Resistant Starch: The New Generation Of Fibre

Dietary fibre in functional food products is not just a passing fashion. Mike Croghan explains the role of resistant starch in a healthy diet and reports on recent trials testing a new concept in 'fibre-full' white bread.

Today's abundance of processed foods has changed diets dramatically. Nutritious raw ingredients, rich in fibre and carbohydrates, have been replaced in favour of convenience.

This has been to the detriment of health. According to the British Heart Foundation, one adult dies of heart disease every three minutes and three per cent of adults have diabetes. Consumers are attuned to nutrition messages. But a healthier diet is correlated with giving up convenient, tasty and appealing foods. That fibre is a core component of a balanced diet is well known — but fibre, as well as being hard to process, has a reputation for being dense, unappetising and virtually inedible in quantity. Until now.

A dietary fibre has been developed which is not only easy to process, but can be incorporated into the best convenience products without affecting eating quality. Good nutrition, light textures and maintenance of tasty natural flavours can now be a feature of convenient ready meal products which also act physiologically like unprocessed food. Resistant starch has a long history of safe consumption in humans and can be found naturally in unprocessed foods, such as bananas, lentils and raw potatoes; minimally processed foods, for example cooked legumes and muesli; and some more highly processed foods such as breakfast cereals (e.g. cornflakes) and some breads (e.g. bread crusts).

The benefits of eating foods with a high dietary fibre content include improved colonic health, increased faecal bulk and controlled energy release. Dietary fibre is defined as components of plant materials in the diet, which are resistant to digestion by enzymes produced by humans in the small intestine and, therefore, reaches the large intestine (colon). Research has shown that, as well as dietary fibre such as bran, other plant materials including resistant starch show similar physiological and health benefits — namely increased faecal bulk and controlled regularity. Suitable claims could include 'promotes colon health'.

For nutritional purposes, starch in foods can be classified into three categories: rapidly digestible (RDS), slowly digestible (SDS) or resistant starch (RS). Resistant starch passes, without being digested or absorbed in the small intestine, to the large intestine. There, as with 'normal' fibre, it is broken down by fermentation in the colon to short-chain fatty acids, carbon dioxide, hydrogen gas and methane. Similarly to traditional fibres, resistant starch therefore performs an important role in digestive physiology.

There are four types of resistant starch:

  • RS1 describes physically inaccessible starch that is locked within cell walls such as those found in partially milled grains, seeds and legumes.
  • RS2 refers to native resistant starch granules like those typically found in bananas, raw potatoes and high amylose maize starch.
  • RS3 is retrograded or crystalline non-granular starch, like the starch found in cooked and cooled potatoes, bread crusts, cornflakes and retrograded high amylose maize starch.
  • RS4 is a relatively new classification that refers to specific chemically modified or re-polymerised starch such as chain linkage altered dextrins.

When subjected to modern food processes most forms of resistant starch are destroyed.

National Starch has developed a technology to produce a resistant starch called Novelose, which can withstand not only attack, by human digestive enzymes but also food processing conditions.

By optimising the profile of the starch's physical structure, the Total Dietary Fibre (TDF) contribution is maximised: Novelose resistant starch was analysed as dietary fibre by the universally accepted AOAC test method for dietary fibre. The TDF level of Novelose is not in general affected by modern processing conditions, so both manufacturers and consumers get the fibre they expect. Novelose resistant starch constitutes the first commercialised concentrated source of enzyme-resistant starch for the food industry.

Novelose behaves similar to unprocessed food in terms of physiological effect, yet contributes a high textural quality in processed products including breakfast cereals, snacks, pasta and noodles and baked goods such as bread, muffins and cakes. Increasing fibre content with Novelose improves the nutritional profile — without causing the deterioration in product quality, characteristic of bran and refined cellulose materials, which have limited the appeal of high fibre products to-date.

The Processing Advatages: A Source Of High Fibre
Novelose comes in various TDF levels. The latest product in the range, Novelose 260 has a TDF of 60 per cent — enabling food manufacturers to develop products with a "source of high fibre" or "rich in fibre" label. Its launch marks a step in the development of physiologically functional ingredients, offering fibre in everyday foods without compromising eating enjoyment.

In contrast to other fibres such as rice, wheat or oat bran, Novelose has a neutral taste and is white in appearance, allowing incorporation into a variety of products without altering their flavour or colour. Fibres such as wheat bran also contain oil and fat which can turn rancid, so some of the ingredients used to increase fibre content have a limited shelf-life because of the develop-ment of an 'off' taste. Virtually fat free (<1%), Novelose overcomes this problem. All the fibre in Novelose is insoluble and contributes only 1.6 ­ 2.8Kcal/gm (by calculation, value depends on the product chosen within the Novelose range).

The high water take-up of other fibre sources causes problems with stickiness, especially in dough which becomes difficult to handle and does not expand sufficiently in processing. Because Novelose holds significantly less water, it does not compete for the water needed by other ingredients. It also gives good expansion in low moisture food systems so light-textured fibre fortified foods can be made, including snack products.

Also unlike fibre sources such as bran, Novelose starches are made up of small crystalline particles or granules, which contribute a uniform cell size thereby improving structure. This avoids the heavy, dense structure associated with high fibre products. As a free-flowing powder, it is very easy to handle.

Novelose is ideally used as a complement to traditional dietary fibres to produce 'fibre-fortified', high quality processed products. A multi-fibre approach combining complementary dietary fibres gives a wide range of benefits. Using a multi-component approach optimises the eating quality and nutritional profile of the final product. Each individual component may have its own limits but a combination allows the formulation of very high fibre products without quality compromises as well as providing an opportunity to improve economics. Nutritionists have long advocated a 'balanced diet' — the multi-fibre approach extends this to a balance of different fibres — all of which have a nutritional impact. The multi-fibre approach was recently tested at trials by National Starch in association with Kampffmeyer Mühlen, the speciality flour company based in Hamburg, Germany.

Trials: Baking Healthy Bread
Trials were carried out to examine the effect of a multi-fibre method in the manufacture of standard white bread ­ to gauge the feasibility of creating a fibre-fortified bread, which is good to eat, and appeals to consumers.

Some of the flour in the bread formulation was replaced by the fibre combination. When flour (starch and protein) is partially replaced with starch and cellulosics, the protein content is also lowered which can affect the structure and lead to volume and quality reduction. Speciality flours developed by Kampffmeyer Mühlen allowed multi-fibres to be added without any extra wheat gluten (protein) which can make the bread too gummy. Optimising the flour system in this way ensured the protein balance was maintained and ensured excellent baking characteristics and final product properties.

The Benefits
The multi-fibre loaf gave outstanding eating quality — an excellent texture, improved cell structure, taste and colour. All this was achieved, plus a very high fibre level — almost 18 per cent total dietary fibre (TDF) — three times more than the required TDF for a product to be classified in Europe as high fibre.

The multi-fibre bread also gave improved processing: less sticky dough, higher volumes and lower variations than other high fibre bread. Moisture retention was improved, which helps the perception of freshness and extends shelf-life.

This concept in bread baking offers manufacturers marketing advantages: inclusion of healthy claims for high fibre such as "made with a unique balance of fibres". It is consumer preference that drives the market, however — people will buy and try the bread for its high fibre content... and buy again because they like it.

Using functional ingredients is a step forward to a balanced approach to eating and improving diets. Balancing nutritional needs and taste preferences is the challenge for today's convenience-based society. Novelose resistant starches are functional ingredients, which will enable food manufacturers to meet this challenge and deliver physiological benefits within the parameters of modern processing.

National Starch & Chemical
Prestbury Court
Greencourts Business Park
333 Styal Road
Manchester M22 5LW, UK
Tel: +44 (0)161 435 3200
Fax: +44 (0) 161 435 3300
Email: [email protected]
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