Microbiological stability and diversity in raw pre-peeled potatoes packed in different atmospheres

Microbial growth on raw pre-peeled potatoes was analysed in relation to different process and storage parameters. Raw peeled potatoes with or without tumbling were packed in vacuum or modified atmosphere (MA) and stored at 4 °C and 15 °C for 7 and 5 days, respectively. Microbial growth was analysed throughout the storage period and growth was observed for mesophilic and psychrotrophic bacteria, lactic acid bacteria, Pseudomonas spp., and coliform bacteria. Growth at 4 °C was significantly lower compared to 15 °C. The number of bacteria was after seven days significantly higher on tumbled potatoes stored at 4 °C than on the untumbled potatoes. The bacterial counts generally exceeded 10⁶ CFU/g on tumbled potatoes after 7 days at 4 °C and 5 days at 15 °C, respectively. The CO₂ content increased during the storage period. A total of 243 isolates were grouped according to ITS-PCR profiles. Of these 47% had similar band profiles and thereby constituted the dominating flora at the end of shelf life. The dominating flora, identified on the basis of sequencing and microbial analysis of a subset of isolates, belonged to Enterobacteriaceae and consisted mainly of Enterobacter spp. and Kluyvera spp.     

Estimation of the quality of frozen cod using a new instrumental method

As part of an EU project (QLK1-2001-01643), the effect of storage time and temperature on the microwave dielectric properties of thawed frozen cod ( Gadus morhua) were studied. The measurements were made in the time domain, collecting the reflected pulse from the sample surface when an incident step pulse was applied through an open-ended coaxial sensor. The data were transformed using the statistical method of principal component analysis. The principal components were regressed (principal component regression) against time and temperature of storage and various sensorial variables to obtain calibration equations. These calibrations were validated using the method of internal cross-validation.