473 research outputs found
Circular Dichroism to Probe the Synthesis, Transfer, and Stability of Fe-S Clusters
No full textAll Fe-S proteins are characterized by distinctive circular dichroism (CD) features in the visible region of the spectrum due to chiral interaction between the cluster itself and the protein backbone. Therefore, the presence of a CD signal in the visible region relates to the presence of the cluster, whereas the disappearance of the signal refers to cluster breakdown or redox changes. The position of the CD features in the spectrum and the intensity of individual components of the CD signal show great variations among different Fe-S proteins. This feature can provide information on transfer processes between proteins, as well as on possible changes in cluster nuclearity. This method can also be used to detect changes in the chemical nature or spatial organization of cluster ligands that may be concurrent with cluster transfer and associated events
Protein structural modifications induced by physical processing
No full textThis contribution focuses on the molecular determinants and the biotechnologically relevant consequences of structural modification of protein ensuing from: 1) physical treatments that alter the structure of solvent water (such as temperature of high pressure); 2) shear forces (as used, for example, in food processing); 3) the interaction of proteins with hydrophobic surfaces (either in liquid or in solid phases). For the sake of simplicity, most of the data to be presented and discussed relate to bovine betalactoglobulin (BLG), that offers a number of distinctive advantages for this type of studies: i) its structure is known in extreme detail; ii) it contains a number of “reporter” residues that facilitate analysis of individual unfolding steps; iii) it is a food allergen with both sequential and conformational epitopes, for which selected monoclonal antibodies are available.
The presentation will take off by considering temperature stability of the protein structure, with a focus on how unfolding can be controlled by the presence/absence of ligands and cosolutes, and on how temperature-swollen conformers of BLG may be used for selective and stable binding of hydrophobes (including bioactives and species of pharmaceutical interest) or to generate non-immunoreactive species upon selective proteolytic breakdown breakdown of sequential epitopes.
Further, focus will shift on mechanical stress, as used in generating BLG conformers trapped at the interface between polar and non-polar liquid phases, as happens when BLG is used as a stabilizing agent in emulsions. The effects of these conformational changes on the protein structure will be discussed also in terms of altered proteolytic patterns and of changes in immunoreactivity.
Finally, recent data on the unfolding of BLG upon contact with the hydrophobic surface of polystyrene nanoparticles (NPs, of various size) will be presented and discussed. Molecular dynamic (MD) studies highlighted that this “contact” unfolding is extensive and extremely fast. Structural features of the NP-bound BLG have been assessed by monitoring the reactivity and the spectroscopic features of “reporter” residues in the protein structure, as well as the immunoreactivity of NP-bound BLG and its sensitivity to proteolysis. Results confirm what predicted by MD studies, and provide also evidence of the relevance of “geometric effects” (related to the NP size) and of “molecular crowding” effects (related to the BLG/NP mass ratio)
Molecular features of protein and starch in African rice relate to their processing behavior
No full textResearch and development interventions in the African rice sector mainly focused on increasing farm-level production, whereas little attention was paid to processing and quality enhancement issues, which play major roles in the definition of the value of rice and rice-derived product.
The aim of this study was to investigate the starch and protein properties of rice varieties popularly cultivated in Africa in order to identify which varieties could be most suitable for the development of various specific food products. These products may include pasta, pasta-like products, and a large variety of ready-to-eat rice-based foods. For this reason a number of African varieties and species representative of various locales and produced in commercially significative amounts were selected also according to distinctive physical and chemical parameteres.
Starch properties and protein content in individual samples were characterized by standard chemical methods. In selected cases, structural organization of starch was investigated by measuring susceptibility to selective enzymatic activities [1]. Viscoamilography was used to investigate the possible relationships between structural features and the pasting behavior of starch [2]. Information on the protein pattern in selected varieties was gathered by electrophoresis, whereas the accessibility of specific residues and of specific regions that may be involved in determining the properties of products was addressed by appropriate reagents and spectroscopic approaches [3].
The approaches presented here seem able to provide useful insights as for the intrinsic structural characteristics of starch and proteinsin various African rice varieties. Further studies will verify whether this information will be able to define proper processing and the possible end uses of some of the materials investigated here.
This work was supported by the “New Products“ Project from the Global Rice Science Partnership (GRiSP).
References
[1] Barbiroli A, Bonomi F, Casiraghi MC, Iametti S, Pagani MA, Marti A (2013). Process conditions affect starch structure and its interactions with proteins in rice pasta. Carbohyd. Polym. 92, 1865–1872.
[2] Marti A, Seetharaman K, Pagani MA (2010). Rice-based pasta: a comparison between conventional pasta-making and extrusion- cooking. J. Cereal Sci., 52, 3, 404-409.
[3] Bonomi F, D’Egidio M G Iametti S, Marengo M, Marti A, Pagani MA, Ragg EM (2012). Structure–quality relationship in commercial pasta: A molecular glimpse. Food Chem. 135, 348–355
Properties of biomacromolecules in African-grown rice species
No full textOryza glaberrima, commonly known as African rice, is the native African domesticated rice and has interesting properties from the sustainability and nutritional standpoints. O. glaberrima is an entirely different species from the more common Asian rice (Oryza sativa). The lower crop yield and some transformability issues make O. glaberrima less popular among rice farmers than O. sativa. The aim of this study was to compare the properties of starch and proteins in O. glaberrima with those of O. sativa cultivars grown in Africa, in order to identify the molecular basis of their possible use in specific food products. These products may include pasta, pasta-like products, and a large variety of ready-to-eat rice-based foods. Starch properties and protein content in individual samples were characterized by standard chemical methods. The structural organization of starch was investigated by measuring susceptibility to selective enzymatic activities [1]. Viscoamilography was used to investigate the possible relationships
between structural features and the pasting behavior of starch [2]. The potential glycemic impact was estimated by using an in vitro method and a predictive equation [3]. O. glaberrima showed different pasting properties and a different fragmentation pattern by amylolytic enzymes with respect to O. sativa, suggesting that O. glaberrima may be best suited for instant food. Information on the protein pattern in was gathered by electrophoresis, and the accessibility of specific residues and of specific regions involved in determining the properties of products was addressed by appropriate chemical and spectroscopic approaches [4]. The overall protein structural organization in O. glaberrima is quite different from the one in O. sativa. In O. glaberrima the proteins are organized in highly polymeric form, generating a compact structure mainly stabilized by disulphide bonds. Moreover, the estimated glycemic index in O. glaberrima resulted slightly lower than that estimated for O. sativa. The approaches presented here seem able to provide useful insights as for the intrinsic structural and nutritional characteristics of starch and proteins in this two African rice species.
This work was supported by the “New Products“ Project from the Global Rice Science Partnership (GRiSP).
References
[1] Barbiroli A, Bonomi F, Casiraghi MC, Iametti S, Pagani MA, Marti A (2013). Process conditions affect
starch structure and its interactions with proteins in rice pasta. Carbohyd. Polym. 92, 1865–1872.
[2] Marti A, Seetharaman K, Pagani MA (2010). Rice-based pasta: a comparison between conventional
pasta-making and extrusion- cooking. J. Cereal Sci., 52, 3, 404-409.
[3] Englyst KN, Hudson GJ, Englyst HN (2000). Starch Analysis in Food. Encyclopedia of Analytical Chemistry. pp. 4246-4262.
[4] Bonomi F, D’Egidio M G Iametti S, Marengo M, Marti A, Pagani MA, Ragg EM (2012). Structure–quality
relationship in commercial pasta: A molecular glimpse. Food Chem. 135, 348–355
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