FREQUENCY-DISTRIBUTION OF STEADY-STATE OXYGEN PARTIAL PRESSURES IN MODIFIED-ATMOSPHERE PACKAGES OF CUT BROCCOLI

In one set of modified-atmosphere (MA) packages of cut broccoli (Brass ica oleracea L., Italica Group), O2 partial pressures ranged from 1.2 to 3.6 kPa at 0C [88 packages, 0.00268-cm-thick low-density polyethyle ne (LDPE) film, 600-cm2 film area, 40 +/- 0.5 g cut broccoli], and in another set (94 packages, same film and area as before, 25 +/- 0.5 g c ut broccoli) they ranged from 5.0 to 9.2 kPa. For characterizing O2 up take as a function of O2 partial pressure and determining anaerobic fe rmentation induction point at OC, a range of steady-state package O2 p artial pressures was generated by placing different amounts of cut bro ccoli (10 to 160 g) in 1,DPE packages. Oxygen uptake was modeled using a Michaelis-Menten-type equation. The maximum rate of product O2 upta ke when O2 partial pressure was nonlimiting and the package O2 partial pressure corresponding to half-maximum O2 uptake were estimated as 14 7 +/- 3 nmol.kg-1.s-1 and 0.26 +/- 0.025 kPa, respectively. Respirator y quotient and head space ethanol increased sharply below package O2 p artial pressures of 0.15 kPa, indicating stimulation of fermentation w ithin the packages. The frequency distributions of CO2 production rate s were measured for 80 samples of 100 g each of cut broccoli at two O2 partial pressures (21.0 kPa and 1.3 kPa) using a now-through method. The average coefficient of variation of the CO2 production rate was al most-equal-to 5 %. Frequency distributions of 02 partial pressures wer e modeled as a function of product-to-product variation in O2 uptake a nd package-to-package variation in film permeability using the estimat ed O2 uptake characteristics and coefficient of variation. The model w as used to predict the target O2 partial pressures for the design of c ut broccoli MA packages. It was predicted that the packages for cut br occoli at 0C should be designed for a target 02 partial pressure of 2. 54 kPa to have actual package O2 partial pressures greater-than-or-equ al-to 1.0 kPa at 0.0001 % probability level. Film specifications for M A packaging of cut broccoli at OC were calculated based on the predict ed target O2 partial pressures.