Optimization of Osmo-Cum-Microwave Dehydration Process for Oyster Mushrooms (Pleurotus sajor-caju)
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Date
2014
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Punjab Agricultural University, Ludhiana
Abstract
Investigations were carried out on “Optimization of Osmo-Cum-Microwave Dehydration Process for
Oyster Mushrooms (Pleurotus sajor-caju)”. The effect of various independent process parameters on
mass transfer kinetics (water loss and solute gain) was studied. These process variables include solution
concentration (salt: 10–20%; salt-sugar: 15 – (45- 65) °B), solution temperature (30–60° C) immersion
time (15–240 min) and solution to fruit ratio (4:1 to 8:1). Water loss and solute gain increased with
solution temperature, solution concentration, duration of osmosis over the entire osmotic dehydration
process. The moisture content reduced from 90.3 to 45 - 48 % (wb). Effective water diffusivity varied
between 1.13 - 2.58 x 10-9 m2/s and 1.59 - 3.0x 10-9 m2/s, solute diffusivity between 3.92 - 9.9 x 10-10
m2/s and 9.44 x 10-10 - 1.02 x 10-9 m2/s respectively for mushrooms treated with salt and salt-sugar
respectively. Power and Page models showed the highest adequacy of fit for osmotic dehydration
of mushrooms treated with salt and salt-sugar solutions respectively. Optimum operating conditions
found were: solution temperature – 45o C, immersion time – 53.54 min, salt concentration – 14.09%
and solution to fruit ratio 6.08:1. Corresponding optimum values for mushrooms treated with salt
solution were, 38.13, 2.1 and 36.02 (g/100 g initial mass) for water loss, solute gain and weight
reduction respectively. Optimum operating conditions for mushrooms treated with salt-sugar were,
solution temperature – 42.3° C, immersion time – 44.21 min, salt-sugar concentration – 15 %: 52.57° B
and solution to fruit ratio 4.99:1. At these optimum values, water loss, solute gain and weight reduction
was 41, 2.15 and 38.6 (g/100 g initial mass). Microwave dehydration of pre-osmosed mushroom was
carried out at three power levels of 540, 810 and 1080 W. Moisture content of dehydrated mushroom
reduced from 45 - 48 to 5.7 – 6 % (wb). Effective moisture diffusivities varied between 1.18 -
2.027x10-9 m2 /s and 1.29 - 2.65x10-9 m2 /s for mushrooms treated with salt and salt-sugar respectively.
Logarithmic model showed the highest adequacy of fit for microwave dehydration in the both the
cases. The quality of dehydrated mushrooms viz. colour, texture, rehydration ratio, shrinkage ratio and
overall acceptability were analyzed for optimization of drying process variables. The optimum
condition of microwave drying found were; microwave power level - 810W, L - 48.77, a - 4.41, b -
10.91, ∆E - 10.24, hardness - 1639.56 g-f, chewiness - 429.05 g/cm2, RR - 1.94, SR - 0.93, aw - 0.461,
ascorbic acid - 1.8 with an overall acceptability of 80.5 %, for dehydrated mushrooms treated with salt.
For mushroom treated with salt-sugar, optimum conditions of microwave drying found were;
microwave power level - 810 W, L - 46.66, a - 5.8, b - 15.74, ∆E - 14.15, hardness - 1342.05 g-f,
chewiness - 1270.97 g/cm2, RR - 1.89, SR - 0.93, aw - 0.453, ascorbic acid - 1.87 with an overall
acceptability of 83 %. The best dried product obtained through optimization was packed in three
materials viz; LDPE, HDPE and LAP and stored under refrigerated and ambient conditions for 3
months. The quality attributes of stored product like colour, texture, rehydration ratio, moisture
content, water activity, ascorbic acid and overall acceptability were evaluated at 15 days interval. The
dried mushrooms packed in laminated aluminium were found to be highly acceptable up to 3 months of
storage.
Description
Keywords
Oyster mushroom, Processing and Food Engineering, osmotic dehydration, osmotic dehydration, drying kinetics