Physical and Chemical Properties of Boiled Oil: A Traditional Method of Extracting Oil from Boiled Olive Fruits

Abstract

Background In some villages in Northern Jordan, farmers boil part of their olive fruit harvest before oil extraction to increase the quantity of oil, get a desirable acquired taste, as they claim, and get additional health benefits. Locals call this oil Boiled oil (BO), and its price is about 20% higher than virgin olive oil (VOO) produced by the same farmer. Objective The hypothesis was that boiling olive fruits may affect the quality of the produced oil. Therefore, our study aimed to determine the chemical and physical characteristics of boiled oil in comparison with VOO and the effect of storage of both types of oils for one year. Methods Total phenolic compounds, ferric-reducing antioxidant power assay (FRAP), and radical scavenging activity (RSA) were evaluated. Moreover, the quality indices of BO and VOO were also evaluated. Results Total phenolic compounds decreased significantly (p <0.05) from 8.7 mg GAE/100g in VOO to 2.47 mg GAE/100g in BO. The antioxidant activity measured using FRAP assay also decreased significantly (p <0.05) from 962 to 379 micromole/kg. Half-maximum inhibitory concentration (IC50) of the RSA was significantly higher (p <0.05) in BO samples (414 mg/ml) in comparison with VOO samples (38.9 mg/ml). Moreover, there was a significant increase (p <0.05) in acid value in BO samples (0.943%) in comparison with VOO samples (0.518%). However, the increase in acid value after one year of storage was higher in VOO than in BO. The peroxide value also increased significantly in boiled oil (500 meq/kg) in comparison with VOO (19 meq/kg). Additionally, a significant increase in ultraviolet absorption was observed in BO at k232 and k270 (3.5), which is considered unsuitable for human consumption compared with VOO (2.43). Conclusion In conclusion, these results showed that boiling olive fruits before oil extraction deteriorates oil quality as expected, and consumers should be educated that this type of oil is hazardous to human health and is a waste of effort and money.