Food processing has been shown to have large effects on a range of nutritional properties.1 Changes in macronutrients, such as starch and protein,2,3 and the destruction of vitamins during food processing,4 have been well documented, and are updated in this book. Most studies have been constrained by experimental design to a few foods and conditions, and apart from effects on nutrient levels measured in standard food analyses, nutritional information that reflects the effects of processing does not generally reach consumers in a form in which it can be widely used to choose foods. Similarly, food processors often do not have available means to apply, either accurately or practically, relevant nutritional criteria to select prototype products during development. Below are listed several reasons for the need for new nutritional information.
7.2.1 Showing effects of food properties on nutritional qualities
Much of the impact of processing on nutritional quality comes about through changes in physicochemical properties of food polymers, such as dietary fibre,5 that cannot be represented by food composition values. Changes in structure associated with such processes as starch hydration and gelatinisation,6 milling,7 and extrusion,8 can have an large impact on the rate and extent of digestion, and consequently on a range of physiological markers linked to disease end-points. For example, the impact of cereals on blood glucose and insulin responses is increased markedly as particle size is reduced by milling,7 or as starch is gelatinised.6,9
Information from rapid, valid, but relevant tests is needed to guide processing to healthy products. Because of the expense, time, ethics, compliance and other issues involved in clinical trials, human subjects are not usually suitable for monitoring effects of processing until potential products have been identified.
Food processing for improved nutrition may require pragmatic choice of different tests at different stages in product development, to maintain momentum in product development. Active ingredients and formulations may be identified with screening tests, using indirect predictors of health effects, such as ingredient properties. Responses in animal models may guide food processing further, and most promising products then taken into clinical trials, in which effects on biomarkers with established links to health end-points are measured,1011 before a claim of efficacy is made. Increasing rigour in nutritional evaluation of functional properties during the course of product development is illustrated in Table 7.1.
As a general principle, the properties of foods that affect physiology should be measured under conditions as close as is reasonable to those in which the food property acts in vivo. Developing a soluble fibre-enriched product to lower blood cholesterol is an example. Ingredients of high soluble fibre content could be identified using soluble fibre analysis under simulated gastrointestinal conditions.12 As hypocholesterolaemic effects of soluble dietary fibres result from increased intestinal viscosity,13 fibre viscosity should be measured, followed by in vitro digestion of products containing selections of viscous fibre sources, with measurement of digesta viscosity. Promising products could be subjected to animal trials to establish that predicted gut viscosity and blood lipid changes occur
Table 7.1 Types of nutritional tests that may be used in food processing at different stages of product development
Level of Use in food processing Comments evidence
In vitro digestion
Identifying ingredients with desired properties.
Defining nutrient retention. Meeting labeling requirements.
Predicting responses to gut conditions.
Predicting effects in the whole body context.
Usually limited application until nearing final product.
Identifies possible health-relevant food factors.
Identifying possible food factors in health by association.
Provides basis for a health claim.
May change in processing. Affected by food matrix and gut milieu. Cheap and quick.
Ignores physiochemical properties, bioavailability, and bioactivity, but relatively cheap.
May give an indication of effects of digestion on food properties, but not take other important food-host interactions into account.
May be physiologically different to humans. Require validation. Compliance good.
Costly, slow, ethically difficult, study population variable, compliance may be poor. Intermediate endpoints required.
Associations identified, but not cause-effect relationship (uncertain). Ecologically valid. Not suitable for product testing.
Less controlled than experimental methods leaving room for doubt about cause-effect.
Most rigorous, but findings apply to the experimental conditions - may lack external validity.
in vivo. Final selections could then be clinically evaluated, to establish firmly their potential as functional foods for humans.
7.2.3 Avoiding unjustified extrapolation between products
The complexity of processing effects on food matrices makes nutritional properties susceptible to processing conditions, and extrapolation of function between different products uncertain.14 Nonetheless, it is a common cost-cutting measure for marketers to use a functional effect of a bioactive in one product, to promote other foods containing the bioactive, but with a different processing history. To reduce unjustified extrapolation, information is required from tests that are practical and inexpensive enough to use for detecting nutritional effects of different processing conditions in large numbers of samples.
168 The nutrition handbook for food processors 7.2.4 Helping consumers choose foods for health
Food properties can be used to select foods for health only if supported by useable efficacy data.15 Information from tests of the nutritional and functional properties of foods needs to be easily used by both processors and consumers, to discriminate between products. Without scientific but communicable efficacy data, food processors cannot develop or ethically promote foods, and consumers cannot choose foods for real health effects.
Consumer confidence in a product or company requires that claimed benefits are delivered. Distrust is associated with perceptions of deliberate distortion of information, and having been proven wrong in the past.16 Therefore, the more that the benefits of a food product are exaggerated and overextrapolated, while scrutiny by food regulators and nutritionists continues, the greater the likelihood of generating mistrust. Investment in tests to demonstrate real differences in efficacy of products is, therefore, a prudent strategy.
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