Aerated Steam Sanitization of Whole Fresh Cantaloupes Reduces and Controls Rind-Associated Listeria but Enhances Fruit Susceptibility to Secondary Colonization

Citation

Bezanson, G.S., Ells, T.C., Fan, L., Forney, C.F., LeBlanc, D.I. (2018). Aerated Steam Sanitization of Whole Fresh Cantaloupes Reduces and Controls Rind-Associated Listeria but Enhances Fruit Susceptibility to Secondary Colonization, 83(4), 1025-1031. http://dx.doi.org/10.1111/1750-3841.14082

Plain language summary

On-going bacterial illnesses and outbreaks associated with the consumption of fresh and fresh-cut fruit and vegetables emphasize the need to supply produce that is microbiologically safe while retaining its quality and nutrient value. The capacity of heated steam vapour to reduce initial levels and control the post-treatment growth of a non-pathogenic surrogate for Listeria monocytogenes as well as microorganisms native to the rind of intact, whole cantaloupe was assessed. Studies were conducted at the pilot-scale level by passing inoculated melons through a prototype stainless-steel, continuous-feed, heating device. Average reductions in surrogate pathogen of 99.99% (4 logs) were achieved while potential spoilage yeast and moulds and coliform bacteria were eliminated. No significant outgrowth of survivor Listeria was observed on heat-treated melons during their storage at 4, 7 and 10°C for 14 days. Treated fruit continued to mature during storage, and, although rind quality was altered, the edible, fleshy portions remained largely intact. Cantaloupe inoculated subsequent to their exposure to heated aerated steam provided a suitable environment for surrogate growth, whereas its proliferation was restricted on non-heated cantaloupe. Steam vapour disinfection provides an effective means for pathogen and spoilage organism control, but the increase in numbers of surrogate organisms on previously treated fruit raises concern regarding the impact of post-processing contamination on consumer health risk.

Abstract

Abstract: Recent bacterial illnesses and outbreaks associated with the consumption of fresh and fresh-cut fruit and vegetables emphasize the need to supply produce that is microbiologically safe while retaining its quality and nutrient value. We assessed the capacity of aerated steam to reduce initial levels and control the posttreatment proliferation of a 4-strain mixture of Listeria innocua, a surrogate for L. monocytogenes, and microflora native to the rind of whole cantaloupes. Studies were conducted at the pilot-scale level by passing deliberately contaminated melons through a prototype stainless-steel, continuous-feed heating device. Exposure for 240 s to aerated steam heated to 85 °C achieved a mean reduction in surface-inoculated L. innocua of 3.9 ± 0.6 log CFU/cm (n = 3) and decreased background microorganisms (yeast, moulds, and coliforms) to undetectable levels. No significant outgrowth of surviving L. innocua or yeast and moulds was observed on heat-treated melons during their storage at 4, 7, and 10 °C for 14 days. Treated fruit continued to respire. Although rind quality was altered, edible fleshy portions remained largely unaffected. Cantaloupe inoculated with L. innocua subsequent to its exposure to aerated steam provided a suitable environment for surrogate growth (mean 3.3 log increase in rind density over 10 days at 7 °C), whereas its proliferation was restricted on nonheated cantaloupe (mean 0.7 log increase). Steam sanitization provides an effective means for the control of pathogen and spoilage organisms, but the proliferation of surrogate organisms on heated cantaloupes raises concern regarding the impact of postprocessing contamination on consumer health risk. Practical Application: Water vapor (steam) at a high temperature can be used to sanitize the surface of fresh, whole cantaloupe melons in a continuous-feed manner. Both Listeria bacteria and spoilage organisms are markedly reduced from initial levels and survivor outgrowth severely restricted during subsequent refrigerated storage. This approach to microorganism control is likely most applicable in situations where rinds and flesh are to be separated immediately via further processing. 10 10 10 2

Publication date

2018-04-01