Determination of limiting factors in a novel superconcentration-granulation based dairy powder manufacturing process

An innovative approach based on superconcentration and granulation was investigated to manufacture dairy ingredients at lab-scale. A wet mass characterization technique, which measured agitator current consumption, was developed to study cohesiveness of super-concentrated products at various dry matter (DM) contents. For all ingredients, a composition-dependent cohesive phase was observed as DM increased, which was typified by a sharp rise and subsequent fall in power consumption. The effect of powder back-mixing on granulation was studied using three superconcentrate:powder (w/w) ratios (1:0.8, 1:1 and 1:1.2, respectively). Minimum powder addition rate for successful granulation was related to DM content at the end of the cohesive phase. Granulated powders had larger particle size, higher densities, lower porosities and enhanced flow properties compared to commercial spray-dried powders. The lab-scale model provided useful information on physical properties and limits during superconcentration and granulation, which increases the scientific knowledge relating to this novel powder production approach.Industrial relevanceSpray drying is the most widely utilized powder manufacturing technology in the dairy industry, especially for producing ingredients and nutritional products. It is, however, extremely energy intense and therefore spray drying of high-volume, low-value dairy streams such as permeate represents a poor use of resources for industry. An alternative spray dryer-free process has been developed for such streams, with significant savings. This process is based on superconcentration of streams to DM content in excess of what is typically seen in a spray-drying process (up to 80% w/w DM) followed by granulation achieved by back-mixing of finished product and, finally, drying of granules. However, little information is available on how various dairy ingredients behave in this system. Therefore, a novel lab-scale production model was produced to determine limits of superconcentration and granulation behavior of various ingredients. This work provides vital information and represents the first step in a larger program which will culminate in demonstration of the industrial applicability of the new approach for drying of various dairy streams.     

The Distribution of Fat in Dried Dairy Particles Determines Flavor Release and Flavor Stability

Dried dairy ingredients are utilized in various food and beverage applications for their nutritional, functional, and sensory properties. Dried dairy ingredients include milk powders of varying fat content and heat treatment and buttermilk powder, along with both milk and whey proteins of varying protein contents. The flavor of these ingredients is the most important characteristic that determines consumer acceptance of the ingredient applications. Lipid oxidation is the main mechanism for off‐flavor development in dried dairy ingredients. The effects of various unit operations on the flavor of dried dairy ingredients have been investigated. Recent research documented that increased surface free fat in spray dried WPC80 was associated with increased lipid oxidation and off‐flavors. Surface free fat in spray‐dried products is fat on the surface of the powder that is not emulsified. The most common emulsifiers present in dried dairy ingredients are proteins and phospholipids. Currently, only an association between surface free fat and lipid oxidation has been presented. The link between surface free fat in dried dairy ingredients and flavor and flavor stability has not been investigated. In this review, some hypotheses for the role of surface free fat on the flavor of dried dairy ingredients are presented along with proposed mechanisms.     

Global Market for Dairy Proteins

This review examines the global market for dairy ingredients by assessing the global demand for dairy products in relation to major dairy ingredient categories. Each broad category of dairy ingredients is reviewed including its definition, production and trade status, key applications, and future trends. Ingredient categories examined include whole and skim milk powders (WMPs, SMPs), whey protein concentrates (WPCs) and whey protein isolates (WPIs), milk protein concentrates (MPCs) and milk protein isolates (MPIs), caseins, and caseinates. Increases in world population and improvements in socioeconomic conditions will continue to drive the demand for dairy products and ingredients in the future. Dairy proteins are increasingly recognized to have nutritional and functional advantages compared to many protein sources, and the variety of ingredients with different protein concentrations, functionality, and flavor can meet the needs of the increasingly global dairy consumption. A thorough understanding of the variety of ingredients, how the ingredients are derived from milk, and how the demand from particular markets affects the supply situation are critical elements in understanding the current ingredient marketplace.     

Why semicarbazide (SEM) is not an appropriate marker for the usage of nitrofurazone on agricultural animals

A comprehensive global database on semicarbazide (SEM) in foodstuffs and food ingredients is presented, with over 4000 data collected in foods such as seafood (crustaceans, fish powders), meat (beef, chicken powders), dairy products (e.g. raw milk, milk powders, whey, sweet buttermilk powder, caseinate, yoghurt, cheese), honey and other ingredients. The results provide evidence that the presence of SEM in certain dairy ingredients (whey, milk protein concentrates) is a by-product of chemical reactions taking place during the manufacturing process. Of the dairy ingredients tested (c. 2000 samples), 5.3% showed traces of SEM > 0.5 µg/kg. The highest incidence of SEM-positive samples in the dairy category were whey (powders, liquid) and milk protein concentrates (35% positive), with up to 13 µg/kg measured in a whey powder. Sweet buttermilk powder and caseinate followed, with 27% and 9.3% positives, respectively. SEM was not detected in raw milk, or in yoghurt or cheese. Of the crustacean products (shrimp and prawn powders) tested, 44% were positive for SEM, the highest value measured at 284 µg/kg. Fish powders revealed an unexpectedly high incidence of positive samples (25%); in this case, fraudulent addition of shellfish shells or carry-over during processing cannot be excluded. Overall, the data provide new insights into the occurrence of SEM (for dairy products and fish powders), substantially strengthening the arguments that SEM in certain food categories is not a conclusive marker of the use of the illegal antibiotic nitrofurazone.     

Enterobacter sakazakii survives spray drying

Four strains of Enterobacter sakazakii were inoculated into 35% reconstituted skim milk at 10⁷ and 10² cfu/g dry wt. After spray-drying in a Buchi mini spray drier (inlet 160°C and outlet 90°C), the resulting powders were analysed for E. sakazakii by enrichment and enumeration. In all cases, E. sakazakii survived the spray drying process and were detected in the powders with a low inoculum and enumerated in all the powders with the high inoculum for at least 12 weeks. The results emphasize that the controls in place to prevent E. sakazakii from getting to the spray drier are essential.     

In-situ lecithination of dairy powders in spray-drying for confectionery applications

Powders are essential ingredients of chocolate. In particular for milk chocolate milk and whey powders are important, together with sucrose, lactose and cocoa solids. During processing to maintain a good flow of the molten chocolate mass, particles with hydrophilic surfaces, such as dairy powders and sugars, are coated with a surface-active compound. Only lecithin and polyglycerol polyricinoleate (PGPR) (at a limited level) are allowed in chocolate, and as these are expensive as little as possible is added, whilst maintaining rheological properties. Conventionally, lecithin is added during conching, and through the intense kneading of the chocolate mass it is distributed throughout the mass. Usually about 0.5% is added, although the level depends upon the composition of the chocolate. Here we present a new approach to lecithination of spray-dried milk and lactose powders, which we call in-situ lecithination. It has been found that the surface of a spray-dried powder is dominated by any surface-active species, and in a competitive situation, the most rapidly adsorbing species dominates. This behaviour is utilised when lecithin is added to the spray-dryer feed, and through the competitive adsorption of surface-active agents during the drying process, it dominates the powder surface composition as measured by X-ray photoelectron spectroscopy (XPS). This is also seen in differences in sedimentation rate when the powders are mixed with cocoa butter to assess the rheological properties of the powder dispersions. The effect was large for lactose powders, but smaller for skim milk powder and whey powder.     

Effects of different saccharides on the microstructure and functional properties of protein in goat milk during processing

This study investigated the changes in the characteristics of goat milk protein in the presence of trehalose, chitooligosaccharide and pectin during two practical dairy processing operations of pasteurisation and spray drying. The highest denaturation temperature and the largest particle size of milk protein were found in goat milk added with pectin after pasteurisation. And particles with more uniform and compact morphology were observed in goat milk protein with these three saccharides. An elevated emulsifying activity index of 24.37 m/g⁻² was observed in protein after spray drying due to chitooligosaccharide. And the foam stability was also improved significantly in the presence of trehalose and pectin during pasteurisation. During spray drying, saccharides showed the stabilizing effect on goat milk protein. This study revealed a complex interplay between the type of saccharides and the processing operation applied to goat milk, which might be of great significance for the production and processing of goat milk.     

The thermostability of spray dried imitation coffee whiteners

Imitation creamer formulations were spray dried and agglomerated on a pilot scale tall-form drier in order to evaluate the stability of the resulting powders when added to hot aqueous coffee solutions. The study explored the effects of different protein ingredients (sodium caseinate; milk protein concentrate; whey protein concentrate; milk proteinate; soluble wheat protein) in combination with non-protein emulsifiers and disodium hydrogen orthophosphate. Adaptation of coffee stability test methodology was necessary to take account of the presence of significantly more 'floaters' in the case of imitation coffee whiteners which did not sediment during centrifugation. A new non-dairy protein, soluble wheat protein, proved to have exceptional stabilizing ability compared to all other protein ingredients evaluated. Sodium caseinate performed the best out of the dairy proteins, while formulations incorporating milk protein concentrate tended to be the least stable. When working with whey protein concentrate as the principal ingredient source, an emulsifier system based on mono/diglycerides was inadequate, and it was necessary to use a combination of polysorbate and sodium stearoyl lactylate in its place.     

Lactose-free skim milk and prebiotics as carrier agents of Bifidobacterium BB-12 microencapsulation: physicochemical properties,survival during storage and in vitro gastrointestinal condition behaviour

Bifidobacterium BB-12 was microencapsulated by spray drying using lactose-free milk, lactose-free milk and inulin, and lactose-free milk and oligofructose, resulting in powders 1, 2 and 3, respectively. The highest encapsulation yield (88.01%) and the highest bifidobacteria viability during 120 days of storage were noted for spray-dried powder 2. Spray-dried powders 1 and 3 show a higher tendency to yellow colour. After being submitted to in vitro-simulated gastrointestinal conditions, the best probiotic survival rate result was found for spray-dried powder 3 (87.59%). Therefore, spray-dried powders containing prebiotics were the most appropriate combinations for microencapsulation of Bifidobacterium BB-12 and maintenance of cell viability during storage and gastrointestinal system, showing great potential to be used in lactose-free dairy products.     

Proposal of a new reference method to determine the water content of dried dairy products

The water content of milk powders is “officially” determined by drying. The result of drying techniques is, however, the mass loss the sample undergoes under the conditions applied. No differentiation between water and other volatile substances is made. A particular problem is the lactose that is present in all dried dairy products. The α-form contains one mole of water of crystallisation per mole. This water fraction is not determined completely by ordinary drying methods. How much of the crystallised water is detected depends very much on the conditions applied. The entity determined by drying is not defined. It is only a tradition to regard the mass loss thus detected as water content. More and more, however, the expression moisture content is used for the result of drying techniques, although this term is also unsatisfactory and misleading. The discrepancy between mass loss on drying and water content becomes more pronounced when the product has high crystalline lactose content, such as whey powders or lactose itself. In these cases the difference between mass loss and water content can be quite significant. The existing reference method for moisture determination in dried milk is therefore not reasonably applicable on dairy products with high crystalline lactose content. It could be shown that the water content of dried dairy products can be determined using the Karl Fischer titration independently of the level of crystallisation water. The results are not only more accurate but also more precise than those obtained by the reference drying method. It is therefore proposed to introduce the Karl Fischer titration as reference method for dried dairy products.     

Fire and explosion hazards associated with milk spray drying operations*

Recent reports in the literature indicate that incidents involving fires and explosions in the spray drying of milk products are increasing in number. While milk powder is not highly explosible, the conditions for a dust explosion, apart from the ignition source, are almost always present in certain areas of a spray drying system during its normal operation. Self-ignition of deposits is known to be possible at the high temperatures in a spray drier. At best, this can cause product degradation and discoloration and at worst it can provide the source of ignition for an explosion. This paper is an attempt to draw together recent work on fire and explosion prevention and protection for milk powders.     

PEKMEZ-DAIRY DESSERTS FORTIFIED WITH SPRAY-DRIED DAIRY POWDERS: EFFECTS OF THE INTERACTION BETWEEN SKIM MILK POWDER, YOGHURT POWDER AND BUTTERMILK POWDER BY A MIXTURE DESIGN APPROACH

A mixture design approach was used to evaluate the interactions between skim milk powder (SMP), yoghurt powder (YP) and buttermilk powder (BMP) on rheological and sensory properties of dairy dessert mixture samples (DDMS). DDMS was prepared with pekmez powder, which was obtained by spray drying of pekmez, also known as concentrated grape molasses. Among the dairy powders, YP was the component that had the most effect on the viscosity of DDMS. The liking of the panelists was more prominent for the dairy dessert samples including the higher concentrations of YP. Optimum values of SMP, YP and BMP in the mixture were found to be 12–46%, 41–90% and 0–39%, respectively with respect to sensory properties.

PRACTICAL APPLICATIONS

The compositional properties of dairy powders can be changed by their usage at particular combinations, which could give rise to an improvement in their rheological and sensory properties. Such modifications would be of great economical importance to food industry. Dairy powders can be used to improve these properties when optimum combination levels of these dairy powders are taken into consideration. Therefore, information obtained in this study may be useful in practical industrial food product process monitoring and development.     

Effects of Co-spray Drying of Surfactants with High Solids Milk on Milk Powder Wettability

Dairy industries often spray lecithin, a food-grade surfactant, to spray-dried whole milk powders while fluidisation to produce instant powders. Though adding surfactant to milk feed was often reported to improve the wettability of dried powders, this approach was not favourably used. The present study investigated the effects of surfactant addition into high solids milk feed before drying on the wettability of whole milk particles. Adding either 0.1 wt.% Tween 80 or 0.1 wt.% lecithin to un-concentrated whole milk led to a significant wettability improvement of spray-dried powders. At higher feed solids levels of 23 and 33 wt.%, the wetting process of pure milk powders was comparatively rapid, but the surfactant-added powders showed similar wettability to the pure milk powders. The development of powder wettability as drying progressed was investigated using single droplet-drying technique for 32 and 43 wt.% whole milk in the presence and absence with surfactants. The technique captured an advanced shell formation during drying of higher solids milk. The wettability of surface shells formed by surfactant-added milk was similar to those formed by pure milk throughout drying, from initial shell formation to final drying stage. By contrast, coating surfactants on the outer layer of particles being dried could substantially improve wettability. The rapid shell formation and the slow material diffusion owing to the high medium viscosity were considered the main factors limiting the migration of surfactant molecules towards droplet surface during drying.     

Effects of ionic and nonionic surfactants on milk shell wettability during co-spray-drying of whole milk particles

Mixing surfactants with whole milk feed before spray drying could be a commercially favorable approach to produce instant whole milk powders in a single step. Pure whole milk powders obtained directly from spray drying often have a high surface fat coverage (up to 98%), rendering them less stable during storage and less wettable upon reconstitution. Dairy industries often coat these powders with lecithin, a food-grade surfactant, in a secondary fluidized-bed drying stage to produce instant powders. This study investigated the changes in wetting behavior on the surface of a whole milk particle caused by the addition of surfactants before drying. Fresh whole milk was mixed with 0.1% (wt/wt) Tween 80 or 1% (wt/wt) lecithin (total solids), and the wetting behavior of the shell formed by each sample was captured using a single-droplet drying device at intermediate drying stages as the shell was forming. The addition of surfactants improved shell wettability from the beginning of shell formation, producing more wettable milk particles after drying. The increase in surfactant loading by 10 times reduced the wetting time from around 30 s to <5 s. At the same loading of 1% (wt/wt; total solids), milk particles with Tween 80 were much more wettable than those with lecithin (<5 s compared with >30 s). We proposed that Tween 80 could adsorb at the oil–water interface of fat globules, making the surface fat more wettable, whereas lecithin tends to combine with milk proteins to form a complex, which then competes for the air–water surface with fat globules. Spray-drying experiments confirmed the greatly improved wettability of whole milk powders by the addition of either 0.1% (wt/wt) Tween 80 or 1% (wt/wt) lecithin; wetting time was reduced from 35 ± 4 s to <15 s. To the best of our knowledge, this is the first time that a dynamic droplet drying system has been used to elucidate the complex interactions between ionic or nonionic surfactants and milk components (both proteins and fat), as well as the resultant effect on the development of milk particle functionality during drying.     

Invited review: The effect of native and nonnative enzymes on the flavor of dried dairy ingredients

Dried dairy ingredients are used in a wide array of foods from soups to bars to beverages. The popularity of dried dairy ingredients, including but not limited to sweet whey powder, whey proteins and milk powders, is increasing. Dried dairy ingredient flavor can carry through into the finished product and influence consumer liking; thus, it is imperative to produce a consistent product with bland flavor. Many different chemical compounds, both desirable and undesirable, contribute to the overall flavor of dried dairy ingredients, making the flavor very complex. Enzymatic reactions play a major role in flavor. Milk contains several native (indigenous) enzymes, such as lactoperoxidase, catalase, xanthine oxidase, proteinases, and lipases, which may affect flavor. In addition, other enzymes are often added to milk or milk products for various functions such as milk clotting (chymosin), bleaching of whey products (fungal peroxidases, catalase to deactivate hydrogen peroxide), flavor (lipases in certain cheeses), or produced during the cheesemaking process from starter culture or nonstarter bacteria. These enzymes and their possible contributions will be discussed in this review. Understanding the sources of flavor is crucial to produce bland, flavorless ingredients.     

Physical properties of goat milk powder with soy lecithin added before spray drying

In this study, physical characteristics of goat milk powder produced with the addition of soy lecithin at levels of 0 (control), 0.4, 0.8 and 1.0 g lecithin/100 g of total solids in concentrated milk before the spray drying process were investigated. Goat milk was pasteurised, concentrated at 40% of total solids, spray dried and packed in plastic bags under vaccum conditions. Lecithin addition decreased the wetting time of milk powders, although no influence was observed on dispersibility, water sorption, water activity and particle size distribution of the powders. Powders with higher levels of lecithin showed significantly lower brightness, with a greater intensity of yellow colour. It was concluded that lecithin addition before spray drying process at the minimal proportion in concentrated milk of 0.4 g lecithin/100 g of total solids in concentrated milk is useful for achieving more rapid wetting time of goat milk powder.     

Behaviour of homogenized fat globules during the spray drying of whole milk

The changes in milk fat globule size and fat globule surface proteins of both low-preheated and high-preheated concentrated milks, which were homogenized at low or high pressure prior to spray drying using a disc atomization drier, were examined. The average fat globule size (d₃₂) of the spray-dried milk powders was smaller than that of the corresponding concentrates, but a small proportion of very large globules (4–80 μm) was also formed during spray drying. As a consequence, total surface protein (mg protein g⁻¹ fat) increased due to the adsorption of casein micelles at the fat globule surface during spray drying. Confocal micrographs of the powders showed some apparent spreading of the fat on the surface of the powder particles, particularly when the concentrates were homogenized at low pressure. These results indicate disruption of the milk fat globules during spray drying, which consequently causes changes in the fat globule surface protein layer.     

Stability of cyclopiazonic acid during storage and processing of milk

The effect of refrigerated storage (4°C) of raw or processed milk on the stability of cyclopiazonic acid (CPA) in milk was investigated. CPA decreased by 1.4% following 4 days of simulating collecting, storing and transporting of contaminated (1 μg CPA ml⁻¹) raw milk. Storage at 4°C for 21 days, simulating retail milk, moderately reduced the CPA level by 5.8%. A similar trend of CPA decrease was observed in frozen and freeze dried milk stored at −18°C. However, in both products, less than 12% of CPA decreased in spite of a storage period of 140 days. The effect of processing milk on component separation of CPA was also studied. Simulating unsweetened condensed milk production by preheating 4 l contaminated milk to 100°C and concentrating under steam injection to 1.5 l led to a decrease of CPA by 39.7%. In contrast, very little CPA (0.7%) was lost from the production of evaporated milk using low temperature (60°C) heating under vacuum to remove water. CPA was stable in both concentrated and evaporated milks throughout an 8 weeks storage period at 4°C. There was no decrease of CPA during the manufacturing of milk powder by spray drying. Persistence of CPA during the above milk storage and processing methods confirmed the potential of CPA to reach consumers of dairy products when the mycotoxin was carried over into processed milks.     

WHAT THE FOOD INDUSTRY REQUIRES FROM DAIRY INGREDIENTS

The role of dairy-based ingredients in food manufacture is reviewed and the importance of safety in food materials, as well as that of nutritional value stressed. The problems of handling milk with its short storage life are considered and the competitive position of dairy ingredients and their alternatives is discussed. The advantages of milk and whey powders and the potential of casemates and proteins in recipe products is emphasized and the need for further technical research suggested.