The effect of temperature and shear rate upon the aggregation of whey protein and its implications for milk fouling

Exploring the formation of surficial whey protein deposits under shear stress by rheofluidic approach

Understanding how shear affects whey protein stability is crucial to deal with typical industrial issues occurring at the bulk solution/surface interface, such as fouling during heat treatments. However, at the state of the art, this effect remains unclear, contrary to that of temperature. This article presents a novel strategy to study the impact of shear rate and concentration on the accumulation of whey protein surficial deposits. It consists in applying a range of shear rates (0-200 s-1) at controlled temperature (65 °C) on whey protein solutions (5-10 wt%) by a parallel plate rheometer equipped with a glass disc, thus allowing the off-line characterization of the deposits by microscopy. Our results highlight an unequivocal effect of increasing shear stress. At 5 wt%, it fosters the formation of primary deposits (≈ 10 μm), whereas at 10 wt% it results in the development of complex branched structures (≈ 50 μm) especially for shear rates ranging from 140 s-1 to 200 s-1. Based on the classification by size of the observed populations, we discuss possible hypotheses for the deposit growth kinetics, involving the interplay of different physico-chemical protein-surface interactions and paving the way to future further investigations.

Effect of Protein Content on Heat Stability of Reconstituted Milk Protein Concentrate under Controlled Shearing

Milk protein concentrates (MPCs) possess significant potential for diverse applications in the food industry. However, their heat stability may be a limitation to achieving optimal functional performance. Shearing, an inherent process in food manufacturing, can also influence the functionality of proteins. The aim of this research was to examine the heat stability of reconstituted MPCs prepared at two protein concentrations (4% and 8% w/w protein) when subjected to varying levels of shearing (100, 1000, or 1500 s-1) during heating at 90 °C for 5 min or 121 °C for 2.6 min. While the impact of shear was relatively minor at 4% protein, it was more pronounced in 8% protein MPC suspensions, leading to a considerable decline in heat stability. An increase in protein concentration to 8% amplified protein interactions, intensified by shearing. This, in turn, resulted in comparatively higher aggregation at elevated temperatures and subsequently reduced the heat stability of the reconstituted MPCs.

Heat-Induced Changes in κ-Carrageenan-Containing Chocolate-Flavoured Milk Protein Concentrate Suspensions under Controlled Shearing

Milk protein dispersions containing added cocoa powder (1.5% (w/w)) and sucrose (7% (w/w)) and varying levels of κ-carrageenan (0.01, 0.03, or 0.05% w/w) were subjected to combined heat treatment (90 °C/5 min or 121 °C/2.6 min) and shear (100 or 1000 s-1) to investigate the heat stability of milk proteins. The application of shear led to a notable reduction in non-sedimentable proteins, resulting in an increase in the average particle size and apparent viscosity of the dispersions, particularly at high concentrations of k-carrageenan and elevated temperatures. This indicates that shear forces induced prominent protein aggregation, especially at higher κ-carrageenan concentrations. This aggregation was primarily attributed to the destabilisation of micelles and presence of loosely bound caseins within the κ-carrageenan network, which exhibited increased susceptibility to aggregation as collision frequencies increased due to shear.

Molecular Understanding of Fouling Induction and Removal: Effect of the Interface Temperature on Milk Deposits

Molecular details concerning the induction phase of milk fouling on stainless steel at an elevated temperature range were established to better understand the effect of temperature on surface fouling during pasteurization. The liquid-solid interface that replicates an industrial heat exchanger (≤75°C), including four stages (preheating, heating, holding, and cooling), was investigated using both a quartz crystal microbalance (QCM-D) and a customized flow cell. We found that the milk fouling induction process is rate-limited by the synergistic effects of bulk reactions, mass transfer, and surface reactions, all of which are controlled by both liquid and surface temperatures. Surface milk foulant becomes more rigid and compact as it builds up. The presence of protein aggregates in the bulk fluid leads to a fast formation of surface deposit with a reduced Young's modulus. Foulant adhesion and cohesion strength was enhanced as both interfacial temperature and processing time increased, while removal force increased with an increasing deposit thickness. During cleaning, caustic swelling and removal showed semilinear correlations with surface temperature (T_S), where higher T_S reduced swelling and enhanced removal. Our findings evidence that adsorption kinetics, characteristics of the foulant, and the subsequent removal mechanism are greatly dependent on the temperature profile, of which the surface temperature is the most critical one.

A critical review on surface modifications mitigating dairy fouling

Thermal treatments performed in food processing industries generate fouling. This fouling deposit impairs heat transfer mechanism by creating a thermal resistance, thus leading to regular shutdown of the processes. Therefore, periodic and harsh cleaning-in-place (CIP) procedures are implemented. This CIP involves the use of chemicals and high amounts of water, thus increasing environmental burden. It has been estimated that 80% of production costs are owed to dairy fouling deposit. Since the 1970s, different types of surface modifications have been performed either to prevent fouling deposition (anti-fouling) or to facilitate removal (fouling-release). This review points out the impacts of surface modification on type A dairy fouling and on cleaning behaviors under batch and continuous flow conditions. Both types of anti-fouling and fouling-release coatings are reported as well as the different techniques used to modify stainless steel surface. Finally, methods for testing and characterising the effectiveness of coatings in mitigating dairy fouling are discussed.

Calcium Chelation by Phosphate Ions and Its Influence on Fouling Mechanisms of Whey Protein Solutions in a Plate Heat Exchanger

Fouling of plate heat exchangers (PHEs) is a recurring problem when pasteurizing whey protein solutions. As Ca²⁺ is involved in denaturation/aggregation mechanisms of whey proteins, the use of calcium chelators seems to be a way to reduce the fouling of PHEs. Unfortunately, in depth studies investigating the changes of the whey protein fouling mechanism in the presence of calcium chelators are scarce. To improve our knowledge, reconstituted whey protein isolate (WPI) solutions were prepared with increasing amounts of phosphate, expressed in phosphorus (P). The fouling experiments were performed on a pilot-scale PHE, while monitoring the evolution of the pressure drop and heat transfer coefficient. The final deposit mass distribution and structure of the fouling layers were investigated, as well as the whey protein denaturation kinetics. Results suggest the existence of two different fouling mechanisms taking place, depending on the added P concentration in WPI solutions. For added P concentrations lower or equal to 20 mg/L, a spongy fouling layer consists of unfolded protein strands bound by available Ca²⁺. When the added P concentration is higher than 20 mg/L, a heterogeneously distributed fouling layer formed of calcium phosphate clusters covered by proteins in an arborescence structure is observed.

Quantifications of Oleocolloid Matrices Made of Whey Protein and Oleogels

Consumer demand for high protein content and plant-based fat has necessitated novel approaches to healthy food products. In response to this need, oleogels (OG) (structured liquid oils) emerged as a possible means of not only replacing saturated and trans fats but also delivering food protein. Nevertheless, an in-depth view of the structure of networks made of OG and protein is deficient. Hence, the objective of this study is developing oleocolloid (OC) (whey protein and rice bran wax OG) and hydro-oleocolloid (HOC) (OC + water) matrices with varying protein content (2.5–7.5%) to characterize their structural properties. Thermal analysis of the matrices via differential scanning calorimetry (DSC) documented the effects of hydrophobic interactions on the protein structure and its stability. Whey protein denaturation temperature increased from 74.9 °C to 102.8 °C in the presence of high oleic soybean oil. The effects of vegetable oil on WPI structure was also verified by FTIR spectroscopy. Data analysis revealed slight structural changes of the WPI secondary structure in the hydrophobic oil medium and the α-helix and β-sheet proportion in the emulsion medium was significantly altered. Similar analysis was performed in OC and HOC networks to quantify possible interactions between protein and rice bran wax. Results indicated that the protein was denatured during the thermal and mechanical conditions required for the oleogelation process, while it did not affect the systems’ solid fat content (SFC) and polymorphic patterns of the oleogels. However, DSC analysis showed different onset of melting for OC and HOC samples due to colloidal interactions between the protein and the lipid phase. The role of these chemistry was confirmed by microscopy analyses where OC and HOC matrices displayed notably different microstructural properties. The observed differences in the structural properties between OC and HOC matrices indicate the different colloidal interactions mediated by oleogelation process and the liquid medium type (oil vs. emulsion).

Formation of heated whey protein isolate-pectin complexes at pH greater than the isoelectric point with improved emulsification properties

In this study, heated whey protein isolate and pectin complexes (HCPX) formed at pH > isoelectric point (pI) were used to stabilize oil-in-water emulsions containing 5% oil and 1.5% (wt%) protein at pH 5.5. The effects of pectin concentration and heating temperature on emulsification and emulsion stabilization properties were determined. The HCPX were produced by heating mixed 3% (wt) whey protein isolate and pectin (0.1 or 0.3 wt%) at pH 6.2 and 75 or 85°C for 15 min. Aggregate sizes significantly increased with increasing heating temperature but decreased with the addition of pectin. The HCPX became more negatively charged with increasing pectin concentration; however, the effect of heating temperature was significant only at 0.1% pectin. Unheated complexes and HCPX successfully adsorbed at the oil-in-water interface and improved the emulsification properties as shown by higher negative charge and smaller droplet sizes. Despite the presence of pectin, rheological properties of the emulsions were not significantly different. All complexes showed increased emulsion stability; however, HCPX made at 85°C formed emulsions that were the most stable against creaming and heating.

Effects of protein properties on ultrafiltration membrane fouling performance in water treatment

Protein-like substances always induce severe ultrafiltration (UF) membrane fouling. To systematically understand the effect of proteins, regenerated cellulose UF membrane (commonly used for protein separation) performance was investigated in the presence of bovine serum albumin (BSA) under various water conditions. Results showed that although trypsin enhanced the membrane flux via proteolysis, catalysis took a long time. Membrane fouling was alleviated at high solution pH and low water temperature owing to the strong electrostatic repulsion force among BSA molecules. Both Na⁺ and Ca²⁺ could increase membrane flux. However, Ca²⁺ played a bridging role between adjacent BSA molecules, whereas membrane fouling was alleviated via a hydration repulsion force with Na⁺. The order of influence on membrane fouling was as follows: Ca²⁺ concentration > Na⁺ concentration > pH > temperature > trypsin concentration. Furthermore, a polyvinylidene fluoride UF membrane experiment showed that Ca²⁺ could reduce the fouling induced by BSA. Thus, the differences in UF membrane performance will have application potential for alleviating UF membrane fouling induced by proteins during water treatment.

Conformational and Functional Properties of Soybean Proteins Produced by Extrusion-Hydrolysis Approach

The conformational and functional changes of soybean protein after a hybrid extrusion-hydrolysis method were evaluated. Three extrusion temperatures (60, 80, and 100°C) were used prior to enzymatic hydrolysis. The hydrolysis degrees, molecular weight profiles, solubilities, surface hydrophobicities, sulphydryl contents, disulfide bound, water holding capacity, emulsion, and foam properties of the protein isolated from the enzyme-hydrolyzed extruded soybeans were analyzed. It shows that extrusion caused significant changes in the hydrophobicity, molecular weight distribution, solubility, surface hydrophobicity, emulsification activity, and stability of the protein. The increase of molecular weights could be attributed to the formation of protein aggregates during extrusion. Extrusion and enzymatic hydrolysis led to a sharp increase in the number of disulfide bonds with a decrease of the sulphydryl group. The water holding capacity and the solubility of protein increased with the increase of extrusion temperature and hydrolysis time. Extrusion improved the emulsifying activity but reduced the emulsifying stability of the recovered proteins. Extrusion improved the foam capacity but reduced the foam stability of the proteins. The data demonstrated that the extrusion-hydrolysis treatment significantly altered the conformational and functional properties of soybean protein, which may be further optimized for the development of new soy protein ingredient with desired functional properties.

A Comparative Study on Fouling and Cleaning Characteristics of Soy Protein Isolate (SPI)

Fouling on heat exchanger surface is a severe problem in food industry. This study investigated the fouling and cleaning behaviors of soy protein isolates (SPI) in heat exchangers, using a previously established real-time monitoring laboratory system. SPI fouling deposit was formed at different surface temperatures of 80, 85 and 90 °C. For cleaning, the effect of the NaOH concentration was investigated. The fouling and cleaning behaviors of whey protein concentrate (WPC) were studied for a qualitative comparison. The two solution concentrations were kept at 6 wt%. Under the constant heat flux condition applied in the experiments, increasing the surface temperature significantly increased the fouling rate of SPI. SPI deposit was much easier to remove compared to WPC deposit. Visualization showed that the cleaning behavior of SPI was different from that of WPC in that it swelled rather quickly followed by the species seeping out from the swollen structure.

Physical, Chemical and Biochemical Modifications of Protein-Based Films and Coatings: An Extensive Review

Protein-based films and coatings are an interesting alternative to traditional petroleum-based materials. However, their mechanical and barrier properties need to be enhanced in order to match those of the latter. Physical, chemical, and biochemical methods can be used for this purpose. The aim of this article is to provide an overview of the effects of various treatments on whey, soy, and wheat gluten protein-based films and coatings. These three protein sources have been chosen since they are among the most abundantly used and are well described in the literature. Similar behavior might be expected for other protein sources. Most of the modifications are still not fully understood at a fundamental level, but all the methods discussed change the properties of the proteins and resulting products. Mastering these modifications is an important step towards the industrial implementation of protein-based films.

Structural Changes in Rice Bran Protein upon Different Extrusion Temperatures: A Raman Spectroscopy Study

Raman spectroscopy is critically evaluated to establish the limits to which it may be used to detect changes in protein conformation upon extrusion. Rice bran protein (RBP) extruded with different temperatures (100, 120, 140, and 160°C, labeled as ERBP-) was considered. DSC showed that extrusion at 100°C increasedTDof RBP but decreased itsΔH, while, after extrusion treatment at 120°C, RBP completely denatured. A progressive increase in unordered structure and a general decrease inα-helix structure andβ-sheet structure of extruded RBP were observed from Raman study. Meanwhile the content of unordered structure increased up to 140°C and then decreased at 160°C, while the trend ofα-helix andβ-sheet content was opposite, which was contributed to the composite effect of formation of some more protein aggregation and protein denaturation. Extrusion generally induced a significant decrease in Trp band near 760 cm−1but an increase at 160°C. No significant difference was observed in Tyr doublet ratios between controlled RBP samples and extruded RBP below 160°C, whereas Tyr doublet ratios of extruded RBP decreased at 160°C. Intensity of the band assigned toCHnbending decreased progressively and then increased as extrusion temperature increased, indicating changes in microenvironment and polarity.