Elsevier

Food Hydrocolloids

Volume 110, January 2021, 106171
Food Hydrocolloids

Amylose content modulates maize starch hydrolysis, rheology, and microstructure during simulated gastrointestinal digestion

https://doi.org/10.1016/j.foodhyd.2020.106171Get rights and content

Highlights

  • Higher rheology and denser gel structure for both NAM and HAM with increasing dry matter content.

  • Higher rheology and more compact microstructures before and during digestion for 50% HAM.

  • Digesta rheology was decreased by both starch hydrolysis and digestive fluid dilution.

  • Amylose mainly decreased starch hydrolysis at the intestinal digestion stage.

  • Higher digesta rheology and denser gel-networks caused lower starch hydrolysis of HAM.

Abstract

In this study, the microstructure, rheology, and starch hydrolysis of cooked normal (NAM) and high (HAM) amylose maize starch solutions with various dry matter contents (10, 30 and 50 wt %) were compared before and during simulated gastrointestinal digestion. Prior to digestion, increased rheology (modulus and shear viscosity) and more compact gel network structure were observed for both the NAM and HAM with increasing dry matter content. As compared to the NAM, the HAM with the same dry matter content (50 wt%) showed higher rheology and denser gel structure with remarkable aggregation of relatively intact starch granules after cooking. The extent of starch hydrolysis was similar (~10%) between the two starch systems at the gastric digestion phase, whereas it was significantly lower for the HAM in relation to that for the NAM at the intestinal digestion phase. At the end of the GIT digestion, the in vitro digestibility was about 81% and 90% for the HAM and NAM, respectively. The starch hydrolysis was strongly supported by the rheology and microstructure of the starch digesta. Due to the dilution of digestive fluids and starch hydrolysis, the rheology was both remarkably decreased, but the HAM showed significantly higher shear viscosity than the NAM at each digestion phase due to its greater retention of relatively intact starch granules that would cause higher resistance toward shearing. The results indicate that the amylose content was crucial for modulating starch hydrolysis by forming denser gel structure and increasing digesta rheology that would retard the access of digestive enzymes to the starch granules during digestion.

Introduction

Starch is one of the most abundant macromolecules, and is a major component of many foods, such as rice, bread, noodles, pasta and snacks. It is a renewable, economical, and biodegradable biopolymer that extends the stability, binding, gelling, nutritional, and biological characteristics of many food, pharmaceutical and cosmetic products (Jeong et al., 2016; Lu et al., 2019; Tangsrianugul, Suphantharika, & McClements, 2015). Starch in its native state is organized into discrete particles, which are called granules, and generally consists of two main macromolecules: amylose and amylopectin. Amylose possesses a linear structure, while amylopectin has a branching structure, and generally its content (72–75%) in starch is higher than amylose (25–28%) (Li, Gidley, & Dhital, 2019). Starch from various sources of plants – e.g. cereals, tubers, and legumes – display variations in shape, size, amylose content, chain length, and crystallographic pattern (Buléon, Colonna, Planchot, & Ball, 1998; Acevedo et al., 2019). Among these variances, amylose content in normal and modified starches plays a significant role in their structural and functional properties (Biduski et al., 2018, Mariscal-Moreno et al., 2018).

Previously, numerous studies have been carried out to investigate the role and mechanisms of amylose in affecting multilayer structures and physiochemical properties of starch from a wide variety of origins. It has been well-documented that starch digestion is strongly correlated with amylose content, with higher amylose generally resulting in lower extent and rate of starch hydrolysis during digestion in vitro and in vivo (Gunaratne et al., 2019; Lin et al., 2016). Amylose starch, having a more linear and flexible structure than amylopectin, can form double helices after cooking (retrogradation) (Li, Gidley, & Dhital, 2019; Miao, Jiang, Cui, Zhang, & Jin, 2015). This situation is stronger in high amylose content starches and increased with increasing of starch concentration (Ai & Jane, 2018). The retrograded amylose starch with increased proportion of recrystallized order is less accessible to digestive enzymes and thus contributes to decreased glucose release and absorption rates in the small intestine during digestion in the gastrointestinal tract (GIT) (Miao et al., 2015; Tangsrianugul et al., 2015). The slowly digested starch, i.e. starch containing larger amount of amylose, has been reported beneficial in the prevention and management of some chronic diseases such as obesity, insulin resistance, type 2 diabetes mellitus (Chung, Shin, & Lim, 2008; Dona, Pages, Gilbert, & Kuchel, 2010). Thus, it is reasonable and desirable to incorporate high amylose starch in the development of starch-based food products with lower glycemic index (GI) value (Giuberti & Gallo, 2018; Gunaratne et al., 2019).

Several studies have showed that the rheological properties of digesta are expected to affect transport, hydrolysis and absorption of hydrolyzed nutrients within the GIT (Lentle & Janssen, 2010; Wu et al., 2017). Nowadays, manipulation of digesta rheology is receiving growing interest in food digestion-related studies. Higher viscosity of digesta has been associated with reduced gastric emptying rate, which is positively correlated with lowering glycemic response and prolonging satiety from ingested foods (Lentle & Janssen, 2008; Wu, Deng, Wu, Dhital, & Chen, 2017). Although the rheology of many starch systems with various compositions or structures have been investigated, knowledge on the rheological behavior of digesta within different GIT compartments (mouth, stomach and small intestine) and its correlations with microstructural and digestive properties is still in its infancy (Wu, Dhital, Williams, Chen, & Gidley, 2016; Wu et al., 2017). Moreover, the specific role of amylose in modulating digesta rheology, microstructure and starch digestion, and the evolutions/changes of these properties during digestion along the GIT have rarely been studied. The rheological and microstructural properties of the starch systems can be altered during digestion due to the dilution effect of digestive fluids and structural breakdown of starch granules caused by enzymatic hydrolysis and mechanical shearing (Jeong et al., 2016). This may produce significant impact on starch digestion rate and extent. To the best of the authors’ knowledge, there are no systematic studies focusing on the effect of amylose content on evolutions of the digesta rheology, microstructure and in vitro digestion of starch solutions with various dry matter contents during the GIT digestion. Further, the relationships or interactions between the rheological, microstructural properties and in vitro starch digestion rate and extent have not been well understood.

In the present study, the changes in microstructure, particle size, rheology, and in vitro digestive characteristics of normal (NAM) and high (HAM) amylose maize starches were examined before and during simulated digestion in the mouth, stomach and small intestine. The main objective of the current study is to achieve an in-depth understanding of the role of amylose content in starch hydrolysis in the various GI compartments by analyzing the changes in the digesta rheology and microstructure during simulated in vitro digestion. The results indicated that the amylose content was crucial in affecting the digestion rate and extent of the highly concentrated maize starch solutions by increasing the digesta viscosity and producing relatively dense gel-networks during the simulated GIT digestion. The knowledge from this work may be useful for the selection and development of healthier starch and starch-based food products in relation to diabetes, obesity, and other chronic diseases through modifying starch rheology and microstructure, i.e. the addition of high amylose, resistant starch components or soluble dietary fiber.

Section snippets

Materials

Normal (NAM) and high (HAM) amylose starches from maize source were used in this study, and purchased from Shanghai Naijin Industrial Co., Ltd, China. The manufacturer reported that NAM consisted of 30% amylose contents, while HAM consisting of 65% amylose content. α-amylase for oral and small intestine phases and Pepsin for stomach phase were purchased from Sigma (Sigma–Aldrich, USA). All other chemicals used in this study were purchase from Sino pharm Chemical Reagent Co., Ltd., Shanghai,

Flow behavior analysis

The flow behavior in terms of shear viscosity of starch solutions with different dry matter contents (10–50 wt%) in their initial state and during GIT digestion, were presented in Fig. 1 & Fig. 2, respectively. The results of shear stress as a function of shear rate ranging from 0.1 to 100 1/s were shown in Fig. S1 of the Supplementary Material. As shown in Fig. 1, the shear viscosity of both the NAM and HAM starch samples regardless of dry matter contents was decreased with increasing shear

Conclusion

In this study the rheological, microstructural and in vitro digestive properties of cooked normal and high amylose maize starch solutions, with various dry matter contents, were compared before and during simulated GIT digestion (mouth, stomach, and small intestine). At relatively low dry matter content (10 wt% and 30 wt%), NAM presented higher shear viscosity and modulus than HAM due to its larger amount of amylopectin, which could produce greater granular swelling capacity during cooking. For

CRediT authorship contribution statement

Shahid Iqbal: Investigation, Writing - original draft, Writing - review & editing. Peng Wu: Conceptualization, Methodology, Writing - review & editing, Funding acquisition. Timothy V. Kirk: Visualization, Writing - review & editing. Xiao Dong Chen: Conceptualization, Supervision, Funding acquisition.

Declaration of competing interest

We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted (“Amylose content modulates maize starch hydrolysis, rheology, and microstructure during simulated gastrointestinal digestion”).

Acknowledgements

We acknowledge the financial support for the current study from the he Natural Science Foundation of the Jiangsu Higher Education Institutions of China (19KJD550001), the National Key R&D Program of China (International S&T Cooperation Program, Contract No. 2016YFE0101200 and 2017YFD0400905), and the National Natural Science Foundation of China-the Optimization Study of the in vitro Soft-elastic Bio-mimic Rat Stomach Digestion System (general program, No. 21676172).

References (32)

Cited by (0)

View full text