STUDIES ON SORPTION ISOTHERMS AND STORAGE LIFE OF SPRAY DRIED GOAT MILK POWDER
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Date
2016-09-30
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UNIVERSITY OF AGRICULTURAL SCIENCES, RAICHUR
Abstract
The aim of this investigation was to study the sorption isotherms and storage life of
spray dried agglomerated goat milk powder. The spray drying feed concentration of 39%, inlet
air temperature of 171 °C and agglomerated at 60 °C with 0.4% binder concentration in
fluidized bed dryer to produce spray dried agglomerated goat milk powder(SDAGMP). The
different temperatures 20, 25 and 30 oC and relative humidities of 10-98% were chosen as
independent variables to study the sorption isotherms. The mean values of moisture uptake by
the SDAGMP were from an initial moisture content of 3.97 (% d.b.) to 49.87, 47.32 and 46.47
(% d.b.) at 20, 25 and 30 oC, respectively. GAB model best described the experimental
adsorption data for SDAGMP. The net isosteric heat of sorption was decreased as the moisture
content increased for temperatures of 20, 25, and 30 °C and moisture contents from 5% to 50%
(d.b.). Net isosteric heat of sorption ranged from 3.49 to 50.35 kJ mol-1.
Storage and shelf-life of milk powders in different packages like aluminium laminated
foil and polyethylene terephthalate (ALF and PET) were carried out under accelerated
condition (38±1 oC; 90±1% RH). Water vapour permeability of the ALF and PET stored at
38 ± 1 oC and 90±1% RH were 5.18410-8 and 2.84310-7 kg.m-2.day-1.Pa-1,respectively. The
mean values of proximate composition of SDAGMP after 49 days of storage viz., moisture
content, fat, protein, carbohydrates, ash, were 5.66%, 23.27%, 25.592%, 39.91% for milk
powder stored in ALF and 6.13% and 6.58%, 22.34%, 22.30%, 40.48% and 5.93 for milk
powder stored in PET, respectively. L*, a* and b* were 72.18, 2.72 and 11.62 for milk powder
stored in ALF and 66.53, 3.88 and 7.22 for milk powder stored in PET, respectively. Predicted
shelf-life period of SDAGMP in ALF and PET based on moisture gain were found to be 245
and 169 days.
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