A Quick, Green and Simple Ultrasound-Assisted Extraction for the Valorization of Antioxidant Phenolic Acids from Moroccan Almond (<em>Prunus dulcis</em> (Mill.) D.A.Webb) Cold-Pressed Oil Residues

Abstract

Almond (Prunus dulcis (Mill.) D.A.Webb) is one of the most important nut crops both in terms of area and production. Over the last decades, an important part of the beneficial actions for health associated with their consumption was attributed to the phenolic compounds, mainly accumulated in almond skin. Interestingly, after cold-pressed oil extraction, most of these antioxidant phenolic compounds are retained in a skin-enriched by-product, so-called almond cold-pressed oil residue. In Morocco, ranked fifth producer in the world, this production generates an important part of this valuable byproduct. In the present study, using a multivariate Box-Behnken design, an ultrasound-assisted extraction (USAE) method of phenolic compounds from Moroccan almond cold-pressed oil residue was developed and validated. Response surface methodology resulted in the optimal extraction conditions: the use of aqueous EtOH 53.0% (v/v) as green solvent, applying an US frequency of 27.0 kHz for an extraction duration of 29.4 min. The present USAE allowed substantial gains in terms of extraction efficiency compared to conventional heat reflux extraction. Applied to 3 different local Beldi genotypes growing at 3 different experimental sites, the optimal USAE conditions led to a total phenolic content of 13.86 mg/g dry weight (DW). HPLC analysis revealed that the main phenolic compounds from this valuable byproduct were: chlorogenic acid followed by protocatechuic acid, p-hydrobenzoic acid and p-coumaric acid. The accumulation of these phenolic compounds appeared to be more dependent on the genetic background than on the environmental impact here represented by the 3 experimental culture sites. Both in vitro cell free and cellular antioxidant assays were performed, and revealed the great potential of these extracts. In particular, correlation analysis evidenced the prominent roles of chlorogenic acid, protocatechuic acid and p-hydrobenzoic acid. To summarize, the USAE method presented here is a quick, green, simple and efficient validated USAE for the possible valorization of antioxidant phenolic compounds from Moroccan almond cold-Pressed oil residues, making it possible to generate extracts with attractive antioxidant activities for future nutraceutical and/or cosmetic applications.

Almond Skin Extracts and Chlorogenic Acid Delay Replicative Aging by Enhanced Oxidative Stress Response Involving SIR2 and SOD2 in Yeast

“…The almonds were then crushed using an oil screw press (KOMET DD85G, IBG Monforts Oekotec GmbH & Co. KG, Monchengladbach, Germany) and the resulting residue was ground to approximately 100-150 μm of particulate using a blender equipped with rotating blades (Grindomix GM 200 blender, Retsch France, Eragny, France). This material was further subjected to an optimized and validated ultrasound-assisted extraction protocol [6]. Almond skin extract (AE) was obtained by ultrasound-assisted extraction completed in an ultrasonic bath (USC1200TH, Prolabo, Sion, Switzerland) consisting of a tank with an internal dimension of 300x 240x 200 mm with an electrical power of 400W corresponding to an acoustic power of 1W/cm 2 and a maximum heating power of 400W.…”

“…Sample was placed in 50-mL quartz tubes equipped with a vapor condenser and was suspended in 10 ml of aqueous EtOH 53.0% (v/v) as extraction solvent using a liquid-to-solid ratio of 10:1 mL/g DW (dry weight). During extraction, optimized and validated conditions -with a US frequency of 27.0 kHz during 29.4 min and an extraction temperature of 45 ° C -were applied [6]. The similar extraction protocol was also used to quantify CHL and RES in yeast cells and the culture medium.…”

“…In addition to the beneficial action attributed to their specific lipid profile, almond skin is also a rich source of antioxidant phenolic compounds that have also attracted attention in recent years [3,4]. Interestingly, after cold-pressed oil extraction, most of the antioxidant phenolic compounds accumulated in the almond skin are retained in a skin-enriched by-product, the so-called coldpressed oil residue, which makes it an attractive raw material for the extraction and recovery of these natural antioxidant phenolics [3][4][5][6]. Morocco, the world's fourth-largest producer, has produced more than 100,000 tons of unshelled almonds in recent years.…”

“…Many native almond trees (local ecotypes called Beldi) are still grown in the Eastern Morocco region [7,8]. These local almond ecotypes are known to accumulate higher levels of tocopherol and phenolic antioxidants compared to other varieties grown in the same region [6,8]. In the Eastern region of Morocco, almond trees occupy a surface of 26,000 ha producing ca 15% of the national production out of almonds.…”

“…This production generates an important part of the by-products, in particular those residues of cold pressed almond oil, enriched with antioxidant phenolic compounds. Recently, an ultrasound-assisted extraction method was developed to obtain an almond extract from Beldi ecotypes rich in chlorogenic acid and other related phenolic acids [6].…”