Elsevier

Food Chemistry

Volume 272, 30 January 2019, Pages 471-477
Food Chemistry

Kinetics of lipid oxidation in omega fatty acids rich blends of sunflower and sesame oils using Rancimat

https://doi.org/10.1016/j.foodchem.2018.08.072Get rights and content

Highlights

  • Sunflower (SO) and sesame oils were blended to improve product thermal stability.

  • Kinetics of oxidation in the blended oils were estimated using Rancimat.

  • A 1:1 mix (OB5) had a higher induction period at 100 °C vs. SO (13.2 vs. 6.1 h).

  • OB5 showed better retention of natural antioxidants (tocopherols + lignans) vs. SO.

  • OB5 had stable ω-fatty acids profile vs. SO (ω-9, 34.5 vs. 28.7%; ω-6, 49 vs. 52%).

Abstract

Blended sunflower (SO) (50–80%) and sesame oils (SEO) (20–50%) were evaluated for thermo-oxidative stability (induction period, IP), oxidation kinetics (rate constant, k), synergy and shelf-life (25 °C) (IP25) using Rancimat (100, 110, 120, and 130 °C). The Arrhenius equation (ln k vs. 1/T) and activated complex theory (ln k/T vs. 1/T) were used to estimate activation energies, activation enthalpies and entropies, which varied from 92.05 to 99.17 kJ/mol, 88.83 to 95.94 kJ/mol, −35.58 to −4.81 J/mol K, respectively (R2 > 0.90, p < 0.05). Oil blend (OB) with 1:1 SO to SEO exhibited greatest synergy (115%), highest IP (100 °C) (13.2 vs. 6.1 h) and most extended IP25 (193 vs. 110 days) with a nutritionally stable composition of ω-fatty acids (ω9, 34.5 vs. 28.7%; ω6, 49 vs. 52%) compared with SO. Better retention of lignans (6205 vs. 3951 mg/kg) and tocopherols (332 vs. 189 mg/kg) were also noted in OB compared with SO alone.

Introduction

The thermal vulnerability of dietary lipids (e.g., fats and oils) rich in omega (ω) fatty acids is a problem in the food industry (Gordon, 1991). Cooking oils are employed globally to serve two distinct functions (1) as a heat transfer medium to aid cooking and (2) to impart characteristic aroma and flavor to cooked food products. However, popular cooking oils (e.g., sunflower oil (SO), soybean oil), rich in ω6-fatty acids, often fall short in satisfying thermal stability requirements resulting in early rancidity. Globally, dietary choices are relying increasingly on fried foods and hence require thermo-oxidatively resilient oils that retain their nutritional attributes (Upadhyay, Sehwag, & Mishra, 2017a). Unfortunately, ω6-fatty acids pre-disposes SO to rancidity, which impaired its nutritional value and organoleptic qualities (Upadhyay & Mishra, 2015). The food oil industry continues to work toward developing varieties with enhanced compositional traits and improved stability.

Synthetic antioxidants are often added to edible oils used in food applications to control oxidation and extend product shelf-life. They have been used successfully and safely for years, but the use of thermally stable oil blends would eliminate the need for such additives, which is vital for consumers seeking more natural ingredients. In the last decade, demands for foods containing natural preservatives have increased and synthetic antioxidants (viz., TBHQ, BHA, and BHT) have been rejected (Upadhyay, Sehwag, & Mishra, 2017c). The food industry is committed to making it easier for consumers by delivering food products that meet the demands for natural ingredients as well as nutrition needs. In the context of cooking oils, blending has extended shelf-life and reduced the need for synthetic antioxidants (Kiralan et al., 2017, Srivastava et al., 2017). The concept of tailoring fatty acid compositions of cooking oils is gaining increased attention. For instance, SO, which is high in ω6-fatty acids, can be blended with oil(s) containing a more balanced ratio of ω-fatty acids and higher contents of natural antioxidants (bioactive phytochemicals). Such blending can serve two purposes: (1) help improve stability/ reduce rancidity and (2) skew the ω-fatty acids towards a more nutritionally balanced composition (ω6 and ω9 fatty acids). Only few commercially available plant oils (e.g. canola, olive) have nutritionally balanced composition of ω-fatty acids (MUFA:PUFA = 1:1) and good thermal stability.

Sesame oil (SEO) is well-known for its balanced ratio of ω-fatty acids (6, 9) and rich content of bioactive lignans (sesamolin, sesamol, sesamin), which also contribute to excellent thermo-oxidative stability (Hemalatha, 2007). Blending of SO and SEO could increase oxidative resistance and eliminate the need to add synthetic antioxidants. Interestingly, the literature on blending of cooking oils describes the addition of (1) unsaponifiable fractions from raw sesame seeds to oils and (2) sesamol, extracted from sesame cakes, to oils, but very few studies have considered blending of the source oils (Hemalatha, 2007, Konsoula and Liakopoulou-Kyriakides, 2010). The growing market in cooking oils has enables food technologists to explore the understanding and advantages of blending and facilitate transfer of this knowledge to household cooking practices.

It is critical to examine the oxidation kinetics of SO–SEO blends before making any recommendation about its culinary applications and the kinetics of lipid oxidation are useful in understanding stability under accelerated storage conditions (Farhoosh et al., 2008, Upadhyay and Mishra, 2016a). Thus, we examined the thermo-oxidative stability of oils (SO, SEO, and SO + SEO) subjected to heating (100–130 °C) in Rancimat. The kinetics of lipid oxidation were followed using the Arrhenius equation and activated complex theory. The kinetic parameters and contents of naturally-occurring antioxidants (viz., total lignans and tocopherols) in heated oils were analyzed using principal component analysis (PCA). The oil blends (OBs) were compared for shelf-life using calculated oxidizability (COX) index (fatty acids composition by gas chromatography) and Rancimat induction period (IP).

Section snippets

Materials

Refined SO and SEO (without added antioxidants) were procured from AAK Kamani Private Limited (Mumbai, India). The initial compositional parameters of oils are presented in Table 1. Analytical grade chemicals and solvents were purchased from Merck (Mumbai, India). Fatty acid methyl esters (FAMEs) (>82%) were obtained from Sigma Chemical Co. (St. Louis, MO, USA). Triple distilled water (electrical conductivity <5 µS/cm) was purified using Mili-Q system (Milipore, Bedford, MA, USA) and used in

Total lignans, tocopherols, and synergism

The initial content of natural antioxidants viz., total tocopherols and total lignans in SOcontrol and SEOcontrol were 298 and 445 mg α-tocopherol/kg oil, respectively, and 6222 and 8611 mg sesamol/kg oil, respectively (Table 1). The overall stability of the oils varied as a function of SEO in the blends (Table 2). More specifically, the antioxidant properties of lignans (mainly sesamols) were associated with a higher degree of OB thermo-oxidative resistance.

Tocopherols are well established as

Conclusions

A thermally stable and nutritionally balanced composition of ω-fatty acids was formulated by the blending plant oils viz., SO and SOE. The addition of lignans (via SEO) increased the innate antioxidant potential of OBs (SO + SEO). The lignans acted synergistically with the more thermally labile tocopherols, present in SO, to delay the onset of rancidity. The accelerated aging of oils using Rancimat provided useful insights into the kinetics of lipid oxidation and could be used to design more

Acknowledgement

The authors thankfully acknowledge AKK Kamani Oil Industries Limited, Mumbai, India for providing the oil samples and Council of Scientific and Industrial Research (CSIR), New Delhi, India for the research funding. The authors have no conflict of interest to declare.

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