Food structure

The absorption and transport processes of many of the phytochemicals present in food are complex and not fully understood, and prediction of their bioavailability is problematic. This is particularly true of the lipid-soluble phytochemicals. In this chapter the measurement of carotenoid bioavailability will be discussed. The carotenoids serve as an excellent example of where too little understanding of food structure, the complexity of their behaviour in foods and human tissues, and the nature and cause of widely different individual response to similar intakes, can lead to misinterpretation of study results and confusion in our understanding of the relevance of these (and other) compounds to human health. 

All the actual or putative functional benefits of carotenoids are dependent on their bioavailability amounts consumed, amounts released from the food structure during digestion and extent of absorption and tissue distribution. The following three sections deal with each of these issues in turn. 

Release from food structures maximising availability for absorption... 

It will be appreciated that the delivery of nutrients from foods is attenuated by the structure of the food and the way in which it is digested. Thus, delivery from the food structure occurs over the same timescale as gastric emptying. Carotenoids, and other compounds, isolated from the food structure are generally emptied from the stomach and absorbed more rapidly. These different rates of delivery may have profound effects on subsequent metabolism. 

Typical attributes for evaluating food quality are safety, shelf life, color, taste, flavor, texture, health, and convenience. The level of a quality attribute is determined by levels of physical, microbial, physiological, chemical, and biochemical food processes, product composition, and applied technological conditions. For example, a combination of enzyme-degrading colorants, compositions and concentrations of pigments, and food structure properties contribute to a certain color level perceived by consumers. Depending on the match of expectation and experience, certain attributes will or will not be perceived as quality. ... 

Moreau RA, Whitaker BD and Hicks KB. 2002. Phytosterols, phytostanols, and their conjugates in foods structural diversity, quantitative analysis, and health-promoting uses. Prog Lipid Res 41 457-500. 

Slade, L. and Levine, H. 1991. Beyond water activity Recent advances based on an alternative approach to the assessment of food quality and safety. Crit. Rev. Food Sci. Nutr. 30, 115-360. Slade, L. and Levine, H. 1995. Glass transitions and water-food structure interactions. Adv. Food Nutr. Res. 38, 103-269. 

Donald, A. M. (2004). Understanding starch structure and functionality. In "Starch in Food-Structure, Function and Applications" (A.-C. Eliasson, ed.), pp. 156-184. Woodhead Publishing Limited, Cambridge. 

Shilton, N.C. and Niranjan, K., Fluidization and its applications to food processing, Food Structure, 12 (1993) 199-215. 

For many years, and still, controlling available carbohydrate intake has been a cornerstone of diabetes management. However, in many foods available carbohydrate, measured as carbohydrate available in food analysis, is not quite the same as carbohydrate that is available in the gut in food as normally consumed. Glycemic response depends not only on the amount of potentially available carbohydrate consumed, but also on how rapidly it is digested, absorbed, and disposed of in the body, and that depends on a myriad of factors including food structure and the influence of other food components that vary in importance from food to food. 

Meaning Is analytically measured as sugars soluble after amylase digestion of finely ground samples, so consists of food sugars and digested starch. But it represents potential availability rather than true availability because fine grinding removes the constraints of food structure. 

Defense is a further category in which plants employ food rewards to acquire protection by arthropod mutualists. The provision of food sources allows plants to recruit or sustain predators or parasitoids, which, in turn, can provide protection against herbivory. The plant-derived food structures involved in indirect defensive interaction can be divided in two main groups food bodies and extrafloral nectaries. 

Lemay, D.G., Dillard, C.J., German, J.B. (2007). Food structure for nutrition. In Dickinson, E., Leser, M.E. (Eds). Food Colloids Self-Assembly and Material Science, Cambridge, UK Royal Society of Chemistry, pp. 1-15. 

McClements, D.J., Decker, E.A., Park, Y., Weiss, J. (2008). Designing food structure to control stability, digestion, release and absorption of lipophilic food components. Food... 

Courthaudon, J.-L., Dickinson, E., Matsumura, Y., Williams, A. (1991b). Influence of emulsifier on the competitive adsorption of whey proteins in emulsions. Food Structure, 10, 109-115. 

Heertje, 1., Nederlof, J., Hendrickx, H., and Lucas-senreynders, E.H. 1990. The observation of the displacement of emulsifiers by confocal scanning laser microscopy. Food Structure 9 305-316. 

Lapsley, K.G., Escher, F.E., and Hoehn, E. 1992. The cellular structure of selected apple varieties. Food Structure 11 339-349. 

Yiu, S.H. 1993. Food microscopy and the nutritional quality of cereal foods. Food Structure 12 123-133. 

The Art and Science of microscopy are quite old [e.g., see 1] and, from early times included studies of food structure [2]. As one might expect with such long usage in fields of endeavor as diverse as Geology, Botany, Medicine, Zoology, Materials and Food Science, a vast array of techniques has been developed. Many of the methods complement one another and are applicable across disciplines. 

Some of the more noteworthy EM techniques which were first described prior to 1990, deserve mention because of their contribution to the advancement of food structure knowledge. The utility of ciyo-SEM in food systems was clearly illustrated by Saigent [57] including over 40 micrographs of diverse food systems as visualized by ciyo-SEM techniques. Since that time numerous papers can be found in the literature utilizing ciyo-SEM methods. An ever expanding list of unique and novel applications to new foods has come from the papers of Heertje and his co-workers and is summarized by Heertje [58]. Here we must focus on the newer techniques which have been developed in recent years the first of these is environmental SEM. 

T.P. O Brien, Cereal Structure An Historical Perspective. In New Frontiers in Food Structure, D.B. Bechtel (ed.), American Association of Cereal Chemists, SL Paul MN, (1983), pp3-26. 

M.R. Heath, The Relevance of Food Structure - A Dental Clinical Perspective, in "Food Structure - Its Creation and Evaluation , J.M. Blanshard and J.R. Mitchell (eds.), Butterworths, London, 1988, pp. 1-6. 

Quality of a food product is related to its sensorial (shape, size, color) and mechanical (texture) characteristics. These features are strongly affected by the food structural organization (Stanley, 1987) that, according to Fardet et al. (1998), can be studied at molecular, microscopic, and macroscopic levels. In particular, micro structure and interactions of components, such as protein, starch, and fat, determine the texture of a food that could be defined as the external manifestation of this structure (Allan-Wojtas et al., 2001). 

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