Experimental design methodology was used to determine significant factors affecting the extraction yield of soluble and insoluble fibres from Agave americana L. and in second time to find optimum conditions leading to the highest yield. Results clearly indicated that the temperature, the powder to water (P/W) ratio, and the agitation speed were the most important factors influencing fibres extraction yield which increased with temperature, P/W ratio, and agitation speed. Ionic strength affected significantly soluble fibre extraction yield and was the most important factor among nonsignificant ones influencing insoluble fibres extraction yield. Then, a Box-Behnken design was carried out to maximise fibres extraction. Selected optimal conditions were temperature: 90°C; P/W ratio: 0.1625; agitation speed: 400？rpm; and ionic strength: 1.5？g/L. These conditions yielded 93.02% and 80.46% of insoluble and soluble fibres, respectively. Concentrates showed high fibres purity and good functional properties. 1. Introduction The Agavaceae is a plant family with nine genera and about 293 species. Agave, a monocotyledonous and monocarpic plant, is the most important genus with about 166 species [1, 2]. It is a voluminous, herbaceous, and perennial plant with long, succulent spiny leaves growing directly out from the central stalk to form a dense rosette. Its floral stalk, sometimes termed the trunk, can reach 10 to 20？m of length [3, 4]. The most important diversity center is the Mexican territory, with species spread from southwestern United States through Central America, the Caribbean and into northern South America [1]. Plants were taken from there to Europe, Africa, and the Far-East by the Spanish and Portuguese, where they naturalized rapidly, especially in the high arid regions around the shores of the Mediterranean [5]. They can prosper there due to their shallow rooting system and succulent morphology, while traditional annual crops cannot [6]. In Tunisia, the Agave americana L. is the most abundant variety of Agave but it has never been exploited, while it is worldwide used for commercial (rope, paper, fibres, pectin, mezcal, aguamiel, pulque, and tequila), ornamental (yucca, century plant and mother-in-law’s tongue) and medicinal applications (steroid extraction and antibacterial salves) [2–7]. Plant’s leaves are characterized by the abundance of agrate bundles of short fibres that are good holders of water, which gives the Agave’s leaves their rigidity and succulence [4]. Like most natural fibres, Agave fibrous bundles are composed mainly of -cellulose
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