Superheated steam effectively inactivates diverse microbial targets despite mediating effects from food matrices in bench-scale assessments

Sanitation in dry food processing environments is challenging due to the exclusion of water. Superheated steam (SHS) is a novel sanitation technique that utilizes high temperature steam to inactivate microorganisms. The high sensible heat of SHS prevents condensation on surfaces. Here we evaluated SHS thermal inactivation of various vegetative and spore forming bacteria and fungi and determined the effect of food matrix composition on SHS efficacy. Capillary tubes with vegetative cells (Salmonella, E. coli O157:H7, Listeria monocytogenes, or Enterococcus faecium), Aspergillus fischeri ascospores, or B. cereus spores (100 μL) were SHS treated at 135 ± 1 °C for 1 or 2 s. After 1 s, SHS achieved a reduction of 10.91 ± 0.63 log₁₀ CFU/mL for vegetative cells, 2.09 ± 0.58 log₁₀ ascospores/mL for A. fischeri, and 0.21 ± 0.10 log₁₀ spores/mL for B. cereus. SHS treatment achieved significant reductions in vegetative cells and fungal ascospores (p < 0.05), however B. cereus spores were not significantly reduced after 2 s and were determined to be the most resistant of the cell types evaluated. Consequently, peanut butter compositions (peanut powder, oil, and water) and milk powder (whole and nonfat) inoculated with B. cereus spores on aluminum foil coupons (2 × 3 × 0.5 cm) were tested. The D_161°C values for B. cereus spores ranged from 46.53 ± 4.48 s (6 % fat, 55 % moisture, a_w: 0.927) to 79.21 ± 14.87 s (43 % fat, 10 % moisture, a_w: 0.771) for various peanut butter compositions. Whole milk powder had higher D_161°C (34.38 ± 20.90 s) than nonfat milk powder (24.73 ± 6.78 s). SHS (135 ± 1 °C) rapidly (1 s) inactivated most common vegetative bacterial cells; however B. cereus spores were more heat resistant. B. cereus spore inactivation was significantly affected by product composition (p < 0.05). Compared to the log-linear model (R² 0.81-0.97), the Weibull model had better fit (R² 0.94-0.99). Finally, the ease of peanut butter removal from surfaces increased while the ease of non-fat dry milk removal decreased with the increasing SHS treatment duration. However, allergen residues were detectable on surfaces regardless of SHS treatment. The findings from this study can inform the development of pilot-scale research on SHS.

Effect of dry sanitizing methods on Bacillus cereus biofilm

Bacillus cereus is a relevant foodborne pathogen and biofilm producer which can contaminate and persist in the processing environment of both high and low water activity foods. Because of this, it is crucial to understand better the resistance of this pathogen biofilm to different sanitation methods. The aim of this study was to evaluate the efficacy of dry sanitizing treatments against B. cereus biofilm formed on stainless steel (SS) and polypropylene (PP). Biofilm formation was held through the static method at 25 °C. After 4 days of incubation, coupons were exposed for up to 30 min to UV-C light, dry heat, gaseous ozone, 70% ethanol, and a commercial sanitizer. Sodium hypochlorite (200 mg/l) was also tested in two different pH values (7 and 11) for comparison purposes. In general, the surface material did not influence (p > 0.05) the performance of the treatments. From 10 min of exposure, 70% ethanol and the commercial product caused the lowest reductions on both surfaces. In addition, dry heat exhibited a poor performance on PP, with reductions < 1 log CFU/cm². UV-C light on SS and PP and ozone on PP achieved reductions around 2 log CFU/cm² after 30 min. The same level of reduction was obtained after 5 or 10 min using sodium hypochlorite (200 mg/l). Therefore, the results showed that dry sanitizing methods are not as effective as sodium hypochlorite against B. cereus biofilms. Further studies to evaluate the efficacy of the combination of dry methods are necessary.

Transfer of Salmonella from Inert Food Contact Surfaces to Wheat Flour, Cornmeal, and NaCl

ABSTRACT

Salmonella contamination in a dry processing facility frequently requires removal methods that are nonaqueous. Removal of pathogens from food processing systems with a purge of uncontaminated dry food materials has been proposed; however, little is known with respect to efficacy. In this study, survival of Salmonella on inert contact surfaces and transfer of Salmonella from inert contact surfaces to low-moisture foods were evaluated. Six stainless steel and polymeric food contact material types, in bead form, were contaminated at 11 log CFU/mL and then stored at two temperatures, 25 and 4°C, for 6 months. Simultaneously, three dry food materials or ingredients were used to remove Salmonella from contaminated beads. Wheat flour, cornmeal, and NaCl (1 g each) were mechanically mixed with 3 beads of each material type. The rate of microbial transfer from contaminated beads to food materials was measured. Further experimentation using multiple transfers was applied on two representative beads types, 316 stainless steel and polypropylene, representing common surface contact materials used in processing equipment. Survival of Salmonella on beads depended on storage temperature, with longer survival (P < 0.05) at 4°C than at 25°C, but survival was not influenced by type of bead material. Transfer of Salmonella from stainless steel beads to flour was significantly greater (P < 0.05) than from plastic. Transfer rates from stainless steel to wheat flour, cornmeal, and NaCl were measured as -0.5713, -0.2592, and -1.4221 log CFU of Salmonella removed per cm2 per g of clean material used. Transfer rates from polypropylene to whole wheat flour, cornmeal, and NaCl were more than 10-fold lower at -0.0156, -0.0148, and -0.0129 log CFU of Salmonella removed per cm2 per g of clean material used. These results indicate that although material type may not influence Salmonella survival during storage, Salmonella is more easily removed from stainless steel than polypropylene.

HIGHLIGHTS

Composting toilets as a sustainable alternative to urban sanitation--a review

In today's flush based urban sanitation systems, toilets are connected to both the centralized water and wastewater infrastructures. This approach is not a sustainable use of our water and energy resources. In addition, in the U.S., there is a shortfall in funding for maintenance and upgrade of the water and wastewater infrastructures. The goal of this paper was to review the current knowledge on composting toilets since this technology is decentralized, requires no water, creates a value product (fertilizer) and can possibly reduce the burden on the current infrastructure as a sustainable sanitation approach. We found a large variety of composting toilet designs and categorized the different types of toilets as being self contained or central; single or multi chamber; waterless or with water/foam flush, electric or non-electric, and no-mix or combined collection. Factors reported as affecting the composting process and their optimum values were identified as; aeration, moisture content (50-60%), temperature (40-65°C), carbon to nitrogen ratio (25-35), pH (5.5-8.0), and porosity (35-50%). Mass and energy balance models have been created for the composting process. However there is a literature gap in the use of this knowledge in design and operation of composting toilets. To evaluate the stability and safety of compost for use as fertilizer, various methods are available and the temperature-time criterion approach is the most common one used. There are many barriers to the use of composting toilets in urban settings including public acceptance, regulations, and lack of knowledge and experience in composting toilet design and operation and program operation.