This paper presents a transparency phenomenon that occurred in hot air and heat pump dried flatrice
noodles, which is explained by the higher colour changes, glassy puffing microstructures,
and lower fat content in comparison to the freeze dried flat-rice noodles. Hot air drying and
heat pump drying recorded the colour changes at an average of 43.87 ± 1.5 twice than colour
change caused by freeze drying at 19.33 ± 1.12 to verify the transparency caused by employing
high temperature to eventually increase the sample lightness. However, the microstructures
study suggested that freeze drying produced distinct pores ranging from 2.05 μm to 27.68
μm whereby hot air drying and heat pump drying merely produced glossy transparent texture.
Indeed, the pores disclose the fat content recorded by freeze drying in flat-rice noodles at 5.62%
± 0.2 twice than the fat content recorded by hot air and heat pump drying at 2.48% ± 0.49.
Therefore, by learning the transparency phenomenon in hot air and heat pump dried noodles
approves that freeze drying eventually preserves the quality attributes of flat-rice noodles as
closest to the fresh flat-rice noodles in terms of colour, microstructures, and fat content.
The effect of chamber pressure of a freeze dryer on essential oil contents, drying kinetics, drying characteristics lemon balm leaves and morphology of lemon balm glandular trichomes (oil reservoirs) were investigated. It was found that overall freeze drying (FD) carried out at high (FD-HP) and low pressure (FD-LP) settings consist of sublimation rate, first falling rate and second falling rate periods. Drying rate of FD-LP dried Lemon Balm leaves are higher than FD-HP dried samples, where the drying rates ranged from 0.063 to 0.449 g H2O/ g DM. s and 0.0365 to 0.395 g H2O/ g DM. s, respectively. 3rd order Polynomial model was found to be the best fit model for both drying kinetics. In terms of product quality, eight (8) major constituents of lemon balm leaves essential oil were quantified. Further to this, electro-microscope was used to observe the peltate glandular hairs structure. Product quality analysis showed that FD-HP retained higher amount of essential oil, shape of glandular hairs, but no positive effect on the freeze drying duration.