Effect of foaming agents and dilution ratio on physicochemical and bioactive compounds profile of dried palmyra pulp

Abstract

The study was carried out to observe the effect of glycerol monostearate (1.0 %, 2.0 %, and 3.0 %), soy protein isolate (0.5 %, 1.0 %, and 1.5 %) and dilution ratio (1:1, 1:1.5) on foam characteristics at whipping time of 4 min. All the samples were incorporated with 0.5 % methyl cellulose (MC) as foam stabiliser and 5 % maltodextrin (MD) as drying aid. The effect of different drying air temperatures (60 °C and 70 °C) at foam thickness of 4 mm on phytochemical, biochemical and functional quality attributes was studied. The efficacy of artificial neural network (ANN) on foam-mat drying kinetics was tested. Foam expansion of the palmyra pulp increased to 108 % when added with 2 % GMS and diluted to 1:1.5. The increase was even more up to 138 % when the same diluted pulp was added with 1.5 % SPI. On the contrary, the foam retention and the foam stability were reduced at a higher dilution ratio. GMS (2 %) or SPI (1 %), each diluted at a 1:1 ratio, exhibited better foaming and colour characteristics. Drying was faster in pulp foamed with SPI (1 %) than in pulp incorporated with GMS (2 %). Non-foamed pulp showed lower drying rates and produced a compact sheet-like mat with a relatively harder and sticky texture. Effective moisture diffusivity values ranged from 1.820 × 10−8 to 2.721 × 10−8 (m2/min) and increased with an increase in the drying temperature. The tansig transfer function of ANN modelling could best predict the moisture ratio with drying time for all the foamed and non-foamed samples. Quality analysis showed that the palmyra pulp foamed with 0.5 % MC, 5 %, MD, and 1 % SPI, diluted at a 1:1 ratio, whipped for 4 min, and dried at 70 °C with foam thickness of 4 mm could produce the powder with best quality attributes. The developed powder was found to possess 79.341 ± 0.998 mg GAE/100 g of total phenolic content, 72.669 ± 0.964 % of antioxidant activity, 60.526 ± 0.975 mg/100 g of ascorbic acid content, 35.287 ± 0.973 % of reducing sugar, 15661 ± 192 µg/100 g of β-carotene with water absorption and hygroscopicity of 2.374 ± 0.827 g/g and 38.487 ± 1.020 % respectively.