Effects of high temperature short time (HTST) pasteurization on milk and whey during commercial whey protein concentrate production
This study found that high temperature short time (HTST) pasteurization, applied to both milk and whey during commercial whey protein concentrate production, leads to a reduction in several key bioactive proteins such as lactoferrin, immunoglobulin A, immunoglobulin M, and xanthine oxidase. The study suggests exploring alternative processing methods to better preserve these valuable components.
College of Health researcher(s)
College unit(s)
Abstract
Two pasteurization steps are often used in the preparation of whey protein concentrate (WPC) before evaporation into a dry product. The Pasteurized Milk Ordinance (PMO) in the United States requires that raw bovine milk be pasteurized using a process that meets minimum heat treatment requirements to achieve reductions in pertinent microorganisms. In addition, WPC produced from USDA-approved plants must comply with CFR Subpart B §58.809, which dictates that all fluid whey used in the manufacture of dry whey products shall be pasteurized before being condensed. These heat treatments are effective at inactivating the most thermally resistant bacterium, such as Coxiella burnetii; however, they can also alter milk proteins—inducing denaturation, aggregation and reduced bioactivity. Though the impact of thermal treatments on whey proteins has been examined, the specific influence of 2 high-temperature-short-time (HTST) pasteurization steps on the retention of proteins in WPC remains unknown. This study aimed to investigate the effect of commercial-scale HTST pasteurization of both raw milk and the resulting sweet whey on the products' overall protein profile. Three distinct batches of raw milk (RM) and corresponding pasteurized milk (PM), the resulting whey (RW) and pasteurized whey (PW) produced at commercial scale were analyzed. Assessments of denaturation were conducted through solubility testing at pH 4.6 and hydrophobicity evaluation via anilinonaphthalene-1-sulfonic acid assay (ANS). Additionally, enzyme-linked immunosorbent assay (ELISA), PAGE (PAGE) and liquid chromatography tandem mass spectroscopy (LC-MS/MS) were employed to compare the retention of key bioactive proteins before and after each HTST pasteurization step. The percentage of soluble whey protein decreased from RM to PM and from RW to PW, but no significant differences were observed via hydrophobicity assay. ELISA revealed a significant reduction in key bioactive proteins, such as lactoferrin, immunoglobulin A and immunoglobulin M, but not immunoglobulin G, after HTST pasteurization of RM and RW. PAGE and LC-MS/MS revealed a significant decrease in the retention of lactoferrin and key milk fat globular membrane proteins, such as xanthine dehydrogenase oxidase/xanthine oxidase, lactadherin and fatty acid binding protein. Additionally, xanthine oxidase activity was significantly reduced after HTST pasteurization of milk and whey. This research helps to identify the limitations of the current processing techniques used in the dairy industry and could lead to innovation in improving the retention of bioactive proteins.
Whey Protein Concentrate Production: An FAQ
What is Whey Protein Concentrate (WPC)?
Whey Protein Concentrate (WPC) is a dried powder derived from whey, a byproduct of cheesemaking. It is a popular dietary supplement and food ingredient due to its high protein content and functional properties, such as foaming and gelation, making it useful in various food applications. WPC typically contains 35–80% protein.
Why is Pasteurization Necessary in WPC Production?
Pasteurization is a crucial step in WPC production to ensure product safety and compliance with regulations like the Pasteurized Milk Ordinance (PMO). The PMO mandates that raw milk and fluid whey used in dry whey product manufacturing be pasteurized to eliminate harmful microorganisms like Coxiella burnetii, the most heat-resistant pathogen found in milk.
How Does Pasteurization Affect Whey Proteins?
While essential for safety, pasteurization, particularly High-Temperature Short-Time (HTST) treatment, can denature whey proteins, disrupting their structure and potentially reducing their bioactivity. This occurs because the high temperatures involved in HTST (at least 72°C for 15 seconds) can alter protein structure, causing them to unfold and aggregate.
Which Whey Proteins are Most Affected by HTST Pasteurization?
HTST pasteurization impacts different whey proteins to varying degrees. Studies show that bioactive proteins like lactoferrin, immunoglobulin A (IgA), and immunoglobulin M (IgM) are significantly reduced after both milk and whey pasteurization. Other proteins like lactoperoxidase and xanthine oxidase also show significant activity reduction. Immunoglobulin G (IgG), α-lactalbumin, and β-lactoglobulin, however, demonstrate higher heat stability and are less affected.
How is Whey Protein Denaturation Measured?
Several methods assess whey protein denaturation, including:
- Solubility Testing: Measures the amount of soluble protein at pH 4.6, indicating the extent of denaturation and aggregation.
- Hydrophobicity Evaluation: Uses anilinonaphthalene-1-sulfonic acid (ANS) assay to assess the exposure of hydrophobic regions in proteins, which increases with denaturation.
- SDS-PAGE: Visualizes protein profiles and reveals changes in protein size and aggregation patterns.
- ELISA: Quantifies specific proteins like lactoferrin and immunoglobulins to assess their retention after pasteurization.
How Does Pasteurization Affect Enzyme Activity in Whey?
Enzymes, like lactoperoxidase and xanthine oxidase, naturally present in milk, are significantly reduced in activity by HTST pasteurization. This reduction is particularly notable after whey pasteurization, likely due to the removal of fat, where these enzymes are typically concentrated, during cheesemaking.
What Are the Implications of Whey Protein Denaturation for Consumers?
Denaturation can decrease the bioactivity and nutritional value of WPC by affecting the functionality and digestibility of proteins. This could reduce the potential health benefits associated with specific whey proteins, such as immune support and antioxidant activity.
What Alternatives to HTST Pasteurization Exist for WPC Production?
To mitigate the negative impacts of HTST on whey proteins, alternative processing techniques are being explored. These include:
- High-Pressure Processing: Inactivates microorganisms using high pressure instead of heat, preserving protein structure and bioactivity.
- UV-C Irradiation: Uses ultraviolet light to disinfect milk and whey, potentially causing less protein damage than heat treatment.
- Microfiltration: Separates whey proteins based on size, allowing for the selective isolation and concentration of specific bioactive proteins before further processing.