Seasonal variations in the functional performance of industrial low-moisture part-skim mozzarella over a 1.5-year period.

Seventy-five blocks of low-moisture part-skim mozzarella cheese were procured from an industrial cheese plant, and the relationships between the physicochemical and functional properties were evaluated during refrigerated storage. In total, cheeses were obtained from 1 cheese vat on 7 different production dates, at 2 to 4 monthly intervals, over a 1.5-yr period; all cheeses were made using a standard recipe. The cheeses were held at 4°C for 0, 1, 2, 4, 8, 16, or 32 d and assayed for composition, primary proteolysis, serum distribution, texture profile analysis, heat-induced changes in viscoelastic behavior, cheese extensibility, and melt characteristics. The results demonstrated a substantial increase in serum uptake by the calcium-phosphate para-casein matrix between 1 and 16 d of storage with a concomitant improvement in the functional performance of the cheese. Extending the storage time to 32 d resulted in further changes in the functional quality, concurrent with ongoing increases in protein hydration and primary proteolysis. Differences in the measured characteristics between the cheeses obtained on different sampling occasions were evident. Principal component analysis separated the cheeses based on their variance in functional performance, which was found to be correlated mainly with the calcium content of the cheese. The results indicate that the manufacturing process should be tightly controlled to minimize variation in calcium content and enhance the quality consistency of the cheese.

Promising perspectives for ruminal protection of polyunsaturated fatty acids through polyphenol-oxidase-mediated crosslinking of interfacial protein in emulsions.

Previously, polyunsaturated fatty acids (PUFA) from linseed oil were effectively protected (>80%) against biohydrogenation through polyphenol-oxidase-mediated protein crosslinking of an emulsion, prepared with polyphenol oxidase (PPO) extract from potato tuber peelings. However, until now, emulsions of only 2 wt% oil have been successfully protected, which implies serious limitations both from a research perspective (e.g. in vivo trials) as well as for further upscaling toward practical applications. Therefore, the aim of this study was to increase the oil/PPO ratio. In the original protocol, the PPO extract served both an emulsifying function as well as a crosslinking function. Here, it was first evaluated whether alternative protein sources could replace the emulsifying function of the PPO extract, with addition of PPO extract and 4-methylcatechol (4MC) to induce crosslinking after emulsion preparation. This approach was then further used to evaluate protection of emulsions with higher oil content. Five candidate emulsifiers (soy glycinin, gelatin, whey protein isolate (WPI), bovine serum albumin and sodium caseinate) were used to prepare 10 wt% oil emulsions, which were diluted five times (w/w) with PPO extract (experiment 1). As a positive control, 2 wt% oil emulsions were prepared directly with PPO extract according to the original protocol. Further, emulsions of 2, 4, 6, 8 and 10 wt% oil were prepared, with 80 wt% PPO extract (experiment 2), or with 90, 80, 70, 60 and 50 wt% PPO extract, respectively (experiment 3) starting from WPI-stabilized emulsions. Enzymatic crosslinking was induced by 24-h incubation with 4MC. Ruminal protection efficiency was evaluated by 24-h in vitro batch simulation of the rumen metabolism. In experiment 1, protection efficiencies were equal or higher than the control (85.5% to 92.5% v. 81.3%). In both experiments 2 and 3, high protection efficiencies (>80%) were achieved, except for emulsions containing 10 wt% oil emulsions (<50% protection), which showed oiling-off after enzymatic crosslinking. This study demonstrated that alternative emulsifier proteins can be used in combination with PPO extract to protect emulsified PUFA-rich oils against ruminal biohydrogenation. By applying the new protocol, 6.5 times less PPO extract was required.

Protection of polyunsaturated oils against ruminal biohydrogenation and oxidation during storage using a polyphenol oxidase containing extract from red clover.

Polyunsaturated fatty acid (PUFA) are to a large extent subject to biohydrogenation in a ruminal environment, which results to the healthy value of these PUFA being lost upon dietary addition to ruminants. PUFA are also prone to lipid oxidation upon storage. Therefore, it was tested whether emulsions could be protected against in vitro ruminal biohydrogenation and oxidation during storage by using protein extracts rich in polyphenol oxidase, an enzyme responsible for browning of plant tissues. PUFA rich emulsions were made with a protein extract from red clover (Trifolium pratense L.) before adding a synthetic diphenol (4-methylcatechol) to induce protection. Results after in vitro incubation confirmed the hypothesis and indicated the potential to prevent PUFA in linseed or fish oil from ruminal biohydrogenation and oxidation during storage through addition of 4-methylcatechol to the emulsions. Protection depended on the amount of oil present and protein concentrations in the emulsions. Protection efficiency increased with increasing the amounts of diphenol present in the emulsion per unit interfacial surface area. It is suggested that protection is caused by an effective encapsulation by cross-linking of the protein layer at the emulsion interface. For the first time, a method is described to protect PUFA using an enzyme abundantly available in nature, polyphenol oxidase, in combination with 4-methylcatechol.

Comparison of emulsifying properties of milk fat globule membrane materials isolated from different dairy by-products.

Emulsifying properties of milk fat globule membrane (MFGM) materials isolated from reconstituted buttermilk (BM; i.e., BM-MFGM) and BM whey (i.e., whey-MFGM), individually or in mixtures with BM powder (BMP) were compared with those of a commercial dairy ingredient (Lacprodan PL-20; Arla Foods Ingredients Group P/S, Viby, Denmark), a material rich in milk polar lipids and proteins. The particle size distribution, viscosity, interfacial protein, and polar lipids load of oil-in-water emulsions prepared using soybean oil were examined. Pronounced droplet aggregation was observed with emulsions stabilized with whey-MFGM or with a mixture of whey-MFGM and BMP. No aggregation was observed for emulsions stabilized with BM-MFGM, Lacprodan PL-20, or a mixture of BM-MFGM and BMP. The surface protein load and polar lipids load were lowest in emulsions with BM-MFGM. The highest protein load and polar lipids load were observed for emulsions made with a mixture of whey-MFGM and BMP. The differences in composition of MFGM materials, such as in whey proteins, caseins, MFGM-specific proteins, polar lipids, minerals, and especially their possible interactions determine their emulsifying properties.

Accurate particle size distribution determination by nanoparticle tracking analysis based on 2-D Brownian dynamics simulation.

A physical model is presented to simulate the average step length distribution during nanoparticle tracking analysis experiments as a function of the particle size distribution and the distribution of the number of steps within the tracks. Considering only tracks of at least five steps, numerical simulation could be replaced by a normal distribution approximation. Based on this model, simulation of a step length distribution allows obtaining a much more reliable estimation of the particle size distribution, thereby reducing the artificial broadening of the distribution, as is typically observed by direct conversion of step length to particle size data. As this fitting procedure also allowed including data from particles that were followed for a relatively low number of steps, the measurement time could be reduced for particles that are known to be monodisperse. Whereas the inversion is less sensitive towards the particle size distribution width, still similar values were obtained for both the average diameter and standard deviation of a polystyrene latex sample irrespective of the track length, provided that the latter included at least five steps.

Implications and remediations of DMAEA-Q type polymer hydrolysis in wastewater treatment plants.

The present paper outlines the impact of hydrolysis occurring in DMAEA-Q type polymers in the dewatering facilities of municipal wastewater treatment plants. Laboratory studies of polymer hydrolysis kinetics were combined with full-scale dewatering experiments to investigate the influence of polymer charge loss on polymer consumption and cake dry matter yields. The results indicate that prolonged polymer storage leads to important charge loss effects, resulting in increased dosage requirements for satisfactory dewatering performance. Fortunately, charge loss effects due to hydrolysis upon polymer storage could be minimized by acidifying the polymer batches. Furthermore, cake dry matter contents obtained from dewatering tests with freshly prepared polymer batches suggested that acidification of the polymer batch also had a beneficial effect on the conditioning efficiency of the polymer solution. The results from this study thus stress the influence of pH on the shelf life and efficiency of polymer solutions in wastewater treatment plants. As a consequence, polymer preparation and storage procedures should be adapted to the polymer consumption pattern and pH of the medium used for polymer batch production.

A methodological approach for direct quantification of the activated sludge floc size distribution by using different techniques.

The activated sludge floc size distribution (FSD) is investigated by using different measurement techniques in order to gain insight in FSD assessment as well as to detect the strengths and limitations of each technique. A second objective was to determine the experimental conditions that allow a representative and accurate measurement of activated sludge floc size distributions. Laser diffraction, Time Of Transition (TOT) and Dynamic Image Analysis (DIA) devices were connected in series. The sample dilution liquid, the dilution factor and hydraulic flow conditions avoiding flocculation proved to be important. All methods had certain advantages and limitations. The MastersizerS has a broader dynamic size range and provides accurate results at high concentrations. However, it suffers from an imprecise evaluation of small size flocs and is susceptible to particle shape effects. TOT suffers less from size overestimation for non-spherical particles. However, care should be taken with the settings of the transparency check. Being primarily a counting technique, DIA suffers from a limited size detection range but is an excellent technique for process visualization. All evaluated techniques turned out to be reliable methods to quantify the floc size distribution. Selection of a certain method depends on the purpose of the measurement.

Partitioning of propranolol in the phospholipid bilayer coat of anionic magnetoliposomes.

This work deals with the partitioning of the cationic amphiphilic drug, propranolol, in the coating of so-called magnetoliposomes (MLs), which consist of nanometre-sized, magnetizable iron oxide cores covered with a phospholipid bilayer. MLs of two types were used: either the ML coat consisted entirely of anionic dimyristoylphosphatidylglycerol, or it was mixed with zwitterionic dimyristoylphosphatidylcholine in a 5/95 molar ratio. To separate sorbed from non-sorbed propranolol, high-gradient magnetophoresis was used. The sorption profiles clearly show that electrostatic interactions play a key role in the sorption process as drug incorporation in the ML coat was favoured by increasing the anionic character of the ML envelope and by reducing the salt concentration of the medium. Also, upon drug binding some phospholipid molecules were expelled from the ML coat. The observations may be of relevance in the biomedical field, i.e. in the development of ML-based, intracellular theranostics.

Hydrophilic lecithins protect milk proteins against heat-induced aggregation.

In the present study, the heat-induced interaction between whey proteins and casein micelles was studied. To that end, the particle size distribution of 5.5% (w/w) casein micellar dispersions was determined by photon correlation spectroscopy as a function of both the whey protein concentration and heating time at 80 degrees C. The results clearly indicated that heat-induced aggregation of the casein micelles only occurred in the presence of whey proteins. In an effort to overcome the heat-induced interactions between whey proteins and casein micelles, the influence of different soybean lecithins was investigated. Comparing native to hydrolysed, as well as hydroxylated soybean lecithin, it was observed that the heat-stabilising effect of the lecithins was directly related to their hydrophilicity: whereas native soybean lecithin had hardly any beneficial effect, highly hydrolysed as well as hydroxylated soybean lecithin largely prevented heat-induced casein micelle aggregation in the presence of whey proteins. From experimental observations on the heat-induced decrease of whey protein solubility both in the absence and presence of hydrolysed lecithin, it was deduced that the latter may stabilise the exposed hydrophobic surface sites of heat-denatured whey proteins. Dynamic surface tension measurements indicated that the heat-stabilising properties of lecithins were mainly determined by their critical aggregation concentration.

Bench- and pilot-scale sludge electrodewatering in a diaphragm filter press.

Electrodewatering is a technique in which pressure dewatering is combined with electrokinetic effects to realize an improved solid/liquid separation and hence increased filter cake dry matter contents. In order to be energy efficient, it is shown that sludge should be dewatered by pressure dewatering to a high extent prior to electric field application, and a sufficient contact time for the electric field must be guaranteed. In order to realize these goals, a bench- and pilot-scale diaphragm filter press suited for electrodewatering were constructed for treatment of sewage and other types of sludges. It was shown that electrodewatering of sludge is a feasible technique, especially for biological sludge types. Other types of sludge are less suited for electrodewatering because of the restricted improvements that can be realized in cake dry matter content and the high electric energy consumption. Furthermore, it was shown in pilot-scale tests that the use of a diaphragm filter press with electrodewatering facilities was very well suited to deliver dry filter cakes of sewage sludge at a moderate energy consumption. Depending on local market prices for investment, operating and sludge disposal costs, this technology may therefore lead to important savings in the sludge management process.

The importance of the cosolvent propylene glycol on the antimicrobial preservative efficacy of a pharmaceutical formulation by DOE-ruggedness testing.

The aim of this study was to statistically evaluate the influence of the concentration of the co-solvent propylene glycol on the preservative efficacy of a complex pharmaceutical suspension-emulsion formulation containing methyl- and propylparaben. Preservative Efficacy Tests (PETs) were performed using the validated pharmacopoeial methodology with five test organisms over 1 month on lab-scale test formulations. These were independently prepared according to a Box-Behnken experimental design with a triplicate central point at 0.22% m/m methylparaben, 0.22% m/m propylparaben, and 2.75% m/m propylene glycol, and with an additional corner point of the Box-Behnken cube. We evaluated the preservative efficacies against the criteria of the United States Pharmacopeia (USP) and European Pharmacopoeias (PhEur) for formulations for oral use, as well as by the statistical comparison of the slopes obtained by linear regression of log (CFU/g) vs. time. With an initial bacterial challenge of 10(6) CFU/g for each of the three bacterial strains, no survivals were detected after 7 days. For the two fungal strains, box plots and analysis of variance showed significant, concentration-dependent, main effects: the three variables significantly influenced the kill-rate of C. albicans, while A. niger was predominantly influenced by the cosolvent propylene glycol, and only to a minor extent by methylparaben and not at all by propylparaben. These findings were confirmed by taking the pharmacopoeial criteria as the evaluation basis, where the dominant influence of propylene glycol concentration is apparent. It was concluded that the cosolvent propylene glycol is at least of equal preservative importance than both parabens.

Classification of spray nozzles based on droplet size distributions and wind tunnel tests.

Droplet size distribution of a pesticide spray is recognised as a main factor affecting spray drift. As a first approximation, nozzles can be classified based on their droplet size spectrum. However, the risk of drift for a given droplet size distribution is also a function of spray structure, droplet velocities and entrained air conditions. Wind tunnel tests to determine actual drift potentials of the different nozzles have been proposed as a method of adding an indication of the risk of spray drift to the existing classification based on droplet size distributions (Miller et al, 1995). In this research wind tunnel tests were performed in the wind tunnel of the International Centre for Eremology (I.C.E.), Ghent University, to determine the drift potential of different types and sizes of nozzles at various spray pressures. Flat Fan (F) nozzles Hardi ISO 110 02, 110 03, 110 04, 110 06; Low-Drift (LD) nozzles Hardi ISO 110 02, 110 03, 110 04 and Injet Air Inclusion (AI) nozzles Hardi ISO 110 02, 110 03, 110 04 were tested at a spray pressures of 2, 3 and 4 bar. The droplet size spectra of the F and the LD nozzles were measured with a Malvern Mastersizer at spray pressures 2 bar, 3 bar and 4 bar. The Malvern spectra were used to calculate the Volume Median Diameters (VMD) of the sprays.

Simultaneous determination of activated sludge floc size distribution by different techniques.

The activated sludge floc size distribution (FSD) is investigated by using different techniques and the results are compared against each other in order to gain insight into the FSD characteristics, as well as to detect the limitations of each measurement technique. The experimental set-up consisted of three devices coupled in series: a MastersizerS, an automated image analysis system (IMAN) and a CIS-100. The latter instrument has two measurement channels, based on time of transition (TOT), and image analysis (SHAPE) principles. In order to minimise the variability between successive measurements, the activated sludge samples collected from a pilot-scale SBR were flocculated until steady state was achieved. The results show that the MastersizerS and SHAPE devices yield similar volume weighted FSD. In contrast, the IMAN overestimated the floc size and TOT frequently showed a bimodal distribution. The number distributions from TOT and SHAPE were in agreement, while those generated by the MastersizerS were mainly located in the submicron range and those of IMAN corresponded to larger sizes. The experimental distributions show a good fit to the log-normal model. It is shown that the measurement principle is of utmost importance and results transformation may lead to data misinterpretation.

Linking floc structure and settling properties to activated sludge population dynamics in an SBR.

Over a period of 227 days properties of activated sludge grown in an sequencing batch reactor (SBR) operated under stable conditions were analyzed. Settling properties (sludge volume index (SVI)) of the activated sludge were compared with on-line measurements of floc size and size distribution obtained by using a laser light scattering technique (Malvern Mastersizer/S, Malvern, UK), and with measurements of microbial community dynamics analyzed by denaturing gradient gel electrophoresis (DGGE) patterns of 16S rRNA genes. In addition, microscopical observations were used to confirm the results. Three distinct stages in the SBR evolution were observed. In the first stage the structural floc properties showed predominant presence of floc-forming bacteria in the activated sludge. A good correlation between floc size, properties and microbial community evolution was observed. The second stage showed a good balance between floc-forming and filamentous bacteria, with good settling properties and a highly dynamic community in the SBR. In the third stage, an increase in the filamentous bacteria, which became predominant in the system was observed. Again, a good correlation between settling properties and floc size distribution was obtained and a new dominant species was observed in the DGGE patterns, which can be assumed to be a filamentous organism.

Simulation of drift of pesticides: development and validation of a model.

Over the last decade drift of pesticides has been recognized as a major problem for the environment. High fractions of pesticides can be transported through the air and deposited in neighbouring ecosystems during and after application. A new computer-two steps-drift model is developed: FYDRIMO or F(ph)Ysical DRift MOdel. In the first step the droplet size spectrum of a nozzle is analysed. In this way the volume percentage of droplets with a certain size is known. In the second step the model results in a prediction of deposition of each droplet with a certain size. This second part of the model runs in MATLAB and is grounded on a combination of two physical factors: gravity force and friction forces. In this stage of development corrections are included for evaporation and wind force following a certain measured wind profile. For validation wind tunnel experiments were performed. Salt solutions were sprayed at two wind velocities and variable distance above the floor. Small gutters in the floor filled with filter paper were used to collect the sprayed droplets. After analysing and comparing the wind tunnel results with the model predictions, FYDRIMO seems to have good predicting capacities.

The effect of adjuvants on atomisation of pesticides.

Four surfactants Tween 20, Agral 90, Silwet L77 and Break Thru, commonly used in the formulations of agricultural products, were evaluated on their spray performance and dynamic surface tension. In a spray test the Dv 50 (micron) or the Volume Median Diameter and the percentage of droplets with diameter below 100 microns (drift sensitive droplets), were measured for different kind of nozzles varying from the classical flat fan up to the low drift nozzles. The spectra changed considerably when different kind of nozzles and different kind of surfactants were used, the concentration effect was less important. The dynamic tension of the different surfactant solutions could not always explain the changes in droplet spectrum.

Enhanced sludge dewatering by electrofiltration. A feasibility study.

Sludge treatment is a major issue in today's waste water treatment. One of the problems encountered is the limiting dewaterability of mainly biological sludges, causing high final treatment costs for incineration or landfill. Although during recent years, improvements are realised in the field of dewatering, the actual dry solids content after dewatering remains at a maximum value of about 35%. In order to increase the dry solids content, the technique of electrofiltration was investigated. Electrofiltration is the combination of two known techniques, traditional pressure filtration and electroosmotic/electrophoretic dewatering. Pressure filtration is based on pressure as the driving force for dewatering a sludge. Limitations hereby lie in the clogging of the filter cloth due to the build-up of the filtercake. Electroosmotic/electrophoretic dewatering is based on an electric field to separate sludge colloid particles from the surrounding liquid by placing the sludge liquor between two oppositely charged electrodes. In this case, mobile sludge particles will move to one electrode due to their natural surface charge, and the liquid phase will be collected at the oppositely charged electrode. Combination of both techniques makes it possible to create a more homogeneous filter cake and prevent the filter from clogging, resulting in higher cake dry solids contents and shorter filtration cycles. To investigate the feasibility of this technique for the dewatering of activated sludge, a filter unit was developed for investigations on lab scale. Multiple dewatering tests were performed in which the electric parameters for electrofiltration were varied. It was derived from these experiments that very high filter cake dry solids contents (to more than 60%), and short filtration cycles were attainable by using a relatively small electric DC field. The power consumption was very low compared to the power needed to dewater sludge by thermal drying techniques. For this reason, this technique seems very promising for the dewatering of biological sludges.

Catalytic durability of magnetoproteoliposomes captured by high-gradient magnetic forces in a miniature fixed-bed reactor.

Cytochrome c-oxidase, used as a model membrane-bound enzyme, was embedded in phospholipid bilayer membranes, attached to nanometer-sized Fe(3)O(4) colloids (so-called magnetoliposomes). In comparison with the lipid-depleted free enzyme, both the activity and the enzymatic stability of the complexes, stored at 4 degrees C, were considerably enhanced. These beneficial properties of magnetoproteoliposomes have been successfully exploited in a magnetically controlled fixed-bed bioreactor, operating in a continuous flow regime. (c) 1996 John Wiley & Sons, Inc.