Enzyme activity and partial characterization of proteases obtained from Bromelia karatas fruit and compared with Bromelia pinguin proteases

Food Science and Biotechnology - The enzymatic activity and partial characterization of proteases from Bromelia karatas fruits were evaluated and compared with Bromelia pinguin proteases. The...     

Combustion of coke deposits in a catalyst pellet

A model of catalyst pellet regeneration is presented that accounts for the separate combustion reactions of the hydrogen and the carbon in the coke. The complete structure of the burn-off time with respect to several system parameters is given. It is shown that there are values of initial coke weight fraction and pellet size that give minimum burn-off time. The model indicates that the combustion of the deposited coke is limited by diffusion at higher temperatures than previously thought, and it predicts relatively high temperature differences between the solid particles and the fluid phase at low levels of conversion for some range of the model parameters.     

XPS Characterization of reduced LaCoO3 perovskite

Three samples of LaCoO₃ were prepared by two different methods and calcined at 800 or 1000 °C. They had BET areas of 1, 12, and 16 m²/g and all of them showed pure perovskite X-ray diffraction patterns with identical unit cell dimensions. In a series of experiments the oxide, having larger surface area, was stepwise reduced in hydrogen at temperatures between 60 and 500 °C. The XPS spectra, taken at room temperature after evacuation at 400 °C at each reduction level, showed that the surface concentration of Co° was very low up to 300 °C but increased sharply between 300 and 350 °C (9–75%). This concentration further increased to 100% after 10 min reduction at 450 °C, but upon heating in hydrogen for an additional 10 min at 500 °C it decreased again to 75%. In another series of experiments the mixed oxide was reoxidized after each reduction. A fresh sample was reduced to 350 and 400 °C by contacting with hydrogen for 1 hr and evacuated at temperatures between 400 and 500 °C. Both high evacuation temperatures and reduction at 400 °C during 1 hr produced a sharp decrease in Co° surface concentration. These results are consistent with the catalytic behavior of this perovskite reported earlier by E. A. Lombardo et al. (4–7). A model is proposed to interpret the reduction of LaCoO₃.     

Fungal pretreatment of wheat straw: Effects on the biodegradability of cell walls,structural polysaccharides,lignin and phenolic acids by rumen microorganisms

Disappearance of cell wall components of untreated straw and straw treated with the ligninolytic white-rot fungi Phanerochaete chrysosporium, Dichomitus squalens and Cyathus stercoreus were determined during the course of rumen digestion of samples in nylon bags. The first fungus degraded hemicelluloses and cellulose non-selectively, adversely affecting the digestion rate of crude cell walls. Dichomitus squalens and C. stercoreus preferentially degraded hemicelluloses and lignin, affording cell wall degradation rates 1.5 times higher than in native straw. Furthermore, the extent of cell wall digestion was also significantly enhanced. Both strains improved the extent of cellulose digestion, whereas the potentially degradable xylan fraction remained unchanged. Polysaccharide digestion rates were influenced in different ways depending on the strain tested: straw degraded by C. stercoreus showed an increase in cellulose digestion rate by 50%, whereas residual arabinose units were slowly degraded. Xylan was degraded 1.8 times faster in straw decayed' by D. squalens, while cellulose digestion remained unchanged. Phanerochaete chrysosporium depressed both xylan and cellulose digestion rates. Fungal-treated lignins were solubilised in the rumen faster than in untreated straw, whereas only treatment by C. stercoreus resulted in higher lignin losses. Esterified phenolic acids were extensively degraded by all three fungi. Residual ferulic and p-coumaric acids accumulated during rumen digestion, although only the former decreased in the original straw.     

Inactivation Kinetics of Geobacillus stearothermophilus Spores in Water Using High-pressure Processing at Elevated Temperatures

ABSTRACT: Establishment of a high-pressure sterilization process requires data on pressure and temperature-dependent inactivation kinetics of target pathogenic, spoilage, or surrogate spore-forming bacteria in the food being tested. The objective of this study was to examine the response of Geobacillus stearothermophilus ATCC10149 spores to various temperature, time, and pressure combination treatments (500 to 700 MPa; 92°C to 111°C, 0.01 to 360 s). The pressure inactivation of spores was characterized at elevated temperatures under isobaric and isothermal conditions during the holding time using a laboratory-scale high-pressure unit. The inactivation kinetics was well described by the log-linear regression model. As expected, the rate of spore inactivation increased with increasing pressure and temperature. Decimal reduction times at constant pressure ( D _T,P values) varied from 29.4 to 108.8 s at 92°C, 17.4 to 76 s at 100°C, and 6.1 to 51.3 s at 111°C within the pressure range of 500 to 700 MPa. The resistance of spores to temperature and pressure was characterized with z_T and z_P values and compared with their resistance to conventional steam heating. The conventional thermal resistance of G. stearothermophilus species did not correlate to the thermal resistance at high pressure. The study provides kinetic data on the effects of pressure and temperature on the inactivation of a heat-resistant bacterial spore species under conditions applicable to the commercial processing of low-acid foods.     

Antibiofilm activity of the essential oil of citronella (Cymbopogon nardus) and its major component,geraniol, on the bacterial biofilms of Staphylococcus aureus

Food Science and Biotechnology - Medicinal plants with antimicrobial action have been investigated for uses against biofilms, among which, Cymbopogon nardus, citronella, stands out as a promising...     

Isolation and partial characterization of Mexican taro (Colocasia esculenta L.) starch

Taro starch was isolated from Mexican variety and its morphological, physicochemical, and molecular characteristics were evaluated. Yield starch (in dry basis) was 81%, and this starch had low AM content (2.5%). Taro starch granules showed a mixture of shapes with sizes between 1 and 5 µm. Taro starch presented an A‐type XRD pattern with a crystallinity level of 38.26%. Solubility and water retention capacity did not change in the temperature range of 50–70°C and thereafter they increased as temperature increased too. Taro starch showed high peak viscosity due to its high AP content. The peak temperature of gelatinization of taro starch was 80.6°C with an enthalpy value of 10.6 J/g, with low retrogradation rate due to its low AM content. Weight‐average molar mass (Mw) and gyration radius (Rz) of taro starch were 1.21 ± 0.8 × 10⁹ g/mol and 424 ± 70 nm, respectively. Taro tuber could be an alternative for starch isolation with functional and physicochemical characteristics for food and non‐food applications.     

Longitudinal Dissemination of Salmonella enterica Clonal Groups through the Slaughter Process of Salmonella-Positive Pig Batches

This study was conducted to assess the dissemination of Salmonella clonal groups in slaughterhouses that received batches of Salmonella -positive pigs and used different routine processing procedures. Eight serial sampling sessions were conducted in three slaughterhouses (A, B, and C). Blood was collected randomly (n = 25) from each batch of pigs and processed for serology. Carcasses (n = 12) were identified and sampled after dehairing, after singeing, after evisceration, and before chilling. A section of cecum also was collected. Salmonella isolates were submitted to pulsed-field gel electrophoresis. The overall seroprevalence of Salmonella was 80.6% (316 of 392 samples), and cecal contents were positive for Salmonella in 23.8% (26 of 109) of the pigs sampled. Carcasses after dehairing had a significantly higher prevalence of Salmonella (P = 0.004) and the highest Salmonella levels (median ～ 0.26 log CFU/300 cm(2)). The singeing step significantly affected the Salmonella status of the carcasses (P = 0.001); however, the efficacy of singeing differed among slaughterhouses. In the prechilling step, 14.7% (16 of 109) of the carcasses were positive for Salmonella. Salmonella pulsotypes found on the prechill carcasses were also found in the lairage, in the cecal contents, and on carcasses after dehairing, suggesting that the main source of contamination was the slaughter process before singeing. Slaughterhouse C was the most likely (odds ration [OR] ～ 6.51) to have pigs carrying Salmonella in the gut, and slaughterhouse B was the most likely (OR ～ 14.66) to have contaminated carcasses at the prechilling step. These findings indicate that the procedures adopted in slaughterhouse B contributed to the spread of Salmonella strains. In contrast, in slaughterhouse C the Salmonella strains carried by the pigs or found in the lairage were not recovered from prechilled carcasses, validating the effectiveness of the slaughterhouse interventions. These results indicate that an effective slaughter process can help decrease the number of Salmonella-positive carcasses in slaughterhouses that receive Salmonella-positive pig batches.