From understanding to modulation of physical barriers for in vitro starch and protein digestion in pulses

Pulses are important constituents of healthy diets because they contain substantial amounts of protein, (slowly digestible) starch, dietary fiber, minerals, and vitamins. Nutrients are encapsulated by a cell wall that commonly remains intact upon ingestion of hydrothermally processed pulses. As a result, the cell wall and cytoplasmic matrix impose physical barriers for enzymatic digestion of encapsulated nutrients (s)lowering their digestion which leads to favorable metabolic responses (e.g., (s)lowly digestible starch). Upon processing several (bio)chemical and mechanical changes can occur that modify the intrinsic structural organization which are likely to affect digestion. Therefore, digestion is anticipated to emerge from a combined effect of intrinsic (i.e., matrix-dependent) and extrinsic (i.e., processed-induced) factors which determine structural aspects, hence nutrient encapsulation upon ingestion. Yet, available literature is mostly reporting on the case of beans and/or is very fragmentary. Understanding the mechanisms through which structural aspects govern digestion kinetics is essential to develop strategies that enable tailoring the macronutrient digestion of pulses. In this doctoral research, we hypothesized that processing can be used to generate (micro)structures with characteristic in vitro starch and protein digestion kinetics. Consequently, the main objective was to understand how in vitro macronutrient digestion kinetics of pulses and pulse-based ingredients are influenced by process-induced structural changes. To elucidate the critical elements influencing digestion kinetic, structures were generated through the application of different processes (sequences) (i.e., hydrothermal processing, mechanical disintegration) on different pulse types. These structures were anticipated to differ in their physical barriers in terms of (i) ratios of starch, protein, and cell wall (intrinsic), (ii) cell wall permeability and/or starch-protein matrix induced by processing (extrinsic), and (iii) cell wall integrity. Subsequently, an integrated kinetic approach was applied to evaluate the in vitro starch and protein digestion properties of the generated structures. Chickpea, pea, and black bean were selected as starting materials to evaluate the impact of intrinsic boundary conditions on starch and protein digestibility. These pulses were selected based on reported intrinsic differences in their physical barriers. At this stage, hydrothermal treatment (95°C; f(t)) of different durations was applied to align macro- and microstructure of pulses. Individual cotyledon cells were the most characteristic fraction of hydrothermally treated pulses. We proved that pulse seed hardness-alignment considering the palatable range resulted in similar (micro)structural and digestion properties regardless of pulse type, (prolonged) processing times, or sample type (isolated versus whole seed). These observations point to the potential of processing to retain pulse macronutrient encapsulation for attenuated macronutrient digestion, including a range of pulses. Milling of raw pulses compromises nutrient encapsulation due to tissue rupture. Our observations indicate that maintaining the cellular integrity during (ingredient) manufacturing could bring functional benefits (e.g., enhanced satiety) which are attributed to (s)lower digestion into mainstream foods. In addition, the effect of different levels of macronutrient encapsulation on in vivo appetite sensations was studied time along with in vitro digestion kinetics. Cellular chickpea-flour was used to replace conventional raw-milled chickpea-flour in suspensions (in vitro digestion) and semi-solid purees (in vivo appetite study). In a randomized crossover design, healthy males (n=26) attended two separate sessions, wherein one of two test meals matched for caloric content was administered followed by an ad libitum lunch. When cellular integrity was kept, (s)lower in vitro macronutrient digestion was accompanied by enhanced subjective appetite responses, whilst no significant differences in AUC and food intake were detected (p>0.05). These observations indicate the influence of cellular integrity in the development of short‑term satiety. Moreover, the physical status of pulse tissue (pre-cooked versus raw) at mechanical disintegration affected structural, in vitro, and in vivo digestion consequences, despite identical nutrient composition. The results demonstrate the potential of ingredient formulations containing (a proportion of) individual cotyledon cells. The last part of this doctoral thesis focused on the simulation and evaluation of macronutrient digestion upon implementation of more complex oro-gastric in vitro digestion methodologies. The effect of a gradual gastric pH change was tested using the INFOGEST static in vitro protocol. As a result, the extent and rate of small intestinal starch digestion increased significantly, while little effect on small intestinal proteolysis was observed. The estimated kinetic parameters of starch and protein digestibility were highly correlated, indicating their interdependent digestion. These observations illustrated for the first time the importance of the chronological action of amylases and proteases for the digestion of co-embedded nutrients, which can be expected when gastric pH evolves. This became evident through the evaluation of the digested protein at the level of its monomeric equivalents. Overall, the findings of this doctoral work demonstrate the potential of targeted processing of pulses and pulse-based ingredients to modulate structural and in vitro and in vivo digestion properties. Retaining the cellular integrity is a key determinant for attenuated in vitro starch and protein digestion kinetics, both in pulses and pulse-based ingredients. The here presented observations provide the fundamental scientific basis for targeted processing of pulse and pulse-based ingredients with improved nutritional properties (e.g., (s)lowly digestible starch). Hereby, pulses can deliver what they promise: being a sustainable ingredient providing attractive nutritional properties for a healthy diet.

Jaar van publicatie:2022

Toegankelijkheid:Open