Pectin mechanical properties

Pectins is a general term for a group of natural polymers based on polymerized galacturonic acid partly esterified with methanol. In addition these polymers must be considered as copolymers due to existence of neutral sugar branched zones. [1]. Some uronic acid units may also be esterified on 0-2 or 0-3 position with acetic acid. The pectins occur in the cell wall of higher plants and control at least partly the mechanical properties, the ion exchange properties and the swelling of the cell walls. 

The HM and LM pectins give two very different types of gels the mechanisms of stabilization of the junction zones in the two cases are described and few characteristics given. The different molecular characteristics (DE, distribution of methoxyl or acetyl substituents, neutral sugar content or rhamnose content) play an important role on the kinetic of gelation, mechanical properties of the gel formed and also on the experimental conditions to form the stronger gels. All these points were briefly discussed. 

Morris, E. R., Gidley, M. J., Murray, E.J., Powell, D. A., and Rees, D. A. (1980). Characterization of pectin gelation under conditions of low water activity, by circular dichroism, competitive inhibition and mechanical properties. Int. J. Biol. Macromol. 2 327-330. 

Antimicrobial Edible films were prepared from natural fiber of pectin and other food hydrocolloids for food packaging or wrapping by extrusion followed by compression or blown film method. Microscopic analysis revealed a well mixed integrated structure of extruded pellets and an even distribution of the synthetic hydrocolloid in the biopolymers. The resultant composite films possess the mechanical properties that are comparable to films cast from most natural hydrocolloids that consumed as foods or components in processed foods. The inclusion of polyethylene oxide) alters the textures of the resultant composite films and therefore, demonstrating a new technique for the modification of film properties. The composite films were produced in mild processing conditions, thus, the films are able to protect the bioactivity of the incorporated nisin, as shown by the inhibition of Listeria monocytogenes bacterial growth by a liquid incubation method. 

In order to preserve the final compostabihty, different blends of biodegradable materials have been developed. There is a vast body of literature available in this domain. We find certain associations with agropolymers such as proteins [ARV 99, FIS 00, OTA 99] or pectins [FIS 00], but most research focuses on blends of plasticized starches and biodegradable polyesters PCL, PHA, PBSA, PBAT, etc. These polyesters, described previously, are produced industrially. They exhibit interesting properties such as a more hydrophobic natiue, limited water permeability and improved mechanical properties, in comparison to polysaccharides. However, the cost of biodegradable polyesters is generally higher than that of starch... 

In this book Song et al (10) described a novel nucleation and mineral growth process to produce a bone-like biomineral con site. The crosslinked gelatin-chitosan blend made by Payne et al fi/J may perhaps be used as biomimetic soft tissue or for bioencapsulation. The sorbitol-based polyesters synthesized by Mei at al (27) and Kulshrestha et al (26) may possibly find applications in tissue engineering. Biswas et al (13) described the preparation and the mechanical properties of modified zein. Fishman et al (12) made pectin-starch and pectin-poly(vinyl alcohol) blends and found them to be strong, flexible films. 

Pectins are water soluble polysaccharides found in the cell walls of higher plants. They have found extensive use in processed foods as a result of their gelling properties. Because pectin is a film forming material it has desirable physical and mechanical properties. 

Recently, mixtures of pectin, starch and glycerol (PSG) were extruded rather than solution cast into films in an effort to reduce the cost of film fabrication (11). SEM images revealed that the temperature profile in the extruder (TP) and the amount of water present during extrusion could control the degree to which starch was gelatinized. TDMA revealed that moisture and TP during extrusion, and by inference that the amount of starch gelatinization had little affect on the mechanical properties of PSG films. TDMA also revealed that extruded films underwent the same thermal transitions as cast PSG films. 

Orts et al. [17] investigated composites of wheat or potato starch blended with pectin and reinforced with cellulose nanofibrils extracted from cotton, softwood, or bacterial cellulose. Mechanical and thermal properties of composites produced by casting and extrusion (extruded under a low and high shear mode) were evaluated. The addition of cellulose microfibrils to starch had a significant effect on mechanical properties at low concentrations. For example. Young s modulus of wheat starch nanocomposites reinforced with cotton nanofibrils increased by five times with the addition of only 2.1 wt% of nanofibrils (see Table 11.1). 

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