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

Abstract

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.

Assessing the Scalability of the High-Pressure High-Temperature Quartz Crystal Microbalance with Dissipation (HPHT QCM-D) for Milk Fouling Studies

“…Yet, within this tube, there is a residence time distribution that can be described by the local residence time along the length of the tube. The results from this research group, as well as the results regarding the fouling distribution within a plate heat exchanger, support predictions for a gradient or distribution of fouling as a function of the local residence time, bulk-fluid temperature, and surface temperature.…”

“…Quartz sensors with a stainless steel coating (US grade 316, QSX 304, Nanoscience Instruments, Phoenix, AZ) were prepared according to the manufacturer’s protocol …”

“…QSense highpressure high-temperature (HPHT) QCM-D equipment (Biolin Scientific, Gothenburg, Sweden) was used for bench-scale experiments. A titanium, high-pressure flow module (HPC 101, Biolin Scientific) was configured with a custom microfluidic handling system custom-designed by Biolin Scientific for this study that removed the floating pistons cylinders from the previous setup 20 to improve ease of use and cleanability.…”

“…Other research provides evidence that supports the presence of the protein in the first layers of milk fouling, specifically if denatured or aggregated proteins are present in the bulk, 38−40 but those studies were not conducted under UHT conditions nor did they use a MFF containing caseins. A second potential explanation is that the soluble mineral environment in the MFF used in this study, 0.25× PBS, could hinder the formation of CaP deposits in comparison to a different buffer system, such as simulated milk ultrafiltrate (SMUF) 30−32 or a higher concentration of PBS, such as 1× PBS, 20 or a system with a more comparable soluble, monovalent sodium ion concentration to the concentration found in milk (∼24.2 mM). 41 Formation of protein deposits instead of CaP deposits in this research agrees with other studies that have shown that the mineral environment in milk significantly affects the fouling behavior.…”

“…Substrate Preparation for QCM-D. Quartz sensors with a stainless steel coating (US grade 316, QSX 304, Nanoscience Instruments, Phoenix, AZ) were prepared according to the manufacturer's protocol. 20 2.2.2. QCM-D System Setup and Data Collection.…”