Valorization of hazelnut shells into natural antioxidants by ultrasound‐assisted extraction: Process optimization and phenolic composition identification

Abstract

The objectives of this study were to optimize the ultrasound‐assisted extraction for phenolic compounds from hazelnut shells and to quantify the individual phenolics. A central composite design was used to optimize extraction time, acetone concentration, and solid to liquid ratio (S/L), for the maximal yield of phenolic compounds and antioxidant capacities. The optimal conditions were 4.0 hr extraction time, 61% acetone, and 10 g/L S/L for the maximal total phenolic content (TPC, 11.23 mg gallic acid equivalents/g shell); 3.7 hr, 60.5% acetone, and 12.9 g/L for the highest ferric reducing antioxidant power (FRAP, 106.3 µmol Trolox equivalents/g shell); and 4.7 hr, 58.3% acetone, and 10 g/L for the highest DPPH radical scavenging capacity (DRSC, 101.83 µmol Trolox equivalents/g shell). Catechin, epicatechin gallate, and gallic acid were the most abundant phenolic compounds in the hazelnut shells. Ultrasound could be a good tool for accelerated recovery of polyphenols from hazelnut shells. Practical applications There has been an increasing production and application of hazelnuts globally. As the main byproduct of hazelnut industry, hazelnut hard shells are a good source of high value polyphenols. The optimized process presented here will allow a better understanding in the extraction of polyphenols from hazelnut shells. The results of this study are expected to improve the extraction efficiency of phenolic compounds and to help with the development of industrial extraction processes of natural antioxidants from hazelnut shells and other hard shells of tree nuts.

Potential Valorization of Hazelnut Shells through Extraction, Purification and Structural Characterization of Prebiotic Compounds: A Critical Review

“…In this sense, several researchers have proposed using HS by exploiting its high lignin content, transforming it into activated carbon which could then be used for the adsorption of heavy metals from the environment, such as lead [21,22], chromium, cadmium, zinc [23,24], nickel [25], copper [26], arsenic [27], but also dyes [28] and CO 2 [29]. Other studies have investigated the possible use of HS to produce hydrogen [30,31], ethanol [32], renewable fuels and chemical feedstocks [33], or fibreboards [34], but also to exploit its content in phenolic compounds [35][36][37][38]. However, in recent years many studies have focused their attention on the hemicellulosic fraction extracted from HS, pointing out the presence of very interesting compounds that could reveal new possible uses of this by-product.…”

Il-based advanced techniques for the extraction of value-added compounds from natural sources and food by-products

“…Advanced extraction techniques such as MAE [32][33][34][35], UAE [36][37][38], accelerated solvent extraction (ASE) [39,40] and pressurised technologies (PLE) [41,42], such as supercritical fluid extraction (SFE) [43][44][45] and subcritical water extraction (SWE) [46,47], also called pressurised hot water extraction (PHWE), are commonly used to obtain value-added compounds. The extraction of bioactive compounds from natural sources and food by-products using ILs with water or organic solvents and combined with advanced extraction technologies has gained relevance in the last years following the new trends based on the twelve principles of green chemistry [48,49] (Figure 4A).…”

Hazelnut Shells as Source of Active Ingredients: Extracts Preparation and Characterization

“…Recently, the demand for efficient and economical extraction processes has been increasing, especially from the food, chemical, and pharmaceutical industries. In response to this, many extraction techniques have been developed, especially for the extraction of phenolic compounds from vegetable materials, such as ultrasound-assisted extraction (either with a bath or with a higher power probe), supercritical fluid extraction and microwaveassisted extraction [16]. Ultrasound-assisted extraction is more efficient than traditional extraction methods in terms of reduced extraction time, extraction solvent volumes, extraction temperatures, and high yield values.…”

“…This extractive technique is "bio accredited" because it is based only on a physical process in which chemical adjuvants are not necessary. Solvents such as water and alcohol are used, regardless of the solubility of the active ingredients [16].…”