Equilibrium Sorption Isotherms and Isosteric Heat of Rose Hip Fruits (Rosa Eglanteria)

Figures & data

Table 1 Characteristics of fruits and salts utilized to obtain atmospheres of known equilibrium relative humidity or a_w.

Fruit	°Brix	dry Moisture basis	% Dry solids
Fresh rose hip	16.0 ± 1.3	1.198 ± 0.049	45.5 ± 1.71
Dehydrated rose hip	—	0.043 ± 0.003	95.7 ± 3.6
Salts and their aw in saturated solutions
Salt	aw at 20°C	aw at 40°C	aw at 60°C
Lithium chloride	0.11	0.11	0.11
Potassium acetate	0.23	0.20	0.175
Magnesium chloride	0.33	0.32	0.30
Potassium carbonate	0.43	0.42	0.42
Magnesium nitrate	0.558	0.49	0.43
Sodium bromide	0.565	0.52	0.50
Potassium iodide	0.699	0.66	0.62
Sodium chloride	0.754	0.745	0.741
Potassium chloride	0.85	0.82	0.807

Figure 1 Experimental equilibrium moistures expressed on a dry basis (Xdb) as a function of water activity (a_w) for rose hip fruits during desorption, and the predictions of the five-parameter GAB model fitted in this work.

Table 2 Parameters obtained for regression of experimental data for the seven models tested.

	Parameters
Models	C1	C2	C3	C4	C5	C6
Crapiste and Rotstein[6]	185.088	1.087E + 10	−0.59	4.661
GAB 3 parameters	0.7E + 07	1.15E + 02	1.9
GAB 5 parameters	0.0887	3.392	554.08	0.394	110.439
Xm = C1 ; C0  = C2 ; ΔHc  = C3
K0  = C4 ; ΔHk  = C5
Iglesias and Chirife[8]	3.423	−0.0017	−1.11
Pfost et al.[10]	2900	−205	4.948
Ratti[11]	1.32	−0.165	2.59	−0.07	−1.903	−2.08
Strohman and Yoerger[13]	4.897	−4.813	0.824	−4.74
C1 , C2 , C3 , C4 , C5 , and C6 , are the constant parameters in the models used; aw is the water activity; T the absolute temperature; R the general gas constant, Pws the saturation vapor pressure; and, Xdb the moisture content in dry basis.

Table 3 Error analysis for obtaining parameters of the different models evaluated in Table 2 with corresponding regression coefficients.

Model	Maximum error %	Minimum error %	MRE %	Standard error %	Average residual %	R^2
Crapiste and Rotstein[6]	173.3	−94.8	−32.4	21.6	17.5	0.905
3 parameters GAB	67.2	−54.9	−19.4	12.6	9.4	0.937
5 parameters GAB	8.0	−11.7	− 2.9	3.2	2.9	0.989
Iglesias and Chirife[8]	75.0	−97.0	−1.5	8.9	7.4	0.961
Pfost et al.[10]	103.7	−27.3	8.2	12.6	11.2	0.902
Ratti[11]	66.3	−63.8	1.9	9.5	8.7	0.931
Strohman and Yoerger[13]	94.6	−20.6	.6	11.8	10.7	0.961

Figure 2 Experimental equilibrium moisture contents, expressed on a dry basis (Xdb) as function of water activity, in rose hip fruits during adsorption and predictions of the five-parameter GAB model fitted in this work for desorption.

Table 4 Statistical analysis on experimental values of equilibrium moisture contents arrived at by desorption and adsorption.

ANOVA Desorption – adsorption
Data	Mean	Variance	N
Desorption	0.18237	0.01003	17
Adsorption	0.17278	0.0863	24
F = 0.09937; p = 0.75427
At a level of 0.05, means are not significantly different.

Figure 3 Isosteric heat of sorption as a function of the moisture content for rose hip fruits, and predictions by Eq. (13).

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