Increasing the resistant starch content of foods 841 Commercial ingredients

The first commercially available RS ingredient was a high-amylose corn RS2 released in Australia in 1993, called Hi-maizeTM starch, with a dietary fiber content of 30%. Since then, the number and type of RS ingredients has increased. Today, commercial sources of RS1, RS2, RS3 and RS4 are available. Each RS ingredient will have a unique profile of physiological and technological functionality, and so should be considered accordingly. For example using AOAC total dietary fiber methods, RS ingredients can differ in their dietary fiber contents from >60% for RS2 made from high-amylose corn starch, to 0-30% for RS3 made from tapioca or high-amylose corn starch. RS4 has been prepared using various techniques, for example by acid hydrolysis or dextrinization to produce a soluble material while more recently RS4 chemically modified starches have been prepared from various starch bases using difunctional phosphate reagents. Depending on the country, some of the RS4 materials are considered novel foods that must seek official regulatory approval.

Some properties that differ between commercial RS ingredients include:

• the relative ratio of digestible to indigestible starch - some ingredients are higher in RS (and/or total dietary fiber) than others;

• the methodology that can be used to determine the resistant component - different ingredients will use different methods to quantify the RS and/or dietary fiber content (e.g. AOAC 985.29, 991.43, 2002.02, 2001.03), not all of which are approved by local regulatory bodies;

• whether the RS and/or dietary fiber content of the ingredient is preserved in the food as eaten;

• the physiological outcome - as for other fibers (e.g. soluble versus insoluble), different RS ingredients behave uniquely within the body;

• the level of supporting evidence - more established RS ingredients such as RS2 and RS3 from high-amylose corn have a broad body of scientific evidence available to support their inclusion into functional foods while newer forms of RS may have little or no supporting clinical evidence;

• the contribution of the starch to technological functionality - different RS ingredients have different technological characteristics, which favor certain food applications;

• impact on the organoleptic properties of foods - RSs from various sources will affect sensory dimensions such as taste in different ways.

Most evidence for the health benefits of RS has been demonstrated using high-amylose corn RS2, largely due to its process tolerance and ease of incorporation into foods relative to other sources of RS and dietary fibers. Table 8.7 describes some important digestive health benefits attributed to high-amylose corn RS2.

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