Fat-free fermented concentrated milk products as milk protein-based microgel dispersions: Particle characteristics as key drivers of textural properties

Influence of Post-Heating Treatment on the Sensory and Textural Properties of Stirred Fermented Milk

The purpose of this study was to investigate the post-heating induced changes in the textural and sensory characteristics of stirred fermented milk. The textural and rheological properties of post-heating fermented milk (55-85 °C, 25 s) with respect to viscoelastic behaviors, viscosity, textural parameters, etc., were monitored, and the friction behaviors and sensory attributes were assessed. Treatments below 65 °C/25 s increased the textural properties of fermented milk such as gel strength, firmness, and viscosity, due to the moderate aggregation and increased linkages of microgels. In this case, despite the size and amount their aggregates increased (~15-~21 μm), they exhibited similar frictional behaviors and sensory attributes. However, treatments above 65 °C/25 s degraded textural properties due to excessive aggregation (~46-~63 μm), accompanied by unacceptable grainy attributes, which could be characterized by their good correlations with tribological coefficients and particle size parameters. These findings could provide an understanding of the quality formation of post-heating fermented milk and a perspective to improve the textural defects of ambient fermented milk products.

Inline Particle Size Analysis during Technical-Scale Processing of a Fermented Concentrated Milk Protein-Based Microgel Dispersion: Feasibility as a Process Control

Particle size is not only important for the sensory perception of fat-free fermented concentrated milk products, but also for processing operations because of the direct relationship with apparent viscosity. The aim of this study was to apply inline particle size analysis using focused beam reflectance measurement (FBRM) to obtain real-time information regarding the particle size of a fat-free fermented concentrated milk product, namely, fresh cheese. By comparing inline particle size data to offline particle size, apparent viscosity, protein content and processing information, the potential to use inline particle size analysis as a process monitoring and control option during fresh cheese production was assessed. Evaluation of inline particle size after fermentation and before further processing, e.g., after a buffering tank, shows promise as a means to control variance of product entering downstream processing and, thus, improve final product consistency over time. Measurement of inline particle size directly before filling could allow for precise control of final product characteristics by the use of mechanical or mixing devices placed before the inline measurement. However, attention should be given to the requirements of the inline measurement technology for accurate measurement, such as product flow rate and pressure.

Unraveling propylene glycol-induced lipolysis of the biosynthesis pathway in ultra-high temperature milk using high resolution mass spectrometry untargeted lipidomics and proteomics

In July 2022, the food safety accident that excessive propylene glycol was detected in milk processing factory raised widespread concerns about quality and nutrition of milk with illegal additive. To the best of our knowledge, the influences of propylene glycol to lipids in milk had not been systematically explored. Therefore, spatiotemporal distributions of lipids related to propylene glycol reaction and changes of sensory quality were investigated by food exogenous. Briefly, 10 subclasses (Cer, DG, HexCer, LPC, LPE, PC, PE, PI, SPH and TG) included 147 lipids and 38 pivotal enzymes were annotated. Propylene glycol altered lysophospholipidase and phospholipase A₂ through altering structural order in lipids domains surrounding proteins to inhibit glycerophospholipid metabolism and initiated obvious changes in PC (10.45-27.91 mg kg^-1) and PE (12.92-49.02 mg kg^-1). This study offered insights into influences of propylene glycol doses and storage time on milk metabolism at molecular level to assess the quality of milk.

Tailoring the Textural Characteristics of Fat-Free Fermented Concentrated Milk-Protein Based Microgel Dispersions by Way of Upstream, Downstream and Post-Production Thermal Inputs

There is a growing demand for new strategies to tailor the texture of fat-free fermented concentrated milk products, also referred to as milk protein-based (MPb) microgel dispersions. Methods should be easy to incorporate into the production scheme, offer labelling without added components and be cost-efficient. Thermal treatments are traditionally used upstream (milk heating) and downstream (pre-concentration heating) in the production of these dispersions, though there is little knowledge as to the effects that combinations of different thermal input levels have on final texture. Therefore, this study investigated combinations of thermal input at different intensities and steps in the production scheme at the pilot scale and the relationships with texture. We demonstrated that increasing the intensity of upstream milk heat treatment, in combination with downstream pre-concentration heating, increases gel firmness and apparent viscosity. Downstream pre-concentration heating produces final fat-free fermented concentrated MPb microgel particles that are resistant to post-heating aggregation. On the other hand, omission of downstream pre-concentration heating results in smaller particles that are sensitive to post-heating aggregation. Furthermore, gel firmness and apparent viscosity increase with post-heating. Consequently, combining different levels of thermal inputs upstream, downstream (pre-concentration) and post-production, can produce fat-free fermented concentrated MPb microgel dispersions with a range of different textures.