5 decreased as the proportion of POO increases from 20% to 40% in SO. And for the POMOO/SO blends, there was no prominent change in the whiteness for POMOO blends with SO. As the POO and POMOO are blended with SO in 20, 30 and 40%, the changes in the redness or greenness value (a* value) also occurred [Fig.1(b2)]. A reduction in redness of POO/SO blend was observed as the proportion of POO increased from 20% to 40%. Similar pattern was observed in case of POMOO blends. Yellowness or blueness value (b* value) also seems to be affected as a result of blending. This can be visualized from Fig.1(b3). It can be observed that, there is a reduction in yellowness for POO/SO blends as the proportion of POO in SO increases from 20:80 to 40:60. On the other hand, the pattern is reverse in case of POMOO/SO blend with an exception of 40:60 blend proportions Changes in FFA and PV As the proportion of POO and POMOO increased from 20:80 to 40:60 in SO, there was a decrease in FFA content and PV. This can be visualized from Fig.1(c and d). As the initial FFA content and PV of POO is lesser than that of POMOO, the resultant FFAs and PVs of the blends for POO/SO recorded lesser FFAs and PVs as compared to that of POMOO/SO blends Changes in sensory properties In case of olive oil blended with sesame oil, as the amount of POO increased from 20% to 40% in SO, it becomes more acceptable whereas 30% of POMOO in SO is preferred over 20% and 40% blends. Of all the stand-alone oils and their blends, the most significantly (p<0.05) preferred POO blend was POO/SO in the ratio of 40:60 and amongst POMOO blends, the most preferred blend was POMOO/SO in the ratio 30:70. These results could be interpreted from Table 2, where lower scores indicate higher preference on a 9-point hedonic scale Oxidative stability Degradation of oils in terms of free fatty acid formation During accelerated oven storage test for 32 days at 60 C, a registered progressive increase in FFA, of POO, POMOO, SO and their blends, can be detected from Fig. 2 (a and b). Addition of POO and POMOO in 40:60 ratios in SO has significant effect (p<0.05) in slowing down the hydrolytic rancidity than other blends and hence can be considered as stable oil blends. 63

6 b* value FFA (% oleic acid) Peroxide value (meq/kg) Viscosity (cp) L* value a* value NATIONAL SEMINAR ON EMERGING TRENDS IN FOOD SAFETY AND QUALITY (a) (b1) (b2) (b3) Oil sample (c) Oil sample (d) Oil sample Oil sample Oil sample Fig.1. Effect of blending POO and POMOO with SO on (a) Viscosity; 64 (b1) Lightness; (b2) Redness; (b3) Yellowness; Oil (c) sample FFA; (d) PV

7 Table 2 Mean hedonic scores (Hedonic scale: 1- Like extremely to 9- Dislike extremely) for preference of raw edible oils and their blends Edible oils and their blends Characteristics Appearnce a Aroma a Stickiness a Overall acceptability a POO 2.76±1.56* 3.76±2.17* 3.40±1.91* 3.44±2.06 POMOO 3.76±1.56* 3.76±1.69* 3.12± ±1.61* SO 3.72±1.24* 4.40±1.78* 3.44±1.12* 3.80±1.08* POO/SO (20:80) 3.60±1.44* 3.96±1.59* 3.44±1.39* 3.92±1.44* POO/SO (30:70) 3.64±1.38* 3.84±1.40* 3.28±1.10* 3.72±1.34* POO/SO (40:60) b 3.00±1.22* 3.40± ±0.79* 3.44±1.42 POMOO/SO (20:80) 4.12±1.69* 4.08±2.08* 3.44±1.64* 3.88±1.83* POMOO/SO (30:70) b 2.56±1.19* 3.20± ±1.05* 2.72±1.31* POMOO/SO (40:60) 2.76±0.93* 3.48± ± ±1.22 POO: Pure olive oil, POMOO: Pomace olive oil, SO: Sesame oil a Mean±S.D *Significant at 5% level b Highly preferred in terms of appearance, aroma, stickiness and overall acceptability (p 0.05) Similar observation is reported by some researchers (Hassanien and Abdel-Razek, 2012; Abdel-Razak et al., 2011). As the proportion of POO increases from 20% to 40%, the rate of FFA formation slows down. Formation of FFA resulted partly from hydrolysis and further oxidation of the secondary products formed during heating (Teah, 1988; Abou-Gharnia et al., 2000; Wanasundara et al., 2001; Abdel-Razak et al., 2011) Degradation of oils in terms of hydro-peroxides formation One of the most important quality parameters of oil is measured in terms of formation of hydro-peroxides on account of oxidation. This degradation in oil is evaluated in terms of peroxide value (PV). Referring to PV during accelerated oven storage test for 32 days at 60 C, a registered progressive increase in PV, of POO, POMOO, SO and their blends, can be observed from Fig. 2.(c and d). Fig. 2.(c and d) indicated that as the proportion of POO and POMOO increases from 20% to 40% in SO, the rate of formation of hydro-peroxides is decreased or in other words, addition of POO caused improvement in the antioxidation potency and accordingly delays the increase in PV as the ratio of POO goes on increasing. Fig.2 (c and d) reflects a steady increase in the formation of PV reaching the maximum values at 20 th day followed by a sharp decrease. Similar observation was reported by Hassanien and Abdel-Razek (2012). 65

8 PV (meq/kg) PV (meq/kg) FFA (% oleic acid) FFA (% oleic acid) NATIONAL SEMINAR ON EMERGING TRENDS IN FOOD SAFETY AND QUALITY (a) Storage period (Days) POO SO POO/SO (20:80) POO/SO (30:70) POO/SO (40:60) (b) Storage period (Days) POMOO SO POMOO/SO (20:80) POMOO/SO (30:70) POMOO/SO (40:60) (c) (d) POMOO POO SO SO POMOO/SO (20:80) POO/SO (20:80) POMOO/SO (30:70) POO/SO (30:70) POMOO/SO (40:60) POO/SO (40:60) Storage period (Days) Storage period (Days) 66 Fig. 2. Periodical changes in FFA content (a and b) and PV (c and d) of POO:SO and POMOO:SO blends during accelerated temperature storage at 60 C for 32 days

9 However, the reason for the declination of peroxide value is not reported by any researcher. The sudden declination in peroxide formation after 20 days of heating might be due to formation of other polymeric compounds or might be due the formation of secondary oxidation products like aldehydes, ketones etc., which do not promote further hydro-peroxides formation in oils and their blends. Results reflect that 40:60 ratios of POO and POMOO in SO yielded desirable results in terms of oxidative stability as compared to other blend ratios. However, POO blends with SO registered still lesser values of PV as compared to POMOO/SO blends, suggesting pure olive oil as a better alternative than the pomace fraction of olives. 4. Conclusions Following conclusions can be drawn from the current study: As compared to stand-alone oils, an improvement can be seen in case of blended olive oils, in terms of physical, chemical, sensory characteristics and oxidative stability. Following order can be suggested for oxidative stability of POO/SO blend: POO/SO (40:60) > POO/SO (30:70) > POO/SO (20:80) Following order can be suggested for oxidative stability of POMOO/SO blend: POMOO/SO (40:60) > POMOO/SO (30:70) > POMOO/SO (20:80) Further investigations are required to explore the oxidation of olive oil blends as affected by light (photo-sensitivity), packaging interactions and storage conditions. Acknowledgements Authors are thankful to Wellkraft Consulting Private Ltd., Chennai, Tamil Nadu, India for funding this research project. Authors are also grateful to Indian Institute of Crop Processing Technology, Ministry of Food Processing Industries, Government of India to avail laboratory and all necessary facilities to carry out such research. References Abdel-Razek, A. G., El-Shami, S. M., El-Mallah, M. H., & Hassanien, M. M. M. (2011). Blending of virgin olive oil with less stable edible oils to strengthen their antioxidative potencies. Australian Journal of Basic and Applied Sciences, 5(10), Abou-Gharbia, H. A., Shehata, A. A. Y., & Shahidi, F. (2000). Effect of processing on oxidative stability and lipid classes of sesame oil. Food Research International, 33(5),

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