Factors Affecting Growth and Survival of Salmonella in Onion Extracts and Onion Bulbs.

This study investigated the survival and growth of Salmonella in onion extracts and bulbs. The inhibition or retardation of Salmonella growth by extracts of red, white, and yellow onions was tested against the onion germplasm and exposure to different light spectra during curing. Separately, survival of Salmonella Newport was tested on red, white, and yellow onion bulbs on the external and internal onion layers with a syringe and needle. Onions exposed to blue, red, and white LED light during curing produced extracts with variable antimicrobial effects (p < 0.05), with those exposed to blue light showing the strongest inhibitory effect on red and white onions only. In survival studies, Salmonella inoculated on the outer scale was reduced by 1.2, >2.7, and >2.4 logs on red, white, and yellow onions, respectively, within 3 days, whereas it grew by 2.4, 2.6, and 2.8 logs inside red, white, and yellow onion bulbs, respectively, over 18 days. In separate trials, the outer layer again did not support the survival of Salmonella Newport. The a(w) increased significantly from 0.51 to 0.58 in the outer scales and 0.96 to 0.98 for the fourth inner scales. Despite being rich in antimicrobial polyphenols, tissue integrity and water content may still promote Salmonella growth in onions.