by Palmitic, Stearic, and Oleic Acid Sophorolipids and Thiamine Dilauryl Sulfate

Food contaminated with human pathogens, such as Salmonella spp. and Listeria monocytogenes, frequently causes outbreaks of foodborne illness. Consumer concern over the use of synthesized antimicrobials to enhance microbial food safety has led to a search of natural alternatives. The objectives of this study were to evaluate the antimicrobial activity of various types of sophorolipids (SLs) and thiamine dilauryl sulfate (TDS) against pathogenic Salmonella spp. and Listeria spp. Both free and lactonic forms of SLs were synthesized from Candida bombicola using palmitic, stearic, and oleic acids as co-feedstocks. TDS and purified SLs were used to treat cocktails of Salmonella spp. and Listeria spp. Results showed that lactonic SLs had higher antimicrobial activity than the free-acid form, and Gram-positive Listeria spp. were more susceptible to SLs and TDS than Gram-negative Salmonella spp. Listeria populations were reduced from an initial concentration of 7.2 log CFU/mL to a non-detectible level within a 1 min treatment of 0.1% (w/v) lactonic SLs and TDS in the presence of 20% ethanol, which itself did not significantly reduce the populations. There were no significant differences in the antimicrobial efficacy among palmitic, stearic, and oleic acid-based SLs against Salmonella or Listeria spp. Ethanol was utilized to improve the antimicrobial activity of free-acid SLs against Gram-negative bacteria. In general, TDS was more effective than the SLs against Salmonella and Listeria spp. scanning electron microscopy and transmission electron microscopy images showed that SLs and TDS damaged Listeria cell membranes and resulted in cell lysis. Overall, our results demonstrated that SLs and TDS in the presence of ethanol can be used to inactivate foodborne pathogens, especially Gram-positive bacteria.

Combined effects of chlorine and thiamine dilauryl sulfate on reduction of Listeria monocytogenes in chicken breast and development of predictive growth models

The inhibitory effect of chlorine (50, 100, and 200 mL/kg) and thiamine dilauryl sulfate (TDS: 100, 500, and 1,000 mg/kg) on Listeria monocytogenes in chicken breast was investigated. Also, predictive growth models as a function of chlorine and TDS concentration, and storage temperature (4, 10, and 15°C) were developed using a polynomial model. Listeria monocytogenes counts were significantly (P < 0.05) different in samples treated with sterile distilled water and combinations of chlorine and TDS. The maximum reduction effect was 0.5 log cfu/g by combined treatment of 200 mL/kg chlorine and 1,000 mg/kg TDS. The largest synergistic effect was 0.38 log cfu/g by combined treatment of 100 mL/kg chlorine and 1,000 mg/kg TDS. The primary models that were developed to obtain the specific growth rates (SGR) and lag time (LT) had good fitness (R(2) > 0.91) determined by the reparameterized Gompertz equation. The secondary polynomial models were calculated by nonlinear regression analysis. In the validation of the developed models, the bias factor (Bf) and accuracy factor (Af) for SGR were 0.54 and 1.84, respectively, whereas those for LT were 0.97 and 1.04, respectively. In quality analysis, chlorine and TDS did not change the color or texture of chicken breast meat during storage at 4°C for 7 d. Thus, our findings indicate that a combined treatment of 100 mL/kg chlorine and 1,000 mg/kg TDS appears to an effective method into reduce L. monocytogenes in broiler carcasses with no negative effects on color and textural quality. The predictive models were in good agreement with the validation and may be used to predict L. monocytogenes growth in chicken breast.

The evaluation of combined chemical and physical treatments on the reduction of resident microorganisms and Salmonella Typhimurium attached to chicken skin

This study was conducted to evaluate the efficacy of sodium hypochlorite (NaOCl, 0-200 mg/kg), thiamine dilauryl sulfate (TDS, 1,000 mg/kg), and ultrasound (37 kHz, 380 W) on reducing Salmonella Typhimurim, mesophilic aerobic bacteria (MAB), and coliforms on chicken skin. Chemical and physical treatments were applied for 5 min either singly or jointly, and Salmonella previously inoculated on chicken skin were quantitatively assessed using brilliant green agar, and the populations of MAB and coliforms in the native flora were enumerated using plate count agar and violet red bile agar, respectively. In the evaluation of bacterial attachment/detachment, chicken skin was quantitatively assessed for loosely, intermediately, and tightly attached bacteria. The treatment effects on bacteria detachment were also visualized using field emission scanning electron microscopy. In addition, color and textural properties of the skin after treatments were evaluated using a color difference meter and texture analyzer. Antimicrobial activity of NaOCl increased as the NaOCl concentration was increased, especially for loosely attached cells. The combination of 200 mg/kg NaOCl and ultrasound (NaOCl/ultrasound) significant reduced loosely, intermediately, and tightly attached bacteria populations by 0.75 to 0.47, 0.43 to 0.41, and 0.83 to 0.54 log cfu/g for MAB, coliforms, and Salmonella Typhimurium, respectively. However, the combination of NaOCl and TDS (NaOCl/TDS) did not sufficiently reduce those cells on chicken skins, except for loosely attached MAB and coliforms. The NaOCl/ultrasound combination produced a higher reduction in numbers of inoculated and native bacteria flora than any single application, with no negative effect on skin color or texture. Generally, the loosely attached bacteria were less resistant to the chemical and physical treatments than the intermediately and tightly attached bacteria in chicken skin, presumably due to their location in deeper skin layer and crevices. Further research is needed to investigate how the intermediately and tightly attached microorganisms can be effectively eliminated from chicken skin.

Effect of Nanoencapsulated Vitamin B1 Derivative on Inhibition of Both Mycelial Growth and Spore Germination of Fusarium oxysporum f. sp. raphani

Nanoencapsulation of thiamine dilauryl sulfate (TDS), a vitamin B1 derivative, was proved to effectively inhibit the spore germination of Fusarium oxysporum f. sp. raphani (F. oxysporum), as well as mycelial growth. The average diameter of nanoparticles was measured as 136 nm by being encapsulated with an edible encapsulant, lecithin, whose encapsulation efficiency was about 55% in containing 200 ppm of TDS concentration: the 100 ppm TDS nanoparticle solution showed a mycelial growth inhibition rate of 59%. These results were about similar or even better than the cases of treating 100 ppm of dazomet, a positive antifungal control (64%). Moreover, kinetic analysis of inhibiting spore germination were estimated as 6.6% reduction of spore germination rates after 24 h treatment, which were 3.3% similar to the case of treating 100 ppm of a positive control (dazomet) for the same treatment time. It was also found that TDS itself could work as an antifungal agent by inhibiting both mycelial growth and spore germination, even though its efficacy was lower than those of nanoparticles. Nanoparticles especially played a more efficient role in limiting the spore germination, due to their easy penetration into hard cell membranes and long resident time on the surface of the spore shell walls. In this work, it was first demonstrated that the nanoparticle of TDS not a harmful chemical can control the growth of F. oxysporum by using a lower dosage than commercial herbicides, as well as the inhibiting mechanism of the TDS. However, field trials of the TDS nanoparticles encapsulated with lecithin should be further studied to be effectively used for field applications.