The growth of thermophiles during the manufacture of milk powder leads to a progressive increase in the number of thermophilic bacteria contaminating the final product. The limited residence time of the milk in the plant during milk powder manufacture and the concentration effect of converting milk into milk powder cannot explain the number of thermophiles found in the final product. This suggests that thermophiles are attaching to the large surface area of stainless steel found within a milk powder plant and then growing and developing into biofilms, with individual cells and/or biofilm fragments sloughing off into the product line and thus contaminating the final product. The aim of the present study was to investigate the attachment mechanisms that enable the thermophile Anoxybacillus flavithermus (B 1 2) to attach to stainless steel surfaces. Passing a B 1 2 culture through a column of stainless steel chips, collecting the first cells to pass through, re-culturing and repeating the process six times, resulted in the isolation of a mutant, labelled X7, with lO-fold reduced ability to attach to stainless steel as well as a reduced ability to attach to plastic and glass. A comparison of bacterial cell surface properties indicated that X7 was less hydrophobic than its parental strain B 1 2 . Cell surface charge measurements also suggest that X7 has less net negative surface charge. Disruption of extracellular polysaccharides and DNA appeared to have no effect on the attachment process. Removal of surface proteins caused a reduction in attachment of B 1 2 and X7 as well as a reduction in surface hydrophobicity suggesting surface protein involvement in both. Analysis by two-dimensional gel electrophoresis of lysozyme/mutanolysin extracted surface proteins revealed two proteins expressed at reduced levels in X 7 compared with B 1 2 . One protein was identified by mass spectrometry as the cytoplasmic enzyme Formate acetyltransferase. The role of Formate acetyltransferase and the second unidentified protein on the attachment process of Anoxybacillus flavithermus remains unclear.

The objective of this study was to investigate the effects of preheat treatments on fouling by fresh whole milk (FWM), recombined whole milk (RCB) and reconstituted whole milk (Recon) in the high-temperature heater of indirect UHT plants. Various preheat treatments prior to evaporation during milk powder manufacture were applied to skim milk powder (SMP, 75 °C 2 s, 85 °C, 155 s and 95 °C, 155 s) and whole milk powder (WMP, 95 °C, 33 s). These preheat treatments were so-called “evaporator preheat treatments”. Skim milk powder (SMP) and whole milk powder (WMP) were derived from the same original batch of pasteurised FWM to remove the effects of the variation in milk composition between different milk batches. These SMPs were recombined with anhydrous milk fat and water to prepare RCB, and WMPs were reconstituted with water to prepare Recon. Then, (homogenized) FWM, RCB and Recon were subjected to various preheat treatments (75 °C, 11 s, 85 °C, 147 s and 95 °C, 147 s) prior to UHT processing. These preheat treatments were so-called “UHT preheat treatments”. Temperature difference (hot water inlet temperature – milk outlet temperature) was taken as a measure of the extent of fouling in the high-temperature heater. The slope of the linear regression of temperature difference versus time (for two hours of UHT processing) was taken as fouling rate (°C/h). Increasing both evaporator and UHT preheat treatments resulted in increasing fouling rate and total deposit weight for all three whole milk types for several milk batches. In the case of FWM, there was no reduction in fouling rate with increasing UHT preheat treatment whether FWM was homogenized then preheated, preheated then homogenized or not homogenized at all. These findings, which are wholly consistent and well replicated, are in apparent conflict with the results of most previous comparable studies. Possible reasons for this are explained. Further investigations of the effects of homogenization relating to the role of whey protein on the surface of the fat globules showed that whey protein associated with the membrane covering the surface of fat globules for homogenized then preheated FWM, RCB and Recon and that association increased with increasing heating process stage. The increasing association of whey protein with the milk fat globules membrane with increasing severity of heating process stage became faster when preheat treatment was more severe: the association of whey protein plateaued on intermediate temperature heating when the milks were preheated at 75°C, 11 s and on preheating when the milks were preheated at 95°C, 147 s. In the case of FWM, the thickness of the membrane covering the surface of fat globules for homogenized then preheated FWM, which increased with the severity of heating process stage, was greater than the thickness of the membrane in preheated then homogenized FWM. Preheating then homogenization resulted in the greater interfacial spreading of small molecules on the surface of fat globules, i.e. whey protein or small molecules from the disintegration of casein micelles during preheating. Possible basic mechanisms for UHT fouling in the high-temperature heater include: the reduction in the solubility of calcium phosphate and the deposition of protein as fat-bound protein and non-fat-bound protein. When non-fat-bound protein in milk plasma deposited, it could be a carrier for the deposition of mineral, such as, the precipitate of calcium phosphate in the casein micelles or the deposition of complexes between whey protein and casein micelles.

The objective of this study was to investigate the effects of preheat treatments on fouling by fresh whole milk (FWM), recombined whole milk (RCB) and reconstituted whole milk (Recon) in the high-temperature heater of indirect UHT plants. Various preheat treatments prior to evaporation during milk powder manufacture were applied to skim milk powder (SMP, 75 °C 2 s, 85 °C, 155 s and 95 °C, 155 s) and whole milk powder (WMP, 95 °C, 33 s). These preheat treatments were so-called “evaporator preheat treatments”. Skim milk powder (SMP) and whole milk powder (WMP) were derived from the same original batch of pasteurised FWM to remove the effects of the variation in milk composition between different milk batches. These SMPs were recombined with anhydrous milk fat and water to prepare RCB, and WMPs were reconstituted with water to prepare Recon. Then, (homogenized) FWM, RCB and Recon were subjected to various preheat treatments (75 °C, 11 s, 85 °C, 147 s and 95 °C, 147 s) prior to UHT processing. These preheat treatments were so-called “UHT preheat treatments”. Temperature difference (hot water inlet temperature – milk outlet temperature) was taken as a measure of the extent of fouling in the high-temperature heater. The slope of the linear regression of temperature difference versus time (for two hours of UHT processing) was taken as fouling rate (°C/h). Increasing both evaporator and UHT preheat treatments resulted in increasing fouling rate and total deposit weight for all three whole milk types for several milk batches. In the case of FWM, there was no reduction in fouling rate with increasing UHT preheat treatment whether FWM was homogenized then preheated, preheated then homogenized or not homogenized at all. These findings, which are wholly consistent and well replicated, are in apparent conflict with the results of most previous comparable studies. Possible reasons for this are explained. Further investigations of the effects of homogenization relating to the role of whey protein on the surface of the fat globules showed that whey protein associated with the membrane covering the surface of fat globules for homogenized then preheated FWM, RCB and Recon and that association increased with increasing heating process stage. The increasing association of whey protein with the milk fat globules membrane with increasing severity of heating process stage became faster when preheat treatment was more severe: the association of whey protein plateaued on intermediate temperature heating when the milks were preheated at 75°C, 11 s and on preheating when the milks were preheated at 95°C, 147 s. In the case of FWM, the thickness of the membrane covering the surface of fat globules for homogenized then preheated FWM, which increased with the severity of heating process stage, was greater than the thickness of the membrane in preheated then homogenized FWM. Preheating then homogenization resulted in the greater interfacial spreading of small molecules on the surface of fat globules, i.e. whey protein or small molecules from the disintegration of casein micelles during preheating. Possible basic mechanisms for UHT fouling in the high-temperature heater include: the reduction in the solubility of calcium phosphate and the deposition of protein as fat-bound protein and non-fat-bound protein. When non-fat-bound protein in milk plasma deposited, it could be a carrier for the deposition of mineral, such as, the precipitate of calcium phosphate in the casein micelles or the deposition of complexes between whey protein and casein micelles.

Agglomerated milk powders are produced to give improved properties such as flowability, dispersibility, reduced dustiness and decreased bulk density. A key function of these powders is to dissolve "instantly" upon addition to water and because of this they are also called "instant milk powders". They are produced by agglomerating the undersized fines that are returned to the top of the spray drier with milk concentrate droplet spray. Interaction occurs in a collision zone, often with multiple sprays and fines return lines. Agglomeration can be a difficult process to control and operators find it hard to fine tune the process to produce specific powder properties. This work aimed to understand the effects of key droplet and fines properties on the extent of agglomeration to allow a mechanistic understanding of the process. Three scales of spray drier were investigated in this study with different rates of evaporation; a small scale drier (0.5 - 7 kg water h-1), a pilot scale drier (80 kg water h-1) and a range of commercial production scale driers (4 - 15 000 kg water h-1). A survey of operators of commercial scale driers showed that control of instant milk powder production to influence bulk density is highly intuitive. Fines recycle rates were expected to be important in control of agglomeration processes and were estimated on a specific plant by using the pressure drop measured in the fines return line. A model based on pressure drop along a pneumatic pipeline under-predicted the experimental values for pressure drop due to solids, which means a calibration curve should be generated for each specific drier. Fines recycle rates were predicted to be significantly higher at 95 to 130 % of production rates compared to those expected by operators of 50%. Experimental measurements agreed with existing models for the effect of temperature on the density and viscosity of milk concentrates. Experimental results showed that the surface tensions of concentrated milks were within the same range as literature values for standard milks below 60°C, but were significantly higher for milk above 60°C. This is thought to be linked to the mechanism of skin formation due to disulphide cross linking at high temperatures and concentrations. Powder properties were also established for selected products produced on the commercial scale driers. These powders were then used in experiments on the two smaller driers. Because collision frequency depends on the velocity and droplet size of sprays; these properties were measured for the small scale drier and estimated, where possible, for the pilot and commercial driers. The small scale agglomerating spray drier was configured to alter droplet and particle properties when interacting a vertical fines particle curtain with a horizontal spray sheet. An extensive design and improvement process was carried out to ensure the system consistently delivered these streams in a controllable manner. The processes of collision and adhesion occur very quickly inside the spray drier. In order to assess the extent of agglomeration that has occurred, the feed streams must be compared to the final product stream. An ideal way to do this is to use an agglomeration index which compares the particle size distributions of the feed (fines recycle and spray streams) and the particle size distribution of the product stream (the agglomerated powder). The index described changes between these steams across the particle size distribution and is called an agglomeration efficiency, ξg. However, it was found that the presence of fines in the product of the one-pass design obscured the agglomerates formed. The agglomeration efficiency, ξg, was modified to become ξh which subtracted the fines stream from the agglomerated product distribution. In this way ξh models industrial operation where the fines are recycled, by effectively just comparing the spray and product streams entering and leaving the process. The small scale drier was used for an experimental study on natural and forced agglomeration, where the drier was operated with spray only, then with spray and fines. For natural agglomeration, SEM images of the product powder indicated that little agglomeration occurred between spray droplets. The product yield was unacceptably low (~ 40%) due to adhesion of spray droplets to the drying chamber wall opposing the horizontal spray. When the fines curtain was introduced in the forced agglomeration experiments, product yield increased above 50% because the fines acted as collectors for the spray droplets. However, the agglomeration performance of the modified spray drier was lower than expected. The equipment design was then optimised by considering three key issues; fines dispersion, droplet dispersion and stickiness, and agglomerate breakdown. Final experiments studied agglomeration at low fines to spray mass flux ratios and showed that increasing the fines size had a positive effect on agglomeration efficiency,ξh. The agglomeration study at pilot scale identified the effect of key variables, total solids, concentrate and fines flow rate, and fines size on the agglomeration efficiency. A dimensionless flux approach was used to explain the experimental results. The fines to spray mass flux ratio and the projected area flux ratio (at constant concentrate flow rate) were found to be the most suitable to represent the physical processes during agglomeration. Experimental results showed that a higher dimensionless flux resulted in more agglomeration and as well as small fines size and atomising low solids concentrate. The critical Stokes number highlighted the importance of particle size and collision velocity on the outcome of the collision as well as the importance of stickiness on adherence following the collision. A statistical analysis established a relational model for predicting the agglomeration efficiency based on fines size, total solids and the fines to spray mass flux ratio. This thesis has gained insight into agglomeration processes during spray drying and knowledge about how to define the extent of agglomeration. Practical findings from this research can have a significant impact on successful spray drying operation for instant powders. There are some practical steps to be taken industrially to promote the control of agglomerating spray driers. The first step is to measure and control the flow of fines recycled to the top of the spray drier. The next step is to validate the findings at industrial scale and link the agglomeration index to the bulk powder properties. However, there are many challenges that remain to be tackled in the area of milk powder agglomeration. Milk powder agglomeration at the top of the spray drier is a complex process involving many different variables. A more detailed study of the micro processes that occur during agglomeration will give increased understanding of the relationships between key operating variables and agglomerate properties.

Made available in DSpace on 2016-08-15T20:31:08Z (GMT). No. of bitstreams: 1 AndrezzaKBM_DISSERT.pdf: 2145673 bytes, checksum: 7eee5441610d3202cb0ad9f1c19338c1 (MD5) Previous issue date: 2013-08-07 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The present workaimed at evaluatingthe performance and yieldofcarcasscomponentsand no carcasscrossbred calvesreceivingcheese wheypowderassociated withpowdered milkduring sucklinguntil 60and 150 days, besides the realizationof economic analysisof substitution.A total of 40male calves, Holstein xwithoutdefined breed, distributed ina completely randomized designwith fourtreatments and tenreplications: whole milk(control), milk powder,milk powder80% +20% cheese wheypowder;60%milk powder+ 40%cheese wheypowder.After 60 days(suckling), 40test animalswere kept16animalsdivided into twotreatments with eight replicates: confinementandpasturewill, to evaluate the performancephaseofweaning.The developmentof the calveswas evaluated throughweeklyweighingandbodymeasurementsofwithers height, rump height, heart girthandbody length. Afterweaningweighingswere carried out fortnightlyup to 150days.To estimateconsumptionmeasurements were madedailyconsumption ofhay andconcentratedby the methodsupply /spare.The animals wereslaughteredat 60 days, where they weretakenmeasurespHand temperatureof thehot carcass, after 24 hoursofcoldcarcasses. Were also evaluatedparameters forcarcassandno carcass components.Theeconomic performance assessmentconsistedof the calculationof indicatorsof costs and revenues, andmeasuresofeconomic outcomes. All variablesweretested withTukeymean comparison, 5% probability.Theweekly consumption oftotal dry matteringestedweight gainandbody measurementsevaluatedshowed nodifferencesbetween treatments(P>.05). Therewereno significant differences (P>0.05) between treatmentsfor the variablesfor carcass traitsandnon-carcass components. The treatment containing20%cheese wheypowder+80% milk powder and40% cheese wheypowder+60% milk powder hadadditional profitof R$ 116.86and114.24respectively, principallyattributed to thefactthatspending onliquid diet. The results showthat the substitution ofwhole milkcheese wheypowder andits association withmilk powder, shownas avery feasible alternativeand not causing anany influenceon the parameters studied / No presente trabalho objetivou-se avaliar o desempenho de bezerros mestiços aleitados com soro de queijo em pó associação ao leite em pó até os 60 dias. Foram utilizados 40 bezerros machos, holandês x sem padrão racial definido, distribuídos em delineamento inteiramente casualizado com quatro tratamentos e dez repetições: leite integral (Controle); leite em pó; 80% leite em pó + 20% de soro de queijo em pó; 60% leite em pó + 40% de Soro de queijo em pó.Após a fase de aleitamento, destes 40 animaisutilizados, foram mantidos 16 bezerros distribuídos em dois tratamentos e oito repetições: confinamento e àpasto, para avaliação do desempenho na fase de desaleitamento.O desenvolvimento dos bezerros foi avaliado através de pesagens semanais e mensurações corporais de altura de cernelha, altura de garupa, perímetro torácico e comprimento do corpo. Na fase de desaleitamento as pesagens foram realizadas quinzenalmente até 150 dias de idade. Para a estimativa de consumo foram feitas medições diárias de consumo de feno e concentrado pelo método oferta/sobra. Todas as variáveis foram submetidas ao teste de comparação de médias Tukey, ao nível de 5% de probabilidade. O consumo semanal de matéria seca total ingerida não apresentou diferença entre os tratamentos (P>0,05), podendo se observar consumo crescente dos animais ao longo das semanas. Com relação ao ganho de peso os animais entraram no período experimental com pesos semelhantes (P>0,05) e ao longo desse período, os resultados apontam também que não houve diferença significativa (P>0,05), demonstrando que os tratamentos que receberam leite em pó e soro de queijo em pó associado ao leite em pó na dieta líquida não diferiu do tratamento controle. Os tratamentos também não influenciaram nenhuma das medidas corporais avaliadas. A substituição do leite integral por leite em pó, ou a associação de soro de queijo em pó ao leite em pó na substituição total do leite integral, não afetou o consumo de matéria seca, o ganho de peso e o desempenho dos animais tanto na fase de aleitamento quanto na fase de desaleitamento

Este trabalho avaliou os efeitos de diferentes períodos de armazenamento do leite de cabra in natura sobre a qualidade do produto em pó. Foram avaliadas as alterações microbiológicas, físico-químicas e bioquímicas do leite cru e a influência nas características microbiológicas, físicas, bioquímicas e sensoriais do leite em pó durante o armazenamento por 0, 60, 120 e 180 dias. Foram realizados 3 ensaios idênticos nos quais cerca de 105 L de leite de cabra recém-ordenhado foram igualmente divididos em 3 partes e armazenados a temperatura controlada de 4 ºC por até 5 dias. Nos dias 1, 3 e 5 após a coleta do leite in natura, uma alíquota de 500 mL foi coletada para a realização das análises. O restante da fração (aproximadamente 35L) foi submetido à pasteurização (65 ºC por 30 min), concentração sob vácuo (40% de sólidos totais) e secagem por atomização. Os lotes de leite de cabra em pó obtidos foram avaliados através de análises de composição (umidade, teores de proteína, gordura, lactose e cinzas), dispersibilidade, cor, atividade de água, índice de peróxidos, atividades proteolítica e lipolítica e análise sensorial por uma equipe de provadores treinados. Foram observados efeitos (P < 0,05) do período de armazenamento do leite in natura e/ou do leite em pó, ou mesmo interação destes efeitos sobre determinadas características durante o armazenamento do leite em pó, como: aumento linear das populações de micro-organismos mesófilos, psicrotróficos lipolíticos e psicrotróficos proteolíticos do leite in natura, aumento da intensidade da cor branca (L*) do leite em pó, da atividade lipolítica e da oxidação do leite em pó. Também foram observados efeitos (P < 0,05) em características sensoriais como: redução da coloração amarela do pó de do leite reconstituído, aumento do odor cáprico e dos sabores rançoso e amargo do leite reconstituído. Considerando-se a avaliação global das variáveis estudadas, recomenda-se que o período de armazenamento a 4 oC do leite de cabra in natura não ultrapasse 3 dias, para que ocorra a preservação da qualidade do leite de cabra em pó por até 180 dias. / This study evaluated the effects of different storage periods of raw goat milk on the quality of the powder product. Alterations in microbiological and physical-chemical properties of raw milk and their influence on the microbiological, physical, biochemical and sensory characteristics of milk powder during storage for 0, 60, 120 and 180 days were evaluated. There were 3 identical tests in which about 105 L of recently milked goat milk were divided into 3 parts and stored at controlled temperature of 4 ºC for up 5 days. On days 1, 3 and 5 after storage, an aliquot (500 mL) of raw milk was collected to perform microbiological, physico-chemical and biochemical analysis. The remaining fraction (about 35 L) was subjected to pasteurization (65 ºC for 30 min), vacuum concentration (40% of total solids) and spray drying. The powders produced were evaluated through analysis of composition (moisture, protein, fat, lactose and ash), dispersibility, color, water activity, granulometry, peroxide value, proteolytic and lipolytic activities and sensory analysis by a selected team of panelists. Effects of storage of raw milk or/and powdered milk or their interaction were observed (P <0.05) on certain characteristics during storage of milk powder, as the increasing of mesophilic, lipolytic psychrotrophic and proteolytic psychrotrophic microorganisms populations in raw milk, increasing of the white color (L*), the lipolytic activity and the peroxide value of milk powder. There were also observed effects (P < 0.05) on sensory characteristics such as decreasing of yellow color of milk powder and reconstituted milk, increasing of capric smell, rancid and bitter flavour of reconstituted milk. Considering the overall evaluation of studied variables, it\'s recommended that the raw goat milk storage at 4 oC does not exceed 3 days to preserve the quality of goat milk powder until 180 days.

Este trabalho avaliou os efeitos de diferentes períodos de armazenamento do leite de cabra in natura sobre a qualidade do produto em pó. Foram avaliadas as alterações microbiológicas, físico-químicas e bioquímicas do leite cru e a influência nas características microbiológicas, físicas, bioquímicas e sensoriais do leite em pó durante o armazenamento por 0, 60, 120 e 180 dias. Foram realizados 3 ensaios idênticos nos quais cerca de 105 L de leite de cabra recém-ordenhado foram igualmente divididos em 3 partes e armazenados a temperatura controlada de 4 ºC por até 5 dias. Nos dias 1, 3 e 5 após a coleta do leite in natura, uma alíquota de 500 mL foi coletada para a realização das análises. O restante da fração (aproximadamente 35L) foi submetido à pasteurização (65 ºC por 30 min), concentração sob vácuo (40% de sólidos totais) e secagem por atomização. Os lotes de leite de cabra em pó obtidos foram avaliados através de análises de composição (umidade, teores de proteína, gordura, lactose e cinzas), dispersibilidade, cor, atividade de água, índice de peróxidos, atividades proteolítica e lipolítica e análise sensorial por uma equipe de provadores treinados. Foram observados efeitos (P < 0,05) do período de armazenamento do leite in natura e/ou do leite em pó, ou mesmo interação destes efeitos sobre determinadas características durante o armazenamento do leite em pó, como: aumento linear das populações de micro-organismos mesófilos, psicrotróficos lipolíticos e psicrotróficos proteolíticos do leite in natura, aumento da intensidade da cor branca (L*) do leite em pó, da atividade lipolítica e da oxidação do leite em pó. Também foram observados efeitos (P < 0,05) em características sensoriais como: redução da coloração amarela do pó de do leite reconstituído, aumento do odor cáprico e dos sabores rançoso e amargo do leite reconstituído. Considerando-se a avaliação global das variáveis estudadas, recomenda-se que o período de armazenamento a 4 oC do leite de cabra in natura não ultrapasse 3 dias, para que ocorra a preservação da qualidade do leite de cabra em pó por até 180 dias. / This study evaluated the effects of different storage periods of raw goat milk on the quality of the powder product. Alterations in microbiological and physical-chemical properties of raw milk and their influence on the microbiological, physical, biochemical and sensory characteristics of milk powder during storage for 0, 60, 120 and 180 days were evaluated. There were 3 identical tests in which about 105 L of recently milked goat milk were divided into 3 parts and stored at controlled temperature of 4 ºC for up 5 days. On days 1, 3 and 5 after storage, an aliquot (500 mL) of raw milk was collected to perform microbiological, physico-chemical and biochemical analysis. The remaining fraction (about 35 L) was subjected to pasteurization (65 ºC for 30 min), vacuum concentration (40% of total solids) and spray drying. The powders produced were evaluated through analysis of composition (moisture, protein, fat, lactose and ash), dispersibility, color, water activity, granulometry, peroxide value, proteolytic and lipolytic activities and sensory analysis by a selected team of panelists. Effects of storage of raw milk or/and powdered milk or their interaction were observed (P <0.05) on certain characteristics during storage of milk powder, as the increasing of mesophilic, lipolytic psychrotrophic and proteolytic psychrotrophic microorganisms populations in raw milk, increasing of the white color (L*), the lipolytic activity and the peroxide value of milk powder. There were also observed effects (P < 0.05) on sensory characteristics such as decreasing of yellow color of milk powder and reconstituted milk, increasing of capric smell, rancid and bitter flavour of reconstituted milk. Considering the overall evaluation of studied variables, it\'s recommended that the raw goat milk storage at 4 oC does not exceed 3 days to preserve the quality of goat milk powder until 180 days.