Isolation and purification phenolic compounds in California olive pomace by pilot-scale C18 gel chromatography

According to the Food and Agriculture Organization, the United States (mainly in California) produced 151,950 tons of olives in 2019, which resulted in a large amount of pomace waste. While many researchers focused on crude extraction and macroporous resin purification from European olive pomace on an analytical scale, few studies have been conducted to isolate fractions of US olive pomase (OP) by pilot-scale C18 chromatography. Hexane defatted Arbequina California OP was extracted by water, and the extract was loaded to a pilot-scale chromatography column with 262.5 mL C18 gel, and the elute syrup (ES) was collected. Desorptions were applied by 1 L of acidified water (AW), 35% methanol (35M) and 70% methanol (70M), respectively. The fractions were concentrated then freeze-dried. Total phenol contents (TPC) were measured by Folin-Ciocalteu assay. Individual phenols were determined by HPLC-DAD. Results showed that the TPC of the fractions of ES, AW, 35M and 70M were 2.88, 29.39, 170.56 and 235.96 mg gallic acid equivalents/g, respectively. Heatmap cluster analysis showed that ES and AW fractions had similar phenol profiles with hydroxytyrosol and tyrosol-glucoside; and 35M had hydroxytyrosol-glucoside, hydroxytyrosol, tyrosol-glucoside, 4-hydroxyphenylacetic acid (4-HPA), verbascoside and oleuropein; 70M contained hydroxytyrosol, tyrosol-glucoside, tyrosol, but generally had more nonpolar compounds such as verbascoside, rutin and oleuropein. Very interestingly, the 3,4-DHPEA-EDA in water extract at 31.43 min disappeared in 35M and 70M fractions, meanwhile a new peak at 29.25 min showed up which could be a new compound derived from 3,4-DHPEA-EDA possibly because of the acidified process. This study could be the first-ever report of phenol profile of pilot-scale C18 fractions of the US OP. This new data on the chemical compositions of the OP C18 fractions provides practical knowledge for the valorization and industrial food applications of the US olive wastes.