Microbial survival and odor in laundry

The survival and distribution of microflora during laundering at 30 or 40 degreesC in commercial U.S. and European Union (E.U.) detergents were determined in laboratory wash experiments. Four test strains-Staphylococcus epidermidis, S. aureus, Escherichia coli, and Pseudomonas aeruginosa-were evaluated on cotton textile.

A significant survival and transfer between textiles were found for all four test strains washed in E.U. and U.S. color detergents (without bleach), whereas no survival was observed in bleach-containing detergents. Gram-negative strains generally survived in greater numbers than Gram-positive strains.

A greater survival was observed in U.S. detergents at U.S. conditions (30 degreesC, 12 min) than in E.U. detergents at E.U. conditions (40 degreesC, 30 min). The adhesion of odorants to cotton and polyester textiles during washing and drying was studied using six previously identified odorants in laundry [ethylbutanoate, (Z)- 4-heptenal, (E)-2-nonenal, 3-methylbutanoic acid, 2- methoxyphenol (guaiacol) and 4-methyloctanoic acid].

All odorants were effectively removed from cotton during wash, whereas the odorants were more strongly associated with polyester fibers. During wash, hydrophobic odorants [(Z)-4- heptenal, (E)-2-nonenal, and guaiacol] adhered more strongly to polyester than the acids. The odor formed by surviving skin microflora attached to textiles soiled with human sebum and sweat after laundering at 30 degreesC was studied by sensory evaluation and aroma extract dilution analysis.

Intensive odor was formed in both cotton and polyester textiles during prolonged drying. Generally, the odor formation in cotton swatches and the bacterial count of the wash liquor from cotton swatches were greater than the odor formation and bacterial count from polyester swatches. Odorants with animal notes (branched fatty acids) dominated the odor profile after prolonged drying.

Polyester swatches possessed a more complex odor profile than cotton; in particular, aldehydes were more dominating in polyester than in cotton. A high-impact and malodorous component, 3-methylindole, was formed during prolonged drying in cotton. The study demonstrates that microbial odor formation is a dominating factor determining the odor impression of laundered cotton and polyester textiles dried under slow drying conditions.

The initial soiling with aromatic components has an additional impact on the odor profile of polyester textiles after wash, due to strong adherence of odorants during the wash cycle