Adsorption isotherms of pear at several temperatures

Abstract

The moisture adsorption isotherms of pear were determined at 15?C, 30?C and 45?C using the standard static gravimetric method over a range of water activity from 0.112 to 0.920. The experimental data were fitted with isotherm equations recommended in ASAE Standard D245.5. In order to find which equation gives the best results, large number of numerical experiments were performed. After that, several statistical criteria proposed in scientific literature for estimation and selection of the best sorption isotherm equations were used. For each equation and experimental data set, the average performance index was calculated and models were ranked afterwards. After that, some statistical rejection criteria were checked (D?Agostino-Pearson test of normality, single-sample run test and significance and precision of the model parameters). The performed statistical analysis shows that the Guggenheim-Anderson-de Boer (GAB) equation has the highest value of average performance index, but higher correlation between pair of parameters leads to lower precision of estimated parameters.[Projekat Ministarstva nauke Republike Srbije, br. TR 31058]

The Power Series as Water Sorption Isotherm Models

“…The values of equilibrium moisture content used for statistical evaluation of pear for A w from 0.112 to 0.920 at three different temperatures, 15, 30 and 45C, are given in Table (Mitrevski et al . ), while experimental values for equilibrium moisture content of potato at three different temperatures, 30, 45 and 60C, and A w water activity from 0.112 to 0.900 (Table ) (Kiranoudis et al . ) were used from literature.…”

“…Because the regression method, estimation method, the initial step size, start values of parameters, convergence criterion and form of the function have significant influence on the accuracy of estimated parameters (Popovski and Mitrevski ; Mitrevski et al . ), a large number of numerical experiments were performed. The method of indirect nonlinear regression and estimation methods of quasi‐Newton, Simplex, Simplex and quasi‐Newton, Hooke‐Jeeves pattern moves, Hooke‐Jeeves pattern moves and quasi‐Newton, Rosenbrock pattern search, Rosenbrock pattern search and quasi‐Newton, Gauss‐Newton and Levenberg‐Marquardt from computer program StatSoft Statistica (Statsoft Inc., Tulsa, OK, http://www.statsoft.com) were used in the numerical experiments.…”

“…In this study, statistical evaluation of newly generated sorption isotherm models and referent Anderson model for experimentally obtained values of equilibrium moisture for pear and potato was made. The values of equilibrium moisture content used for statistical evaluation of pear for Aw from 0.112 to 0.920 at three different temperatures, 15, 30 and 45C, are given in Table 1 (Mitrevski et al 2014), while experimental values for equilibrium moisture content of potato at three different temperatures, 30, 45 and 60C, and Aw water activity from 0.112 to 0.900 (Table 2) (Kiranoudis et al 1993) were used from literature.…”

“…Several measurements were made using a calliper and only samples with a tolerance of ±5% were used (Mitrevski et al . ). The representative samples taken for determination of sorption isotherms were pre‐dried to final moisture content in a convective dryer at a drying air temperature of 60C and drying air velocity of 1 m/s for a period of 7 h. The equilibrium moisture content of pears was determined at temperatures of 15, 30 and 45C using static gravimetric method (Rahman and Sablani ).…”

“…The pears were peeled and sliced in thin slices in order to obtain uniform samples, with thickness of 4 ± 0.1 mm, before being reduced to a cylinder form with a diameter of 20 ± 0.1 mm. Several measurements were made using a calliper and only samples with a tolerance of ±5% were used (Mitrevski et al 2014). The representative samples taken for determination of sorption isotherms were pre-dried to final moisture content in a convective dryer at a drying air temperature of 60C and drying air velocity of 1 m/s for a period of 7 h. The equilibrium moisture content of pears was determined at temperatures of 15, 30 and 45C using static gravimetric method (Rahman and Sablani 2009 Balingen -Germany) with precision of 0.001 g. The equilibrium between samples and their environment was reached after 21 days as evidenced by the constant weight after two successive weighing of the samples.…”