| Abstract | The effect of fish powder and frying conditions on physico-chemical properties in deep fried rice crackers and vacuum fried rice crackers were investigated. The optimum condition of deep fried rice crackers was determined. The effect of fish powder incorporated with methylcellulose in oil uptake was also studied. A two-dimensional model developed from the two scale hybrid mixture theory was numerically solved using finite element method to simulate the frying process. Frying parameters such as temperature distribution and heat flux, volume fraction of water, volume fraction of oil, pressure distribution were obtained. The model predicted average moisture content and oil content were validated by comparing with the experimental data. Physico-chemical properties of fried rice crackers were studied as a function of fish powder content, processing condition, frying temperature and frying time. The results showed that addition of fish powder to tend of 5, 10 and 15 g/100 g reduced the oil uptake by approximately 10, 14 and 22 g/100g (dm b), respectively, in comparison to the control without fish powder. The deep fried rice crackers mixed with fish powder lowered the crispiness and the expansion ratio, but enhanced the bulk density as compared to the control samples. The color parameter, L * of fried rice crackers decreased with increase in fish powder content. In contrast, a* and b* values increased with increase in fish powder content. The moisture content of deep fried rice crackers decreased with increase in frying temperature and time. The oil uptake in fried rice crackers increased with increase in frying time but decreased with increase in frying temperature. With increase in frying temperature and time, the texture of the rice crackers became harder, the bulk density increased, and the expansion ratio decreased. The optimum condition obtained in desirable physico-chemical properties and minimum oil uptake were rice crackers with fish powder content of 9g/100 g, fried at a temperature of 220 °C for 60 s. In the study on the physico-chemical properties of vacuum fried rice crackers, the fish powder content of 5 and 10 g/100 g fried at 100, 120 and 140°C for 2, 4 and 6 min were investigated. The vacuum pressure was set at 9.33 x 10⁴ Pa. The vacuum fried rice crackers mixed with 5 and 10 g/100 g of fish powder content reduced oil content by approximately 15 and 22 g/1 00 g ( dm b), respectively in comparison to the control samples. The fried rice crackers mixed with fish powder content were lower in hardness and expansion ratio, but higher in bulk density in comparison to the control crackers. The L * value of vacuum fried rice crackers decreased when the fish powder content increased. Conversely, a* and b* values increased with increase in fish powder content. The moisture content in the vacuum fried rice crackers decreased with increase in frying time and temperature. In contrast, the oil content in the vacuum fried rice crackers increased with increase in the frying time and temperature. As the frying time and frying temperature increased, the vacuum fried rice crackers attained low hardness, slightly higher expansion ratio, and slightly lower bulk density. The effect of fish powder content incorporated with methylcellulose in moisture and oil content in deep fried rice crackers were also studied. Methylcellulose of 1 and 2 g/100 g were added to the rice crackers with the fish power content of 5 g/1 00 g and the crackers without fish powder. The addition of methylcellu10se combined with fish powder content helped to reduce the oil content by approximately 15 g/100 g (dm b) in comparison to the crackers without fish powder content. In contrast, the addition of only methylcellulose slightly decreased the oil content in the crackers. The moisture content in the fried rice crackers increased with increase in the amount of methylcellulose. However, there was no significant difference (P 2: 0.05) between the rice crackers with fish powder content of 5 g/IOO g and methylcellulose of I and 2 g/l 00 g. A two-scale hybrid mixture theory based transport equations for the swelling of biopolymeric media were used to predict the heat and mass transfer during frying in deep fried rice crackers. Solid, water, oil and vapor interacted by exchange of thermodynamic properties including mass, momentum, energy and entropy at mesoscale. The bulk fluid interacted with the solid polymeric matrix. At microscale, the solid phase was assumed as elastic and the solvent phase was considered as viscous. Four coupled relations, consisted of water, oil, vapor and heat transfer equations, were solved by using the finite element method. A novel formula for near equilibrium evaporation was used in this study and expressed in terms of the evaporation rate during frying. The distribution profiles of the volume fraction of water and oil including pressure and temperature were obtained as a function of frying time and position. The predicted average moisture and oil content were in good agreement with the experimental data. The purposed formula for near equilibrium evaporation was able to describe well the evaporation process. The evaporation rate was occurred rapidly for the first 20 s of frying time. This resulted in a quick high pressure buildup and a significantly decrease in volume fraction of water. After 20 s of frying time, the crust began to develop resulting in low heat capacity in the crust's region, which contributed to marked increase in the temperature. The spatial distribution profiles showed that the higher the frying temperature, the faster the evaporation rate. Faster increase in evaporation rate, were also the result of increasing pressure and water loss. The volume fraction of oil increased with the increase in frying time. The frying simulation can be developed by using three-scale hybrid mixture theory in order to suit the real situation of porous media food. Furthermore, the input parameters should be also developed to give the better results. |