Research – Survival of Salmonella – Tea – Fruit and Leafy Greens – E.coli O157 – Fruit and Leafy Greens

Ingenta Connect – Survival of Salmonella on Chamomile, Peppermint, and Green Tea during Storage and Subsequent Survival or Growth following Tea Brewing

The survival of Salmonella on dried chamomile flowers, peppermint leaves, and green tea leaves stored under different conditions was examined. Survival and growth of Salmonella was also assessed after subsequent brewing using dried inoculated teas. A Salmonella enterica serovar cocktail was inoculated onto different dried tea leaves or flowers to give starting populations of approximately 10 log CFU/g. The inoculum was allowed to dry (at ambient temperature for 24 h) onto the dried leaves or flowers prior to storage under 25 and 35°C at low (<30% relative humidity [RH]) and high (>90% RH) humidity levels. Under the four storage conditions tested, survival followed the order 25°C with low RH > 35°C with low RH > 25°C with high RH > 35°C with high RH. Salmonella losses at 25°C with low RH occurred primarily during drying, after which populations showed little decline over 6 months. In contrast, Salmonella decreased below detection after 45 days at 35°C and high RH in all teas tested. The thermal resistance of Salmonella was assessed at 55°C immediately after inoculation of tea leaves or flowers, after drying (24 h) onto tea leaves or flowers, and after 28 days of storage at 25°C with low RH. All conditions resulted in similar D-values (2.78 ± 0.12, 3.04 ± 0.07, and 2.78 ± 0.56, at 0 h, 24 h, and 28 days, respectively), indicating thermal resistance of Salmonella in brewed tea did not change after desiccation and 28 days of storage. In addition, all brewed teas tested supported the growth of Salmonella. If Salmonella survives after storage, it may also survive and grow after a home brewing process.

Ingenta Connect – Survival of Salmonella and Escherichia coli O157:H7 on Strawberries, Basil, and Other Leafy Greens during Storage

he survival of Salmonella and Escherichia coli O157:H7 on strawberries, basil leaves, and other leafy greens (spinach leaves, lamb and butterhead lettuce leaves, baby leaves, and fresh-cut iceberg lettuce) was assessed at cold (<7°C) and ambient temperatures. All commodities were spot inoculated with E. coli O157:H7 or Salmonella to obtain an initial inoculum of 5 to 6 log and 4 to 5 log CFU/g for strawberries and leafy greens, respectively. Samples were air packed. Strawberries were stored at 4, 10, 15, and 22°C and basil leaves and other leafy greens at 7, 15, and 22°C for up to 7 days (or less if spoiled before). Both Salmonella and E. coli O157:H7 showed a gradual decrease in numbers if inoculated on strawberries, with a similar reduction observed at 4, 10, and 15°C (2 to 3 log after 5 days). However, at 15°C (and 10°C for E. coli O157:H7), the survival experiment stopped before day 7, as die-off of both pathogens below the lower limit of detection was achieved or spoilage occurred. At 22°C, strawberries were moldy after 2 or 4 days. At that time, a 1- to 2-log reduction of both pathogens had occurred. A restricted die-off (on average 1.0 log) and increase (on average , 0.5 log) of both pathogens on basil leaves occurred after 7 days of storage at 7 and 22°C, respectively. On leafy greens, a comparable decrease as on basil was observed after 3 days at 7°C. At 22°C, both pathogens increased to higher numbers on fresh-cut iceberg and butterhead lettuce leaves (on average 1.0 log), probably due to the presence of exudates. However, by using spot inoculation, the increase was rather limited, probably due to minimized contact between the inoculum and cell exudates. Avoiding contamination, in particular, at cultivation (and harvest or postharvest) is important, as both pathogens survive during storage, and strawberries, basil, and other leafy green leaves are consumed without inactivation treatment.