14A-8

M. MARCOTTE, Food Research and Development Centre, Agriculture and Agri-food Canada, 3600 Casavant O., Saint-Hyacinthe, QC J2S 8E3, Canada and S. Grabowski.

For small fruits, such as cranberries, blueberries or cherries, skin pretreatment before osmotic or air dehydration plays an important role. Cut cranberries were found the most suitable for osmotic process as the consumers prefer foods without any chemicals or thermal treatment.

The objective of this study was to develop simple mathematical model of mass diffusion during osmotic dehydration and sugar infusion of cranberries cut to different ratios (a) of open-by-cut to a whole surface.

Cranberries of Steven variety were cut: (1) centrally, into halves (which gives 30% open surface), (2) to 50% open surface (cuts from both ends of berries), (3) to 20%, or (4) to 10%. Sucrose syrup of 40, 50, 60 and 67.5 °Brix and temperatures 40, 50 and 60 °C were used to determine kinetics of water loss (WL) and sugar gain (SG).

The results for both WL and SG show strong effect of surface ratio (a), temperature (T) and syrup concentration (C_s), with prevailing effect of a. For the temperature effect, an Arhenius model described well the process. Almost linear increase of WL and SG with sucrose concentration was observed. For the effect of surface ratio a simple mathematical model for effective mass diffusivity was proposed: D_eff=D_op (C_s,T) x a + D_wh (C_s,T) x (1-a) , where D_op and D_wh are effective diffusivities of the cut and uncut parts of cranberry, respectively. Both parameters are function of the syrup concentration (C_s) and temperature (T). For water loss, at a specific conditions (60 °Brix and 50 °C), the values of D_op and D_wh were 2.4 x 10^-9 m²/s and 1.7x10^-11 m²/s, respectively, while for sugar infusion 10^-9 m²/s and 1.65x10^-11 m²/s, respectively.

Proposed model as well as process characteristics can be applied to other fruits and vegetables cut before next steps of processing.