Effect of Drying Methods on Phenolic Compounds and Antioxidant Activity of Urtica dioica L. Leaves

Leani Martìnez Garcìa,Alberto Pardossi,Lucia Guidi,Carmine Negro,Costanza Ceccanti,Luca Incrocci,Luigi De Bellis

doi:10.3390/horticulturae7010010

Leani Martìnez Garcìa, Alberto Pardossi + Show 5 more

Open Access

https://doi.org/10.3390/horticulturae7010010

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Journal: Horticulturae	Publication Date: Jan 19, 2021
Citations: 31	License type: CC BY 4.0

Affiliation: University of Pisa, University of Salento

Abstract

Stinging nettle (Urtica dioica) is a plant well known in traditional medicine for its many beneficial properties, but the lack of standardization regarding the product to offer to consumers limits its diffusion. To this end, drying appears to be a useful technique to offer a low-cost product that can be stored for long time, but the different drying procedures may give rise to end-products of very different quality as nutraceutical and antioxidant compounds. Nettle leaves have been dehydrated employing freeze-drying (FD), oven-drying (OD) or heat pump drying (HPD) and compared with fresh leaves following water extraction to emulate the use by final consumers. Results indicate that the best dehydration technique is HPD, which apparently gives rise to more than a doubling of total phenols and antioxidant activity in the extract compared to the water extract obtained from fresh leaves but a reduction in the level of ascorbic acid of about 39%. In addition, the content of some phenolic compounds is 10 to over a hundred times higher in the extract after HPD than that obtained from fresh samples. This confirms that the dehydration technique should be tuned in relation to the compounds of greatest interest or value.

Highlights

Urtica dioica L., commonly named stinging nettle, is an herbaceous perennial plant belonging to the family of Urticaceae and native of Eurasia
The presented data clearly indicate that the best dehydration technique is heat pump drying (HPD) since the resulting aqueous extract exhibited a high content in total phenols and a high antiox
The presented data clearly indicate that the best dehydration technique is HPD since the resulting aqueous extract exhibited a high content in total phenols and a high antioxidant activity, as well as considerable levels in some phenolic compounds such as caffeoylmalic acid and caffeoylmalic acid dimer

Summary

Introduction

Urtica dioica L., commonly named stinging nettle, is an herbaceous perennial plant belonging to the family of Urticaceae and native of Eurasia. Recent reviews by Kregiel et al [2] and Grauso et al [3] revealed the isolation by stinging nettle leaves of some important phenolic compounds such as caffeic acid, hydroxybenzoic acid, vanillic acid, coumaric acid, gentisic acid, protocatechuic acid, gallic acid, syringic acid, quinic acid and many caffeic and quinic acid derivatives, quercetin, catechin, pelargonidin and apigenin in both the glycosidic and non-glycosidic forms, performed by other authors. The stinging nettle leaves revealed the presence of important compounds belonging to the terpenoid and carotenoid classes such as 3-oxo-a-ionol, 3-hydroxy-damascone, 3,5,5-trimethyl-4-(1-oxo-2-buten-1-yl)-3-cyclohexen-1-one, 4-(4-hydroxy-2,6,6-trimethyl-1cyclohexen-1-yl)-3-buten-2-one, 4-(3-hydroxy-1-butyn-1-yl)-3,5,5-trimethyl-2-cyclohexen1-ol and 3-hydroxy-5,6-epoxy-b-ionol as well as lutein, violaxanthin, neoxanthin, lycopene and β-carotene. Horticulturae 2021, 7, 10 tension, and for its anti-microbial, anti-inflammatory, antirheumatic and acute diuretic effects [2]. Understanding of the molecular mechanisms underlying the nutraceutical effects may open a new horizon for new therapeutic strategies [1]

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