European food research and technology vol:226 issue:3 pages:437-448
Strawberry halves were infused with pectinmethylesterase (PME) and calcium and subsequently frozen by slow, rapid, cryogenic or high-pressure shift freezing (HPSF). A microscopic procedure including detailed image analysis was used to study the effect of vacuum infusion (VI) and/or freezing on the strawberry tissue structure. Hereto, parameters characterizing the size, the shape and/or smoothness of tissue particles were compared for the different samples. It was found that VI seemed to stabilize the cell walls and the cell-cell contact and did not affect the integrity of the strawberry tissue. Structural damage of untreated strawberry tissue due to freezing was large for all freezing methods applied. Rapid and cryogenic freezing conditions were most favorable. VI was effective to minimize the structural damage of rapidly, cryogenically and high-pressure shift frozen strawberries. Infused strawberries frozen by HPSF showed the most smooth and largest particles from all the frozen samples, indicating the importance of both infusion and a high and homogenous degree of undercooling to obtain maximal structure retention of frozen strawberries.