Effect of processing techniques on yield and quality of Western Australian olive oil

Abstract

Many studies have shown that regular consumption of olive oil lowers the risk of cardiovascular diseases, breast, ovarian and prostate cancers. These benefits are thought to be due primarily to the high level of monounsaturated fatty acids and bioactive phenolic compounds in the olive oil. An increased awareness of these health benefits has led to a significant increase in the demand for olive oil around the world. However, the current production volume of olive oil is unable to meet the increasing demand. The techniques currently used by the industry extract less than 60 % of oil and 10 % of bioactive phenolic compounds from the olive fruits. There is therefore a need to not only increase the yield of oil extraction but also the extent of recovery of bioactive phenolic compounds.The objective of this study was to investigate the effect of extending the length of olive paste mixing period to 60 minutes and addition of processing aids to the olive paste (citric acid, Viscozymes and Pectolyase) on the extraction and quality of olive oil. The study was conducted over a 2 year period on Frantoio olives harvested from Gingin, Swan Valley and Margaret River in Western Australia at various maturity levels. The effects of these processing techniques were assessed on the yield of oil extraction, oil recovery, concentration of total phenolic compounds, antiradical activity, peroxides value, acidity level, fatty acid composition in terms of palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1) and linoleic acid (C18:2), level of conjugated diene (K232) and conjugated triene (K270), variation of specific extinction (AK), colour in terms of brightness (L*), greenness (a*) and yellowness (b*) as well as the sensory properties of the extracted olive oil samples. The oil samples extracted were also compared to the commercial olive oil samples in terms of these parameters. Significant differences between the quality of the extracted olive oil samples were detected at C=0.05 level on the estimated marginal means value as generated by the Univariate ANOVA procedure.The results from this study indicate that the interaction between the processing techniques and maturity levels did not significantly affect the quality of extracted oil. However, the interaction between the processing techniques and the olive growing sites did significantly affect the quality of the extracted oil. In addition, the quality of the olive oil samples varied in relation to the different processing techniques applied.Among the processing techniques investigated, addition of 0.15 g/mL of citric acid or Viscozymes were both effective in increasing the yield of oil extraction to around 12 % and the oil recovery to above 60 %. However, they were not effective at improving the extraction of phenolic compounds to the oil. Addition of citric acid at the higher concentration of 0.30 g/mL was the most effective technique in increasing the concentration of total phenolic compounds in the extracted oil. The concentration of total phenolic compounds was increased to 266.32 mg/kg oil when compared to the control sample (113.09 mg/kg oil). The antiradical activity of the extracted oil (47.61 % inhibition of DPPH radicals) was also higher than that of the control sample (32.49 % inhibition of DPPH radicals). Addition of 0.30 g/mL citric acid to olive paste lowered the percentage of saturated palmitic acid and increased the monounsaturated fatty acids: polyunsaturated fatty acids ratio. The addition of citric acid at 0.30 g/mL to the olive paste was beneficial in protecting the extracted olive oil against oxidation, as the peroxides value was significantly reduced. The olive oil extracted by addition of 0.30 g/mL citric acid also has comparable colour compared to the control olive oil sample. In addition, the quality of olive oil extracted by addition of 0.30 g/mL citric acid has comparable sensory profile to the commercial EVOO samples.