Fouling of plate heat exchangers (PHE) is a severe problem in the dairy industry, notably because the relationship between the build-up of protein fouling deposits and the chemical reactions taking ...place in the fouling solution has not yet been fully elucidated. Experiments were conducted at pilot scale in a corrugated PHE, and fouling deposits were generated using a model β-lactoglobulin (β-LG) fouling solution for which the β-LG thermal denaturation reaction constants had been previously determined experimentally. Then 18 different bulk temperature profiles within the PHE were imposed. Analysis of the fouling runs shows that the dry deposit mass per channel versus the ratio R=kunf/kagg (with kunf and kagg representing, respectively, the unfolding and aggregation rate constants computed from both the identification of the β-LG thermal denaturation process and knowledge of the imposed bulk temperature profile into the PHE channel) is able to gather reasonably well the experimental fouling mass data into a unique master curve. This type of representation of the results clearly shows that the heat-induced reactions (unfolding and aggregation) of the various β-LG molecular species in the bulk fluid are essential to capture the trend of the fouling mass distribution inside a PHE. This investigation also illustrates unambiguously that the release of the unfolded β-LG (also called β-LG molten globule) within the bulk fluid (and the absence of its consumption in the form of aggregates) is a key phenomenon that controls the extent of protein fouling as well as its location inside the PHE.
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Spray drying of dairy products consists of spraying droplets of feed solution into a hot air flow to quickly evaporate water and finally to form dried particles. In order to ...understand the role of the two-major milk protein (whey proteins and micellar caseins) in the mechanisms of particle formation the evaporation of mixtures containing different whey protein to casein ratios the obtained milk protein concentrates was investigated at single droplet and jet monodispersed stages. The results obtained suggest that the evolution of skin mechanical properties with time strongly depends on the composition of the mix and most of all on both size and mechanical characteristics of the colloidal components. Interestingly, the remarkable shape analogies observed in spray dried particles compared to the single droplets suggest that, despite the significant difference in terms of experimental conditions and process characteristic time scale, the ongoing evaporation dynamics are almost equivalent. Moreover, our results showed an overrepresentation of the smaller size whey proteins at the particle surface of dairy colloidal mixes, in agreement with reported results on model colloids.
Infant formula (IF) is submitted to several heat treatments during production, which can lead to denaturation or aggregation of proteins and promote Maillard reaction. The objective of this study was ...to investigate innovative minimal processing routes for the production of first-age IF powder, thus ensuring microbial safety with minimal level of protein denaturation. Three nutritionally complete IF powders were produced at a semi-industrial scale based on ingredients obtained by fresh bovine milk microfiltration (0.8 and 0.1-µm pore size membranes). Low-temperature vacuum evaporation (50°C) and spray-drying (inlet and outlet temperatures of 160 and 70°C, respectively) were conducted to produce the T− formula with no additional heat treatment. The T+ formula was produced with a moderate heat treatment (75°C for 2 min) applied before spray-drying, whereas the T+++ formula received successive heat treatments (72°C for 30 s on the milk; 90°C for 2–3 s before evaporation; 85°C for 2 min before spray-drying), thus mimicking commercial powdered IF. Protein denaturation and Maillard reaction products were followed throughout the production steps and the physicochemical properties of the powders were characterized. The 3 IF powders presented satisfactory physical properties in terms of aw, free fat content, glass transition temperature, and solubility index, as well as satisfactory bacteriological quality with a total flora <103 cfu/g and an absence of pathogens when a high level of bacteriological quality of the ingredients was ensured. Protein denaturation occurred mostly during the heat treatments of T+ and T+++ and was limited during the spray-drying process. The IF powder produced without heat treatment (T-) presented a protein denaturation extent (6 ± 4%) significantly lower than that in T+++ (58 ± 0%), but not significantly different from that in T+ (10 ± 4%). Although T− tended to contain less Maillard reaction products than T+ and T+++, the Maillard reaction products did not significantly discriminate the infant formulas in the frame of this work. The present study demonstrated the feasibility of producing at a semi-industrial scale an infant formula being bacteriologically safe and containing a high content of native proteins. Application of a moderate heat treatment before spray-drying could further guarantee the microbiological quality of the IF powders while maintaining a low protein denaturation extent. This study opens up new avenues for the production of minimally processed IF powders.
Breakthrough energy savings were recently projected by a spray-dryer free dairy powder manufacturing process based on superconcentration and granulation. The extent of superconcentration and the ...recirculation rate of powder for granulation, determines process performance. In this study, the evolution of physical properties during superconcentration and granulation was investigated for a model system (skim milk microfiltrate) using rheological and shear-cell based techniques. Results demonstrated that superconcentration leads to the development of a cohesive non-flowing state. The transition from concentrate to cohesive wet powder regime, manifested as a sharp increase in cohesiveness, occurring at around 82% w/w dry matter (DM). Powder addition for successful granulation was related to DM at the end of the cohesive phase (∼89% w/w DM). Interestingly, laboratory-based rheological and shear cell measurements were well correlated with the amperage of the mixer used; similar measurements could be applied in-process providing a better understanding and control of the product behavior within the system.
•Flow behavior of dairy superconcentrates was successfully modelled.•Onset of a highly cohesive phase restricts superconcentration processes.•Shear-cell based tests provide critical information about cohesive phase.•Agitator power consumption reliably reflects evolution in product flow behavior.
The key role of calcium in whey protein fouling behavior is well known in plate heat exchangers (PHEs), as it affects both the thermal denaturation of proteins and deposition reaction on the surface. ...However, the complex flow pattern and the closed configuration of PHEs make it hard to investigate this phenomenon in situ. In this paper, a microchannel benchtop fouling device was designed, making it possible to achieve a similar temperature profile to that performed in PHEs but in a laminar regime. A 3D simulation was developed to predict the thermal denaturation of β-lactoglobulin (BLG) as well as its deposition in the microchannel using computational fluid dynamics (CFD). The thermodynamics and heat transfer of the numerical model was validated by experimentally measuring the bulk fluid temperature profile in the microchannel using fluorescence microscopy, where Pyrromethene 556 was used as a temperature indicator. Results revealed a quasi-linear relationship between the pre-exponential factor of deposition reaction and the calcium concentration, implying that the fouling was built in such a pattern that only one calcium ion per one BLG molecule is involved. The imaging of the fouling deposit in situ showed spherical structures of deposits at low calcium levels, while denser and more rod-like ones were found at higher calcium concentrations. The fouling behavior was found to follow a crystallization-like pattern with preference upon the previously fouled layer instead of clean stainless steel surface. These findings confirm the essential role of ionic calcium on the formation of fouling deposits by anchoring the denatured BLG protein upon the surface as well as strengthening the protein-protein interactions for fouling build-up.
Granulation of whey permeate (WP) and demineralised whey (DW) superconcentrates was evaluated by addition of powder using a high-shear mixer during which consumption of electrical current was ...monitored. Granulation of DW required 50% more energy than that of WP and the resulting DW granules were larger (∼2×) indicating greater resistance to fragmentation. Furthermore, addition of whey protein isolate (WPI) into the back-mix powder resulted in more efficient granulation (reduced energy, finer granules etc.) of superconcentrated WP. This was linked to the higher water-holding capacity of WPI and a simple model based on protein content was proposed to predict occurrence of granulation. This study sheds light on granulation behaviour under these conditions. Interestingly, while high cohesiveness of superconcentrates, which is related to protein content, has been previously shown to negatively impact granulation, increasing the protein content of the granulating powder was shown here to have positive effects, which offers great potential for design of formulated products.
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•Protein content plays a key role in determining granulation efficiency.•High protein content in superconcentrates negatively affects granulation.•High protein content in the back-mixed powder improves granulation efficiency.
The drying process for dairy products is based on rapid removal of water, quickly concentrating milk components to finally form dry particles. The change in concentration may have a considerable ...effect on the product structure and influence the final characteristics of the dry material. The aim of this study was to investigate the drying behaviour of a major milk protein, i.e. caseins. The droplet – particle conversion was investigated through a single droplet system and by combining complementary methods. Our results showed that the drying process for caseins comprised three stages involving different evaporation rates and droplet dynamics. A thin layer was formed in the early stage of drying that underwent surface instabilities such as buckling and invagination of the droplet. The drying of caseins led to the formation of a deflated and wrinkled particle shape. These results suggest particular mechanical properties of the casein shell leading to a predictable and a characteristic particle shape.
Caking of lactose and other dry ingredients is a common problem in the dairy and food industries. The lactose production process includes different purification steps, depending on the type of ...lactose produced. The aim of this study was therefore to investigate how the remaining impurities (i.e. non-lactose components) affect the caking tendency of the final powder. The results from a combination of different methods, including dynamic vapor sorption, characterization of the physicochemical composition and assessment of caking with a ring shear tester, suggested humidity caking. Larger amounts of impurities in the lactose powder resulted in enhanced moisture sorption and greater caking tendency. These findings emphasize the importance of controlling the washing and purification steps throughout the production process in order to limit caking in the final product.
•Caking of lactose results in non-conform products and significant economic loss.•Impurities in the lactose powder increased moisture sorption and caking tendency.•The ring shear tester is a valuable tool to assess caking.•The washing and purification steps should be closely monitored to limit caking.
Dairy ingredients with highly concentrated protein contents are high added value products with expanding market. The manufacture of such ingredients includes a succession of unit operations of which ...heat treatment is a key step to guarantee the microbial safety, that induces major changes in protein structures and thus ingredients functionalities. However, due to an incomplete understanding of phenomena taking place at high protein concentrations, shedding light on their mechanisms is a scientific challenge as well as an industrial need. In this study, the influence of heat treatment (74 • C/ 30 s) of highly concentrated milk protein systems (up to 20 % w/ w) on protein denaturation/aggregation and enzymatic coagulation properties was studied using an original semi-industrial approach. 10 % w/w protein solutions constituted with whey protein and casein micelles at milk ratio, standardized in osmosed water or ultrafiltration permeate were used. These protein solutions were processed in different ways prior the manufacture of powders: heat treatment of the 10 % w/w protein solution before vacuum evaporation, heat treatment of the 20 % w/w protein solution after vacuum concentration, two consecutive heat treatments before and after vacuum evaporation. A fourth powder was prepared from unheated 10 % w/w protein solution. An increase in protein concentration led to a higher heat-induced protein denaturation. This phenomenon was reduced when increasing the lactose content. The effect of heat treatment on the extent of protein denaturation was not cumulative. At high protein concentration, interactions between κ-casein and whey protein were modified compared to milk, as mainly micelle-bound aggregates were formed at pH about 6.7. This phenomenon was enhanced at low ionic strength and lactose content. Our study showed that the enzymatic coagulation properties of reconstituted protein powders could be correlated with their physico-chemical compositions. An increase in protein denaturation disrupted the gel reorganization and led to the formation of weaker gels but did not interfere on the micelles aggregation phase and the early gelation. On the contrary, an increase in ionic strength and lactose content led to higher gel time.
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