| Author | Ullah, Javid |
| Call Number | AIT Diss. no.AE-98-05 |
| Subject(s) | Food--Drying
|
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | Drying is one of the most important means of food preservation for solid and liquid foods. Many kinds of dryers are in use for the drying of liquids like drum drying freeze drying, foam mat drying, spray drying, etc. Drying of liquid foods in a spouted bed dryer of inert particles offers an alternative to spray drying with distinct advantages of very compact design, high thermal efficiency and less stringent operating requirements. The liquid is sprayed on the surface of inert particles in the spouted bed. As the liquid on the surface of inert particles is dried and peeled off for simultaneously due to particles agitation, it is subsequently collected in a cyclone. In this study soymilk was dried into free flowing powder form which can be used as a source of protein and for fortification of bakery products, confectionery and sweets. Two different sizes of drying chambers were used with Teflon pellets as inert materials when using water as well as soymilk as feeds. The performance of both the drying chambers was studied to determine surface heat transfer coefficient (h) and empirical models were developed for estimating h values both for water and soymilk. The h values during feeding of water ranged from 8.5 to 160.3 W/m2. ฺC and 8.3 to 172.2 W/m2. ฺC for smaller and bigger drying chamber, respectively. During drying of soymilk the h values ranged from 9.4 to 101.3 W/m2. ฺC and 6.4 to 88.6 W/m2. ฺC for smaller and bigger drying chamber, respectively. Experimental drying conditions included inlet air temperature, airflow rate, feed rate and mass of Teflon pellets in their respective ranges. The outlet air temperature was found to be the function of inlet air temperature, feed rate and airflow rate. Soymilk powder was analyzed for moisture content, solubility index, whiteness, mean particle size and density. The final moisture content of soymilk powder ranged from 1.91 to 7.02 percent wet basis. The powder moisture content decreased with the increase in inlet or outlet air temperature and increased with an increase in the feed rate. The airflow rate and amount of Teflon pellets apparently had no effect on product moisture content. The overall differences in the solubility index of dried powder samples were small but distinct ranging from 0.736 to 0.979. In general the solubility decreased with increasing of inlet or outlet air temperature. Other factors like airflow, amount of Teflon pellets and feed rate had no effect on the solubility of soymilk powder. The whiteness index of soymilk powder ranged from 69.2 to 77.7 and was mainly affected by the inlet or outlet air temperatures. The average values of whiteness index increased with an increase in inlet or outlet air temperatures. Particle density of soymilk powder ranged form 1.1 to 1.287 g/ml. Although the range of particle density was narrow but it showed a slight decrease with the increase in inlet air temperature. The average particle size ranged from 144.2 to 328.3 microns and it increased mainly with an increase in the feed rate. Addition of maltodextrin (10, 30 and 50% dry basis) resulted in slight increase of the solubility of soymilk powder. Sensory tests showed that soymilk powder when reconstituted, boiled, and sweetened, resulted in a better quality beverage compared to freshly prepared and commercially available samples. The contamination of dried powder with the dust of inert particles (Teflon pellets) was estimated to range from 0.005 to 0.067 percent by weight of dried powder. The weight loss in pellets apparently increased with an increase in airflow rate and amount of Teflon pellets present in the drying chamber. Experiments with a small laboratory type spray dryer indicated that the moisture content ans solubility index of dried soymilk decreased with an increase in the outlet and inlet air temperatures similar to spouted bed drying. However, the whiteness of powder decreased with the increase in inlet or outlet air temperature. Particle density of spray dried powder was lower than spouted bed dried product and ranged from 0.82 to 1.01 g/ml showing an increase with increasing feed rate. |
| Year | 1998 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Agricultural and Food Engineering (AE) |
| Chairperson(s) | Jindal, V. Kumar; |
| Examination Committee(s) | Jindal, V. Kumar;Athapol Noomhorm;Vincent, Jean Claude;Kumar, S; |
| Scholarship Donor(s) | DAAD; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1998 |