Search Results (51)

The effect of UV-C was assessed on microbiological stability, functional compounds, and quality factors of white grape juice compared to mild thermal treatment (MTT). The inactivation kinetics of Escherichia coli (target microorganism) and Saccharomyces cerevisiae in grape juice by UV-C and MTT (75 °C) were evaluated to define the processing time. The comparative effect on the functional compounds was evaluated. Additionally, microbiological stability and quality factors were assessed during storage at 4 °C. The grape juice was characterized (pH 3.7, 25 °Brix, absorption coefficient 44.2 cm⁻¹, total phenols (TP) 214 mg GAE/L). UV-C (569 mJ/cm²) reduced E. coli to 5.03 log CFU/mL in 12.5 min, preserved TP (235 mg GAE/L), and antioxidant capacity (AC 4.5 mM TE/L). Thermal treatment reduced E. coli to 5.14 log CFU/mL in 180 s, increased TP (237–312 mg GAE/L), and maintained the AC of the juice. During storage, UV-C and MTT controlled microbiota growth, extending the time of microbiological stability by 42%. All the treatments showed a similar gradual loss of TP during storage. However, MTT has better-preserved color parameters. In conclusion, UV-C was effective from a microbiological perspective without compromising the functional quality of juice. However, further research is needed to improve color. Full article

Meat products are highly susceptible to contamination with Listeria monocytogenes, a foodborne pathogen associated with high mortality. To mitigate this risk, this study explored the use of Poliomintha longiflora oregano essential oil, both in its pure (PEO) and fractionated (FIV, fraction IV obtained at 140 °C) forms, as part of a hurdle technology combining natural antimicrobials with mild thermal treatments. In vitro thermal inactivation experiments were conducted at 52, 54, 57.5, and 63 °C using a simulated meat medium. The FIV group, characterized by 60.23% carvacrol and 21.17% thymol, exhibited significantly enhanced bactericidal activity, achieving up to 5.5 log-reductions in L. monocytogenes at 57.5 °C within 3 min, compared to <2 log-reductions for the control group. Inactivation kinetics were well described by the Weibull–Mafart model. The δ-values, defined as the time required to achieve a 1-log reduction in bacterial population, were consistently lower for FIV compared to the control across all tested temperatures (e.g., δ₅₂°C = 0.64 min vs. 8.47 min for control). The estimated z-values, which represent the temperature increase required to achieve a tenfold change in δ-value, were 5.75 °C (control), 5.20 °C (PEO), and 5.00 °C (FIV), suggesting a consistent thermal sensitivity but enhanced inactivation efficacy with the essential oils. These findings suggest that fractionated oregano essential oil is a promising hurdle to shorten thermal treatments in meat products, thereby lowering L. monocytogenes contamination risk while preserving product quality. Full article

The European Food Safety Authority (EFSA) has raised concerns regarding the use of alkaline phosphatase (ALP) as a pasteurization marker in non-cow milk due to compositional differences. This study investigates the thermal inactivation kinetics of ALP in six milk species (cow, sheep, goat, donkey, buffalo and camel) to assess its reliability as an indicator. The thermal inactivation of ALP in different milk types was evaluated by heating samples at 63–75 °C at various times, then measuring residual enzyme activity using a spectrophotometric method. The results revealed a sharp increase in ALP inactivation with rising temperatures, consistent with previous findings on the enzyme’s thermal sensitivity. Notably, donkey milk exhibited the highest ALP inactivation at 72 °C, probably due to lower fat content compared to the rest of milk types studied, while camel milk showed the lowest inactivation rate constant (k_T) at 75 °C, highlighting its higher heat resistance compared to bovine milk. These findings highlight potential limitations of using the ALP test to verify pasteurization in non-bovine milk, which is directly linked to microbial safety, as well as the preservation of nutritional and sensory characteristics. This study reinforces the importance of considering milk composition, particularly fat and protein structures, in optimizing pasteurization conditions for diverse milk varieties. Full article

In this study, a kinetic analysis was conducted to clarify the thermal inactivation behavior of AMP deaminase and IMPase, enzymes involved in the generation and degradation of inosine 5′-monophosphate (IMP) in the dorsal ordinary muscle (OM) and dark muscle (DM) of yellowtail Seriola quinqueradiata. Both enzymes were extracted from each part of the fish muscle, heated in the range of 50–60 °C, and then measured for residual enzyme activity. Based on these data, kinetic analysis was performed. When comparing fish muscle types, the thermal stability at 50 °C and 55 °C and the temperature dependence of both AMP deaminase and IMPase tended to be higher in the DM. When comparing the two enzymes, the thermal stability of IMPase was higher than that of AMP deaminase at 50 °C in both muscle types. These results suggest that to prepare heated yellowtail muscle with a high IMP content, it is important to consider the thermal inactivation behavior of enzymes and use slow heating to maintain AMP deaminase activity and produce sufficient IMP in OM. For DM, rapidly increasing the product temperature to ≥60 °C to inactivate IMPase is required to preserve the IMP content. Full article

A study was conducted to validate the plain bagel baking process as an effective kill-step in controlling Shiga toxin-producing Escherichia coli (STEC) in the event of pre-baking contamination originating from flour. Unbleached bread flour was inoculated with five strains of STEC and dried back to its original water activity levels. The inoculated flour was used to prepare the bagel dough, proofed, boiled for 2 min, and baked at 232.2 °C (450 °F) for 14 min mimicking the commercial manufacturing process. Additionally, water activity (a_w) and pH in plain bagels during baking, and thermal inactivation kinetics (D- and z-values) of STEC in plain bagel dough were studied. The results clearly demonstrated that baking plain bagels at 232.2 °C (450 °F) for 14 min will result in at least a >5 log reduction in the STEC population, thus providing an effective kill-step assuring the safety of the finished food products. The pH of plain bagels increased significantly from pre-proofed plain bagel dough to seven min into the baking process, reaching a final value of 5.83. The water activity of the crust and crumb portions of plain bagels was significantly different during the baking process. The D-values of STEC in plain bagels at, 56, 59, and 62 °C were 26.3 ± 1.55, 9.0 ± 0.27, and 2.50 ± 0.15 min with a z-value of 5.8 ± 0.16 °C. Full article

Due to the increasing consumer demand for healthy, beneficial foods, natural fruit juices have gained popularity for their rich nutritional value and appealing flavor. However, traditional thermal processing can compromise these quality attributes. This study investigates using pulsed thermosonication, a novel mild thermal processing method, on Listeria innocua inactivation in blueberry juice, chosen for its high phenolic and anthocyanin content. Ultrasonication was applied at 60% and 100% amplitudes combined with heat treatments at 45 °C and 55 °C and compared to control heat treatments. The Weibull model effectively described the inactivation kinetics, showing that the thermosonicated samples required significantly shorter times (1 and 25 min) for a 5-log reduction compared to the heated samples (10 and 60 min). While pH, total soluble solids, and water activity remained unaffected, color parameters improved, and the best retention of phenolics and anthocyanins was observed at 100% amplitude and 45 °C. Rheological properties were unchanged. The findings demonstrate that thermosonication at milder temperatures is more effective than conventional heat treatment for microbial inactivation and quality retention in blueberry juice, suggesting it is a superior processing method for preserving fruit juices’ nutritional and sensory attributes. Full article

The mathematical modeling of a combination of non-thermal technologies for E. coli inactivation is of great interest for describing the dynamic behavior of microorganisms in food, with the goal of process control, optimization, and prediction. This research focused on the design and implementation of a mathematical model to predict the effect of power ultrasound (US), high-pressure processing (HPP), and the combination of both non-thermal technologies on the inactivation kinetics of E. coli (DSM682) inoculated in orange juice. Samples were processed by US, HPP, and a combination of both technologies at varying process parameters, and a mathematical model for microbial inactivation was developed using a System Dynamics approach. The results showed that the combination of these technologies exhibited a synergistic effect, resulting in no detectable colony-forming units per mL of juice. The developed model accurately predicted the inactivation of E. coli following the combination of these technologies (R² = 0.82) and can be used to predict microbial load reduction or optimize it based on process parameters. Additionally, combining both techniques offers a promising approach for extending the shelf life of fresh juices using non-thermal stabilization technology. Full article

The high amount of starch in fruits is responsible for its post-processing cloudiness. In the current study, α-amylase from porcine pancreases was immobilized onto carboxymethyl cellulose/polyacrylamide (CMC/PAM) hydrogel. This in-house-built CMC/PAM-Amy hydrogel offers a more efficient and sustainable solution for apple juice clarification. To acquire the best immobilization efficiency, the concentration of glutaraldehyde crosslinker was optimized. Biocatalytic characterization studies were brought into consideration for free and immobilized α-amylase. The synthesized native and immobilized CMC/PAM-Amy hydrogels were also characterized using SEM, FTIR and XRD. Under ideal circumstances, the activity of CMC/PAM-Amy was up to 604 μmolmin⁻¹, and its immobilization efficiency was 96.29 ± 1.15%. A kinetic parameters study resulted in a conspicuously lowered Km value for immobilized amylase, signifying its higher affinity for its substrate. CMC/PAM-Amy showed a half-life (t_1/2) 3.5 times higher than free-Amy at 50, 55 and 60 °C. The higher values of the inactivation rate constant (k_d), free energy of inactivation (ΔG*), enthalpy of inactivation (ΔH*) and change in entropy (ΔS*) of CMC/PAM-Amy manifested the enhanced thermal stability of amylase after immobilization. A reusability study revealed that immobilized amylase retained roughly 70% of its initial catalytic activity after six successive repetitions of the process. CMC/PAM-Amy displayed improved recycling ability operational stability and biocatalytic activity, rendering it an auspicious tool in decreasing the starch content of crude apple juice to about 61% of its total starch content before treatment. Moreover, the values of Brix, viscosity, acidity and turbidity were also decreased in CMC/PAM-Amyclarified apple juice. Therefore, immobilized amylases with other industrial enzymes could be an efficient tool for potential industrial application. Full article

Histidine ammonia-lyase (HAL) plays a pivotal role in the non-oxidative deamination of L-histidine to produce trans-urocanic, a crucial process in amino acid metabolism. This study examines the cloning, purification, and biochemical characterization of a novel HAL from Geobacillus kaustophilus (GkHAL) and eight active site mutants to assess their effects on substrate binding, catalysis, thermostability, and secondary structure. The GkHAL enzyme was successfully overexpressed and purified to homogeneity. Its primary sequence displayed 40.7% to 43.7% similarity with other known HALs and shared the same oligomeric structure in solution. Kinetic assays showed that GkHAL has optimal activity at 85 °C and pH 8.5, with high thermal stability even after preincubation at high temperatures. Mutations at Y52, H82, N194, and E411 resulted in a complete loss of catalytic activity, underscoring their essential role in enzyme function, while mutations at residues Q274, R280, and F325 did not abolish activity but did reduce catalytic efficiency. Notably, mutants R280K and F325Y displayed novel activity with L-histidinamide, expanding the substrate specificity of HAL enzymes. Circular dichroism (CD) analysis showed minor secondary structure changes in the mutants but no significant effect on global GkHAL folding. These findings suggest that GkHAL could be a promising candidate for potential biotechnological applications. Full article

Derived from the denitrifying bacterium Aromatoleum aromaticum EbN1 (Azoarcus sp.), the enzyme S-1-(4-hydroxyphenyl)-ethanol dehydrogenase (S-HPED) belongs to the short-chain dehydrogenase/reductase family. Using research techniques like UV-Vis spectroscopy, dynamic light scattering, thermal-shift assay and HPLC, we investigated the catalytic and structural stability of S-HPED over a wide temperature range and within the pH range of 5.5 to 9.0 under storage and reaction conditions. The relationship between aggregation and inactivation of the enzyme in various pH environments was also examined and interpreted. At pH 9.0, where the enzyme exhibited no aggregation, we characterized thermally induced enzyme inactivation. Through isothermal and multitemperature analysis of inactivation data, we identified and confirmed the first-order inactivation mechanism under these pH conditions and determined the kinetic parameters of the inactivation process. Additionally, we report the positive impact of glucose as an enzyme stabilizer, which slows down the dynamics of S-HPED inactivation over a wide range of pH and temperature and limits enzyme aggregation. Besides characterizing the stability of S-HPED, the enzyme’s catalytic activity and high stereospecificity for 10 prochiral carbonyl compounds were positively verified, thus expanding the spectrum of substrates reduced by S-HPED. Our research contributes to advancing knowledge about the biocatalytic potential of this catalyst. Full article

Water stress and water quality represent major environmental challenges in the 21st century. In response, wastewater management and its potential reuse emerge as strategies to mitigate these problems. This research aims to verify the law of reciprocity in the solar disinfection process of real secondary wastewater effluents for different faecal microorganisms. Flat disinfection reactors, subjected only to natural and continuous UV radiation, were used. The study focused on the optical effect of UV radiation, eliminating the significant influence of the thermal effect and its synergy in solar disinfection at temperatures above 45 °C, by controlling the temperatures of the water samples to levels below 20 °C. Three experimental tests were carried out on sunny days. Each test comprised two trials, under the following conditions: (a) low solar irradiance over a prolonged time (duration approximately: 2.6 h) and (b) high solar irradiance and a shorter period of time (approximately 2 h), with each receiving the same UV dose. Inactivation kinetics was analysed for E. coli, E. faecalis, and C. perfringens (including spores). The results validated the reciprocity law for E. coli in all tests for UV doses > 20 Wh/m², showing no significant deviations, with inactivation rates of 0.44 to 0.51 m²/Wh for initial concentrations of 10⁶–10⁷ CFU/100 mL. In contrast, for E. faecalis, the reciprocity was only valid at intensities < 700 W/m², with rates of 0.04 and 0.035 m²/Wh for 10⁵–10⁶ CFU/100 mL; above this irradiance value, the law varied significantly and was not valid. C. perfringens did not show significant disinfection results during the experiments to verify this law, mainly due to the resistance of its spores. Additional experimentation with C. perfringens is necessary, by extending the length of the experiments and/or conducting them at higher irradiance values, in order to reach bacterial inactivation to enable the analysis of the reciprocity law. In general, the main conclusion from these results is that the reciprocity law in solar disinfection would be difficult to use for the estimation of water solar disinfection based on the irradiance and exposure times, as there are deviations from it at least in one specie (E. faecalis). Mores studies should be carried out to fully understand and determine the validity of this law and its potential application for forecasting solar water disinfection. Full article

This study explores the potential of thermosonication as an alternative to traditional heat treatments, such as pasteurization, in the processing of fruit juices. Conventional methods often lead to undesirable quality changes in fruit juices, whereas thermosonication offers promising results regarding microbial inactivation and quality preservation. This work focused on the inactivation kinetics of Listeria innocua 2030c, a surrogate for pathogenic L. monocytogenes, in kiwifruit juice using thermosonication at 45 °C, 50 °C, and 55 °C. These treatments were compared with equivalent heat treatments. Quality attributes of the juice were also evaluated to assess process efficiency. Survival data of L. innocua were fitted with the Weibull model, estimating first decimal reduction times (δ) and shape parameters (n). The results reveal temperature and process dependencies on δ, while n remains mostly temperature and treatment independent. Thermosonication outperforms heat treatment, achieving higher L. innocua reductions while retaining quality attributes like pH, soluble solid content, and total phenolics and chlorophylls. Thermosonication at 55 °C stands out, providing a 6.2-log-cycle reduction in just 3 min with superior quality retention. These findings highlight the synergistic effect of temperature and ultrasound, making mild heat processes feasible while enhancing product quality. Thermosonication, particularly at 55 °C, emerges as an effective alternative to traditional thermal treatments for fruit juices, offering improved microbial safety without compromising product quality. Full article

The contamination and spoilage of heat-treated fruit juices by heat-resistant mold ascospores present significant challenges to the food industry. Understanding effective strategies to mitigate this contamination is vital for ensuring the shelf-life and microbial safety of heat-treated fruit juices. This study investigated the thermal resistance of ascospores from different heat-resistant mold species, including Aspergillus laciniosus, A. chevalieri, A. denticulatus, A. siamensis, Hamigera pallida, and Talaromyces macrosporus, isolated from pineapple and sugarcane field soils. Ascospores inactivation kinetics in pineapple juice under heat treatment (75–97 °C) were analyzed using log-linear and Weibull models. Among these species, A. laciniosus displayed the highest heat resistance (δ-value: 104.59 min at 85 °C), while A. siamensis exhibited the lowest (δ-value: 3.39 min at 80 °C). Furthermore, A. laciniosus, the most heat-resistant species, showed notable tolerance to sanitizers. The most effective inactivation was achieved using 1.0% (w/v) sodium hypochlorite for 15 min. Chlorine dioxide, however, was generally ineffective and even activated dormant ascospores in some cases. The combination of hot water (65 °C for 5 min) with sanitizer increased ascospore reduction in most species but did not achieve the 3-log reduction required by the European Standard N13697. This study revealed a correlation between ascospore resistance to heat and chlorine dioxide, offering significant findings for practical inactivation strategies. Full article

In this study, Salmonella Typhimurium, Escherichia coli, and Listeria monocytogenes were separately inoculated in sterilized carrot juice and subjected to various types of high-pressure processing (HPP) at 200–600 MPa for 0.1–15 min to observe the effects of HPP on the inactivation kinetics of foodborne pathogens in carrot juice. The first-order model fits the destruction kinetics of high pressure on foodborne pathogens during the pressure hold period. An increase in pressure from 200 to 600 MPa decreased the decimal reduction time (D values) of S. Typhimurium, E. coli, and L. monocytogenes. Under pressure ≥ 400 MPa, the D values of E. coli were significantly higher than those of S. Typhimurium and L. monocytogenes, indicating that E. coli had greater resistance to high pressures than the others. The Zp values (the pressure range that causes the D values to change by 90%) of E. coli, S. Typhimurium, and L. monocytogenes were 195, 175, and 170 MPa, respectively. These results indicated that L. monocytogenes and E. coli were the most and least sensitive, respectively, to pressure changes. Additionally, the three bacteria were separately inoculated into thermal-sterilized carrot juice and subjected to 200–600 MPa HPP for 3 min. The treated carrot juices were stored at 4 °C for 27 d. Following S. Typhimurium and E. coli inoculation, the bacterial counts of the control and 200 MPa treatments remained the same during the storage duration. However, they decreased for the 300 and 400 MPa treatment groups with increasing storage duration. During the storage period, no bacterial growth was observed in the 500 and 600 MPa treatments. However, the bacterial number for the control and pressure treatment groups increased with prolonged storage duration following inoculation with L. monocytogenes. Therefore, following HPP, residual L. monocytogenes continued growing stably at low temperatures. Overall, HPP could inhibit and delay the growth of S. Typhimurium and E. coli in carrot juice during cold storage, but it was ineffective at inhibiting the growth of L. monocytogenes. There was a risk of foodborne illness despite the low-temperature storage of juice. The innovation of this preliminary study is to find the impact of high pressure on the inactivate kinetics of three food pathogens in carrot juice and its practical application in simulated contaminated juice. Full article

In this study, trypsin from the porcine pancreas was immobilized on a heterofunctional support prepared by activating chitosan (Chit) hydrogel with glutaraldehyde (GA), then functionalizing it with glycine (Chit–GA–Gly). The catalytic performance of the immobilized trypsin in the hydrolysis reactions was compared with the catalytic performance of the immobilized enzyme on glutaraldehyde-activated chitosan (Chit–GA) and chitosan hydrogel (Chit). The maximum concentration of immobilized protein on Chit–GA–Gly was approximately 16 mg·g⁻¹ at pH 9.0 (5 mmol·L⁻¹ buffer sodium carbonate) at 25 °C from an offered protein loading of 20 mg·g⁻¹. This biocatalyst exhibited maximum specific activity (SA) of 33.1 ± 0.2 nmol·min⁻¹·mg⁻¹ for benzoyl-DL-arginine-p-nitroanilide (BAPNA) hydrolysis, twice as high as the enzyme immobilized on the classic Chit–GA support (SA values ranging between 6.7 ± 0.1 nmol·min⁻¹·mg⁻¹ and 8.1 ± 0.1 nmol·min⁻¹·mg⁻¹). The Elovich kinetic model was used to describe the adsorption process using low (3 mg·g⁻¹) and high (20 mg·g⁻¹) initial protein loadings. The optimum temperature for BAPNA hydrolysis catalyzed by the immobilized trypsin (60 °C) was 10 °C higher than that of its soluble form. Additionally, the immobilized enzyme was 16 to 20 times more stable than its soluble form at 50–55 °C. Thermodynamic studies were conducted to elucidate the kinetics of the thermal inactivation process of soluble and immobilized forms. Complete hydrolysis of bovine serum albumin (BSA) at 37 °C was achieved after 2 h using a soluble enzyme, while for its immobilized form, the hydrolysis yield was 47%. Reuse tests revealed that this biocatalyst retained 37% of its original activity after 10 successive hydrolysis batches. Based on these results, this support could be used as an interesting alternative for producing heterogeneous biocatalysts with high catalytic activity and thermal stability when producing protein hydrolysates. Full article