Modified agar diffusion bioassay for better quantification of Nisaplin(®).

AIMS: To investigate the effect of different well sizes and pre-diffusion times at 4 °C, on the sensitivity, accuracy and precision of nisin quantification by agar diffusion bioassay. METHODS AND RESULTS: Nisin solution (0.625-125 µg ml(-1) ) was filled in wells (3.5 mm or 7 mm diameter) made on agar plates inoculated with Micrococcus luteus, followed by pre-diffusion (0, 24, 48 or 72 h), incubation and measurement of inhibition zone. Regression analysis indicated that wells with 3.5 mm diameter had smaller standard deviation and higher predictive accuracy, compared to wells with 7 mm diameter. Based on Tukey's test, pre-diffusion resulted in significantly different inhibition zones at different nisin concentrations. Pre-diffusion also improved sensitivity of the assay. Different regression models were considered to explore the relationship between inhibition zone and nisin concentration for different pre-diffusion times. A spline model was determined to be the best-fit model, and 48 h was the best pre-diffusion time. CONCLUSIONS: Wells with 3.5 mm diameter demonstrated higher accuracy for nisin quantification compared to wells with 7 mm diameter. 48 h was the best pre-diffusion time for nisin concentration in the range 0.625-125 µg ml(-1) . SIGNIFICANCE AND IMPACT OF THE STUDY: The findings from this study will be helpful in quantifying nisin and compounds with antimicrobial properties accurately over a wide range of concentrations using agar diffusion bioassay.

Fat, moisture, and ethanol migration through chocolates and confectionary coatings.

The migration of fat, moisture, and ethanol is a common problem with chocolate-coated confectionery products. Migration of one of these components into the coating leads to visual and sensory defects such as sugar or fat bloom, making the product unacceptable to the consumer. The migration rate depends on the structure and composition of the coating. The migration of each of these species can be slowed to a certain extent by proper tempering of the coating, because proper tempering will give a structure that resists migration. In the continuous lipid phase, these chemical species migrate mainly through the liquid portion. Thus, the migration rate depends on the amount of liquid oil present in the product. Migration can be delayed either by reducing the liquid fat content or by immobilizing the liquid phase. The actual mechanisms for the migration processes are speculative, and a more thorough understanding is necessary to better abate quality deterioration. Armed with this understanding, a manufacturer would know a priori the effect of changing the ingredient or process. A few methods for control have been suggested, but have found limited application. Mathematical models have been proposed to predict the migration behavior, but their application is hindered because of the simplified assumptions employed. There is a need for developing better models that combine mass transfer with the phase behavior to be able to accurately predict the migration process. This review discusses the current understanding of fat, moisture, and ethanol migration through chocolate coatings and also includes a brief description of the theoretical aspects governing migration.

Characterization of guided microwave spectrometry using water-ethanol mixtures.

On-line measurement of food composition plays an important role in ensuring good quality control during processing operations. Microwave based instruments provide on-line measurement of the bulk sample due to the relatively long wavelength. Characterization of Guided Microwave Spectrometry (GMS) was conducted in this study. The GMS spectra and dielectric properties of water-ethanol mixtures with ethanol contents (v/v) of 0, 25 and 50% were measured at 10 degrees C, 23 degrees C and 40 degrees C. The effects of coaxial cables and antenna were examined and the detection limits of the GMS analyzer were determined. The dielectric properties of the material being measured affected the GMS spectrum by shifting the cutoff region and changing the spectral amplitude over the entire operating frequency span. Temperature affected the spectrum by changing the dielectric properties of the material. Coaxial cables did not have a significant effect on the spectrum and the characteristic dip in the passband region was due to antenna resonance. The antenna affected the number of the resonances present in the spectrum, the frequency location and the amplitude of the resonances. GMS system has both a lower and upper amplitude limit beyond which its resolution decreases significantly. This can be resolved by using a signal attenuator and a smaller sensor body.

Effects of electrical shielding and salt concentration on microwave heating in cylindrical containers.

Time-temperature distributions in water and salt solutions were collected in a cylindrical container with and without electrical top shielding during microwave heating. A cold spot was found to exist for both water and salt solutions close to the bottom of the container with and without electrical top shielding. Surface heating was observed in unshielded salt solutions and resulted in a stagnant layer close to the top of the container. Surface heating was eliminated in salt solutions with electrical shielding at the top of the container. Flow profiles within the container were monitored using a potassium permanganate dye tracer and a video camera. The flow profiles for water showed an upward flow in the central region and a descending flow along the side walls. An upward flow along the side walls and a downward flow along the central axis was observed for salt solutions.

Optimization of iron supplementation for enhanced detection of Salmonella Enteritidis in eggs.

Mixed raw egg contents were inoculated with approximately 10 CFU of Salmonella Enteritidis and supplemented with 0 to 7 mg of FeSO4 per g of egg contents. Egg contents were then incubated at 37 degrees C, and Salmonella Enteritidis colonies were enumerated for up to 106 h. Iron supplementation significantly enhanced the growth of Salmonella Enteritidis. Within the first 24 h of incubation, the optimum iron level for Salmonella Enteritidis growth in egg contents was between 0.2 and 2 mg of FeSO4 per g of egg contents. After 24 h of incubation at 37 degrees C. Salmonella Enteritidis counts in eggs supplemented with 0.5 mg of FeSO4 per g of egg contents consistently reached approximately 1 x 10(9) CFU/ml, whereas Salmonella Enteritidis counts in eggs without iron supplementation varied from less than 5 CFU/ml to 8.4 x 10(6) CFU/ml. A 3 by 3 factorial design was used to study the effect of type of preenrichment and level of iron supplementation on the growth of Salmonella Enteritidis in egg contents. No significant differences in Salmonella Enteritidis counts between preenrichment and nonpreenrichment treatments were observed when egg contents were supplemented with 0.5 mg of FeSO4 per g of egg contents. It was concluded that preenrichment was not necessary for isolation of Salmonella Enteritidis from eggs. The effect of iron supplementation on the sensitivity of detection by the direct plating method was investigated. The direct plating method detected a significantly higher percentage of Salmonella Enteritidis in raw egg contents supplemented with 0.5 mg of FeSO4 per g of egg contents (90%) than in raw egg contents without iron supplementation (63.3%).

Influence of sodium chloride on growth of lactic acid bacteria and subsequent destruction of Escherichia coli O157:H7 during processing of Lebanon bologna.

Due to undesirable quality changes, Lebanon bologna is often processed at temperatures that do not exceed 48.8 degrees C (120 degrees F). Therefore, it is important to study parameters that influence the destruction of Escherichia coli O157:H7 in Lebanon bologna. The objective of the present study was to determine the influence of curing salts (NaCl and NaNO2) on the destruction of E. coli O157:H7 during Lebanon bologna processing. Fermentation to pH 4.7 at 37.7 degrees C reduced populations of E. coli O157:H7 by approximately 0.3 log10, either in the presence or absence of curing salts. Subsequent destruction of E. coli O157:H7 during heating of fermented product to 46.1 degrees C was significantly reduced by the presence of 3.5% NaCl and 156 ppm NaNO2, compared to product without curing salts (P < 0.01). The presence of a higher level of NaCl (5%) in Lebanon bologna inhibited the growth of lactic acid bacteria (LAB), which yielded product with higher pH (approximately 5.0) and significantly reduced the destruction of E. coli O157:H7 even further (P < 0.05). Lower concentrations of NaCl (0, 2.5%) yielded Lebanon bologna with higher LAB counts and lower pHs, compared to product with 5% NaCl. When lactic acid was used to adjust pH in product containing different levels of NaCl, it was determined that low pH was directly influencing destruction of E. coli O157:H7, not NaCl concentration.

Effect of initial product temperature and initial pH on foaming time during vacuum evaporation of liquid whole eggs.

During earlier studies on vacuum concentration of liquid egg white, the phenomena of foaming during the initial stages of the process were reported. In these studies, it was also shown that no concentration took place during the foaming period that varied from test to test. To minimize the total process time, this present study was undertaken to investigate what variables contributed to foaming, how they could be controlled, and what effect they had on product quality and functional properties. This study investigated the relationships among initial product temperature, initial pH, and foaming of liquid whole eggs. Two temperatures (9 and 20 C) and three pH levels (6.5, 7.3, and 8.5) were studied using a vacuum evaporation system with a maximum vacuum of 5 kPa. Tests showed that higher initial pH levels had decreased foaming times. At the end of foaming experiments, the liquid whole egg was evaluated to determine the extent of functional property change during foaming. A decrease in foaming time resulted in a decrease in whip time. The cakes made from the processed liquid whole egg had larger volumes than those from the unprocessed control. Furthermore, the liquid whole egg, which foamed the longest, had higher (P < 0.05) cake volumes. Our current experiments also verified our earlier findings that no product concentration takes place during the foaming process.

Destruction of Escherichia coli O157:H7 and Salmonella typhimurium in Lebanon bologna by interaction of fermentation pH, heating temperature, and time.

Fermented meats have caused food-borne illness due to enterohemorrhagic Escherichia coli. Consumption of Lebanon bologna was epidemiologically associated wit a recent outbreak of salmonellosis. The present study was conducted to determine the effect of pH (after the fermentation step), final heating temperature, and time on destruction of E. coli O157:H7 and Salmonella typhimurium in Lebanon bologna. Raw Lebanon bologna mix was inoculate with either of the pathogens (ca.10(8) CFR/g and fermented for 12 h at 80 degrees F (26.7 degrees C) and then at 100 degrees F (37.8 degrees C) unit the pH reached wither 5.2 or 4.7. The mix was then heated to 110, 115, or 120 degrees F (43.3, 46.1, or 48.9 degrees C). The bologna was sampled at various times, decimally diluted, and plated on either McConkey sorbitol agar or XLD agar to enumerate E. coli O157:H7 and S. typhimurium, respectively. Fermentation alone reduced populations of both pathogens by < 2 log units and heating alone reduced populations of E. coli O157:H7 by < 3 log units. A combination of fermenting to either pH 5.2 or 4.7, followed by heating at 110 degrees F (43.3 degrees C) for 20h, 115 degrees F (46.1 degrees C) for 10 h, or 120 degrees F (48.9 degrees C) for 3 h reduced populations of both pathogens by > 7 log units. Overall S. typhimurium cells were either equally or significantly less resistant (P < 0.01) than cells of E. coli O157:H7. Significantly interactions (P < 0.01) among the three factors for the destruction of E. coli O157:H7 were observed. A process-specific regression equation was developed to predict the destruction of E. coli O157:H7 in Lebanon bologna.

Penetration of Salmonella enteritidis into Eggs Subjected to Rapid Cooling.

Eggs were cooled to 0°C using two different cooling rates, natural convection, and forced convection at an air speed of 30.5 m/min. Upon rapid cooling using forced convection and when brought back to room temperature, eggs were more prone to penetration by Salmonella enteritidis (strain PS8NSR). Eggs cooled using forced convection had 100% penetration by PS8NSR; eggs cooled using natural convection had 91.3% penetration; and uncooled eggs had 48% penetration. Scanning electron microscopy revealed that shells of both cooled and uncooled eggs had microscopic cracks; however, cracks were more numerous and larger in shells of cooled eggs.