Effect of process-induced common bean hardness on structural properties of in vivo generated boluses and consequences for in vitro starch digestion kinetics

From static to semi-dynamic in vitro digestion conditions relevant for the older population: starch and protein digestion of cooked lentils

In the context of adequately feeding the rising older population, lentils have an important potential as sources of (plant-based) protein as well as slowly digestible bio-encapsulated starch and fibre. This study evaluated in vitro digestion of protein and starch in lentils under conditions representing the gastrointestinal tract of older adults. Both static and semi-dynamic simulations were applied to analyze the effect of specific gastrointestinal conditions (healthy versus older adult) on macronutrient digestion patterns. Gastric proteolysis was strongly dependent on applied gastric pH (gradient), leading to a lower extent of protein hydrolysis for simulations relevant for older adults. Fewer and smaller (lower degree of polymerization, DP) bioaccessible peptides were formed during gastric proteolysis under older adult compared to healthy adult conditions. These differences, developed during the in vitro gastric phase, were compensated during small intestinal digestion, yielding similar final proteolysis levels regardless of the applied simulation conditions. In contrast, in the presence of saliva, amylolysis was generally accelerated under older adult conditions. Moreover, the current work highlighted the importance of considering saliva (or salivary amylase) incorporation in simulations where the applied gastric pH (gradient) allows salivary amylase activity. Under both healthy and older adult conditions, in vitro starch hydrolysis bio-encapsulated in cotyledon cells of cooked lentils was attenuated, compared to a white bread reference.

Non-starch polysaccharides from kidney beans: comprehensive insight into their extraction, structure and physicochemical and nutritional properties

Kidney beans (Phaseolus vulgaris L.) are an important legume source of carbohydrates, proteins, and bioactive molecules and thus have attracted increasing attention for their high nutritional value and sustainability. Non-starch polysaccharides (NSPs) in kidney beans account for a high proportion and have a significant impact on their biological functions. Herein, we critically update the information on kidney bean varieties and factors that influence the physicochemical properties of carbohydrates, proteins, and phenolic compounds. Furthermore, their extraction methods, structural characteristics, and health regulatory effects, such as the regulation of intestinal health and anti-obesity and anti-diabetic effects, are also summarized. This review will provide suggestions for further investigation of the structure of kidney bean NSPs, their relationships with biological functions, and the development of NSPs as novel plant carbohydrate resources.

In vitro digestion properties and use of automatic image analysis to assess the quality of wheat bread enriched with whole faba bean (Vicia faba L.) flour and its protein-rich fraction

The trend of incorporating faba bean (Vicia faba L.) in breadmaking has been increasing, but its application is still facing technological difficulties. The objective of this study was to understand the influence of substituting the wheat flour (WF) with 10, 20, 30 and 40 % mass of whole bean flour (FBF) or 10 and 20 % mass of faba bean protein-rich fraction (FBPI) on the quality (volume, specific volume, density, colour, and texture), nutritional composition (total starch, free glucose, and protein contents), and kinetics of in vitro starch and protein digestibility (IVSD and IVPD, respectively) of the breads. Automated image analysis algorithm was developed to quantitatively estimate the changes in the crumb (i.e., air pockets) and crust (i.e., thickness) due to the use of FBF or FBPI as part of the partial substitution of wheat flour. Higher levels of both FBF and FBPI substitution were associated with breads having significant (p < 0.05) lower (specific) volume (at least 25 % reduction) and higher density (up to 35 %), increased brownness (up to 49 % and 78 % for crust and crumb respectively), and up to 2.3-fold increase in hardness. Result from the image analysis has provided useful insights on how FBF and FBPI affecting bread characteristics during baking such as loss of crumb expansion, decrease in air pocket expansion and increase in crust thickness. Overall, incorporation of FBF or FBPI in wheat bread were favourable in reducing the starch content and improving the protein content and IVPD of wheat bread. Since bread remains as a staple food due to its convenience, versatility and affordability for individuals and families on a budget, wheat bread enriched with faba bean could be a perfect food matrix to increase daily protein intake.

Particle size and water content impact breakdown and starch digestibility of chickpea snacks during in vitro gastrointestinal digestion

Chickpeas are an agriculturally-important legume that are an excellent source of protein, fiber, and minerals. Developing chickpea-based snacks could provide consumers with snack products rich in protein and other nutrients. In this study, chickpea puree (high moisture content) and cracker (low moisture content) were each produced with large (7 mm sieve; coarse) or small (2 mm sieve; fine) particle size to investigate the impact of initial particle size and moisture content on particle breakdown, starch hydrolysis, and protein hydrolysis during in vitro digestion. All treatments underwent static in vitro oral digestion, dynamic gastric digestion in the Human Gastric Simulator (HGS), and static in vitro small intestinal digestion. The emptying rate from the HGS was significantly (p < 0.05) higher for fine puree compared to the other treatments, due to higher saturation ratio and smaller initial particle size. The reducing sugars and free amino groups released (representing starch and protein hydrolysis, respectively) from fine puree were higher than coarse puree, and fine cracker was higher than coarse cracker due to the influence of initial particle size. For example, after 360 min total in vitro digestion, the starch hydrolysis of the fine cracker (48.1 ± 3.2%) was significantly higher than (p < 0.05) the coarse cracker (36.3 ± 5.8%). Overall, crackers had higher protein and starch hydrolysis compared to puree in the liquid phase during digestion. The study showed that both the smaller initial particle size and drying significantly (p < 0.05) increased the particle size reduction during gastric digestion and starch and protein digestibility in chickpea-based snacks.

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.

Influence of oral processing behaviour and bolus properties of brown rice and chickpeas on in vitro starch digestion and postprandial glycaemic response

PURPOSE

Oral processing behaviour may contribute to individual differences in glycaemic response to foods, especially in plant tissue where chewing behaviour can modulate release of starch from the cellular matrix. The aim of this study was to assess the impact of chewing time of two starch based foods (brown rice and chickpeas) on bolus properties, in vitro starch digestion and postprandial glycaemic excursion in healthy subjects.

METHODS

In a cross-over trial participants (n = 26) consumed two carbohydrates-identical test meals (brown rice: 233 g; chickpeas: 323 g) with either long (brown rice: 41 s/bite; chickpeas: 37 s/bite) or short (brown rice: 23 s/bite; chickpeas: 20 s/bite) chewing time in duplicate while glycaemic responses were monitored using a continuous glucose monitoring device. Expectorated boli were collected, then bolus properties (number, mean area, saliva amylase activity) and in vitro starch digestion were determined.

RESULTS

Longer chewing resulted in significantly (p < 0.05) more and smaller bolus particles, higher bolus saliva uptake and higher in vitro degree of intestinal starch hydrolysis (DH_S_{chewing time}%) than shorter chewing for both foods (brown rice: DH_S%_23 s = 84 ± 4% and DH_%S_41s = 90 ± 6%; chickpeas: DH_S%_20 s = 27 ± 3% and DH_%S_37s = 34 ± 5%, p < 0.001). No significant effect of chewing time on glycaemic response (iAUC) (p > 0.05) was found for both meals. Brown rice showed significantly and considerably higher in vitro degree of intestinal starch hydrolysis and glycaemic response (iAUC) than chickpeas regardless of chewing time. No significant correlations were observed between bolus properties and in vitro starch hydrolysis or glycaemic response (p > 0.05).

CONCLUSION

Differences in the innate structure of starch based foods (brown rice compared to chickpeas) have a larger effect on postprandial glucose response than differences in mastication behaviour although oral processing behaviour showed consistent effects on bolus properties and in vitro starch digestion. Trial registration ClinicalTrials.gov identifier: NCT04648397 (First posted: December 1, 2020).

Studying semi-dynamic digestion kinetics of food: Establishing a computer-controlled multireactor approach

In this work, a multireactor system to study digestion (MuReDi) kinetics is introduced. For this, a custom-made automated system with four independent syringe pumps (BioXplorer 100, H.E.L Group) was acquired. This system consists of multiple, small-scale reactors allowing to study digestion as a function of time and thus to determine digestion kinetics. The different digestion conditions used in the oral, gastric, and small intestinal phase were based on the digestion protocols published by the INFOGEST consortium. We showed that the minimum working volume of a reactor is 30 mL. Besides, repeatability of the digestion kinetics was shown for two food systems: a liquid Ensure® Plus Vanilla drink, and a solid, cooked lentil sample. When comparing static digestion kinetics with semi-dynamic ones, a significantly different digestion pattern was observed. In the static case, a relatively fast hydrolysis rate was observed until a clear plateau was reached. Oppositely, for the semi-dynamic case, a delayed start of the hydrolysis process was noticed. In the gastric phase, this was explained by the decreasing pH and the large pH dependency of pepsin activity. In the small intestine, the lag phase was relatively shorter, yet clearly present. Here we related it to the gradual enzyme (and bile salt) secretion that had to diffuse towards the substrate before hydrolysis could start. Generally, this work showed that the MuReDi system could be used to perform a semi-dynamic digestion approach which largely impacted the overall digestion kinetics. This is important to consider in future in vitro food digestion simulation work to come closer to physiologically relevant digestion kinetics.

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.

Chew on it: influence of oral processing behaviour on in vitro protein digestion of chicken and soya-based vegetarian chicken

Oral processing behaviour can affect the bioavailability of macronutrients. The aim of the present study was to determine the influence of oral processing behaviour on bolus properties and in vitro protein digestion of chicken and soya-based vegetarian chicken. Natural chewing time and chewing frequency of both foods were determined in healthy adults (n 96). While natural chewing time differed considerably between consumers (chicken: 7·7-39·4 s; soya-based vegetarian chicken: 7·8-46·2 s), chewing frequency (1·4 chews/s) did not differ considerably between consumers and was independent of product type. Natural chewing times of 11 and 24 s were found for clusters of consumers showing shortest and longest chewing time for both products. Chicken and soya-based vegetarian chicken were chewed for 11 and 24 s and boli expectorated by n 16 consumers to determine in vitro gastric digestion and by n 7 to determine in vitro intestinal digestion. For both foods, longer chewing time resulted in the formation of significantly (P < 0·05) more and smaller bolus fragments and higher in vitro degree of protein hydrolysis (DH%) than shorter chewing time (chicken: DH%11s = 7 ± 23 % and DH%24s = 89 ± 26 %; soya-based vegetarian chicken: DH%11s = 57 ± 18 % and DH%24s = 70 ± 21 %, P < 0·001). In vitro degree of protein hydrolysis was higher for chicken than that for soya-based vegetarian chicken regardless of chewing time. We conclude that naturally occurring longer chewing time leads to more and smaller bolus particles of chicken and soya-based vegetarian chicken and thereby increases in vitro protein hydrolysis compared with shorter chewing time.

Understanding In Vivo Mastication Behaviour and In Vitro Starch and Protein Digestibility of Pulsed Electric Field-Treated Black Beans after Cooking

The aim of this study was to understand (i) the in vivo mastication behaviour of cooked black beans (chewing duration, texture perception, oral bolus particle size, microstructure, and salivary α-amylase) and (ii) the in vitro digestibility of starch and protein of in vivo-generated black bean oral bolus under simulated gastrointestinal condition. The beans were pre-treated using pulsed electric field (PEF) with and without calcium chloride (CaCl₂) addition prior to cooking. The surface response model based on least square was used to optimise PEF processing condition in order to achieve the same texture properties of cooked legumes except for chewiness. In vivo mastication behaviour of the participants (n = 17) was characterized for the particle size of the resulting bolus, their salivary α-amylase activity, and the total chewing duration before the bolus was deemed ready for swallowing. In vitro starch and protein digestibility of the masticated bolus generated in vivo by each participant along the gastrointestinal phase were then studied. This study found two distinct groups of chewers—fast and slow chewers who masticated all black bean beans, on average, for <25 and >29 s, respectively, to achieve a bolus ready for swallowing. Longer durations of chewing resulted in boluses with small-sized particles (majorly composed of a higher number of broken-down cotyledons (2–5 mm² particle size), fewer seed coats (5–13 mm² particle size)), and higher activity of α-amylase. Therefore, slow chewers consistently exhibited a higher in vitro digestibility of both the starch and protein of processed black beans compared to fast chewers. Despite such distinct difference in the nutritional implication for both groups of chewers, the in vivo masticated oral bolus generated by fast chewers revealed that the processing conditions involving the PEF and addition of CaCl₂ of black beans appeared to significantly (p < 0.05) enhance the in vitro digestibility of protein (by two-fold compared to untreated samples) without stimulating a considerable increase in the starch digestibility. These findings clearly demonstrated that the food structure of cooked black beans created through PEF treatment combined with masticatory action has the potential to modulate a faster hydrolysis of protein during gastrointestinal digestion, thus offering an opportunity to upgrade the quality of legume protein intake in the daily diet.

Relationship between masticatory variables and bolus characteristics of meat with different textures

The physiological transformations that happen during oral processing are complex and challenging to capture and measure; however, their knowledge can help design new products for people who struggle with mastication and swallowing. Here we relate chewing, saliva incorporation and bolus properties with initial meat texture. Three different textures (T1-tender, T2-intermediate, T3-tough) were created by cooking meat in different temperature time combinations and "ready-to-swallow" meat boluses were collected from 10 healthy individuals. Masticatory variables, saliva incorporation, and bolus mechanical and geometrical characteristics were analyzed. Meat texture showed significant effect on masticatory variables (number of chews and chewing duration) but not on saliva incorporation. Bolus mechanical characteristics (hardness, cohesiveness and adhesiveness) varied significantly (p < .05) with meat texture, where meat with a harder texture resulted in a harder bolus. Number of bolus particles changed significantly (p < .05) with increasing meat hardness, where harder meat produced more bolus particles. Significant (p < .05) intersubject variability was recorded for masticatory parameters and saliva incorporation. Mechanical and geometrical characteristics of "ready-to-swallow" meat bolus did not vary among subjects.

Effects of Hydrothermal Processing Duration on the Texture, Starch and Protein In Vitro Digestibility of Cowpeas, Chickpeas and Kidney Beans

Legumes are a vital candidate in the fight for food security as a sustainable and nutritious food source. The current study systematically investigated the effects of hydrothermal processing of varying durations (15-120 min) on the texture, starch and protein digestibility of cowpeas (Vigna unguiculata), chickpeas (Cicer arietinum) and kidney beans (Phaseolus vulgaris). Texture analysis and in vitro oral-gastro-intestinal digestion of each legume was combined with kinetic modelling to explore the rate and extent of their changes observed during hydrothermal processing. All three legumes showed rapid initial texture decay in the first 30 min of processing. Chickpeas showed the fastest rate of texture degradation with processing duration, whereas texture degradation of kidney bean was slower but reached the lowest hardness value among all beans when processed up to 120 min. The rate of starch and protein digestion increased with prolonged processing duration, whilst showing an inverse relationship with texture values. The extent of starch digestion continually increased with processing duration for all three legumes, whereas the extent of protein digestion decreased after 60 min in cowpeas. This study systematically demonstrated how choosing different processing times can modulate the rate of texture degradation, starch and protein digestion in legumes. The findings of this study can aid consumers and manufacturers on optimal processing to achieve the desired texture or modulate starch and protein digestibility.

Combined Effects of Calcium Addition and Thermal Processing on the Texture and In Vitro Digestibility of Starch and Protein of Black Beans (Phaseolus vulgaris)

Legumes are typically soaked overnight to reduce antinutrients and then cooked prior to consumption. However, thermal processing can cause over-softening of legumes. This study aimed to determine the effect of calcium addition (0, 100, 300, and 500 ppm in the form of calcium chloride, CaCl₂), starting from the overnight soaking step, in reducing the loss of firmness of black beans during thermal processing for up to 2 h. The impact of calcium addition on the in vitro starch and protein digestibility of cooked beans was also assessed. Two strategies of calcium addition were employed in this study: (Strategy 1/S1) beans were soaked and then cooked in the same CaCl₂ solution, or (Strategy 2/S2) cooked in a freshly prepared CaCl₂ solution after the calcium-containing soaking medium was discarded. Despite the texture degradation of black beans brought about by increasing the cooking time, texture profile analysis (TPA) revealed that their hardness, cohesiveness, springiness, chewiness, and resilience improved significantly (p < 0.05) with increasing calcium concentration. Interestingly, beans cooked for 2 h with 300 ppm CaCl₂ shared similar hardness with beans cooked for 1 h without calcium addition. Starch and protein digestibility of calcium-treated beans generally improved with prolonged cooking. However, calcium-treated beans cooked for 1 h under S2 achieved a reduced texture loss and a lower starch digestibility than those beans treated in S1. A lower starch digestion could be desired as this reflects a slow rise in blood glucose levels. Findings from this result also showed that treating black beans with high level of CaCl₂ (i.e., 500 ppm) was not necessary, otherwise this would limit protein digestibility of cooked black beans.

Thermal treatment of common beans (Phaseolus vulgaris L.): Factors determining cooking time and its consequences for sensory and nutritional quality

Over the past years, the shift toward plant-based foods has largely increased the global awareness of the nutritional importance of legumes (common beans (Phaseolus vulgaris L.) in particular) and their potential role in sustainable food systems. Nevertheless, the many benefits of bean consumption may not be realized in large parts of the world, since long cooking time (lack of convenience) limits their utilization. This review focuses on the current insights in the cooking behavior (cookability) of common beans and the variables that have a direct and/or indirect impact on cooking time. The review includes the various methods to evaluate textural changes and the effect of cooking on sensory attributes and nutritional quality of beans. In this review, it is revealed that the factors involved in cooking time of beans are diverse and complex and thus necessitate a careful consideration of the choice of (pre)processing conditions to conveniently achieve palatability while ensuring maximum nutrient retention in beans. In order to harness the full potential of beans, there is a need for a multisectoral collaboration between breeders, processors, and nutritionists.

The impact of replacing wheat flour with cellular legume powder on starch bioaccessibility, glycaemic response and bread roll quality: A double-blind randomised controlled trial in healthy participants

The global rise in obesity and type 2 diabetes has generated significant interest in regulating the glycaemic impact of staple foods. Wheat breads (white or wholemeal) are popular staples, but have a high-glycaemic index, due to the highly digestible wheat starch. Reducing the glycaemic potency of white bread is challenging because the bread-making conditions are mostly conducive to starch gelatinisation. Cellular legume powders are a new source of type 1 resistant starch, where the starch is encapsulated by dietary fibre in the form of intact plant cell walls. The starch in these cell powders is less susceptible to gelatinisation and digestion than starch in conventional legume flours. However, legume cell resilience to baking conditions and the effects of this ingredient on glycaemic responses and product quality are unknown. Here we show that the integrity of cell wall fibre in chickpea powder was preserved on baking and this led to a ~40% reduction in in vivo glycaemic responses (iAUC120) to white bread rolls (~50 g available carbohydrate and 12 g wheat protein per serving) when 30% or 60% (w/w) of the wheat flour was replaced with intact cell powder. Significant reductions in glycaemic responses were achieved without adverse effects on bread texture, appearance or palatability. Starch digestibility analysis and microscopy confirmed the importance of cell integrity in attenuating glycaemic responses. Alternative processing methods that preserve cell integrity are a new, promising way to provide healthier low glycaemic staple foods; we anticipate that this will improve dietary options for diabetes care.

Structural breakdown of starch-based foods during gastric digestion and its link to glycemic response: In vivo and in vitro considerations

The digestion of starch-based foods in the small intestine as well as factors affecting their digestibility have been previously investigated and reviewed in detail. Starch digestibility has been studied both in vivo and in vitro, with increasing interest in the use of in vitro models. Although previous in vivo studies have indicated the effect of mastication and gastric digestion on the digestibility of solid starch-based foods, the physical breakdown of starch-based foods prior to small intestinal digestion is often less considered. Moreover, gastric digestion has received little attention in the attempt to understand the digestion of solid starch-based foods in the digestive tract. In this review, the physical breakdown of starch-based foods in the mouth and stomach, the quantification of these breakdown processes, and their links to physiological outcomes, such as gastric emptying and glycemic response, are discussed. In addition, the physical breakdown aspects related to gastric digestion that need to be considered when developing in vitro-in vivo correlation in starch digestion studies are discussed. The discussion demonstrates that physical breakdown prior to small intestinal digestion, especially during gastric digestion, should not be neglected in understanding the digestion of solid starch-based foods.

Microscopic evidence for pectin changes in hard-to-cook development of common beans during storage

In this study, pectin changes during Red haricot bean storage under high temperature and high humidity conditions were investigated to understand the hard-to-cook (HTC) development from a microstructural point of view. First, to ensure repeatability of the microscopy results, a classification of the fresh and stored beans (aged at 35 °C and 83% relative humidity) into different hardening levels (the Non-aged, Aged and Very-hard aged sample) was performed based on the texture values of cooked half-cotyledons. Cell wall strength of the cotyledons was evaluated, showing that the aged samples (HTC seeds) exhibit stronger cell walls with more/stronger pectic cross-linkages than the Non-aged sample. After a sequential pectin extraction aiming at removing pectin fractions of different solubility, cell wall autofluorescence and immunolabeling of JIM7, LM9 and 2F4 epitopes in the residual materials were examined. Upon ageing, the samples exhibited an increased Ca²⁺-pectin and ferulic acid-pectin crosslinking, these pectic complexes being accumulated primarily at the intercellular spaces. The results suggest a contribution of both the pectin-cation-phytate hypothesis and the involvement of phenolic-pectin crosslinks in HTC development at the cotyledon during storage of common beans.

Structure-function studies of chickpea and durum wheat uncover mechanisms by which cell wall properties influence starch bioaccessibility

Positive health effects of dietary fibre have been established; however, the underpinning mechanisms are not well understood. Plant cell walls are the predominant source of fibre in the diet. They encapsulate intracellular starch and delay digestive enzyme ingress, but food processing can disrupt the structure. Here we compare digestion kinetics of chickpea (cotyledon) and durum wheat (endosperm), which have contrasting cell wall structures (Type I and II, respectively), to investigate a 'cell-wall barrier' mechanism that may underpin the health effects of dietary fibre. Using in vitro models, including the Dynamic Gastric Model, to simulate human digestion together with microscopy, we show that starch bioaccessibility is limited from intact plant cells and that processing treatments can have different effects on cell integrity and digestion kinetics when applied to tissues with contrasting cell wall properties. This new understanding of dietary fibre structure is important for effective fibre supplementation to benefit human health.

Pectin and phytic acid reduce mineral bioaccessibility in cooked common bean cotyledons regardless of cell wall integrity

Common bean cotyledons are rich in minerals (Mg, Ca, Fe and Zn), but they also contain natural barriers that can potentially prevent mineral absorption during digestion. In this study, both the cell wall integrity and mineral chelators/antinutrients (phytic acid and pectin) were investigated as natural barriers in common bean cotyledons. To examine the cell wall integrity as a physical barrier for mineral diffusion, soluble mineral content was determined in a cooked cotyledon sample before and after disruption of intact cell walls. While this study showed that the cell wall in cooked common bean cotyledons does not hinder mineral diffusion, it also demonstrated that the presence of antinutrients decreases mineral bioaccessibility. It was shown that a certain mineral fraction is naturally bound to phytic acid and/or pectin and, by enzymatically degrading these antinutrients, the antinutrient-chelated mineral fraction decreased. Moreover, although pH changes are occurring during simulated digestion experiments, which might affect charge of the antinutrients and thus their chelating capacity for minerals, no difference in mineral distribution over antinutrients was observed due to digestion. In addition, this study showed that mineral bioaccessibility in common bean cotyledons could be potentially increased by degrading antinutrients during digestion in the small intestinal phase.

The impact of postharvest storage and cooking time on mineral bioaccessibility in common beans

Mineral (Mg, Ca, Fe and Zn) bioaccessibility in common beans was evaluated taking into consideration the common bean food chain from postharvest storage over processing (soaking and cooking) until consumption. Beans were stored under realistic tropical conditions (35 °C and 80% RH) which resulted in significantly different cooking behaviour after 8 weeks compared to freshly harvested beans. Based on postcooking hardness, different storage times were selected: unstored, 8 and 20 weeks. Independently of storage conditions, beans were soaked overnight and cooked for 30, 60 or 120 min. The mineral bioaccessibility decreased with increase in both storage and cooking times. Decrease in mineral bioaccessibility with increasing storage time was proved to be the result of increasing mineral chelation of cell wall polymers (e.g. pectin). Additionally, we hypothesize that by cooking, mineral chelators become more accessible, e.g. through pectin solubilization phenomena, in turn capturing more free minerals leading to a reduced mineral bioaccessibility.

In vitro starch and protein digestion kinetics of cooked Bambara groundnuts depend on processing intensity and hardness sorting

When pulse seeds from a single batch are cooked, considerable variability of hardness values in the population is usually observed. Sorting the seeds into hardness categories could reduce the observed diversity and increase uniformity. Therefore, we investigated the effect of processing intensity whether or not combined with sorting into hardness categories on the in vitro starch and protein digestion kinetics of cooked Bambara groundnuts (cooking times 40 min and 120 min). The average hardness values were 89 ± 32 N and 42 ± 20 N for 40 min and 120 min cooking time, respectively. The high standard deviation of hardness for each cooking time revealed a high level of diversity amongst the seeds. Individual cells were isolated from (non-)sorted seeds before simulating digestion. The estimated lag phase describing the initial phase of starch digestion was not significantly different despite the processing intensity or the hardness category, implying that cell wall barrier properties for these samples were not majorly different. However, the rate constants and the extents of starch digestion of samples cooked for 40 min were significantly higher for the low hardness (50-65 N) compared to the high hardness (80-95 N) category (0.71 vs 1.02 starch%/min and 63 vs 77%, respectively). Kinetic evaluation of digested soluble protein (after acid hydrolysis of the digestive supernatant) showed that low hardness samples were digested faster than high hardness samples (0.037 vs 0.050 min^-1). The faster protein hydrolysis in the low hardness samples was accompanied by faster starch digestion, indicating the possible role of the protein matrix barrier. Individual cells of comparable hardness obtained from the two different processing times had similar starch and protein digestion kinetics. Our work demonstrated that, beyond cooking time, hardness is a suitable food design attribute that can be used to modulate starch and protein digestion kinetics of pulse cotyledon cells.