TY - JOUR
T1 - Survival of Salmonella enterica and Listeria monocytogenes in date palm paste and syrup at different storage temperatures
AU - Olaimat, Amin N.
AU - Al-Holy, Murad A.
AU - Abughoush, Mahmoud H.
AU - Daseh, Lamees
AU - Al-Nabulsi, Anas A.
AU - Osaili, Tareq M.
AU - Al-Rousan, Walid
AU - Maghaydah, Sofyan
AU - Ayyash, Mutamed
AU - Holley, Richard A.
N1 - Funding Information:
Five strains each of S. enterica (S. Typhimurium 02:8423, S. Enteritidis CRIFS 1016, S. Kentucky 64701, S. Heidelberg 271, and S. Copenhagen PT 99) and L. monocytogenes (2-243, 2–138, GLM-5, GLM-3, and GLM-1) were used in this study. The strains were from the culture collection of The Food Microbiology lab in the Hashemite University. The L. monocytogenes strains were isolated from meat plant, whereas Salmonella isolates were either food (plant and animal) or human clinical isolates. All strains have been used in the previous work (Olaimat et al., 2018, 2022). Five strains each of S. enterica (S. Typhimurium 02:8423, S. Enteritidis CRIFS 1016, S. Kentucky 64701, S. Heidelberg 271, and S. Copenhagen PT 99) and L. monocytogenes (2-243, 2–138, GLM-5, GLM-3, and GLM-1) were used in this study. The strains were from the culture collection of The Food Microbiology lab in the Hashemite University. The L. monocytogenes strains were isolated from meat plant, whereas Salmonella isolates were either food (plant and animal) or human clinical isolates. All strains have been used in the previous work (Olaimat et al., 2018, 2022). The strains were retrieved from the freezer at −40°C by inoculating them on Tryptone Soy Agar (TSA, Oxoid, Basingstoke, UK) plates using the streak plate method, followed by incubation for 18–24 h at 37°C. Single colonies from strains were plated onto Salmonella Shigella (SS) agar (Oxoid) for S. enterica and Listeria selective agar (LSA, Oxoid) supplemented with Listeria selective supplement (Oxoid) for L. monocytogenes and incubated at 37°C for 24 h for S. enterica and 48 h for L. monocytogenes. A typical colony of each pathogen was inoculated into Brain Heart Infusion Broth (BHIB, Oxoid) and incubated at 37°C for 18–24 h. Subsequently, three culture transfers were conducted by transferring 100 µL of the 18–24 h old cultures into 10 mL of sterile BHIB tubes that were incubated at 37°C for 18–24 h to be used in the trials. A separate cocktail of each of S. enterica and L. monocytogenes was prepared by combining 2 mL of the same inoculum level of each strain at in a sterilized tube. The strains were mixed and centrifuged for 18 min at 1500 rpm, and the pellets were washed twice with 0.1% peptone water, suspended in 10 mL peptone water (0.1%) to yield 8–9 log CFU/mL and used for inoculation of date products. Samples of date syrup and paste were purchased from a local supermarket in Zarqa, Jordan. The samples were tested for the presence of S. enterica and L. monocytogenes by diluting 10 g in 90 mL buffered peptone water, and then 0.1 mL of each sample was directly plated onto the corresponding selective media, and the pathogens were not detected. Each of the commercial date paste and syrup samples were divided into two portions of 400 g. The syrup was placed in sterilized beakers, and the date paste was placed in a sterilized plastic bag. The portions of date paste or date syrup were inoculated with 4 mL of either S. enterica or L. monocytogenes. The inoculated syrup was mixed well with a sterile spoon for 2 min, whereas date paste was vigorously hand squeezed and massaged for 5 min to uniformly distribute the inoculum. Thereafter, the inoculated date paste and syrup portions were divided into six samples of 50 g each in sterile bottles, which were stored at 4, 10, and 24 ± 0.5°C with two replicates at each temperature. The experiment was independently repeated twice with a total of four replicates. Samples of date paste and syrup weighing 5 g were taken at 0, 1, 3, 7, 14, 30, 50, and 90 days from samples stored at the different temperatures using a sterile spoon, placed into a sterile stomacher bag, diluted with 45 mL peptone water, and treated for 2 min using a stomacher (Stomacher, Easy Mix, AES Laboratories, Combourg, France). Each sample was serially diluted, and 100 µL was spread-plated onto the surfaces of SS agar plates for S. enterica or LSA agar plates for L. monocytogenes. The mesophilic aerobic bacteria (MAB) were also monitored in both L. monocytogenes- and S. enterica-inoculated date paste and syrup using TSA plates. The inoculated plates were aerobically incubated at 37°C for 24 h for S. enterica or 48 h for L. monocytogenes and MAB. The colonies on selective media and TSA were enumerated. When bacterial cells were not detectable on agar plates, the diluted samples in the stomacher bags were mixed with 50 mL double-strength BHIB and incubated for 24 h at 37°C. A loopfull from each bag was streaked on selective agar and incubated at 37°C for 24 h for S. enterica or 48 h for L. monocytogenes to detect the presence of S. enterica or L. monocytogenes. Presumptive colonies were identified using gram staining and biochemical tests such as triple sugar iron, indole, and urease tests for Salmonella and hemolysis, methyl red and indole for L. monocytogenes. Date paste and syrup pH values were measured at room temperature at 0 and 90 days of storage at the different temperatures using a pH meter (Adwa pH meter, AD1000, Adwa, Romania), and the initial aw values of paste and syrup were measured using a water activity meter (Novasina AG, Labmaster-aw, Lachen, Switzerland) at room temperature. Numbers of surviving bacteria were measured and reported as mean ± standard deviation (SD) and are the average of four replicates. The data were analyzed using JMP 15.0 software from SAS, and Tukey's HD test was used to evaluate the differences between the date products and storage time. Significant differences were declared when p was <0.05.
Publisher Copyright:
© 2023 Institute of Food Technologists.
PY - 2023/7
Y1 - 2023/7
N2 - Abstract: This study aimed to investigate the behavior of Salmonella enterica and Listeria monocytogenes in processed date paste and syrup at different temperatures. Commercial products were inoculated with approximately 6 log CFU/mL of S. enterica or L. monocytogenes and stored at 4, 10, and 24°C for 90 days. S. enterica was able to survive in date products until the end of storage at 4°C. At this temperature, numbers decreased by 2.1 log CFU/g in date paste and by 3.4 log CFU/g in date syrup; however, at 10°C, cells were reduced >4.2 log CFU/g and were undetectable by direct plating in date paste or by enrichment (complete elimination) in syrup. Further, at 24°C, complete elimination of S. enterica was achieved in date paste and syrup by 30 and 7 days, respectively. L. monocytogenes numbers decreased by 1.4, 4.4, and >4.6 log CFU/g in date paste stored at 4, 10, and 24°C for 90 days, respectively. In date syrup, numbers of L. monocytogenes decreased to undetectable levels by 50, 14, and 4 days at 4, 10, and 24°C, respectively, by direct plating and complete elimination was observed at 10 and 24°C by 50 and 30 days of storage, respectively. The initial pH values of date paste and syrup were 4.7 and 4.8, respectively, and remained stable until the end of storage except for L. monocytogenes-inoculated syrup. Practical Application: Salmonella enterica and Listeria monocytogenes can easily survive in date paste and syrup particularly at refrigerator temperature, which explains the necessity of preventing the contamination of date products with foodborne pathogens.
AB - Abstract: This study aimed to investigate the behavior of Salmonella enterica and Listeria monocytogenes in processed date paste and syrup at different temperatures. Commercial products were inoculated with approximately 6 log CFU/mL of S. enterica or L. monocytogenes and stored at 4, 10, and 24°C for 90 days. S. enterica was able to survive in date products until the end of storage at 4°C. At this temperature, numbers decreased by 2.1 log CFU/g in date paste and by 3.4 log CFU/g in date syrup; however, at 10°C, cells were reduced >4.2 log CFU/g and were undetectable by direct plating in date paste or by enrichment (complete elimination) in syrup. Further, at 24°C, complete elimination of S. enterica was achieved in date paste and syrup by 30 and 7 days, respectively. L. monocytogenes numbers decreased by 1.4, 4.4, and >4.6 log CFU/g in date paste stored at 4, 10, and 24°C for 90 days, respectively. In date syrup, numbers of L. monocytogenes decreased to undetectable levels by 50, 14, and 4 days at 4, 10, and 24°C, respectively, by direct plating and complete elimination was observed at 10 and 24°C by 50 and 30 days of storage, respectively. The initial pH values of date paste and syrup were 4.7 and 4.8, respectively, and remained stable until the end of storage except for L. monocytogenes-inoculated syrup. Practical Application: Salmonella enterica and Listeria monocytogenes can easily survive in date paste and syrup particularly at refrigerator temperature, which explains the necessity of preventing the contamination of date products with foodborne pathogens.
KW - Salmonella
KW - date palm
KW - food contamination
KW - foodborne pathogens
KW - low water activity
KW - ready-to-eat foods
UR - http://www.scopus.com/inward/record.url?scp=85160807414&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85160807414&partnerID=8YFLogxK
U2 - 10.1111/1750-3841.16620
DO - 10.1111/1750-3841.16620
M3 - Article
C2 - 37243359
AN - SCOPUS:85160807414
SN - 0022-1147
VL - 88
SP - 2950
EP - 2959
JO - Journal of Food Science
JF - Journal of Food Science
IS - 7
ER -