Coating with phenolic branched-chain fatty acid reduces Listeria innocua populations on apple fruit.

An antimicrobial coating was produced by mixing phenolic branched-chain fatty acid (PBC-FA) with glycerol and a carboxymethyl cellulose solution (CMC) at pH 7. The resulting PBC-FA-CMC solution formed an emulsion with an average droplet size of 77 nm. The emulsion in the coating solution was stable for at least 30 days at 20 °C. The in vitro antimicrobial activity of the film formed from the PBC-FA emulsion was tested against a mixture of 3 strains of Listeria innocua (7 log CFU/mL). Film with a concentration of 1000 µg/mL of PBC-FA effectively reduced the population of L. innocua below the limit of detection (<1.48 log CFU/mL) in vitro. The effect of the 1000 µg/mL PBC-FA-CMC coating formulation was then evaluated against L. innocua inoculated on "Gala" apples. Results showed that compared with the non-coated control, the coating reduced L. innocua populations by ~2 log CFU/fruit and ~6 log CFU/fruit on the apple when enumerated on tryptic soy agar and selective media (PALCAM), respectively, indicating that PBC-FA applied as a coating on apples resulted in the sub-lethal injury of bacterial cells. When L. innocua was inoculated onto PBC-FA-coated apples, the L. innocua population decreased by ~4 log CFU/fruit during 14 days of shelf-life at 20 °C. The PBC-FA coating lowered the moisture loss but did not affect the color, firmness, or soluble solids content of apples during the 14-day at 20 °C. Overall, this study revealed that there is a potential that PBC-FA can be used as an antimicrobial coating to inactivate Listeria and preserve the quality of apples.

Depletion of Free Chlorine and Generation of Trichloromethane in the Presence of pH Control Agents in Chlorinated Water at pH 6.5.

Chlorine is commonly used by the fresh produce industry to sanitize water and minimize pathogen cross-contamination during handling. The pH of chlorinated water is often reduced to values of pH 6-7, most commonly with citric acid to stabilize the active antimicrobial, hypochlorous acid (a form of free chlorine). Previous studies have demonstrated that citric acid reacts with chlorine to form trichloromethane, a major chlorine by-product in water and a potential human carcinogen. However, it is unclear if other pH control agents could be used in the place of citric acid to minimize the formation of trichloromethane. The objective of the present study was to determine the reactivity of organic and inorganic pH control agents, with chlorine, to generate trichloromethane. Free chlorine (∼100 mg/L) was mixed with 10 mM of each of twelve organic acids and two inorganic pH control agents (i.e., sodium acid sulfate and phosphoric acid) to effect a pH level of 6.5. Free chlorine and trichloromethane levels were measured over 3 h at 3 and 22°C. Results demonstrated that ascorbic acid, dehydroascorbic acid, citric acid, and malic acid rapidly depleted free chlorine concentrations at both 22°C and 3°C, while tartaric acid and lactic acid decreased chlorine concentrations more slowly. Other pH control agents did not significantly reduce free chlorine either at 22 or 3°C. Citric acid led to the generation of significantly higher concentrations of trichloromethane than did other acids. Chloroacetone was also found in chlorinated water in the presence of citric acid and ascorbic acid. Taking buffering capacity and pKa values into account, phosphoric acid and some organic acids may be used to replace citric acid as pH control agents in chlorinated water for washing fresh produce, to stabilize free chlorine level and reduce the generation of trichloromethane.

Inactivation of Desiccation-Resistant Salmonella on Apple Slices Following Treatment with ε-Polylysine, Sodium Bisulfate, or Peracetic Acid and Subsequent Dehydration.

Salmonella is capable of surviving dehydration within various foods, such as dried fruit. Dried fruit, including apple slices, have been the subject of product recalls due to contamination with Salmonella. A study was conducted to determine the fate of Salmonella on apple slices, following immersion in three antimicrobial solutions (viz., ε-polylysine [epsilon-polylysine or EP], sodium bisulfate [SBS], or peracetic acid [PAA]), and subsequent hot air dehydration. Gala apples were aseptically cored and sliced into 0.4 cm thick rings, bisected, and inoculated with a five-strain composite of desiccation-resistant Salmonella, to a population of 8.28 log CFU/slice. Slices were then immersed for 2 min in various concentrations of antimicrobial solutions, including EP (0.005, 0.02, 0.05, and 0.1%), SBS (0.05, 0.1, 0.2, and 0.3%), PAA (18 or 42 ppm), or varying concentrations of PAA + EP, and then dehydrated at 60°C for 5 h. Salmonella populations in positive control samples (inoculated apple slices washed in sterile water) declined by 2.64 log after drying. In the present study, the inactivation of Salmonella, following EP and SBS treatments, increased with increasing concentrations, with maximum reductions of 3.87 and 6.20 log (with 0.1 and 0.3% of the two compounds, respectively). Based on preliminary studies, EP concentrations greater than 0.1% did not result in lower populations of Salmonella. Pretreatment washes with either 18 or 42 ppm of PAA inactivated Salmonella populations by 4.62 and 5.63 log, respectively, following desiccation. Combining PAA with up to 0.1% EP induced no greater population reductions of Salmonella than washing with PAA alone. The addition of EP to PAA solutions appeared to destabilize PAA concentrations, reducing its biocidal efficacy. These results may provide antimicrobial predrying treatment alternatives to promote the reduction of Salmonella during commercial or consumer hot air drying of apple slices.

Environmental sustainability assessment of a new food waste anaerobic digestion and pyrolysis hybridization system.

This research conducted an environmental life cycle assessment (LCA) to evaluate an anaerobic digestion-co-pyrolysis (ADCo-Py) system in which pyrolysis was added to traditional food waste (FW) anaerobic digestion (AD) systems to treat the solid fraction and impurities separated from FW. The solid fraction, including impurities such as wooden chopsticks, plastics, eggshells, and bones, is usually incinerated, while pyrolysis can be a viable alternative to optimize FW treatment. The environmental impact of ADCo-Py was compared with stand-alone AD, pyrolysis, and ADCo-INC (AD with incineration of separated solids). The results indicated that both ADCo-Py (-1.726 kg CO2-Eq/kgFW) and ADCo-INC (-1.535 kg CO2-Eq/kgFW) outperform stand-alone AD (-0.855 kg CO2-Eq/kgFW) and pyrolysis (-0.181 kg CO2-Eq/kgFW) in mitigating global warming potential (GWP). Additionally, pretreatments were found to have the most significant influence on GWP, ecotoxicity potential (ETP), and acidification potential (AP). The two-step pretreatment in ADCo-Py, including the separation of solids and drying, significantly improved the environmental sustainability of the system when compared with standalone pyrolysis.

Bio-based phenolic branched-chain fatty acid in wash water reduced populations of Listeria innocua on apple fruit.

Phenolic branched-chain fatty acid (PBC-FA) emulsion was produced by dissolving it in ethanol and mixing with water (pH 7). The resulting monodispersed emulsion droplets were approximately 200 nm in diameter. The stability of the emulsion was evaluated by storing it at 4 and 20 °C for 30 days. The antimicrobial activity of the PBC-FA emulsion was tested against Escherichia coli and Listeria innocua (8 log CFU/mL) by determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using a microdilution method. The PBC-FA was effective against L. innocua with MIC and MBC of 14.1 µg/mL and caused membrane permeation as determined with SEM and Live/Dead cell assay, but was not effective against E. coli O157:H7 at the tested concentrations (5-250 µg/mL). We also evaluated PBC-FA emulsion's potential to be used as a wash against L. innocua inoculated on apples. The results showed that the 500 µg/mL PBC-FA emulsion with 5 % ethanol had equivalent antimicrobial activity (2-3 logs reductions) against L. innocua as the 20 µg/mL chlorine solution, a commonly used sanitizer. 500 µg/mL PBC-FA emulsion had better antimicrobial efficacy when organic matter (chemical oxygen demand: 9.0 g/L) was present compared to 20 µg/mL of chlorine. The effect of PBC-FA on the quality of the apples, was determined by measuring changes in color, firmness, and soluble solids content over a 14-day storage period at 20 °C. The quality of the apples was not affected by PBC-FA over the 14-day storage period, suggesting that PBC-FA emulsion can be used as a wash for apples without affecting their quality.

Combined treatment of pulsed light and nisin-organic acid based antimicrobial wash for inactivation of Escherichia coli O157:H7 in Romaine lettuce, reduction of microbial loads, and retention of quality.

Microbial safety of fresh produce continues to be a major concern. Novel antimicrobial methods are needed to minimize the risk of contamination. This study investigated the antimicrobial efficacy of pulsed light (PL), a novel nisin-organic acid based antimicrobial wash (AW) and the synergy thereof in inactivating E. coli O157:H7 on Romaine lettuce. Treatment effects on background microbiota and produce quality during storage at 4 °C for 7 days was also investigated. A bacterial cocktail containing three outbreak strains of E. coli O157:H7 was used as inoculum. Lettuce leaves were spot inoculated on the surface before treating with PL (1-60 s), AW (2 min) or combinations of PL with AW. PL treatment for 10 s, equivalent to fluence dose of 10.5 J/cm2, was optimal and resulted in 2.3 log CFU/g reduction of E. coli O157:H7, while a 2 min AW treatment, provided a comparable pathogen reduction of 2.2 log CFU/g. Two possible treatment sequences of PL and AW combinations were investigated. For PL-AW combination, inoculated lettuce leaves were initially exposed to optimum PL dose followed by 2 min AW treatment, whereas for AW-PL combination, inoculated lettuce were subjected to 2 min AW treatment prior to 10 s PL treatment. Both combination treatments (PL-AW and AW-PL) resulted in synergistic inactivation as E. coli cells were not detectable after treatment, indicating >5 log pathogen reductions. Combination treatments significantly (P < 0.05) reduced spoilage microbial populations on Romaine lettuce and also hindered their growth in storage for 7 days. The firmness and visual quality appearance of lettuce were not significantly (P > 0.05) influenced due to combination treatments. Overall, the results reveal that PL and AW combination treatments can be implemented as a novel approach to enhance microbial safety, quality and shelf life of Romaine lettuce.

Possible Sources of Listeria monocytogenes Contamination of Fresh-cut Apples and Antimicrobial Interventions During Antibrowning Treatments: A Review.

Fresh-cut apples, being rich in antioxidants and other nutrients, have emerged as popular snacks in restaurants, at home, and in school lunch programs, partially due to freshness, convenience, and portion size availability. Two major challenges in processing fresh-cut apples are the browning of cut surfaces and contamination with human pathogens. Regarding human pathogens, contamination by Listeria monocytogenes is a major concern, as evidenced by two outbreaks of whole apples and numerous recalls of fresh-cut apples. Antibrowning agents currently used by the industry have little to no antimicrobial properties. The present review discusses the possible origins of L. monocytogenes in fresh-cut apples, including contaminated whole apples, and contamination via the processing environment and the equipment in fresh-cut facilities. Treatment with antibrowning solutions could possibly be an opportunity for Listeria contamination and represents the last chance to inactivate pathogens. The discussion is focused on the antibrowning treatments where formulations and coatings with antibrowning and antimicrobial properties have been developed and evaluated against Listeria and other microorganisms. In addition, several research needs and considerations are discussed to further reduce the chance of pathogen contamination on fresh-cut apples.

Enzymatic browning and polyphenol oxidase control strategies.

Significant amounts of fresh and fresh-cut fruits and vegetables are wasted every year due to enzymatic browning. Polyphenol oxidase (PPO) is the key enzyme involved in the enzymatic browning. In the past decades, various methods have been developed to inhibit browning of various fresh produce items. However, for most fresh horticultural produce, ideal measures accepted by industries and consumers are still scarce. This review provides up-to-date knowledge of browning control technologies, including physical methods, chemical methods such as natural inhibitors, molecular biotechnology, and nanotechnology. In addition, we propose some ideas to improve the efficacies of these strategies with fewer side effects. To better inhibit tissue browning, new research directions are also discussed, for example, regulation of PPO substrate techniques.

Lipid Oxidation and Volatile Compounds of Almonds as Affected by Gaseous Chlorine Dioxide Treatment to Reduce Salmonella Populations.

The effects of gaseous chlorine dioxide (ClO2) treatment, applied to inactivate Salmonella, on lipid oxidation, volatile compounds, and chlorate levels of dehulled almonds were evaluated during a 3 month accelerated storage at 39 °C. At treatment levels that yielded a 2.91 log reduction of Salmonella, ClO2 promoted lipid oxidation as indicated by increased peroxide values, total acid number, conjugated dienes, and thiobarbituric acid-reactive substances. Furthermore, several chlorine-containing volatile compounds including trichloromethane, 1-chloro-2-propanol, 1,1,1-trichloro-2-propanol, and 1,3-dichloro-2-propanol were identified in ClO2-treated samples. However, all the volatile chlorine-containing compounds decreased during the 3 months of storage. Chlorate (26.4 ± 5.1 µg/g) was found on the ClO2-treated samples. The amounts of non-ethanol alcohols, aldehydes, and carboxylic acids increased following ClO2 treatments. Some volatiles such as 2,3-butanediol that were present in non-treated samples became non-detectable during post-ClO2 treatment storage. Overall, our results demonstrated that gaseous ClO2 treatment promoted lipid oxidation, generation of volatiles of lipid origin, and several chlorine-containing compounds.

Chemical inhibition of polyphenol oxidase and cut surface browning of fresh-cut apples.

Fresh-cut apples, which offer consumers health benefits and convenience, have become popular in recent years. One of the main challenges for processing fresh-cut apples is rapid development of cut surface browning, immediately after fruits are cut. Browning, a physiological response that impacts organoleptic properties and deters consumer purchase of fresh-cut fresh produce, is mainly a result of enzymatic reaction of phenolic compounds with oxygen catalyzed by polyphenol oxidase (PPO), a decapper enzyme. Many antibrowning agents have been developed and evaluated to inhibit PPO activities by using reducing agents (antioxidants), chelating agents, acidulants, etc. The present manuscript reviews the diverse characteristics of PPO (such as optimum pH and temperature, and molecular weight) in apples reported in the literature and the enzyme's latency, multiplicity and copper states in the active site. It also summarizes the latest development in the investigation and formulations of antibrowning compounds, and discusses future research needs. This review should stimulate further research to discover more effective, low cost, and natural antibrowning compounds to meet the demand of consumers as well as the food industry for clean label and long shelf-life of fresh-cut apples.

Mechanism of Synergistic Photoinactivation Utilizing Curcumin and Lauric Arginate Ethyl Ester against Escherichia coli and Listeria innocua.

This study investigated the mechanism of how lauric arginate ethyl ester (LAE) improves the photoinactivation of bacteria by curcumin after diluting the 100 µmol/L stock curcumin-LAE micelle solution to the concentration used during the treatment based on the curcumin concentration. The photoinactivation of bacteria was conducted by irradiating the 1 µmol/L curcumin-LAE solution containing cocktails of Escherichia coli and Listeria innocua strains (7 log CFU/mL) for 5 min with UV-A light (λ = 365 nm). The changes in solution turbidity, curcumin stability, and bacterial morphology, viability, and recovery were observed using SEM, TEM, and live/dead cell assays. The study found that LAE enhances the photoinactivation of bacteria by increasing the permeability of cell membranes which could promote the interaction of reactive oxygen species produced by photosensitized curcumin with the cell components. The combination of curcumin and LAE was demonstrated to be more effective in inhibiting bacterial recovery at pH 3.5 for E. coli, while LAE alone was more effective at pH 7.0 for L. innocua.

Sustainable bio-based antimicrobials derived from fatty acids: Synthesis, safety, and efficacy.

Some conventional sanitizers and antibiotics used in food industry may be of concerns due to generation of toxic byproducts, impact on the environment, and the emergence of antibiotic resistance bacteria. Bio-based antimicrobials can be an alternative to conventional sanitizers since they are produced from renewable resources, and the bacterial resistance to these compounds is of less concern than those of currently used antibiotics. Among the bio-based antimicrobial compounds, those produced via either fermentation or chemical synthesis by covalently or electrovalently attaching specific moieties to the fatty acid have drawn attention in recent years. Disaccharide, arginine, vitamin B1, and phenolics are linked to fatty acids resulting in the production of sophorolipid, lauric arginate ethyl ester, thiamin dilauryl sulfate, and phenolic branched-chain fatty acid, respectively, all of which are reported to exhibit antimicrobial activity by targeting the cell membrane of the bacteria. Also, studies that applied these compounds as food preservatives by combining them with other compounds or treatments have been reviewed regarding extending the shelf life and inactivating foodborne pathogens of foods and food products. In addition, the phenolic branched-chain fatty acids, which are relatively new compounds compared to the others, are highlighted in this review.

Antimicrobial coating with organic acids and essential oil for the enhancement of safety and shelf life of grape tomatoes.

This study investigated the antimicrobial efficacy of two coatings against populations of nalidixic acid-resistant Salmonella, Listeria monocytogenes and native microorganisms on whole grape tomatoes. Tomatoes were surface-coated in two chitosan-acid coating solutions. Solution 1 (Chitosan) consisted of 1 % chitosan and 2 % acetic, lactic and levulinic acids. Solution 2 (Chitosan+AIT) consisted of Solution 1 plus 2 % allyl isothiocyanate (AIT). After the treatments, tomatoes were placed in PET containers and stored at 10 °C for 21 days. Chitosan and Chitosan+AIT treatments reduced Salmonella populations from 3.65 to 1.28 and <0.70 log CFU/tomato on day 1, respectively. Both treatments reduced Salmonella populations to undetectable levels (<0.70 log CFU/tomato) from Day 2 through Day 21. Similarly, Chitosan+AIT treatments caused a greater reduction in Listeria populations than Chitosan treatment on day 1, but there were no significant differences between the two treatments after day 2. Chitosan and Chitosan+AIT reduced native bacteria populations to an undetectable level after 2 days and reduced the population of native yeasts & molds to an undetectable level after 1 day. The presence of mold was only observed on control sample after 21 days. Quality analyses showed that samples which were subject to coating treatment maintained their texture and color for 21 days at 10 °C with less water loss compared to the controls. This study suggests that chitosan-acid coating is applicable for extending the shelf-life and enhancing the safety of grape tomatoes.

Quality of fresh and fresh-cut produce impacted by nonthermal physical technologies intended to enhance microbial safety.

Nonthermal physical intervention technologies are able to reduce populations of foodborne pathogens on/in fresh produce. As highly perishable and living organisms, fresh produce is inherently sensitive to any physical or chemical treatment in terms of quality damage. The aims of the present review are to summarize current knowledge on non-thermal technologies (ionizing radiation, UV and pulsed light, ultrasound, high hydrostatic pressure, and cold plasma) with an emphasis on their impact on quality of fresh produce and to discuss advantages, disadvantages, and considerations for the commercialization of each technology. The impact of nonthermal physical technologies on fresh produce quality is related to pathogen inactivation mechanisms of each individual technology, and the nature and intensity of changes in quality due to the technologies depend on the treatment intensity/time and other processing conditions. Common symptoms of quality deterioration due to nonthermal processing include tissue softening, browning, and loss of nutrients. In general, there is a lack of systematic assessment, particularly sensory evaluations using taste panels of the product quality after treatments. For emerging technologies, such as cold plasma, more studies are necessary in order to assess quality changes during post-treatment storage at relevant temperatures. Quality of fresh produce must be carefully investigated to facilitate the commercialization of technologies.

UV-C treatment inhibits browning, inactivates Pseudomonas tolaasii and reduces associated chemical and enzymatic changes of button mushrooms.

BACKGROUND: Button mushrooms with completely white appearance are popular with consumers. However, button mushrooms are susceptible to infection with Pseudomonas tolaasii, which results in browning. This study evaluates the effects of ultraviolet-C (UV-C) treatment on the inactivation of P. tolaasii in vitro and in vivo and on the physiological and chemical changes of button mushrooms during storage for 21 days at 4 °C. RESULTS: UV-C doses of 0.5 to 9.0 kJ m-2 resulted in 3.91-6.26 log CFU mL-1 reduction of P. tolaasii populations in vitro, and UV-C treatment reduced P. tolaasii populations inoculated on mushroom cap surfaces and browning severity. Moreover, P. tolaasii increased polyphenol oxidase (PPO) activity, and decreased phenylalanine ammonia-lyase (PAL) activity, the accumulation of phenolics and contents of brown melanin precursors, including γ-l-glutaminyl-4-hydroxybenzene (GHB), γ-l-glutaminyl-3,4-dihydroxybenzene (GDHB), and tyrosine in button mushrooms. UV-C treatment was found to reduce the negative changes due to P. tolaasii infection. CONCLUSION: These results indicated that the application of UV-C treatment inhibited browning, inactivated P. tolaasii and reduced P. tolaasii - associated chemical and enzymatic changes of button mushrooms. © 2021 Society of Chemical Industry.

Moving Chemistry from Bench to Market: An Introduction to the Agricultural and Food Chemistry Technical Program at the 260th American Chemical Society Fall 2020 Virtual Meeting & Expo.

This is the second special issue of the Journal of Agricultural and Food Chemistry (JAFC) that reviews the Agricultural and Food Chemistry Division (AGFD) technical program from a national meeting of the American Chemical Society (ACS). The 260th meeting was virtually held on August 17-20, 2020 as a result of the COVID-19 pandemic. Although it was the first-ever all online meeting in ACS history, a total of 311 abstracts were submitted to the AGFD technical program for oral and poster presentations and 34 technical sessions were held in 22 symposia, which covered a broad range of food and agricultural topics. The very first virtual ACS meeting was successful with the high quality of presentations, the number of online audiences, and seamless technology.

Gaseous ozone to preserve quality and enhance microbial safety of fresh produce: Recent developments and research needs.

Fresh fruits and vegetables are highly perishable and are subject to large postharvest losses due to physiological (senescence), pathologic (decay), and physical (mechanical damage) factors. In addition, contamination of fresh produce with foodborne human pathogens has become a concern. Gaseous ozone has multiple benefits including destruction of ethylene, inactivation of foodborne and spoilage microorganisms, and degradation of chemical residues. This article reviews the beneficial effects of gaseous ozone, its influence on quality and biochemical changes, foodborne human pathogens, and spoilage microorganisms, and discusses research needs with an emphasis on fruits. Ozone may induce synthesis of a number of antioxidants and bioactive compounds by activating secondary metabolisms involving a wide range of enzymes. Disparities exist in the literature regarding the impact of gaseous ozone on quality and physiological processes of fresh produce, such as weight loss, ascorbic acid, and fruit ripening. The disparities are complicated by incomplete reporting of the necessary information, such as relative humidity and temperatures at which ozone measurement and treatment were performed, which is needed for accurate comparison of results among studies. In order to fully realize the benefits of gaseous ozone, research is needed to evaluate the molecular mechanisms of gaseous ozone in inhibiting ripening, influence of relative humidity on the antimicrobial efficacy, interaction between ozone and the cuticle of fresh produce, ozone signaling pathways in the cells and tissues, and so forth. Possible adverse effects of gaseous ozone on quality of fresh produce also need to be carefully evaluated for the purpose of enhancing microbial and chemical safety of fresh produce.

Hydrogen Peroxide Residue on Tomato, Apple, Cantaloupe, and Romaine Lettuce after Treatments with Cold Plasma-Activated Hydrogen Peroxide Aerosols.

ABSTRACT: Hydrogen peroxide (H2O2) has long been studied as an aqueous sanitizer to enhance microbial safety of fresh produce. Recently, we demonstrated that cold plasma-activated H2O2 aerosols, hereafter called ionized hydrogen peroxide (iHP), reduced populations of Salmonella, Listeria, and Escherichia coli by up to 5.5 log on surfaces of various produce items. However, the amount and fate of H2O2 residue left on fresh produce after treatments have not been evaluated. In the present study, H2O2 residue levels on apples, tomatoes, cantaloupe, and romaine lettuce were analyzed after treatments with 7.8% iHP at conditions that had been optimized and tailored for Salmonella reductions and each produce item. Results showed that higher residue levels were found on lettuce than on cantaloupe, tomatoes, and apples immediately after treatments. During storage at 10 and 22°C, H2O2 levels decreased rapidly and fell below 1 mg/kg within 1 day after treatments for all fresh produce items. Furthermore, the decrease was faster at 22°C than at 10°C. Most importantly, the levels of H2O2 residue on the fresh produce items were lower than those after wash with 1% H2O2 for 1 min. Overall, our results demonstrated that levels of H2O2 residue on fresh produce surfaces decomposed rapidly after treatment with iHP and did not appear to pose a safety concern after 1 day of storage.

Effects of intense pulsed light and gamma irradiation on Bacillus cereus spores in mesquite pod flour.

This study was conducted to evaluate the inactivation of Bacillus cereus spore in mesquite flour with intense pulsed light (IPL) and gamma radiation. The physical, chemical, and toxicity of treated mesquite flour were also investigated. The results showed that up to 3.51 log10CFU/g B. cereus spore inactivation was achieved with 8 kGy of gamma radiation, and up to 1.69 log10CFU/g reductions could be achieved after 28s of catalytic IPL exposure. Although chemometric analysis showed 9-hydroxy-10,12-octadecadienoic acid was slightly increased after a 28s-catalytic IPL treatment, the concentration is within the acceptable range. No significant increase in acetic or propionic acids (typical off-flavor volatile compounds) was observed after either treatment. For cytotoxicity, the Caco-2 cell viability analysis revealed that these two technologies did not induce significant cytotoxicity to the treated mesquite flour. Overall, these two technologies exhibit strong potential for the decontamination of B. cereus in mesquite flour.

Thermal Reduction of Bacillus spp. in Naturally Contaminated Mesquite Flour with Two Different Water Activities.

ABSTRACT: Mesquite flour with endogenous high sugar content is often contaminated with Bacillus cereus. The purpose of the present study was to evaluate the thermal resistance of Bacillus spp. in naturally contaminated mesquite flour. Flours with and without adjusted water activity (aw) were treated at various temperatures (100 to 140°C) and times (up to 2 h). Total mesophilic bacteria and Bacillus spp. were enumerated using tryptic soy agar and Brilliance Bacillus cereus Agar, respectively. Results revealed that naturally contaminated Bacillus spp. and other mesophilic bacteria in mesquite flour (aw = 0.34) were highly resistant to heat. To reduce the initial populations (4.75 log CFU/g) of Bacillus spp. to nondetectable levels (<1.18 log CFU/g), thermal treatments of 120°C for 2 h were required. D100°C-values for total mesophilic bacteria were 5.6-fold higher than those of Bacillus spp. With increasing treatment temperature, the difference in D-value between total mesophilic bacteria and Bacillus spp. became smaller. When the aw of flour was adjusted from 0.34 to 0.71, the D-values for Bacillus decreased significantly. Treatment at 100°C for 1 h reduced Bacillus spp. populations to nondetectable levels. Our results demonstrate that naturally present Bacillus spp. in flour are highly resistant to heat, whereas increasing the aw increased their heat sensitivity. The high thermal resistance of microbes in mesquite flour warrants further investigations.