Although the rheological properties such as viscosity, flow behavior index of guava juice have been investigated, most of them limited to high concentrations and different varieties. Such as guava juice at 9 and 11 oBrix (Zainal et al., 2000; Zainal et al., 2001) and guava juice at 10 – 40 oBrix (Shamsudin et al., 2005). However, the rheological properties of guava juice and puree have not been investigated using the master-curve technique. Furthermore, the comparison on the rheological behavior of guava juice and puree has not done.
The objective of this study was to investigate the effect of temperature and concentration on rheological properties of guava puree and juice and to presents the results of Power law model fitting of the master-curve.
Material and Methods
Preparation of juice
Pink guava purees (Psidium guajava L.) was obtained from Golden Hope Fruit Industries (M) Sdn. and was diluted by adding water in the ratio 1:3 (pink guava puree/ water, w/v) or 300ml: 700ml.
Total soluble solids (0Brix)
Total soluble solids (0Brix) were determined in duplicates by digital refractometer
(Palette series PR-101 cat. No. 3412 ATAGO CO., LTD TOKYO, JAPAN),
Density (? =Kg/m3) of guava juice was determined in triplicate by fluid displacement in pycnometer in an analytical balance, for temperature from 30 to 75°C at 10 °C intervals for guava juice at 3.8°Brix. (Constenla et al., 1989). The temperature was controlled using a thermostatic water bath.
Thermal conductivity and thermal diffusivity were determined using a thermal properties analyzer type KD2, manufactured by Decagon Devices, Inc. USA. It was operating based on the line heat source method and the values were obtained directly from the digital readout.