Abstract
The objective of the present work was to improve the quality of high-free fatty acid olive (HFFAO) oil. Silica gel (SG) was used as adsorbent by applying filtration and stirring techniques. Chemical treatments with alkali using NaOH and/or Ca(OH)2 were also conducted to neutralize the acidity of HFFAO oil. The percentages of linoleic acid (C18:2) in the neutralized oils were lower than those in the reference olive oil. Untreated and treated HFFAO oil samples were stored under accelerated conditions for 30 days. The progress of oxidation at 60°C was followed by measuring acid value (AV), the formation of oxidative products (peroxide value (PV) and p-anisidine value (AnV)), total phenolic compounds (TPC), recording radical scavenging activity (RSA) toward 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and inhibition of β-carotene in a linoleate model system. The results indicated that SG and alkali treatments were effective in reducing the acidity of HFFAO oil. Generally, alkali treatments reduced the AV of HFFAO oil, while treatments with SG induced variable degrees of improvements in HFFAO oil acidity. Alkali treatments resulted in increasing the PV levels to 35 and 28 meq peroxide kg−1 oil for HFFAO treated with soda and lime, respectively. The corresponding improvement in the PV reduction (%) for HFFAO oil using SG was in the range of 10.5% to 47.3%.Treatments with SG or alkali resulted in reduction of AnV, wherein filtration with SG had a remarkable effect on AnV. Levels of TPC were reduced (ca. 70%) with alkali treatments, while treatments with SG resulted in reduction of about 22-48%. Antiradical properties of HFFAO oils were compared using stable DPPH free radicals. After 60 min incubation with DPPH, 78% of DPPH radicals were quenched by control sample, while HFFAO oils treated with SG or alkali were able to quench from 48 to 56%. Different SG and alkali treatments were not effective in inhibiting the oxidation of linoleic acid and the subsequent bleaching of β-carotene in comparison with the control. During autoxidation experiments the same trends of results was noted for both control and treated oils. Practical application: Olive oil is one of the most important edible oils in the world. Crude vegetable oils refined to remove free fatty acids (FFA) as well as other impurities that affect flavor, odor and appearance of oils. Deacidification process significantly influences the economics of oil production. Several methods to remove FFA have been developed to enhance the value of degraded vegetable oils, for example, physical refining based on distillation and chemical refining with sodium hydroxide. In this work, the quality of high-free fatty acid olive (HFFAO) oil was improved using silica gel (SG) as an adsorbent by applying filtration and stirring methods. The results stated that SG with small particle size permitted high adsorbing capacity and close to that induced with chemical treatments which are used commercially in a large scale to improve oil quality.
Highlights
The world productions of olive oil reach 2,800,000 ton and 98% of this production is to be found in the Mediterranean basin, where this agricultural system has been developed for thousands of years, characterized by its adaptation to the environment and its empiricism
Several methods to remove free fatty acids (FFA) have been developed to enhance the value of degraded vegetable oils, for example, physical refining based on distillation and chemical refining with soda
Stirring techniques with Silica gel (SG) leads to higher percentages of weight losing (16-14%) followed by filtration technique (13-12%), while alkali treatments with soda and lime resulted in moderate weight losing (8-7%)
Summary
The world productions of olive oil reach 2,800,000 ton and 98% of this production is to be found in the Mediterranean basin, where this agricultural system has been developed for thousands of years, characterized by its adaptation to the environment and its empiricism. Neutralization, bleaching and deodorization are typical refining steps of oil processing. Conventional approaches to refining include degumming, dewaxing, alkali refining, bleaching, and deodorization, and are best used with low-FFA oils. Several methods to remove FFA have been developed to enhance the value of degraded vegetable oils, for example, physical refining based on distillation and chemical refining with soda (sodium hydroxide). Several authors have proposed physical refining for high-FFA oils [5,6,7,8]. This process removes FFA along with odoriferous compounds by purging saturated steam through the oil at Received October 15, 2011; Accepted November 15, 2011; Published November 18, 2011
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