Pea protein extraction method impacts the protein (micro)structural organisation and in vitro digestion kinetics.

There is increasing interest in including pulse proteins into food products due to their nutrient-rich and sustainable character. However, little is known regarding the consequences of different extraction approaches on the pulse protein structure and the subsequent protein (micro)structural organization and protein digestion kinetics. Therefore, three green pea protein extracts were created: (i) cooking followed by cotyledon cell isolation, (ii) alkaline extraction followed by isoelectric precipitation, or (iii) salt extraction, and compared to the original pea flour as well as to sodium caseinate. The results showed that encapsulated, denatured protein inside pea cotyledon cells presented the (s)lowest digestion, while accessible and more native protein (e.g., pea flour, pea protein salt extract) presented much faster and higher digestion. Moreover, the alkali extracted pea protein was denatured to some extent, significantly lowering in vitro digestion kinetics. In the second part, three different in vitro approaches were applied to digest the salt extracted pea protein. Semi-dynamic gastric digestion approaches simulate in vivo conditions more closely which especially impacted the rate of digestion.

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.

Size exclusion chromatography to evaluate in vitro proteolysis: A case study on the impact of microstructure in pulse powders.

Cellular pulse ingredients are increasingly being studied but little knowledge on their proteolysis patterns upon digestion is available. This study investigated a size exclusion chromatography (SEC) approach to study in vitro protein digestion in chickpea and lentil powders, providing novel insights into proteolysis kinetics and the evolution of molecular weight distributions in the (solubilized) supernatant and (non-solubilized) pellet fractions. For the quantification of proteolysis, SEC-based analysis was compared to the commonly used OPA (o-phthaldialdehyde) approach and nitrogen solubilized upon digestion, leading to highly correlated proteolysis kinetics. Generally, all approaches confirmed that microstructure dictated proteolysis kinetics. However, SEC analysis delivered an additional level of molecular insight. For the first time, SEC revealed that while bioaccessible fractions reached a plateau in the small intestinal phase (around 45-60 min), proteolysis continued in the pellet, forming smaller but mostly insoluble peptides. SEC elutograms showed pulse-specific proteolysis patterns, unidentified using other current state-of-the-art methods.

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.

Effect of processing and microstructural properties of chickpea-flours on in vitro digestion and appetite sensations.

Nowadays, pulse flours are ingredients that are more and more used as substitutes in traditional staples (i.e., pasta, bread). In this study, cellular chickpea-flour was used as an ingredient to replace conventional raw-milled chickpea-flour in suspensions and semi-solid purees. The contribution of cellular integrity on in vitro macronutrient digestion and the subsequent effect on in vivo appetite sensations were investigated. Alternating the flour preparation sequence by interchanging hydrothermal treatment and mechanical disintegration (thermo-mechanical treatment) resulted in three chickpea-flours with distinct levels of cellular integrity, and thus nutrient accessibility. The study showed that cellular integrity in chickpea-flours was preserved upon secondary hydrothermal treatment and led to significant attenuation of in vitro macronutrient digestion as compared to conventional chickpea-flour. In a randomized crossover design, significant increase of mean in vivo subjective appetite sensations satiety and fullness along with decreases in hunger, desire to eat, and prospective food consumption were achieved when cellular integrity was kept without an effect on palatability and appearance of the purees (n = 22). In vitro digestion along with microstructural assessment confirmed the importance of cellular integrity for attenuating macronutrient digestion and thereby contributing to enhanced subjective satiety and fullness in pulses. Overall, this study highlights the promising potential of altarenating the flour preparation sequence resulting in macronutrient and energy-matched flours with different nutrient encapsulation which lead to different in vitro digestion kinetics and in vivo appetite sensations.

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.

How postharvest variables in the pulse value chain affect nutrient digestibility and bioaccessibility.

Pulses are increasingly being put forward as part of healthy diets because they are rich in protein, (slowly digestible) starch, dietary fiber, minerals, and vitamins. In pulses, nutrients are bioencapsulated by a cell wall, which mostly survives cooking followed by mechanical disintegration (e.g., mastication). In this review, we describe how different steps in the postharvest pulse value chain affect starch and protein digestion and the mineral bioaccessibility of pulses by influencing both their nutritional composition and structural integrity. Processing conditions that influence structural characteristics, and thus potentially the starch and protein digestive properties of (fresh and hard-to-cook [HTC]) pulses, have been reported in literature and are summarized in this review. The effect of thermal treatment on the pulse microstructure seems highly dependent on pulse type-specific cell wall properties and postharvest storage, which requires further investigation. In contrast to starch and protein digestion, the bioaccessibility of minerals is not dependent on the integrity of the pulse (cellular) tissue, but is affected by the presence of mineral antinutrients (chelators). Although pulses have a high overall mineral content, the presence of mineral antinutrients makes them rather poorly accessible for absorption. The negative effect of HTC on mineral bioaccessibility cannot be counteracted by thermal processing. This review also summarizes lessons learned on the use of pulses for the preparation of foods, from the traditional use of raw-milled pulse flours, to purified pulse ingredients (e.g., protein), to more innovative pulse ingredients in which cellular arrangement and bioencapsulation of macronutrients are (partially) preserved.

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.

Pulse seeds as promising and sustainable source of ingredients with naturally bioencapsulated nutrients: Literature review and outlook.

Pulse seeds are nutritious and sustainable matrices with a high level of intrinsic microstructural complexity. They contain high-quality plant-based protein and substantial amounts of slowly digestible starch and dietary fiber. Starch and protein in pulses are located inside cotyledon cells that survive cooking and subsequent mechanical disintegration, hence preserving natural nutrient bioencapsulation. In this context, several authors have explored a number of techniques to isolate individual cotyledon cells from these seeds, aiming to unveil their digestive and physicochemical properties. In recent years, isolated pulse cotyledon cells are also being highlighted as promising novel ingredients that could improve the nutritional properties of traditionally consumed food products. Even more, they could enable to implement a strategy for increasing pulse intake in populations where these seeds have not been traditionally consumed. This review mainly focuses on the reported digestive, physicochemical, and technofunctional properties of pulse cotyledon cells isolated through different techniques, preceded by a descriptive summary of the nutritional properties, structural organization, and traditional process chain of pulse seeds. It also offers an outlook of research directions to take, based on the identified research gaps. All in all, it is clear that isolation of pulse cotyledon cells using diverse techniques constitutes a promising strategy for the development of pulse-based ingredients where natural bioencapsulation of macronutrients is preserved. However, much more research is needed at the level of ingredient characterization to better understand the effect of starting pulse seed material, isolation technique, and isolation conditions on the nutritional and functional properties of the finished product(s) where the isolated cells are (to be) used.

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.