Spray Freeze Drying
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Spray freeze drying is a technique wherein an atomized liquid spray is sprayed into a cryogenic medium, and the spray droplets are quickly frozen.
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Spray Freeze Drying
- 2. Drying • Drying is one of the oldest methods of preserving food. • Drying involves the removal of water from the material via the vapour phase. Spray-drying (SD) and freeze-drying (FD) INTRODUCTION
- 3. Atomization of liquid into a spray chamber Hot air flows inside the chamber, evaporating water from the atomized particles. Producing free flowing powders Significant losses of volatile materials and thermal degradation. SPRAY DRYING (SD)
- 4. Preserving heat labile components High product quality Long drying times, batch nature, low temperatures, high vaccum and the resultant high operational cost FREEZE DRYING (FD) Freezing Ice crystals Drying
- 5. SPRAY FREEZE DRYING (SFD)
- 6. Combination of SD & FD Three-step process SPRAY FREEZE DRYING (SFD) Atomisation Freezing Drying
- 7. 1. ATOMISATION Bulk liquid breaks up into a large number of small droplets Four fluid nozzles and ultrasonic nozzles
- 8. Particles has a fine porous structure producing a vast specific surface area Gas Liquid Gas Collision Accelerating zone for liquid flow Four Fluid Nozzle Nozzle edge
- 9. Ultrasonic Nozzle Produce large, porous particles Ultrasonic nozzle frequency Provide a high degree of control over particle
- 10. 2. FREEZING
- 11. 2. FREEZING
- 12. Spray freezing into vapour (SFV) Spray freezing into vapour over liquid (SFV/L) Spray freezing into liquid (SFL) Methods of spray freezing
- 13. Spray Freezing into Vapour (SFV) cold desiccated gas
- 14. Spray Freezing into Vapour (SFV) cold desiccated gas
- 15. Spray Freezing into Vapour over Liquid (SFV/L)
- 16. Spray Freezing into Liquid (SFL)
- 17. Vacuum drying Atmospheric freeze drying 3. FREEZE DRYING
- 18. Process: Collection of frozen droplets Transferred to pre-chilled shelves Primary drying (low pressure & 2 0C to 5 0C ) Secondary drying Conventional freeze drying
- 19. Use of cold gas (such as air, nitrogen or helium) as a water removal and heat transfer medium to cause sublimation . Convective freeze drying medium i.e., cold air stream, kept dry by a molecular sieve desiccant or by a refrigerated condenser. Carried out under atmospheric condition. Atmospheric freeze drying
- 20. SFD - a comparison with FD and SD
- 21. SFD - a comparison with SD and FD Rehydration time Percentage oxidation Oxidative stability Encapsulation efficiency Processing time
- 22. Drying of high value foods Drying of pharmaceutical products Encapsulation of active compounds sensitive to the surrounding condition. Unique aerodynamic qualities of the porous particles produced Producing particles for pulmonary delivery. APPLICATIONS OF SFD
- 23. Limitations of SFD High fixed and operating cost SFD with conventional freeze drying Loss of protein stability during the atomisation SFD with SFV/L technique Less encapsulation efficiency
- 25. Case study 1 Title: Spray Freeze Drying approach for soluble coffee processing and its effect on quality characteristics. Done by: Padma Ishwarya S. and Anandharamakrishnan C.
- 26. Objective To evaluate the suitability of SFD as a soluble coffee processing technique with SD and FD.
- 27. Materials and Methods Feed solution preparation Spray freeze drying Twin fluid nozzle (compressed air pressure) Polystyrene container connected to a liquid nitrogen dewar Feed flow rate - at 6 ml/min
- 28. Temperature range Primary drying : - 25 0C to -10 0C under vacuum of 107 Pa Secondary drying : 10 0C under a vacuum of 40 Pa Packed in polythene bags, sealed, and wrapped in aluminium foil Stored in a desiccator at the ambient temperature
- 29. Spray drying Single stage, short type, pilot scale Spray Dryer Twin fluid nozzle Inlet air temperature 150 ± 2 0C Outlet air temperature 100 ±2 0C Product was packed in polythene bags, sealed, and wrapped in aluminium foil Stored in a desiccator at the ambient temperature
- 30. Freeze drying Pilot scale freeze dryer Coffee powder packed in polythene bags, sealed, and wrapped in aluminium foil Stored in a desiccator at the ambient temperature.
- 31. Moisture content Volatiles Solubility Morphology Particle size
- 32. Results and Discussion Moisture content SFD and FD samples - higher than SD
- 33. 1 Volatile retention analysis A: methyl pyrazine; B:acetic acid; C: 2,3-butanedione; D: pyridine; E: 2-furanmethanol; F: maltol
- 35. Particle size analysis Greater mean volume diameter in SFD Solubility SFD exhibited more instantaneous solubility
- 36. Spray-freeze drying technique can be potentially employed for the production of soluble coffee with improved product characteristics. CONCLUSION
- 37. CASE STUDY 2 TITLE : Preparation of probiotic powder by the spray freeze-drying method. Done by: Jae-Young Her, Min Suk Kim, Kwang-Geun Lee
- 38. OBJECTIVE To examine a new process for producing probiotic powder using SFD
- 39. Materials and methods Bacterial srtain L. casei strains were grown in MRS broth medium and stored with 20% glycerol at 80°C until use.
- 40. The L. casei strain was inoculated into MRS broth Next, 20 ml of each suspension were poured into liquid nitrogen freeze-dryed for 24 h and rehydrated CFU ml-1 was determined by the plate dilution method
- 41. SEM An SEM was used to evaluate the powder surface and structure after SFD. A laser particle size analyzer was used to determine the particle size and particle size distribution. Particle diameter was indicated by volume (%).
- 42. STATISTICAL EVALUATION Data are expressed as means ± SD. Differences between groups were analyzed using a paired t-test and an ANOVA. A p-value < 0.05 was considered statistically significant.
- 43. Results and Discussion Growth media composition had a strong influence on the viability of probiotics
- 44. The survival rates 0.1M NaOH (Ph 8.0) → 94.9 0.1% (w/v) CaCO3 → 94.5 1% (w/v) mannose → 96.4 0.1 M NaOH & 1% (w/v) mannose → 98 0.1% CaCO3 & 1% (w/v) mannose → 98.9
- 46. Effect of the spraying process on the viability of L. casei Air pressure is one of the most important factors for SFD powder The survival rates of L. casei after the spraying process at 20 and 30 kPa were not significantly different (p>0.05) As a result, the spraying stage did not affect the probiotic viability
- 47. Protective agents during spray freeze- drying The viability in the 1% glucose solution was the highest. 100% BPW was selected as the optimum protective agent The SFD powder with BPW formed the most stable powder against humidity Low decreasing rates of viability (0.22 log CFU/ml)
- 48. CONCLUSION The protective agents used in traditional FD were not suitable for the SFD process, The survival rate of the final SFD probiotic powder under optimized conditions was 97.7%. The diameter of the optimized powder was 24.8 μm. This study contributes to the basic process of producing SFD probiotic powder in the food industry.
- 49. CONCLUSION Spray Freeze-Drying technique possesses the main merits of spray drying and freeze drying SFD technique produces highly valued shelf stable biological and food products with superior quality than existing drying techniques. SFD is an effective alternative to SD and FD techniques Computational Fluid Dynamics on SFD can lead to better designs of spray freeze dryers.
- 50. REFERENCE • Anandaraman, S. and Reineccius, G.A. 1987. Analysis of the encapsulated orange peel oil. Perfumer Flavorist. 12: 33–39. • Anandharamakrishnan, C., Rielly, C.D., and Stapley, A.G.F. 2008. Loss of solubility of alactalbumin and b-lactoglobulin during the spray drying of whey proteins. LWT– Food Sci. Technol. 41: 270- 277. • Anandharamakrishnan, C., Rielly, C.D., and Stapley, A.G.F., 2010. Spray-freeze-drying of whey proteins at sub-atmospheric pressures. Dairy Sci. Technol. 90: 321–334. • Costantino, H. R., Firouzabadian, L., Hogeland, K., Wu, C. C., Carrasquillo, K. G., and Cordova, M. 2002. Protein Spray freeze drying- Effect of formulation variables on particle size and stability. J. Pharma. Sci. 91(2): 388-395.
- 51. • Hundre, S.Y., Karthik, P.,and Anandharamakrishnan, C. 2015. Effect of whey protein isolate and b-cyclodextrin wall systems on stability of microencapsulated vanillin by spray freeze drying method. Food Chem. 174: 16–24. • Ishwarya, S.P.and Anandharamakrishnan, C. 2015. Spray-Freeze- Drying approach for soluble coffee processing and its effect on quality characteristics. J. Food Eng. 149: 171-180. • Leuenberger, H. 2002. Spray Freeze drying - the process of choice for low water soluble drugs. J. Nanoparticle Res. 4: 111-119. • Wang, Y., Ye, H., Zhou, C., Lv, F., Bie, X., and Lu, Z. 2012. Study on the spray drying encapsulation of lutein in the porous starch and gelatin mixture. Eur. Food Res. Technol. 234: 157–163 REFERENCE
- 52. THANKYOU
Editor's Notes
- Drying is one of the oldest methods of preserving food. For almost all foods and bioproducts, drying involves the removal of water from the material via the vapour phase Drying results in shelf stable products which can be kept in a good condition for months or even years at ambient temperature. The principal reasons for this are that the microorganisms which cause food spoilage and decay are unable to grow and multiply in the absence of sufficient water and many of the enzymes which promote undesired changes in the chemical composition of the food cannot function without water (SD) and (FD) are widely used methods for drying of heat-sensitive materials for long-term preservation and transport
- Spray drying (SD) is a well-established technique for producing dried powdered products, involving rapid evaporation of water from an atomized liquid fed into a spray chamber Hot air flows inside the chamber in a co-current or counter current direction, evaporating water from the atomized particles and transforming the aqueous feed into a dry powdered product Spray drying is advantageous in terms of producing free flowing powders with a controlled particle size range at a fast drying rate Despite this positive aspects, the method can suffer from significant losses of volatile materials and thermal degradation of heat sensitive materials owing to the operation at high inlet temperatures.
- Freeze drying (FD), preserving heat labile components In the FD process, the material is first frozen at a low temperature, forming ice crystals. These crystals are sublimed from the solid state directly into the vapour phase in a vacuum chamber in a process known as primary drying. The prerequisite for sublimation is that the vapour pressure and the temperature should both be held below that of the triple point of water The sorbed water that remains in the solute matrix (the freeze concentrated non-ice phase), is then further reduced by desorption (secondary drying)
- The researchers extensively studied the different freezing mechanisms by microscopic examination. Malecki et al. (1970) attempted to reduce the drying time by atomizing liquid foods into a cryogenic medium (liquid nitrogen) and the frozen particles are sublimed. He reported that the reduction in droplet size greatly enhanced the sublimation rate When Heldman and Hohner (1974) mathematically modelled the simultaneous heat and mass transfer taking place during the atmospheric freeze drying process, they concluded that reducing particle size and increase in surface mass transfer coefficient are effective ways to increase the drying rate. Both freezing and freeze drying times vary approximately with the square of the sample thickness. Hence reducing both freezing and freeze drying times. This is the basis of the spray-freeze-drying (SFD) technique.
- SFD is a unique drying technique as it is a combination of both spray drying and freeze drying which is a three-step process involves a liquid or solution being atomized into droplets, solidified by contact with a cold fluid, and sublimed at low temperature and pressure. Atomisation- Liquid or solution being atomized into droplets Freezing-Solidified by contact with a cold fluid Drying- Sublimed at low temperature and pressure
- As in spray drying, the process involves spraying or atomizing a feedstock, which can be a solution, a suspension or a fluid with a complex rheology. This is done by using a variety of nozzles such as one fluid (hydraulic), two fluid (pneumatic), or ultrasonic nozzles. 2. Two fluid nozzles generally produce a finer spray but do introduce warm gas into the system which will affect cooling rates 3. More recent experiments with SFD have made use of four fluid nozzles and ultrasonic nozzles
- Two separate liquid feeds are supplied which are atomized by separate air streams, and the droplets collide with each other at the nozzle tip. These are then passed into liquid nitrogen 20 cm below the nozzle. It is found that the particles has a fine porous structure producing a vast specific surface area.
- Ultrasonic nozzles are a type of spray nozzle that uses high frequency sound waves produced by piezoelectric transducers acting upon the nozzle tip that will create capillary wave in a liquid film The ultrasonic nozzle atomizers can be used to prepare large, porous particles from a range of water soluble materials. The key parameter controlling the geometric size of particles is the ultrasonic nozzle frequency, which controlled the size of liquid droplets. Provide a high degree of control over particle size by varying the frequency of the ultrasonic atomiser.
- After atomisation, the fine droplets are quickly frozen upon contact with a cryogen to form icy particles. The freezing process comprises of a number of stages. The figure shows the time temperature profile of coffee solution In Figure: (a) initial cooling to a super cooled temperature below the normal freezing temperature, Next slide…
- (b) nucleation followed by growth of ice crystals and the subsequent rapid evolution of latent heat associated with fast crystal growth, ( termed recalescence, ) (c) further, slower crystal growth which is limited by heat transfer from the cryogenic fluid, during which some freezing point depression may occur. (d) once freezing is complete, cooling of the frozen particle down to the cryogen temperature. However, substances other than pure water will not solidify completely owing to the freeze concentration of solution in the interstices between ice crystals. Freezing-point depression describes the process in which adding a solute to a solvent decreases the freezing point of the solvent
- A number of different methods for spray freezing are in existence. These are categorised as……
- SFV involves the atomisation of a liquid and contacting the resulting spray with cold desiccated gas to freeze the droplets SFV is a complex process which involves a number of mechanisms: the formation and motion of individual droplets with respect to each other and the gas heat transfer between the gas and the droplets, that depends on the local conditions, e.g. gas temperature, droplet temperature and droplet-gas slip velocity Next slide…
- (iii) freezing and ice crystallization within the drops. During spray freezing, the freezing rate (cooling rate) and the nucleation rate are the two important factors that influence the microstructure of the frozen droplets.
- In this process, the feed solution is atomized through a nozzle positioned a small distance above a boiling cryogenic liquid The droplets may begin to solidify while passing through the vapour gap and then freeze completely as contact is made with the liquid. The suspended frozen particles are then separated from the liquid nitrogen.
- In this, with SFL, the nozzle is inserted beneath the surface and directly into a cold liquid The liquid can be a cryogenic liquid such as liquid nitrogen, argon, hydrofluoroether or pentane and these can be used at atmospheric pressure The cryogen may be stirred by an impeller inserted into the vessel to avoid clumping of the particles The frozen particles are then lyophilized to obtain dry, free flowing powders The much greater viscosity and density of a liquid compared to a gas means that much smaller droplets can be produced than when atomizing into a gas The very fast freezing rates prevent the phase separation of solutes within the feed solution and induce the rapid formation of amorphous structures, which can reduce protein denaturation when spray freezing
- Once spray freezing is complete, the suspended frozen droplets are collected by sieves or separated after the cryogen is allowed to boil off The collected frozen droplets are transferred to pre-chilled shelves (typically, ≤ - 40 0C) in a lyophilizer for subsequent drying primary drying phase is performed at low pressure and 2 0C to 5 0C below the product collapse temperature (Tc) to avoid collapse and maintain an elegant cake structure Next slide
- Conventional freeze dryers are operated under vacuum which is one reason for the expense of the process In principle, freeze drying is thermodynamically possible even at higher overall pressures so long as the partial pressure of water remains low. atmospheric freeze-drying process in which the partial pressure of water in the drying chamber is held at very low value Hence the “atmospheric freeze drying” (AFD) process which uses a cold gas (such as air, nitrogen or helium) as a water removal and heat transfer medium to cause sublimation of moisture from a frozen material at or near atmospheric pressure The convective freeze drying medium i.e., cold air stream, kept dry by a molecular sieve desiccant or by a refrigerated condenser, should be circulated
- The SFD particles are spherical with fine pores on the surface while powder from FD forms a cake-like structure with a highly porous surface. SD encapsulated powder has a smooth surface morphology with spherical structure As discussed earlier, the porous structure of the powder obtained from SFD and FD is attributed to the ice crystal formation in the freezing step and the subsequent sublimation in the freeze drying stage.
- The highly porous spherical shaped particles produced using SFD exhibites less rehydration time comparable to FD and far superior than that from SD The percentage oxidation during drying is less in SFD against SD and FD. So SFD has high oxidative stability under different storage conditions SFD microencapsulated product has lower encapsulation efficiency as compared to SD and FD. SFD is needed a two-thirds reduction in processing time than SD and FD processes.
- Every process has its own merits and demerits. It is always important to understand the limitations of any technique When conventional freeze drying is employed after the spray freezing step of SFD, the major disadvantage is the high fixed and operating cost. This is due to the energy intensive operation demanded by the requirement of vacuum and the batch mode operation which leads to additional cost. The disadvantage with the SFV/L technique, particularly when being used for biological products, is the loss of protein stability during the atomisation step. In addition, the rapid cooling of liquid droplets produces a large ice-liquid interface which is found to denature proteins.
- Soluble coffee refers to the coffee powder obtained from freshly roasted and ground pure coffee beans Spray drying (SD) and freeze drying (FD) are the conventional soluble coffee manufacturing techniques SD and FD are associated with some limitations
- The work comprises of a detailed comparative study between the SFD, FD and SD coffee samples for their aroma profile, volatile retention, solubility, morphology, particle size analysis, flow characteristics and colour.
- Coffee solution was prepared by dissolving commercial instant pure coffee powder in distilled water at a mass fraction of 40% w/w of the solution. The rig is an arrangement comprising of a twin fluid nozzle, peristaltic pump and polystyrene container (32 × 10-2 m × 16 × 10-2 m) connected to a liquid nitrogen dewar. A disk blade impeller was used for mixing the contents. The distance between nozzle and liquid nitrogen was optimized and maintained at 10 cm. A twin fluid nozzle atomizer was used with compressed air pressure of 588.39 kPa. Feed flow rate was set at 6 mL/min
- The resultant frozen particles were transferred to stainless steel trays and loaded to the freeze dryer where the frozen particles were subjected to primary and secondary freeze drying Temperature range of primary drying stage was - 25 0C to -10 0C under vacuum of 107 Pa and secondary drying was carried out at 10 0C under a vacuum of 40 Pa On completion of drying, product was collected from the trays, packed in polythene bags, sealed, and wrapped in aluminium foil and stored in a desiccator at the ambient temperature.
- SD was carried out in a single stage, short type, pilot scale dryer of co-current drying configuration A twin fluid nozzle atomizer was used at a compressed air pressure of 392.27 kPa. Ambient air was directly heated in a burner using LPG gas, allowing control of the inlet air temperature at 150 ± 2 0C. outlet air temperature was maintained at 100 ±2 0C by the adjusted feed flow rate Product was collected from the outlet chamber, packed in polythene bags, sealed, and wrapped in aluminium foil and stored in a desiccator at the ambient temperature.
- The coffee solution was freeze-dried using the pilot scale freeze dryer (Model: Lyodryer-LT-5S; Lyophilization systems Inc., USA) at a shelf temperature starting from -40 0C, progressing towards 10 0C. The freeze dried coffee powder was collected from the trays, packed in polythene bags, sealed, and wrapped in aluminium foil and stored in a desiccator at the ambient temperature.
- The moisture content (% wet basis) was analyzed based on the gravimetric determination of the mass loss on drying Volatile analysis was done using headspace solid phase microextraction (HS–SPME) followed by gas chromatography-mass spectrometry (GC–MS). Solubility The time taken for complete dissolution without any lumps on the surface Scanning electron microscope (SEM) was used to study the morphology of the SFD, FD and SD coffee powder samples Particle size and shape of dried coffee powder samples (SFD, FD and SD) was measured using laser diffraction-based particle size and shape analyzer
- Moisture content of SFD and FD coffee samples were higher than that of SD The lower moisture content of SD coffee was an expected outcome due to the high temperature employed, which accelerated the drying rate of droplets and promoted lower moisture content
- Fig. shows the comparison of volatile retention between the SFD, FD and SD coffee samples. SFD sample showed highest retention of all the chosen marker compounds, followed by FD and SD samples. During the freezing step of FD, the aroma components were permanently encapsulated by the dissolved solids and hence protected from losses. The higher solids concentration along with lower sublimation temperature might have facilitated the earlier selective diffusion phenomenon and eventually higher volatile retention of SFD powder.
- Fig shows the SEM images of the SFD, FD and SD coffee samples which clearly revealed the difference in the product microstructure SFD coffee particles showed highly porous and rough surface with a spherical shape (indicating no collapse); SD sample exhibited smooth and spherical shape 4. FD coffee powder showed relatively less porous (than SFD), with flaky structure. Fine pores on the surface of SFD powder was possibly due to the formation of numerous fine ice crystals during the spray freezing step which subsequently sublimed during the primary phase of the freeze drying step. the finely divided droplets generated by atomization promoted a rapid freezing rate in SFD, leading to the formation of a larger number of smaller ice crystals, which on subsequent sublimation resulted in a porous surface.
- The greater mean volume diameter resultant from SFD over SD can possibly be attributed to the gradual agglomeration and solidification of the atomized feed droplets as they pass through the vapour phase before settling to the surface of the cryogenic liquid. SFD exhibited comparatively more instantaneous solubility compared to SD and FD samples. The relationship between particle size and solubility is that the solubility increases with decrease in particle size due to increased specific surface area and an additional surface energy of the particle.
- So the paper concluded that……..
- An SEM was used to evaluate the powder surface and structure after SFD. The dried powder samples were attached to double-sided carbon tabs and mounted on the SEM support, which was coated with a thin layer of gold for 10 min. A laser particle size analyzer was used to determine the particle size and particle size distribution. Particle diameter was indicated by volume (%). Each dried powder sample (10 mg) was dispersed in 40 ml of hexane and then analyzed.
- The moisture content of microencapsulated vanillin power was determined gravimetrically on wet basis Scanning electron microscope was used to study the morphology of microencapsulated vanillin powder The particle size distribution of the microencapsulated vanillin powders were measured using a laser light diffraction particle size analyser Microencapsulation efficiency (MEE) and surface vanillin efficiency (SVE) were determined