Hydroxytyrosol and tyrosol as the main compounds found in the phenolic fraction of steam‐exploded olive stones

Abstract

The lignocellulosic by-products, whole stones, and seed husks obtained from processing pitted table olives and oil olives were pretreated under various conditions of steam explosion, with and without previous acid impregnation. The various water-soluble noncarbohydrate compounds generated during steam explosion, such as sugar degradation compounds (furfural and hydroxymethylfurfural), lignin degradation compounds (vanillic acid, syringic acid, vanillin, and syringaldehyde) and the simple phenolic compounds characteristic of olive fruit (tyrosol and hydroxytyrosol), were identified. The amount of hydroxytyrosol solubilized was higher than that of the other compounds, and increased with increasing steaming temperature and time. This suggests its presence as a structural component of the olive stone.Olive stones have a high content of lignocellulosic material and are an important by-product of table olive processing. Pitted table olives make up 70-75% of total table olive production (1). The olive pomace obtained from olive fruit processing contains seed husk and a small amount of seeds, pulp, and peel, which can be separated by common industrial methods.Research related to oil, proteins, sugars, and phenolic compounds of olive seed has been carried out (2-5), but information related to the seed husk is scarce. However, the fiber of olive seed husks has been studied (6), and its polysaccharides have been characterized (7).The lignocellulosic products are currently used as an energy source, and have recently been employed to produce activated carbon (8). Steam explosion treatment (explosive autohydrolysis) has been extensively studied as a promising pretreatment process (9,10) to separate and increase the accessibility of main components of lignocellulosic biomass (cellulose, hemicellulose, and lignin). During steam explosion, the lignocellulosic material is split, and lignin is partly depolymerized (11), giving rise to phenolic compounds which are water-soluble and have inhibitory action against microorganisms (12,13).Olive leaves and fruit contain a considerable amount of phenolic compounds, mainly oleuropein, which, apart from their inhibitory action against microorganisms (14), have an antioxidant effect on the oxidative stability of oils (15). Some of these phenolic compounds are contained in the olive fruit processing by-products.In this study, the simple phenolic compounds obtained from the steam explosion of whole stones and seed husks were characterized and quantified, and the effect of temperature and time during steam explosion on the yield of these phenolic substances was evaluated. EXPERIMENTAL PROCEDURESMaterials. Whole olive stones were obtained from pitted table olives dried in an air stove at 30ºC and rubbed vigorously on a filter paper to remove any loosely adhering pulp tissue. Olive seed husks were supplied by an oil extraction plant (Oleícola el Tejar, Córdoba, Spain). The husks were obtained from olive pomace after separating peel, pulp, and seeds.Steam treatment. The steam explosion treatments ...

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

“…Olive phenolic compounds are eliminated in the olive oil and waste water, therefore, olive stones contain few PCs. Phenolic compounds present in the DAH were similar to those identified by Fernández-Bolañose et al [27] in the study of olive stones treated by steam explosion. Hydroxytyrosol and syringic acid (4-hydroxy-3,5-dimethoxybenzoic acid) are identified in olive stones treated by steam explosion.…”

Use of Whole Cells ofPseudomonas aeruginosafor Synthesis of the Antioxidant Hydroxytyrosol via Conversion of Tyrosol

“…Tyrosol, occurring naturally in olive mill wastewater (24), would be an excellent starting material for microbial conversion to hydroxytyrosol. Tyrosol can also be obtained from olive cake (18) and olive stones (19), in both cases by means of steam treatment.…”

Valorisation of waste fractions from autohydrolysis of selected lignocellulosic materials

“…In this field, ethyl acetate extraction allows the removal of a variety of potentially valuable compounds coming from extractives and acid-soluble lignin. In literature studies, [14][15][16] lignin-derived products (such as p-hydroxybenzoic acid and other hydroxyphenyl acids including ferulic, vanillic, syringic and coumaric as well as aldehydes such as syringaldehyde, p-hydroxybenzaldehyde and vanillin) have been identified.…”