Exploring thermosonication as non-chemical disinfection technology for strawberries

The scope of this work was to study the efficacy of the combination of sonication at 35 or 130 kHz with three temperature treatments: 20, 50 and 55 ºC, on the population of artificially inoculated Listeria innocua in strawberries, and on their overall quality. Prior in vitro results showed that temperature was the main factor in decreasing L. innocua population: a maximum of 3.8 log reductions was obtained with sonication at 130 kHz and 55 ºC for 15 min Treatments combining—or not—sonication at 130 kHz with mild temperatures (50 and 55 ºC) for 5 or 10 min were able to decrease about 3 log units of artificially inoculated L. innocua in strawberries and about 2 log units of total aerobic mesophilic and yeasts and molds populations naturally occurring in strawberries. Thermosonication treatments did not exert a detrimental impact on fruit quality, except for those at the higher temperatures and times, which caused a change in color to more purplish and a little softening of the strawberries, which were proposed to be assessed for further processing other than fresh commercialization. Overall, the impact of sonication in fresh strawberries needs to be further investigated to find the adequate conditions to enhance the effects of temperature itself.

Molecular Identification of Lactic Acid Bacteria Approach to Sustainable food Security

Background: Dadiah is a traditional dish from West Sumatra made from buffalo milk, which is fermented in bamboo tubes and left at room temperature for ±2 days. Dadiah is included in the staple food category because it contains Lactic Acid Bacteria (LAB) which has the potential to be a probiotic. This study aims to determine the identification and characterization of LAB from Dadiah from Halaban, Kab. Fifty Cities, West Sumatra. Design and Methods: A survey method was used in this research with a descriptive analysis, Antimicrobial activity testing was done with bacteria Escherichia coli O157, Staphylococcus aureus, Listeria monocytogenes, and Listeria innocua. Molecular identification was done using the 16S rRNA gene. Results: Probiotic candidate test with the best results in testing for resistance to stomach acid at pH3 with the viability of 65.98%, bile salt resistance 0.3%, viability of 54.90% from 2DA isolates. Antimicrobial activity with the best clear zone area results was obtained in 2DA isolates with Escherichia coli O157 test bacteria of 21.16 mm, Staphylococcus aureus with a clear zone area of 23.17 mm, Listeria innocua of 19.24 mm and Listeria monocytogenes with a clear zone area 18.23 mm in 4DA isolate, LAB identification using 16S sRNA gene, results of running PCR base length 1419bp. Conclusions: Phylogenetic analysis shows that Dadiah of Limapuluh Kota Regency is a kin to Lactobacillus plantarum. The superiority of identification technology by using 16S rRNA gene only can be conducted if the nucleotide sequence information of the targeted bacteria is known beforehand.

Effectiveness of Low-Dose Continuous Gaseous Ozone in Controlling Listeria innocua on Red Delicious Apples During 9-Month Commercial Cold Storage

This study aimed to investigate the effects of low-dose continuous ozone gas in controlling Listeria innocua and quality attributes and disorders of Red Delicious apples during long-term commercial cold storage. Red Delicious apples were inoculated with a three-strain L. innocua cocktail at ∼6.2 log10 CFU/apple, treated with or without 1-methylcyclopropene, and then subjected to controlled atmosphere (CA) storage with or without continuous gaseous ozone in a commercial facility for 36 weeks. Uninoculated Red Delicious apples subjected to the above storage conditions were used for yeast/mold counts and quality attributes evaluation. The 36 weeks of refrigerated air (RA) or CA storage caused ∼2.2 log10 CFU/apple reduction of L. innocua. Ozone gas application caused an additional > 3 log10 CFU/apple reduction of L. innocua compared to RA and CA storage alone. During the 36-week CA storage, low-dose continuous gaseous ozone application significantly retarded the growth of yeast/mold, delayed apple firmness loss, and had no negative influence on ozone burn, lenticel decay, russet, CO2 damage, superficial scald, and soft scald of Red Delicious apples compared to CA-alone storage. In summary, the application of continuous low-dose gaseous ozone has the potential to control Listeria on Red Delicious apples without negatively influencing apple quality attributes.

Prevalence, Molecular Identification, Antimicrobial Resistance, and Disinfectant Susceptibility of Listeria innocua Isolated from Ready-to-Eat Foods Sold in Johannesburg, South Africa

Background: Food contamination with Listeria spp. can occur at all stages of the food chain. The aim of this research was to investigate the prevalence, molecular identification, antimicrobial resistance, and disinfectant susceptibility of Listeria innocua isolated from Ready-To-Eat (RTE) foods sold in Johannesburg, South Africa. Methods: Eighty RTE foods were collected from Johannesburg, South Africa. The 16S rRNA region of L. innocua isolates was amplified, sequenced, and identified using Basic Alignment Search Tool (BLAST). The antimicrobial resistance and disinfectant susceptibility (against four commercial disinfectants) of the isolates were evaluated using disk diffusion and microdilution assays. Data were statistically analyzed using SPSS v. 23.0. Results: Listeria strains revealed a high 16S rRNA gene sequence analogy to L. innocua of between 98-99%. The overall prevalence of L. innocua was 21.3% (17 out of 80) in the RTE food samples. Most isolates were susceptible to the studied commercial disinfectants. All the L. innocua isolates from food sources were found to be resistant to ampicillin and cephalothin, while 83 and 74% of isolates were resistant to colistin sulphate and sulphatriad. Conclusion: Prevalence of L. innocua was considerable in the RTE food samples sold in Johannesburg, South Africa. The L. innocua isolates showed high antibiotic resistance against ampicillin, cephalothin, colistin sulphate, and sulphatriad.

The Effect Ultrasound and Surfactants on Nanobubbles Efficacy against Listeria innocua and Escherichia coli O157:H7, in Cell Suspension and on Fresh Produce Surfaces

Removing foodborne pathogens from food surfaces and inactivating them in wash water are critical steps for reducing the number of foodborne illnesses. In this study we evaluated the impact of surfactants on enhancing nanobubbles’ efficacy on Escherichia coli O157:H7, and Listeria innocua removal from spinach leaves. We evaluated the synergistic impact of nanobubbles and ultrasound on these two pathogens inactivation in the cell suspension. The results indicated that nanobubbles or ultrasound alone could not significantly reduce bacteria in cell suspension after 15 min. However, a combination of nanobubbles and ultrasonication caused more than 6 log cfu/mL reduction after 15 min, and 7 log cfu/mL reduction after 10 min of L. innocua and E. coli, respectively. Nanobubbles also enhanced bacterial removal from spinach surface in combination with ultrasonication. Nanobubbles with ultrasound removed more than 2 and 4 log cfu/cm2 of L. innocua and E. coli, respectively, while ultrasound alone caused 0.5 and 1 log cfu/cm2 of L. innocua and E. coli reduction, respectively. No reduction was observed in the solutions with PBS and nanobubbles. Adding food-grade surfactants (0.1% Sodium dodecyl sulfate-SDS, and 0.1% Tween 20), did not significantly enhance nanobubbles efficacy on bacterial removal from spinach surface.