Age Gelation, Sedimentation, and Creaming in UHT Milk: A Review

Abstract

Demand for ultra‐high‐temperature (UHT) milk and milk protein‐based beverages is growing. UHT milk is microbiologically stable. However, on storage, a number of chemical and physical changes occur and these can reduce the quality of the milk. These changes can be sufficiently undesirable so as to limit acceptance or shelf life of the milk. The most severe changes in UHT milk during storage are age gelation, with an irreversible three‐dimensional protein network forming throughout, excessive sedimentation with a compact layer of protein‐enriched material forming rapidly at the bottom of the pack, and creaming with excessive fat accumulating at the top. For age gelation, it is known that at least two mechanisms can lead to gelation during storage. One mechanism involves proteolytic degradation of the proteins through heat‐stable indigenous or exogenous enzymes, destabilizing milk and ultimately forming a gel. The other mechanism is referred to as a physico‐chemical mechanism. Several factors are known to affect the physico‐chemical age gelation, such as milk/protein concentration, heat load during processing (direct compared with indirect UHT processes), and milk composition. Similar factors to age gelation are known to affect sedimentation. There are relatively few studies on the creaming of UHT milk during storage, suggesting that this defect is less common or less detrimental compared with gelation and sedimentation. This review focuses on the current state of knowledge of age gelation, sedimentation, and creaming of UHT milks during storage, providing a critical evaluation of the available literature and, based on this, mechanisms for age gelation and sedimentation are proposed.

Changes in stability and shelf-life of ultra-high temperature treated milk during long term storage at different temperatures

“…The result is the formation of larger heavy particles setting at the bottom following Stoke's law (Deeth and Lewis, 2016). Increased storage temperature is suggested to accelerate sedimentation, due to a lower viscosity of the milk serum (Anema, 2018), also explaining the sedimentation observed at higher storage temperatures in our study. Possible explanations for sediment formation after 30–40 weeks of storage at 4 °C are hard to find in the literature.…”

Changes in Milk Protein Interactions and Associated Molecular Modification Resulting from Thermal Treatments and Storage

“…One major defect in UHT milk resulting from the casein and whey protein interactions and aggregate formation is the rise in viscosity (> 10 mPa⋅s at 20 °C) that occurs upon storage, and the formation of a three‐dimensional protein network gel, which combine to cause a loss of fluidity in UHT milk. The phenomenon is known as ‘age gelation’ (Anema ; Datta & Deeth, ; McMahon, ). The gelation is irreversible and generally renders the product unacceptable to consumers.…”

“…In addition to redistribution of proteins between the colloidal and serum phases and denaturation of whey proteins, thermal treatment of milk has been reported to induce other major chemical changes such as covalent cross-linking of proteins, lactosylation leading to Maillard reactions, and degradation of individual amino acids via deamidation (Deeth & Lewis, 2016). These changes to milk proteins have implications for product sensory and textural attributes (for example, color and physical stability; Anema, 2019;Sunds, Rauh, Sørensen, & Larsen, 2018). The Maillard reaction may progress over time in UHT milk during storage, as indicated by previously-observed changes in color and furosine as markers of quality deterioration (Gaucher, Mollé, Gagnaire, & Gaucheron, 2008;Sunds et al, 2018).…”

Plant protein ingredients with food functionality potential

“…For example, high‐protein nutrition bars often become very hard as a result of protein aggregation (Loveday et al . 2010), and protein gelation or sedimentation in UHT milks is a common problem (Anema 2019).…”