Physical, chemical and quality properties of starfruit juice, agglomerate and drink

Y.S. Lee and M.S. Faridah

Abstract

Starfruit juice can be converted into powder or agglomerate by the process of fluidized bed drying and agglomeration. One kilogramme of ground sugar was used as a carrier for the fluidized bed drying agglomeration process. Essential minor additives i.e. anhydrous citric acid, starfruit flavour and permitted food colour were used to boost up flavour, sugar-acid balance and eye appeal of the product. Suitable process variables used were 40 °C as the process temperature, 20 m³/h as the volumetric airflow rate which resulted in an air velocity of 1.5 m/s, an atomization pressure of 3 bar and a pump flow rate of 8 g/min. Fresh starfruit juice was used as a binder for the agglomeration process in the fluidized bed dryer which was sprayed at the beginning of the drying process. The juice recovery was 65.07%, the moisture content of the fruit was 90.12% and the colour values were L* = 6.31, a* = – 0.22, b* = 8.76. The total titratable acidity (TTA) of the juice was 0.25%, the pH was 3.52, the total soluble solid (TSS) was 8.0 and the viscosity was 3.0 cP. The bulk density of the agglomerate was 0.63 g/ml, the moisture content ranged from 1.63–1.68% for the storage period of 0–12 months. As the storage time progressed, the colour changed from light yellow to a darker dull yellow. The particle size distribution of the starfruit agglomerate showed that a higher percentage of the particles were retained on the larger meshes. From the cumulative distribution plot, the median diameter for the carrier and agglomerate obtained was 350 μm and 500 μm respectively. The critical moisture content of the agglomerate was 6.0% and the equilibrium relative humidity was 58.5%. Organoleptic evaluation of starfruit drink compared to the juice for the whole storage period was based on five sensory attributes. The nutrient compositions of the agglomerate at zero month of storage did not differ much from the 12th month of storage. Microbiological quality remained the same throughout the 12 months of storage. This indicated laminated OPP/PE/AL/PP (with thickness 20 μ:15 μ:7 μ:25 μ) was suitable to be used for the storage of the starfruit agglomerate for 12 months at room temperature.

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