Date of Award

1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Engineering Science (Interdepartmental Program)

First Advisor

John Henry Wells

Abstract

Headspace gas composition in food packaging undergoes dynamic changes as a result of film permeability, postmortem metabolic activity, CO$\sb2$ absorption in water and lipid, and bacteria growth and respiration. A methodology to study dynamic behavior of headspace CO$\sb2$ was developed and used to identify the significant factors influencing CO$\sb2$ behavior within modified atmosphere packaging (MAP) systems for beef. Additionally, a mathematical structure suitable for modeling microbial growth in MAP systems was presented. A combined analytical and experimental method was developed to investigate headspace CO$\sb2$ changes during isothermal storage. The ideal gas law was used as a theoretical basis, and a gas impermeable and constant volume chamber was constructed to evaluate the theoretical derivation. Changes in headspace pressure caused by dynamic interactions between beef and MAP atmospheres were monitored to predict concentration changes of CO$\sb2$ within the chamber. Two sets of independent experiments were conducted to evaluate the effects of initial packaging/product parameters and storage conditions on headspace CO$\sb2$ changes. The proposed methodology for measuring CO$\sb2$ concentration changes was confirmed by gas analysis and proved valid for prediction of headspace CO$\sb2$ concentration changes in MAP atmosphere within the range of initial gas composition 20% to 100% CO$\sb2$ balanced with N$\sb2$, temperature 3$\sp\circ$ to 13$\sp\circ$C, and initial headspace pressure 111 to 155 kPa. Headspace-to-meat volume ratio was the most significant packaging parameter affecting headspace CO$\sb2$ changes, and surface area and volume of meat sample also influenced headspace CO$\sb2$ changes. Decreased storage temperature reduced CO$\sb2$ concentration remaining in headspace. Higher initial CO$\sb2$ concentration resulted in more pronounced CO$\sb2$ concentration changes. Higher headspace gas pressures caused increased rates of CO$\sb2$ change. Biological factors of meat also affected headspace CO$\sb2$ changes. Two mathematical descriptions based on (1) a modified and additive Arrhenius equation and (2) a modified Arrhenius temperature characteristic equation were developed to describe the combined effects of temperature and initial gas composition of modified atmosphere storage on the population growth rate coefficients of Listeria monocytogenes and Pseudomonas fluorescens. The mathematical descriptions were shown applicable for oxygen concentration from 0% to 20.99% and carbon dioxide concentration from 0.03% to 80%.

Pages

179

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