Mechanisms controlling wheat starch gelatinization and pasting behaviour in presence of sugars and sugar replacers : Role of hydrogen bonding and plasticizer molar volume

The effect of sugars and sugar replacers (i.e. plasticizers) on the gelatinization and pasting behaviour of wheat starch was studied. The intrinsic properties of the plasticizers, i.e. the molar volume density of effective hydroxyl groups NOH,s/vs, and the volumetric density of hydrogen bonds in the sugar solutions treated as a single solvent, i.e. Φw,eff, were proposed as factors controlling swelling (i.e. pasting) and gelatinization behaviour. Different classes of plasticizers were used including sugars, polyols, amino acids, soluble fibres such as oligofructoses, and mixtures thereof. The onset, peak and end temperature of starch gelatinization obtained by differential scanning calorimetry could be well described by Φw,eff for all solutions, following predictions from an adapted Flory-Huggins model for polymer melting. The multiple transitions involved in starch gelatinization could be well related to different ranges of Φw,eff following a side chain liquid crystalline model for starch. Deviations from the model predictions were observed mainly for Tonset in conditions of intermediate and excess solvent with high sugar concentrations (50% w/w). In such conditions phase separation likely occurs, increasing the effective starch concentration and consequently gelatinization temperatures. Pasting behaviour related to swelling, i.e. peak viscosity, was found to be a sigmoidal Fermi function of NOH,s/vs of the plasticizers. Plasticizers with high NOH,s/vs enhanced swelling compared to water while those with low NOH,s/vs had an inhibition effect. Overall, a comprehensive mechanism of starch plasticization, swelling and melting is proposed. Swelling associated with solvent ingress and helix-helix dissociation is affected by kinetic factors related to size and viscosity of the plasticizers (both described by NOH,s/vs) and by thermodynamic factors related to sugar partitioning and H-bonding ability (both related to Φw,eff). Melting of crystalline domains associated to helix-coil transition is controlled by thermodynamics, based on solvent H-bonding ability Φw,eff

Amino acids, polyols and soluble fibres as sugar replacers in bakery applications : Egg white proteins denaturation controlled by hydrogen bond density of solutions

In this paper we demonstrate that the denaturation behavior, i.e. Tden, of egg white proteins in sugar and sugar replacer solutions is explained by the volumetric density of hydrogen bonds in the solutions, i.e. nOH,eff. The validity of the presented approach is demonstrated using 18 solutions comprising single compounds as well as 7 ternary/quaternary mixtures. Different classes of plasticizers are used at various concentrations and at various ratio with proteins. Sweet amino acids such as L-proline and glycine are included as novel alternatives to polyols. The experimental data are modelled with the Flory-Huggins (FH) theory for biopolymer melting. For such purpose, solutions are treated as a single solvent, which is described by the effective volume fraction of the solvent Φw,eff (⁓nOH,eff). Overall, the FH model can well describe the denaturation behavior of egg white proteins in sugar and sugar replacer solutions up to 30% concentration. Deviations from the model become particularly evident at high sugar concentrations (i.e. 50%), which relate to conditions of phase separation in a protein-rich and sugar-rich domain. In such conditions, Φw,eff does not reflect the composition of the solvent around the proteins. An elevation in Tden is observed due to a reduction in hydrogen bond density in the protein-rich domain. The results indicate that phase separation is driven by both the concentration and the molar volume density of effective hydroxyl groups NOH,s/vs of the plasticizers or plasticizer mixtures. Finally, the proposed approach can predict key phase-transitions which result in protein network formation in pound cake baking

The impact of heating and freeze or spray drying on the interface and foam stabilising properties of pea protein extracts : Explained by aggregation and protein composition

The processing of plant protein extracts can affect the protein structure, leading to altered functional properties. In this work, we evaluated the impact of two common processes in pea protein extraction: heating and drying. Non-heated and heated (5 min at 95 °C) samples were compared, which were either freeze- or spray-dried. These processes led to alterations of the proteins, and resulted in changes of their interface and foam-stabilising properties. A mild protein extraction method was used to preserve the native protein structure during aqueous extraction, allowing the extraction of both albumin and globulin proteins. Spray-drying of these fractions led to higher surface hydrophobicity, which resulted in increased surface activity and stiffer interfacial layers at pH 3.8 and 7.0. The heating step induced aggregation of the globulins, while albumins remained soluble. Here, we demonstrated that the albumins had a dominant effect on the interfacial (rheology and ellipsometry) and foaming properties after heating, as the globulin aggregates were too large for effective interface stabilisation. A similar mechanism was also shown at pH 3.8, where the globulins precipitated, as the pH was close to their pI, while albumins remained soluble. Again, the albumins dictated the interfacial properties, leading to highly stable foams after removing the insoluble globulins. We have shown marginal differences in protein functionality after freeze- or spray-drying. More importantly, the changes in soluble protein composition dictate the protein functionality after heating or pH shifts

Plant protein aggregates induced by extraction and fractionation processes: Impact on techno-functional properties

Currently, plant proteins are fractionated to ingredients with high purities, but an often ignored point is the impact of the extraction and fractionation process on protein functionality. To allow a fair and effective comparison, it is key to understand the changes in protein's aggregated state occurring in the extracted ingredients during processing. We review conventional and upcoming plant protein extraction and fractionation processes (on pulses and oilseeds) and focus on how the processing history influences the macroscopic functional properties of the proteins. To establish this link, we dive into seed morphology and give an overview of the plant seed composition. In addition, we explain the essence of each process step and how it impacts the protein's aggregated state. The latter is linked to the macroscopic functionality (foaming, emulsification, and gelation). We identified three major protein structure-changing steps in the conventional protein extraction process: defatting, alkaline extraction, and isoelectric point precipitation. These steps lead to large, insoluble aggregated structures, which strongly impacts the protein macroscopic functionality. Milder extraction methods reduce these alterations, but a potential consequence is the presence of non-proteinaceous components, which could give challenges in sensory and nutritional aspects and affect the techno-functional properties of the ingredient. The take-home-message is that we need to consider the process-induced change of the protein aggregated structures, which are likely to dominate the functionality over the protein's molecular parameters.Multi Phase System

Genome-wide association identifies nine common variants associated with fasting proinsulin levels and provides new insights into the pathophysiology of type 2 diabetes

OBJECTIVE - Proinsulin is a precursor of mature insulin and C-peptide. Higher circulating proinsulin levels are associated with impaired b-cell function, raised glucose levels, insulin resistance, and type 2 diabetes (T2D). Studies of the insulin processing pathway could provide new insights about T2D pathophysiology. RESEARCH DESIGN AND METHODS - We have conducted a meta-analysis of genome-wide association tests of ;2.5 million genotyped or imputed single nucleotide polymorphisms (SNPs) and fasting proinsulin levels in 10,701 nondiabetic adults of European ancestry, with follow-up of 23 loci in up to 16,378 individuals, using additive genetic models adjusted for age, sex, fasting insulin, and study-specific covariates. RESULTS - Nine SNPs at eight loci were associated with proinsulin levels (P < 5 × 10-8). Two loci (LARP6 and SGSM2) have not been previously related to metabolic traits, one (MADD) has been associated with fasting glucose, one (PCSK1) has been implicated in obesity, and four (TCF7L2, SLC30A8, VPS13C/ C2CD4A/B, and ARAP1, formerly CENTD2) increase T2D risk. The proinsulin-raising allele of ARAP1 was associated with a lower fasting glucose (P = 1.7 3 10-4), improved b-cell function (P = 1.1 × 10-5), and lower risk of T2D (odds ratio 0.88; P = 7.8 × 10-6). Notably, PCSK1 encodes the protein prohormone convertase 1/3, the first enzyme in the insulin processing pathway. A genotype score composed of the nine proinsulin-raising alleles was not associated with coronary disease in two large case-control datasets. CONCLUSIONS - We have identified nine genetic variants associated with fasting proinsulin. Our findings illuminate the biology underlying glucose homeostasis and T2D development in humans and argue against a direct role of proinsulin in coronary artery disease pathogenesis