Mechanistic insight into common bean pectic polysaccharide changes during storage, soaking and thermal treatment in relation to the hard-to-cook defect

Different mechanisms responsible for the development of the hard-to-cook defect in common beans during storage, their soaking behavior and softening during thermal treatment have been previously suggested. However, these mechanisms have not been sufficiently confirmed by direct molecular evidence. This research aimed at gaining a detailed mechanistic insight into changes occurring in Canadian wonder bean pectic polysaccharides during storage, soaking and/or thermal treatment in different brine solutions in relation to the development and manifestation of the hard-to-cook (HTC) defect. Both fresh or easy-to-cook (ETC) and stored (HTC) bean samples were either soaked or soaked and thermally treated in demineralized water, solutions of Na2CO3 and CaCl2 salts followed by extraction of cell wall materials. Pectic polysaccharide properties examined included sugar composition, degree of methylesterification (DM), extractability and molar mass (MM). The DM of pectin from ETC and HTC beans was similar but low (<50%). Upon (pre)treatment in a Na2CO3 solution, solubilization of pectic polysaccharides, especially the strongly bound chelator- (CEP) and Na2CO3- (NEP) extractable pectins was enhanced leading to increased amounts of water extractable pectin (WEP). Also, there was a decrease in high MM polymers paralleled by an increase in -elimination degradation products. These observations are in line with the fast cooking behavior of beans (pre)treated in a Na2CO3 solution. In contrast, (pre)treatment in a CaCl2 solution hindered softening leading to the failure of the beans to cook. The beans (pre)treated in a CaCl2 solution showed increased high MM polymers and lack of cell wall separation. Therefore, it can be inferred that development of the hard-to-cook defect in Canadian wonder beans during storage and its manifestation during soaking and subsequent thermal treatment is largely reflected by the pectic polysaccharide properties in line with the pectin hypothesis. Our data suggest the release of Ca++ leading to pectin cross-linking and the increase or decrease of -elimination depolymerization. However, the relatively high amounts of neutral sugars and strongly bound NEP in HTC seeds do not allow to rule out the possible existence of non-Ca++ based pectin cross-linking.status: publishe

Role of structural barriers for carotenoid bioaccessibility upon high pressure homogenization

A specific approach to investigate the effect of high pressure homogenization on the carotenoid bioaccessibility in tomato-based products was developed. Six different tomato-based model systems were reconstituted in order to target the specific role of the natural structural barriers (chromoplast substructure/cell wall) and of the phases (soluble/insoluble) in determining the carotenoid bioaccessibility and viscosity changes upon high pressure homogenization. Results indicated that in the absence of natural structural barriers (carotenoid enriched oil), the soluble and insoluble phases determined the carotenoid bioaccessibility upon processing whereas, in their presence, these barriers governed the bioaccessibility. Furthermore, it was shown that the increment of the viscosity upon high pressure homogenization is determined by the presence of insoluble phase, however, this result was related to the initial ratio of the soluble:insoluble phases in the system. In addition, no relationship between the changes in viscosity and carotenoid bioaccessibility upon high pressure homogenization was found.publisher: Elsevier articletitle: Role of structural barriers for carotenoid bioaccessibility upon high pressure homogenization journaltitle: Food Chemistry articlelink: http://dx.doi.org/10.1016/j.foodchem.2015.12.062 content_type: article copyright: Copyright © 2015 Elsevier Ltd. All rights reserved.status: publishe

Temperature-pressure-time combinations for the generation of common bean microstructures with different starch susceptibilities to hydrolysis

© 2017 Elsevier Ltd In common beans, starch is enclosed by natural (micro)structural barriers influencing its behaviour during processing and digestion. Such barriers and their process-induced modifications could modulate nutrient delivery if adequate processing variables could be selected. In this study, the potential of different processing variables for generating common bean microstructures with different susceptibilities to in vitro starch hydrolysis was assessed. A traditional thermal treatment (95 °C, 0.1 MPa) and two alternative treatments including high hydrostatic pressure at room temperature (25 °C, 600 MPa) and at high temperature (95 °C, 600 MPa) were applied to common beans following a kinetic approach. (Micro)structural properties of (mechanically disintegrated) common beans were evaluated at each processing time. Mostly free, non-swollen and birefringent starch granules were obtained after mechanical disintegration of samples subjected to high pressure at room temperature. In mechanically disintegrated samples obtained by processes involving high temperature, either in combination with high pressure or not, there was major presence of cell clusters at early processing times (7–15 min) and individual cells at intermediate and long times (≥ 45 min). Following, specific process-induced common bean microstructures were evaluated in terms of in vitro starch hydrolysis kinetics. Rate constants of all microstructures obtained after high temperature treatments were similar, whereas final values of digested starch and initial reaction rates exhibited differences. The variations observed in the later parameters were correlated with the starch bio-encapsulation degree. Furthermore, in samples with the same starch bio-encapsulation degree (individual cells), differences in final digested starch and initial reaction rate were hypothesised to originate from differences in cell wall porosity/fragility.status: publishe

Process-induced cell wall permeability modulates the in vitro starch digestion kinetics of common bean cotyledon cells

The presence of cell walls entrapping starch granules in common bean cotyledons, prevailing after thermal processing and mechanical disintegration, has been identified as the main reason for their (s)low in vitro starch digestibility. Nevertheless, it is unknown if the role of cell walls on starch digestion changes as processing conditions (e.g. time) are modified. In this study it was hypothesised that cell wall permeability would be differently affected depending on thermal process intensity, giving origin to distinct in vitro starch digestion kinetic profiles. Cotyledon cells were isolated from common beans by applying processing conditions normally found at household level (95°C and times between 30 and 180 min (palatable range)). Isolated cells were characterised and subsequently subjected to in vitro simulated digestion. Microstructural properties, starch gelatinisation degree, and total starch content were similar among samples. In contrast, a higher diffusion of fluorescently labelled pancreatic α-amylase inside the cells was evident as processing time increased. From the kinetic analysis of digestion products, it was determined that longer lag phases and slower reaction rate constants were present in samples with a lower degree of process-induced cell wall permeability. Qualitative analysis of remaining pellets showed that cellular integrity was kept throughout in vitro digestion. A mechanism for the in vitro starch digestion of isolated common bean cotyledon cells was proposed, as well as an alternative kinetic model to describe this process. Overall, our work demonstrated that in vitro starch digestion kinetics of common bean cotyledon cells can be modulated by influencing cell wall permeability through thermal processing time.status: publishe

Insight into the evolution of flavor compounds during cooking of common beans utilizing a headspace untargeted fingerprinting approach

Beans age during storage leading to prolonged cooking times. Chemical reactions that occur during cooking lead to volatile production and flavor generation. Whereas few studies profiled the volatile fingerprint of either non-cooked beans or beans cooked for a specific time, this study explored the evolution of volatiles through headspace fingerprinting of beans cooked at 95 °C to different extents. The influence of aging of beans on this evolution was investigated. Cooking time clearly influenced the evolution of volatiles for both fresh (non-aged) and aged beans. Aged beans exhibited more discriminant compounds than fresh beans regardless of texture considerations due to differences in pre-history of the beans. Strecker aldehydes, sulphur compounds and furan compounds were identified as marker compounds and were linked to mainly lipid oxidation and Maillard reactions. In conclusion, both aging prior to cooking and the cooking process itself largely influence the evolution of volatile compounds during cooking.status: publishe

Mechanistic insight into softening of Canadian wonder common beans (Phaseolus vulgaris) during cooking

The relative contributions of cotyledons and seed coats towards hardening of common beans (Phaseolus vulgaris) were investigated and the rate-limiting process which controls bean softening during cooking was determined. Fresh or aged whole beans and cotyledons were soaked and cooked in demineralised water or 0.1 M NaHCO3 solution, and texture evolution, microstructure changes and thermal properties were studied. Fresh and aged whole beans cooked in demineralised water had significantly different softening rate constants and so did fresh and aged cotyledons. The comparable softening rate constants of aged whole beans and cotyledons indicated an insignificant role of the seed coat in hardening during storage. All samples cooked faster in 0.1 M NaHCO3 solution. Disintegration of cooked tissues followed by microscopic examination revealed a transition from cell breakage through a phase of cell breakage and separation to complete cell separation with increased cooking time wherefore texture decayed. Therefore, progressive solubilization of pectin in the middle lamella greatly promoted texture decay. While residual birefringence even after substantial cooking time suggested some molecular order of the starch, calorimetric analyses revealed complete starch gelatinisation before complete cell separation occurred. This implies an insignificant role of starch in texture decay during cooking but its hindered uncoiling into a viscous gel after gelatinisation due to the restricting cell wall could promote its retrogradation. Therefore, we suggest that the rate-determining process in bean softening relates to cell wall/middle lamella changes influencing pectin solubilization.status: publishe