Amit Pal - Academia.edu (original) (raw)
Papers by Amit Pal
Renewable Energy, 2010
This paper presents the details of development of a biodiesel production test rig based on hydrod... more This paper presents the details of development of a biodiesel production test rig based on hydrodynamic cavitation followed by results of experimental investigation carried out on a four cylinder, direct injection water cooled diesel engine operating on diesel and biodiesel blend of Citrullus colocyntis (Thumba) oil. The experiment covers a wide range of engine rpm. Results show that biodiesel of Thumba oil produced through hydrodynamic cavitation technique can be used as an alternative fuel with better performance and lower emissions compared to diesel. The most significant conclusions are that (i) Biodiesel production through hydrodynamic cavitation technique seems to be a simple, efficient, time saving, ecofriendly and industrially viable process. (ii) 30% biodiesel blend of Thumba oil shows relatively higher brake power, brake thermal efficiency, reduced bsfc and smoke opacity with favourable p-q diagram as compared to diesel.
Fems Microbiology Letters, 2001
In response to heat-stable enterotoxin of Vibrio cholerae non-O1, the initial rise of cytosolic C... more In response to heat-stable enterotoxin of Vibrio cholerae non-O1, the initial rise of cytosolic Ca 2 occurred with activation of IP 3 . Chelation of extracellular Ca 2 with EGTA and suspension of cells in Ca 2 free buffer both demonstrated the involvement of internal stores in the rise of [Ca 2 ]i. Cells pretreated with dantrolene resulted in decrease of [Ca 2 ]i response which suggested that the rise of intracellular level of Ca 2 was mostly due to the mobilization from IP 3 sensitive stores. When the cytosolic Ca 2 was chelated by loading the cells with BAPTA, NAG-ST could not induce Ca 2 entry to the cell as assessed by Mn 2 quenching of fura-2 fluorescence which suggested that calcium influx across the plasma membrane depends upon initial rise of this bivalent cation that maintained the sustained phase of [Ca 2 ]i response. Addition of toxin to the fura-2-loaded cells, preincubated with lanthanum chloride, resulted in reduction of [Ca 2 ]i level with a short duration of irregular sustained phase further suggesting that the influx of Ca 2 across the plasma membrane might be through the calcium channel. ß
Journal of Medical Microbiology, 1993
A collection of 28 strains of Vibrio cholerae non-0 1 isolated during a 3-year period (1989-199 1... more A collection of 28 strains of Vibrio cholerae non-0 1 isolated during a 3-year period (1989-199 1) from hospitalised patients with acute diarrhoea in Calcutta, India, were examined with regard to virulence-associated factors. Of the 28 isolates (each representing a case), 18 were isolated as the sole infecting agent; the remaining 10 were recovered as cocultures from cases infected with V. cholerae 01. Of the strains isolated in this study, 82 YO could be serotyped, with serovars 0 5 (32.1 %), 0 1 1 and 034 (14.3 YO each) predominant. Serovars 0 7 , 014, 034, 039 and 097 were associated exclusively with sole infections. Two strains of V. cholerae non-0 1 produced anti-cholera toxin IgG-absorbable cholera toxin (CT). Both CT-producing V. cholerae non-01 strains hybridised with the DNA probe specific for the zonula occludens toxin (ZOT) but none of the remaining 26 strains hybridised with the ZOT probe. The majority of the strains were cytotoxic for CHO, HeLa and Vero cells, with end-point titres of 4-512. Fewer strains produced a cytotonic effect, with end-point titres of 2-16. Of the 28 strains of V. cholerae non-01 examined, 7 5 % , 75Y0, 25% and 14.3% produced haemolysin that was active against erythrocytes of rabbit, sheep (Eltor haemolysin), chicken and man, respectively. Strains that produced a haemolysin active against both rabbit and sheep erythrocytes were dominant (35.7%). Ten (35.7%) of the 28 strains examined showed cell-associated haemagglutinating activity on human blood. Of the 10 strains, nine were isolated as sole pathogen and only one strain was associated with mixed infection. Three distinct patterns of inhibition by sugars were detected ; inhibition of haemagglutination by mannose 1 YO but not by fucose and galactose 1 YO was the dominant haemagglutination inhibition pattern. Six different virulence phenotypes were encountered among strains of V. cholerae non-01 in this study. The prominent phenotype, which was associated commonly with isolates from patients solely infected by V. cholerae non-0 1, was exhibited by strains that produced the Eltor haemolysin, a cytotoxin and a cell-associated haemagglutinin. The production 9f cell-associated haemagglutinin appeared to be the only distinctive phenotype that could distinguish between isolates from patients solely infected with V. cholerae non-0 1 and those associated with mixed infections. From this study, it is apparent that the virulence of V. cholerae non-01 is multifactorial and mediated by several traits functioning in an integrated fashion. The clinical significance of V. cholerae non-01 must be assessed in its totality; the presence of a single factor should not be construed as the cause of en teropa t hogenici t y .
We investigated the prevalence of Shiga toxin-producing Escherichia coli (STEC) in hospitalized d... more We investigated the prevalence of Shiga toxin-producing Escherichia coli (STEC) in hospitalized diarrhea patients in Calcutta, India, as well as in healthy domestic cattle and raw beef samples collected from the city's abattoir. Multiplex polymerase chain reaction using primers specific for stx1 and stx2 detected STEC in 18% of cow stool samples, 50% of raw beef samples, and 1.4% and 0.6% of bloody and watery stool samples, respectively, from hospitalized diarrhea patients. Various virulence genes in the STEC isolates indicated that stx1 allele predominated. Plasmid-borne markers, namely, hlyA, katP, espP, and etpD, were also identified. Bead enzyme-linked immunosorbent assay and Vero cell assay were performed to detect and evaluate the cytotoxic effect of the Shiga toxins produced by the strains. STEC is not an important cause of diarrhea in India; however, its presence in domestic cattle and beef samples suggests that this enteropathogen may become a major public health problem in the future.
Microbial Pathogenesis, 1995
and ¥. Takeda. Distribution of genes encoding cholera toxin, zonula occludens toxin, accessory ch... more and ¥. Takeda. Distribution of genes encoding cholera toxin, zonula occludens toxin, accessory cholera toxin, and El Tor hemolysin in Vibrio cholerae. Microbial Pathogenesis 1995; 18, 231-
Food Microbiology, 2008
This study compared the performance of four primary mathematical models to study the growth kinet... more This study compared the performance of four primary mathematical models to study the growth kinetics of Listeria monocytogenes ribotypes grown at low temperature so as to identify the best predictive model. The parameters of the best-fitting model were used to select the fastest growing strains with the shortest lag time and greatest growth rate. Nineteen food, human and animal L. monocytogenes isolates with distinct ribotype were grown at 4, 8, and 12 degrees C in tryptic soy broth and slurries prepared from cooked uncured sliced turkey breasts (with or without potassium lactate and sodium diacetate, PL/SD) and cooked cured frankfurters (with or without PL/SD). Separate regressions were performed on semi-logarithm growth curves to fit linear (based on Monod) and non-linear (Gompertz, Baranyi-Roberts, and Logistic) equations and performance of each model was evaluated using an F-test. No significant differences were found in the performance of linear and non-linear models, but the Baranyi model had the best fit for most growth curves. The maximum growth rate (MGR) of Listeria strains increased with the temperature. Similarly MGR was found significantly greater when no antimicrobials were present in the formulation of turkey or frankfurter products. The variability in lag times and MGRs in all media as determined by the Baranyi model was not consistent among strains. No single strain consistently had the fastest growth (shortest lag time, fastest MGR, or shortest time to increase 100-fold), but nine strains were identified as fastest growing strains under most growth conditions. The lack of association between serotype and fastest strain was also observed in the slurry media study. The fastest growing strains resulting from this study can be recommended for future use in L. monocytogenes challenge studies in delicatessen meat and poultry food matrices, so as to develop conservative pathogen growth predictions.
International Journal of Food Microbiology, 2008
The growth variability of three Listeria monocytogenes ribotypes in ready-to-eat (RTE) sliced unc... more The growth variability of three Listeria monocytogenes ribotypes in ready-to-eat (RTE) sliced uncured turkey breast and cured ham was studied under storage conditions that RTE foods are likely to encounter. Three product treatments studied were: (1) a control; (2) a formulation subjected to high pressure processing to reduce initial microbial load (HPP); (3) a formulation containing 2.0% potassium lactate and 0.2% sodium diacetate (PL/SD). After separate inoculation with individual L. monocytogenes ribotypes and packaging each treatment under air and vacuum, the packages were stored at 4, 8, or 12°C and the counts of L. monocytogenes and psychrotrophic bacteria (PPC) were determined for several weeks. The Baranyi model was used to estimate lag times and growth rates. Significant effect of strain difference was noted in both sliced products (P b 0.05). In the absence of antimicrobials (HPP and control), the growth rate (GR) of L. monocytogenes strains increment from 4 to 8°C and from 8 to 12°C was approximately 10 and 2 fold, respectively. The addition of PL/SD was effective in restricting the growth of L. monocytogenes and PPC at 4°C, but at 8 and 12°C significant growth was observed (more than 100-fold increase) (P b 0.05). In PL/SD samples, vacuum packaging slowed down the onset and the rate of growth of L. monocytogenes at 12°C in sliced ham and at 8 and 12°C in sliced turkey breast. Generally, the time to increase by 2-logs was greater in control samples than as observed in HPP-treated samples. When antimicrobials were present, the current results showed that L. monocytogenes was able to grow more than 100-fold within the typical quality-based shelf life of 60 to 90 days at 8 and 12°C. The findings of this study should be useful in setting the duration of a safetybased shelf life for RTE sliced meat and poultry foods.
International Journal of Food Microbiology, 2007
In the current study, temperature dependent growth of Listeria monocytogenes strain H7776, with a... more In the current study, temperature dependent growth of Listeria monocytogenes strain H7776, with an initial inoculum level of approximately 0.1 CFU/mL or g, was modeled based on "time to detect" (TTD) using the Arrhenius equation. The activation energies (E a ) obtained from specific growth rate and lag phase duration in tryptic soy broth (TSB) and frankfurters were compared. At 4°C, the TTD for L. monocytogenes was 217 h in TSB and 48 h in portions of frankfurters. The TTD decreased as temperature increased from 4 to 36°C in both culture media and frankfurters, and this relationship was modeled using the Arrhenius equation. Based on this model, the E a values for the TTD in TSB and frankfurters averaged 22.7 and 18.7 kcal/mol, respectively, and were not significantly different ( p b 0.05). Linear regression was performed on the exponential part of the growth curve to evaluate specific growth rate constants at each temperature using the Monod model. The E a values were also calculated based on the specific growth rate and the lag phase of L. monocytogenes in TSB and frankfurters incubated in the same range of temperatures. The average E a values for the specific growth rates and the lag phase durations in TSB cultures were 19 and 21 kcal/mol, respectively. In frankfurters, the average E a values were slightly greater for both specific growth rate and lag phase duration (29 and 35 kcal/mol, respectively), but these values were not significantly different from the E a calculated for the TTD in each medium. These results indicate that the TTD concept can be used to develop and validate safety-based shelf life models.
Renewable Energy, 2010
This paper presents the details of development of a biodiesel production test rig based on hydrod... more This paper presents the details of development of a biodiesel production test rig based on hydrodynamic cavitation followed by results of experimental investigation carried out on a four cylinder, direct injection water cooled diesel engine operating on diesel and biodiesel blend of Citrullus colocyntis (Thumba) oil. The experiment covers a wide range of engine rpm. Results show that biodiesel of Thumba oil produced through hydrodynamic cavitation technique can be used as an alternative fuel with better performance and lower emissions compared to diesel. The most significant conclusions are that (i) Biodiesel production through hydrodynamic cavitation technique seems to be a simple, efficient, time saving, ecofriendly and industrially viable process. (ii) 30% biodiesel blend of Thumba oil shows relatively higher brake power, brake thermal efficiency, reduced bsfc and smoke opacity with favourable p-q diagram as compared to diesel.
Fems Microbiology Letters, 2001
In response to heat-stable enterotoxin of Vibrio cholerae non-O1, the initial rise of cytosolic C... more In response to heat-stable enterotoxin of Vibrio cholerae non-O1, the initial rise of cytosolic Ca 2 occurred with activation of IP 3 . Chelation of extracellular Ca 2 with EGTA and suspension of cells in Ca 2 free buffer both demonstrated the involvement of internal stores in the rise of [Ca 2 ]i. Cells pretreated with dantrolene resulted in decrease of [Ca 2 ]i response which suggested that the rise of intracellular level of Ca 2 was mostly due to the mobilization from IP 3 sensitive stores. When the cytosolic Ca 2 was chelated by loading the cells with BAPTA, NAG-ST could not induce Ca 2 entry to the cell as assessed by Mn 2 quenching of fura-2 fluorescence which suggested that calcium influx across the plasma membrane depends upon initial rise of this bivalent cation that maintained the sustained phase of [Ca 2 ]i response. Addition of toxin to the fura-2-loaded cells, preincubated with lanthanum chloride, resulted in reduction of [Ca 2 ]i level with a short duration of irregular sustained phase further suggesting that the influx of Ca 2 across the plasma membrane might be through the calcium channel. ß
Journal of Medical Microbiology, 1993
A collection of 28 strains of Vibrio cholerae non-0 1 isolated during a 3-year period (1989-199 1... more A collection of 28 strains of Vibrio cholerae non-0 1 isolated during a 3-year period (1989-199 1) from hospitalised patients with acute diarrhoea in Calcutta, India, were examined with regard to virulence-associated factors. Of the 28 isolates (each representing a case), 18 were isolated as the sole infecting agent; the remaining 10 were recovered as cocultures from cases infected with V. cholerae 01. Of the strains isolated in this study, 82 YO could be serotyped, with serovars 0 5 (32.1 %), 0 1 1 and 034 (14.3 YO each) predominant. Serovars 0 7 , 014, 034, 039 and 097 were associated exclusively with sole infections. Two strains of V. cholerae non-0 1 produced anti-cholera toxin IgG-absorbable cholera toxin (CT). Both CT-producing V. cholerae non-01 strains hybridised with the DNA probe specific for the zonula occludens toxin (ZOT) but none of the remaining 26 strains hybridised with the ZOT probe. The majority of the strains were cytotoxic for CHO, HeLa and Vero cells, with end-point titres of 4-512. Fewer strains produced a cytotonic effect, with end-point titres of 2-16. Of the 28 strains of V. cholerae non-01 examined, 7 5 % , 75Y0, 25% and 14.3% produced haemolysin that was active against erythrocytes of rabbit, sheep (Eltor haemolysin), chicken and man, respectively. Strains that produced a haemolysin active against both rabbit and sheep erythrocytes were dominant (35.7%). Ten (35.7%) of the 28 strains examined showed cell-associated haemagglutinating activity on human blood. Of the 10 strains, nine were isolated as sole pathogen and only one strain was associated with mixed infection. Three distinct patterns of inhibition by sugars were detected ; inhibition of haemagglutination by mannose 1 YO but not by fucose and galactose 1 YO was the dominant haemagglutination inhibition pattern. Six different virulence phenotypes were encountered among strains of V. cholerae non-01 in this study. The prominent phenotype, which was associated commonly with isolates from patients solely infected by V. cholerae non-0 1, was exhibited by strains that produced the Eltor haemolysin, a cytotoxin and a cell-associated haemagglutinin. The production 9f cell-associated haemagglutinin appeared to be the only distinctive phenotype that could distinguish between isolates from patients solely infected with V. cholerae non-0 1 and those associated with mixed infections. From this study, it is apparent that the virulence of V. cholerae non-01 is multifactorial and mediated by several traits functioning in an integrated fashion. The clinical significance of V. cholerae non-01 must be assessed in its totality; the presence of a single factor should not be construed as the cause of en teropa t hogenici t y .
We investigated the prevalence of Shiga toxin-producing Escherichia coli (STEC) in hospitalized d... more We investigated the prevalence of Shiga toxin-producing Escherichia coli (STEC) in hospitalized diarrhea patients in Calcutta, India, as well as in healthy domestic cattle and raw beef samples collected from the city's abattoir. Multiplex polymerase chain reaction using primers specific for stx1 and stx2 detected STEC in 18% of cow stool samples, 50% of raw beef samples, and 1.4% and 0.6% of bloody and watery stool samples, respectively, from hospitalized diarrhea patients. Various virulence genes in the STEC isolates indicated that stx1 allele predominated. Plasmid-borne markers, namely, hlyA, katP, espP, and etpD, were also identified. Bead enzyme-linked immunosorbent assay and Vero cell assay were performed to detect and evaluate the cytotoxic effect of the Shiga toxins produced by the strains. STEC is not an important cause of diarrhea in India; however, its presence in domestic cattle and beef samples suggests that this enteropathogen may become a major public health problem in the future.
Microbial Pathogenesis, 1995
and ¥. Takeda. Distribution of genes encoding cholera toxin, zonula occludens toxin, accessory ch... more and ¥. Takeda. Distribution of genes encoding cholera toxin, zonula occludens toxin, accessory cholera toxin, and El Tor hemolysin in Vibrio cholerae. Microbial Pathogenesis 1995; 18, 231-
Food Microbiology, 2008
This study compared the performance of four primary mathematical models to study the growth kinet... more This study compared the performance of four primary mathematical models to study the growth kinetics of Listeria monocytogenes ribotypes grown at low temperature so as to identify the best predictive model. The parameters of the best-fitting model were used to select the fastest growing strains with the shortest lag time and greatest growth rate. Nineteen food, human and animal L. monocytogenes isolates with distinct ribotype were grown at 4, 8, and 12 degrees C in tryptic soy broth and slurries prepared from cooked uncured sliced turkey breasts (with or without potassium lactate and sodium diacetate, PL/SD) and cooked cured frankfurters (with or without PL/SD). Separate regressions were performed on semi-logarithm growth curves to fit linear (based on Monod) and non-linear (Gompertz, Baranyi-Roberts, and Logistic) equations and performance of each model was evaluated using an F-test. No significant differences were found in the performance of linear and non-linear models, but the Baranyi model had the best fit for most growth curves. The maximum growth rate (MGR) of Listeria strains increased with the temperature. Similarly MGR was found significantly greater when no antimicrobials were present in the formulation of turkey or frankfurter products. The variability in lag times and MGRs in all media as determined by the Baranyi model was not consistent among strains. No single strain consistently had the fastest growth (shortest lag time, fastest MGR, or shortest time to increase 100-fold), but nine strains were identified as fastest growing strains under most growth conditions. The lack of association between serotype and fastest strain was also observed in the slurry media study. The fastest growing strains resulting from this study can be recommended for future use in L. monocytogenes challenge studies in delicatessen meat and poultry food matrices, so as to develop conservative pathogen growth predictions.
International Journal of Food Microbiology, 2008
The growth variability of three Listeria monocytogenes ribotypes in ready-to-eat (RTE) sliced unc... more The growth variability of three Listeria monocytogenes ribotypes in ready-to-eat (RTE) sliced uncured turkey breast and cured ham was studied under storage conditions that RTE foods are likely to encounter. Three product treatments studied were: (1) a control; (2) a formulation subjected to high pressure processing to reduce initial microbial load (HPP); (3) a formulation containing 2.0% potassium lactate and 0.2% sodium diacetate (PL/SD). After separate inoculation with individual L. monocytogenes ribotypes and packaging each treatment under air and vacuum, the packages were stored at 4, 8, or 12°C and the counts of L. monocytogenes and psychrotrophic bacteria (PPC) were determined for several weeks. The Baranyi model was used to estimate lag times and growth rates. Significant effect of strain difference was noted in both sliced products (P b 0.05). In the absence of antimicrobials (HPP and control), the growth rate (GR) of L. monocytogenes strains increment from 4 to 8°C and from 8 to 12°C was approximately 10 and 2 fold, respectively. The addition of PL/SD was effective in restricting the growth of L. monocytogenes and PPC at 4°C, but at 8 and 12°C significant growth was observed (more than 100-fold increase) (P b 0.05). In PL/SD samples, vacuum packaging slowed down the onset and the rate of growth of L. monocytogenes at 12°C in sliced ham and at 8 and 12°C in sliced turkey breast. Generally, the time to increase by 2-logs was greater in control samples than as observed in HPP-treated samples. When antimicrobials were present, the current results showed that L. monocytogenes was able to grow more than 100-fold within the typical quality-based shelf life of 60 to 90 days at 8 and 12°C. The findings of this study should be useful in setting the duration of a safetybased shelf life for RTE sliced meat and poultry foods.
International Journal of Food Microbiology, 2007
In the current study, temperature dependent growth of Listeria monocytogenes strain H7776, with a... more In the current study, temperature dependent growth of Listeria monocytogenes strain H7776, with an initial inoculum level of approximately 0.1 CFU/mL or g, was modeled based on "time to detect" (TTD) using the Arrhenius equation. The activation energies (E a ) obtained from specific growth rate and lag phase duration in tryptic soy broth (TSB) and frankfurters were compared. At 4°C, the TTD for L. monocytogenes was 217 h in TSB and 48 h in portions of frankfurters. The TTD decreased as temperature increased from 4 to 36°C in both culture media and frankfurters, and this relationship was modeled using the Arrhenius equation. Based on this model, the E a values for the TTD in TSB and frankfurters averaged 22.7 and 18.7 kcal/mol, respectively, and were not significantly different ( p b 0.05). Linear regression was performed on the exponential part of the growth curve to evaluate specific growth rate constants at each temperature using the Monod model. The E a values were also calculated based on the specific growth rate and the lag phase of L. monocytogenes in TSB and frankfurters incubated in the same range of temperatures. The average E a values for the specific growth rates and the lag phase durations in TSB cultures were 19 and 21 kcal/mol, respectively. In frankfurters, the average E a values were slightly greater for both specific growth rate and lag phase duration (29 and 35 kcal/mol, respectively), but these values were not significantly different from the E a calculated for the TTD in each medium. These results indicate that the TTD concept can be used to develop and validate safety-based shelf life models.