Key in the ability of milk and dairy products to function as excellent food matrices is the fact that milk, in essence, is designed to deliver. It is the sole source of nutrition for the neonate and contains essential structural elements, e.g., in the form of casein micelles and milk fat globules, which deliver a multitude of nutrients, including salts, vitamins and proteins. In addition, colloidal stability of these structure elements in the GI tract also leads to important control of the kinetics of digestion and release of nutrients, enabling maximum utilization of nutrients from milk and dairy products. Hence, understanding of these key structure elements and their biological function, and their interaction with (micro-)nutrients is key to creating products that fit in a healthy and sustainable diet.
Effie Tsakalidou (Agricultural University of Athens, Greece)
Arla Foods amba, Denmark
Angella Velazquez1,3, Marie Hennetier2, Paulo Peixoto1, Guillaume Delaplace1, Manon Hiolle3
1 France National Institute of Agronomical Research (INRA) - Unité Matériaux et Transformation (UMET), équipe Processus aux Interfaces et Hygiène des Matériaux (PIHM), Université de Lille
2 Ecole d'Ingenieurs de PURPAN, Toulouse, France
3 Ingredia Dairy Experts, Arras, France
The casein micelle is a structure that dissociates at the isoelectric point (pH 4.6). The prevention of its dissociation can be achieved by the formation of covalent cross- links with the transglutaminase (mTGase). We evaluated the effect of mTGase cross- linking to improve the stability of the casein micelle in an acidic environment.
-Cross- linking performed at neutral pH induced a decrease in the size and an increase in the apparent density of the micelles.
-The decrease of pH (3.0) of non-cross-linked caseins are completely disrupted, while cross-linked particles were denser, more compact, and had a bigger molar mass than the native micelle as a function of the cross-linking degree.
-Highly cross-linked aggregates (pH 3.0) possess a spherical conformation that is rather constant and close to the native micelle (Rg/Rh= 0.72 -0.81) regardless of the molar mass and size. The non-cross-linked particles are very polydisperse, as the ratio Rg/Rh varies as a function of the molar mass and the size.
- The apparent viscosity (pH 3.0), measured at the value given at a shear rate of 150 s-1 decreases as a function of the incubation time and enzyme concentration.
Caseins represents about 80% of the proteins in milk. Most of the sports and nutritional acidic beverages uses whey or vegetal protein as the base on formulations. It is therefore relevant to explore different ways to stabilize the caseins in an acidic medium and to study the structural changes linked to these modifications.
Thea Lykkegaard Møller1, Søren Bang Nielsen2, Milena Corredig1
1 Department of Food Science, Aarhus University, Denmark
2 Arla Foods Ingredients, Denmark
Membrane filtration is increasingly employed as a gentle process to fractionate individual milk components. This is bringing new opportunities to create new ingredients, by changing the compositional balance between soluble and colloidal phases, and modulating their permeation through the membranes. Although the dissociation of caseins upon pH and temperature conditions has been studied in great detail, most of the research reported has been carried out with skim milk. The aim of this work was to assess if there are differences in the micellar dissociation of caseins and minerals when skim milk is depleted of whey proteins. Native casein micelles were resuspended in skim milk serum (containing whey proteins (WP)) or in ultrafiltration permeate, milk serum without whey proteins. The dissociation behavior of the casein micelles as a function of pH and temperature was studied.
Data showed that the absence of WP in the serum phase caused a decreased release of κ- and α-caseins in response to cooling and pH decrease. The results suggested that WP interact with micellar caseins also in the absence of heating treatment. These results are relevant for dairy industries in which filtration processes are used to separate specific fractions of the skim milk protein pool.
Arantza Garcia1,2, Arno Alting2, Thom Huppertz2,3
1 IS-FOOD, Public University of Navarra, Spain
2 FrieslandCampina, The Netherlands
3 Wageningen University, The Netherlands
Calcium chelators are widely used in the dairy industry to modify physical properties of milk systems, like heat stability. They work by sequestering calcium ions from the continuous phase, modifying the electrostatic environment and the dissolution of calcium from the micelle, altering the mineral equilibrium. In this work, the influence of sodium hexametaphosphate (SHMP), a strong calcium chelator with 6 negative charges, on heat-induced changes in micellar casein (MC) during UHT treatment and retort treatment was investigated. SHMP was found to simultaneously bind free calcium ions and calcium from colloidal calcium phosphate nanoclusters, but also to bind to caseins (CN). These interactions promote several changes in the MC system, such as an important increase in viscosity and solubilization of micellar casein. During the heat treatment, the SHMP was hydrolyzed and, as a consequence, there was a notable decrease in pH. The formed complexes of SHMP-CN were broken on heat treatment and this induced an important reduction in viscosity. Another factor that contributed to these effects is the intensity of the heat treatments.
This study aimed to better understand the heat-induced changes of SHMP on micellar solutions. The SHMP can be used to improve heat stability and increase the shelf-life of micellar casein concentrate-based systems.
Jiangnan University, China
Miguel Aguilera Toro1, Amalie Vestergård Thomasen1, Yinghua Xiao2, Valentin Rauh2, Vittoria Piccini2, Lisbeth Truelstrup Hansen3, Martin Laage Kragh3, Lars Wiking1, Nina Aagaard Poulsen1, Lotte Bach Larsen1
1 Department of Food Science, Aarhus University, Denmark
2 Arla Foods amba, Denmark
3 Food Microbiology and Hygiene Research Group, Technical University of Denmark, Denmark
One of the main problems in UHT production is the spoilage by exogenous enzymes from psychrotrophic microorganisms. Among these, AprX, a thermoresistant protease produced by Pseudomonas, is considered the most prolific and relevant. Prediction of the spoilage potential of Pseudomonas populations present in raw milk samples is a coveted analytical technology by the dairy industry. However, the high proteolytic and genetic variability of Pseudomonas strains is a challenge when trying to implement a detection method.
In order to understand the complex differences between strains, 59 Pseudomonas strains were tested for proteolytic activity before and after simulated UHT treatment. A high heterogeneity was found between strains. It was assessed that 32% were highly proteolytic, 29% intermediate and 39% low or no proteolytic. Furthermore, most of the strains showed a high residual activity after the lab-scale UHT treatment.
In addition, RNA expression of aprX was assessed by qPCR in selected Pseudomonas strains and correlated to proteolytic activity with promising results.
The knowledge generated in this project will help to understand better the spoilage of UHT milk by Pseudomonas. Prediction of spoilage potential will allow the dairy industry to be more efficient when handling, processing, storing and distributing UHT milk. Additionally, the optimization of the production of UHT milk will reduce the volume of wasted product and the overall environmental impact.
Santhoshani Thiyaga Saumya Kumarihami Warakaulle, Afaf Kamal-Eldin1
1Department of Food Science, United Arab Emirates University, United Arab Emirates
The significance of proteolytic effect of plasmin on camel milk has remained unexamined, thus forming the objective of this study using primarily HPLC to follow changes in milk exposed to plasmin. Fresh pasteurized camel and cow milks were centrifuged at 8000 rpm at 4°C for 15 minutes to remove the fat. Milk samples 160 mL were treated with plasmin 0.01 U at 37°C for 0, 3, 6, 12, 24, 36, 48, and 72 hours and analyzed by HPLC. The separation of milk protein was performed in a Poroshell 300SB C8 column and eluates were monitored at 214 nm by DAD detector. Significant peaks were observed to be eluted from 10 minutes up till 18 minutes. After 12 hours of incubation, many new small peaks were observed, at the early chromatogram for camel milk but not for cow milk and the hydrolysis of camel milk caseins was more compared to cow milk. The casein peaks were reduced and the hydrolysis peaks were increased with hydrolysis time.
The examination of the enhanced proteolytic process that occurs in camel milk as compared to other milk types during plasmin activity may reveal the reasons behind the unique texture of the camel milk products and enabling the identification of resulting proteolytic products. Thus, the information gained may prove of significant use in the optimization of protocols in the camel milk industry.
Maria Tsevdou, Thaleia Vintzilaiou, George Dimopoulos, Athanasios Limnaios, Petros Taoukis1
1Laboratory of Food Chemistry & Technology, School of Chemical Engineering, National Technical University of Athens, Greece
Sweet whey (SW) is valorized via the production of soft cheeses or feed, in bioethanol production, and/or the production of whey protein concentrates and isolates. The study aims to investigate whether SW can be alternatively used for the production of yogurt-like products, and for this purpose, Pulsed Electric Fields (PEF) and Transglutaminase (TGase) pretreatment of SW was investigated. SW samples of 3.5-10% w/w protein content were prepared using skim milk powder. Mixtures were thermally treated (Control), and then subjected to PEF and/or TGase treatment. The mixtures were inoculated with yogurt starter culture, incubated until pH end point, and then evaluated in terms of acidification kinetics, and quality parameters. Results indicated that in order to produce acid gels from SW with equal or even improved quality properties than those of products from raw milk, fortification of SW with milk powder is necessary, and that mainly PEF and secondarily TGase treatment are capable of improving the characteristics of the final product. Particularly, samples prepared from SW mixtures followed by PEF and TGase pretreatment at 500 pulses exhibited the most improved quality attributes.
The reuse of SW in dairy-based products may constitute a useful alternative for the valorisation of cheese industry by-products.
Wageningen University & Research, The Netherlands
Effie Tsakalidou, Ulf Andersen, Markus Stieger and Peng Zhou