Frequency Distribution of Steady-state Oxygen Partial Pressures in Modified-atmosphere Packages of Cut Broccoli

Additional index words. Brassica oleracea, packaging, respiration rate, film permeability, vegetables, modeling Abstract. In one set of modified-atmosphere (MA) packages of cut broccoli ( Brassica oleracea L., Italica Group), O 2 partial pressures ranged from 1.2 to 3.6 kPa at 0C (88 packages, 0.00268-cm-thick low-density polyethylene (LDPE) film, 600- cm 2 film area, 40 ± 0.5 g cut broccoli), and in another set (94 packages, same film and area as before, 25 ± 0.5 g cut broccoli) they ranged from 5.0 to 9.2 kPa. For characterizing O 2 uptake as a function of O 2 partial pressure and determining anaerobic fermentation induction point at 0C, a range of steady-state package O 2 partial pressures was generated by placing different amounts of cut broccoli (10 to 160 g) in LDPE packages. Oxygen uptake was modeled using a Michaelis-Menten-type equation. The maximum rate of product O 2 uptake when O 2 partial pressure was nonlimiting and the package O 2 partial pressure corresponding to half-maximum O 2 uptake were estimated as 147 ± 3 nmol·kg -1 ·s -1 and 0.26 ± 0.025 kPa, respectively. Respiratory quotient and head space ethanol increased sharply below package O 2 partial pressures of 0.15 kPa, indicating stimulation of fermentation within the packages. The frequency distributions of CO 2 production rates were measured for 80 samples of 100 g each of cut broccoli at two O 2 partial pressures (21.0 kPa and 1.3 kPa) using a flow-through method. The average coefficient of variation of the CO 2 production rate was ≈5%. Frequency distributions of O 2 partial pressures were modeled as a function of product-to-product variation in O 2 uptake and package-to-package variation in film permeability using the estimated O 2 uptake characteristics and coefficient of variation. The model was used to predict the target O 2 partial pressures for the design of cut broccoli MA packages. It was predicted that the packages for cut broccoli at 0C should be designed for a target O 2 partial pressure of 2.54 kPa to have actual package O 2 partial pressures ≥1.0 kPa at 0.0001% probability level. Film specifications for MA packaging of cut broccoli at 0C were calculated based on the predicted target O 2 partial pressures.