The concept of resistant starch (RS) has evoked new interest in the bioavailability of starch and its use as a source of dietary fibre. Resistant starch has received much attention for both its potential health benefit (similar to soluble fibre) and functional properties. Resistant starch positively influences the functioning of the digestive tract, microbial flora, blood cholesterol level, glycaemic index and assists in the control of diabetes. Apart from the potential health benefits of resistant starch, another positive advantage is its lower impact on the sensory properties of food compared with traditional sources of fibre, as whole grains, fruits or bran.

The five distinct types of resistant starch in foods are:

1. RS1 – Physically inaccessible starch, which is entrapped within whole or partly milled grains or seeds.
2. RS2 – Some types of raw starch granules (such as banana and potato) and high-amylose starches like high-amylose corn.
3. RS3 – Retrograded starch, which can be processed from unmodified starch or result from food processing applications.
4. RS4 – Chemically modified starches that resist enzymatic digestion, including starch ethers, starch esters, and cross-linked starches.
5. RS5 – The V-type crystalline structure typically found in starch-lipid complexes. RS5 has stable properties for processing, limiting swelling in starch granules, and influencing the pasting properties of starch.

Understanding these types of resistant starch can help in selecting the right starch for specific food formulations and dietary needs.

RS4, one of the types of resistant starch describes a group of starches that have been chemically modified and include starches which have been etherised, esterified or cross-bonded with chemicals in such a manner as to decrease their digestibility. RS4 may be further subdivided into four subcategories according to their solubility in water and the experimental methods by which they can be analysed. RS4 can be produced by chemical modifications, such as conversion, substitution, or cross-linking, which can prevent its digestion by blocking enzyme access and forming atypical linkages such as alpha (1-4) and alpha (1-6) linkages. RS4 is made up of chemically-modified starches, with many modifications.

RS4 (chemically modified starch) promoted the proliferation of unclassified clostriadiales , Parabacteroides distasonis , Roseburia ,Bifidobacterium, adolescentic and Blautia , and production of proportionate , butyrate , and valerate , whereas starch- lipid complexes (RS5) increased the relative abundance of butyrate-producing bacteria such as Bifidobacterium , Dialister , Roseburia and Megamonas, as well as the production of SCFAs, compared to RS 3 and RS 2.

Resistant starch type 5 (RS5) is highly valued in the food industry for its versatility and functional properties. Its popularity stems from its accessibility, cost-effectiveness, non-toxicity, biodegradability, and ability to selectively release bioactive compounds within the gastrointestinal tract, making it an excellent candidate for targeted nutritional applications.

The formation of resistant starch type 5 (RS5), primarily associated with amylose lipid complexes, is typically attributed to starches with high-amylose content due to their affinity for lipid interactions. Recently, studies have also investigated the potential of amylopectin rich starches to form amylopectin–lipid complexes (ALCs), expanding RS5 sources.