Characterization of Polyphenolic Compounds Extracted from Different Varieties of Almond Hulls (Prunus dulcis L.).

Maher Kahlaoui,Giuseppe Zeppa,Hayet Ben Haj Kbaier,Letricia Barbosa Pereira,Nabiha Bouzouita,Stefania Borotto Dalla Vecchia,Francesco Giovine

doi:10.3390/antiox8120647

Abstract

Ultrasound-assisted extraction (UAE) was applied as a pretreatment technique to improve the recovery of polyphenols from the almond hulls of four Tunisian and three Italian almond varieties, followed by the characterization with HPLC-DAD. The operating parameters (solid/liquid ratio, extraction time, and ethanol concentrations) were optimized using a Response Surface Methodology. A polynomial equation was calculated to describe the relationship between the operating parameters and dependent variables as total polyphenolic content (TPC) and antioxidant activity (RSA). A desirability function approach was used to determine the optimum conditions for operating parameters: a solid:solvent ratio of 2 g/100 mL, an extraction time of 13 min, and an ethanol concentration of 51.2%. Among the almond varieties, Pizzuta and Fakhfekh showed the highest polyphenol content and antioxidant activity. HPLC-DAD analysis of almond hull extracts confirmed that chlorogenic acid, catechin, and protocatechuic acid were the most important polyphenols in almond hull. The results highlighted that UAE could be an effective technique for the recovery of phenolic compounds from almond hull, thereby making this byproduct a promising source of compounds with potential applications in food and healthcare sectors.

Highlights

Almond (Prunus dulcis (Mill.), Prunus amygdalus (Batch), or Amygdalus communis (L.)), is a deciduous tree native to Iran, its surrounding countries, and Central Asia, but is widely cultivated elsewhere under different climates and growing conditions
The range for each Central Composite Design (CCD) variable was determined based on a preliminary test, where Ultrasound-assisted extraction (UAE) was applied to almond hulls of the Zahaf variety and the total polyphenolic content (TPC) yield was evaluated (Table 1)
3-O-glucoside, quercetin, and isorhamnetin, from the extracts of whole almond seed, the brown skin, and the hulls. This is the first study describing the polyphenols of almond hulls recovered from different varieties by applying UAE

Summary

Introduction

Almond (Prunus dulcis (Mill.), Prunus amygdalus (Batch), or Amygdalus communis (L.)), is a deciduous tree native to Iran, its surrounding countries, and Central Asia, but is widely cultivated elsewhere under different climates and growing conditions. The United States of America, and in particular, California, is the main producer of almonds globally, with a production of about 1.02 million tons in 2017, compared with the worldwide production of about 2.2 million tons in the same year [1]. The edible part of almonds, the kernel, is a seed with two large cotyledons. In the last several years, market demand for almonds as edible nuts and as an ingredient in manufactured food products. Almond kernel is consumed worldwide raw, cooked or dry-roasted, sliced or whole, and blanched (without the skin) or unblanched (with the skin). It is extensively used in bakery and confectionery products and in food preparation in general, and in pharmaceutical and cosmetic applications. Recent studies have evidenced their beneficial effects due to the capacity of their bioactive nutrients and nonnutrients to lower the plasma level of low-density lipoprotein cholesterol and the incidence and severity of cardiovascular disorder [2]

Objectives

Methods

Results

Conclusion