Determination of Particle Density and Porosity in Foods and Porous Materials with High Moisture Content

Figures & data

Figure 1 Schematic diagram of the gas pycnometer.

Figure 2 Picture of the gas pycnometer.

Table 1 Operation steps for the gas pycnometer

Calibration	Analysis
1	Measure pressure and temperature (Patm and Tatm) with empty pycnometer and valves 1 and 3 closed.
2	Close valve 2 and open valve 1 setting the pressure at the desired value.
3	After equilibration, measure P1 and T1.
4	Open valve 2 and after equilibration measure P2 and T2.
5	Open valve 3 to exhaust air.
6	After equilibration measure ambient pressure and temperature with calibration cylinder in the sample chamber keeping valves 1 and 3 closed.
7	Repeat steps 2 to 5 at least 3 times.
8	Replace calibration cylinders by the porous material sample with unknown volume.
9	Measure the ambient pressure and temperature with porous material in the sample chamber keeping valves 1 and 3 closed.
10	Repeat steps 2 to 5 at least 5 times.

Table 2 Volume of reference and sample chambers with applied pressure

	Reference chamber (V1), cm^3		Sample chamber (V2), cm^3
Absolute applied pressure (P1), MPa	Eq. 13	n2e=0 in Eq. 12	Eq. 19	n2k=0 in Eq. 18
0.3489	44.5	87.3	46.6	50.5
0.5042	44.3	70.4	46.6	49.3
0.6550	44.3	63.2	46.5	48.6

Table 3 Comparison of tests performed in the gas pycnometer and with other methods of particle volume analysis

	Volume (cm^3)					Relative deviation (%)
	Gas pycnometer		Other methods^(1)
Material	VS	σ	Vom	σ	^(1)Method
Non-porous Metallic Cylinder	29.390	0.019	29.4053	0.0004	Callipers	0.05
Glass spheres	19.635	0.015	19.486	0.005	Liquid Pycnometry	0.76
Sintered sand Cylinder	2.80	0.02	2.811	0.003	Helium Pycnometer	0.39

Table 4 Sensitivity of the results related to the accuracy of the pressure and temperature measurements

P1 (MPa)	ΔP2 (MPa)	ΔVS (cm^3)	ΔT (°C)	ΔVS (cm^3)
0.20	± 0.0001	∓0.10	± 0.1	∓0.054
0.25	± 0.0001	∓0.07	± 0.1	∓0.045
0.35	± 0.0001	∓0.04	± 0.1	∓0.038
0.50	± 0.0001	∓0.03	± 0.1	∓0.034
0.65	± 0.0001	∓0.02	± 0.1	∓0.032

Figure 3 Particle and apparent densities of Golden Delicious apple at different moisture contents.

Figure 4 Porosity of Golden Delicious apple at different moisture contents.

Table 5 Porosity of Golden Delicious apple at different moisture content

Experiment 1			Experiment 2
Moisture content (kgwater/kgdry solid)	Porosity (%)	Standard deviation for the porosity	Moisture content (kgwater/kgdry solid)	Porosity (%)	Standard deviation for the porosity
6.4524	24.38	0.005	6.4524	22.67	0.009
5.4283	31.35	0.002	5.2422	25.71	0.003
4.7354	33.79	0.005	4.4850	27.65	0.004
3.8436	39.20	0.005	3.6195	30.53	0.011
3.0858	42.08	0.004	2.9147	34.31	0.003
2.5875	47.32	0.005	1.8860	40.74	0.005
1.9598	47.25	0.010