Comparison of characteristics and antioxidant activities of sesame protein hydrolysates and their fractions.

Sesame meal is a by-product obtained from oil extraction. We investigated the characteristics and antioxidant activities of a sesame protein hydrolysate (SPH-B), as well as its peptide fractions. Four peptide fractions (F1; >100 kDa, F2; 10-100 kDa, F3; 1-10 kDa, and F4; <1 kDa) of SPH-B were prepared. The characteristics and antioxidant properties of SPH-B and its peptide fractions were evaluated. Sesame protein (SP) contained protein fractions with molecular weights ranging from 10 to 44 kDa, whereas SPH-B had peptide fractions ranging from 8 to 44 kDa. The peptide fractions had molecular weight ranging from 7 to 10 kDa. The four peptide fractions had a higher α-helix content and lower surface hydrophobicity than SPH-B and SP. They exhibited better antioxidant properties, with higher ABTS and DPPH radical scavenging activities, higher metal chelating activity, and greater inhibition of linoleic acid peroxidation, suggesting that sesame peptide fractions can use as plant-based functional ingredients and potentially health-promoting properties.

Use of Micellar Delivery Systems to Enhance Curcumin's Stability and Microbial Photoinactivation Capacity.

Microbial photoinactivation using ultraviolet (UV) or visible light can be enhanced by photosensitizers. This study assessed the efficacy of encapsulating a food-grade photosensitizer (curcumin) in surfactant micelles on its water dispersibility, chemical stability, and antimicrobial activity. Stock curcumin-surfactant solutions were prepared with Surfynol 465 (S465) or Tween 80 (T80) (5 mM sodium citrate buffer). The antimicrobial activity of curcumin-loaded surfactant solutions was determined by monitoring the inactivation of Escherichia coli O157: H7 and Listeria innocua after 5-min irradiation with UV-A light (λ = 365 nm). The solutions mixed with the bacterial suspensions contained 1 µM curcumin and each surfactant below, near, and above their critical micelle concentrations (CMCs). The addition of surfactants at any level to the curcumin solution enhanced its dispersibility, stability, and efficacy as a photosensitizer, thereby enhancing its antimicrobial activity. Gram-positive bacteria were more susceptible than Gram-negative bacteria when curcumin-loaded micelles were used against them. The photoinactivation efficacy of curcumin-surfactant solutions depended on the pH of the solution (low > high), surfactant type (S465 > T80), and the amount of surfactant present (below CMC ≥ near CMC > above CMC = unencapsulated curcumin). This result suggests that excessive partitioning of curcumin into micelles reduced its ability to interact with microbial cells. Synergistic antimicrobial activity was observed when S465 was present below or near the CMC with curcumin at pH 3.5, which could be attributed to a more effective interaction of the photosensitizer with the cell membranes as supported by the fluorescence lifetime micrographs. The use of a micelle-based delivery system facilitates adsorption and generation of reactive oxygen species in the immediate environment of the microbial cell, enhancing photoinactivation.

Efficacy of ATP Monitoring for Measuring Organic Matter on Postharvest Food Contact Surfaces.

ABSTRACT: The Food Safety Modernization Act, specifically the Produce Safety Rule, requires growers to clean and sanitize food contact surfaces to protect against produce contamination. An ATP monitoring device is a potential sanitation tool to monitor the efficacy of an on-farm cleaning and sanitation program that could help growers meet regulatory expectations mandated by the Produce Safety Rule. This ATP monitoring device uses bioluminescence to detect all ATP (found in bacteria and produce matter cells) from a swabbed surface. Because little work has been done to test the efficacy of these tools under postharvest conditions, the present study evaluated ATP measurement for postharvest food contact surface cleanliness evaluation. Concentrations of leafy greens (spinach, romaine, and red cabbage, with or without Listeria innocua) were used as organic matter applied to stainless steel, high-density polyethylene plastic, and bamboo wood coupons to represent postharvest food contact surfaces. The ATP levels on the coupons were then measured by using swabs and an ATP monitoring device. Results showed that the concentration of L. innocua and leafy greens on a food contact surface had a highly significant effect on the ATP monitoring device reading (P < 0.0001). The ATP monitoring device had a lower limit of detection for L. innocua at 4.5 log CFU per coupon. The type of leafy green on a food contact surface did not affect the ATP reading (P = 0.88). Leafy greens with added L. innocua had a higher ATP reading when compared with saline and L. innocua, demonstrating the presence of leafy green matter contributes to ATP reading when combined with L. innocua. The different food contact surfaces had different ATP response readings (P = 0.03), resulting in no detectable levels of bacteria and/or leafy green material from bamboo wood surfaces (P = 0.16). On the basis of our results, the ATP measurement is an appropriate tool to measure produce or bacterial contamination on stainless steel or high-density polyethylene plastic surfaces; however, it is not recommended for wood surfaces.

Adhesion and removal kinetics of Bacillus cereus biofilms on Ni-PTFE modified stainless steel.

Biofilm control remains a challenge to food safety. A well-studied non-fouling coating involves codeposition of polytetrafluoroethylene (PTFE) during electroless plating. This coating has been reported to reduce foulant build-up during pasteurization, but opportunities remain in demonstrating its efficacy in inhibiting biofilm formation. Herein, the initial adhesion, biofilm formation, and removal kinetics of Bacillus cereus on Ni-PTFE-modified stainless steel (SS) are characterized. Coatings lowered the surface energy of SS and reduced biofilm formation by > 2 log CFU cm(-2). Characterization of the kinetics of biofilm removal during cleaning demonstrated improved cleanability on the Ni-PTFE coated steel. There was no evidence of biofilm after cleaning by either solution on the Ni-PTFE coated steel, whereas more than 3 log and 1 log CFU cm(-2) of bacteria remained on the native steel after cleaning with water and an alkaline cleaner, respectively. This work demonstrates the potential application of Ni-PTFE non-fouling coatings on SS to improve food safety by reducing biofilm formation and improving the cleaning efficiency of food processing equipment.

Antimicrobial N-halamine modified polyethylene: characterization, biocidal efficacy, regeneration, and stability.

UNLABELLED: Development of antimicrobial materials that regenerate antimicrobial activity represents a novel technology in preventing microbial cross-contamination. We report a method for the application of regenerably antimicrobial N-halamines onto the surface of polyethylene (PE) materials through layer-by-layer (LbL) assembly of polyethyleneimine and poly(acrylic acid). A total of 5, 10, 15, and 20 bilayers were applied. Modified PE had from 49.3 to 293.5 nmol cm(-2) antimicrobial N-halamines from 5 to 20 bilayers after 10 min of chlorination. Each variant of N-halamine modified PE was able to reduce by >5 logarithmic cycles Listeria monocytogenes. The stability of N-halamine modified PE was characterized after extended exposure to chlorine, acidic solutions, and an alkaline cleaner. After an initial conditioning period, materials generated more than double the quantity of N-halamines present on as prepared materials, retaining regenerability for up to 100 chlorination cycles. After the equivalent of 300 washing cycles by buffers (pH values 3, 5, and 7) or a commercial alkaline detergent, there was no change in the number of antimicrobial N-halamines on the modified materials. These results indicate that the reported LbL deposition technique results in antimicrobial N-halamine materials capable of long-term reuse and exposure to harsh chemicals as expected in a food-processing environment. Such robust, regenerably antimicrobial materials could be an effective technology in the food industry to prevent cross-contamination of pathogenic and spoilage microorganisms. PRACTICAL APPLICATION: The food contact surface of polyethylene was modified by layer-by-layer deposition of 2 polymers, resulting in a rechargeably antimicrobial surface. Repeated exposure to chlorine regenerated its antimicrobial activity, resulting in greater than 99.999% reduction in Listeria monocytogenes. Materials were stable against repeated washing and exposure to acidic environments. These food contact materials could support current cleaning and sanitization protocols in improving food safety in the processing environment.

Concentration and application order effects of sodium benzoate and eugenol mixtures on the growth inhibition of Saccharomyces cerevisiae and Zygosaccharomyces bailii.

UNLABELLED: Growth of Saccharomyces cerevisiae and Zygosaccharomyces bailii cells was monitored in the presence of sodium benzoate and eugenol alone or combined. The two antimicrobials' concentration, addition order, and timing were varied to determine and quantify any additive inhibitory effect on the yeasts. The yeast growth was also followed in the presence of ethanol, which served as solubilizer, at pertinent concentrations. The growth patterns are depicted as adjusted optical density compared with time curves. They all had sigmoid shape, described mathematically by a shifted logistic model that had an almost perfect fit to the data. The model's 3 parameters accounted for the curve's asymptote, the location of its inflection point and slope, which are rough measures of the overall growth level and its degree of suppression, the time to reach the peak growth rate and its retardation, and the overall growth rate, respectively. Maximum growth inhibition was achieved when the sodium benzoate and eugenol were administered together or alone in full dose. When each was administered alone but in 2 half dose additions, their efficacy dropped. When they were used together but added sequentially with a 24 h pause, their administration order had a noticeable effect on the treatment's efficacy, which depended on their respective concentrations. These observations are presented in a slightly modified version of the "hurdle" ideogram. They suggest that sequencing the administration of antimicrobials can be a simple tool to probe their mode of activity and quantify their efficacy. PRACTICAL APPLICATION: Reducing the amount of additives in foods is a goal pursued by many branches of the food industry. In microbial growth suppression, a promising way to accomplish such a reduction is through the administration of 2 or more antimicrobials, preferably natural, exploiting their synergism. To search for effective combinations, in respect to type and concentration, one needs an insight into their mode of activity. Sequencing their administration, as demonstrated with 2 antimicrobials and 2 common yeasts that are involved in beverage spoilage, has offered a simple way to probe into certain aspects of the effect of antimicrobial combinations on microorganisms. The presented algebraic growth model enables to quantify, separately, the growth overall suppression, its retardation, and lowering its peak rate. The proposed modified version of the "hurdles paradigm" helps to visualize the differences in the antimicrobials' general mode of activity and how it is affected by their sequencing.

Effect of surface roughness and stainless steel finish on Listeria monocytogenes attachment and biofilm formation.

The purpose of this study was to evaluate the effect of surface roughness (Ra) and finish of mechanically polished stainless steel (Ra = 0.26 +/- 0.05, 0.49 +/- 0.10, and 0.69 +/- 0.05 microm) and electropolished stainless steel (Ra = 0.16 +/- 0.06, 0.40 +/- 0.003, and 0.67 +/- 0.02 microm) on Listeria adhesion and biofilm formation. A four-strain cocktail of Listeria monocytogenes was used. Each strain (0.1%) was added to 200 ml of tryptic soy broth (TSB), and coupons were inserted to the mixture for 5 min. For biofilm formation, coupons with adhesive cells were incubated in 1:20 diluted TSB at 32 degrees C for 48 h. The experiment was performed by a randomized block design. Our results show that the level of Listeria present after 48 h of incubation (mean = 7 log CFU/cm2) was significantly higher than after 5 min (mean = 6.0 log CFU/cm2) (P < 0.01). No differences in initial adhesion were seen in mechanically finished (mean = 6.7 log CFU/cm2) when compared with electropolished stainless steel (mean = 6.7 log CFU/cm2) (P > 0.05). Listeria initial adhesion (values ranged from 5.9 to 6.1 log CFU/cm2) or biofilm formation (values ranged from 6.9 to 7.2 log CFU/cm2) was not significantly correlated with Ra values (P > 0.05). Image analysis with an atomic force microscope showed that bacteria did not colonize the complete surface after 48 h but were individual cells or grouped in microcolonies that ranged from 5 to 10 microm in diameter and one to three cell layers in thickness. Exopolymeric substances were observed to be associated with the colonies. According to our results, electropolishing stainless steel does not pose a significant advantage for food sanitation over mechanically finished stainless steel.

Effect of biofilm dryness on the transfer of Listeria monocytogenes biofilms grown on stainless steel to bologna and hard salami.

Listeria monocytogenes continues to be a major cause of class I food recalls in the United States. Very little is known about its transfer and cross-contamination in processing scenarios. The objective of this study was to evaluate the effect of hydration level on L. monocytogenes biofilms grown on stainless steel and its effect on the biofilm transfer to foods. Biofilms were grown on stainless steel in diluted tryptic soy broth 1:20 for 48 h at 32 degrees C. After this, biofilms were equilibrated over saturated salt solutions at 20 degrees C for 24 h (94, 75, 58, and 33% relative humidity; % RH) prior to transferring. Transfer experiments were conducted from inoculated stainless steel to bologna and hard salami at a constant pressure (45 kPa) and time (30 s) with a universal testing machine. The experiment was designed with a factorial design 4 x 2 (biofilms equilibrated at 4% RH and two foods) and duplicated every day, and the whole experiment was repeated nine times. The results were analyzed with an analysis of variance by SAS Statistical Analysis Software. Our results showed that more bacteria were transferred to bologna (mean efficiency of transfer [EOT] = 3.0) than to hard salami (mean EOT = 0.35, P < 0.01). As biofilms became drier, the transfer of Listeria from stainless steel to both foods increased (P < 0.05). The EOT increased from 2 to 3.8 and from 0.2 to 0.51 upon transfer when drying the biofilm for bologna and hard salami, respectively. This study may be an indication that as biofilms were dried, the cell-cell and cell-surface interactions became weaker, and bacterial transfer increased. This phenomenon was enhanced in foods containing higher water activity levels. We hypothesize that this increased in transfer was due to the presence of capillary forces in the food.

Effects of inoculation level, material hydration, and stainless steel surface roughness on the transfer of listeria monocytogenes from inoculated bologna to stainless steel and high-density polyethylene.

The influence of inoculation level, material hydration, and stainless steel surface roughness on the transfer of Listeria monocytogenes from inoculated bologna to processing surfaces (stainless steel and polyethylene) was assessed. Slices of bologna (14 g) were inoculated with Listeria at different levels, from 10(5) to 10(9) CFU/cm2. Transfer experiments were done at a constant contact time (30 s) and pressure (45 kPa) with a universal testing machine. After transfer, cells that had been transferred to sterile stainless steel and polyethylene were removed and counted, and the efficiency of transfer (EOT) was calculated. As the inoculation level increased from 10(5) to 10(9) CFU/cm(2), the absolute level of transfer increased in a similar fashion. By calculating EOTs, the data were normalized, and the initial inoculation level had no effect on the transfer (P > 0.05). The influence of hydration level on stainless steel, high-density polyethylene, and material type was investigated, and the EOTs ranged from 0.1 to 1 under all the conditions tested. Our results show that transfers to wetted processing surfaces (mean EOT = 0.43) were no different from dried processing surfaces (mean EOT = 0.35) (P > 0.05). Material type was shown to be a significant factor, with greater numbers of Listeria transferring from bologna to stainless steel (mean EOT = 0.49) than from bologna to polyethylene (mean EOT = 0.28) (P < 0.01). Stainless steel with three different surface roughness (Ra) values of <0.8 microm (target Ra = 0.25, 0.50, and 0.75 Vmicrom) and two different finishes (mechanically polished versus mechanically polished and further electropolished) was used to evaluate its effect on the transfer. The surface roughness and finish on the stainless steel did not have any effect on the transfer of Listeria (P > 0.05). Our results showed that when evaluating the transfer of Listeria, the use of EOTs rather than the absolute transfer values is essential to allow comparisons of transfer conditions or comparisons between research groups.

Evaluation of the transfer of Listeria monocytogenes from stainless steel and high-density polyethylene to Bologna and American cheese.

The objective of this study was to determine the factors involved in the transfer of Listeria monocytogenes from surfaces to foods. We evaluated the influence of surface type (stainless steel and high-density polyethylene), inoculation method (biofilm growth and attached cells), hydration level (visibly dry and wet), and food type (bologna and American cheese). Each experiment included all 16 combinations and was repeated 11 times. A four-strain cocktail of L. monocytogenes was used to inoculate stainless steel and high-density polyethylene either as growing biofilms or attached cells. Slides were placed on a universal testing machine and brought into contact with food at a constant pressure (45 kPa) and time (30 s). Food slices were blended, the number of transferred cells was determined by plating, and the efficiency of transfer (EOT) was calculated. The results strongly suggest that stainless steel surfaces transferred more L. monocytogenes to foods than did polyethylene (P = 0.05). Independent of the surface, biofilms tended to transfer more L. monocytogenes to foods (EOT = 0.57) than did attached cells (EOT = 0.16). Among foods, L. monocytogenes was transferred to bologna more easily than to cheese (P < 0.05). The impact of hydration on transfer was significantly higher for dried biofilms growing on stainless steel (P < 0.05). No significant differences for hydration were seen under other conditions (P > 0.05). We hypothesize that drying weakens cell-to-cell interactions in biofilms and cell-to-surface interactions of biofilms and thus allows increased transfer of cells to food products.