Cellulose polysaccharide is the most important component in plants with a fascinating structure and properties. Despite the origin, cellulose is a linear homopolymer of ß-(1-4)-linked D-glucopyranose units varying mainly on purity, degree of polymerization (DP) and crystallinity index. This linear stiff-chain homopolymer is characterized by its hydrophilicity, chirality, biodegradability, broad chemical modifying capacity, and its formation of versatile semicrystalline fiber morphologies. This chapter aims to show the most important applications of cellulose in food, presenting other cellulose derivatives as methylcellulose, carboxymethyl cellulose, and novel cellulose forms as bacterial cellulose. New frontiers, including environmentally friendly cellulose fiber technologies for food packaging, bacterial cellulose in foodstuff and other applications as thickening agent, stabilizing agent, gelling agent, suspending agent were highlighted with future aims, strategies, and perspectives of cellulose research and its applications.
TopIntroduction
In the last years, cellulose has become a popular food additive due to its unique chemical and physical properties. Cellulose is the most abundant natural polymer in the world and its properties have been exploited by mankind for millennia, especially to manufacture products for sectors such as paper, textile, construction, new materials, pharmaceutical, cosmetic, food, coatings and adhesives, gaskets and packing.Even other potential applications for this renewable resource are being increasingly hunted (Klemm et al., 2005)especially due to the lack of fossil resources (Martins et al., 2009).
Cellulose is a linear polymer composed of β-D-glucopyranose units linked by (1-4) glycosidic bonds forming chains(Klemm et al., 2005) with approximately 10.000 to 15.000 units (in native cellulose) (O’sullivan, 1997). The cellulose chain structure is indicated in Figure 1. Three hydroxyl groups in equatorial position in each glucose unit are responsible for its supramolecular structure, which determines many of its chemical and physical properties. The hydroxyl groups can be modified by chemical reactions generating esterified fibers with DS (degree of substitution) from 0.002 to 0.41; and in all instances, the cellulose surface acquires high hydrophobicity (Tomé et al., 2011).
Figure 1.
Cellulose chain structure
By characterization techniques like infrared spectroscopy, X-ray diffraction and 13C nuclear magnetic resonance, it has been possible to establish the formation of intramolecular hydrogen bonds between the hydroxyl group of C3 of a glucose unit and the oxygen of pyranose ring of contiguous glucose.Formation of intramolecular and intermolecular hydrogen bonds are shown in Figure 2. These are responsible for the relative rigidity of the cellulose molecule, which is reflected in the high tendency to crystallize in parallel arrangementsand the ability to form fibrillary structures (Krassig, 1993; Fengel& Wegener, 1984).
Figure 2.
Formation of intramolecular and intermolecular hydrogen bonds between two adjacent cellulose molecules
Therefore, molecules tend to organize into individual cellulose nanofibrils of 2 to 5 nm in widthwise in higher plants, 2 to 4 nm for bacterial cellulose and 15 to 30 nm for algae (Meshitsuke & Isogai, 1995). Within nanofibrils, chains form crystalline domains with different arrangements that give rise to several polymorphisms (I, II, III, and IV), in which each of the unit cell has a specific diffraction pattern. The most abundant polymorphism is cellulose I in native cellulose and it can be converted reversibly or irreversibly into the others polymorphisms by chemical, physical and thermal treatments. Transformation between different cellulose polymorphisms are shown in Figure 3.
Figure 3.
Transformations between different cellulose polymorphisms