Electrostatic spraying of food-grade organic and inorganic acids and plant extracts to decontaminate Escherichia coli O157:H7 on spinach and iceberg lettuce.

UNLABELLED: The prevalence of foodborne illnesses is continually on rise. In the U.S.A., Escherichia coli O157:H7 (E. coli) has been associated with several outbreaks in minimally processed foods. Spinach and lettuce pose higher food safety risks and recurring food recalls suggest the insufficiency of current disinfection strategies. We aimed at offering a natural antimicrobial alternative using organic acids (malic, tartaric, and lactic acids [MA, TA, and LA, respectively]) and grape seed extract (GSE) and a novel application method using electrostatic spraying to evenly distribute the antimicrobials onto produce. Spinach and lettuce samples were washed, sanitized with sodium hypochlorite solution (6.25 mL/L), dip inoculated in water containing E. coli (7.0 log CFU/mL) for 24 h, and rewashed with sterile water to remove nonadhered pathogens. The samples were sprayed electrostatically with MA, LA, and GSE alone and in combinations and for comparison, with phosphoric acid (PA) and pH controls with deionized water adjusted to 1.5/2.3/3.6 and stored at 4 °C. When combined with LA (3%), MA (3%) showed 2.1 to 4.0 log CFU/g reduction of E. coli between the days 1 and 14 on spinach and 1.1 to 2.5 log CFU/g reduction on lettuce. Treatment with PA (1.5%) and PA (1.5%)-GSE (2%) exhibited 1.1 to 2.1 log CFU/g inhibition of E. coli on spinach during the 14-d storage. Our findings demonstrated the efficacy of electrostatic spraying of MA, LA, and GSE on fresh produce to improve the safety and lower the public health burden linked to produce contamination. PRACTICAL APPLICATION: Electrostatic spraying is an emerging technique that can be adopted to improve the distribution and application of antimicrobials during fresh produce sanitation. Relatively simple and quick, the process can access most/all parts of produce surface and offer protection from food pathogens. The use of malic and lactic acids with or without grape seed extract can serve as effective antimicrobials when sprayed electrostatically, lowering the risk from postcontamination issues with spinach and iceberg lettuce. This application technology can be extended to improve the commercial food safety of other produce, fruits, poultry, and meat.

Spray application of liquid smoke to reduce or eliminate Listeria monocytogenes surface inoculated on frankfurters.

In a simulated post process contamination scenario liquid smoke was sprayed on the frankfurters after peeling, and then inoculated with Listeria monocytogenes (Lm). Samples that did not receive a liquid smoke spray remained at approximately 2 log cfu/cm(2) during the 48h of storage while the levels on the liquid smoke treated frankfurters continued to decline until they were below detection level (1 cfu/100 cm(2)). A shelf-life study lasting 140 days indicated that liquid smoke suppressed the growth of Lm for up to 130 days. An application of 2 or 3 ml liquid smoke at packaging resulted in at least a 1 log reduction of Lm within 12h post packaging.

Electrostatic sprays of food-grade acids and plant extracts are more effective than conventional sprays in decontaminating Salmonella Typhimurium on spinach.

About 40000 people fall victim to Salmonella infections every year in the United States. Recent occurrences of Salmonella contaminated spinach and its recalls have accelerated the need for efficient antimicrobials targeting these pathogens. Our study was aimed at evaluating the inhibitory properties of malic, tartaric, and lactic acids, and grape seed extract (GSE) alone and in combinations and their application methods against Salmonella Typhimurium-inoculated spinach using a response surface method. Fresh spinach leaves were washed, disinfected with sodium hypochlorite solution (0.04% v/v), rewashed with sterile deionized (DI) water, and inoculated with a 2nd-day culture of S. Typhimurium (7.0 log CFU/mL). Adhered S. Typhimurium population on day 0 were 7.5 log CFU/g. These were treated with individual and combinations of organic acids with GSE or DI water (control) adjusted to the same pH as that of the test solutions with both the modes of application and leaves were refrigerated at 4 °C. Malic acid (2%) in combination with GSE (3%) or lactic acid (3%) sprayed electrostatically showed reductions of 2.6 to 3.3 log CFU/g compared to lower log reductions (0.0 to 0.3 log CFU/g) by day 14 if sprayed conventionally. These findings indicate that malic acid in combination with GSE/lactic acid solutions applied by electrostatic spraying exhibited higher inhibition of pathogens than conventional spraying and can be used for commercial applications to enhance food safety.

Pressurized water versus ethanol as a Silybum marianum extraction solvent for inhibition of low-density lipoprotein oxidation mediated by copper and J774 macrophage cells.

Silybum marianum contains flavonolignans, termed silymarin (SM), that are therapeutic agents for many inflammation-based diseases including atherosclerosis. Oxidation of human low-density lipoprotein was induced by CuSO4 or J774 macrophage cells and measured by the formation of thiobarbituric acid reactive substances (TBARS). SM was extracted by pressurized hot water (PHWE) or ethanol, and the effects of these extracts on TBARS formation were evaluated in comparison with those of SM preparations made from blending masses of individual flavonolignan standards in ratios identical to those of the water and ethanol extracts. Ethanol-extracted SM and its blended counterpart inhibited the generation of TBARS by 82% and 43%, respectively, at 150 mumol/L doses. TBARS levels in the presence of 150 micromol/L of the PHWE and its blended SM counterpart were reduced by 84% and 38%, respectively. Extracts from milk thistle fruit displayed higher protective effects than blended SM solutions of the same concentration with an identical compositional makeup. The appearance of degradation peaks in the water extract did not create any cytotoxic effects. Results of this study confirm that PHWE can be used to extract flavonolignans from milk thistle and that these extracts may possess therapeutic potential different from or beyond that of traditional organic solvent preparations.

Interdigitated microelectrode (IME) impedance sensor for the detection of viable Salmonella typhimurium.

Interdigitated microelectrodes (IMEs) were used as impedance sensors for rapid detection of viable Salmonella typhimurium in a selective medium and milk samples. The impedance growth curves, impedance against bacterial growth time, were recorded at four frequencies (10Hz, 100Hz, 1kHz, and 10kHz) during the growth of S. typhimurium. The impedance did not change until the cell number reached 10(5)-10(6) CFUml(-1). The greatest change in impedance was observed at 10Hz. To better understand the mechanism of the IME impedance sensor, an equivalent electrical circuit, consisting of double layer capacitors, a dielectric capacitor, and a medium resistor, was introduced and used for interpreting the change in impedance during bacterial growth. Bacterial attachment to the electrode surface was observed with scanning electron microscopy, and it had effect on the impedance measurement. The detection time, t(D), defined as the time for the impedance to start change, was obtained from the impedance growth curve at 10Hz and had a linear relationship with the logarithmic value of the initial cell number of S. typhimurium in the medium and milk samples. The regression equations for the cell numbers between 4.8 and 5.4 x 10(5) CFUml(-1) were t(D) = -1.38 log N + 10.18 with R(2) = 0.99 in the pure medium and t(D) = -1.54 log N + 11.33 with R(2) = 0.98 in milk samples, respectively. The detection times for 4.8 and 5.4 x 10(5) CFUml(-1) initial cell numbers were 9.3 and 2.2 h, respectively, and the detection limit could be as low as 1 cell in a sample.

Attachment of Salmonella typhimurium to Skins of Chicken Scalded at Various Temperatures.

Microtopography of chicken skin was studied by varying scalding temperature to determine the least favorable skin surface for salmonellae attachment. Birds were scalded at 52, 56, and 60°C, and the changes of skin morphology were examined by light and transmission electron microscopy throughout the whole processing. Breast skins obtained immediately after picking were inoculated with Salmonella typhimurium, and the attachment was quantified by using scanning electron microscopy and microbiological plating techniques. Skins scalded at 52 and 56°C retained most of the epidermis, although the latter temperature caused the loss of twice as much stratum corneum layers and produced a smoother surface than the former. Skins at 60°C began to lose most of epidermal layers during scalding and exposed dermal surface after picking, which was sometimes covered with thin fragmental epidermis or basal tissue. The number of salmonellae attached to 60°C-processed skins was 1.1~1.3 logs higher than those attached to the skins processed at 52 and 56°C, as measured by scanning electron microscopy. Microbiological plating, however, showed no significant difference in attachment among three skins processed at different temperatures. This was probably due to the insensitivity of the plating method to differentiate attachment strengths of salmonellae to the skin. The above results suggest that removal of whole epidermis should be avoided in processing to reduce salmonellae attachment to the skin.