Phenolic Compounds from Diluted Acid Hydrolysates of Olive Stones: Effect of Overliming

Abstract

Annually, important quantities of olive residue are produced and may be the source of ecological damages. Like agricultural residues, which are abundant, renewable, low cost raw materials, olive stones are mainly subjected to biotechnological or chemical modifications in order to be transformed into valuable products (biofuels, biofertilizers, animal feed and chemical feed-stock). In aim to valorize olive stones, we are trying to identify the presence of different phenolic compounds in their dilute-acid hydrolysate (DAH). Phenolic compounds (PC) are considered as toxic material for fermentation process, therefore, their behavior are studied under overliming treatment with distinct pH levels (10 and 12), temperature (25 and 60°C) and detoxification time (15,30 and 60 min). Identification and quantification of phenolic compounds were performed by two chromatographic methods: Gas Chromatography mass spectrometry (GC-MS) and High-Performance Liquid Chromatography (HPLC). A liquid-liquid microextraction procedure is used in conjunction with silylation prior to the analysis of the compounds by GC-MS. Derivatives of benzoic acid, cinnamic acid, simple phenols, and aldehydes were identified. For all treatments combinations, pH 12 was more effective in reducing the total amount of phenolic compounds. Treatment of the hydrolysate with alkali at pH 12, 60°C and 60 min resulted in up to 29% decrease in the concentration of total phenolic compounds. Tyrosol, which was the main phenolic compound decreased by 73% under the same treatment. Chromatographic methods contributed to an accurate quantification and better understanding of the behavior of each PC, solely.