Alicyclobacillus acidoterrestris spore inactivation by high pressure combined with mild heat: Modeling the effects of temperature and soluble solids

High pressure processing (HPP) comprises the application of pressures between 100 and 1000 MPa to foods for microbial inactivation and food preservation. HPP has been commercially applied to pasteurize fruit juices with the advantage of retaining its bioactive constituents and original organoleptic properties. Alicyclobacillus acidoterrestris has been suggested as a reference in the design of pasteurization for high-acid fruit products, due to spore resistance and spoilage incidents in fruit juices. In this study, A. acidoterrestris spore inactivation by 600 MPa combined with mild heat (35–65 °C) in malt extract broth adjusted to 10, 20 and 30 °Brix was carried out and the inactivation was modeled.The soluble solids increased the resistance of the spores to 600 MPa-thermal process, while the temperature decreased its resistance. Although the nonlinear Weibull model gave better fittings, the first-order kinetic parameters were also determined. For example for 600 MPa at 55 °C D_10°Brix = 4.2 min, D_20°Brix = 7.6 min, D_30°Brix = 13.7 min, and z_T-values were 20–21 °C. The z-values for the effect of soluble solids on D_T-values were 39–40 °Brix for 45 and 55 °C 600 MPa HPP. The results obtained with broth were validated with fruit juices and concentrates. The combination of HPP with heat was an effective alternative to conventional thermal processing for the inactivation of A. acidoterrestris spores in juices up to 30 °Brix, allowing the use of less 30–40 °C of temperature for the same microbial inactivation, which potentially results in more nutritious, fresher and tastier juices/concentrates.     

The effect of polyesterurethane belt surface roughness on Listeria monocytogenes biofilm formation and its cleaning efficiency

Contamination of surfaces in direct contact with food in the processing line is the major cause of finished product cross-contamination, especially conveyor belt surfaces that transfer food products. Polyesterurethane (PSU) is one of the materials widely used in conveyor belt systems; therefore, the objective of this study was to examine the effect of PSU conveyor belt surface roughness on the ability of biofilm formation by two strains of Listeria monocytogenes, i.e. ATCC19114 and ATCC51782. Additionally, the efficiency of a cleaning and sanitizing procedure adopted by a chicken meat plant in Thailand in eliminating biofilm formation on belt surfaces was assessed. The roughness values (Ra) were 0.05 ± 0.00 μm and 1.44 ± 0.01 μm for new (unused) and old conveyor belts (in use for 5 years), respectively. It was found that at 30 °C, both strains of L. monocytogenes formed robust biofilms regardless of differences in surface roughness. Conversely, at 15 °C, the ability of L. monocytogenes to form biofilms decreased with the lower Ra value. Under a simulated processing environment, cleaning and sanitizing reduced L. monocytogenes biofilms from both old and new conveyor belt surfaces to certain levels; however, a total reduction could not be achieved. In addition, more highly concentrated cleaning and sanitizing agents resulted in greater reduction. Results from this study clearly illustrate that surface roughness of material is also an important factor which may hinder effective cleaning and sanitizing. Therefore, the roughness value may be used as an indicator for evaluating the life of conveyor belts being used in the food industry.     

Screening and identification of a Bacillus amyloliquefaciens strain for aqueous enzymatic extraction of medium-chain triglycerides

A strain with a high yield of neutral proteinase and low yield of lipase, resistance to medium chain fatty acid triglycerides is the key to increasing yield and quality of Cinnamomum camphora seed kernel oil (CCSKO) with aqueous enzymatic extraction technology. A bacterial strain, NCU116 isolated from the waste residue produced in CCSKO production through primary screening with plate and secondary screening with shake-flask fermentation. It was found to be suitable for the extraction of CCSKO or other medium-chain triglycerides by using the extraction technology. Its activity of neutral proteinase was 4536.5 U/mL, and only 0.088 U/mL for lipase production. The strain was identified as Bacillus amyloliquefaciens by morphological, physiological, biochemical and 16S rDNA molecular identification. The extracellular enzymes produced by NCU116 included neutral proteinase, pectinase, glucoamylase, cellulase, amylase and lipase. The neutral proteinase had the maximum activity at 50 °C, but was unstable. Its optimum temperature and pH value were approximately 40 °C and 7.0 respectively. Mn²⁺ was an activator of neutral proteinase. The glucoamylase had the maximum activity at 45 °C, and was activated by Ca²⁺, Zn²⁺, Fe³⁺ and Mn²⁺. Its optimum temperatures and pH value were 45–50 °C and 6.0 respectively. The pectinase had the maximum activity at 40 °C, and was activated by Cu²⁺, Fe²⁺, Mn²⁺ and Ca²⁺. Its optimum temperatures and pH value were 35–40 °C and 7.0 respectively. The cellulase had the maximum activity at 35 °C, and was activated by Ca²⁺ and Mn²⁺. Its optimum temperatures and pH value were 30–40 °C and 7.0 respectively.     

Determination of thermal inactivation kinetics of Listeria monocytogenes in chicken meats by isothermal and dynamic methods

The objective of this research is to determine the thermal inactivation kinetics of Listeria monocytogenes in chicken breast meat under both isothermal and dynamic conditions. A four-strain cocktail of L. monocytogenes was inoculated to chicken breast meat. Isothermal studies were performed by submerging samples under hot water maintained at constant temperatures ranging from 54 to 66 °C. The D values at each temperature were determined and used to calculate the z value, using log(D) = log(D₀) − T/z. Dynamic studies were conducted by submerging samples in a water bath with its temperature programmed to increase linearly from 30 to 65 °C at 1.25 °C/min or 1.73 °C/min. A method was developed to determine the kinetic parameters from linear heating temperature profiles.The thermal inactivation of L. monocytogenes in chicken breast meat followed the first-order kinetics. The z value determined from the isothermal studies was 4.95 °C, which is very close to the values reported in the literature. The dynamic method can also be used to determine the thermal inactivation kinetics of L. monocytogenes. The average z value (4.10 °C) determined by the dynamic method was slightly lower than that determined by the isothermal method. However, the parameters (D₀ and z) determined from both isothermal and dynamic methods can be used to estimate the survival of L. monocytogenes exposed to linear heating temperature profiles, with statistically equal accuracies.The dynamic method explored in this study can be used to determine the D₀ and z values of microorganisms that exhibit first-order kinetics and are exposed to linear heating temperature profiles. Compared to the isothermal method, the dynamic method requires few data points and is equally accurate.     

Effect of temperature on pathogenic and non-pathogenic Vibrio parahaemolyticus biofilm formation

Biofilm formation is crucial for the environmental survival and transmission of Vibrio parahaemolyticus, an important food-borne pathogen in seafood. The biofilm developmental process of pathogenic (n = 22) and non-pathogenic (n = 17) V. parahaemolyticus strains on polystyrene microtiter plates under 15 °C, 25 °C and 37 °C was investigated using crystal violet staining, and validated by confocal laser scanning microscopy. The results indicated that biofilm developmental process at 15 °C and 25 °C were divergent, biofilm formation increased continuously at 15 °C, while at 25 °C biofilm formation increased gradually and peaked at 12 h. Also the biofilm formation was dramatically elevated at 25 °C in comparison with that at 15 °C and 37 °C. Additionally, pathogenic strains, on average, formed more biofilm than non-pathogenic strains at all temperatures measured. Moreover, extensive strain variability was observed during biofilm formation and indexed using the coefficient of variation (CV). This index increased with increasing temperature and this index, at all temperatures, peaked after 12 h. The results of this study provide insight into the developmental process of biofilm, which allow us to further optimize strategies to control V. parahaemolyticus biofilm in food industry.     

Larval migration of the zoonotic parasite Anisakis pegreffii (Nematoda: Anisakidae) in European anchovy,Engraulis encrasicolus: Implications to seafood safety

Anisakid nematodes belonging to the species Anisakis pegreffii are distributed in a wide variety of fishes from the Mediterranean Sea and they are known to cause the human zoonosis anisakiasis. The present study investigated, for the first time, the response of A. pegreffii larvae (identified to species level by allozymes and mtDNA cox2 sequence analysis) to the storage temperature of European anchovies, Engraulis encrasicolus. The larval motility of A. pegreffii was studied in 1300 fish specimens, captured from a highly infested area (FAO 37.2.1, 43°8′N, 14°16′E), maintained under different temperatures (2 °C, 5 °C, 7 °C), and examined at different time intervals (immediately after fishing, 24 h, 48 h and 72 h). Parasitological analysis was carried out with the UV-press method. The results showed that the increase of infection values with A. pegreffii in the fillets of anchovies was statistically positively related to the increase of the temperature (at 5 °C and 7 °C) and time of storage (after 24 h, 48 h, and 72 h). Accordingly, a significant statistical correlation between the increasing of the worm burden in the fillets and a decreasing of A. pegreffii in the viscera was observed. In contrast, those fish constantly maintained at 2 °C showed no statistically significant variation in infection either in the viscera or the fillets, after 24, 48 and 72 h. In the same batches of anchovies, larvae of the non-zoonotic nematode parasite Hysterothylacium aduncum (identified to the species level by ITS rDNA sequences analysis) were found, but they were never observed infecting the musculature of the anchovies. Our results suggest that temperature plays an important role in the post-mortem motility of A. pegreffii larvae in anchovies. In addition, the presence of A. pegreffii in the fillets inspected immediately after their capture indicates that intra-vitam migration may also occur. As a consequence, the importance of the adoption of rules to prevent human anisakiasis, as the deep freezing to −20 °C for 24 h, was underlined.     

A mathematical model for predicting growth/no-growth of psychrotrophic C. botulinum in meat products with five variables

The objective of this study was to develop a mathematical model for predicting growth/no-growth of psychrotrophic Clostridium botulinum in pasteurised meat products packed in modified atmosphere for combinations of storage temperature, pH, NaCl, added sodium nitrite and sodium lactate.Data for developing and training the artificial neural network (ANN) were generated in meat products. A total of 249 growth experiments were carried out in three different meat products with different combinations of storage temperature, pH, NaCl, sodium nitrite and sodium lactate. The meat batter was inoculated with approx. 10⁴ spores/g using a 4-strain cocktail of gas-producing C. botulinum. The meat products were sliced, packed in modified atmosphere (30% CO₂/70% N₂) and stored at 4 °C, 8 °C and 12 °C, respectively, for up to 8 weeks. The enumeration of C. botulinum was performed when the volume of the package had increased by 9% or more, or at the end of the storage period.Based on 10–20 replicates for each combination, the “frequency of growth” was calculated. An ANN with 5 input neurons, 3 hidden and a single output neuron was trained using the 5 hurdle values as inputs and the observed “frequency of growth” as target value.The inputs for the final model are the five variables: temperature, pH, added sodium nitrite, NaCl and sodium lactate within the ranges 4–12 °C, 5.4–6.4, 0–150 ppm, 1.2–2.4% and 0–3% respectively. As reference a logistic regression method was also applied and subsequently compared to the full neural network model. Based on RMSEC value of 0.104 and 0.144 for ANN and the logistic regression model respectively, the ANN was preferred. On a separate set of test data (n = 60) the ANN model was validated by comparing the predicted “probability of growth” with the observed growth. A bias of 0.0166 was obtained, indicative of a model that is slightly fail-safe.     

Inactivation of Bacillus subtilis spores by pulsed electric fields (PEF) in combination with thermal energy – I. Influence of process- and product parameters

In addition to inactivation of vegetative microorganisms, PEF can be used to inactivate bacterial endospores when combined with thermal energy. In the first part of this study, the impact of the product parameters pH value (4 and 7), sugar level (5 and 10%) and conductivity (4 and 15 mS/cm) as well as the process parameters specific energy (up to 350 kJ/kg), electric field strength (6–11 kV/cm) and inlet temperature (56, 70 and 80 °C) on the inactivation of Bacillus subtilis spores were analyzed.The results of spore inactivation by PEF at different inlet temperatures indicated less energy requirements for sufficient inactivation at higher inlet temperatures. Comparing the inactivation at different pH values, the inactivation at acid pH value required less energy than at neutral pH value. A 1.6 log reduction using 167 kJ/kg was detected in Ringer solution at pH 4 compared to 0.6 log in neutral medium at an energy of 165 kJ/kg (inlet temperature of 80 °C and 9 kV/cm as electric field strength). Under the same process conditions (9 kV/cm and 80 °C inlet temperature), the addition of 10% sugar permitted to reduce the energy from 178 to 146 kJ/kg, require to reach a 3 log cycles inactivation of B. subtilis spores. The results showed a successful inactivation of B. subtilis spores by PEF in combination with thermal energy and represent therefore a promising process for spore inactivation with reduced heat load.     

Bacteriological quality of bottled natural mineral waters commercialized in Hungary

The purpose of the present study was to examine the bacteriological quality of bottled natural mineral waters sold in Hungary because, in recent years, there has been a tremendous increase in consumer demand for these products in the country. In total, 492 samples of domestic and imported brands of carbonated and non-carbonated mineral waters (246 samples each) were purchased from retail outlets, and were then screened for the presence of the following indicator and potentially pathogenic bacteria: spore-forming sulfite-reducing anaerobes (clostridia), total coliforms, Escherichia coli, Enterococcus spp., and Pseudomonas aeruginosa. Heterotrophic plate counts (HPC) were also determined by incubation at 37 °C for 24 h and at 22 °C for 72 h. The data generated were compared to the reference criteria set by Directive 2009/54/EC of the European Parliament and the Council of the European Union on the exploitation and marketing of natural mineral waters. The results showed that 5.3% and 10.2% of the carbonated and non-carbonated mineral water samples tested, respectively, were positive for at least one of the specific indicator or potentially pathogenic bacteria. Overall, a total of 38 sample units (7.7%) failed to comply with the standards set by Directive 2009/54/EC. None of the samples were judged non-compliant with current regulations on the basis of the presence of HPC bacteria at levels reaching or exceeding the acceptability limit (i.e., 100 CFU/ml at 22 °C or 20 CFU/ml at 37 °C) because the analyses were not carried out within 12 h after bottling, as required by Directive 2009/54/EC. The findings of this study highlight the need for a more stringent self-control by some producers of mineral water. In addition, a more systematic surveillance by the official authorities of food control is also necessary.     

Effect of packaging material headspace,oxygen and light transmission,temperature and storage time on quality characteristics of extra virgin olive oil

The effect of packaging parameters (transmission to light and oxygen, headspace volume) and storage temperature on quality characteristics of extra virgin olive oil (EVOO) was studied as a function of storage time (0–12 months). Packaging materials tested included clear glass, clear polyethylene terephthalate (PET), clear PET + UV blocker, clear PET covered with aluminum foil and clear polypropylene (PP) bottles. Quality parameters monitored over the 12 month storage period included: acidity, peroxide value (PV), spectrophotometric indices (K₂₃₂, K₂₇₀) and color. Results showed that the best packaging material for olive oil packaging was glass followed by PET. PP proved to be unsuitable for such an application. Exposure of olive oil samples to light, high storage temperatures (35 °C) and large headspace volumes caused substantial deterioration in product quality parameters. The most pronounced effect was that of temperature and light while the smallest effect was that of headspace volume and packaging material permeability to oxygen. Olive oil color was not substantially affected by storage conditions with the exception of storage of olive oil at 35 °C exposed to light for 12 months. Shelf life of extra virgin olive oil was 6 months packaged in clear glass in the dark at temperatures up to 22 °C; 3 months in clear PET in the dark at 22 °C and less than 3 months in clear PP in the dark at 22 °C. When exposed to light, shelf life of olive oil was 9 months when packaged in PET + aluminum foil; 3 months in PET + UV blocker and less than 3 months in clear PET at 22 °C. Product shelf life was less than 3 months at 35 °C. Finally oxygen in the headspace of olive oil resulted in deterioration of product quality. The relative contribution of parameters studied to the retention of olive oil quality was: temperature ≈ light > container headspace > packaging material oxygen permeability.     

Pomegranate peel (Punica granatum L) extract and Chinese gall (Galla chinensis) extract inhibit Vibrio parahaemolyticus and Listeria monocytogenes on cooked shrimp and raw tuna

Vibrio parahaemolyticus and Listeria monocytogenes are bacterial pathogens associated with raw or ready-to-eat seafood products. Many compounds extracted from plant material have shown promise for inhibiting bacterial pathogens when applied to some foods. In this study, aqueous methanol extracts from pomegranate peel (Punica granatum L.) and Chinese gallnut (Galla chinensis) were tested against V. parahaemolyticus and L. monocytogenes on cooked shrimp and raw homogenized tuna. The extracts were applied to the shrimp by soaking for 2 min (5 mg/ml). The extracts (1.7 mg ml) were added to homogenized tuna and stirred. The antimicrobial assay on V. parahaemolyticus was conducted at 12 °C, and the assay on tuna was conducted at both 4° and 12 °C. Both Chinese gall and pomegranate peel extracts significantly inhibited the growth of V. parahaemolyticus in both shrimp and tuna. Only Chinese gall extract significantly inhibited growth of L. monocytogenes. Overall V. parahaemolyticus was more sensitive to both plant extracts compared with L. monocytogenes. Both plant extracts had stronger antimicrobial activity on shrimp compared with the tuna. Neither extract completely inhibited the growth of V. parahaemolyticus or L. monocytogenes.     

Inactivation of Shiga toxin-producing and nonpathogenic Escherichia coli in non-intact steaks cooked in a radio frequency oven

This study evaluated the thermal inactivation of Shiga toxin-producing Escherichia coli (O157:H7, O26:H11 and O111) (STEC) and non-pathogenic E. coli in non-intact beefsteaks (NIBS) cooked by radio frequency (RF). Blade tenderized steaks were inoculated with nalidixic (Nal) acid resistant E. coli strains, vacuum packaged in thermal pouches and cooked using pre-determined cooking times to 60 °C (rare) or 65 °C (medium-rare) inside a RF oven. Log reduction ranged from 0.99, 3.08, 2.85 and 5.0 for O157:H7, O26:H11, O111 and non-pathogenic E. coli respectively at 60 °C and a 5.0 log reduction at 65 °C for all strains. Non-pathogenic E. coli strains selected for the present study did not behave similar to the pathogenic strains being significantly more sensitive; therefore, they were not considered for testing at 63 °C. A second part of the study focused on the extent of thermal inactivation of STEC when NIBS were cooked to 63 °C (minimum safe cooking temperature recommended by USDA-FSIS). There was a 5.0 log reduction for E. coli O157:H7 and E. coli O111; but not for E. coli O26:H11. The results indicated that cooking steaks to 65 °C with a holding time at room temperature of 5 min before refrigeration would be enough to reduce numbers of E. coli O157:H7, O26:H11 and O111 using RF. The cooking protocol developed on the present study, has a practical relevance for the industry since the experiments were carried on a pilot-scale RF oven and also pathogens were tested under realistic processing conditions.     

Composition of MSM from Brazilian catfish and technological properties of fish flour

The goal of this study was to analyze the physical and physicochemical composition and microbiological properties of mechanically separated meat (MSM) from Brazilian catfish (Brachyplatystoma vaillantii) and to prepare fish flour from this byproduct while assessing its technological properties, physicochemical and microscopic characteristics. After filleting, the residue was transported and stored at −22 °C and then subjected to mechanical meat separation so the fish flour could be prepared. The MSM analysis identified 17 fatty acids, of which the main ones were palmitic, oleic, stearic, palmitoleic, myristic, EPA, and DHA. The catfish MSM's amino acid profile had mainly glutamic and aspartic acids, arginine, lysine, and leucine. Salmonella spp or sulphite-reducing clostridia were not found in the MSM or the fish flour, while counts of coliforms at 45 °C (<3.0 MPN/g) and coagulase-positive staphylococcus (<1 × 101 CFU/g) were within the limits set by the Brazilian legislation. The fish residue had 78.36 g/100 g moisture, 9.52 g/100 g proteins, 10.80 g/100 g lipids and 18.41 mg TVB-N/100 g (within the Brazilian legislation standards). The best condition to prepare the fish flour was defined as 60 °C due to the best fit to the experimental data. The results suggest that using residues from Brazilian catfish filleting to make fish flour resulted in a product with high nutritional value able to increase value of several foodstuffs, besides contributing to the reduction of waste production in the region's fish industries.     

Effects of changes in pH and temperature on the inhibition of Salmonella and Listeria monocytogenes by Allyl isothiocyanate

The minimum inhibitory (MIC) and minimum bactericidal concentrations (MBC) of mustard allyl isothiocyanate (AITC) against five strains each of Salmonella and Listeria monocytogenes individually, and when combined by genus were studied in Mueller-Hinton broth at 21 or 37 °C as well as the interactive effects of pH (5.0–9.0) at temperatures of 4–21 °C on cell viability when held under these conditions for up to 10 d. The stability of 200 ppm AITC was monitored during these trials. The MIC and MBC values of AITC ranged from 60 to 100 ppm and 120–180 ppm, respectively, at 37 °C and ranged from 10 to 40 ppm and 200–600 ppm, respectively, at 21 °C against both pathogens. AITC had no antimicrobial activity at low temperatures (4 or 10 °C) and alkaline pH over 10 d, but at neutral pH, AITC reduced L. monocytogenes by 4.14 and 8.45 log₁₀ CFU/ml at 4 or 10 °C, respectively. At acidic pH, AITC was more effective against Salmonella which was reduced by 2.56 and 6.48 log₁₀ CFU/ml at 4 and 10 °C, respectively. However, AITC was more effective at combinations of 21 °C and neutral pH against L. monocytogenes (cells were not detected at and beyond 3 d) and at combinations of the higher temperature and acidic pH against Salmonella (cells were not detected at and beyond 6 d). Mustard AITC was more stable at low pH and temperature indicating that it can be an effective antimicrobial at combinations of low or neutral pH values and room or refrigerator temperatures (4–10 °C) against these foodborne pathogens.     

Improving the safety and quality of raw tuna fillets by X-ray irradiation

In this study, raw tuna fillet (25 g) samples were inoculated by immersing in 0.1% peptone water that contained 10⁸⁻⁹ CFU ml⁻¹ of a three-strain mixture of Salmonella enterica for 1 min. The samples were then air dried at 22 °C for 30 min (to allow bacterial attachment) in the biosafety cabinet and were packaged separately in sterilized bags prior to X-ray treatments (0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 kGy). The surviving Salmonella populations on raw tuna fillets samples were evaluated using a nonselective medium (tryptic soy agar) for 6 h with xylose lysine desoxycholate (XLD) selective medium overlay. The plates were then incubated for an additional 18 h at 37 °C. Finally, the colonies were counted and the results were expressed as log CFU g⁻¹. Furthermore, un-inoculated tuna samples (25 g) were packaged separately in sterilized bags and exposed to the lowest and highest X-ray doses (0.0 and 6.0 kGy), then stored at 5 °C, 10 °C or 25 °C for 25, 15 or 5 days, respectively. On the testing-dates, samples were withdrawn and microflora (psychrotrophic and mesophilic) counts, quality [color (using Hunter colorimeter) and texture (using Instron machine)] were evaluated. The results indicated that more than a 6 log CFU reduction of Salmonella population being achieved with 0.6 kGy X-ray treatment. Furthermore, treatment with X-ray significantly reduced the initial inherent microbiota on raw tuna fillets and inherent levels were significantly (p < 0.05) lower than the control samples throughout the shelf-life storage at 5, 10 or 25 °C for 25, 15 or 5 days, respectively. There was a significant effect of X-ray treatment on tuna color after treatment (day 0). However, no significant differences (p > 0.05) in color or texture of control and treated samples were observed after (day 0). These results indicated that X-ray is a good preservative technology for seafood products intended to be consumed raw.     

High pressure processing pretreatment enhanced the thermosonication inactivation of Alicyclobacillus acidoterrestris spores in orange juice

The spoilage of high acid fruit juices and nectars by Alicyclobacillus acidoterrestris is a major concern to juice manufacturers around the world since it is difficult to detect. In this study, thermosonication (ultrasound and heat, TS) and thermal inactivation of A. acidoterrestris spores in pretreated orange juice were carried out and resistance parameters were estimated. First, the effect of TS acoustic energy density (AED, 0.3–20.2 W/mL) on the inactivation at 75 °C was investigated. Then, the influence of TS temperature (70–78 °C) on the spore inactivation (AED = 20.2 W/mL) was studied. Next, we explored the effect of high pressure processing (HPP) pretreatment of juice on the 20.2 W/mL TS inactivation at the best temperature (78 °C). Lastly, the thermal inactivation of spores in juice heat shocked + 1 min sonicated vs. untreated juice was also investigated.Results of TS showed higher spore inactivation for higher AED (D_75°C-value of 49 min for 20.2 W/mL vs. 217 min for 0.33 W/mL). Lower D-values were obtained at higher temperatures (D_78°C-value of 28 min vs. D_70°C-value of 139 min at 20.2 W/mL). The TS D_78°C-value (at 20.2 W/mL) decreased further from 28 min to 14 min when the orange juice was previously submitted to 600 MPa for 15 min. Thermal treatment alone at 78 °C resulted in almost no spore inactivation, whereas the heat shock + ultrasound pretreatment of juice enhanced the thermal inactivation of spores (D_85°C-value decreased from 69 to 29 min). To conclude, HPP-assisted TS provided the best method for spore inactivation, indicating the benefit of high pressure and power ultrasound technology in addition to heat. TS required at least 8 °C lower temperatures than thermal treatments to achieve the same spore inactivation, which could enhance juice quality and energy savings.     

Thermal death times of acid-habituated Escherichia coli and Salmonella enterica in selected fruit beverages

The study established the decimal reduction times at 60 and 73 °C (D₆₀ and D₇₃) of each of acid-adapted cocktails of Escherichia coli (NRRL 3704, ATCC 8739, ATCC 92522) and Salmonella enterica serovars Typhimurium (NRRL B-4420), Typhi (NRRL B-573), and Enteritidis (Biotech 1963) in some fruit beverages. Tested beverages included apple and orange juices, which are most commonly reported vectors of diseases; and tropical fruit beverages such as mango, guava, and soursop nectars, which are not frequently used as suspending media in thermal inactivation studies. The fruit beverages had pH of 3.30–4.73, titratable acidities of 0.15–0.64% organic acid, and soluble solids of 11.13–14.33 °Brix. At 60 °C, E. coli and Salmonella were 1.26–3.13 and 1.21–2.33 folds, respectively, more resistant to heating than at 73 °C. At 60 °C, E. coli and S. enterica had D₆₀ value ranges of 5.90 s (orange juice) to 12.42 s (guava nectar) and 7.50 s (orange juice) to 11.46 s (soursop nectar), respectively. At 73 °C, E. coli had D₇₃ values ranging from 3.56 s (apple juice) to 5.82 s (soursop nectar), while those of S. enterica ranged from 3.59 s (guava nectar) to 9.74 s (soursop nectar). The variations in the observed heat resistance in both heating temperatures were attributed to the differences in the physicochemical properties of the suspending fruit beverages. The results obtained in this work contribute to further understanding the behaviors of these pertinent pathogens in heat-treated fruit beverages. These data also provide baseline information for the establishment of heat pasteurization process schedules for better control of fruit juice product safety.     

Development of carrot parenchyma softening during heating detected in vivo by dynamic mechanical analysis

Dynamic mechanical analysis was employed to explore the development of carrot parenchyma softening during heating in the range of 30–90 °C. Results indicated that compared with raw carrots the toughness of carrots at 60 °C decreased significantly (P < 0.05) at 0.5 °C/min while there was no significant deference (P > 0.05) at 2 °C/min. Samples at 0.5 °C/min finally obtained the lower toughness. Besides, both loss tangent (LT) and two negative peaks on the temperature–slope plot were heating rate dependent. At 0.5 °C/min, distinct increases of LT started at about 48 °C while at about 67 °C at 2 °C/min. With increasing rate, LT effect decreased obviously. Increasing rates caused a shift of both peaks from low temperatures (49–60 °C) to high ones (67–75 °C). Values of both peaks were significantly higher (P < 0.05) at 0.5 °C/min than at 2 °C/min. Furthermore, the microstructure of samples at 0.5 °C/min was more rigid and irregular shrinkage, accompanied by more small pores as well as bigger cracks in comparison to that at 2 °C/min. And cell walls of samples at 0.5 °C/min seemed to thinner. Therefore, the development of carrot parenchyma softening during heating was both temperature and heating rate dependent. We suggested that the breakdown of pore proteins and middle lamella in cell walls induced the dramatic loss of cell turgidity and the subsequent changes of elastic modulus, collectively causing tissue softening.     

Bacillus cereus in fresh ricotta: Comparison of growth and Haemolysin BL production after artificial contamination during production or post processing

Bacillus cereus is of particular concern for the production of fresh ricotta, due to the ability of spores to survive to the thermal treatment, leading to a potential germination, growth and toxin production in the product. This study aimed to evaluate the effect of a B. cereus contamination occurring in the whey used for the production of ricotta, or in the final product as post-production event.Four B. cereus strains (ATCC 14579 and three clinical isolates, GGu1, GPe2 and RCe1) were first evaluated for their ability to grow at different temperatures (from 5 to 55 °C) and spore survival rate to different thermal treatments (65, 70, 80 and 90 °C for 30, 15. 10 and 3 min, respectively). None of the strains showed to be psychrotrophic, as no growth below 10 °C was observed. Strains ATCC 14579 and GPe2 were the most resistant to thermal stresses and were selected for the inoculation tests.In the first trial, two aliquots of whey were inoculated with ATCC 14579 or GPe2 strain and used for the production of fresh ricotta samples, that were stored at 10 °C for 7 days (only GPe2) or 15 °C for 5 days (both the strains). In the second trial, the inoculation was made on fresh ricotta just after production. Samples were stored in the same conditions and analysed daily for the quantification of B. cereus vegetative cells and spores; the L2 component of Haemolysin BL was also quantified in the product.At 15 °C, a very fast germination of spores, followed by an active growth, was constantly observed in the two trials for both B. cereus strains. An earlier growth was detected in the whey-inoculated samples, suggesting the potential activation of spore germination caused by high temperatures reached during ricotta production. A slightly faster growth was observed for ATCC 14579 strain. At 10 °C, GPe2 strain showed a slow growth, with similar rates between whey- or product-inoculated ricotta samples. The production of HBL toxin was significant only in samples kept at 15 °C, starting from the 4th day of storage.In order to ensure the consumers’ protection, these results suggest the suitability of fresh ricotta as a substrate for the growth and metabolic activity of B. cereus, highlighting the need to prevent the contamination of the product and, above all, to apply a correct refrigeration during its storage.     

Modeling the inactivation of Neosartorya fischeri ascospores in apple juice by high pressure,power ultrasound and thermal processing

Neosartorya fischeri is a mould that spoils acid foods and can produce mycotoxins. In this work, the efficacy of high pressure processing (HPP, 600 MPa) and power ultrasound (24 kHz, 0.33 W/mL) in combination with 75 °C for the inactivation of four week old N. fischeri ascospores in apple juice was investigated and compared with 75 °C thermal processing alone. The HPP-75 °C process was the most effective technique for inactivating N. fischeri spores, resulting in 3.3 log reductions after 10 min vs. no inactivation for thermosonication (TS) and thermal processing. Unexpectedly, activation shoulders were observed during the TS process. Then, the effect of different temperatures on the ascospore inactivation in apple juice by HPP-thermal, TS and thermal processing was investigated, and the log survivors vs. time were modeled. Faster inactivation was achieved at higher temperatures for all the technologies tested, indicating the significant role of temperature for the spore inactivation, alone or combined with other processes. The Weibull model described the spore inactivation better by 600 MPa HPP-thermal (50, 60, 75 °C) and thermal (85, 90 °C), whereas Lorentzian was more appropriate for the TS treatment (65, 70, 75 °C). In conclusion, HPP is the best food preservation technology due to higher spore inactivation in apple juice at the same temperature.