Predicting the distribution of whey protein fouling in a plate heat exchanger using the kinetic parameters of the thermal denaturation reaction of β-lactoglobulin and the bulk temperature profiles

SVR Chemometrics to Quantify β-Lactoglobulin and α-Lactalbumin in Milk Using MIR

Protein content variation in milk can impact the quality and consistency of dairy products, necessitating access to in-line real time monitoring. Here, we present a chemometric approach for the qualitative and quantitative monitoring of β-lactoglobulin and α-lactalbumin, using mid-infrared spectroscopy (MIR). In this study, we employed Hotelling T2 and Q-residual for outlier detection, automated preprocessing using nippy, conducted wavenumber selection with genetic algorithms, and evaluated four chemometric models, including partial least squares, support vector regression (SVR), ridge, and logistic regression to accurately predict the concentrations of β-lactoglobulin and α-lactalbumin in milk. For the quantitative analysis of these two whey proteins, SVR performed the best to interpret protein concentration from 197 MIR spectra originating from 42 Cornell University samples of preserved pasteurized modified milk. The R2 values obtained for β-lactoglobulin and α-lactalbumin using leave one out cross-validation (LOOCV) are 92.8% and 92.7%, respectively, which is the highest correlation reported to date. Our approach introduced a combination of preprocessing automation, genetic algorithm-based wavenumber selection, and used Optuna to optimize the framework for tuning hyperparameters of the chemometric models, resulting in the best chemometric analysis of MIR data to quantitate β-lactoglobulin and α-lactalbumin to date.

Monitoring and Characterization of Milk Fouling on Stainless Steel Using a High-Pressure High-Temperature Quartz Crystal Microbalance with Dissipation

Fouling at interfaces deteriorates the efficiency and hygiene of processes within numerous industrial sectors, including the oil and gas, biomedical device, and food industries. In the food industry, the fouling of a complex food matrix to a heated stainless steel surface reduces production efficiency by increasing heating resistance, pumping requirements, and the frequency of cleaning operations. In this work, quartz crystal microbalance with dissipation (QCM-D) was used to study the interface formed by the fouling of milk on a stainless steel surface at different flow rates and protein concentrations at high temperatures (135 °C). Subsequently, the QCM-D response was recorded during the cleaning of the foulant. Two phases of fouling were identified. During phase-1, the fouling rate was dependent on the flow rate, while the fouling rate during phase-2 was dependent on the flow rate and protein concentration. During cleaning, foulants deposited at the higher flow rate swelled more than those deposited at the lower flow rate. The composition of the fouling deposits consisted of both protein and mineral species. Two crystalline phases of calcium phosphate, β-tricalcium phosphate and hydroxyapatite, were identified at both flow rates. Stratification in topography was observed across the surface of the QCM-D sensor with a brittle and cracked structure for deposits formed at 0.2 mL/min and a smooth and close-packed structure for deposits formed at 0.1 mL/min. These stratifications in the composition and topography were correlated to differences in the reaction time and flow dynamics at different flow rates. This high-temperature application of QCM-D to complex food systems illuminates the initial interaction between proteins and minerals and a stainless steel surface, which might otherwise be undetectable in low-temperature applications of QCM-D or at larger bench and industrial scales. The methods and results presented here have implications for optimizing processing scenarios that limit fouling formation while also enhancing removal during cleaning.

Calcium: A comprehensive review on quantification, interaction with milk proteins and implications for processing of dairy products

Calcium (Ca) is a key micronutrient of high relevance for human nutrition that also influences the texture and taste of dairy products and their processability. In bovine milk, Ca is presented in several speciation forms, such as complexed with other milk components or free as ionic calcium while being distributed between colloidal and serum phases of milk. Partitioning of Ca between these phases is highly dynamic and influenced by factors, such as temperature, ionic strength, pH, and milk composition. Processing steps used during the manufacture of dairy products, such as preconditioning, concentration, acidification, salting, cooling, and heating, all contribute to modify Ca speciation and partition, thereby influencing product functionality, product yield, and fouling of equipment. This review aims to provide a comprehensive understanding of the influence of Ca partition on dairy products properties to support the development of kinetics models to reduce product losses and develop added-value products with improved functionality. To achieve this objective, approaches to separate milk phases, analytical approaches to determine Ca partition and speciation, the role of Ca on protein-protein interactions, and their influence on processing of dairy products are discussed.

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.

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.

Formation of β-Lactoglobulin Aggregates from Quite, Unfolded Conformations upon Heat Activation

In presence of calcium ions, β-lactoglobulin (BLG) unfolds and subsequently aggregates after heating. This process has important pharmaceutical and agroalimentary applications. Nowadays, the molecular mechanism of unfolding and BLG aggregation, and the role of calcium in the mechanism, is poorly understood. Actually, in most studies, data have been acquired at room temperature, after heating and after aggregation, which makes it difficult to establish a clear causal-temporal relation between calcium binding, heat, and aggregation. Thus, the goal of the present study is to get accurate, nanoscale data about the molecular events leading to BLG unfolding and calcium-dependent aggregation. The molecular transformation of BLG during heating has been investigated, using the NMR pulse field gradient technique, operating in a high field (900 MHz). Thanks to this technique, the molecular conformation of newly formed unfolded BLG molecules can be distinguished in a large pool of native ones. The present work shows that BLG at neutral pH at 65 °C displays fast, cooperative-like unfolding, in which no long-lived intermediary state (as a molten globule one) is detected, before aggregation. These data also indicate that calcium ions bind unfolded BLG in specific sites which might be a necessary feature to form the aggregate. Finally, these data also provide an NMR-based methodology to monitor the rate of protein unfolding using NMR.

Development and Validation of CFD Models of Thermal Treatment on Milk Whey Proteins Dispersion In Batch and Continuous Process Condition

The objective of this study was to develop and experimentally validate CFD models of thermal treatments on whey protein dispersions both in batch and continuous conditions, considering several processing times (2 to 9.92 min), shear rates (191 to 519 s−1) and temperatures (70, 80 and 85 °C). Regarding thermo-rheological properties of WP dispersions, the viscosity peak (raising up at 66 °C) decreased as the shear rate increased. Two different CFD models were developed to simulate the thermal process: results showed a good fitting between experimental and simulated data (RMSE <1.7 °C for batch model and mean temperature difference of 0.93 °C for the continuous one). Based on the developed models, cook values of both processes were calculated and slowest heating points were exactly located; by means of these data, equations to estimate the cook value in processing conditions within experimental range were obtained, overcoming the need of experimental tests or in-silico simulations.

Evaluation of Models for Temperature-Dependent Viscosity Changes in Dairy Protein Beverage Formulations During Thermal Processing

Rheological modeling as a function of temperature is a useful tool for describing products undergoing thermal processing. The rheological behavior of a range of dairy-based (4%, w/w) protein beverages was investigated for applicability to semi-empirical temperature-dependent viscosity equations. The viscosity at 16.8 rad/s of the beverages was measured during heating, holding, and cooling over a temperature range of 25 to 90 ^o C using a rheometer with starch pasting cell geometry. Five established fitting methods were applied based on the Arrhenius and Williams-Landel-Ferry (WLF) equations using nonlinear regression analysis. A two-parameter WLF (WLF₂ ) model, using viscosity at a reference temperature of 25 ^o C resulted in high R² values (0.974 to 0.988) and a statistically superior fit compared to the Arrhenius, Generalized Arrhenius, and exponential equations (P < 0.001). Deviation from the WLF₂ modeled equation was used to describe and investigate the effect formulation had on the changes in viscosity during thermal heating. This study successfully applied the WLF equation to a liquid protein system, proving that a consistent and close fit can be achieved across a range of formulations. A rapid, quantitative method for viscosity-temperature profile evaluation is presented, which can ease product development and optimization of product processing stability.

PRACTICAL APPLICATION

This study validated the use of the Williams-Landel-Ferry equation to describe the behavior of dairy beverages during thermal processing, providing a better fit to rheological data than the widely used Arrhenius-based equations. In conjunction with the WLF equation, a method was presented which reduced the complex rheological data to a single value, which can aid in the comparison of formulations for product development and optimization in both research and industry.