Microbial stability of soy/polyethylene composites and pure polyethylene fibers

A study was performed to understand the surface dispersion of soy material in Soy/Polyethylene (soy/PE) composite fibers that was examined under magnification by staining fiber surfaces with Coomassie Blue. The main objective was to determine the microbial stability and a comparison of growth of soy/PE composite fibers and pure Polyethylene (PE) fiber against pathogenic and natural bacterial growth and environmental yeast and mold growth. A detailed study was performed to predict the safe storage period of soy/PE fibers under various temperature (T) and humidity conditions by moisture sorption. Understanding of environmental effects on mold growth is important for safe processing manufacturing, storage and use of soy/PE biocomposite. Statistical models would be valuable to predict mold free days (MFD) under controlled storage conditions and could be used to determine appropriate storage conditions and use conditions for bio-composites. Mold spoilage was visually monitored for 109 days on soy/PE fibers maintained under controlled temperatures (T) and water activities (a w). Container with saturated salt solutions generating water activities ranging from 0.11 to 0.98 were placed in temperature-controlled incubators with temperatures ranging from 10°C to 40°C. Soy/PE fibers that were held at 0.823 water activity (aw) or higher exhibited mold growth at all temperatures. As postulated, increased aw (greater than 0.89) and temperature (higher than 25°C) accelerated mold growth on soy/PE fibers. A slower mold growth was observed on soy/PE fibers that were held at 0.87 aw and 10°C. A Weibull model was employed to fit the observed logarithmic values of T, aw and a interaction term Log T × Log aw and was chosen as the final model as it gave the best fit to the raw mold growth data. These growth models predict the expected mold-free storage period of soy/PE fibers when exposed to various environmental temperatures and humidities.