Available online xxxxKeywords: Conduction Diffusivity Drying Model Moisture Simulation Solar Turmeric A B S T R A C T Drying of turmeric was carried out in a solar conduction dryer (SCD). Drying air temperature was achieved around 39-51°C for an ambient temperature in the range of 25-28°C. Moisture content from 78.65% (wb), was reduced to 6.36% (wb) and 5.50% (wb) for solid and sliced samples respectively in 12 h effective drying time. Drying curve of sliced samples showed more uniform falling in comparison to that of whole samples. The average effective moisture diffusivity was found to be 1.852 · 10 À10 m 2 s À1 for slab samples and 1.456 · 10 À10 m 2 s À1 for solid samples. Out of four models tried for simulation, Page model was found as best fitted thin layer drying model when simulation was done for all the drying data. The overall thermal efficiency of the dryer was found to be 55%. Drying of sliced rhizomes showed better drying kinetics and effective drying time could be reduced by slicing instead of drying in whole form.
Spices are more preferred in powdered form and this invariably demands drying without compromising its quality attributes before grinding. Four different drying methods viz. integrated drying system (IDS), fluidized bed dryer (FBD), electrical oven (EO) and open sun drying (OSD) were selected for comparative study of textural and color changes of ginger and turmeric. The texture values of ginger differed significantly among different drying methods. Minimum crushing strength of 1,124.597 g (IDS) and highest of 1,421.62 g (OSD) was observed. Turmeric dried in IDS reflected maximum (8,789.01 g) and dried in EO showed minimum (6,307.619 g) crushing strength. Color loss values in dried ginger was minimum in IDS (34.795) followed by OSD (32.214), EO (37.479) and FBD (38.131), respectively. Color of dried turmeric was affected maximum in EO (67.354) followed by FBD (61.001) and OSD (58.213). Minimum color loss was observed in IDS (52.681). Instrumental measurement of texture and color attributes showed spices dried in IDS retained best quality attributes among the selected methods.
PRACTICAL APPLICATIONSThe developed solar-biomass integrated drying system, apart from advantage of independence from grid power dependency, could safely be promoted for drying of ginger and turmeric to the stakeholders as evident from the comparative instrumental measurement study of texture and color attributes of the dried products.
Drying of food product helps in reducing the water activity of the farm product to a level below which deterioration does not occur for a definite duration. Spices are invariably dried and used in powdered form. Turmeric is one of the main spices of India which is 80 % of the world's supply of commercial turmeric in fresh weight per year. A natural convection solar-biomass integrated drying system (IDS) was designed and developed. The system was capable of generating adequate and continuous flow of hot air of temperature between 55 and 60C from ambient temperature of 28-30C during experimentation. Blanched turmeric rhizomes were successfully dried. The moisture content was brought down to 6.68 % (db) from initial level of 831.09 % (db). Among different thin layer drying models tested, Page and Modified Page models were found as best fit, when simulation was done for all the drying data. The effective moisture diffusivity of turmeric was calculated as 1.667 3 10 29 m 2 s 21 . Effective drying time in IDS was 14 h while in traditional open sun drying (OSD), the same was 25 h. Negligible effect of drying on curcumin content was observed during the study.
PRACTICAL APPLICATIONSUse of solar energy as well as bio-waste material simultaneously for drying purpose is an effective method of drying to reduce drying cost, provided quality is maintained. Use of a simulation model is an important tool for prediction of performance of drying systems. The work carried out established the quality retention of dried turmeric while satisfying widely accepted simulation models.
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