Modify packaging conditions to increase shelf life, product stability.

The primary focus of recent European research involves increasing the stability and shelf life of low-salt hams and prepackaged breads by optimizing packaging conditions. Scientists also are trying to incorporate a phosphorescent sensor that measures residual oxygen levels in packaging films.

Investigators found that the chemical and microbial stability of low-salt hams with residual salt concentrations of 0.75%, 1.5% and 3% was very similar over a 28-day storage period when packaged in a high-barrier laminate film of low density polyethylene (LDPE) and polyamide. Each pack was gas-flushed with a 60%-to-40% ratio of nitrogen to carbon dioxide. The color of the 0.75% ham faded over the 28 days.

This ham also had the shortest shelf life, with bacterial counts of 105 colony-forming units (cfu)/g after 20 days. Similar counts were detected in the 1.5% ham after 22 days and after 25 days in the 3% residual sodium chloride ham. For the first seven days, bacterial counts were negligible. Lactic acid bacteria accounted for the majority of the bacteria present between 7 and 28 days.

In another project, standard white bread loaves were baked, cooled and packaged in several environments: in 100% carbon dioxide, using a high-barrier laminate film; in atmospheric conditions using a metallized film; and in atmospheric conditions using micro-perforated polypropylene. A control was unpackaged. Researchers stored the breads at room temperature for 5 days.

Breads stored in a high-barrier film and in an atmosphere of 100% carbon dioxide showed the slowest rate of staling. The metallized film retarded the rate of staling better than the microperforated polyproylene film, which kept the bread fresher than the unpackaged control bread.

The moisture content of the crumb did not vary between packaging systems after five days of storage. Large differences in crust moisture content and water activity developed between the different storage conditions. Visible signs of microbial growth were not observed on any of the breads after five days. Microbial analysis is being carried out to examine the stability of the breads.

Meanwhile, the performance of the phosphorescent oxygen sensor is being examined at between -170 C and 300 C. It appears that the sensor is not stable at temperatures less than 170 C. Scientists are assessing the compatibility of a phosphorescent dye with different packaging polymers.

Further information. Joe Kerry, Department of Food Science and Technology, University College, Cork, Ireland; phone: [phone]; fax: [phone]; email [e-mail].