Abstract
The aim of this investigation was to enhance the quality of high free fatty acid olive oil (HFFAO). Silica gel (SG) was used as adsorbent by applying filtration and stirring techniques. Alkali treatments with NaOH and Ca(OH)2 were also conducted to neutralize high acidity of HFFAO. The levels of linoleic acid (C18:2) in neutralized oils were lower than in reference olive oil. Untreated and treated HFFAO samples were stored under oxidative conditions for 30 days at 60 °C. The progress of oxidation was followed by measuring acid value (AV), the formation of oxidative products [i.e., peroxide value (PV) and p-anisidine value (AnV)], total phenolic compounds (TPC), radical scavenging activity 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. Alkali treatments reduced the AV of HFFAO, while treatments with SG induced variable degrees of reduction in HFFAO acidity. The percentage of reduction in the PV for HFFAO using SG was in the range of 10.5–47.3 %. Filtration with SG had a significant effect on AnV. Levels of TPC were reduced (ca. 70 %) with alkali treatments, while treatments with SG resulted in reduction of about 22–48 %. After 60 min incubation with DPPH, 78 % of DPPH radicals were quenched by control sample, while HFFAO treated with SG or alkali were able to quench from 48 to 56 %. SG and alkali treatments were not effective in inhibiting the oxidation of linoleic acid and the subsequent bleaching of β-carotene in comparison with control oil. During autoxidation experiments the same trends of results were noted for both control and treated oils. The results stated that SG with permitted high adsorbing capacity reduced free fatty acids levels in HFFAO and the effect was close to that induced with chemical treatments which are used commercially in a large scale to improve oil quality.
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