A recent study published within the journal Foods discusses the results of starch structure on human health.

Study: Effects of the Molecular Structure of Starch in Foods on Human Health. Image Credit: ibreakstock / Shutterstock.com

What’s starch?

Starch represents probably the most significant factor of food energy for a lot of the global population. Abnormal starch consists of amylose and amylopectin, whereas starches from some plants and mutants have intermediate structures.

A recent review described on the connection between starch structure, digestibility, and thermal properties. Comparatively, the current study focused on the connection between the chain length distribution (CLD) of starch and health-related effects.

Starch properties and biosynthesis

The placement and rate of digestion of starch foods within the gastrointestinal (GI) tract correlate with human health. The speed of starch digestion rate also appears to affect mental health.

Rapidly digested starch (RDS) causes a spike in blood sugar levels that might strain the insulin system and may lead to diabetes if chronic. Slowly digested starch (SDS) decreases the glycemic load of the food product, thereby reducing the chance of breast or colon cancers and kind 2 diabetes and increasing satiety.

Previous studies suggest a correlation between long-term SDS intake and improved metabolic profile. In actual fact, SDS intake can reduce postprandial glucose peaks, which is useful for diabetes management.

Resistant starch (RS) reaching the colon is a substrate for microbial fermentation, which yields carbon dioxide, hydrogen, short-chain fatty acids, and methane. This may attenuate postprandial glucose and insulin responses to ultimately profit human health.

CLD is a necessary determinant of the digestibility and pasting properties of starch. Furthermore, CLD reflects the distribution of individual chains obtained following the cleavage of all (1→6)-α linkages by a debranching enzyme (DBE). CLD is derived by measuring the number or weight distribution as a function of the degree of polymerization (DP) of linear glucans.

The biosynthesis of starch primarily involves five enzymes, including starch synthase (SS), granule-bound SS I (GBSSI), starch branching (SBE) enzyme, DBE, and adenosine diphosphate (ADP)-glucose pyrophosphorylase (AGPase).

SS, DBE, and SBE are the major enzymes for amylopectin biosynthesis, whereas GBSSI, DBE, and SBE are involved in amylose biosynthesis. SBE cleaves (1→4)-α linkages and adds the short chain to a parent or other chain to create (1→6)-α linkages. In contrast, DBE directly hydrolyzes (1→6)-α linkages of polyglucans. AGPase catalyzes and generates

ADP-glucose is elongated through (1→4)-α linkages by SS, whereas GBSS elongates amylose chains and increases the variety of amylopectin’s extra-long chains (ELCs). In contrast, SS isoforms (I-IV) are primarily involved in amylopectin synthesis.

Starch structure and health-related effects

The superb structure of starch can influence its digestibility, amongst other functional features. Various studies suggest that short A chains of amylopectin (DP 6 – 12) affect the amount of SDS and RDS.

One study has reported a correlation between lower proportions of A chains of amylopectin and lower RDS, thus contributing to a better SDS in long-grain rice. Moreover, one other study reported a negative correlation between short-chain proportion in cooked maize starch and digestion rate.

The next proportion of long B chains of amylopectin (DP > 40) has the potential to affect the retrogradation of SDS on cooling and contribute to slow digestion. Amylopectin from cooked maize starch, with short chains, high branching density, and shortened non-reducing ends is slowly digested.

This is perhaps attributable to the preferential cleavage of (1→4)-α linkages by α-amylase. Notably, the speed of (1→6)-α cleavage by amyloglucosidase is slower than (1→4)-α cleavage.

Amylose CLD can even significantly impact digestibility. The in vitro digestibility of cooked rice starch and native starch was affected by amylose content and the degree of branching of short or medium amylose chains (DP 100 – 500). Shorter amylose chains form double helices in debranching waxy starches aggregating into crystalline arrays upon cooling, that are slowly digested.

Intermediate chains (DP 500 – 1000) of amylose in non-waxy cooked rice starch and native starch prevent aggregation and form cross-linked networks, thereby slowing the digestion rate. The long chains of amylose (DP 1000 – 1500) can even have an impact. One previous study showed that long amylose chains correlated with rice starch digestibility but not as significantly as short and medium amylose chains.

Conclusions

While quite a few studies have examined the connection between the structural and functional features of starch, more research is required to know the results of starch structure on human health. Although the impact of amylose content on digestibility is established, the results of amylose CLD is comparatively less studied.

Modifying the structural features of starch can have positive health advantages. Future studies may give attention to the results of intermediate or long amylopectin chains on digestibility.