Fire and explosion hazards in the spray drying of milk

Recent reports in the literature indicate that incidents involving fires and explosions in the spray drying of milk products are increasing in number. Whilst 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 dryer during its normal operation. Self-ignition of deposits is known to be possible at the high temperatures in a spray dryer. At best, this can cause product degradation and discolouration whilst 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 formilk powders.     

Innovation in milk powder technology

Global trade in preserved milks is on the increase as new markets open up in regions of the world that have not been traditionally associated with milk consumption. Equally, a rise in world milk production is forecasted to continue, and the indications are that significant quantities of the extra milk produced will be converted to commodity products such as butter and powders. Consequently, on-going investment in new spray drying capability is likely to track geographical shifts in milk production. Successful application of advanced process control to the operation of large scale drying plant is both a priority and a challenge.
  Meanwhile, opportunities for the exploitation of milk as a source of functional ingredients are being availed of by the dairy industry as it continues to achieve added value and unique key selling points. Recent research on the role of spray drying, along with other processes in the development of dairy ingredients for applications in chocolate and the preparation of microencapsulated powders, is reviewed.     

干燥方式对湿法加工奶茶固体饮料感官和稳定性的影响

为了考察干燥方式对湿法加工奶茶固体饮料感官和稳定性的影响,本实验以喷雾干燥和真空干燥两种方式干燥奶茶固体饮料。结果表明,经过真空干燥的奶茶粉冲泡浮油严重,口感和组织状态显著差于喷雾干燥奶茶粉。真空干燥奶茶粉表面油含量为13.44%,而喷雾干燥仅为0.78%,通过粒径分布和透光率测定,均显示真空干燥奶茶粉稳定性差,喷雾干燥稳定性较佳。在得率方面,喷雾干燥得率59%,真空干燥74%。综合各项结果,喷雾干燥更适合干燥湿法奶茶固体饮料。     

纯乳成分全脂速溶乳粉及其制备方法

采用乳成分制品制备喷涂物料,生产分散度８５％以上的全脂乳粉,称之为“纯乳成分全脂速溶乳粉”;其制备方法又可适用于各种配制乳粉,强化乳粉,豆乳粉及其他速溶饮品,配套设备“三分流组合式离心喷雾器”,可在乳粉喷雾干燥过程中,塔内直接进行颗粒附聚和喷涂,起到与流化床相同作用。     

喷雾干燥温度对牦牛乳粉溶解特性的影响

为探讨喷雾干燥温度对牦牛乳粉溶解特性的影响,分析了在进风温度（出口温度）分别为130（56）、150 （64）、170（73）、190（81）、210（90）℃条件下喷雾干燥牦牛乳粉样品的溶解特性参数,并通过相关性分析对其进行聚类分析。结果表明：喷雾干燥温度对牦牛乳粉的溶解特具有显著影响（P＜0.05）,170（73）℃下喷雾干燥牦牛乳粉样品具有较高的水合能力、堆积密度、溶解度,较小的休止角和分散时间,具有较好的溶解特性,优于在其他温度下干燥牦牛乳粉的溶解特性;牦牛乳粉溶解特性参数间具有较好的相关性,聚类分析可实现对不同喷雾干燥温度条件下牦牛乳粉溶解特性的区分,为对喷雾干燥温度的评价提供参考。     

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.     

Pulsed electric field pre-treatment for enhanced bacterial survival after drying: Effect of carrier matrix and strain variability

Previous studies suggest that increased intracellular trehalose concentrations can result in increased robustness of probiotics and starter cultures after processing. We evaluated whether pulsed electric field (PEF) pre-treatment, resulting in increased intracellular trehalose concentrations, can lead to enhanced survival during spray drying and subsequent storage and what the effect of the carrier matrix during drying herein is on survival. The applied PEF pre-treatment resulted in increased survival of Lactobacillus plantarum WCFS1 after spray drying and subsequent storage in reconstituted skim milk (RSM), though not in the other evaluated carrier matrices. The same PEF pre-treatment in lactose instead of trehalose electroporation medium resulted also in an increased survival after spray drying in RSM. Further analysis of intracellular trehalose and lactose concentrations revealed that survival after spray drying cannot only be explained by intracellular trehalose and/or lactose concentrations. Experiments with other bacterial strains indicated that strain variability cannot be neglected when designing a process aimed at enhanced bacterial survival after processing. Overall, PEF pre-treatment is promising for enhancing survival of bacteria after drying and storage, though further understanding of the applicability is required for industrial application.Industrial relevance textProbiotics and starter cultures are very common in food industry. Survival of these cultures during drying processes is essential for their application. A pulsed electric field pre-treatment resulting in increased bacterial survival after spray drying and powder storage may contribute to more energy efficient production processes of dried bacterial cultures.     

巧克力专用乳粉

研究了不同乳粉的颗粒大小和结构、游离脂肪含量对巧克力浆料粘度的关系。滚筒乳粉与喷雾乳粉之对比，滚筒干燥的全乳粉具有下列优点；游离脂肪含量高，可减少可脂的用量，赋与巧克力以更好的风味；可降低巧克力浆料的粘度。乳粉中羟甲基糠醛含量可增进巧克力风味、口感，提高喷雾乳粉中游离脂肪含量改进的工艺。     

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.     

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.     

Technological advances in the production of spray dried milk

This paper deals with developments in concentrating and drying milk products during the 1970s and to the present. These developments are characterized by:
- a considerable increase in both maximum and average capacity of milk spray dryers, as well as of total production capacity.
- a tremendous increase in the number of milk-based products being spray dried,
- upgrading the quality of products both in retention of nutritive values and tailoring of functional properties,
- a considerable improvement in the economy of production, and
- the introduction of sophisticated instrumentation through microprocessors and computer control.
The development of dryers with integrated fluid beds during that period are described in some detail. Two such types of dryer have been developed, the Compact Spray Dryer (CSD) and the Multi-stage Dryer (MSD). The integrated fluid beds in these dryers are stationary (non-vibrating) fluid beds having annular (CSD) and circular (MSD) shape, respectively, forming the base of the spray drying chambers. Apart from improved powder quality and production economy these dryers can also cope better with difficult products having high lactose and fat content.
Finally, expected future trends for further development of milk drying technology are discussed.     

喷雾干燥生产苦瓜复合粉工艺研究

以苦瓜和牛奶为原料(苦瓜汁与牛奶的配比为1:2),通过喷雾干燥制取复合粉。采用单因素和L(934)正交试验,以产品得率和水分含量为评价指标,并结合喷雾干燥效果,确定较优的喷雾干燥工艺参数为:进料浓度25%、进口温度150℃、进料速度5.0×180ml/h。     

Production of agglomerated fat-filled milk powder

The production of fat-filled milk powder as an agglomerated product and the determining factors for wettability and flow properties are discussed. The melting point of the used fat with its effect on the content of free fat in the milk powder is examined with the importance of homogenization of the concentrate emphasized. Results are considered of a modified method of agglomerating fat-filled milk powder and figures given showing the influence of inlet and outlet temperatures on milk powder, also a flow diagram of spray drying plant for production of agglomerated fat-filled milk powder. (Editor's summary)     

Short communication: Effect of lactose on the spray drying of Lactococcus lactis in dairy matrices

The effects of unfavorable conditions responsible for the viability loss of Lactococcus cells during spray drying can be minimized by the application of dairy matrices as encapsulating materials. This study aimed to evaluate the use of dairy matrices with different lactose contents on the survival of Lactococcus lactis during drying and storage. The use of hydrolyzed-lactose milk resulted in notable loss of cell viability (3.90 log cycles). However, milk enriched with lactose or without fat showed better protection (viability loss between 0.26 and 1.41 log cfu/g) and greater cell survival during storage at room temperature. The enrichment of milk with lactose seems to be ideal for the drying of heat-sensitive bacteria.     

Technology of skimmed milk drying

A survey is presented of various processes and spray drying installations for obtaining skimmed milk powders with desired qualities. The spray dryers discussed are: spray dryer with pneumatic conveying system, two-stage drying system, spray dryer with cooling bed, and spray dryer with straight-through instantizer. The rewet agglomeration process is also described.
The second part deals with the most important final product properties (moisture, bulk density, and solubility index) and with the parameters controlling them.
In the third part the possibilities are discussed of saving energy and reducing stockloss. Two types of heat recuperators (air-to-air and air-to-liquid-to-air) and wet scrubber are described.     

Proteomic study on the stability of proteins in bovine,camel, and caprine milk sera after processing

Milk proteins have been shown to be very sensitive to processing. This study aims to investigate the changes of the bovine, camel, and caprine milk proteins after freezing, pasteurization (62 °C, 30 min), and spray drying by proteomic techniques, filter-aided sample preparation (FASP) and dimethyl labeling followed by liquid chromatography–tandem mass spectrometry (LC–MS/MS). A total of 129, 125, and 74 proteins were quantified in bovine, camel, and caprine milk sera, respectively. The milk serum protein content decreased significantly after freezing, pasteurization, or spray drying, which can be ascribed to the removal of protein aggregates by the pH adjustment and ultracentrifugation during sample preparation. Some of the immune-related proteins were heat-sensitive, such as lactoferrin (LTF), glycosylation-dependent cell adhesion molecule 1 (GLYCAM1), and lactadherin (MFGE8), with losses of approximately 25% to 85% after pasteurization and 85% to 95% after spray drying. α-Lactalbumin (LALBA), osteopontin (SPP1), and whey acidic protein (WAP) were relatively heat stable with losses of 10% to 50% after pasteurization and 25% to 85% after spray drying. The increase of some individual proteins in concentration after freezing may be caused by the proteins originating from damaged milk fat globules and somatic cells. GLYCAM1 decreased significantly after pasteurization in bovine and camel milk but this protein is relatively stable in caprine milk. In conclusion, milk proteins changed differently in concentration after different processing steps, as well as among different species.     

OPTIMIZATION OF SPRAY DRYING CONDITIONS FOR PRODUCTION OF BIFIDUS MILK POWDER FROM COW MILK

Bifidus milk powder was prepared by supplementing cow's milk with predetermined level of additives to obtain slurry of desired concentration. The slurry was sterilized, cooled and inoculated with 24‐h‐old bulk culture of Bifidobacterium bifidum at 10% and incubated at 37C for 24 h, cooled and dried in SM Scientech Lab model spray dryer with predetermined spray drying conditions. The bifidus milk powder contains bifidobacteria counts from 1.88 × 10⁹ to 15.80 × 10⁹ cells/g dry weight and their percent survival was 4.17–35.11%. Maximum survival was obtained by using the following spray drying conditions: inlet temperature of 164.02C, slurry concentration of 25.62% total soluble solids and air pressure of 2.5 kg/cm². The high temperature and air pressure of spray drying markedly influenced the color and appearance of final product. The inlet temperature and air pressure showed a significant effect on survival of bifidobacteria in the final product.     

Tracking Amazonian cheese microbial diversity: Development of an original,sustainable, and robust starter by freeze drying/spray drying

Marajó cheese made with raw buffalo milk in the Amazon region of Brazil can be considered a good source of wild lactic acid bacteria strains with unexplored and promising characteristics. The aim of this study was to develop a potential probiotic starter culture for industrial applications using freeze drying and spray drying. A decrease in the survival rates of freeze-dried samples compared with spray-dried samples was noted. The spray-dried cultures remained approximately 10⁹ cfu·g⁻¹, whereas the freeze-dried samples showed 10⁷ cfu·g⁻¹ after 60 d of storage at 4°C. All of the spray-dried samples showed a greater ability to decrease the pH in 10% skim milk over 24 h compared with the freeze-dried samples. The spray-dried samples showed a greater resistance to acidic conditions and to the presence of bile salts. In addition, under heat stress conditions, reduction was under 2 log cycles in all samples. Although the survival rate was similar among the evaluated samples after drying, the technological performance for skim milk showed some differences. This study may direct further investigations into how to preserve lactic acid bacteria probiotics to produce spray-dried starters that have a high number of viable cells that can then be used for industrial applications in a cost-effective way.