Inulin, a Flexible Oligosaccharide I: 2 Review of Its Physicochemical Characteristics 3 4 Authors: Maarten A
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Accepted Manuscript Title: Inulin, a flexible oligosaccharide I: Review of its physicochemical characteristics Author: Maarten A. Mensink Henderik W. Frijlink Kees van der Voort Maarschalk Wouter L.J. Hinrichs PII: S0144-8617(15)00425-7 DOI: http://dx.doi.org/doi:10.1016/j.carbpol.2015.05.026 Reference: CARP 9930 To appear in: Received date: 22-12-2014 Revised date: 8-5-2015 Accepted date: 12-5-2015 Please cite this article as: Mensink, M. A., Frijlink, H. W., Maarschalk, K. V., and Hinrichs, W. L. J.,Inulin, a flexible oligosaccharide I: Review of its physicochemical characteristics, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.05.026 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. 1 Inulin, a flexible oligosaccharide I: 2 Review of its physicochemical characteristics 3 4 Authors: Maarten A. Mensinka, Henderik W. Frijlinka, Kees van der Voort Maarschalka,b, Wouter L.J. 5 Hinrichsa,* 6 7 a. Department of Pharmaceutical Technology and Biopharmacy, University of Groningen, Antonius 8 Deusinglaan 1, 9713 AV Groningen, The Netherlands 9 b. Process Technology, Corbion Purac, PO Box 21, 4200 AA Gorinchem, The Netherlands 10 11 Keywords: Physical; Chemical; Carbohydrate; Polysaccharide; Oligofructose; Polymer 12 13 Abstract 14 Inulin, a fructan-type polysaccharide, consists of (2→1) linked ß-D-fructosyl residues (n=2-60), usually 15 with an (1↔2) α-D-glucose end group. The applications of inulin and its hydrolyzed form oligofructose 16 (n=2-10) are diverse. It is widely used in food industry to modify texture, replace fat or as low-calorie 17 sweetener. Additionally, it has several applications in other fields like the pharmaceutical arena. Most 18 notably it is used as a diagnostic agent for kidney function and as a protein stabilizer. This work reviews 19 the physicochemical characteristics of inulin that make it such a versatile substance. Topics that are 20 addressed include morphology (crystal morphology, crystal structure, structure in solution); solubility; 21 rheology (viscosity, hydrodynamic shape, gelling); thermal characteristics and physical stability (glass 22 transition temperature, vapor sorption, melting temperature) and chemical stability. When using inulin, 23 the degree of polymerization and processing history should be taken into account, as they have a large 24 impact on physicochemical behavior of inulin. 25 26 27 Contents 28 1. Introduction ..........................................................................................................................................2 29 1.1 Chemical structure........................................................................................................................2 30 1.2 Isolation and production...............................................................................................................4 31 1.3 Uses...............................................................................................................................................6 32 2 Physicochemical characteristics............................................................................................................7 33 2.1 Chain length ..................................................................................................................................7 34 2.2 Morphology...................................................................................................................................9Accepted Manuscript 35 2.2.1 Crystal morphology...............................................................................................................9 36 2.2.2 Crystal structure....................................................................................................................9 37 2.2.3 Structure in solution ...........................................................................................................10 * Corresponding author. Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands. Tel.: +31 50 363 2398; fax.: +31 50 363 2500 ; E-mail address: [email protected] (W.L.J. Hinrichs) 1 Page 1 of 34 38 2.3 Solubility......................................................................................................................................11 39 2.4 Rheology .....................................................................................................................................12 40 2.4.1 Viscosity ..............................................................................................................................12 41 2.4.2 Hydrodynamic shape ..........................................................................................................14 42 2.4.3 Gelling .................................................................................................................................15 43 2.5 Thermal characteristics and physical stability ............................................................................17 44 2.5.1 Glass transition temperature (Tg).......................................................................................17 45 2.5.2 Vapor sorption ....................................................................................................................19 46 2.5.3 Melting temperature ..........................................................................................................20 47 2.6 Chemical stability........................................................................................................................21 48 3 Overview ................................................................................................ Error! Bookmark not defined. 49 4 Acknowledgements.............................................................................................................................22 50 5 Citations ..............................................................................................................................................23 51 52 1. Introduction 53 Inulin was discovered over two centuries ago by Rose (Fluckiger & Hanbury, 1879) and since then its 54 presence in many plants became apparent (Livingston, Hincha, & Heyer, 2007). Some examples of plants 55 containing large quantities of inulin are Jerusalem artichoke, chicory root, garlic, asparagus root, salisfy 56 and dandelion root (Kaur & Gupta, 2002). More commonly consumed vegetables and fruits containing 57 inulin are onion, leek, garlic, banana, wheat, rye and barley. Daily intakes have been estimated to range 58 from 1 to 10 g per day in the Western diet (Coussement, 1999; Van Loo et al., 1995). The average 59 American diet contains between 1.3 and 3.5 g of inulin per day, with an average of 2.6 g (Coussement, 60 1999). The European consumption of inulin appears to be substantially higher at 3 to 11 g per day, which 61 is below reported tolerances of at least 10 to 20 g per day (Bonnema, Kolberg, Thomas, & Slavin, 2010; 62 Carabin & Flamm, 1999). Inulin has also been used safely in infant nutrition (Closa-Monasterolo et al., 63 2013). This has led to the American Food and Drug Administration to issuing a Generally Recognized As 64 Safe notification for inulin in 1992 (Kruger, 2002). Inulin is also used pharmaceutically, most notably as a 65 diagnostic agent for the determination of kidney function (Orlando, Floreani, Padrini, & Palatini, 1998; 66 The editors of Encyclopaedia Brittanica, 2015). 67 68 Over the past decades, a lot of research has been done showing that inulin is a versatile substance with 69 numerous promisingAccepted applications. Several reviews have beenManuscript published on inulin, its characteristics and 70 functionality in food (Boeckner, Schnepf, & Tungland, 2001; Kelly, 2008, 2009; Seifert & Watzl, 2007) 71 and pharma (Imran, Gillis, Kok, Harding, & Adams, 2012). This review aims to provide an overview of the 72 relevant physicochemical properties of inulin, which make it such a useful excipient in food and pharma. 73 74 1.1 Chemical structure 75 Inulin, depending on its chain length, is classified as either an oligo- or polysaccharide and it belongs to 76 the fructan carbohydrate subgroup. It is composed of β-D-fructosyl subgroups linked together by (2→1) 2 Page 2 of 34 77 glycosidic bonds and the molecule usually ends with a (1↔2) bonded α-D-glucosyl group (Kelly, 2008; 78 Ronkart et al., 2007a). The length of these fructose chains varies and ranges from 2 to 60 monomers. 79 Inulin containing maximally 10 fructose units is also referred to as oligofructose (Flamm, Glinsmann, 80 Kritchevsky, Prosky, & Roberfroid, 2001). In food, oligofructose is more commonly used a sweet-replacer 81 and longer chain inulin is used mostly as a fat replacer and texture modifier (Kelly, 2008). Both inulin and 82 oligofructose are used as dietary fiber and prebiotics in functional foods. Its longer chain length makes 83 inulin more useful pharmaceutically than oligofructose. 84 Before processing, the degree of polymerization of inulin depends on the plant source, time of harvest, 85 and the duration and conditions of post-harvest storage (Kruger, 2002; Ronkart et al., 2006b; 86 Saengthongpinit & Sajjaanantakul,