Stabilization of beta-lactoglobulin by polyols and sugars against temperature-induced denaturation involves diverse and specific structural regions of the protein

Phycobiliproteins, the pigment-protein complex form of natural food colorants and bioactive ingredients

Currently, the use of synthetic pigments in foods is restricted since synthetic pigments are proven and suspected to be harmful to human health. Phycobiliproteins (PBPs), existed in phycobilisomes (PBSs) of algae, are a kind of pigment-proteins with intense color. The specific color of PBPs (red and blue) is given by the water-soluble open-chained tetrapyrrole chromophore (phycobilin) that covalently attaches to the apo-protein via thioether linkages to cysteine residues. According to the spectral characteristics of PBPs, they can be categorized as phycoerythrins (PEs), phycocyanins (PCs), allophycocyanins (APCs), and phycoerythrocyanins (PECs). PBPs can be used as natural food colorants, fluorescent substances, and bioactive ingredients in food applications owing to their color characteristics and physiological activities. This paper mainly summarizes the extraction and purification methods of the PBPs and reviews their characteristics and applications. Moreover, the use of several strategies such as additives, microencapsulation, electrospray, and cross-linking to improve the stability and bioavailability of PBPs as well as the future outlooks of PBPs as natural colorants in food commercialization are elucidated.

The role of the glycerol transporter channel Fps1p in cellular proteostasis during enhanced proteotoxic stress

In response to osmotic shock, the components of high-osmolarity glycerol (HOG) pathway regulate the level of intracellular glycerol in yeast and ensure cell survival. Glycerol is a compatible solute and a stabiliser of proteins. Its role in maintaining proteostasis is less explored. We show that mild stress in the form of dietary restriction leads to increased glycerol level which increases cell viability. However, dietary restriction coupled with protein aggregation decreases intracellular glycerol level and attenuates cell viability. The transcript level of FPS1, the glycerol transporter channel, remains unchanged. However, its activity is altered under enhanced proteotoxic stress. Our results provide evidence for a probable role of the Fps1p channel in the cellular proteostasis network. KEY POINTS: • Dietary restriction led to increased accumulation of glycerol in Fps1-deleted yeast cells. • This led to lower protein aggregation in these cells. • Increased production of glycerol under dietary restriction was not linked to increased level of Fps1.

Improving the Thermal and Oxidative Stability of Food-Grade Phycocyanin from Arthrospira platensis by Addition of Saccharides and Sugar Alcohols

The water-soluble pigment protein phycocyanin (C-PC) from cyanobacteria Arthrospira sp. is an excellent natural food colorant and nutritional supplement with a brilliant blue color. However, C-PC is highly unstable, especially at high temperatures and when exposed to oxidative stress. The lack of simple and economical methods for improving the stability of C-PC greatly limits the application of this functional protein in the food industry. This study investigated the effect of adding saccharides (glucose, mannose, galactose, and maltose) and sugar alcohols (mannitol and maltitol) on the stability of food-grade C-PC extracted from Arthrospira platensis; the relevant reaction kinetics were also analyzed. The results revealed that glucose, mannose, mannitol, galactose, and maltose could effectively improve the thermal stability of C-PC. This improvement was positively correlated with the concentration of the additives and decreased sharply when the temperature exceeded 60 °C. Furthermore, the results also revealed the instability of C-PC when subjected to oxidative stress and the effectiveness of glucose, mannose, mannitol, and maltose in preventing the oxidative degradation of C-PC. In general, this study demonstrates that glucose, mannose, mannitol, and maltose are promising compounds for promoting the thermal and oxidative stability of C-PC, providing an economical and effective method for C-PC preservation.

Beta-Lactoglobulin as a Model Food Protein: How to Promote, Prevent, and Exploit Its Unfolding Processes

Bovine milk beta-lactoglobulin (BLG) is a small whey protein that is a common ingredient in many foods. Many of the properties of BLG relevant to the food industry are related to its unfolding processes induced by physical or chemical treatments. Unfolding occurs through a number of individual steps, generating transient intermediates through reversible and irreversible modifications. The rate of formation of these intermediates and of their further evolution into different structures often dictates the outcome of a given process. This report addresses the main structural features of the BLG unfolding intermediates under conditions that may facilitate or impair their formation in response to chemical or physical denaturing agents. In consideration of the short lifespan of the transient species generated upon unfolding, this review also discusses how various methodological approaches may be adapted in exploring the process-dependent structural modifications of BLG from a kinetic and/or a thermodynamic standpoint. Some of the conceptual and methodological approaches presented and discussed in this review can provide hints for improving the understanding of transient conformers formation by proteins present in other food systems, as well as when other physical or chemical denaturing agents are acting on proteins much different from BLG in complex food systems.

Effect of Trehalose on the Physicochemical Properties of Freeze-Dried Powder of Royal Jelly of Northeastern Black Bee

Trehalose is known for its effect of improving the stability of freeze-dried foods. In this work, vacuum freeze-drying (VFD) technology was employed to prepare northeast black bee royal jelly into lyophilized powder and a novel method mixing trehalose into royal jelly is successfully developed to enhance the free radical scavenging ability and the nutrition stability of royal jelly lyophilized powder. The effects of different trehalose content (0, 0.1, 0.3, 0.5, 0.7 and 0.9 wt.%) on the physicochemical properties of lyophilized royal jelly powder were studied. With systematic analysis, it was found that the incorporation of suitable trehalose content in lyophilized royal jelly powder can reduce the loss of the protein, total sugar, total flavone content during the VFD process and enhance the total phenolic antioxidant capacity, solubility, angle of repose, and bulk density of the royal jelly powder. Finally, lyophilized royal jelly with 0.5 wt.% trehalose is selected as the suitable addition content which exhibits the best radical scavenging ability as well as the lowest hygroscopicity. From the perspective of sensory evaluation, all royal jelly lyophilized powders with trehalose are acceptable.

Water Activity Prediction in Sugar and Polyol Systems Using Theoretical Molecular Descriptors

Water activity is a key factor in the development of pharmaceutical, cosmetic, and food products. In aqueous solutions of nonelectrolytes, the Norrish model provides a simple and effective way to evaluate this quantity. However, it contains a parameter, known as the Norrish constant, that must be estimated from experimental data. In this study, a new strategy is proposed for the prediction of water activity in the absence of experimental information, based on the use of theoretical molecular descriptors for characterizing the effects of a solute. This approach was applied to the evaluation of water activity in the presence of sugars (glucose, fructose, xylose, sucrose) and polyols (sorbitol, xylitol, glycerol, erythritol). The use of two descriptors related to the constitutional and connectivity properties of the solutes was first investigated. Subsequently, a new theoretical descriptor, named the global information index (G), was developed. By using this index, the water activity curves in the binary systems were reconstructed. The positive results obtained support the proposed strategy, as well as the possibility of including, in a single information index, the main molecular features of a solute that determine its effects on water activity.

Science and art of protein formulation development

Protein pharmaceuticals have become a significant class of marketed drug products and are expected to grow steadily over the next decade. Development of a commercial protein product is, however, a rather complex process. A critical step in this process is formulation development, enabling the final product configuration. A number of challenges still exist in the formulation development process. This review is intended to discuss these challenges, to illustrate the basic formulation development processes, and to compare the options and strategies in practical formulation development.

Greetings from foodland: Teaching biochemistry to BS students in food-related courses in Italy

Biochemistry has always been a mandatory topic within BS courses aimed at food science students at the University of Milan, namely: Food Science & Technology and Catering Sciences. Addressing biochemistry topics in this peculiar setting requires: (i) specific focus on topics that are seldom considered in courses offered in bio-medical curricula; (ii) close integration with other area disciplines, such as food biotechnology; (iii) ad hoc design of laboratory classes; and (iv) an array of elective courses covering specific aspects of biochemistry. In this context, for example, protein chemistry is presented by using food proteins of known structure and discussed in terms of structural features in the raw materials and of structural and chemical modifications occurring upon processing. Along the same lines, metabolic pathways and their regulation are presented starting from widespread metabolism-related issues and to issues related to food safety (including food allergies and intolerances). A similar "hands on" approach is used for laboratory classes, that cover about one third of total credits and are aimed at providing fundamental-type information by analyzing practical situations in the food chain. In spite of their inherent complexity and volume, biochemistry courses score very well with the students in mandatory anonymous surveys. Our approach to biochemistry courses seems to help the students in "visualizing" the practical implications of concepts acquired in other courses within their curricula. The students' appreciation is confirmed by the sizeable attendance to elective and specialized biochemical-themed courses. © 2019 International Union of Biochemistry and Molecular Biology, 47(4):394-403, 2019.

Do Osmolytes Impact the Structure and Dynamics of Myoglobin?

Osmolytes are small organic compounds that can affect the stability of proteins in living cells. The mechanism of osmolytes' protective effects on protein structure and dynamics has not been fully explained, but in general, two possibilities have been suggested and examined: a direct interaction of osmolytes with proteins (water replacement hypothesis), and an indirect interaction (vitrification hypothesis). Here, to investigate these two possible mechanisms, we studied myoglobin-osmolyte systems using FTIR, UV-vis, CD, and femtosecond IR pump-probe spectroscopy. Interestingly, noticeable changes are observed in both the lifetime of the CO stretch of CO-bound myoglobin and the spectra of UV-vis, CD, and FTIR upon addition of the osmolytes. In addition, the temperature-dependent CD studies reveal that the protein's thermal stability depends on molecular structure, hydrogen-bonding ability, and size of osmolytes. We anticipate that the present experimental results provide important clues about the complicated and intricate mechanism of osmolyte effects on protein structure and dynamics in a crowded cellular environment.

Amphiphilic spherical nanoparticles with a nitrogen-enriched carbon-like surface by using β-lactoglobulin as a template

We demonstrate a versatile and facile method for fabrication of a new class of amphiphilic spherical nanoparticles having a nitrogen-enriched carbonised surface and precisely-controlled morphology. They are prepared by one-pot polymerization with β-lactoglobulin aggregates as a template with tunable size (70-750 nm) and mild heat-treatment to extend the π-conjugated structures.