ABSTRACT. The effect of osmotic pretreatment using 50 %(w/v) sucrose, trehaloseormaltitol syrups on the physicochemical properties of frozen pineapple pieces (Josapine variety) of ~6.7 cm in external diameter (without core) and ~0.9 cm in thickness was investigated. Maltitol-treated pineapple pieces had a higher water loss than those treated with sucrose and trehalose (p ≤ 0.05). All three syrups resulted in similar solid gain. Prior to freezing, pineapple pieces were subjected to osmotic pretreatment for 1 hour. This was followed by cooling the pineapple pieces at either slow (0.25ºC/min) or fast (6.13°C/min) cooling rates to -20°C with an untreated sample used as a control. Physicochemical properties including drip loss, firmness, pH, titratable acidity, total soluble solids and colour of samples stored at -20°C for 0, 3, 10, 14, 17 and 24 days were determined. Untreated pineapple pieces exhibited a smaller change in firmness at fast cooling rate compared to slow cooling rate. At fast cooling rate, a higher drip loss was observed for thawed pineapple pieces compared to slow cooling rate. In the presence of maltitol and trehalose, a small change in firmness and higher drip loss was found at slow cooling compared to fast cooling. In the presence of sucrose, there was no significant change in drip loss at both slow and fast cooling rates. Fast cooling in the presence of sucrose, maltitol or trehalose had no effect on firmness of osmo-dehydrofrozen pineapple pieces. Frozen storage of 24 days did not affect the physiochemical properties of osmo-dehydrofrozen pineapples.
KEYWORDS. Ananascomosus, cooling rate, maltitol, sucrose, trehalose