Starch-Based Materials in Food Packaging

Processing, Characterization and Applications

Silvia Elena Barbosa, Maria Alejandra García, Luciana Castillo, Olívia Valeria Lopez

• Publisher: Academic Press
• Year: 2017
• Print ISBN: 9780128094396
• eBook ISBN: 9780128122570
• Topic: Technology & Engineering
• Subtopic: Industrial Design
• Index: Technology & Engineering

Starch-Based Materials in Food Packaging: Processing, Characterization and Applications comprises an experimental approach related to the processing and characterization of biopolymers derived from different starches. The book includes fundamental knowledge and practical applications, and it also covers valuable experimental case studies. The book not only provides a comprehensive overview concerning biodegradable polymers, but also supplies the new trends in their applications in food packaging.The book is focused toward an ecological proposal to partially replace synthetics polymers arising from non-renewable sources for specific applications. This tender implies the protection of natural resources. Thus, the use of starch as feedstock to develop biodegradable materials is a good and promissory alternative. With the contributions and collaboration of experts in the development and study of starch based materials, this book demonstrates the versatility of this polysaccharide and its potential use.- Brings the latest advances in the development of biomaterials from different starches, applying several technologies at laboratory and semi-industrial scales- Examines the effect of formulations and processing conditions on structural and final properties of starch-based materials (blends and composites)- Discusses the potential applications of starch materials in different fields, especially in food packaging- Includes chapters on active and intelligent food packages

Chapter 1

Starch

Luis A. Bello Perez and Edith Agama-Acevedo, Instituto Politécnico Nacional, Yautepec, México

Abstract

Starch granules are mainly found in seeds, roots, and tubers. The organization of starch components (amylose and amylopectin) as well as the presence of minor constituents (lipids, phosphate ester groups, and proteins) in the granules depends on botanical source, and they determine the functionality and end-use of starch. A comprehension of granular internal organization of starch components gives information to understand starch functionality and its behavior during processing. These polysaccharides can be isolated employing several methodologies, which mainly rely on the starch origin. In general, these methods include milling (wet or dry), gravity sedimentation, centrifugation, and filtration steps. In this chapter, the organization of starch components in the granule and the diverse isolation methods from different botanical sources are described. Besides, functional and physicochemical properties of several native starches, such as pasting and thermal properties are mentioned. Usually, native starches present inappropriate characteristics for most industrial applications and, hence, they must be modified by chemical and/or physical methods in order to broad their usage possibilities. Thus, in this section, several methodologies used to modify starches are described and the properties of the obtained derivatives are also reported.

Keywords

Starch granule; molecular structure; amylose; amylopectin; chain-length distribution

1.1 General Aspects

Starch is considered the main storage carbohydrate of green plants and it is produced in two organelles. In the photosynthesis process, during light periods, starch is produced in the chloroplasts and is used as energy source by the plant to achieve the metabolic process. Starch that is not used in this via is accumulated in the chloroplasts for its later usage during the dark periods, named as transitory starch. Additionally, this polysaccharide is stored in other organelles called amyloplasts for long time. This stored starch can be used during the seeds sprouting process. On the other hand, it can be isolated and used as raw material in different applications, for example, foods and pharmaceutical products, plastics, fermentation, adhesives, paints, paperboard, etc. Commercial starches are obtained mainly from maize, potato, wheat, rice, and cassava (Fig. 1.1). The use of starch in those products is due to its physicochemical and functional properties such as water retention, viscosity, gel formation, etc. However, the properties native starches are limited and hence they are modified by chemical, physical, or enzymatic methods to improve their functionality.

Figure 1.1 Isolation of starch from diverse botanical sources.

Many years ago, it was suggested that both the shape and size of starch granules are responsible for their physicochemical and functional characteristics. Also, granule size distribution is related to starch functionality. In addition, the amylose/amylopectin ratio and the chain-length distribution of amylopectin are suggested as important characteristics to explain starch physicochemical and functional features. More recently, starch structure, which is the arrangement of its components in the granules of both native and modified derivatives, is also reported as a factor of its functionality.

Diverse microscopy techniques have been reported to analyze the shape and surface of starch granules. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) give information about the appearance of granules surfaces. Thus, small protrusions of 10–50 nm were observed on granules surface of native wheat starch by AFM (Baldwin, Adler, Davies, & Melia, 1995). Additionally, large spherical protrusions (200–500 nm) were detected for native potato granules. Besides, SEM is a useful technique to examine their internal structures. In this sense, the presence of pores and channels in cereal starches and in granules hydrolyzed by α-amylase was evidenced. On the other hand, the internal arrangement of starch components in concentric rings was evidenced by transmission electron microscopy (TEM) (Fig. 1.2). In addition, this technique has been employed to obtain information about the starch structure modifications during its hydrolysis. Thus, the structure of starch nanocrystals produced by acid hydrolysis has been revealed by TEM (Wang, Yu, & Yu, 2008).

Figure 1.2 Projection of starch granule, figure modified of O’neill C.O & Field R.A (2015).

Starch is classified as a homo-polysaccharide and its basic unit is glucose. It is considered as a biopolymer mainly due to its natural origin, constituted by two main components: amylose and amylopectin. Amylose is an essential lineal polymer where glucose units are joined by α-(1–4) bonds, with few branching points, conforming the amorphous regions of the starch granules. On the other hand, amylopectin is the branched component where glucose units are also joined by α-(1–4) bonds in the lineal sections, and by α-(1–6) bonds in the branching points. Amylopectin is responsible of the starch crystalline lamella, although their branching points are part of the amorphous one. The presence of amorphous and crystalline regions in starch granules confers to this biopolymer a semicrystalline entity. In the “cluster” model, it is suggested that amylose is intermixed with amylopectin in the branching points (Pérez & Bertoft, 2010). Also, gelatinization studies suggest that amylose is concentrated toward the periphery of the granules (Jane, 2007). However, amylose location as well as the nature of the amorphous regions within starch granules is not well understood yet (Wang & Copeland, 2013). Generally, “normal” starches are constituted by 25–30% amylose and 70–75% amylopectin. However, there are some starches that show high amylopectin content (98–99%), named “waxy”; and others with high-amylose content (50–70%).

All of the aforementioned characteristics as well as other starch granules aspects, for example, shape and size, amylose/amylopectin ratio, chain-length distribution, and components arrangement are involved in the functionality of this biopolymer. For example, “waxy” rice starch, which presents small granule size and a great amount of short amylopectin chains, is widely used to formulate coatings for mushrooms to maintain their turgor during storage.

Isolated starch from some botanical sources can present minor constituents as proteins, lipids, and phosphates groups. Particularly, starch from potato presents phosphate monoesters and phospholipids that give special functional gel characteristics. Meanwhile, potato starch gels show high peak viscosity and transparency attributed to those phosphate groups joined to the amylopectin branching points, being the amylose/amylopectin ratio not responsible of these functional characteristics. The lipids present in some starches as maize and rice can complex with amylose and modify their functionality and digestibility.

1.2 Structural Characteristics of Starch Granules

In general, isolated native starches present an ordering of the components, organized in concentric rings, which is observed by a Maltase cross under polarized light. The positive birefringence showed by the Maltase cross indicates a radial orientation of the principal axis of lineal amylopectin chains that form the crystalline zones of starch granules. The Maltase cross indicates that order of starch components is present in the granule without reference to any crystalline form. When starch disorganization is occurred, the level of birefringence lost depends on the starch granules damage.

Crystalline zones that are formed due to the lineal section of amylopectin chains have a specific X-ray diffraction (XRD) pattern, indicating a periodicity of about 9–10 nm within the granular structure. Besides, this technique has been used to identify starches from different botanical sources. Thus, cereal starches present patterns arbitrary named A-type; meanwhile diffractograms of starches from tubers, rhizomes, and high-amylose maize are designed as B-type. On the other hand, some seeds and legumes show a C-type pattern that is a mix of A- and B-types. Besides, modified starches can present these C-type specific diffractograms. However, XRD pattern of native starches is modified or lost when structure disorganization occurred, for example, during gelatinization process. The crystallites of both A- and B-type are organized in left-handed, parallel-stranded double helices, sixfold structures, with a crystallographic repeat distance of 1.05 nm. The double helix of glucose chains presents hydrogen bonds between the two strands; being this conformation very compact, without any space for water or any other molecule. In the A-type, amylopectin chains are crystallized in a monoclinic lattice. In this unit cell, 12 glucopyranosyl units are located in the two double helices that are packed in a parallel arrangement. Meanwhile, four water molecules are located between the helices, producing a more densely packed crystal structure. In the B-type, chains are crystallized in a hexagonal lattice in double helices like to A-type unit cell, but 36 water molecules are present, producing a more opened crystal structure. It is important to mention that the arrangement of starch components, observed by the Maltase cross and the XRD pattern, is lost when starch dispersion is heated, a mandatory step during...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Preface
• Chapter 1. Starch
• Chapter 2. Bio-Based Materials from Traditional and Nonconventional Native and Modified Starches
• Chapter 3. Disadvantages of Starch-Based Materials, Feasible Alternatives in Order to Overcome These Limitations
• Chapter 4. Development of Biodegradable Products from Modified Starches
• Chapter 5. Composites and Nanocomposites Based on Starches. Effect of Mineral and Organic Fillers on Processing, Structure, and Final Properties of Starch
• Chapter 6. Thermoplastic Starch-Based Blends: Processing, Structural, and Final Properties
• Chapter 7. Starch Thermal Processing: Technologies at Laboratory and Semi-Industrial Scales
• Chapter 8. Use of Starch in Food Packaging
• Chapter 9. Future of Starch-Based Materials in Food Packaging
• Index