J. Antonio Torres

Clostridium perfringens Spore Germination: Characterization of Germinants and Their Receptors

Clostridium perfringens food poisoning is caused by type A isolates carrying a chromosomal enterotoxin (cpe) gene (C-cpe), while C. perfringens-associated non-food-borne gastrointestinal (GI) diseases are caused by isolates carrying a plasmid-borne cpe gene (P-cpe). C. perfringens spores are thought to be the important infectious cell morphotype, and after inoculation into a suitable host, these spores must germinate and return to active growth to cause GI disease. We have found differences in the germination of spores of C-cpe and P-cpe isolates in that (i) while a mixture of L-asparagine and KCl was a good germinant for spores of C-cpe and P-cpe isolates, KCl and, to a lesser extent, L-asparagine triggered spore germination in C-cpe isolates only; and (ii) L-alanine or L-valine induced significant germination of spores of P-cpe but not C-cpe isolates. Spores of a gerK mutant of a C-cpe isolate in which two of the proteins of a spore nutrient germinant receptor were absent germinated slower than wild-type spores with KCl, did not germinate with L-asparagine, and germinated poorly compared to wild-type spores with the nonnutrient germinants dodecylamine and a 1:1 chelate of Ca2+ and dipicolinic acid. In contrast, spores of a gerAA mutant of a C-cpe isolate that lacked another component of a nutrient germinant receptor germinated at the same rate as that of wild-type spores with high concentrations of KCl, although they germinated slightly slower with a lower KCl concentration, suggesting an auxiliary role for GerAA in C. perfringens spore germination. In sum, this study identified nutrient germinants for spores of both C-cpe and P-cpe isolates of C. perfringens and provided evidence that proteins encoded by the gerK operon are required for both nutrient-induced and non-nutrient-induced spore germination.

Formation and characterization of an insoluble polyelectrolyte complex: chitosan-polyacrylic acid

Chitosan and polyacrylic acid mixtures were prepared in different mole ratios and at different pH values and ionic strengths (0.025–0.300). Complex formation was detected by turbidity measurement and quantified by weighing the freeze dried pellet recovered by centrifugation. No insoluble complex formation at pH=2 was detected. In the 3 to 6 pH range, the maximum complex formation occurred at different mole ratios. Quantitative analysis of the supernatant showed that pH affects the complex composition. Solution ionic strength in the 0.025–0.300 range did not affect complex formation.Supernatant pH measurement showed that in the 3 to 5 pH range, the pH of the mixture decreased as the complex was formed. At pH=6, the opposite behavior was observed. This information was used to propose a mechanism for complex formation which was confirmed by quantitative analysis of the supernatant and IR analysis of the insoluble complex. These studies showed that an electrostatic interaction between COO− and NH3+ groups was involved in complex formation.

Strategy to inactivate Clostridium perfringens spores in meat products.

The current study aimed to develop an inactivation strategy for Clostridium perfringens spores in meat through a combination of spore activation at low pressure (100-200 MPa, 7 min) and elevated temperature (80 degrees C, 10 min); spore germination at high temperatures (55, 60 or 65 degrees C); and inactivation of germinated spores with elevated temperatures (80 and 90 degrees C, 10 and 20 min) and high pressure (586 MPa, at 23 and 73 degrees C, 10 min). Low pressures (100-200 MPa) were insufficient to efficiently activate C. perfringens spores for germination. However, C. perfringens spores were efficiently activated with elevated temperature (80 degrees C, 10 min), and germinated at temperatures lethal for vegetative cells (>or= 55 degrees C) when incubated for 60 min with a mixture of L-asparagine and KCl (AK) in phosphate buffer (pH 7) and in poultry meat. Inactivation of spores (approximately 4 decimal reduction) in meat by elevated temperatures (80-90 degrees C for 20 min) required a long germination period (55 degrees C for 60 min). However, similar inactivation level was reached with shorter germination period (55 degrees C for 15 min) when spore contaminated-meat was treated with pressure-assisted thermal processing (568 MPa, 73 degrees C, 10 min). Therefore, the most efficient strategy to inactivate C. perfringens spores in poultry meat containing 50 mM AK consisted: (i) a primary heat treatment (80 degrees C, 10 min) to pasteurize and denature the meat proteins and to activate C. perfringens spores for germination; (ii) cooling of the product to 55 degrees C in about 20 min and further incubation at 55 degrees C for about 15 min for spore germination; and (iii) inactivation of germinated spores by pressure-assisted thermal processing (586 MPa at 73 degrees C for 10 min). Collectively, this study demonstrates the feasibility of an alternative and novel strategy to inactivate C. perfringens spores in meat products formulated with germinants specific for C. perfringens.

Chitosan-based coagulating agents for treatment of Cheddar cheese whey.

Chitosan‐Polyanion (Chi‐Pol) complexes were used as coagulating agents for treating Cheddar cheese whey. Complexation and coagulation time played a significant role in adsorption, whereas polymer concentration was significant only for chitosan‐alginate complexes. Complexes of chitosan with alginate (ALG), pectin (PEC), and carrageenan (CAR) used at 30 mg complex/L whey showed turbidity reductions of 40−43% and 65−72% after 1 and 39 h, respectively. At 10 mg/L, the percent reduction in turbidity after 1 and 39 h were 35−39% and 61−64%, respectively. No significant differences in turbidity reduction (P > 0.05) were observed when using complexes at different Chi‐Pol monomeric mixing ratios (MR) except for Chi‐Alg at 30 mg/L, wherein reduction at 0.2 was higher than 0.8 MR. Also, UV‐vis spectroscopy suggested the preference of this complex for the absorption of specific whey protein fractions. This study successfully demonstrated the effectiveness of Chi‐Pol complexes in flocculation of suspended solid wastes in cheese whey with over 70% protein recovery.

Mathematical models to evaluate temperature abuse effects during distribution of refrigerated solid foods

Abstract The increasing consumption of refrigerated foods in the USA opens new opportunities for food processors to satisfy consumer demands for minimally processed foods. Previous work has shown the need to reduce the frequency of temperature abuse. The development of a personal computer-based tool to evaluate the consequences of temperature abuse shows that, even when the fraction of the total storage time at an undesirable room temperature is rather small (2–3%), the reduction in shelf-life can be highly significant (20–30%). The effect of package size and heat transfer properties was also significant. These types of evaluations, needed to help reduce product losses, are expensive and time consuming without the help of the tool here presented.

Ultra-high pressure pasteurization of fresh cut pineapple

Ultra-high pressure (200, 270 and 340 MPa), temperature (~4, 21 and 38°C), and time (5, 15, 40 and 60 min) combinations were evaluated as a means to extend the shelf-life of fresh cut pineapple chunks. Cut pineapple obtained from an industrial processor was packed in heat-sealed polyethylene pouches. Triplicate samples were temperature adjusted and treated in an Autoclave Engineers IP2-22-60 isostatic press. Surviving bacteria and total yeast and mold counts were determined using plate count agar (PCA) and acidified potato dextrose agar (PDA), respectively. At the highest pressure (340 MPa) and 15 min, decimal reductions measured by growth on PCA were 3.0 (~4°C), 3.1 (21°C) and >2.5 (38°C). Pressure treated pineapple pieces had PCA counts < 50 colony forming units (CFU)/g. At 270 MPa and 15 min, greater than two decimal reductions were observed only at 38°C. Exposure to pressures of 200 MPa resulted in about one decimal reduction in PCA counts for all temperature and time combinations tested. PDA counts followed a similar behavior for all pressure treatments.

Comparison of static and step-pulsed ultra-high pressure on the microbial stability of fresh cut pineapple

Fresh cut pineapple cubes inoculated with 104–5 CFU g−1Saccharomyces cerevisiae were packed in heat-sealed polyethylene pouches and subjected at ambient temperature to static and step-pulsed ultra-high pressure (UHP) treatments. Static treatments included 100 and 9000 s at 270 MPa and 9000 s at 340 MPa. Step-pulsed pressure treatments included 100, 300 and 600 s at 0–270 MPa using 0·5-s and 10-s pulses. Inoculated treated and untreated samples were held at 4°C for 60 days. Bacteria and yeast counts were determined using plate count agar and yeast extract peptone dextrose agar, respectively. Static treatment at 270 and 340 MPa for 9000 s resulted in <240 CFU g−1 yeast and bacteria counts for up to 60 days. Step-pulsed pressure treatments for 100 s at 0–270 MPa using 0·5-s (200 pulses) and 10-s pulses (10 pulses) were more effective than a 100-s static 270-MPa treatment. Step-pulsed pressure treatments (300 and 600 s) using 0·5-s pulses (600 and 1200 pulses) and 10-s pulses (30 and 60 pulses) were as effective as 9000-s static pressure treatments at 270 and 340 MPa. This storage study confirmed the superiority of step-pulsed over static pressure treatments.

Role of small, acid-soluble spore proteins in the resistance of Clostridium perfringens spores to chemicals

Previous work showed that C. perfringens spores lacking the majority of alpha/beta-type small, acid-soluble spore proteins (SASPs) (termed alpha(-) beta(-) spores) exhibit greatly decreased resistance to moist heat and UV radiation. The current study demonstrated that these alpha(-) beta(-) spores had reduced resistance to hydrogen peroxide, hydrochloric acid, nitrous acid and formaldehyde. These results clearly demonstrate the important role of alpha/beta-type SASPs in the resistance of C. perfringens spores to chemicals.

Mathematical models and logic for the computer control of batch retorts: Conduction-heated foods

Abstract A computer program was developed to implement a mathematical model to control on-line batch retort operations for conduction-heated foods. The model is based on a numeric solution for heat transfer in cylindrical cans. The heat transfer equation was solved using a numeric method with a variable grid. Integrated lethality values are calculated assuming first-order kinetics for microbial inactivation, taking into account the cumulative lethality of the heating and cooling period. The program adjusts process time automatically to compensate for any unexpected variation in retort temperature, and was validated using processes reported in the literature. The computational speed of the numeric method described could be applied to other calculation-intensive simulations.

Benefits and limitations of food processing by high-pressure technologies: effects on functional compounds and abiotic contaminants

The continuing and worldwide growth of pressure processing technologies to pasteurize and sterilize foods justifies the need to study the effects on functional compounds and abiotic contaminants as affected by high-pressure processing (HPP) and pressure-assisted thermal processing (PATP). Substantially more research will be required to determine the complex effects of the food matrix on chemical reactions leading to losses of nutrients and functional components, production of toxic compounds, and to modifications of toxic residues of chemicals used in food production or coming from food contact materials. In PATP treatments, pressure can also increase, decrease or have no effect on the thermal degradation rate of these substances. HPP has no major negative and often beneficial effects on the retention of nutrients and functional components. However, information on PATP effects is very limited and additional research will be required before implementing this promising new technology. El crecimiento mundial de las tecnologías basadas en alta presión hidrostática (APH) y de procesado térmico asistido por presión (PTAP) empleadas para pasterizar y esterilizar alimentos justifica la necesidad de estudiar los efectos que provocan en componentes funcionales y en contaminantes abióticos. Se necesita mucha investigación para conocer los efectos de la presurización y del tipo de alimento sobre las reacciones químicas que provocan pérdida de componentes nutritivos y funcionales y sobre aquellas que forman compuestos tóxicos o modifican residuos tóxicos de sustancias químicas empleadas para producir alimentos o procedentes de materiales en contacto con ellos. En el tratamiento PATP, el aumento de presión puede incrementar, disminuir o no afectar la velocidad de la degradación térmica de componentes del alimento. En general, los tratamientos APH no tienen efectos negativos y suelen ser beneficiosos en cuanto a retención de componentes nutritivos y funcionales. Sin embargo, la información sobre los efectos PATP es muy limitada, requiriéndose investigación adicional para poder implementar de forma segura esta tecnología innovadora.