Extraction, purification and In Vitro antioxidant activity evaluation of phenolic compounds in California olive pomace

Authors: ZHAO, HEFEI - University Of California, Davis; Avena-Bustillos, Roberto; WANG, SELINA - University Of California, Davis

Submitted to: Foods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2022
Publication Date: 1/10/2022
Citation: Zhao, H., Avena Bustillos, R.D., Wang, S.C. 2022. Extraction, purification and In Vitro antioxidant activity evaluation of phenolic compounds in California olive pomace. Foods. 11(2). Article 174. https://doi.org/10.3390/foods11020174.
DOI: https://doi.org/10.3390/foods11020174

Interpretive Summary: Olive pomace (OP), the main residue derived from olive oil extraction, is a valuable food byproduct containing natural phenolic compounds (phenols and polyphenols) with health benefits related to their antioxidant activities. According to the Food and Agriculture Organization (FAO), the United States (mainly in California) produced 151,950 tons of olives in 2019. We developed a practical process to produce pitted drum dried OP and used this product to extract and quantify phenolics from Arbequina OP. The objective of our work was to identify phenolic compounds, compare TPC and antioxidant activities of crude extracts from water, 70% methanol, 70% ethanol, and purified extracts from preparative chromatography columns of macroporous adsorption resin, using the most common olive cultivar in the United States. The efficacy of the removal of sugar was also monitored and reported. Our study demonstrated that major phenols in the Aberquina olive pomace from California, are hydroxytyrosol, oleuropein, rutin, verbascoside, 4-HPA, hydroxytyrosol-glucoside, and tyrosol-glucoside. Macroporous resin purification increased the total phenolic content (TPC) by 4.6 times the ethanol crude extracts of DOP while removing 37.33% of total sugar while the extractable TPC was 36-43 mg GAE/g DOP. Meanwhile, the antioxidant activities increased 3.7 times Trolox equivalent (TrE) for DPPH and 4.7 times TrE for FRAP compared to the ethanol crude extracts. This new data on the chemical compositions of selected US OP provides important and practical knowledge for the valorization and industrial food applications of the US olive wastes. Extracting bioactive compounds from the US OP not only could directly produce value-added products from food byproducts and increase consumers' health via the delivery of natural antioxidants but also reduce negative environmental impact. The chemical and phenolic composition of more olive cultivars in the US should be determined and compared for better assessment of the valorization of the US OP.

Technical Abstract: Olive pomace (OP) is a valuable food byproduct that contains natural phenolic compounds with health benefits related to their antioxidant activities. Few investigations have been conducted on the OP from the United States while many studies on the European OP have been reported. OP of Arbequina, the most common cultivar from California, was collected, extracted by water, 70 % methanol, and 70% ethanol, followed by purification using macroporous absorbing resin. Results showed that the extractable total phenolic content (TPC) was 36-43 mg gallic acid equivalents (GAE)/g in pitted, drum dried defatted olive pomace (DOP), with major contributions from hydroxytyrosol, oleuropein, rutin, verbascoside, 4-hydroxyphenyl acetic acid, hydroxytyrosol-glucoside and tyrosol-glucoside. Macroporous resin purification increased TPC by 4.6 times the ethanol crude extracts of DOP, while removed 37.33% total sugar. The antioxidant activities increased 3.7 times Trolox equivalents (TrE) by DPPH and 4.7 times TrE by ferric reducing antioxidant power (FRAP) in the resin purified extracts compared to the ethanol crude extracts. This study provided a new understanding of the extraction of the bioactive compounds from OP which could lead to practical applications as natural antioxidants, preservatives, and antimicrobials in clean-label foods in the US.