Vegetable nitrate: Isolation of nitrate reducing bacteria for fermentation of nitrate to nitrite and use of vegetable-derived nitrite to inhibit germination of Clostridium spores in RTE meats
Abstract
Nitrate reducing bacteria (NRB) are used to produce vegetable-derived nitrite allowing clean label status as per USDA-FSIS definition of 'natural nitrite' which can be used in place of sodium nitrite. Nitrite in processed meats is also responsible for cured meat color, microbial inhibition of spores, and contributes to flavor. One objective was to isolate NRB's that could possibly be used to generate nitrite from vegetable nitrate for use in processed meats. An 'on-agar' colony-screening assay was developed using the principle of the liquid nitrate reduction assay to detect the conversion of nitrate to nitrite on agar plates using M17 agar base plates. Samples that might have NRBs were spread-plated onto this base agar, and overlaid with sterile M17-Nitrate agar as the source of nitrate. Another objective was to use Clostridium sporogenes as a 'surrogate organism' for evaluating nitrite suppression of spore germination and identify permissive conditions to facilitate validation and confirmation of spore inhibition during the comparison of sodium and vegetable (celery) nitrite in cooked meat products. A three-strain spore crop from Clostridium sporogenes (ATCC 3584, ATCC 19404, and ATCC BAA-2695) was applied during ingredient formulation of low and high fat hotdogs that were divided into 3 batches (control without nitrite, hotdogs with sodium nitrite, hotdogs with celery nitrite). In both processes, effects with celery nitrite was compared to comparable levels of sodium nitrite. Manufactured hotdogs followed standard preparation procedures and cook processes (nitrite was used at 156 ppm). In assays, we examined spore germination at 5 degrees C, 15 degrees C, 35 degrees C so that we could best understand the contribution of temperature on the inhibition of spore germination by nitrite under various conditions, compared to controls processed without nitrite. Celery nitrite was as good or better than sodium nitrite in both low and high fat hotdogs and spore outgrowth was only observed at 35 degrees C abuse temperature conditions and not at 5 degrees C or 15 degrees C even after extended shelf life periods. HPLC analysis was used to quantify nitrite in culture fermentations and during hotdog manufacture and shelf life. The nitrite spore validation assay described herein allows easy determination of nitrite levels and whether nitrite can prevent spore germination under the most permissive conditions to help keep processed meat safe.
Collections
- OSU Theses [15752]