Analysis of Composition and Study on Antioxidant and Antibacterial Properties of Ethanol Extract from Olive Fruit Residue
Olive oil is mainly produced in the Mediterranean region and is a subtropical woody oil and fruit tree species. The olive flesh is rich in high-quality edible vegetable oil – olive oil, and enjoys the reputation of the queen of vegetable oil. Olive tree, as a woody oil tree species, is famous for its “high quality, high efficiency, and high yield” characteristics, and is also known as a long-lived tree species due to its preference for light, cold resistance, and strong vitality. With the rapid development of olive processing industry in various countries around the world, a large amount of waste from the olive oil industry – olive pomace – is generated every year. During the processing of olive oil, approximately 2% of phenolic compounds in olive fruit enter the oil phase, while the majority of phenolic compounds (98%) remain in the solid residue.

Olive pomace is composed of olive skin, olive pulp, olive core, and wastewater. According to reports, the phenolic content of olive pomace is very high, 100 times higher than that of extra virgin olive oil (EVOO). Its phenolic compounds are a complex mixture of components, including hydroxytyrosol (HT) and tyrosol derivatives, cyclohexene ether terpene precursors, cyclohexene ether terpene compounds and derivatives (oleuropein, oleuropein glycosidic ligands, Ligustrum lucidum glycosides and their derivatives), flavonoids (paclitaxel and its derivatives, luteolin, apigenin, and rutin), phenylpropanoids (verbascoside and its derivatives), lignans (turpentine and its derivatives), and phenolic acids (ferulic acid, vanillic acid, shikimic acid, gallic acid, caffeic acid). Acid, cinnamic acid, and p-coumaric acid. These phenolic compounds all contain hydroxyl groups in their structures, which have a certain ability to scavenge free radicals, therefore they have certain antioxidant activity. A study has found that the content of hydroxytyrosol in olive pomace has reached 1624-2873mg/kg. HT, together with Maslin acid (MA, high concentration olive wax) and oleanolic acid (OA, a triterpene acid), has many functions, such as antioxidant, antibacterial, anti-inflammatory, anti diabetes, anti-cancer and anti HIV activities.

In recent years, research on olive pomace extract has found that it has certain effects in preventing cardiovascular and cerebrovascular diseases, antioxidation, and inhibiting bacteria, but its inhibitory effect on fungal growth is rarely reported. A large number of scholars have studied the extraction and separation of active ingredients from olive pomace, using methods such as ultrasound assisted enzymatic hydrolysis, hydrolysis, and organic solvent extraction. Although these methods yield high yields of active ingredients, comprehensive evaluation has found that they require high costs and some of the organic solvents used in the extraction process are relatively toxic. Therefore, this article uses green and environmentally friendly extractants H2O, 50% ethanol, 70% ethanol, and 90% ethanol, and obtains extracts by heating reflux method. The components of the extracts are analyzed by HPLC and GC-MS, and the antioxidant activity and antibacterial activity against Botrytis cinerea are evaluated. The research results provide a theoretical basis for the effective utilization of olive pomace in the field of antibacterial activity.

Olive pomace contains olive oil, water, and a large amount of water-soluble and fat soluble bioactive substances. In particular, the olive pomace separated from the two-phase system used in this study has a proportion of about 65% in the aqueous phase. Analysis of the composition of olive pomace reveals that the total fat content accounts for a relatively high proportion in both dry and wet weight ratios, indicating that olive pomace contains a significant amount of olive oil and can be used for refining pomace oil. This pomace oil can be applied in the food or cosmetics industry. For example, excipients in soap manufacturing, cosmetic formulations, and even active ingredients added to products. Studies have shown that in addition to other factors such as agricultural practices, varieties, or maturity stages, soil, light, and climate factors can also affect the composition of olive pomace and the distribution of bioactive compounds. The total phenolic content and hydroxytyrosol content of olive pomace were determined, and the results showed that the hydroxytyrosol content was higher in the 90% ethanol extract. Similarly, the highest total phenolic content was detected in the 90% ethanol extract, indicating that the higher the ethanol content in the extraction agent, the more phenolic substances in the extract. The volatile component analysis results showed that the H2O extract and 50% extract had similar composition, while the 70% ethanol extract and 90% ethanol extract had similar composition. The main volatile components in the H2O extract and 50% ethanol extract were acetic acid, (E) – basilene, 3-ethyl-4-methylpyridine, hexyl isovalerate, and butyl hexanoate. The main volatile components in 70% ethanol and 90% ethanol extracts are styrene, 5-ethoxy-4,5-dihydro-2 (3H) – furanone, 4,6-heptadienoic acid-3,3,6-trimethyl-ethyl ester, and 3-methyl-2-cyclohexen-1-one. Classifying the GC-MS spectrum data reveals that the content of acids, esters, and olefins is relatively high among the four substances. This indicates that the main volatile components in olive pomace are acids, esters, and olefins.

The evaluation of the antioxidant activity of the extract showed that the 90% ethanol extract had higher DPPH · scavenging and Fe3+reducing abilities than the H2O extract, 50% ethanol extract, and 70% ethanol extract. Analysis suggests that this may be due to the higher phenolic content in the 90% ethanol extract compared to the other three extracts, resulting in the 90% ethanol extract having higher DPPH · scavenging and Fe3+reducing abilities than the other three extracts. The overall antioxidant level of 90% ethanol extract is higher than the other three extracts, which is consistent with the results of phenolic content, indicating that the presence of phenolic substances is the main reason for the antioxidant properties of the extract.

The research results on the inhibitory effect of 90% ethanol extract on Botrytis cinerea show that 90% ethanol extract has a significant inhibitory effect on the growth of Botrytis cinerea. When the concentration of the corresponding medicinal medium is 10mg/mL, the inhibitory effect on Botrytis cinerea is the most significant. This research result is basically consistent with the research results of Qi et al. and Zhang et al. on the inhibitory effect of Botrytis cinerea.