272 The Philippine Agricultural Scientist Vol. 90 No. 4 (December 2007) Respiration Modeling of Cherry Tomato K. F. Yaptenco et al. THE PHILIPPINE AGRICULTURAL SCIENTIST ISSN 0031-7454 Vol. 90 No. 4, 272-282 December 2007 Respiration Modeling of Cherry Tomato (cv. Coco) at Different Tempera- tures for Modified Atmosphere Packaging Applications Kevin F. Yaptenco 1* , Ji Gang Kim 2 and Hye Eun Lee 2 Funded by the Post-Doctoral Course Program, NHRI – RDA, South Korea 1 Postharvest Horticulture Training and Research Center, Crop Science Cluster, College of Agriculture, University of the Philippines Los Baños, College, Laguna 4031, Philippines. Tel. no. (49) 536 – 2444; Fax no. (49) 536 – 3259 2 National Horticultural Research Institute – Rural Development Administration, Suwon, South Korea * Author for correspondence; e-mail: kfyaptenco@yahoo.com Oxygen depletion and CO 2 accumulation in a closed respiration system containing fresh cherry tomato (cv. Coco) at the light-red stage of ripeness was monitored. Experiments were carried out at 10, 12.5, 17 and 20 o C. Five models based on enzyme kinetics equations were evaluated using the data gener- ated; the uncompetitive inhibition model was selected for further validation based on goodness of fit to experimental data. Effect of temperature on model parameter V m followed Arrhenius kinetics for both O 2 consumption and CO 2 production rates (R 2 of 0.999 and 0.974, respectively). Computer simulations showed that 0.30–0.45 kg of cherry tomato (cv. Coco) could be packed in 20 cm x 20 cm 30-µm polyethylene (PE) bags and held at 10–20 o C without producing anaerobic O 2 levels; for 40-µm PE, predicted headspace O 2 concentration was below the recommended minimum of 3% at this tempera- ture range. The model predicted gas levels accurately in respiration chambers containing a batch of fruits harvested from a different farm and on a different harvest date; comparison of predicted and measured gas levels showed r 2 of 0.992 for both O 2 and CO 2 . The model was less accurate in predicting O 2 levels in actual 30-µm PE packs; r 2 of predicted and measured gas levels were 0.975 and 0.939 for O 2 and CO 2 , respectively. Packaging trials proved that 30-µm PE could maintain an acceptable quality of fruits for 5 d at 20 o C if fruits were defect-free. Optimum fill weight for a 20 cm x 20 cm pack was 0.45 kg. Key Words: cherry tomato, modelling, modified atmosphere, packaging, respiration Abbreviations: MAP – modified atmosphere package/ing, NHRI – National Horticultural Research Institute, PCI – peel color index, PE – polyethylene, RDA – Rural Development Administration, RQ – respiratory quotient, VQR – visual quality rating INTRODUCTION Modified atmosphere packaging (MAP) is a widely used method to extend the shelf life of many fresh and fresh-cut fruits and vegetables. It commonly involves enclosing the commodity in a plastic film that is permeable to gases, mainly oxygen (O 2 ) and carbon dioxide (CO 2 ). Since the process of respiration requires sufficient O 2 to break down stored carbohydrates, the barrier presented by the plastic film re- sults in a depletion of O 2 that slows down respiration and the changes associated with it, e.g. ripening. On the other hand, CO 2 , as a by-product of respiration, gradually accu- mulates in the pack; in theory, CO 2 can also inhibit respira- tion at sufficiently high levels by (a) simple feedback inhi- bition, (b) affecting mitochondrial activity, (c) altered func- tioning of the citric acid cycle, or (d) competing with the ripening hormone ethylene during enzymatic processes related to respiration (Fonseca et al. 2002). As respiration is gradually inhibited, a state of equilibrium is produced in the package that is determined by the balance between respiration rate of the product (expressed as O 2 consump- tion or CO 2 production) and diffusion rate of gases through the film. If gas diffusion is excessive, modification of the package atmosphere is minimal and results in little or no extension of the shelf life. However, if movement of gases is insufficient, O 2 may be depleted to hypoxic levels (<1%) that could result in physiological disorders in the product (Kader 2002). Hence, an accurate and reliable prediction of the product response to modified atmospheres (MA) is needed to determine the required properties of the pack- age material without the need for extensive trial-and-error experiments. Mathematical models based on Michaelis-Menten type equations for describing enzyme reactions have been