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Digestion of macro-nutrients (protein and starch) in pulses is a consequence of the interplay of both extrinsic (process-related) and intrinsic (matrix-dependent) factors which influence their level of encapsulation and physical state, and therefore, their accessibility by the digestive enzymes. The current work aimed at understanding the consequences of hydrothermally induced changes in the physical state of cell biopolymers (cell wall, protein, and starch) in modulating the digestion kinetics of starch and proteins in common beans. The hydrothermal treatments were designed such that targeted microstructural/biopolymer changes occurred. Therefore, bean samples were processed at temperatures between 60 and 95 °C for 90 minutes. It was demonstrated that these treatments allowed the modulation of starch gelatinization, protein denaturation and cell separation. The specific role of hydrothermally induced starch gelatinization and protein denaturation, alongside enhanced cell wall permeability on the digestion kinetics of common bean starch and proteins is illustrated. For instance, bean samples processed at T > 70 °C were marked by higher levels of starch digestibility (Cf values above 47%) compared to the partially (un-)gelatinized samples (processed at T ≤ 70 °C) (Cf values below 35%). Similarly, samples processed at T > 85 °C exhibited significantly higher levels of protein digestibility (Cf values above 47%) resulting from complete protein denaturation. Moreover, increased permeability of the cell wall to digestive enzymes in these samples (T > 85 °C) increased levels of digestibility of both gelatinized starch and denatured proteins. This study provides an understanding of the potential use of hydrothermal processing to obtain pulse-based ingredients with pre-determined microstructural and nutritional characteristics.

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The volatile profiles of Brussels sprouts and leek, as affected by pretreatment combined with frozen storage were analyzed in the present work. The data revealed that, notwithstanding the effect upon pretreatment seemed to be major compared to the effect upon frozen storage, the latter was existent. Pretreatment yielded volatile compounds that could be associated with (bio)chemical reaction pathways in both vegetables. For frozen storage at -20 °C, the effect for leek appeared to be the largest for the blanched and raw samples, possibly due to a substantial amount of substrates present when frozen storage was initiated in this sample compared to the other samples. Those substrates were apparently more prone to be affected upon frozen storage. For Brussels sprouts, this observation was less outspoken. Remarkably, the abundance of markers in pretreated Brussels sprouts seemed to show a decreasing linear trend towards the end of the frozen storage period at -20 °C. As industrial relevant conditions were considered and compared, the insights gained in this study might be relevant to implement on industrial level.

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Brassica oleracea and Allium vegetables are known for their unique, family specific, water-soluble phytochemicals, glucosinolates, and S-alk(en)yl-l-cysteine sulfoxides, respectively. However, they are also important delivery systems of several other health-related compounds, such as carotenoids (lipid-soluble phytochemicals), vitamin C (water-soluble micronutrient), and vitamin K1 (lipid-soluble micronutrient). When all-year-round availability or transport over long distances is targeted for these often seasonal, locally grown vegetables, processing becomes indispensable. However, the vegetable processing chain, which consists of multiple steps (e.g., pretreatment, preservation, storage, preparation), can impact the nutritional quality of these vegetables corresponding to the nature of the health-related compounds and their susceptibility to (bio)chemical conversions. Since information about the impact of the vegetable processing chain is scattered per compound or processing step, this review targets an integration of the state of the art and discusses needs for future research. Starting with a discussion on substrate-enzyme location within the vegetable matrix, an overview is provided of the impact and potential of processing, encompassing a wide range of (nonenzymatic) conversions.

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Quantitative changes at different length scales (molecular, microscopic, and macroscopic levels) during cooking were evaluated to better understand the cooking behavior of common beans. The microstructural evolution of presoaked fresh and aged red kidney beans during cooking at 95 °C was quantified using light microscopy coupled with image analysis. These data were related to macroscopic properties, being hardness and volume changes representing texture and swelling of the beans during cooking. Microstructural properties included the cell area (Acell), the fraction of intercellular spaces (%Ais), and the fraction of starch area within the cells (%As/c), reflecting respectively cell expansion, cell separation, and starch swelling. A strong linear correlation between hardness and %Ais (r = -0.886, p = 0.07), along with a significant relative change in %Ais (∼5 times), suggests that softening is predominantly due to cell separation rather than cell expansion. Regarding volume changes, substantial cell expansion (Acell increased by ∼1.5 times) during the initial 30 min of cooking was greatly associated with the increase in the cotyledon volume, while the significance of cell separation became more prominent during the later stages of cooking. Furthermore, we found that the seed coat, rather than the cotyledon, played a major role in the swelling of whole beans, which became less pronounced after aging. The macroscopic properties did not correlate with %As/c. However, the evolution of %As/c conveyed information on the swelling of the starch granules during cooking. During the initial phase, the starch granule swelling mainly filled the cells, while during the later phase, the further swelling was confined by the cell wall. This study provides strong microscopic evidence supporting the direct involvement of the cell wall/ middle lamella network in microstructural changes during cooking as affected by aging, which is in line with the results of molecular changes.

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Vegetables are frequently processed before consumption. However, vegetable functionalization continues beyond ingestion as the human digestive tract exposes vegetable products to various conditions (e.g. elevated temperature, pH alterations, enzymes, electrolytes, mechanical disintegration) which can affect the stability of micronutrients and phytochemicals. Besides the extent to which these compounds withstand the challenges posed by digestive conditions, it is equally important to consider their accessibility for potential absorption by the body. Therefore, this study investigated the impact of static in vitro digestion on the stability (i.e. concentration) and bioaccessibility of vitamin C, vitamin K1, glucosinolates, S-alk(en)yl-l-cysteine sulfoxides (ACSOs) and carotenoids in Brussels sprouts (Brassica oleracea var. gemmifera) and leek (Allium ampeloprasum var. porrum). Water-soluble compounds, glucosinolates and ACSOs, remained stable during digestion while vitamin C decreased by >48%. However, all water-soluble compounds were completely bioaccessible. Lipid-soluble compounds were also stable during digestion but were only bioaccessible for 26-81%.

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Vegetable processing often consists of multiple processing steps. Research mostly focused on the impact of individual processing steps on individual health-related compounds. However, there is a need for more holistic approaches to understand the overall impact of the processing chain on the health potential of vegetables. Therefore, this work studied the impact of pretreatment (relatively intact versus pureed vegetable systems), pasteurization and subsequent refrigerated storage (kinetic evaluation) on multiple health-related compounds (vitamin C, vitamin K1, carotenoids, glucosinolates and S-alk(en)yl-L-cysteine sulfoxides (ACSOs)) in Brussels sprouts and leek. It could be shown that differences introduced by different types of pretreatment were not nullified during pasteurization and refrigerated storage. Clearly, enzymatic conversions controlled during pretreatment resulted in different health-related compound profiles still observable after pasteurization. Moreover, about -42% and -100% relative concentration differences of ACSOs and dehydroascorbic acid, respectively, were detected immediately after pasteurization, while glucosinolates concentrations decreased by about 47% during refrigerated storage. All other compounds were stable during pasteurization and refrigerated storage.

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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.

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Hard-to-cook (HTC) is a textural defect that delays the softening of common bean seeds during cooking. While this defect is commonly associated with conventionally stored beans, soaking/cooking of beans in CaCl2 solutions or sodium acetate buffer can also prolong the cooking time of beans due to formation of Ca2+ crosslinked pectin retarding bean softening during cooking. In this study, the role of the cell wall-bound Mg2+/Ca2+ content and the degree of pectin methyl esterification (DM) was quantified, as important factors for bean texture-related changes stipulated in the pectin-cation-phytate hypothesis, the most plausible hypothesis of HTC development. Evaluation of texture changes during cooking of conventionally aged beans (35 °C and 83% RH for up to 20 weeks), beans soaked/cooked in CaCl2 solutions (0.01 to 0.1 M) or soaked in 0.1 M sodium acetate buffer (pH 4.4) revealed large bean-to-bean variations. Therefore a texture-based classification approach was used to better capture the relation between texture characteristics and cell wall polymer, in particular pectin, related changes. While cell wall-bound Ca2+ and pectin DM did not change/were not related to the texture variation during cooking of fresh beans, increased cell wall-bound Ca2+ and decreased pectin DM were associated with prolonged conventional storage of beans and their texture changes during subsequent cooking (due to pectin cross linking, retarding its solubilization during cooking). Exogenously added Ca2+ from pre-treating beans in CaCl2 solutions promoted to a great extent the cell wall-bound Ca2+ during soaking but even more so during cooking, complementing the harder texture associated with these beans during cooking (compared to conventionally stored and fresh beans). Similarly, free Ca2+ endogenously generated by phytase-catalysed phytate hydrolysis (beans treated by acetate buffer) promoted crosslinking of pectin by Ca2+ (cell wall-bound Ca2+), delaying softening of beans during cooking.

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The emulsion forming and stabilizing capacities of water-soluble biopolymers originating from the aqueous (serum) phase of heat-treated and high pressure homogenized purées were investigated. The serum biopolymers were characterized and then utilized as emulsifier/stabilizer in simple oil-in-water emulsions. The resulting emulsions were stored at 4 °C and monitored for 2 weeks. Results revealed that carrot and tomato sera contained higher amounts of pectin and lower protein compared to broccoli. The serum pectic biopolymers exhibited distinct molecular structures, depending on the vegetable origin. Given these natural biopolymer composition and characteristics, emulsions with small droplet sizes were observed at pH 3.5. However, emulsions at pH 6.0 showed large mean droplet sizes, except for the emulsion formulated with carrot serum. Regardless of the pH, emulsions containing carrot serum biopolymers exhibited high capacity to form fine emulsions that were stable during the 2-week storage period at low temperature. This study clearly shows the capacity of natural water-soluble biopolymers isolated from the serum phase of vegetable purées to form fine emulsion droplets and maintain its stability during storage, especially in the case of carrot serum biopolymers.

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To establish the HTC defect development, the cooking kinetics of seeds of ten bean accessions (belonging to seven common bean market classes), fresh and conventionally aged (35 °C, 83% RH, 3 months) were compared to those obtained after soaking in specific salt solutions (in 0.1 M sodium acetate buffer at pH 4.4, 41 °C for 12 h, or 0.01 M CaCl2 at pH 6.2, 25 °C for 16 h and subsequently cooking in CaCl2 solution, or deionised water). The extent of phytate (inositol hexaphosphate, IP6) hydrolysis was evaluated to better understand the role of endogenous Ca2+ in the changes of the bean cooking kinetics. A significant decrease in the IP6 content was observed after conventional ageing and after soaking in a sodium acetate solution suggesting phytate hydrolysis (release of endogenous Ca2+). These changes were accompanied by an increase in the cooking time of the beans. Smaller changes in cooking times after soaking in a sodium acetate solution (compared to conventionally aged beans) was attributed to a lower ionisation level of the COOH groups in pectin (pH 4.4, being close to pKa value of pectin) limiting pectin Ca2+ cross-linking. In beans soaked in a CaCl2 solution, the uptake of exogenous cations increased the cooking times (with no IP6 hydrolysis). The change in cooking time of conventionally aged beans was strongly correlated with the extent of IP6 hydrolysis, although two groups of beans with low or high IP6 hydrolysis were distinguished. Comparable trends were observed when soaking in CaCl2 solution (r = 0.67, p = 0.14 or r = 0.97, p = 0.03 for two groups of beans with softer or harder texture during cooking). Therefore a test based on the Ca2+ sensitivity of the cooking times, implemented through a Ca2+ soaking experiment followed by cooking can be used as an accelerated test to predict susceptibility to HTC defect development during conventional ageing. On the other hand, a sodium acetate soaking experiment can be used to predict IP6 hydrolysis of conventionally aged bean accessions and changes of cooking times for these bean accessions (with exception of yellow bean-KATB1).

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Storage is a fundamental part of the common bean postharvest chain that ensures a steady supply of safe and nutritious beans of acceptable cooking quality to the consumers. Although it is known that extrinsic factors of temperature and relative humidity (influencing the bean moisture content) control the cooking quality deterioration of beans during storage, the precise interactions among these extrinsic factors and the physical state of the bean matrix in influencing the rate of quality deteriorative reactions is poorly understood. Understanding the types and kinetics of (bio)chemical reactions that influence the cooking quality of beans during storage is important in establishing suitable storage conditions to ensure quality stability. In this review, we integrate the current insights on glass transition phenomena and its significance in describing the kinetics of (bio)chemical reactions that influence the cooking quality changes during storage of common beans. Furthermore, a storage stability map based on the glass transition temperature of beans as well as kinetics of the main (bio)chemical reactions linked to cooking quality deterioration during storage was designed as a guide for determining appropriate storage conditions to ensure cooking quality stability.

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Processing can affect (bio)chemical conversions in vegetables and can act on their volatile properties accordingly. In this study, the integrated effect of pretreatment and pasteurization on the volatile profile of leek and Brussels sprouts and the change of this profile upon refrigerated storage were investigated. Pretreatments were specifically selected to steer biochemical reactivities to different extents. Volatile profiles were analyzed by headspace-solid phase microextraction-gas chromatography-mass spectrometry. For both vegetables, it was observed that different pretreatments prior to a pasteurization step led to diverse volatile profiles. The differences in volatile profiles observed in the different samples were presumably attributed to the different degrees of enzymatic conversions, further conversions of enzymatically formed products and thermally induced reactivities. Interestingly, the observed initial relative differences between volatile profiles of differently pretreated pasteurized samples were still observed after a refrigerated storage of 4 weeks at 4 °C. In conclusion, refrigerated storage only limitedly affected the resulting volatile profile.

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The digestion of lipids in the human body has several health and nutritional implications. Lipid digestion is an interfacial phenomenon meaning that water-soluble lipases need to first adsorb to the oil-water interface before enzymatic conversions can start. The digestion of lipids mainly occurs on colloidal structures dispersed in water, such as oil-in-water (o/w) emulsions, which can be designed during food formulation/processing or structured during digestion. From a food design perspective, different in vitro studies have demonstrated that the kinetics of lipid digestion can be influenced by emulsion properties. However, most of these studies have been performed with pancreatic enzymes to simulate lipolysis in the small intestine. Only few studies have dealt with lipid digestion in the gastric phase and its subsequent impact on intestinal lipolysis. In this aspect, this review compiles information on the physiological aspects of gastric lipid digestion. In addition, it deals with colloidal and interfacial aspects starting from emulsion design factors and how they evolve during in vitro digestion. Finally, molecular mechanisms describing gastric lipolysis are discussed.

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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.

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The rate liming step of bean softening during cooking was evaluated. Red kidney beans (fresh/non-aged and aged) were cooked at different temperatures (70-95 °C) and their texture evolution established. Softening of beans (loss of hard texture) with cooking and increasing cooking temperature was evident at ≥ 80 °C more so for non-aged than aged beans, evidencing hard-to-cook development during storage. Beans at each cooking time and temperature were subsequently classified into narrow texture ranges and bean cotyledons in the most frequent texture class evaluated for the extent of starch gelatinization, protein denaturation and pectin solubilization. During cooking, starch gelatinization was shown to precede pectin solubilization and protein denaturation, with these reactions progressing faster and to a greater extent with increasing cooking temperature. At 95 °C for instance (practical bean processing temperature), complete starch gelatinization and protein denaturation is attained earlier (∼10 and 60 min cooking, respectively and at comparable time moments for both non-aged and aged beans) than plateau bean texture (∼120 and 270 min for non-aged and aged beans)/plateau pectin solubilization. The extent of pectin solubilization in the cotyledons was consequently most correlated (negatively, r = 0.95) with and plays the most significant role (P < 0.0001) in directing the relative texture of beans during cooking. Ageing was shown to significantly retard bean softening. Protein denaturation plays a less significant role (P = 0.007) while the contribution of starch gelatinization is insignificant (P = 0.181). Thermo-solubilization of pectin in bean cotyledons is therefore the rate limiting step of bean softening towards attaining a palatable texture during cooking.

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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.

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In vitro digestion studies demonstrate large potential to gain more and quicker insights into the underlying mechanisms of feed additives, allowing the optimization of feed design. Unfortunately, current in vitro digestion models relevant for broiler chickens lack sufficient description in terms of protocols and standardisation used. Furthermore, no distinction is made between the different life phases of these animals (starter, grower, and finisher). Hence, our research aimed to establish adapted in vitro digestion conditions, corresponding to the 3 life phases in broilers, with specific focus on lipid digestion. The effect of 3 different bile salt concentrations of 2, 10, and 20 mM, and 3 different lipase activities of 5, 20, and 100 U/mL, on in vitro lipid digestion kinetics were evaluated using a full factorial design. These values were selected to represent starter, grower, and finisher birds, respectively. Our findings showed that the extent of lipid digestion was mainly influenced by lipase activity. The rate of lipid digestion was affected by an interplay between bile salt concentration and lipase activity, due to possible lipase inhibition at certain bile salt concentrations. Overall, this work resulted in 3 in vitro lipid digestion models representative for starter, grower, and finisher birds. In conclusion, this research showed the impact of adapted in vitro digestion conditions on lipid digestion kinetics and thus the need for these conditions relevant for each life phase of broilers.

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Utilization of common beans is greatly hampered by the hard-to-cook (HTC) defect induced by ageing of the beans under adverse storage. Large bean-to-bean variations exist in a single batch of beans. Therefore, a texture-based bean classification approach was applied in this detailed study on beans with known textures, to gain in-depth insights into the role of the pectin-cation-phytate mechanism in relation to the texture changes during subsequent cooking of Red haricot fresh and aged beans. For the first time, a correlation between the texture (exhibited after cooking) of a single bean seed before ageing (fresh) and its texture after ageing was established. Furthermore, scanning electron microscopy coupled with energy dispersive spectrometry (SEM-EDS) based in situ cell wall associated mineral quantification revealed that the cell wall associated Ca concentration was significantly positively correlated with the texture of both fresh and aged cooked Red haricot bean cotyledons, with ageing resulting in a significant enrichment of Ca at the cell wall. These additional Ca cations originate from intracellular phytate hydrolysis during ageing, which was shown to affect the texture distribution of aged beans during cooking significantly. The relocation of the mineral cations from the cell interior to the cell wall occurs mainly during storage rather than subsequent soaking of the cotyledons. In addition, the pectin-cation-phytate hypothesis of HTC was further confirmed by demethylesterification of the cell wall pectin and increased pectin-Ca interactions upon ageing of the cotyledons, finally leading to HTC development of the cotyledon tissue.

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During adverse postharvest storage of Red haricot beans, the inositol phosphate content, particularly InsP6, decreased significantly, along with a significant increase in InsP5. Using a texture-based classification approach, the InsP6 content in cotyledons was shown an indicator for the extent of hard-to-cook (HTC) development during bean aging. This textural defect development was predominated by storage-induced InsP6 degradation, rather than phytate interconversions during soaking. Ca cations, released during storage, did not leach out significantly during subsequent soaking, suggesting that they were bound with the cell wall pectin in cotyledons, while Mg cations were mostly leached out into the soaking water due to their weak binding capacity to the pectin, and the cell membrane damages developed during HTC. Results obtained herein provide evidence for the pectin-cation-phytate mechanism in textural hardening (and its distribution after cooking) of common beans, and call for a more detailed Ca-relocation study during postharvest storage, soaking and cooking.

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Cell wall material was isolated from selected non-aged and aged Red haricot bean cotyledons using a texture-based classification approach. Pectin-depleted residual cell wall fractions were obtained by sequential pectin extraction and were characterized to investigate in situ cell wall related molecular changes upon ageing during adverse storage of the beans. Particularly, involvement of phenolic compounds in cell wall strengthening during the ageing process, resulting in the hard-to-cook defect, was evaluated. Results show that ageing induces substantial changes at a cell-wall-structural level in the Aged sample compared to the Non-aged sample, with mainly vanillin, 4-hydroxybenzoic acid and 4-hydroxybenzaldehyde covalently bound with sugar side-chains of pectin and/or involved in lignification-like mechanisms. FT-IR spectroscopy coupled with chemometric analysis reveals that lignin-like phenolic-cell wall polymers, which are known to reinforce cell wall structure, are present in the cell wall polysaccharide network of the Aged sample, and are therefore contributing factors to the hard-to-cook development during Red haricot bean ageing.

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