Along with the increase in the fresh cheese production market, there is a concomitant increase in the volume of its by-product, lactic acid whey (LAW). This type of whey is especially rich in organic ...acids and ash content, making it more difficult to develop applications for human food. In view of its hygroscopicity, this type of whey is in fact clearly the most difficult to dry properly, and its high level of mineralization narrows its potential uses for nutritional reasons. The aim of this study was to evaluate the ability to use nanofiltration (NF) for the production of partially demineralized LAW powder with regard to the dryability of the concentrate and the quality of the powder at a semi-industrial scale. The strong selectivity of this demineralization process results in a 30% reduction in lactic acid content and a reduction of between 46 and 60% in monovalent ions. The dryability of the NF LAW concentrate is improved as well. Moreover, the energy cost of the overall process is reduced by 43%. These elements highlight the benefit of inserting an industrial NF step into the overall processing of LAW and should significantly contribute to the production of partially demineralized LAW powder.
•The semi-industrial scale-up of nanofiltered lactic acid whey drying is possible.•The results are similar to those obtained on a small pilot plant in the laboratory.•The nanofiltration of lactic acid whey reduces stickiness during drying.•The nanofiltration of lactic acid whey decreases the hygroscopicity of the powder.
Spray-drying is expected to be a cost-efficient way to produce probiotic powders. Indeed, a novel simplified process was recently reported, using concentrated sweet whey (30 wt %) as a sole medium ...for both growth and spray drying of probiotics. The feasibility of scaling up this process was validated in the present work with a semi industrial pilot scale spray dryer. A multi-stage mild-conditions drying process, coupling spray-drying with belt drying and fluid-bed drying, was also applied in this work, in which the final probiotic survival was improved to approximately 100% (>109 CFU g−1). The change of probiotic viability in the powders was monitored during a 6-month storage, which indicated that storage temperature and moisture content of powders play crucial roles in the stability of probiotic powders. Moreover, spray-drying afforded a strain-dependent enhancement of bacterial tolerance in simulated intestinal fluid, in comparison with fresh cultures.
•Concentrated sweet whey was used for both probiotic growth and spray-drying.•Drying was conducted at semi industrial pilot scale (500 L level).•Multi-stage drying coupled spray-drying, belt drying and fluid-bed drying.•High probiotic survival (∼100%) was obtained in multi-stage drying process.•Enhanced storage stability and protection towards digestion was observed.
The most frequently used technique for dehydration of dairy products is spray drying. This is an effective method for preserving biological products as it does not involve severe heat treatment and ...it allows storage of powders at an ambient temperature. Due to the variety and complexity of the concentrates to be dried, a more rigorous understanding of spray drying based on physico-chemical and thermodynamic properties has now become necessary. However, the current state of the art and knowledge do not allow determination of the parameters of spray drying of dairy products. The only way to determine these parameters is to perform several complex and expensive experiments with spray dryer pilots. In this study, a new method was developed to evaluate the ratio of bound to unbound water by using drying by desorption. The results, combined with thermodynamic and physico-chemical parameters (such as, absolute and relative humidity of air, total solids and temperature of concentrate, and air flow rate), provide more precise determination of certain spray drying parameters such as inlet air temperature and mass flow rate. More than 50 experiments were performed to correlate calculated and measured parameters in a pilot plant (Bionov) using water, skim milk, infant formula milk, caseinate maltodextrin and other food concentrates. The results showed that the difference between the calculated and measured inlet air temperature was less than 5%, the determination coefficient being close to 0.96.
The economic value of this system is obvious, because it is easy to anticipate the spray drying parameters by using a controller integrating the water availability of the concentrate and certain thermodynamic parameters. Software based on this step was developed (SD
2P
®, spray drying parameter simulation and determination) and registered at the APP (Association pour la Protection des Programmes).
Vacuum concentration and drying are valuable techniques for the removal of water and the resulting stabilization of most dairy and feed ingredients. In this study, we present methodology to calculate ...and compare the energy consumption for the production of dairy and feed powders at different processing stages of the dehydration process. The results show that the energy costs to produce 1 kg of dairy and feed powders were 6,120 and 20,232 kJ · kg ⁻¹ powder for pregelatinized starch and soy protein concentrate, respectively. For dairy products, the values were 9,072 and 15,120 kJ · kg ⁻¹ for fat-filled and demineralized whey powders, respectively. According to the type of product (biochemical composition, ratio of bound and free water) and process (demineralization, vacuum evaporation, lactose crystallization, roller and spray drying), the energy consumption for the production of powders could be calculated. These findings could be valuable for studies focusing on improvement of energy efficiency for dairy and feed processes.
•Droplet size varies in a complex way according to the distance to the nozzle.•Droplet size was modelled by dimensional analysis of the atomisation process.•Both the atomisation and coalescence ...mechanisms contribute to the droplet size.•Air velocity prevail in the spray characteristics.
This paper presents a dimensional analysis (DA) § approach of the atomisation process using a bi-fluid nozzle, allowing to predict droplet sizes of model solutions and skimmed milk concentrates in large ranges of operating conditions. Experimental results confirmed the atomisation mechanism described in the literature, by underlining that the spraying operation is controlled by the coupling of liquid physicochemical properties (viscosity, surface tension, density) and operating conditions (air pressure and liquid flow rate). It was also highlighted that droplet coalescence occurs from a certain distance to the nozzle, counteracting the atomisation mechanism and leading to a reincrease in the droplet size when moving away from the nozzle. Consequently, the modelling of droplet size by DA was improved by adapting the model coefficients of the dimensionless process relationship to the involved mechanisms: either atomisation only close to the nozzle outlet or atomisation followed by droplet coalescence at longer distance to the nozzle.
•Higher total solids were reached with a Centritherm evaporator for skim milk and WPC80.•After the 2-hour concentration, no noticeable thermal damage on protein was observed.•Resulting powders ...retained satisfactory rehydration properties.
A new thin film concentration device based on a spinning cone evaporator has been specifically designed to process viscous products at low evaporation temperatures. Its effectiveness was evaluated for the concentration of skim milk and a whey protein concentrate with 80% (w/w) protein on a dry-matter basis (WPC80). The concentrates were dried and the powders were compared to standard products obtained with conventional technology.
WPC80 at 259.1gkg−1 total solids (TS) and preconcentrated skim milk at 404.9gkg−1TS were concentrated up to 425.4 and 570.5gkg−1TS, respectively. No noticeable protein denaturation was evidenced on either concentrate. Particle size and bulk density were higher in the WPC80 powder than a standard product. Although the skim milk concentrate was highly viscous, drying was possible by applying a higher pressure at the inlet of the dryer. The resulting powder had physical properties (density, particle size, solubility) comparable to those of a standard product.
A predictive tool (SD
2P®) based on a drying by desorption method was recently developed in order to determine the key process parameters values prior to spray drying. However, the SD
2P® software ...cannot currently take into account the risk of stickiness during the process. In the study reported here, new standardized desorption method was tested and with this new method an equation was proposed to evaluate the dry glass transition temperature (
T
g) of a concentrate according to its total solid content, its viscosity and its average evaporation rate. The concentrate’s behaviour during spray drying could then be predicted on the basis of the
T
g. Four validation experiments were performed using different infant formula samples; the concentrates prepared from the four infant formula powders were then spray dried using a one-stage pilot dryer. The drying parameters were predicted using the SD
2P® software. The results showed that the
T
g predicted using this method were 18–30
°C higher than
T
g measured by DSC (Differential Scanning Calorimetry). The drying temperatures predicted by SD
2P® corresponded well to the values measured and this new method can correctly predict the behaviour of a concentrate with regard to spray drying. The advantage of the method presented here is that it can easily and quickly evaluate a concentrate’s
T
g range and spray drying behaviour by direct analysis of the fresh concentrate sample.
The most widely used technique for dehydration of dairy products is spray drying. This is an effective method for preserving biological products as it does not involve severe heat treatment and ...allows storage of powders at an ambient temperature. The maximum moisture content of a dairy powder (max 4% for skim milk powder) is defined in the product specification in relation to the water activity, and this must be close to 0.2 at 25 °C for optimum preservation. From an economic point of view, it is very important to operate as closely as possible to this limit. Many dairy manufacturers and researchers have demonstrated and reported that powder moisture is related to the outlet air temperature, but this is not always true. The aims of this study were to evaluate the direct and indirect relationships between outlet air temperature and moisture content of skim milk powder in relation to the spray-drying parameters (concentrate mass flow rate, absolute humidity of inlet air and inlet air temperature) using a thermodynamic approach. Our experiments showed that moisture content of skim milk powder can be close to 5.1 ± 0.0% with variations in outlet air temperature of 77 to 87 °C. Other experiments showed that the powder moisture content can vary from 4.6 ± 0.0% to 5.2 ± 0.0% even when the outlet air temperature remains close to 86 ± 1 °C. These results indicate that there is no direct relationship between outlet air temperature and powder moisture content. It is preferable to use the Enthalpic Mollier-Ramzine diagram of wet air and certain transfer equations related to the Fick and Fourier laws to demonstrate that the powder moisture content is directly related to the relative humidity (RH) of the outlet air. The moisture content and water activity of skim milk powder were close to 5.1 ± 0.0% and 0.27 ± 0.01 for outlet air RH close to 7.0 ± 0.1%, respectively, whatever the other drying parameter values. We demonstrated in this study that control of the RH of the outlet air is at least as important as control of the outlet air temperature to optimize the moisture content of a dairy powder, regardless of the absolute humidity of the inlet air, concentrate mass flow rate or inlet air temperature.
A desorption method based on a thermodynamic approach has recently been developed to evaluate the behaviour of dairy concentrates during drying. Involving overall heat and mass balance throughout the ...dryer, this approach can determine several key gas-feed parameters for industrial spray-drying processes. Spray-drying software (SD²P®) was then designed following this approach to predict the optimal inlet drying air temperatures with acceptable accuracy (95–99% accuracy) for spray-drying of dairy products. However, the mass change of the sample was indirectly determined from the change in the relative humidity of the air during desorption, which could be a source of error below the detection threshold of the thermo-hygrometric sensor. In order to measure directly the mass change during drying by desorption, a modified drying-by-desorption method was investigated in this study. The novel method used a precise microbalance and a modified desorption cell which permitted measurement of the mass change of the sample and the relative humidity of the air at the same time. Different materials (water, skim milk, infant formulae, etc.) were tested using this new method. The results obtained with direct (microbalance) and indirect (thermo-hygrometer) measurements were found to be highly consistent (coefficient of determination 1). This confirmed that the mass change estimation by the original desorption method was correct overall under current conditions. Moreover, the proposed new desorption method makes it possible to monitor water transfer with constant accuracy over the entire desorption process, thus permitting reliable study of the mass transfer phenomena throughout experiments.
Adapting and combining specific biochemical and physical methods to investigate the properties of fat is the first step of an integrated approach conducted on fat-filled dairy powders, which have an ...economic and qualitative importance. The study includes the isolation, quantification and characterization of the free fat fraction, and the investigation of fat properties in situ in the powder. Free fat isolation is achieved by solvent extraction; the extracted fat can be quantified and further studied from thermal profile features by differential scanning calorimetry (DSC). Fat droplet sizes are investigated by laser light scattering: measurements are achieved on emulsions obtained after the rehydration of the powders. In situ methods mainly include investigation of the thermal properties by DSC, composition of the surface by X-ray photoelectron spectroscopy and qualitative observations by confocal laser scanning microscopy. After this study, reliable and connected methods are available (i) to quantify and locate the different types of fat within a powder particle and (ii) to investigate fat composition, structure and thermal properties. The need to combine several methods to conclude on a data set was demonstrated.
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