Modified starch, coating

Ben Arfa, A. L. Preziosi-Belloy P. Chalier N. Gontard. Antimicrobial paper based on a soy protein isolate or modified starch coating including carvacrol and cinnamaldehyde. /. Agric. Food Chem. 2007,55, 2155-2162. 

Enzymes in Pulp and Paper Production. Enzyme-modified starch has been used for adhesives to strengthen paper base and for surface coating. Developments since the late 1980s of further uses of enzymes in papermaking include pitch control and bleach boosting, (see Paper Pulp). 

Amylopectin is the polymeric component of starch and consists mainly of glucose units joined at the 1,4-positions. Relative molar mass tends to be very high, e.g. between 7 and 70 million. A variety of modified starches are used commercially which are produced by derivatisation to give materials such as ethanoates (acetates), phosphates, and hydroxyalkyl ethers. Modified and unmodified starches are used in approximately equal tonnages, mainly in papermaking, paper coatings, paper adhesives, textile sizes, and food thickeners. 

Before weaving, the warp is covered with a layer of polymer to withstand the mechanical stress (abrasion, tension) during weaving. These polymer coatings are so-called sizes. Normally native starch, modified starch like carboxymethyl-starch (CMS), carboxymethyl-cellulose (CMC), polyvinylalcohols (PVA), polyacrylates, and proteins can be used. The amount of added polymer for staple yarns like Co is between 8 and 20% of the weight of the warp. As a result, in many cases the final amount of polymer to be removed in the desizing step is approximately 5-10% of the weight of the fabric. 

Until recently, the use of enzymes in the paper and pulp industry was not cortsidered technically or economically feasible. Quite simply, suitable enzymes were not readily available, except for the limited use of enzymes to modify starch for paper coatings. However, research by scientific institutions and enzyme producers has led to the development of new enzymes that offer significant benefits for the industry, particrrlarly from the environmental point of view. Two examples of applications, in addition to the starch modification, made possible by new enzyme developments are given here bleach boosting and pitch control. 

In the manufacture of paper, starch-based adhesives are used either to strengthen the paper base or for coating the surface of the paper. Raw starch is unsuitable for either purpose. To achieve sufficient adhesive power with raw starch would require the application of a solution that was far too thick for practical use. Instead, chemically modified starch, with a much lower viscosity in solution, is used. As an economical alternative to modifying the starch with aggressive oxidizing agents, the starch can be treated with enzymes ( df-amylases) to obtain the same thinning effect... 

Szymanowski, H., Kaczmarek, M., Gazicki-Lipman, M., Klimek, L., Wozniak, B. (2005). New biodegradable material based on RF plasma modified starch. Surface and Coatings Technology, 200, 539-543. 

Currently, only hydrolases (amylases) are used to modify starch. The use of amylases to produce products derived from hydrolysis of starch is described in Chapters 7,20, 21 and 22. Starch hydrolyzates with good adhesion property that can be applied at high solids to minimize the energy required to remove moisture after application are very desirable for coating food items with seasonings, flavors and colorants. This property can be achieved by treating starch with an amylase or amylases to a dextrose equivalency (DE) (see Chapter 21) of 2-40.228 Waxy maize is the preferred starch. 

A previous trend in the paper industry of limiting starch purchases to unmodified grades and effecting modification on-site in the paper mill has changed. The variance in products thus obtained was frequently wider than in products supplied by the starch manufacturer. As a result, there is now more preference to utilize modified starches with specific application properties. Growth in paper recycling should lead to an increased use of starch as a coating binder in place of synthetic materials. 

After fibres and fillers, starch is still the third most important raw material for paper making. Various types of modified starches are applied throughout the papermaking process from the wet-end via the size- or film-press to coating and paper converting. 

In the food industry, because the spray dryer is commonly available, economical, fast, and produces good-quality material [16], it becomes the most common means of encapsulation. The encapsulation process is simple and similar to the one-stage spray drying process. The coated material is called the active or core material, and the coating material is called the shell, wall material, carrier, or encapsulant [43]. The active material to be encapsulated, such as an oil or fia-vor in an oil base, is dispersed in a hydrocolloid carrier, e.g., gelatin, modified starch, dextrin or maltodextrin, or gum arabic. After the emulsifier is added, the mixture must be... 

Starches are modified chemically in various ways. Some acetate and phosphate esters are produced commercially, as well as hydroxyalkyl and tertiary aminoalkyl ethers. Both unmodified and modified starches are used principally in paper making, paper coating, paper adhesives, textile sizes, and as food thickeners. There are many reports in the literature on graft copolymers of starch. The work is often conducted is search of biodegradable materials for packaging and agricultural mulches. Most chemical modifications of starch parallel those of cellulose. 

Starches are very common natural products heavily used by the paper and other industries (29). In paper coatings, they are used as both binders and co-binders (thickeners). They naturally occur in two fractions, namely linear amylose and branched amylopectin, with usually the latter being the more abundant. Modification may be performed in numerous ways (29) in order to provide desirable physico-chemical properties, tailored to usage. For example, it is possible to cationically modify starch by using cationization reagents at high pH, in order to produce starches suitable as pigment binders. Nonionic, oxidized, anionic, amphoteric, hydrophobi-cally modified, and other starch variants may also be produced. 

The opacity is a critical property if the starch-based films are used for food coatings applications. Transparent films are characterized by low values of the area below the absorption curve. The obtained values showed that films with addition of organic acid modified starch microparticles CMSt were more transparent than films with no chemically modified starch [74]. Besides, the opacity of films decreased due to addition of CMSt, this tendency being more noticeable in sample modified with tartaric acid. Film opacity decreased in order TAMSt/Stcellulose filler composite samples is represented [75]. 

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