Purpose: To develop an effective detection method for Salmonella from spices with antimicrobial substances, using clove flower buds as a model.
Methods: Two clove varieties, Ceylon and Madagascar, were used in the study. Cloves were inoculated with Salmonella Montevideo, Salmonella Typhimurium, or Salmonella Weltevreden at 1, 3 or 6 log CFU/g. Two sample sizes, 10 and 25g, were compared. Trypticase soy broth (TSB) was used as preenrichment broth at a broth:clove ratio of 9:1. After adding TSB to the weighed cloves for preenrichment, three different preenrichment treatments were evaluated: cloves were left in the preenrichment TSB broth during preenrichment (preE 1); the mixture was shaken vigorously for 30 s and decants were transferred to a new bag for preenrichment (preE 2); and the mixture was shaken vigorously for 60 s and decants were transferred to a new bag for preenrichment (preE 3). The rest of the procedures were carried out according to the FDA BAM. Five trials were conducted so far and each trial had 4 replicates.
Results: Combining the data from the 5 trials together, all 10 and 25g samples from preE 2 and preE 3, at inoculation levels 6 log CFU/g or 3 log CFU/g, were positive for Salmonella. However, treatment preE 1 only produced 30 positive results among a total of 40 samples, at inoculation levels 6 log CFU/g; it had 12 positive results among 40 samples, at inoculation levels 3 log CFU/g. At inoculation levels 1 log CFU/g, only 1 of 40 samples tested was positive for Salmonella by preE 1; 17 of 40 positive by preE 2; and 18 of 40 positive by preE 3. The results clearly indicated that a modified soak procedure, where cloves were removed from the preenrichment broth after 60 sec, can greatly improve the sensitivity of the detection method.
Significance: This discovery reduced the detection limit for Salmonella on clove flower buds from 3 log CFU/g to 1 log CFU/g.