Optimization of the extraction of phenolic compounds from olive mill waste by acid hydrolysis and ultrafiltration

Abstract The olive oil production process generates significant quantities of waste, including value-added substances such as residual oil, carbohydrates, and phenolic compounds. This study presents a scalable laboratory process for optimizing the extraction of phenolic compounds from olive mill waste derived from a two-phase olive mill. The proposed process combines acidic hydrolysis with ultrafiltration. The acidic hydrolysis was optimized using a full factorial design followed by a central composite design to identify key operational parameters and determine the conditions for maximum extraction efficiency. The optimal conditions involved the addition of 304 mL of water to 50 g of waste (solid-liquid ratio: 0.164), 3.5 mL of H 2 SO 4 , and continuous stirring at 70 °C for 60 min. The phenolic-rich aqueous solution was then processed through a series of ultrafiltration stages using membranes with nominal molecular weight cut-offs of 30 kDa, 10 kDa, and 5 kDa. Phenolic compound retention rates were 15.1% for the 30 kDa membrane, 33.4% for the 10 kDa membrane, and 73.7% for the 5 kDa membrane. In terms of sugar reduction, the 5 kDa membrane achieved a 90.3% decrease in sugar concentration in the filtrate corresponding to a 99.1% reduction relative to the original waste. The 10 kDa permeate offers the optimal balance, featuring a high TPC/TOC ratio and a low SUG/TOC ratio, indicating a phenolic-rich solution with reduced sugar content. This study demonstrates a practical and efficient approach for recovering phenolic compounds from OMW, highlighting its potential for sustainable waste valorization and production of high-value bioactive compounds.