Pears freezing

For adsorption isotherms, pear cubes (10 mm X 10 mm) were frozen at — 40°C and freeze-dried (Telstar Lioalfa-6 lyophyliser) at 10 Pa. Afterwards, samples were placed in chambers with controlled relative humidity (RH) up to equilibrium was reached. Desorption isotherms were obtained in pear slices with skin (with approximately 8 cm diameter and 10 mm thickness), partially dehydrated in a conventional dryer at 45°C for different times to ensure different final water contents in the samples. After the drying treatment, samples were kept in plastic bags under refrigeration to ensure the internal moisture equilibration and then their water activity was measured. Experiments were carried out in triplicate for each sample. 

Figure 4. Photomicrographs of pear cells freezing under different cooling regimes on the cryomicroscope stage, a-d, fast freezing at a cooling rate of 40 C/min. Photographs in time sequence, top to bottom. Continued on next page.

Appearance Opaque, pearly, white liquid pH, as is 6.5-7.5 Solids, % 41-43 Viscosity 25C, cps 250-300 Freeze/thaw, 3 cycles Pass Use Instructions ... 

Chemical Designations — Synonyms Amyl Acetate, Mixed Isomers Pentyl Acetates Chemical Formula CH3COOC5H,. Observable Characteristics — Physical State (as normally shipped) Liquid Color Colorless to yellow Odor Pleasant banana-like mild characteristic banana- or pear-like odor Physical and Chemical Properties — Physical State at 15"C and 1 atm. Liquid Molecular Weight 130.19 Boiling Point at 1 atm. 295, 146, 419 Freezing Point <-148, <-100, <173 Critical Temperature Not pertinent Critical Pressure Not pertinent Specific Gravity 0.876 at 20"C (liquid) Vapor (Gas) Density Not pertinent Ratio of Specific Heats of Vapor (Gas) Not pertinent Latent Heat of Vaporization 140, 75, 3.1 Heat of Combustion -13,360, -7423, -310.8 Heat of... 

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