Abstract
Walnut green husk is an agricultural waste produced during the walnut (Juglans regia L.) harvest, that could be valued as a source of high-value compounds. In this respect, walnut green husks from two areas of Southern Italy (Montalto Uffugo and Zumpano), with different soil conditions, were investigated. Glucans and pectins were isolated from dry walnut husks by carrying out alkaline and acidic extractions, respectively, and then they were characterized by FT-IR, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The colorimetric method for the enzymatic measurement of α- and β-glucans was performed. The maximum total glucan yield was recovered from Montalto walnut husks (4.6 ± 0.2 g/100 g DM) with a β-glucan percentage (6.3 ± 0.4) higher than that calculated for Zumpano walnut husks (3.6 ± 0.5). Thermal analysis (DSC) confirmed the higher degree of crystallinity of glucans from Zumpano. The pectin content for Montalto husks was found to be 2.6 times that of Zumpano husks, and the esterification degree was more than 65%. The results suggested that J. regia L. green husks could be a source of glucans and pectins, whose content and morphological and thermal characteristics were influenced by different soil and climate conditions.
Highlights
The walnut husk is the fleshy part of the fruit of the walnut fruit (Juglans regia L.) that covers the shell enclosing the edible kernel
Data reported in the table show that the content of glucans was slightly higher in walnut husks from Montalto
The obtained results showed that the pectin content of husks from Montalto (PM, 69.8 ± 0.1 g/100 g degree of methoxylation (DM) ) was about three times higher than that extracted from Zumpano hulls (PZ, 27.1 ± 0.3 g/100 g DM ), which indicated that different pedoclimatic areas influenced fibre content
Summary
The walnut husk is the fleshy part of the fruit of the walnut fruit (Juglans regia L.) that covers the shell enclosing the edible kernel. Scientific attention towards the valuable active constituents of walnut husks has been increasing The potential of this lowcost natural material as a source of phenolic compounds with antiradical and antimicrobial activities has been demonstrated by several studies [5]. Fermentation 2021, 7, 305 ntation 2021, 7, x FOR PEER and pectins from walnut husks for the valorization of these agricultural waste products. With the aim of providing additional added value to these residual sources and basic support for their functional uses, the present study investigated glucan and pectin contents from the green husks of walnuts grown in two different soil and climate areas of Southern Italy (Montalto Uffugo e Zumpano). Morphological and thermal characterizations of the extracted high-value compounds were performed in order to determine if the effect of the different pedoclimatic conditions of the two areas could lead to significant differences both in the content of glucans and pectins and their characteristics, which could affect their functional uses
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