Experimental and computational fluid dynamics studies on spray-freeze-drying and spray-drying of proteins

This thesis presents an experimental and computational fluid dynamics (CFD) study of spray-drying, spray-freezing and spray-freeze-drying of whey proteins. The effects of varying feed concentration (20 - 40% w/v) and outlet temperature (600 - 120 degrees Celcius) on whey protein denaturation (determined by DSC) and solubility at pH 4.6 (by Kjeldhal and RP-HPLC methods) have been investigated in a pilot-scale cocurrent spray dryer. The study confirms that low outlet gas temperatures (60 and 80 degrees Celcius) produce the lowest amount of denaturation, with almost complete denaturation observed at 120 degrees Celcius. Slightly more denaturation was found with a 40% feed concentration. A reversed phase HPLC technique has been applied to measure the loss of solubility of a-lactalbumin and P-lactoglobulin. Significantly higher losses in solubility were observed for P-lactoglobulin compared to alactalburnin. Increasing the feed concentratioq at higher outlet temperatures also caused noticeable increases in insolubility. The reversed phase HPLC results were consistent with those obtained from total protein nitrogen content (Kjeldhal) analyses. This comparative study suggests that the protein solubility can also be calculated from RP-HPLC technique. Spray-freeze drying is an alternative approach to spray drying, which is less likely to cause protein denaturation and loss of solubility. Conventional freeze-drying involves high capital and operating costs, due to the low temperatures, high vacuum and very long drying times. One solution to this problem is to reduce the dimensions of the material being dried. This is the basis of the spray-freeze-drying technique, involving atomisation of a liquid to form droplets, freezing the droplets and subliming off the ice at low temperature and atmospheric pressure in a fluidised bed. However, the quantities of gas required for atmospheric freeze-drying are prohibitively expensive. A pilot-scale spray-freeze-drying process was investigated, in which fluidisation was performed at sub-atmospheric pressures, allowing rapid freezedrying (in about one hour) but using much less gas. This was demonstrated using whey protein which yields a product with a highly porous structure, with little loss of protein solubility. This process has potential to produce high-value-added food and pharmaceutical products more quickly and cheaply than is currently possible by commercial vacuum freeze-drying processes. CFD simulations were developed for short and tall form spray-dryers to study the particle velocity, temperature and residence time during drying. These simulation results agreed well with the published experimental data. The tall-form spray dryer model predictions showed that more particles impact on the cylindrical wall position and this may affect the protein denaturation and solubility. This study suggests that a short form dryer with a bottom outlet is more suitable for drying of proteins. Similarly, a CFD simulation for the spray-freezing operation was developed to study the gas flow pattern and particle trajectories and histories. This CFD model also includes the latent heat effects during the phase change. The simulation predictions agreed reasonably well with the experimental results. A comparison of simulations for a solid and a hollow cone spray suggested that the latter yields lower particle temperatures with low particle collection efficiency. A modified chamber geometry was proposed and the simulation showed that the new design could achieve higher particle collection efficiencies

Spray-freeze-drying of whey proteins at sub-atmospheric pressures

Spray-freeze-drying (SFD) involves spraying a solution into a cold medium, and freeze-drying the resultant frozen particles, which can be performed by contacting the particles with a cold, dry gas stream in a fluidized bed, typically at atmospheric pressure. This enables much faster drying rates than are usually possible by conventional freeze-drying, due to the small particle sizes involved. However, the quantities of gas required for atmospheric fluidized bed freeze-drying are prohibitively expensive. This has led to a process modification whereby fluidization is performed at sub-atmospheric pressures, which still allows rapid freeze-drying, but using much less gas. This study demonstrates the fluidized bed spray-freeze-drying technique at sub-atmospheric pressures (0.1 bar) using whey protein isolate solution (20% w/w solids) at gas inlet drying temperatures ranging from -10°C to -30°C. The process yields a powder consisting of highly porous particles and shows little loss of solubility for β-lactoglobulin and a-lactalbumin, the principal proteins in the isolate. A wet basis moisture content of 8.1% was achieved after freeze drying at -10 °C for only 1 hour, whilst at 30 °C a longer drying time (100 minutes) produced a wetter product (14% w.b.)

Influence of different hydrocolloids on dispersion of sweet basil seeds (Ocimum basilicum) in fruit-flavoured beverages

Sweet basil seeds (Ocimum basilicum) are a rich source of dietary fiber. Considering the importance of dietary fiber on human health and the rising market demand for functional beverages, an attempt was made to develop fruit-flavoured beverages with basil seeds suspension. Different hydrocolloids like carrageenan, xanthan gum, gelatin and gum arabic were used at 0.02, 0.3, 1 and 2% w/v, respectively, to understand the stability of dispersed sweet basil seeds in fruit-flavoured beverages. The developed beverage samples were analyzed for colour (L*, a*, b*), zeta potential (Z), viscosity and relevant organoleptic qualities. Results showed that beverage composition with xanthan gum had Z value of -34.1 mV and viscosity of 232.6 cP, provided better stability for the dispersion of basil seeds. The hydrocolloids gelatin and xanthan gum showed a slight variation in colour values. Beverages containing 0.3% w/v xanthan gum were found to be the best formulation for the production of fruit-flavoured beverages with uniformly suspended basil seeds

Hermetic storage - an ecofriendly safe storage method for long term storage of black gram: Poster

India is the primary origin of the black gram that is majorly cultivated in the southern part of Asian countries. About 70% of world black gram production comes from India. Black gram is more prone to insect infestation and microorganisms resulting in deterioration of grain quality. These losses can be controlled by following appropriate storage method at farmer’s level. Eco-friendly, safe storage methods are demanded by the customers due to food safety, quality and environmental issues. Hermetic storage is a safe storage method, suitable for long term storage without usage of chemical pesticides. It creates an air tight environment to rapidly exterminate insect development and suppresses micro floral activity. A study was conducted to identify the suitable, cost effective storage method for safe storage of black gram at the farm level. Hermetic bags were made by using different combinations of gunny, polypropylene & storezo bags for the safe storage of black gram. The properties of packaging materials viz., thickness, and water vapour transmission rate significantly affected the quality parameters of the black gram stored in various bags. Moisture content, thousand grain mass, bulk density, insect emergence, and germination percentage of black gram stored in various bags were studied over a storage period of 12 months. Black gram stored in polypropylene and gunny bags was infested with pulse beetle by the third month of the storage period. But black gram stored in bags with hermetic bag as inner layer was not infested up to 12 months and could retain the grain quality.India is the primary origin of the black gram that is majorly cultivated in the southern part of Asian countries. About 70% of world black gram production comes from India. Black gram is more prone to insect infestation and microorganisms resulting in deterioration of grain quality. These losses can be controlled by following appropriate storage method at farmer’s level. Eco-friendly, safe storage methods are demanded by the customers due to food safety, quality and environmental issues. Hermetic storage is a safe storage method, suitable for long term storage without usage of chemical pesticides. It creates an air tight environment to rapidly exterminate insect development and suppresses micro floral activity. A study was conducted to identify the suitable, cost effective storage method for safe storage of black gram at the farm level. Hermetic bags were made by using different combinations of gunny, polypropylene & storezo bags for the safe storage of black gram. The properties of packaging materials viz., thickness, and water vapour transmission rate significantly affected the quality parameters of the black gram stored in various bags. Moisture content, thousand grain mass, bulk density, insect emergence, and germination percentage of black gram stored in various bags were studied over a storage period of 12 months. Black gram stored in polypropylene and gunny bags was infested with pulse beetle by the third month of the storage period. But black gram stored in bags with hermetic bag as inner layer was not infested up to 12 months and could retain the grain quality

A study of particle histories during spray drying using computational fluid dynamic simulations

Computational fluid dynamics (CFD) models for short-form and tall-form spray dryers have been developed, assuming constant rate drying and including particle tracking using the source-in-cell method. The predictions from these models have been validated against published experimental data and other simulations. This study differs from previous work in that particle time histories for velocity, temperature, and residence time and their impact positions on walls during spray drying have been extracted from the simulations. Due to wet-bulb protection effects, particle temperatures are often substantially different from gas temperatures, which is important, because the particle temperature–time history has the most direct impact on product quality. The CFD simulation of an existing tall-form spray dryer indicated that more than 60% of the particles impacted on the cylindrical wall and this may adversely affect product quality, because solids may adhere to the wall for appreciable times, dry out, and lose their wet-bulb protection. The model also predicts differences between the particle primary residence time distributions (RTD) and the gas phase RTD. This study indicates that a short-form dryer with a bottom outlet is more suitable for drying of heat-sensitive products, such as proteins, due to the low amounts of recirculated gas and hence shorter residence time of the particles

Application of computational fluid dynamic (CFD) simulations to spray-freezing operations

A 3-D computational fluid dynamics (CFD) simulation for spray-freezing in a cold gas has been developed and used to identify design improvements. This model includes an approximate method to model the latent heat of fusion, and is able to track particle trajectories. The simulation predictions agreed reasonably well with experimentally measured gas temperatures and droplet velocities. The results suggest that a hollow cone spray is more effective in cooling the particles uniformly. The CFD simulation suggested that build up of an icy layer on the cone walls observed experimentally was due to incomplete freezing of larger particles (> 100 µm). Collection efficiencies could be raised (from 20% to 57%) by increasing the diameter of the chamber outlet

Instrument-based detection methods for adulteration in spice and spice products – A review

Spices play an important role as flavorants, colorants, preservatives and bioactive compounds in medical, food and cosmetic applications. India is the spice bowl of the world and spice production is scattered across the country. Almost every stage of production, including cultivation, harvest, handling, storage, transportation and distribution has impact on spice quality. Adulterants are often intentionally added to fetch better market value through inferior/ unacceptable quality products. Adulterants are a concern to quality, market compliancy and food safety. Over the years, several approaches for quantitative and qualitative detection of adulterants have been developed. Though basic and simple testing methods are available to detect the presence of adulterants, instrument based techniques are often adapted to detect the adulterants quantitatively. The objective of this work is to present a detailed note on these approaches with emphasis on the various analytical techniques used in the detection and quantification of adulterants in spice and spice products

Residence Time Distribution of Glass Ballotini in Isothermal Swirling Flows in a Counter-Current Spray Drying Tower

The particle residence time in counter-current spray drying towers has a significant influence on the moisture content of the powder exiting the tower. Therefore, the reliability of predictions of residence time by numerical methods is highly desirable. A combined experimental and computational fluid dynamics investigation is reported for the prediction of the residence time distributions of glass beads with a narrow size range of 300-425 m in a counter-current tower with isothermal swirling flows of air. The particle-wall collision is taken into account using a rough-wall collision model. Overall, a reasonably good agreement is obtained between the measurements and predictions. Consideration of wall roughness results in greater axial dispersion of particles in the tower compared to a smooth wall assumption. The rough particle-wall collision is important for a reliable prediction of residence time distributions. In addition, analysis of the results infers that the clustering effect of particles on drag and particle-particle interactions are important and should be investigated in a future study

Partitioning of bovine lactoferrin in aqueous two-phase system containing poly(ethylene glycol) and sodium citrate

The partitioning of the whey protein lactoferrin, which is an iron transporter glycoprotein, in an aqueous two-phase system composed of poly(ethylene glycol) (PEG) and sodium citrate was evaluated. Equilibrium data at 25 °C were determined for each system studied using PEG with a molar mass of 1000 and 4000 g·mol1 at pH values of 5.5, 6.5, and 7.5. An increase in the molar mass of the polymer promoted the expansion of the two-phase region and caused the migration of the lactoferrin to the salt-rich bottom phase. An increase in pH also led to the expansion of the biphasic region. However, changing the pH over the tested range slightly affected protein partitioning. Lactoferrin recovery percentages greater than 94% were observed for all of the systems evaluated. The results indicated that lactoferrin can be successfully partitioned in an aqueous two-phase system formed of 14% (w/w) PEG and 10% (w/w) sodium citrate at pH 5.5 and 25 °C. The protein was concentrated 1000-fold in the salt-rich bottom phase in this system.Brazilian agencies FAPESB,CNPq, and FAPEMIG for their financial suppor