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Vitamin C contents of pretreated strawberries did not change during 2 mo of freezing, but after jam cooking and storage, the vitamin C contents of all the studied jams decreased dramatically. Jams made from strawberries treated with CaCl 2 and PME in a vacuum had the highest firmness compared to the reference or other pretreated jam strawberries (p , 0.05). According to sensory evaluation of the jams, different prefreezing treatments were shown to have a significant influence on the sensory attributes evaluated (p , 0.001), the only exception being the redness of color after 4 mo storage. EnzymeA liquid enzyme preparation of a microbial pectin methylesterase (PME) from

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Different calcium chloride (CaCl 2 ) and pectin methylesterase (PME) prefreezing treatments in a vacuum were used to clarify the most effective prefreezing factors for strawberries and traditional jams. Fractional factorial design and modeling were used. CaCl 2 had the greatest effect on the majority of the 15 studied responses (p < 0.001). The pretreatment time should be short (about 5 to 10 min), the temperature low (less than 20°C), the vacuum level high (pressure less than 10 kPa), the CaCl 2 concentration moderate (about 1%) and the dosage of PME comparatively low (about 50 to 100 nkat/g) in order to yield high quality frozen strawberries for jam making.