Murad A. Al-Holy

Rapid and quantitative detection of the microbial spoilage in chicken meat by diffuse reflectance spectroscopy (600–1100 nm)

Aims:  To evaluate the feasibility of visible and short‐wavelength near‐infrared (SW‐NIR) diffuse reflectance spectroscopy (600–1100 nm) to quantify the microbial loads in chicken meat and to develop a rapid methodology for monitoring the onset of spoilage.

Using Fourier Transform Infrared (FT-IR) Absorbance Spectroscopy and Multivariate Analysis To Study the Effect of Chlorine-Induced Bacterial Injury in Water

The effect of chlorine-induced bacterial injury on spectral features using Fourier transform infrared (FT-IR) absorbance spectroscopy was studied using a mixed bacterial culture of (1:1) ca. 500 CFU/mL each Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 15442 in 0.9% saline. Bacterial cells were treated with 0, 0.3, or 1.0 ppm of initial free chlorine (21 degrees C, 1 h of contact time). Chlorine-injured and dead bacterial cells retained the ATR spectral properties of uninjured or live cells in the region of C-O-C stretching vibrations of polysaccharides, indicative of the cell wall peptidoglycan layer and lipopolysaccharide outer leaflet. This confirms the observations of others that extensive bacterial membrane damage is not a key factor in the inactivation of bacteria by chlorine. The bactericidal effect of chlorine caused changes in the spectral features of bacterial ester functional groups of lipids, structural proteins, and nucleic acids, with apparent denaturation reflected between 1800 and 1300 cm (-1) for injured bacterial cells. Three-dimensional principal component analysis (PCA) showed distinct segregation and clustering of chlorine-treated and untreated cells. Cells exposed to chlorine at 0.3 or 1.0 ppm could be distinguished from the untreated control 73 and 80% of the time, respectively, using soft independent modeling of class analogy (SIMCA) analysis. This study suggests that FT-IR spectroscopy may be applicable for detecting the presence of injured and viable but not culturable (VBNC) waterborne pathogens that are underestimated or not discernible using conventional microbial techniques.

Detection of Sublethal Thermal Injury in Salmonella enterica Serotype Typhimurium and Listeria monocytogenes Using Fourier Transform Infrared (FT-IR) Spectroscopy (4000 to 600 cm−1)

Fourier transform infrared (FT-IR) spectroscopy (4000 to 600 cm(-1)) was utilized to detect sublethally heat-injured microorganisms: Salmonella enterica serotype Typhimurium ATCC 14028, a Gram-negative bacterium, and Listeria monocytogenes ATCC 19113, a Gram-positive bacterium. A range of heat treatments (N= 2) at 60 degrees C were evaluated: 0D (control), 2D, 4D, 6D, and 8D using a D(60 degrees C) (S. enterica serotype Typhimurium ATCC 14028 = 0.30 min, L. monocytogenes ATCC 19113 = 0.43 min). The mechanism of cell injury appeared to be different for Gram-negative and Gram-positive microbes as observed from differences in the 2nd derivative transformations and loadings plot of bacterial spectra following heat treatment. The loadings for PC1 and PC2 confirmed that the amide I and amide II bands were the major contribution to spectral variation, with relatively small contributions from C-H deformations, the antisymmetric P==O stretching modes of the phosphodiester nucleic acid backbone, and the C-O-C stretching modes of polysaccharides. Using soft independent modeling of class analogy (SIMCA), the extent of injury could be predicted correctly at least 83% of the time. Partial least squares (PLS) calibration analysis was constructed using 5 latent variables for predicting the bacterial counts for survivors of the different heat treatments and yielded a high correlation coefficient (R= 0.97 [S. enterica serotype Typhimurium] and 0.98 [L. monocytogenes]) and a standard error of prediction (SEP= 0.51 [S. enterica serotype Typhimurium] and 0.39 log(10) CFU/mL [L. monocytogenes]), indicating that the degree of heat injury could be predicted.

Inactivation of Listeria innocua in Nisin-Treated Salmon (Oncorhynchus keta) and Sturgeon (Acipenser transmontanus) Caviar Heated by Radio Frequency

Recent regulatory concerns about the presence of the pathogen Listeria monocytogenes in ready-to-eat aquatic foods such as caviar has prompted the development of postpackaging pasteurization processes. However, caviar is heat labile, and conventional pasteurization processes affect the texture, color, and flavor of these foods negatively. In this study, chum salmon (Oncorhynchus keta, 2.5% total salt) caviar or ikura and sturgeon (Acipenser transmontanus, 3.5% total salt) caviar were inoculated with three strains of Listeria innocua in stationary phase at a level of more than 10(7) CFU/g. L innocua strains were used because they exhibit an equivalent response to L monocytogenes for many physicochemical processing treatments, including heat treatment. The products were treated by immersion in 500 IU/ml nisin solution and heat processed (an 8-D process without nisin or a 4-D process with 500 IU/ml nisin) in a newly developed radio frequency (RF; 27 MHz) heating method at 60, 63, and 65 degrees C. RF heating along with nisin acted synergistically to inactivate L. innocua cells and total mesophilic microorganisms. In the RF-nisin treatment at 65 degrees C, no surviving L. innocua microbes were recovered in sturgeon caviar or ikura. The come-up times in the RF-heated product were significantly lower compared with the water bath-heated caviar at all treatment temperatures. The visual quality of the caviar products treated by RF with or without nisin was comparable to the untreated control.

Inactivation of Cronobacter spp. (Enterobacter sakazakii) in infant formula using lactic acid, copper sulfate and monolaurin

Aims:  To investigate the effect of lactic acid (LA), copper (II), and monolaurin as natural antimicrobials against Cronobacter in infant formula.

Thermal Inactivation of Listeria innocua in Salmon (Oncorhynchus keta) Caviar Using Conventional Glass and Novel Aluminum Thermal-Death-Time Tubes

Differences in the come-up times and thermal inactivation parameters of Listeria innocua in salmon (Oncorhynchus keta) caviar containing 2.5% salt using conventional thermal-death-time (TDT) glass tubes and a novel aluminum tube were tested and compared. Generally, the come-up times and decimal reduction times (D-values) were shorter and the change in temperature required to change the D-value (z-value) was longer in the aluminum than in the glass tubes. The D-values at 60, 63, and 65 degrees C for the aluminum TDT tubes were 2.97, 0.77, and 0.40 min, respectively, and for the glass TDT tubes, these values were 3.55, 0.84, and 0.41 min. The z-values were 5.7 degrees C in the aluminum and 5.3 degrees C in the glass. Because of the shorter come-up time, the aluminum TDT tubes may provide a more precise measurement of microbial thermal inactivation than the glass TDT tubes, particularly for viscous materials, solid foods, and foods containing particulate matter.

Influence of desiccation on the sensitivity of Cronobacter spp. to lactoferrin or nisin in broth and powdered infant formula

Although outbreaks caused by Cronobacter spp. (Enterobacter sakazakii) are rare, infections by this organism have a case-fatality rate which may reach 80%. Powdered infant milk formula (PIMF) is considered a major source for human infection with Cronobacter spp. The organism has the capability to survive in dry environments for long periods (approximately 2 years). Current interest in the use of natural antimicrobials including lactoferrin (LF) and nisin has developed because of the desire for preservative-free food products. The objective of the present study was to evaluate the antimicrobial activity of bovine LF or nisin against undesiccated and desiccated Cronobacter spp. cells in 0.2% peptone water (PW) and reconstituted PIMF at different temperatures. In 0.2% PW, 2.5 mg/ml LF was able to inactivate 4 log(10) CFU/ml of undesiccated cells of Cronobacter spp. in 4 h at 37 degrees C but at lower temperatures, higher concentrations of LF as well as longer exposure were needed to achieve the same effect as at 37 degrees C. Similarly, the effect of nisin against undesiccated cells of Cronobacter spp. was concentration and temperature dependent in 0.2% PW. It was found that 1500 IU/ml caused a 4 log(10) CFU/ml reduction of undesiccated cells of Cronobacter spp. at 21 degrees C and 37 degrees C. Desiccated Cronobacter spp. cells in 0.2% PW were more sensitive to LF action than were undesiccated cells. A 4 log(10) CFU/ml reduction was obtained with 2.5 mg/ml LF after 1 h at 21 and 37 degrees C or 8 h at 10 degrees C. In contrast, desiccated cells of Cronobacter spp. were more resistant to nisin. Furthermore, neither LF nor nisin had detectable antimicrobial activity against desiccated or undesiccated Cronobacter spp. in reconstituted PIFM. Heating at 55 degrees C for 5 min with nisin in reconstituted PIFM did not enhance the antimicrobial activity of nisin. Unexpectedly, nisin appeared to protect Cronobacter spp. from the damaging effects of heat treatment. The reduced antimicrobial activity of LF and nisin in reconstituted PIMF was potentially explained by the higher concentration of Ca(2+), Mg(2+) and Fe(3+) in the latter.

Monitoring quality loss of pasteurized skim milk using visible and short wavelength near-infrared spectroscopy and multivariate analysis.

Visible and short wavelength near-infrared diffuse reflectance spectroscopy (600 to 1,100 nm) was evaluated as a technique for detecting and monitoring spoilage of pasteurized skim milk at 3 storage temperatures (6, 21, and 37 degrees C) over 3 to 30 h (control, t = 0 h; n = 3). Spectra, total aerobic plate count, and pH were obtained, with a total of 60 spectra acquired per sample. Multivariate statistical procedures, including principal component analysis, soft independent modeling of class analogy, and partial least squares calibration models were developed for predicting the degree of milk spoilage. Principal component analysis showed apparent clustering and segregation of milk samples that were stored at different time intervals. Milk samples that were stored for 30 h or less at different temperatures were noticeably separated from control and distinctly clustered. Soft independent modeling of class analogy analysis could correctly classify 88 to 93% of spectra of incubated samples from control at 30 h. A partial least squares model with 5 latent variables correlating spectral features with bacterial counts and pH yielded a correlation coefficient (R = 0.99 and 0.99) and a standard error of prediction (0.34 log(10) cfu/mL and 0.031 pH unit), respectively. It may be feasible to use short wavelength near-infrared spectroscopy to detect and monitor milk spoilage rapidly and noninvasively by correlating changes in spectral features with the level of bacterial proliferation and milk spoilage.

Destruction of Listeria monocytogenes in sturgeon (Acipenser transmontanus) caviar by a combination of nisin with chemical antimicrobials or moderate heat.

The objective of this study was to investigate the effect of nisin in combination with heat or antimicrobial chemical treatments (such as lactic acid, chlorous acid, and sodium hypochlorite) on the inhibition of Listeria monocytogenes and total mesophiles in sturgeon (Acipenser transmontanus) caviar. The effects of nisin (250, 500, 750, and 1,000 IU/ml), lactic acid (1, 2, and 3%), chlorous acid (134 and 268 ppm), sodium hypochlorite (150 and 300 ppm), and heat at 60 degrees C for 3 min were evaluated for a five-strain mixture of L. monocytogenes and total mesophiles in sturgeon caviar containing 3.5% salt. Selected combinations of these antimicrobial treatments were also tested. Injured and viable L. monocytogenes cells were recovered using an overlay method. Treating caviar with > or =500 IU/ml nisin initially reduced L. monocytogenes by 2 to 2.5 log units. Chlorous acid (268 ppm) reduced L. monocytogenes from 7.7 log units to undetectable (<0.48 log units) after 4 days of storage at 4 degrees C. However, there were no synergistic effects observed for combinations of nisin (500 or 750 IU/ml) plus either lactic acid or chlorous acid. Lactic acid caused a slight reduction (approximately 1 log unit) in the microbial load during a 6-day period at 4 degrees C. Sodium hypochlorite was ineffective at the levels tested. Mild heating (60 degrees C for 3 min) with nisin synergistically reduced viable counts of L. monocytogenes and total mesophiles. No L. monocytogenes cells (<0.48 log units) were recovered from caviar treated with heat and nisin (750 IU/ml) after a storage period of 28 days at 4 degrees C.

Detergent and Sanitizer Stresses Decrease the Thermal Resistance of Enterobacter sakazakii in Infant Milk Formula

This study determined the effect of acid, alkaline, chlorine, and ethanol stresses on the thermal inactivation of Enterobacter sakazakii in infant milk formula. Unstressed or stressed cells were mixed with reconstituted powdered infant milk formula (PIMF) at temperatures between 52 and 58 degrees C for various time periods or mixed with PIMF prior to reconstitution with hot water between 50 and 100 degrees C. D- and z-values were determined using liner regression analysis. In general, detergent and sanitizer stresses decreased the thermal resistance of E. sakazakii in infant milk formula. The results of this study may be of use to regulatory agencies, manufacturers, and infant caregivers to design heating processes to eliminate E. sakazakii.