Molecular Size Distribution Research Articles

High-pressure pasting performance and multilevel structures of short-term microwave-treated high-amylose maize starch

Microwave treatment is an environmentally friendly method for modification of high-amylose maize starch (HAMS). Here, the effects of short-time (≤120 s) microwave treatment on the structure and pasting of two types of HAMSs, Gelose 50 (HAMSI) and Gelose 80 (HAMSII), with apparent amylose content (AAC) of 45 % and 58 %, respectively, was studied using a multiscale approach including X-ray scattering, surface structures, particle size distribution, molecular size distributions and high temperature/pressure Rapid Visco Analysis (RVA)-4800 pasting. As compared to starch with no amylose (waxy maize starch, WMS) and 25 % amylose content (normal maize starch, NMS), HAMSI underwent similar structural and pasting changes as WMS and NMS upon microwave treatment, and it might primarily be attributed to the amylopectin fraction that was affected by cleavage of the connector chains between double helices and backbone chains, which decreased the crystallinity and thickness of the crystalline lamellae. However, the multi-scale structure of HAMSII was almost unaffected by this treatment. The pasting properties of fully gelatinized HAMSI starch showed a decrease in RVA-4800 peak and final viscosities after microwave treatment. In contrast, for HAMSII starch, the microwave treatment led to an increase in these viscosities. The combined results highlight the influence of varying AAC on the effects of microwave-mediated modification, leading to diverse alterations in the structure and functionality of starches.

Effect of sheeting stress and heating on the molecular chain structure, size, and conformation of gluten proteins during noodle processing

In this paper, the changes in molecular structure, size distribution, and conformation of gluten induced by the mechanical stress during sheeting and the heating effect during cooking of noodles were investigated by atomic force microscopy (AFM), X-ray scattering (SAXS), and size-exclusion chromatography multi-angle laser light scattering (SEC-MALLS). AFM results showed that the height and width of gluten molecular chains were decreased after calendering and increased post-cooking. Calendering reduced the molecular size and compacted the gluten network (increased Dm). The SDS extractable gluten components showed a quasi-spherical chain conformation but gradually changed to a random coil conformation due to heating. According to SEC-MALLS profiles, calendering and appropriate heating (4 min) promoted the homogeneity of molecular mass of glutenin polymer. The mechanical depolymerization and the heat-promoted polymerization of gluten could be due to the breakage and formation of disulfide bonds and the interconversion of sulfhydryl groups.

Deagglomeration of Asphalt Binder Using Kraft Lignin: A Sustainable Valorization of Waste from the Pulping Industry

This study assessed the potential of lignin, derived from black liquor, for deagglomerating asphaltene fractions. Chemical and rheological tests were employed to evaluate the efficacy of the lignin additives. Gas chromatography-mass spectrometry (GC–MS) analyzed the chemical components of lignin (L1) isolated with sulfuric acid and lignin (L2) isolated with hydrochloric acid. Gel permeation chromatography (GPC) examined changes in molecular size distribution and deagglomeration effectiveness of the lignin additives. Fourier transform infrared spectroscopy (FTIR) assessed the chemical functional groups of asphalt, while the rheological performance of asphalt was evaluated through the crossover modulus (|G*c|) and frequency (ωc) analysis. L1, possessing high phenolic content and low pH, demonstrated deagglomeration effectiveness, achieving a 6% reduction in weight-average molecular weight, 3% in polydispersity index (PDI), and 16% in asphaltene fraction. Both L1 and L2 decreased the combination aging index of aged asphalt by 28% and 7%, respectively. Moreover, L1 and L2 enhanced the |G*c| of virgin and aged asphalt, consistent with the reduction in the PDI value. These findings suggest that lignin additives possess the potential to deagglomerate asphaltene fractions. The study highlights the potential of repurposing harmful substances from black liquor, traditionally incinerated to reclaim certain chemicals in pulp mills, for use in the pavement industry, promoting sustainability and resource conservation.

Stability of lyophilized Meningococcal A conjugate vaccine, (MenAfriVac™) at elevated temperatures to support controlled temperature chain (CTC) claim

Meningococcal A Conjugate Vaccine (MenAfriVac) is the world’s first Monovalent Conjugate Vaccine against Neisseria Meningitidis serogroup A which has obtained Controlled Temperature Chain (CTC) label claim of “stable upto 40°C for 4 days prior to reconstitution” developed by Serum Institute of India Pvt. Ltd. Pune, India and the vaccine was granted permission from World health Organization. This paper elucidates and talks about the layout of various studies performed to characterize the product to declare as CTC at the time when the knowledge and mechanism to describe CTC was not fully known which in term helped to design the CTC guidelines.Product stability was assessed using clinical, consistency and regular lots released by NRA. The critical stability indicating parameters like free polysaccharide, molecular size distribution along with Potency and safety tests were carried out to support the product stability making sure it also qualifies for Vaccine Vial Monitor label claim of VVM30. An additional in use stability (reconstitution) was also performed. All studies indicated that the product remains stable at real time as well as elevated temperatures and well within the specifications approved by NRA and formed the strong basis for CTC claim which is now recommended by WHO.

Control of morphology of covalent organic framework-5 for chemiresistive low-temperature ammonia sensors

Covalent organic frameworks (COFs) have attracted much attention due to their unique structures and properties. However, the morphology regulation of COFs has always been a challenge, and the application field of COFs need to be further explored. Herein, three different regular morphologies of COF-5 crystals, including nanoparticles, nanorods and nanosheets, are firstly regulated by adjusting the reaction parameters under the convenient and mild conditions. The molecular configuration and pore size distribution of the as-prepared COF-5 crystals were revealed by DFT calculation and experimental tests. The ammonia sensing test proves that all three COF-5 crystals with different morphologies have good response at room temperature, and COF-5 nanosheets with maximum specific surface area possess the lowest detection limit of 600 ppb towards ammonia gas. Furthermore, COF-5 crystals-based gas sensors have excellent reversibility, gas selectivity and long-term stability. Gas sensing mechanism illustrates that abundant boronate esters with Lewis acidity of COF-5 crystals act as the active site to realize the ammonia sensitive detection.

Characterization of physical and chemical antioxidative performance of asphalt using Bio-additive from paper pulp black liquor

The main objective of this research is to investigate the effectiveness of lignin bio-additives derived from black liquor paper pulp as asphalt antioxidants. Two lignin bio-additives, H-L and S-L, were developed by acidifying black liquor with hydrochloric and sulfuric acid. The laboratory aging procedures used in this study included the Rolling Thin Film Oven and the Ultraviolet Chamber methods. The crossover modulus (|G*c|) and linear amplitude sweep (LAS) were measured using a Dynamic Shear Rheometer (DSR). Gel Permeation Chromatography (GPC) was also used to characterize the molecular size distribution of the asphalt binder. The combination of carbonyl and sulfoxide aging indices was measured using Fourier Transform Infrared (FTIR) spectroscopy. The S-L modified binder (S-LMB) demonstrated superior aging resistance compared to both the control binder (CB) and the H-L modified binder (H-LMB) by exhibiting the lowest reduction in |G*c|. Furthermore, the LAS test results showed that S-LMB provided the best resistance to aging due to the lowest decrease in fatigue life with age conditioning, followed by CB and H-LMB, with rates of 11%, 13%, and 16%, respectively. The GPC results also confirmed the efficacy of the S-L bio-additive as an antioxidant, exhibiting the lowest increment in asphaltene proportion attributed to age conditioning. The FTIR measurements successfully captured the antioxidant capability of both H-L and S-L bio-additives, with S-L performing better than H-L. Overall, the results suggest that S-L demonstrates superior antioxidant performance compared to H-L.

A collaborative study to establish the second national standard for hepatitis B immunoglobulin in Korea

This study aimed to establish a second national standard for hepatitis B immunoglobulin (HBIG) that can be used for potency assays of hepatitis B and normal immunoglobulin. The candidate material was manufactured using a process approved as Good Manufacturing Practice. The freeze-dried candidate preparation was tested for physicochemical and biological properties, including pH, residual moisture, molecular size distribution, and potency. A collaborative study was performed involving four laboratories, including the National Institute of Food and Drug Safety Evaluation, as an official national control laboratory in Korea and manufacturers. The potency was calibrated against the second international standard for HBIG using two enzyme immunoassays: enzyme-linked immunosorbent assay and electrochemiluminescence immunoassay. Results from 240 assays were obtained from four laboratories, and combined potency estimates were obtained by calculating the geometric means. Intra- and inter-laboratory variability showed acceptable geometric coefficients of variation of 1.3–6.0 and 3.2–3.6%, respectively. The candidate preparation showed satisfactory stability in accelerated thermal degradation and real-time stability tests. Based on these results, the potency value of 105 IU/vial was assigned (95% confidence intervals: 100.0–109.2 IU/vial), and it was deemed suitable to serve as the Korean national standard for HBIG.

Preparation and optimization of WPU dispersion from polyether/polyester polyols for film and coating applications

BackgroundCastor oil and polytetramethylene ether glycol (PTMG) are used as polyester and polyether polyols. The waterborne polyurethane (WPU) resin is synthesized from polyether/polyester polyols following a ketone and catalyst-free pre-polymerization process. MethodsWPU resins are prepared from PTMG/castor oil with various hydroxyl molar ratios, such as 1/0, 3/1, 1/1, 1/3, and 0/1. Significant findingsThe results indicate that the WPU dispersions has a long shelf-life, high colloidal stability, and narrow distribution of molecular size. The addition of castor oil can increase the proportion of the cross-linking density, hard segments and hydrogen bonds of the WPU molecular chain. The addition of PTMG/castor oil increases from the molar ratio 1/0 to 1/1, the tensile strength of WPU film increases from 17.1 MPa to 25.6 MPa; the T5% increases from 250°C to 262°C; the water swelling ratio at 24 h decreases from 33.2 g/g to 19.4 g/g. The results indicate the using PTMG/castor oil can improve the mechanical strength, water resistance, and thermal stability of WPU film. The WPU could be applied to wood coatings with high properties. This study provides a cleaner process for optimizing the performance of WPU resin, which can replace conventional ketone- and organotin-based films and coatings.

Modulating the Mixing Gibbs Free Energy to Enhance Solid–Liquid Phase Separation for High‐Performance Organic Solar Cells

AbstractOrganic solar cells (OSC) feature a hierarchical structure with the electron donor/acceptor layer sandwiched by anode and cathode, which raises the importance of controlling the molecular crystal orientation, domain size, and vertical distribution to facilitate the charge collection at electrodes. However, the similar conjugated backbone of donor/acceptor material and fast film‐formation kinetics have led to spinodal‐decomposition‐orientated phase separation that result in the film presenting an intimately mixed morphology and random molecular orientation. To solve the issue, the mixing Gibbs free energy‐triggered solid–liquid phase separation during the film formation process is enhanced by solidifying one component and solvating the other based on a liquid additive. Following the liquid evaporation process, a favorable vertical distribution is obtained. Meanwhile, the prolonged solvation process enlarges the domain size and assists the molecules to diffuse and orient properly, enabling better exciton/charge dynamics during the power conversion processes. As a result, the fabricated devices exhibit a fill factor over 80% and an efficiency of 18.72%, which is one of the top efficiencies for binary OSCs. Insights and a methodology is provided here to manipulate the organic donor/acceptor phase separation in terms of mixing Gibbs free energy.

Molecular Composition, Seasonal Variation, and Size Distribution of n-Alkanes, PAHs, and Saccharides in a Medium-Sized City of Guanzhong Plain, Northwest China: Evaluation of Control Measures Executed in the Past Decade.

Baoji is a medium-sized city in the Guanzhong Plain of northwest China. The compositions of three important organic groups, namely n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and saccharides in atmospheric aerosol with different aerodynamic diameters in power were determined. Both seasonal and daily trends of the target organic chemical groups were demonstrated. The concentration levels of total quantified n-alkanes and saccharides in total suspended particles (TSP) in winter were 541 ± 39 and 651 ± 74 ng·m-3, respectively, much higher than those of the other three seasons. A high total quantified PAHs concentration level of 59.6 ± 6.4 ng·m-3 was also seen in wintertime. n-Alkanes showed a bimodal percent distribution in spring, autumn, and winter. Two peaks were found with the particle sizes of 0.7 μm < Dp < 2.1 μm and 3.3 μm < Dp < 4.7 μm, respectively. In summer, a unimodal was seen with a peak of 4.7 μm < Dp < 5.8 μm. Dehydrated saccharides and PAHs present a unimodal size distribution peaking at the aerodynamic diameters of 0.7 µm < Dp < 2.1 µm. In contrast to glucose and fructose, they mainly exist in the coarse mode particles and have the highest concentrations at aerodynamic diameters of 4.7 µm < Dp < 9.0 µm. The geometric mean diameters (GMD) of n-alkanes and saccharides of the fine particles in winter were higher than in the other seasons. Compared with the data in 2008, the fossil fuel-derived n-alkanes and PAHs in winter decreased by nearly an order of magnitude in 2017. Both the carbon preference index (CPI) of n-alkanes and the diagnostic ratios of PAHs suggest that coal combustion and vehicle exhaust were the major pollution sources of the organic groups in the two decades. It should be noted that the contribution of traffic emissions greatly increased from 2008 to 2017, consistently with a large raise of registered vehicles in Baoji city. The overall results confirm that the control measures conducted by the local government in the recent decade mitigated the air pollution in this city.

Molecular mechanism of core planar cell polarity complex function elucidated with single-molecule methods.

The planar cell polarity (PCP) signaling pathway polarizes epithelial cells along an axis parallel to the epithelial sheet in order to generate front-back asymmetry at the tissue level. Failures in PCP signaling underlie developmental defects and diseases such as neural tube and heart defects, deafness and contribute to cancer. Six core PCP proteins assemble into large, asymmetric complexes at cell-cell junctions, with Vang and Prickle recruited to one side of the cell-cell junction while Frizzled and Dishevelled are recruited to the other. How this asymmetric assembly process occurs is not known. Genetic evidence suggests that the process of symmetry breaking at PCP clusters is coupled to cluster formation. To test how this occurs, we developed a method to count the number of each of the six core proteins in individual PCP complexes. Specifically, by analyzing bleaching traces obtained with a high frame rate in live Drosophila wing cells imaged using total internal reflection microscopy, we quantify the intensity of single fluorophores in each complex and thereby calculate the molecular number in the corresponding PCP complex. Using this approach, we find that the molecular size distribution of PCP complexes follows an exponential function, indicating a single underlying growth mechanism. We report that specifically, the number of Vang molecules in PCP complexes increases from 15 hours after puparium formation until reaching a steady state around 28 hours. Besides, we measure the asymmetry as a function of cluster size and test the dependence of the observed relationship by introducing gain and loss of function mutations that perturb cluster assembly. In conclusion, our findings provide a detailed understanding of how the PCP mechanism generates stable polarization during embryonic development.

Tracking swelling of lignocellulosic biomass during acid hydrolysis by using size-exclusion chromatography to evaluate molecular size

The two-step concentrated acid hydrolysis process is very efficient in producing fermentable sugars from lignocellulosic biomass, but acid recovery is important for the economic viability of the process. During membrane or precipitation-based separation of the acid catalyst from sugar oligomers and monomers, the molecular sizes of the sugar molecules will influence sugar entrainment with the acid. This study applied size-exclusion chromatography to determine the molecular size distribution of the water-soluble sugar molecules generated during the concentrated acid swelling of lignocellulosic biomass. Two indicators were calculated from the chromatograms to describe the distribution: the relative area of the chromatogram and the ratio of small molecules versus large molecules. Measurable changes in these indicators could be related to changes in the operating conditions of the swelling step, and to downstream hydrolysis performance. This approach provided important information about the swelling progression that will be useful for optimizing the hydrolysis process, and especially when implementing an acid recovery step.

Investigations on the rheological and swelling-degradation behavior of crumb rubber within the bituminous matrix

This paper focuses on the rheological and swelling-degradation behavior of crumb rubber within the bituminous matrix. Three different penetration-grade asphalts were modified by crumb rubber in a four-paddle mixer at various curing times and treatment temperatures. Rotational viscosity, dynamic shear rheometer, solubility and gel permeation chromatography tests were conducted to evaluate the viscosity, rheological property, crumb rubber solubility and molecular weight distribution of the rubber-modified asphalts, respectively. Moreover, the microstructure of the rubber-modified asphalts was characterized by fluorescence microscopy and Fourier transform infrared spectroscopy tests. The results reveal that the viscosity and complex modulus of the rubber-modified asphalts decrease and the infiltrating ability of crumb rubber within the bituminous matrix increases with increasing treatment temperature (or curing time). However, serious degradation of crumb rubber and asphalt ageing happen with the increased treatment temperature or prolonged curing time, which causes a noticeable increase in viscosity and stiffness. The increase in asphaltenes content within the bituminous matrix causes an enhancement in viscosity and complex modulus, and releases of the large (or medium) molecules, improving rutting deformation resistance. There is no obvious difference in small molecules, illustrating that asphalt type does not affect the distribution of small molecular size. When the treatment temperature increases from 200 °C to 220 °C, the curing time required to achieve 60 % solubility of crumb rubber in asphalt X is from 25 h to 15 h, which indicates that the higher the treatment temperature, the shorter the curing time required to reach the maximum solubility. Moreover, the swollen crumb rubber molecules are degraded into some small molecule substances dissolving into asphalt binder for modification. It makes the adsorption peaks of typical function groups increase significantly. The outputs from this study can provide the guidance for the selection of preparation conditions and asphalt binders that fabricate the rubber-modified asphalt with desired properties.

Preliminary characteristics of non-starch polysaccharide from chayote (Sechium edule)

Chayote is rich in non-starch polysaccharides. The physicochemical properties of non-starch polysaccharide from chayote were not study extensively. In the present research, non-starch polysaccharide of chayote (CP-CHE) extracted by conventional heating extraction method was obtained, and the preliminary physicochemical and functional properties of CP-CHE had been carried out. The results indicated that the CP-CHE was rich in galactan, glucoses and galacturonic acid. Also, CP-CHE had the negatively charged, a wide distribution of molecular weight and particle size. Additionally, CP-CHE solutions had shear thinned fluid property when the concentrations between 1% to 4%. The results of this study would be beneficial to the application of CP-CHE in food and improve the economic value of chayote.

Use of Tuna Visceral Pepsin in Combination with Trypsin as Digestion Aid: Enhanced Protein Hydrolysis and Bioavailability.

Freeze-dried tuna pepsin powder (TPP) was prepared using maltodextrin (10%) and trehalose (5%), while trypsin-loaded beads (TLB) with 5% glycerol were obtained via chitosan/alginate ionotropic gelation. The storage stability of TPP and TLB and their proteolytic activity toward red kidney bean protein (RKB), threadfin bream surimi (TBS) and egg white protein (EWP) in varying simulated in vitro gastrointestinal (GI) tract conditions were studied. The intestinal transepithelial transportation of generated peptides was also carried out through Caco-2 cell monolayers after the cytotoxicity test. Enzyme activity was dropped when TPP and TLB in blister packs were kept for 10 weeks of storage at room (28 °C) and refrigerated (4 °C) temperatures. TPP and TLB at a level of 50% (w/w of proteins) effectively hydrolyzed RKB, TBS and EWP in a simulated in vitro GI tract, as indicated by marked protein degradation and increased degree of hydrolysis. Some peptides generated after GI digestion could transport through Caco-2 cell monolayers. Those peptides had different molecular size distribution and antioxidant activities. The highest antioxidant activity was observed for RKB hydrolysate after passing through the Caco-2 cell monolayer. Therefore, TPP and TLB from skipjack tuna viscera could potentially be used for enzyme supplementation to help digest food proteins. Food-derived bioactive peptides generated after GI digestion could assist in improving human health due to their antioxidant activity.

Molecular Dynamics and Chain Length of Edible Oil Using Low-Field Nuclear Magnetic Resonance

Nuclear magnetic resonance (NMR) techniques are widely used to identify pure substances and probe protein dynamics. Edible oil is a complex mixture composed of hydrocarbons, which have a wide range of molecular size distribution. In this research, low-field NMR (LF-NMR) relaxation characteristic data from various sample oils were analyzed. We also suggest a new method for predicting the size of edible oil molecules using LF-NMR relaxation time. According to the relative molecular mass, the carbon chain length and the transverse relaxation time of different sample oils, combined with oil viscosity and other factors, the relationship between carbon chain length and transverse relaxation time rate was analyzed. Various oils and fats in the mixed fluid were displayed, reflecting the composition information of different oils. We further studied the correlation between the rotation correlation time and the molecular information of oil molecules. The molecular composition of the resulting fluid determines its properties, such as viscosity and phase behavior. The results show that low-field NMR can obtain information on the composition, macromolecular aggregation and molecular dynamics of complex fluids. The measurements of grease in the free-fluid state show that the relaxation time can reflect the intrinsic properties of the fluid. It is shown that the composition characteristics and states of complex fluids can be measured using low-field nuclear magnetic resonance.

The Effects of Starch Molecular Fine Structure on Thermal and Digestion Properties of Rice Starch.

Whole white rice is a major staple food for human consumption, with its starch digestion rate and location in the gastrointestinal tract having a critical role for human health. Starch has a multi-scale structure, which undergoes order-disorder transitions during rice cooking, and this structure is a major determinant of its digestibility. The length distributions of amylose and amylopectin chains are important determinants of rice starch gelatinization properties. Starch chain-length and molecular-size distributions are important determinants of nucleation and crystal growth rates, as well as of intra- and intermolecular interactions during retrogradation. A number of first-order kinetics models have been developed to fit starch digestograms, producing new information on the structural basis for starch digestive characteristics of cooked whole rice. Different starch digestible fractions with distinct digestion patterns have been found for the digestion of rice starch in fully gelatinized and retrograded states, the digestion kinetics of which are largely determined by starch fine molecular structures. Current insights and future directions to better understand digestibility of starch in whole cooked rice are summarized, pointing to ways of developing whole rice into a healthier food by way of having slower starch digestibility.

Isolation, Characterization, and Compositional Analysis of Polysaccharides from Pinot Noir Wines: An Exploratory Study

It has been reported that polysaccharides in wine can interact with tannins and other wine components and modify the sensory properties of the wine. Unfortunately, the contribution of polysaccharides to wine quality is poorly understood, mainly due to their complicated structure and varied composition. In addition, the composition and molecular structure of polysaccharides in different wines can vary greatly. In this study, the polysaccharides were isolated from pinot noir wine, then separated into high-molecular-weight (PNWP-H) and low-molecular-weight (PNWP-L) fractions using membrane-based ultrafiltration. Each polysaccharide fraction was further studied using size exclusion chromatography, UV-Vis, FT-IR, matrix-assisted laser desorption/ionization-high-resolution mass spectrometry, and gas chromatography-mass spectrometry (GC-MS). The results showed that PNWP-L and PNWP-H had different chemical properties and compositions. The FT-IR analysis showed that PNWPs were acidic polysaccharides with α- and β-type glycosidic linkages. PNWP-L and PNWP-H had different α- and β-type glycosidic linkage structures. FT-IR showed stronger antisymmetric and symmetric stretching vibrations of carboxylate anions of uronic acids in PNWP-L, suggesting more uronic acid in PNWP-L. The size exclusion chromatography results showed that over 72% of the PNWP-H fraction had molecular sizes from 25 kDa to 670 kDa. Only a small percentage of smaller molecular polysaccharides was found in the PNWP-H fraction. In comparison, all of the polysaccharides in the PNWP-L fraction were below 25 KDa, with a majority distributed approximately 6 kDa (95.1%). GC-MS sugar composition analysis showed that PNWP-L was mainly composed of galacturonic acid, rhamnose, galactose, and arabinose, while PNWP-H was mainly composed of mannose, arabinose, and galactose. The molecular size distribution and sugar composition analysis suggested that the PNWP-L primarily consisted of rhamnogalacturonans and polysaccharides rich in arabinose and galactose (PRAG). In comparison, PNWP-H were mostly mannoproteins and polysaccharides rich in arabinose and galactose (PRAG). Further research is needed to understand the impacts of these fractions on wine organoleptic properties.

Can Enzymatic Treatment of Sugar Beet Pectins Reduce Coalescence Effects in High-Pressure Processes?

While sugar beet pectins (SBPs) are well known for effectively stabilizing fine oil droplets in low-fat food and beverages, e.g., low-fat dressings and soft drinks, it often fails in products of higher oil contents. The aim of this study was to improve the emulsifying properties of SBPs and, consequently, their ability to reduce coalescence during high pressure homogenization of products with increased oil content. Therefore, the molecular size of SBPs was reduced by partial cleavage of the homogalacturonan backbone using the enzymes exo- and endo-polygalacturonanase and varying incubation times. The sizes of SBPs were compared based on the molecular size distribution and hydrodynamic diameter. In addition, to obtain information on the interfacial activity and adsorption rate of SBPs, the dynamic interfacial tension was measured by drop profile analysis tensiometry. The (non)modified SBPs were used as emulsifying agents in 30 wt% mct oil–water emulsions stabilized with 0.5 wt% SBP at pH 3, prepared by high-pressure homogenization (400–1000 bar). By analyzing the droplet size distributions, conclusions could be drawn about the coalescence that occurred after droplet breakup. It could be shown that SBPs modified by exo-polygalacturonanase stabilized the oil–water interface more rapidly, resulting in less coalescence and the smallest oil droplets. In contrast, SBPs modified with endo-polygalacturonanase resulted in poorer emulsification properties, and thus larger oil droplets with increasing incubation time. The differences could be attributed to the different cleavage pattern of the enzymes used. The results suggest that a minimum molecular size is required for the stabilization of fine oil droplets with SBPs as emulsifiers.

Kinetic modelling of total organic carbon degradation in dairy wastewater

ABSTRACT Several treatment strategies have been proposed to minimize the environmental impact of dairy wastewaters. However, their complex and variable composition makes it difficult to predict the degradation kinetics of organic compounds. In this study, we used a mathematical approach to describe the kinetics of total organic carbon degradation in real dairy wastewater by photo-Fenton oxidation. The reactions were conducted under different ultraviolet light intensities, pH, temperature and Fenton reagent concentrations, obtaining a maximum TOC removal of 90.84%. The kinetic model was developed based on well-established photo-Fenton reactions. The present approach considers that account that small and large molecules of unknown contaminants are present in the effluent, and the smaller molecules are consumed first. The specific degradation rate (kd ) was considered as an exponential function of total organic carbon conversion, comprising this effect of molecular size distribution on the treatment process. Fitting of experimental data to model predictions provided mean R 2 values of 0.843–0.953.