Blanching of olive fruits before storage at different conditions: Effects on oil yield, lipase activity and oxidation

Abstract

In order to investigate the effect of post-harvest olive fruit storage temperatures, storage materials and blanching process on extra virgin olive oil production parameters, composition and quality, the fruits were subjected to dipping in hot water and were kept plastic perforated crates or woven sacks under ambient conditions or cool temperatures (8–10 °C) for 10 days. Blanching did not cause a decrease in oil yield (16–26 % blanched, 20–23 % unblanched) and in the amount of phenolic compounds transferred into the oil and supported the oxidative stability of oil, especially when cold (8–10 °C) storage conditions were provided. Blanching inhibited the lipase activity and ensured that it remained at almost the same level as the newly harvested olives after 10 days of storage (0.061 U/g). This level was half the level detected in unblanched olives stored at ambient temperature. Peroxide and K232 values were also significantly lower in oils obtained from blanched olives. Although storage in woven sacks resulted in higher total phenolics content (above 180 mg/kg) in olive oil compared to storage in crates, it negatively affected the oil yield, oxidative stability and free acidity of the oil. The results of the lipid oxidation analysis revealed the positive effect of cold storage, and superiority of perforated crates over woven sacks as storage materials. Storing the olives at 8–10 °C and in perforated crates after blanching is recommended in order to obtain superior oil quality, but in this case, it will be necessary to face a decrease of up to 30 % in yield compared to storage at ambient temperature.

Keywords

• Blanching
• Cold storage
• Lipase
• Olive