Purpose: The efficacy of agar overlay with or without media supplementation was examined to improve recovery of Salmonella on peppercorn and cumin seeds treated with steam and ethylene oxide.
Methods: Peppercorns and cumin seeds were inoculated with Salmonella, dried to 0.3 to 0.4 aw, and treated with steam under vacuum (65.4 to 69.7°C) for 15 s dwell time. Following steam treatment, spices were stomached for 1 min in 0.1% peptone + 0.1% Tween, serially diluted, and plated onto TSA, XLT4 or TSA with added supplements followed by XLT4 overlay. TSA was supplemented with sodium pyruvate (9.09 mmol) + yeast extract (0.6%) [SPY], 3,3’-thiodipropionic acid (5.6 mmol)[TDP], glycerophosphate (10 mmol)[GP], lactate (10 mmol) [LAC], or mannitol (100 mmol) [MAN]. Plated samples were incubated (37°C) for 3 h then molten XLT4 medium was used to overlay. Plates were then incubated at 37°C for 21 h prior to colony enumeration. For peppercorns and cumin seeds subjected to ethylene oxide treatment, TSA was supplemented with SPY, TDP, GP, ATP (8.34 mmol), guanine (64.5 mmol), or magnesium (52.5 mmol). Samples were plated as described above.
Results: TSA supplemented with SPY or TDP resulted in better recovery of Salmonella from steam-treated peppercorns (P<0.05). No supplement was associated with improved recovery of Salmonella on cumin seeds (P>0.05) following steam treatment. For ethylene oxide-treated peppercorns and cumin seeds, no supplement improved recovery of Salmonella (P>0.05)
Significance: For steam-treated peppercorns, supplementation of TSA with sodium pyruvate + yeast extract or 3,3’-thiodipropionic acid may improve recovery of Salmonella when overlay plating methods are used.