Thom Huppertz Principal Scientist, Dairy and Ingredient Technology, NIZO food research Inge Gazi Project Manager, NIZO food research Milk protein concentrate functionality through optimised product-process interactions Milk has long been known as an excellent source of nutrition, not only for the neonate, but for people of all ages. In addition to direct consumption in the form of liquid milk, it is also processed into a wide variety of other, widely popular dairy products, such as cheese, yoghurt and other fermented dairy products, all of which are found in a wide diversity of local variants throughout the world. In addition, a wide range of ingredients are produced from milk, including milk fat, lactose and derivatives thereof, such as galacto-oligosaccharides, and a wide variety of milk protein ingredients. Of the dairy ingredients, milk protein ingredients currently represent the highest economic value, despite the fact that concentrations of lactose and fat are typically higher in milk than those of lactose. Within the wide range of milk proteins, a wide variety of ingredients can be found, isolated either directly from milk or from whey. Milk protein ingredients may consist of high purity individual proteins, protein classes, or blends thereof. In addition, distinction should be made between intact proteins and protein hydrolysates. The latter may be applied in hypoallergenic New Food, Volume 18, Issue 1, 2015 12 www.newfoodmagazine.com
Figure 1: Schematic process for milk protein concentrate manufacture infant formulas, for example. In the class of milk protein ingredients, milk protein concentrates (MPCs) present a relatively recent arrival. Nonetheless, since their introduction into the market, they have found a wide range of applications, including yoghurt, cheese, processed cheese, ice cream, infant formula, clinical formulations and nutritional Considerable research effort in both industry and academia has been dedicated to understanding factors causing reduced solubility of MPCs and possible solutions to the problem beverages. Both more extensive use within these product categories and expansion into other product categories remains ongoing, further expanding the success of this class of ingredients. Within this range of applications, MPCs confer a wide range of functionalities, including emulsification, viscosity, gelation and water binding. Figure 2: Typical composition (protein, lactose and ash) of different milk protein concen - trates. The number reflects the protein content in dry matter. Figure 3: Lowest and highest values for compositional and physicochemical properties observed in a benchmarking study of 32 commercial milk protein concentrates Unlike other milk protein ingredients, such as whey protein concentrate (WPC), whey protein isolate (WPI), micellar casein isolate (MCI) or caseinates, the ratio of the different milk proteins in MPCs is unchanged compared to that of the milk it is prepared from. This is the case because of the ultrafiltration (UF) process used in MPC manufacture (Figure 1), which concentrates the proteins from the skim milk in the retentate, whereas lactose and soluble salts are removed in the permeate. The concentration factor achieved determines the concentration of protein in dry matter. With concentration by UF, up to 70% protein in dry matter can be achieved, with viscosity of the concentrate becoming a limiting factor at higher concentrations. If higher concentrations of protein are required, diafiltration can be applied, to result in additional removal of lactose and salts. Extensive diafiltration can eventually achieve a protein in dry matter content of ~90%. After UF, the retentates are subsequently evaporated to a higher dry matter content and spray dried into a powder. Within the market, MPCs with a variety of protein contents are available, ranging from 56-85% protein in dry matter. In addition, milk protein isolate (MPI) with at least 90% protein in dry matter is available. Typically, MPCs are denoted with their protein content. For instance, MPC60 and MPC80 contain 60% and 80% protein respectively, on a dry matter basis. With increasing protein content, lactose content decreases, whereas ash content remains constant (Figure 2). The constant ash content is due to the fact that parts of the minerals are removed in the serum, but part is also bound to the proteins and therefore concentrated. Within the process of producing MPCs, the main variables are the extent of heat www.newfoodmagazine.com 13 New Food, Volume 18, Issue 1, 2015
Figure 4: Correlation between the protein content and nitrogen solubility index of 32 comm - ercial milk protein concentrates A survey conducted by NIZO food research on 32 commercial samples of MPCs highlighted strong differences between MPCs, both from a compositional as well as a functionality perspective Figure 5: Nitrogen solubility index after 0 and 12 months of storage for 32 commercial milk protein concentrates grouped into classes of low-protein (<65% protein in dry matter), medium protein (65-75% protein in dry matter) and high protein (>75% protein in dry matter) protein denaturation), solubility, as well as functional properties (emulsification, acid gelation, foaming, suspension stability, and heat stability). In addition, changes in properties, most notably solubility, were also monitored during storage for 12 months. The aim of the survey was to gather insights into treatment applied to the milk, the degree of concentration and variations throughout the MPC market and to evaluate regional diafiltration applied, the dry matter content achieved in evaporation differences in MPC quality. and the conditions applied during spray drying. The combination of these factors determines the ultimate compositional and functional properties of the product, which vary widely between commercial samples. A survey conducted by NIZO food research on 32 commercial samples of MPCs highlighted strong differences between MPCs, both from a compositional as well as a functionality perspective. Within this survey, 32 samples were collected from suppliers in North America, Europe and Oceania to provide a representative overview of the market. MPCs with declared protein contents from 56%-85% protein in dry matter were included in the survey. Samples were collected fresh from manufacturers and subsequently analysed for compositional properties (gross composition, mineral composition, protein composition), powder properties (particle size, dispersibility, bulk Figure 6: Scanning electron micrographs of skim milk powder and milk protein concentrates containing 60 or density), physicochemical properties (ph, 80% protein in dry matter New Food, Volume 18, Issue 1, 2015 14 www.newfoodmagazine.com
Figure 3 (page 13) outlines the extent of variation observed in the survey of commercial samples of MPCs in all aspects. The variation in protein content from 55-85% outlines that the entire commercial spectrum of MPCs was included. Large variations were observed in powder moisture, calcium and sodium content, but, for all of these, no direct correlation was observed with protein content of the powder. The level of denaturation of the main whey protein, β-lactoglobulin, varied from 20-80%, i.e. from low heat to high heat when considering them as milk powder equivalents, which impacts functional properties and solubility. Protein denaturation may have occurred during various stages of processing, i.e. during heat treatment, evaporation and drying. Like all protein ingredients, solubility is the crucial prerequisite for functionality of the ingredient. Solubility was determined as both dispersibility of the powder and the nitrogen solubility index (NSI the solubility of the protein fraction alone). For both parameters, a large variation was observed within the survey, from very low to very high values. For solubility as determined by the NSI, a negative correlation was observed between protein content of the MPC and NSI; meaning high protein MPCs were found to have a lower NSI than low protein MPCs (Figure 4, page 14). However, it should also be noted that for a given protein content, large variations in NSI were observed. For instance, for MPCs with protein contents in the range 80-85%, NSI values ranging from <25% to >80% Figure 7: Heat coagulation time (at ph 6.7 and 140 C) of milk protein concentrates of different protein content suspended at a protein content of 3.5% (w/w). All MPCs were prepared from the same batch of milk under identical processing conditions The final desired functional properties like emulsification, gelation, heat stability or foaming are the key selection criteria for the end user were found, indicating extremely large differences between MPCs. Further to these differences in solubility apparent soon after manufacture, solubility also was found after storage of the samples. Particularly high protein MPCs were found to be prone to loss in solubility during storage (Figure 5, page 14). Further study, on a set of MPCs with varying protein contents prepared under controlled conditions from a single batch of milk has confirmed that high protein MPCs are more prone to losses in solubility. These losses in solubility are accelerated strongly at higher storage temperatures. Such effects Trends in Food Flavour April 13-17 2015 A comprehensive week long programme, combining cutting edge flavour training and the inaugural Trends in Food Flavour conference, has been launched by the University of Nottingham. Delegates can attend three days of training at the University s Food Sciences Division (April 13-15 2015), learning how the science and application of flavour technology can be instrumental in successful food and drink innovation. They will then join internationally renowned academic and industry experts from the UK, Europe, China and the USA at a 2 day Trends in Food Flavour conference (April 16-17 2015), reviewing current drivers in food flavour and debating the latest developments in research, technology and sustainability. The conference, which can also be booked as a standalone event, will feature sessions on flavour and the world market, product applica - tion, healthy eating, research and technological developments. Confirmed speakers include Stephen Parry, Chair of the Food Sector KTN, Professor Jianshe Chen (Zhejiang Gongshang University), and industry experts from companies including Mars, Sensient, Cara Technology Ltd, Nestle, Sensory Dimensions and Wrigley. Further information and registration for the training programme and the conference is available at www.nottingham.ac.uk/facts or email facts@nottingham.ac.uk. Part funding for the five day course fee is available for most UK industry delegates through the AgriFood Advanced Training Partnership. Find out more by visiting www.agrifoodatp.ac.uk/aatp/courses/food/ food-flavour.aspx, where you can also apply www.nottingham.ac.uk/facts online for a bursary. Alternatively, please contact jennifer.drury@nottingham.ac.uk or call 0115 951 6132. www.newfoodmagazine.com 15 New Food, Volume 18, Issue 1, 2015
are particularly relevant considering that most MPCs are produced in Oceania, North America and Western Europe and a large proportion of these products are exported by boat to Asian markets. Hence, tempera - tures of >40 C are not uncommon during transport of MPCs. Considerable research effort in both industry and academia has been dedicated to understanding factors causing reduced solubility of MPCs and possible solutions to the problem. Primary areas of attention here have been the influence of drying conditions, ph and mineral balance. As outlined in Figure 6 Figure 8: Heat coagulation time (at natural ph and 140 C) of 32 commercial milk protein concentrates suspended at a protein content of 3.5% (w/w) (page 14), powder particle structure of high protein MPCs differed considerably from those of skim milk powder. beverages which are subjected to sterilisation or UHT treatment. A wide MPCs showed smaller powder particles, less agglomeration, as well as a variation in heat stability was also observed when heating the commercial partial collapse of powder particle structure, all of which could hinder MPCs from the benchmark study at a protein content of 3.5% at 140 C at reconstitution. Because of the higher protein content and lower lactose their natural ph (Figure 8). Heat coagulation times varied from zero to >40 content of MPCs, the concentrate before drying has a lower solid content minutes. Similarly large variation was observed in the hardness of yoghurttype gels (Figure 9) and the viscosity (Figure 10) of suspensions of the 32 commercial MPCs. The wide variation observed in functional properties of MPCs necessitates both careful process control by the manufacturer and careful ingredient selection by the end user. The main factors controlling this are schematically outlined in Figure 11 (page 17). The final desired functional properties like emulsification, gelation, heat stability or foaming are the key selection criteria for the end user. In achieving any of these, solubility of the powder is naturally key. Again, it should Figure 9: Hardness of yoghurt-type acid gels (4.5% protein) prepared from 32 commercial milk protein concentrates be noted that storage time and temperature than a skim milk concentrate before drying. As a result, different drying are strong determinants here. Compositional and physicochemical patterns will arise. A further consideration in choosing suitable properties like protein and mineral content and composition, protein drying conditions is the low heat stability of MPCs due to an inherently high denaturation and moisture content are strong determinants here. These calcium ion activity. Hence, high temperature, for example during drying, in turn are strongly influenced by both initial milk composition and combined with high protein content can lead to extensive heat-induced quality and by the conditions applied during the processing steps (heat coagulation of proteins, which is a major cause of poor solubility of MPCs. treatment, UF, evaporation and spray drying). When applied properly, Reducing calcium ion activity by ph control, for example, the addition of a these processing steps facilitate the creation of a range of MPCs with calcium binding agent or the removal of calcium by treatment with an ion exchange resin, present options for increasing stability of MPCs to heat induced coagulation. Figure 7 (page 15) shows how the heat stability of MPCs, as determined by the heat coagulation time at ph 6.7 for suspensions containing 3.5% protein, is affected by the protein content of MPC powder. Whereas low protein MPCs, like skim milk, can be heated extensively at this temperature, high protein MPCs are highly susceptible to heat coagulation at this temperature, which should be taken into Figure 10: Viscosity of suspensions of suspensions (10.0% protein) prepared from 32 commercial milk account when applying these products in protein concentrates New Food, Volume 18, Issue 1, 2015 16 www.newfoodmagazine.com
Figure 11: Factors influencing the functionality of milk protein concentrates The wide variation observed in functional properties of MPCs necessitates both careful process control by the manufacturer and careful ingredient selection by the end user excellent functionality. However, a cautionary note is also required that compared to skim milk powder, for example, MPCs are far more susceptible to processing induced instabilities. Therefore, MPCs and related products are likely to remain a key product category of research in both academic and industrial research from a processing and functionality perspective. About the Authors Dr Thom Huppertz works as a Principal Scientist, Dairy and Ingredient Technology at NIZO food research (Ede, the Netherlands). He holds an MSc in Dairy Science from Wageningen University (The Netherlands) and a PhD in Dairy Science from University College Cork (Ireland). His research focuses on the physical chemistry of dairy products, with particular emphasis on the protein functionality and product-process interactions. In addition, he is an Adjunct Professor in Dairy Science and Technology at South Dakota State University and editor of the International Dairy Journal. Inge Gazi is a Project Leader at NIZO food research (Ede, the Netherlands). Her work focuses on protein functionality, with emphasis on dairy proteins. She has a BSc in Food Science and Engineering from Dunarea de Jos University (Romania) and an MSc in Dairy Science and Technology from Wageningen University (The Netherlands). New Food, Volume 18, Issue 1, 2015 Visit us at Anuga Foodtec, Hall 8.1, Stand E98 F99 AVENTICS GmbH Ulmer Straße 4 30880 Laatzen, Germany www.advanced-valve.com info@aventics.com Tel +49 511 2136-0 THE NEXT GENERATION HYGIENIC DESIGN ICS-D1 NCT-PK MH1 CL03 Geert-Jan Stöver, General Manager Netherlands, has long seen excellent sales figures in his native country, particularly in the food industry. Surfaces that prevent the adhesion of residues and microscopic organisms, no incidental contact of lubricants with the product, and simple cleaning and disinfection to ensure food safety in the production process: The food industry demands safe, ultra- hygienic, and efficient automation solutions. Hygienic design is the result of a series of meticulously planned and executed steps: with a hygienic design, suitable materials, and the chemical resistance of our individual components, applications in even the most sensitive of areas pose no problems. AVENTICS has outstanding expertise and many years of experience in this field.