There have been a number of methods developed for the extraction of inulin from Jerusalem artichoke tubers (Aravina et al., 2001; Barta, 1993; Ji et al., 2002; Vogel, 1993), a composite of which is illustrated in Figure 5.3. The specific method selected will depend on the end product desired, resources available, volume, and other factors.
Jerusalem artichoke tubers arriving from the field or storage are first washed to remove any soil and extraneous matter, and then mechanically cleaned (Barta, 1993). At this point, the tubers can be ground to produce Jerusalem artichoke flour for bread and other products (Leyst-Kushenmeister,
1937) or chipped, dried, and then ground (Figure 5.3). Heating the tubers prior to grinding inactivates polyphenol oxidase and other enzymes, improving the color of the flour (Modler et al., 1993a).
For the production of inulin and related products, the tubers are chopped or sliced and then pasteurized to deactivate enzymes (e.g., inulinase). Slicing is used for aqueous diffusion extraction (Barta, 1993). After extraction, the residual pulp is pressed and the combined extracts (aqueous and pressed) cooled. Aqueous extraction of slices followed by pressing gives a slightly higher yield than pressing of chopped material without water (~80 vs. 75%). Extraction is facilitated by the elevated temperature of the water and product (~80°C), which increases the yield to 95 to 98% (Vukov and Barta, 1987). The extract is primarily composed of inulin; however, it also contains mono- and disaccharides, amino acids, cations, colloids, floating contaminants, and colorants, which require removal. Clarification utilizes calcium hydroxide; the temperature during clarification varies depending upon whether the liquid represents a pressed or extracted juice. Colloids and floating contaminants can be coagulated at pH 10 to 11.5 using calcium hydroxide at 0.2% for extracted material or 0.4% calcium oxide equivalent for pressed juice. The cleared material is then filtered, at which point it may be fractionated to increase the purity of the individual fractions or handled as native inulin (a composite of sugars and inulin of varying degrees of polymerization). Chro-matographic fractionation by size exclusion generally yields two fractions: short-chain fructooli-gosaccharides with mono- and disaccharides, and a high-dp fraction. Fractionation may also be achieved using low temperature (Silver, 2002) or ethanol precipitation of the high molecular weight fraction (Aravina et al., 2001), or using ultra- and nanofiltration (Kamada et al., 2002).
Another option for native inulin is fermentation using microorganisms that utilize only sugars and short-chain fructooligosaccharides that yield ethanol and a residual high molecular weight inulin fraction. This fraction, regardless of the method of separation, can then be either processed as is or treated with endo- or exo-inulinase to produce a high-purity fructose syrup, or with endo-inulinase to give short-chain fructooligosaccharides. Alternatively, instead of fractionation via chromatography or other means, the filtered material can be passed through an ultrafiltration system, concentrated, and either spray-dried to produce dried "native inulin" or aseptically packaged to give an inulin concentrate. Dried inulin should be stored in moisture-proof packages.
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