Natural ‘capsule’ in food plants: Cell wall porosity controls starch digestion and fermentation

Targeting gut microbiota by starch molecular size and chain-length distribution to produce various short-chain fatty acids

The detailed relationships among starch fine molecular structures, gut microbiota, and short-chain fatty acids (SCFAs) are not fully understood. We hypothesized that specific starch molecular size and chain-length distribution are favored by gut bacteria for the secretion of SCFAs. To investigate this, different types of starches with diverse molecular size and chain-length distributions (e.g., amylose content ranging from about 1 % to 38 %) were subjected to in vitro fermentation with human fecal inocula. Tapioca and waxy maize starches were notably more effective at producing acetate and propionate compared to lentil, wheat, and pea starches (p < 0.05). Correlation analysis revealed, for the first time, that the number of amylose chains with a degree of polymerization between 500 and 5000 was positively correlated with the abundance of Bacteroides_coprocola_DSM_17136 and Bacteroides_plebeius, possibly relating to the higher production of acetate and propionate. These results indicate that starches with certain fine molecular structures could be used to target gut bacteria to produce various types of SCFAs, thereby amplifying beneficial effects on human health.

The combined effect of gluten addition and semolina cell wall integrity reduces the oral sugar release and the insulinemic response to bread in healthy volunteers

PURPOSE

A strategy to reduce starch digestibility is to limit its accessibility to α-amylase by preserving the integrity of cells where starch is encapsulated. Coarse flour is rich in intact cells and can be used for this purpose. However, making bread with coarse flour negatively affects crumb cohesiveness, which may increase the gastric disintegration rate, and enhance starch accessibility. Therefore, this study aimed to assess the combined effect of coarse semolina and its 20% gluten substitution in bread in healthy volunteers on glycemic and insulinemic responses, oral processing and bolus characteristics.

METHODS

Apparently, healthy volunteers (n = 16) randomly consumed bread made with coarse semolina and 20% gluten substitution (80CS_20G), its counterpart with fine semolina (80FS_20G), and bread with fine semolina and 5% gluten (95FS_5G). The glycemic and insulinemic responses were measured over 2 h after bread consumption. Mastication behaviour, bolus properties and reducing sugar were also evaluated.

RESULTS

No differences in glycemic responses and mastication were observed among the samples. 80CS_20G and 80FS_20G exhibited similar textural properties but 80CS_20G released less reducing sugars and elicited a lower insulin response at 30 min than 80FS_20G, probably due to intact cells that limit starch accessibility. Also, 95FS_5G released lower reducing sugars and had lower insulin peak than 80FS_20G. The compact structure of 95FS_5G may have delayed starch hydrolysis by restricting α-amylase accessibility.

CONCLUSION

Combining gluten and coarse semolina resulted in bread with a lower release of reducing sugars, a reduced insulinemic peak and textural properties similar to the counterpart with fine semolina.

CLINICAL TRIAL REGISTRATION NUMBER

The trial is registered at ClinicalTrials.gov: NCT06152874.

Modulation of rice starch physicochemical properties and digestibility: The role of highland barley non-starch polysaccharide fractions

Highland barley non-starch polysaccharides (HBNP), particularly β-glucans, are known for their health-promoting effects, including modulation of glycemic response and enhancement of gut health. This study investigated the impact of different HBNP fractions on the properties and digestibility of high-glycemic index rice starch. HBNP was segmented into five fractions (HBNP-15, HBNP-30, HBNP-45, HBNP-60, and HBNP-75) using gradient ethanol precipitation, and these fractions exhibited varying molecular weights, monosaccharide compositions, and β-glucan contents. All fractions reduced rice starch's pasting viscosity, with 1 % HBNP-75 leading to a 99.1 % decrease in final viscosity. Morphological and size distribution analyses showed that HBNP fractions limited granule swelling and disrupted starch's continuous phase structure. HBNPs also reduced starch digestibility and increased the formation of resistant starch from 10 % to 28 %. These results suggest potential uses for HBNP fractions in developing low-glycemic starch-based foods.

The mechanisms in the gut microbiota regulation and type 2 diabetes therapeutic activity of resistant starches

Resistant starch (RS) can potentially prevent type 2 diabetes through the modulation of intestinal microbiota and microbial metabolites. Currently, it has been wildly noted that altering the intestinal microbial composition and short-chain fatty acids levels can achieve therapeutic effects, although the specific mechanisms were rarely elucidated. This review systematically explores the structural characteristics of different RS, analyzes the cross-feeding mechanism utilized by intestinal microbiota, and outlines the pathways and targets of butyrate, a primary microbial metabolite, for treating diabetes. Different RS types may have a unique impact on microbiota composition and their cross-feeding, thus exploring regulatory mechanisms of RS on diabetes through intestinal flora interaction and their metabolites could pave the way for more effective treatment outcomes for host health. Furthermore, by understanding the mechanisms of strain-level cross-feeding and metabolites of RS, precise dietary supplementation methods targeted at intestinal composition and metabolites can be achieved to improve T2DM.

Effects of protein morphological structures on the cereal processing, sensorial property and starch digestion: a review

In cereals, the protein body and protein matrix are usually two morphological protein structures. However, processing treatments can affect protein structures, change protein bodies into the matrix, or induce a change in the matrix structure; therefore, the processing-induced matrix was listed as the third morphological structure of the protein. Previous research on the effect of proteins was mainly based on protein content and composition, but these studies arrived at different conclusions. Studying the effect of protein morphological structures on sensorial property and starch digestion can provide a theoretical basis for selecting cultivars with high sensorial property and help produce low-glycemic index foods for people with diabetes, controlling their postprandial blood sugar. This study aimed to review the distribution and structure of protein bodies, protein matrices, and processing-induced matrices, as well as their influence on cereal sensorial property and starch digestion. Therefore, we determined the protein morphological structures in different cereal cultivars and summarized its impact. Protein bodies mainly have steric stabilization effects on starch gelatinization, whereas the protein matrix serves as a physical barrier surrounding the starch to inhibit water absorption and α-amylase. Processing can change protein morphological structures, enabling protein bodies to act as a physical matrix barrier.

Combined techniques for revealing the mechanism beneath the inhibition effects of pectin on gluten digestibility using static in vitro gastro-duodenal protocols

In the current study, how pectin retards the digestibility of wheat gluten was investigated using a static in vitro gastric-duodenal model. The degree of protein hydrolysis was estimated using the o-phthaldialdehyde method, while the in vitro digestograms were mathematically fitted using a single first-order kinetics model. Peptides' profile, free amino acids compositions, gluten-pectin interactions and their effects on enzymatic activities of proteolytic enzymes as well as on the gluten secondary structures under digestive conditions were studied using combined techniques. Results showed that pectin could retard gluten digestibility through 1). preferential absorption to insoluble gluten aggregates by electrostatic interactions; 2). increasing the helix and reducing the β-sheet content of the solubilized gluten protein fractions in terms of their secondary molecular structures; 3). reducing pepsin activity by forming negatively charged pectin-gluten mixtures which then interacted with the positively charged pepsin molecules. The deeper insight into gluten-pectin interactions and their influences on gluten digestibility under gastrointestinal conditions provides important clues for developing effective forms of dietary fiber to improve the nutritional benefits of plant protein in individuals.

Different influences of dietary fiber from various sources on the in vitro digestibility of casein as uncovered by the study of protein-dietary fiber interactions

How different dietary fibers including pectin, cellulose and lignin affect casein digestibility was studied using in vitro static protocols. Peptides' profile, free amino acids (AAs) content, casein-DF interactions and their influences on enzymatic activities of proteolytic enzymes were studied using combined techniques. Under gastric and intestinal digestive conditions, while pectin could reduce casein digestibility (with an averaged decrease of 12.15% and 7.83, respectively) through both depletion flocculation and hydrogen-binding interactions, lignin inhibited the digestion of casein straightly through reducing the enzymatic activity of proteolytic enzymes, thereby altering the production of free AAs. Although cellulose showed the least detrimental effects, it still significantly reduced the content of Thr, Glu, Val, Leu, Phe, Lys, and no Arg was released. Deeper insight into casein-DF interactions and their influences on casein digestibility improves the development of more effective forms of DF for improving AA homeostasis in individuals.

Probing covalent and non-covalent interactions between vanillic acid and starch and their effects on digestibility by solid-state NMR

Intermolecular interactions play a significant role on the physicochemical properties and digestibility of starchy foods. This study investigated the covalent and non-covalent interactions between vanillic acid (VA) and porous starch (PS) as well as their effects on digestibility using solid-state NMR. VA-PS conjugates and mixtures were synthesized and characterized using 1H NMR, FT-IR, SEM and XRD. 13C NMR peaks at 163 ppm and FT-IR signals at 1737 cm-1 indicated the formation of ester bond in VA-PS conjugates. While differences between covalent and non-covalent interactions were also probed by solid-state NMR. The specific binding sites between VA and PS were subsequently identified by 1H13C HETCOR spectra before assessing the impact of covalent and non-covalent interactions on digestibility through an in vitro digestion test. The results revealed 13C chemical shifts of about 2.0 ppm, indicating stronger intermolecular interactions, and reduced mobility of the VA-PS conjugate due to its covalent bonding. Overall, the results showed that the VA-PS conjugate, characterized by stronger covalent interactions, exhibited superior effects in inhibiting starch digestibility compared with non-covalent interactions.

Hard-to-cook phenomenon in common legumes: Chemistry, mechanisms and utilisation

Future dietary protein demand will focus more on plant-based sources than animal-based products. In this scenario, legumes and pulses (lentils, beans, chickpeas, etc.) can play a crucial role as they are one of the richest sources of plant proteins with many health benefits. However, legume consumption is undermined due to the hard-to-cook (HTC) phenomenon, which refers to legumes that have high resistance to softening during cooking. This review provides mechanistic insight into the development of the HTC phenomenon in legumes with a special focus on common beans and their nutrition, health benefits, and hydration behaviour. Furthermore, detailed elucidation of HTC mechanisms, mainly pectin-cation-phytate hypothesis and compositional changes of macronutrients like starch, protein, lipids and micronutrients like minerals, phytochemicals and cell wall polysaccharides during HTC development are critically reviewed based on the current research findings. Finally, strategies to improve the hydration and cooking quality of beans are proposed, and a perspective is provided.

How Cooking Time Affects In Vitro Starch and Protein Digestibility of Whole Cooked Lentil Seeds versus Isolated Cotyledon Cells

Lentils are sustainable sources of bioencapsulated macronutrients, meaning physical barriers hinder the permeation of digestive enzymes into cotyledon cells, slowing down macronutrient digestion. While lentils are typically consumed as cooked seeds, insights into the effect of cooking time on microstructural and related digestive properties are lacking. Therefore, the effect of cooking time (15, 30, or 60 min) on in vitro amylolysis and proteolysis kinetics of lentil seeds (CL) and an important microstructural fraction, i.e., cotyledon cells isolated thereof (ICC), were studied. For ICC, cooking time had no significant effect on amylolysis kinetics, while small but significant differences in proteolysis were observed (p < 0.05). In contrast, cooking time importantly affected the microstructure obtained upon the mechanical disintegration of whole lentils, resulting in significantly different digestion kinetics. Upon long cooking times (60 min), digestion kinetics approached those of ICC since mechanical disintegration yielded a high fraction of individual cotyledon cells (67 g/100 g dry matter). However, cooked lentils with a short cooking time (15 min) showed significantly slower amylolysis with a lower final extent (~30%), due to the presence of more cell clusters upon disintegration. In conclusion, cooking time can be used to obtain distinct microstructures and digestive functionalities with perspectives for household and industrial preparation.

Dietary compounds slow starch enzymatic digestion: A review

Dietary compounds significantly affected starch enzymatic digestion. However, effects of dietary compounds on starch digestion and their underlying mechanisms have been not systematically discussed yet. This review summarized the effects of dietary compounds including cell walls, proteins, lipids, non-starchy polysaccharides, and polyphenols on starch enzymatic digestion. Cell walls, proteins, and non-starchy polysaccharides restricted starch disruption during hydrothermal treatment and the retained ordered structures limited enzymatic binding. Moreover, they encapsulated starch granules and formed physical barriers for enzyme accessibility. Proteins, non-starchy polysaccharides along with lipids and polyphenols interacted with starch and formed ordered assemblies. Furthermore, non-starchy polysaccharides and polyphenols showed robust abilities to reduce activities of α-amylase and α-glucosidase. Accordingly, it can be concluded that dietary compounds lowered starch digestion mainly by three modes: (i) prevented ordered structures from disruption and formed ordered assemblies chaperoned with these dietary compounds; (ii) formed physical barriers and prevented enzymes from accessing/binding to starch; (iii) reduced enzymes activities. Dietary compounds showed great potentials in lowering starch enzymatic digestion, thereby modulating postprandial glucose response to food and preventing or treating type II diabetes disease.

Monitoring the effect of cell wall integrity in modulating the starch digestibility of durum wheat during different steps of bread making

Reduction of starch digestibility in starchy foods is beneficial for lowering the risks for major non-communicable diseases. Preserving cell integrity is known to delay starch digestibility in flour but its effect in bread is not clear. In this study, the effect of increasing particle size on in vitro starch digestibility of durum wheat flour, dough, and bread was investigated. Cell integrity was retained during bread processing for medium (1000 µm-1800 µm), and large (>1800 µm) flour, whereas in small one cell walls were mostly damaged (<350 µm). In vitro starch digestibility of flour decreased increasing particle size, but no difference was found in dough. In bread, instead, a modest decrease of starch digestibility for the bread made by large particle was observed, likely due to its dense structure. In conclusion, a high particle size could limit starch digestibility in durum wheat flour but not in bread.

New definition of resistant starch types from the gut microbiota perspectives - a review

Current definition of resistant starch (RS) types is largely based on their interactions with digestive enzymes from human upper gastrointestinal tract. However, this is frequently inadequate to reflect their effects on the gut microbiota, which is an important mechanism for RS to fulfill its function to improve human health. Distinct shifts of gut microbiota compositions and alterations of fermented metabolites could be resulted by the consumption of RS from the same type. This review summarized these defects from the current definitions of RS types, while more importantly proposed pioneering concepts for new definitions of RS types from the gut microbiota perspectives. New RS types considered the aspects of RS fermentation rate, fermentation end products, specificity toward gut microbiota and shifts of gut microbiota caused by the consumption of RS. These definitions were depending on the known outcomes from RS-gut microbiota interactions. The application of new RS types in understanding the complex RS-gut microbiota interactions and promoting human health should be focused in the future.

Utilizing Hydrothermal Processing to Align Structure and In Vitro Digestion Kinetics between Three Different Pulse Types

Processing results in the transformation of pulses’ structural architecture. Consequently, digestion is anticipated to emerge from the combined effect of intrinsic (matrix-dependent) and extrinsic (processed-induced) factors. In this work, we aimed to investigate the interrelated effect of intrinsic and extrinsic factors on pulses’ structural architecture and resulting digestive consequences. Three commercially relevant pulses (chickpea, pea, black bean) were selected based on reported differences in macronutrient and cell wall composition. Starch and protein digestion kinetics of hydrothermally processed whole pulses were assessed along with microstructural and physicochemical characteristics and compared to the digestion behavior of individual cotyledon cells isolated thereof. Despite different rates of hardness decay upon hydrothermal processing, the pulses reached similar residual hardness values (40 N). Aligning the pulses at the level of this macrostructural property translated into similar microstructural characteristics after mechanical disintegration (isolated cotyledon cells) with comparable yields of cotyledon cells for all pulses (41–62%). We observed that processing to equivalent microstructural properties resulted in similar starch and protein digestion kinetics, regardless of the pulse type and (prolonged) processing times. This demonstrated the capacity of (residual) hardness as a food structuring parameter in pulses. Furthermore, we illustrated that the digestive behavior of isolated cotyledon cells was representative of the digestion behavior of corresponding whole pulses, opening up perspectives for the incorporation of complete hydrothermally processed pulses as food ingredients.

Possible regulation of liver glycogen structure through the gut-liver axis by resistant starch: a review

Liver glycogen α particles in diabetic patients are fragile relative to those in healthy individuals, and restoring these fragile glycogen particles to a normal state shows potential to contribute to the remission of diabetes. Resistant starch (RS) is beneficial for diabetes management through its interactions with the gut microbiota. However, its effects on glycogen fragility are not fully understood. This review aims to summarize the recent understanding of the interactions between RS and the human gut microbiota and the possible connections to liver glycogen biosynthesis to elucidate its role in the development of glycogen fragility. RS might regulate glycogen fragility in diabetes by modulating the postprandial glycemic response and glycogen biosynthesis pathways. Before RS can be applied to repair fragile glycogen, more work should be done to better understand in vivo RS structures and identify the factor binding glycogen β particles together. This review contains important information on the connections between glycogen fragility and RS-gut microbiota interactions, which could help to better understand the health benefits of RS consumption.

Align resistant starch structures from plant-based foods with human gut microbiome for personalized health promotion

Resistant starch (RS) is beneficial for human health through its interactions with gut microbiota. However, the alignment between RS structures with gut microbiota profile and consequentially health benefits remain elusive. This review summarizes current understanding of RS complex structures and their interactions with the gut microbiota, aiming to highlight the possibility of manipulating RS structures for a targeted and predictable gut microbiota shift for human health in a personalized way. Current definition of RS types is strongly associated with starch digestion behaviors in small intestine, which does not precisely reflect their interactions with human gut microbiota. Distinct alterations of gut microbiota could be associated with the same RS type. The principles to describe the specificity of different RS structural characteristics in terms of aligning with human gut microbiota shift was proposed in this review, which could result in new definitions of RS types from the microbial perspectives. To consider the highly variable personal features, a machine-learning algorithm to integrate different personalized factors and better understand the complex interaction between RS and gut microbiota and its effects on individual health was explained. This review contains important information to bring interactions between RS and gut microbiota to translational practice.

Effects of Different Processing Methods and Internal Components on Physicochemical Properties and Glycemic Index of Adzuki Bean Powder

The estimated glycemic index (eGI) value of adzuki bean powder prepared by steamed cooking (SC), extruded cooking (EC) and roller cooking (RC) was studied comparatively. Results showed that RC had the highest eGI, with 80.1, and both EC and SC resulted in a lower eGI value of 70.0 and 49.7, respectively. Compared with the EC and RC methods, the SC method provided a more intact physical barrier for starch digestion, resulting in a less destroyed cell structure. As the essential components that form the cell wall, the study further investigated the effects of protein and fiber on physicochemical properties, in vitro starch digestibility and the eGI of adzuki bean powder processed with the SC method. Viscozyme and Protamax were used to obtain the deprotein and defiber samples. Results showed that the SC treatment with Viscozyme and Protamax, respectively, had significant effects on in vitro starch digestibility. The eGI of different samples were given as follows: steamed cooking adzuki bean powder (49.7) < deproteined adzuki bean powder (60.5) < defibered adzuki bean powder (83.1), which indicates that fiber may have a greater influence on the eGI than protein.

In vitro protein and starch digestion kinetics of individual chickpea cells: from static to more complex in vitro digestion approaches

Attention has been given to more (semi-)dynamic in vitro digestion approaches ascertaining the consequences of dynamic in vivo aspects on in vitro digestion kinetics. As these often come with time and economical constraints, evaluating the consequence of stepwise increasing the complexity of static in vitro approaches using easy-to-handle digestion set-ups has been the center of our interest. Starting from the INFOGEST static in vitro protocol, we studied the influence of static gastric pH versus gradual gastric pH change (pH 6.3 to pH 2.5 in 2 h) on macronutrient digestion in individual cotyledon cells derived from chickpeas. Little effect on small intestinal proteolysis was observed comparing the applied digestion conditions. Contrary, the implementation of a gradual gastric pH change, with and without the addition of salivary α-amylase, altered starch digestion kinetics rates, and extents by 25%. The evaluation of starch and protein digestion, being co-embedded in cotyledon cells, did not only confirm but account for the interdependent digestion behavior. The insights generated in this study demonstrate the possibility of using a hypothesis-based approach to introduce dynamic factors to in vitro models while sticking to simple and cost-efficient set-ups.