Peter A Williams is Professor of Polymer and Colloid Chemistry and Director of the Centre for Water Soluble Polymers at the North East Wales Institute. Has published over 170 scientific papers and edited over 30 books. He is Editor-in-Chief of the international journal Food Hydrocolloids. His research is in the area of physicochemical characterisation, solution properties and interfacial behaviour of both natural and synthetic polymers. Recent work has been involved with the determination of molecular mass distribution using flow field flow fractionation coupled to light scattering, rheological behaviour of polymer solutions and gels, associative and segregative interaction of polysaccharides, development of polysaccharide-protein complexes as novel emulsifiers.

Gums and Stabilisers for the Food Industry 16

By Peter A. Williams, Glyn O. Phillips

The Royal Society of Chemistry

Copyright © 2012 The Royal Society of Chemistry
All rights reserved.
ISBN: 978-1-84973-358-8

Contents

Chapter 1 Market overview, 1,
Isolation, characterisation and modification,
Chapter 2 Mixed hydrocolloid systems,
Chapter 3 Hydrocolloid gels,
Chapter 4 Emulsions,
Chapter 5 Fibres and films,
Chapter 6 Microstructure and texture,
Chapter 7 Food applications,
Chapter 8 Health – related aspects,
Subject index, 425,

CHAPTER 1

Market overview

OVERVIEW OF THE FOOD HYDROCOLLOIDS MARKET

Dennis Seisun

IMR International, San Diego CA, USA [www.hydrocolloids.com; email dseisun:hydrocolloid.com]

This paper focuses on the various definitions and classifications of hydrocolloids and presents a global overview of hydrocolloids from both a numerical and perceptual point of view. Hydrocolloids for all the studying and analyzing conducted on them, remain a nebulous subject. Ask ten scientists for an exact definition and one is likely to receive ten somewhat different answers. In general, hydrocolloids ‘work with water’, they thicken, suspend, gel or stabilize a solution. As colloids they fall between a true solution and solid suspension. A range of novel, nutraceutical properties are being discovered and established for hydrocolloids. A key property of some is that of providing fiber, both soluble and/or insoluble.

Hydrocolloids are used in three key segments, industrial, food and oilfield applications. The relative importance of each segment in terms of hydrocolloid value and volume is given in the table below:

[TABLE OMITTED]

The individual hydrocolloids in food can be roughly divided into three major segments, based on overall value. Starches and gelatin are the giant category with over $1 billion in sales each. The second group includes five hydrocolloids with sales between $200-700 million and the remainder are those with sales less than $200 million as indicated in the table below:

[TABLE OMITTED]

Unfortunately, data for Chinese production and consumption of hydrocolloids is sporadic and unreliable. The above estimates therefore, do not include China. There is no doubt, however, that China represents a significant additional volume. In the case of CMC for food applications in China, reliable data has been obtained. Chinese consumption of food grade CMC is thought to be twice the volume of CMC consumption in all other parts of the world. Chinese food CMC specifications require a purity level of 95% whereas other parts of the world specify purity above 99%. IMR is gathering estimates of Chinese hydrocolloid consumption as an on-going effort. Results of these efforts will be published in future issues of The Quarterly Review of Food Hydrocolloids as they are obtained.

Prices of hydrocolloids vary widely, with the costliest, pure gellan gum (approx $60.00/kg), being as much as 60 times the price of native starch ($1.00/kg). Even within a hydrocolloid category, there is a wide range of different grades, eg gum arabic of the emulsifying Acacia senegal grade may cost double the price of non-emulsifying Acacia seyal grade. Despite these variations, IMR has established a rough average for each hydrocolloid category as indicated in the below table:

[TABLE OMITTED]

The above are averages based on the four quarterly prices published in IMR’s Quarterly Review of Food Hydrocolloids for 2010. There is much volatility in price s and readers are encouraged to obtain up to date price information, from IMR or elsewhere. Guar gum for example, has more than doubled in price since the above table was produced. Xanthan prices vary widely depending on country of origin. Most prices are directly linked to upstream raw material costs which have increased significantly for most hydrocolloids in 2010-2011.

The rapidly changing world of commerce has wrought many changes on the hydrocolloid industry. Channels of distribution have changed as have relationships between producers themselves with strategic alliances being made. Distributors are more widely used even by the large multinational hydrocolloid producers. Technical service and formulation development are also being offered by some distributors in an effort to differentiate themselves. Overall channels, however, remain the same as indicated in the below diagram established decades ago by IMR:

[ILLUSTRATION OMITTED]

Crystal ball gazing and forecasting in any industry is an inexact science if a science at all. Forecasting the future of hydrocolloids is no easier or more accurate. Nevertheless with a knowledge of properties, applications, consumer trends and raw material tendencies an ‘informed guess’ can be made. The table below is presented on a best effort basis:

[TABLE OMITTED]

Pectin, xanthan and MC/HPMC are expected to be the most rapidly growing hydrocolloids each for their specific reasons. Pectin is the most label and consumer friendly of all hydrocolloids. Consumer concerns and label preferences are paramount in hydrocolloid selection and likely to remain so in the foreseeable future. Pectin is a ‘no problem’ hydrocolloid on a food label. Xanthan gum has become the ‘ubiquitous’ hydrocolloid which is appearing on an increasing number of labels worldwide. Xanthan in many cases, has gained the reputation of ‘try this hydrocolloid first’ in a formulator’s product development efforts. If xanthan works it is likely to be used. Only if xanthan fails, will efforts then focus on alternative hydrocolloids. The group of cellulosics in the MC/HPMC category are rapidly growing for two primary reasons, a) they are currently a small volume item and high growth more easily achieved and b) formulators are discovering properties well beyond the thermal gelation for which they were initially known.

Of course the above are generalizations each subject to their own limitations. Also, what is applicable now may not apply in the future. Gelatin for example was, along with pectin, amongst the most consumer friendly items on a food label. And then, mad cow disease appeared, the number of vegetarians grew exponentially and kosher/halal requirements became more widespread. Change is the only steady factor.

A large part of the future of hydrocolloids will remain in thickening, stabilizing, gelling and suspending. A growing value however is found in nutritional and nutraceutical aspects which had never before been considered. Hydrocolloids as sources of soluble and/or insoluble fiber is only one such aspect. Satiety control and even nutraceutical benefits are all in the pipeline of evaluation and certification.

Isolation, characterisation and modification

RAMAN AND FT-IR MICROSCOPY OF NATIVE AND HIGH-AMYLOSE MAIZE STARCH IN SITU

N. Wellner, M.L. Parker, D.M.R Georget and V.J. Morris

1 INTRODUCTION

Knowledge of the structure of starch granules has advanced considerably over the last 30 years. For wild-type starches the granule structures are homogeneous and the properties of individual granules can be deduced from studies on populations of isolated granules. Natural or induced mutations in the biosynthesis of starch can be used to generate so-called high-amylose or low-amylose starches. Despite this nomenclature it is clear that such mutations actually lead to significant modifications of the starch granule structure rather than simply altering the levels of amylose and amylopectin which can be isolated from the granules. Even in the case of isogenic mutants such as amylose extender ae (high-amylase) maize, studies on individual granules reveal substantial heterogeneity in the structure for isolated populations of starch granules. In order to understand the effects of mutations in biosynthesis on granule structure it is necessary to map the chemical and physical structures of individual granules. Based on a previously described method for in situ imaging of starch in dry seeds, it is shown in this article that Raman microscopy can be used for mapping the chemical and physical structures of starch granules within the dry seeds of wildtype and ae maize, an isogenic mutant resulting from the suppression of starch branching enzyme IIb (SBEIIb) during biosynthesis.

2 MATERIALS AND METHODS

2.1 Maize kernel samples

Kernels of wild-type maize (cultivated Oh 43) and the high-amylase amylose extender (ae) mutant in an Oh 43 background were provided by Dr K. Denyer (John Innes Centre, Norwich, UK). Thick (2 mm) transverse slices were cut from the wild-type and mutant maize samples approximately 2 mm from the crown end of the kernels using a fine-toothed saw. These slices were cut in half across the long axis to obtain blocks including the pericarp, aleurone and outer endosperm. The blocks were glued onto aluminium scanning electron microscopy stubs with the transverse orientation uppermost. An ultra-microtome (Reichert-Jung Ultracut E) and a glass knife were used to polish the face of these blocks (Figure 1a). Sections of endosperm tissue (1.5-2.0 µm) were cut from these polished blocks with a glass knife (Figure 1b).

2.2 Conventional light microscopy

For polarised light microscopy, sections were mounted in water and examined using an Olympus BX60 (Olympus, Japan). Sections stained with 0.2% iodine in 2% potassium iodide diluted 2:1 with distilled water were viewed by bright field optics.

Sections for FT-IR and Raman microscopy/spectroscopy were floated onto a small drop of distilled water or 30% ethanol on infra-red transparent BaF2 discs (Figure 1b). Any excess liquid was removed with a strip of filter paper and the samples were allowed to dry under ambient conditions.

2.3 Raman microscopy

Raman images were obtained using an upgraded WITec CRM200 (Witec GmbH, Ulm, Germany) confocal microscope using a frequency doubled Nd YAG laser (532 nm) and a 100x objective. Raman data were collected using a 600 nm grating in the spectral range -30 to 3980 cm-1. A 50 x 50 mm2 areal region of the sample was scanned in 0.39 mm steps, producing a map containing 128 x 128 pixels. An initial scan (100 ms integration time) was used to determine the quality of the sample in the chosen area before collecting a full scan at 1 s/pixel in order to obtain spectra with a reasonable signal to noise ratio. The Raman maps were analysed with Matlab 7.9 (The MathWorks, Inc, USA). Spectra were baseline corrected by subtraction of the value at 1800 cm-1 as a linear offset: the background was approximately linear in the starch-rich areas but contained broad fluorescence bands in the carotenerich areas. Areas of bands were calculated by integrating the three values closest to the peak maximum, assuming a 12 cm-1 band width, in order to avoid overlap of neighbouring bands. Several sections from different maize kernels were examined, and images were recorded from different areas in each section. All gave consistent results, although the extent of the observed differences varied because of the variability of kernels and locations. The data shown are typical of the observed variations in the wild-type and ae maize samples.

2.4 FT-IR microscopy

FT-IR data were acquired with a Varian UMA600 Microscope interfaced to a FTS6000 FT-IR spectrometer (Digilab/Varian). Average spectra were collected with a MCT detector (128 scans at 2 cm-1 resolution) from a 1 mm diameter spot. Microscopic FT-IR images of the sections were acquired with a 128 x 128 pixel FPA detector. The image area was 0.64 x 0.64 mm2. Using a 15x objective, the nominal spatial resolution was 5 x 5 µm per pixel, however, the effective spatial resolution was diffraction limited by the IR wavelength (2-10 µm). 128 scans at 8 cm-1 resolution were co-added in transmission and referenced against a background from an empty area of the BaF2 disk FT-IR maps were imported into ENVI 4.6 (ITT Visual Information Solutions). The spectra were baseline corrected in the region 1800-900 cm-1 with the inbuilt continuum removal function, and then classified according to the shapes of the carbohydrate band regions.

3 RESULTS AND DISCUSSION

Optical microscopy reveals marked changes in the structure of the starch granules in the wild-type and ae mutants (Figures 2 & 3). For the wild type the granules are similar in shape and size, and stain uniformly blue with KI/I2 in cells across the endosperm (Figure 2a). Images obtained using polarising optics reveal characteristic Maltese cross patterns indicating radial orientation of the crystalline regions within the granules (Figure 2b): at higher magnification the granules reveal growth ring structures indicating a periodic radial variation in the crystalline/amorphous ratio within the granules. The granules structures are homogeneous and the population of granules within the seeds is homogeneous.

For the ae mutant, the optical microscopy reveals gross heterogeneity of the starch granule structure within individual granules, between granules within cells, and between cells across the starchy endosperm (Figure 3). Figures 3b and d show representative regions of the KI/I2 stained sections from the outer and inner regions of the starchy endosperm. The spheroidal starch granules tend to be smaller than the wild-type granules, with evidence for the presence of elongated and dimpled granules, reported in previous studies on isolated ae mutant maize starch. In the outer endosperm regions, the granules tend to stain blue in KI/I2 with occasional granules showing central regions which stain blue and outer regions which stain pink: the central hilum region enlarges when the starch granule swells in the aqueous mounting conditions and remains unstained (Figure 3b). The heterogeneity of the starch granule structure can vary markedly between neighbouring cells and, in general, becomes more heterogeneous as sampling progresses from the outer to the inner endosperm. In the inner endosperm, there is a wider variation between blue and pink stained granules with a greater propensity for pink stained regions at the periphery of granules (Figure 3d). The difference between the pink and blue stained granules, or regions within granules, is well illustrated if the granules are exposed to KI/I2 or iodine vapour. However, prolonged exposure results in the pink regions eventually staining blue: this suggests that the difference in colour is due to differences in the structure which influences the rate of diffusion of the iodine into the structure, rather than the length of the ordered helical regions within the structure. Polarised light microscopy of regions within the inner endosperm also emphasise the structural heterogeneity (Figure 3c). These images reveal some granules in which the crystal structures are radially aligned and homogeneous, some granules that show no radial alignment, and further granules with various intermediate structures showing one or more radially aligned regions within the granules, and a peripheral region with no radial alignment (Figure 3c). These images show that a single mutation in an isogenic line does not result in a simple change in the ratio of amylase and amylopectin within the granules, but rather results in a complete and variable heterogeneous population of granular structures. FT-IR and Raman chemical mapping of the starch structures within seeds provides a basis for defining the chemical and physical structures within and across the endosperm, within and across individual cells and within individual granules.

The FT-IR absorption spectra provide information on the composition and structure of the samples which can be mapped in the FT-IR images for the wild-type and ae mutant maize samples (Figure 4). The FT-IR spectra of maize showed strong absorption in the protein and carbohydrate regions. The carbohydrate region is dominated by the starch content with only a minor contribution from the non-starch cell wall components. Fourier deconvolution of the spectra resolved bands at 1153, 1126, 1105, 1078, 1050, 1044, 1023, 1002, 933 and 924 cm-1 in the carbohydrate region. Comparison of the FT-IR spectra for the wild-type and ae mutant show similar protein bands at 1650 cm-1 but differ for the starch bands, particularly in the absorption region sensitive to the crystal structure of the starch (Figure 4a). The ae maize spectra showed a large increase in the 1002 cm-1 band and also some broadening, which resulted in greater overlap with the main 1023 cm-1 band, and a broader wing around 970 cm-1. In addition, the band at 1050 cm-1 was slightly smaller than in the equivalent band for the wild-type samples. The band at 1022 cm-1 has been assigned to the amorphous starch phase, whereas lintnerised starches and granular starches are characterised by a band at 1000 cm-1 However, the ratio of these two bands is also highly influenced by water content and, in this case, indicates a change in the short-range order of amylosic helices within the crystal structure, because the 1047 cm-1 band, which has been linked to starch crystallinity, is slightly lower in the ae maize samples. The differences in the two bands at 1050 and 1002 cm-1 in the ae maize when compared to the data for the ae mutant indicates that the starch structure in the maize mutant was significantly different from that in the wild type. These data are consistent with the well documented observations from x-ray diffraction data that the mutation in the biosynthesis leads to a progressive transition from A- to B-type crystals.

(Continues…)Excerpted from Gums and Stabilisers for the Food Industry 16 by Peter A. Williams, Glyn O. Phillips. Copyright © 2012 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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