14A-29

V. GHOSH¹, L. Xiong, and R. C. Anantheswaran. (1) Department of Food Science, Pennsylvania State University, 111 Borland Lab., University Park, PA 16802

Modified atmosphere packaging (MAP) is used for packaging fruits and vegetables to increase their shelf life. In the design of MAP, a plastic film is selected to allow a desired gas concentration inside the package. The plastic films currently available are suited for products with low to medium respiration rates. For products with high respiration rates (> 60 cc h^-1 at 10^oC) it is necessary to use micro-perforations to allow enough oxygen to diffuse through the film. In order to design a package with micro-perforated films, the size and the number of micro-perforation for a package should be known. The objective of this work was to design a modified atmosphere package for mushrooms using micro-perforated films.

A mass balance equation was used to develop a mathematical model. The model took into consideration, the respiration rate of mushrooms, gas transfer through the micro-perforations, and gas transfer through the film. For modeling diffusion through the micro-perforations, the model proposed by Fishman et al. (1996) (J=-D(C - C_A)/L_h; L_h=thickness of the film + radius of the perforation) was used to determine the number of micro-perforations needed at 12^oC. Two different types of mushrooms were considered, normally grown and CaCl₂ irrigated. Micro-perforations of sizes 100, 150 and 200 mm were considered for modeling.

The model was applied to a package of 225 g of mushrooms, with a steady state in-package oxygen concentration of 10%. For the normally grown mushroom, the number of perforations required for each size were 29 x100 mm, 17 x 150 mm or 11 for 200 mm. For the CaCl₂ irrigated mushrooms the number of perforations required in each case, were 29 for 100 mm, 18 for 150 mm and 12 for 200 mm.