Question Statement:
Which of the following statements regarding the freeze drying (lyophilization) of biological and food products is/are correct?
Options:
- (A) The operating chamber pressure must be maintained strictly below the triple-point pressure of water ($611.65\text{ Pa}$ or $4.58\text{ mm Hg}$).
- (B) Primary drying involves the sublimation of frozen free ice crystals from the product.
- (C) Secondary drying involves the desorption of bound unfrozen moisture at elevated shelf temperatures under high vacuum.
- (D) Freeze-dried products undergo extensive structural shrinkage and irreversible case hardening.