Abstract
The aim of the work was the optimization of the subcritical water extraction process of chestnut bark using Box–Behnken response surface methodology. The influence of process parameters, such as temperature, extraction time and solvent-solid ratio, on extraction yield, yield of the main compounds, total phenol content, total tannin content and antioxidant activity has been investigated. The identified compounds were ellagic and gallic acids, ellagitannins (vescalagin, castalagin, 1-o-galloyl castalagin, vescalin and castalin), sugars (maltose, glucose, fructose and arabinose) and sugar derivatives (5-HMF, furfural and levulinic acid). Finally, the optimal process conditions for obtaining the bark extract highly rich in ellagic acid and with satisfactory levels of total phenols and total tannins have been determined.
Highlights
Biomass represents the natural source of valuable components which could found application in many industries
By comparing the results of the present study with data published by Živković et al [3], it can be observed that ultrasound-assisted extraction of chestnut bark with 50% ethanol gave significantly lower extraction yields (7.84% for new and 3.40% (w/w) for old chestnut bark) than that obtained by subcritical water extraction
Comandini et al [9] and Chiarini et al [7] obtained higher contents of ellagitannins and gallic acid in extracts when chestnut bark was treated with methanol, but the ellagic acid content in the extracts was lower than that obtained by subcritical water extraction (Table 6)
Summary
Biomass represents the natural source of valuable components which could found application in many industries. The chestnut tree is the source of many important compounds [1]. Hydrolysable tannins are composed of esters of gallic acid or ellagic acid with a sugar core, mainly glucose, and are divided into two subclasses: gallotannins or ellagitannins, respectively [8]. Ellagitannins are complex derivatives of ellagic acid, which represent polyphenolic thermostable compounds which are slightly soluble in water, ether and alcohol [4]. Both ellagitannins and ellagic acid possess a number of health benefits and bioactivities, such as antioxidant, anticancer, anti-inflammatory, antibacterial, antimalarial, antiviral, cardioprotective and many others [4,10,11]. The content of biologically active compounds in the chestnut tree depends on type, location and climatic conditions where it grows, chestnuts from
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