Thermo‐physical Properties of Selected Vegetables as Influenced by Temperature and Moisture Content

Abstract

Thermo‐physical properties of selected vegetables (cassava, eggplant, ginger, green pepper, white radish and zucchini) were evaluated under different conditions of temperature (5 to 40C) and moisture content (30 to 94% wb). Test samples were equilibrated to a given temperature and moisture content prior to use. The thermal conductivity and heat capacity were measured using the line heat source probe and the differential scanning calorimeter, respectively. Depending on the state, temperature, moisture content and the type of vegetable, average heat capacity varied from 1.5 to 4 kJ/kgC, while the thermal conductivity varied from 0.08 to 0.60 W/mC. Heat capacity of the unfrozen vegetables was found to be approximately twice as much as values obtained for the frozen ones. Although both temperature and moisture affected the thermal conductivity, the latter had the greater influence. Generally, differences in measured data and responses to both temperature and moisture content were attributed to differences in structural characteristics and composition. Correlations were developed for estimating thermo‐physical properties of several vegetables.

Physical, mechanical, thermal and electrical properties of cooked red bean (Phaseolus vulgaris L.) for continuous ohmic heating process

“…On the other hand, major differences between the experimental data and the values calculated by Ali et al (2002) were observed. They could be explained by the parameters included in the equation.…”

“…Experimental thermal conductivities at 20°C were compared to those calculated by Zuritz et al (1989) and Ali et al (2002). It may be noted in this table that the mean thermal conductivities measured by Zuritz et al (1989) were within ±4% of the calculated values, which is approximately within the experimental error.…”

“…porosity, anisotropy). The last three decades have seen much effort and progress in developing measurement techniques to obtain new data on the thermal properties of foodstuffs (Ali, Ramaswamy, & Awuah, 2002;Mayer, 2003;Nesvadba et al, 2004;Pakkala, Reinivuo, & Ovaskainen, 2006).…”

“…(13)). Ali et al (2002) proposed an expression developed from experimental data to predict the thermal conductivity of vegetables as a function of temperature, moisture content and density. Table 3 Experimental and predicted thermal properties (q, c, k, a) of particles and liquids at 20°C -mean value, NR: not recorded This correlation is valid for a large range of temperatures and water content and for various vegetables (Eq.…”

Thermophysical properties of Thai seedless guava juice as affected by temperature and concentration

“…That is, rather than freezing at 0°C, many liquid foods freeze at lower temperatures, depending on the concentration and type of the dissolved solids. The higher the level of dissolved solids, the greater the extent of the (Ali, Ramaswamy, & Awuah, 2002). The line heat source thermal conductivity probe is recommended for most food applications because it is simple, fast, convenience, low cost and suitable for small sample sizes (Sweat, 1995).…”