Hayriye Bozkurt

Ohmic and Conventional Heating of Pomegranate Juice: Effects on Rheology, Color, and Total Phenolics

Ohmic heating is an alternative fast-heating method especially for liquid foods. In this study, pomegranate juice samples, prepared by two different extraction methods, were heated ohmically by matching the same thermal history, with that of the conventional method. The ohmic heating application was conducted by changing the voltage gradient (10—40 V/cm) at 50 Hz. The samples were heated from 20 ° C to 90°C and held at 90 °C for different treatment times (0, 3, 6, 9 or 12 min). Although rheological properties, color, and total phenolic content (TPC) values changed at the initial heating up period, there were no significant changes during holding period (p < 0.05). Non-Newtonian (power law) rheology model had higher regression coefficient than Newtonian model, and the extraction method affected the consistency of pomegranate juice samples (p < 0.05). Color values of juice extracted from arils (APJ) was better than that of juice extracted from whole fruits (PPJ), as PPJ contained higher amount of TPC (p < 0.05). Since the heating method did not affect the rheological properties, color, and TPC values, it could be said that there was no electrical effect rather than thermal effects during ohmic heating of pomegranate juice. Ohmic heating could be recommended as an alternative fast-heating method for fruit juices.

Determination of the thermal inactivation kinetics of the human norovirus surrogates, murine norovirus and feline calicivirus.

Studies are needed to bridge existing data gaps and determine appropriate parameters for thermal inactivation methods for human noroviruses. Cultivable surrogates, such as feline calicivirus (FCV-F9) and murine norovirus (MNV-1), have been used in the absence of human norovirus infectivity assays. This study aimed to characterize the thermal inactivation kinetics of MNV-1 and FCV-F9 at 50, 56, 60, 65, and 72°C for different treatment times (0 to 60 min). Thermal inactivation was performed using the capillary tube method with titers of 4.0 × 10(7) (MNV-1) and 5.8 × 10(8) (FCV-F9) PFU/ml in triplicate experiments, followed by standard plaque assays in duplicate for each experiment. Weibull and first-order models were compared to describe survival curve kinetics. Model fitness was investigated by comparing the regression coefficients (R(2)) and the chi-square (χ(2)) and root mean square error (RMSE) values. The D-values calculated from the first-order model (50 to 72°C) were 0.15 to 34.49 min for MNV-1 and 0.11 to 20.23 min for FCV-9. Using the Weibull model, the t(D) values needed to destroy 1 log PFU of MNV-1 and FCV-F9 at the same temperatures were 0.11 to 28.26 and 0.06 to 13.86 min, respectively. In terms of thermal resistance, MNV-1 was more sensitive than FCV-F9 up to 65°C. At 72°C, FCV-F9 was slightly more susceptible to heat inactivation. Results revealed that the Weibull model was more appropriate to represent the thermal inactivation behavior of both tested surrogates. The z-values were calculated using D-values for the first-order model and the t(D) values for the Weibull model. The z-values were 9.31 and 9.19°C for MNV-1 and 9.36 and 9.31°C for FCV-F9 for the first-order and Weibull models, respectively. This study provides more precise information than previous reports on the thermal inactivation kinetics of two norovirus surrogates for use in thermal process calculations.

Rheological Characteristics of Quince Nectar During Ohmic Heating

Electrical heating of food products provides rapid and uniform heating, resulting in less thermal damage to the product. In this study, ohmic heating as an electrical heating method was applied to the quince nectar by matching the same heating curve of conventional method by changing voltage gradient (10–40 V/cm) at 50 Hz. The change of rheological constants of quince nectar was determined for different holding times (0, 10, 15, 20, and 30 minutes) in the temperature range of 65–75ºC by using concentric type viscosimeter. Shear stress–shear rate data were fitted to the Newtonian, Bingham, Herschel Bulkley, Power law and Casson Models. It was found that Herschel-Bulkley model was the best model to fit the experimental rheogram adequately since higher regression coefficients (R2; 0.9997) and low standard errors (SE; 0.054) were obtained by Herschel-Bulkley equation compared to other model equations. It was concluded that quince nectar showed time independent non-Newtonian pseudoplastic character during heating in the range of 20–75ºC, independent on heating method. The activation energy values were 9.88 ± 3.24 kJ/mol and 10.08 ± 2.53 kJ/mol for ohmic heating and conventional heating respectively. Results showed that there was no electrical effect rather than thermal effects of ohmic heating since similar rheological constants were obtained with both methods statistically (p < 0.05). Ohmic heating could be recommended as an alternative fas heating method for fruit nectars.

Thermal Inactivation of Human Norovirus Surrogates in Spinach and Measurement of Its Uncertainty

Leafy greens, including spinach, have potential for human norovirus transmission through improper handling and/or contact with contaminated water. Inactivation of norovirus prior to consumption is essential to protect public health. Because of the inability to propagate human noroviruses in vitro, murine norovirus (MNV-1) and feline calicivirus (FCV-F9) have been used as surrogates to model human norovirus behavior under laboratory conditions. The objectives of this study were to determine thermal inactivation kinetics of MNV-1 and FCV-F9 in spinach, compare first-order and Weibull models, and measure the uncertainty associated with the process. D-values were determined for viruses at 50, 56, 60, 65, and 72 °C in 2-ml vials. The D-values calculated from the first-order model (50 to 72 °C) ranged from 0.16 to 14.57 min for MNV-1 and 0.15 to 17.39 min for FCV-9. Using the Weibull model, the tD for MNV-1 and FCV-F9 to destroy 1 log (D ≈ 1) at the same temperatures ranged from 0.22 to 15.26 and 0.27 to 20.71 min, respectively. The z-values determined for MNV-1 were 11.66 ± 0.42 °C using the Weibull model and 10.98 ± 0.58 °C for the first-order model and for FCV-F9 were 10.85 ± 0.67 °C and 9.89 ± 0.79 °C, respectively. There was no difference in D- or z-value using the two models (P > 0.05). Relative uncertainty for dilution factor, personal counting, and test volume were 0.005, 0.0004, and ca. 0.84%, respectively. The major contribution to total uncertainty was from the model selected. Total uncertainties for FCV-F9 for the Weibull and first-order models were 3.53 to 7.56% and 11.99 to 21.01%, respectively, and for MNV-1, 3.10 to 7.01% and 13.14 to 16.94%, respectively. Novel and precise information on thermal inactivation of human norovirus surrogates in spinach was generated, enabling more reliable thermal process calculations to control noroviruses. The results of this study may be useful to the frozen food industry in designing blanching processes for spinach to inactivate or control noroviruses.

Determination of Thermal Inactivation Kinetics of Hepatitis A Virus in Blue Mussel (Mytilus edulis) Homogenate

ABSTRACT Hepatitis A virus (HAV) is a food-borne enteric virus responsible for outbreaks of hepatitis associated with shellfish consumption. The objectives of this study were to determine the thermal inactivation behavior of HAV in blue mussels, to compare the first-order and Weibull models to describe the data, to calculate Arrhenius activation energy for each model, and to evaluate model efficiency by using selected statistical criteria. The times required to reduce the population by 1 log cycle (D-values) calculated from the first-order model (50 to 72°C) ranged from 1.07 to 54.17 min for HAV. Using the Weibull model, the times required to destroy 1 log unit (tD = 1) of HAV at the same temperatures were 1.57 to 37.91 min. At 72°C, the treatment times required to achieve a 6-log reduction were 7.49 min for the first-order model and 8.47 min for the Weibull model. The z-values (changes in temperature required for a 90% change in the log D-values) calculated for HAV were 15.88 ± 3.97°C (R 2, 0.94) with the Weibull model and 12.97 ± 0.59°C (R 2, 0.93) with the first-order model. The calculated activation energies for the first-order model and the Weibull model were 165 and 153 kJ/mol, respectively. The results revealed that the Weibull model was more appropriate for representing the thermal inactivation behavior of HAV in blue mussels. Correct understanding of the thermal inactivation behavior of HAV could allow precise determination of the thermal process conditions to prevent food-borne viral outbreaks associated with the consumption of contaminated mussels.

Thermal inactivation kinetic modeling of human norovirus surrogates in blue mussel (Mytilus edulis) homogenate.

Control of seafood-associated norovirus outbreaks has become an important priority for public health authorities. Due to the absence of human norovirus infectivity assays, cultivable surrogates such as feline calicivirus (FCV-F9) and murine norovirus (MNV-1) have been used to begin to understand their thermal inactivation behavior. In this study, the effect of thermal treatment on inactivation of human norovirus surrogates in blue mussels was investigated at 50, 56, 60, 65, and 72 °C for various times (0-6 min). The results obtained were analyzed using the Weibull and first-order models. The Theil error splitting method was used for model comparison. This method splits the error in the predicted data into fixed and random error. This method was applied to select satisfactory models for determination of thermal inactivation of norovirus surrogates and kinetic modeling. The D-values calculated from the first-order model (50-72 °C) were in the range of 0.07 to 5.20 min for FCV-F9 and 0.18 to 20.19 min for MNV-1. Using the Weibull model, the t(D=1) for FCV-F9 and MNV-1 to destroy 1 log (D=1) at the same temperatures were in the range of 0.08 to 4.03 min and 0.15 to 19.80 min, respectively. The z-values determined for MNV-1 were 9.91±0.71 °C (R²=0.95) using the Weibull model and 11.62±0.59 °C (R²=0.93) for the first-order model. For FCV-F9 the z-values were 12.38±0.68 °C (R²=0.94) and 11.39±0.41 °C (R²=0.97) for the Weibull and first-order models, respectively. The Theil method revealed that the Weibull model was satisfactory to represent thermal inactivation data of norovirus surrogates and that the model chosen for calculation of thermal inactivation parameters is important. Knowledge of the thermal inactivation kinetics of norovirus surrogates will allow development of processes that produce safer shellfish products and improve consumer safety.

Thermal Inactivation of Foodborne Enteric Viruses and Their Viral Surrogates in Foods.

Foodborne viruses, in particular human norovirus and hepatitis A virus, are the most common causes of food-associated infections and foodborne illness outbreaks around the world. Since it is currently not possible to cultivate human noroviruses and the wild-type strain of hepatitis A virus in vitro, the use of a variety of viral surrogates is essential to determine appropriate thermal processing conditions to reduce the risk associated with their contamination of food. Therefore, the objectives of this review are to (i) present pertinent characteristics of enteric foodborne viruses and their viral surrogates, (ii) discuss the viral surrogates currently used in thermal inactivation studies and their significance and value, (iii) summarize available data on thermal inactivation kinetics of enteric viruses, (iv) discuss factors affecting the efficacy of thermal treatment, (v) discuss suggested mechanisms of thermal inactivation, and (vi) provide insights on foodborne enteric viruses and viral surrogates for future studies and industrial applications. The overall goal of this review is to contribute to the development of appropriate thermal processing protocols to ensure safe food for human consumption.

Processing of Fruits and Fruit Juices by Novel Electrotechnologies

Recent demands from consumers for fresh-like quality foods with less and/or no artificial additives have introduced innovative processing technologies. These technologies due to their potential for food processing with preservation of important properties may cause to introduce new products in the market, to improve the competitiveness of the food, to eliminate the use of some artificial food additives, and to reduce energy cost. Pulsed electric fields for microbial and enzyme inactivation, shelf-life extension, moderate electric fields for yield and extraction, and ohmic heating are among these novel technologies that are based on the application of electric current on food materials. It has been well established that these technologies can successfully be applied to different food products. Among all, fruit juices have special importance due to the suitability of their physical properties to be processed by the electrotechnologies. This article covers the fundamentals of these technologies, their current use, research activities, and trends.

Thermal inactivation kinetics of hepatitis A virus in spinach.

Leafy vegetables have been recognized as important vehicles for the transmission of foodborne viral pathogens. To control hepatitis A viral foodborne illness outbreaks associated with mildly heated (e.g., blanched) leafy vegetables such as spinach, generation of adequate thermal processes is important both for consumers and the food industry. Therefore, the objectives of this study were to determine the thermal inactivation behavior of hepatitis A virus (HAV) in spinach, and provide insights on HAV inactivation in spinach for future studies and industrial applications. The D-values calculated from the first-order model (50-72 °C) ranged from 34.40 ± 4.08 to 0.91 ± 0.12 min with a z-value of 13.92 ± 0.87 °C. The calculated activation energy value was 162 ± 11 kJ/mol. Using the information generated in the present study and the thermal parameters of industrial blanching conditions for spinach as a basis (100 °C for 120-180 s), the blanching of spinach in water at 100 °C for 120-180 s under atmospheric conditions will provide greater than 6 log reduction of HAV. The results of this study may be useful to the frozen food industry in designing blanching conditions for spinach to inactivate or control hepatitis A virus outbreaks.

Thermal Inactivation Kinetics of Human Norovirus Surrogates and Hepatitis A Virus in Turkey Deli Meat

ABSTRACT Human noroviruses (HNoV) and hepatitis A virus (HAV) have been implicated in outbreaks linked to the consumption of presliced ready-to-eat deli meats. The objectives of this research were to determine the thermal inactivation kinetics of HNoV surrogates (murine norovirus 1 [MNV-1] and feline calicivirus strain F9 [FCV-F9]) and HAV in turkey deli meat, compare first-order and Weibull models to describe the data, and calculate Arrhenius activation energy values for each model. The D (decimal reduction time) values in the temperature range of 50 to 72°C calculated from the first-order model were 0.1 ± 0.0 to 9.9 ± 3.9 min for FCV-F9, 0.2 ± 0.0 to 21.0 ± 0.8 min for MNV-1, and 1.0 ± 0.1 to 42.0 ± 5.6 min for HAV. Using the Weibull model, the t D = 1 (time to destroy 1 log) values for FCV-F9, MNV-1, and HAV at the same temperatures ranged from 0.1 ± 0.0 to 11.9 ± 5.1 min, from 0.3 ± 0.1 to 17.8 ± 1.8 min, and from 0.6 ± 0.3 to 25.9 ± 3.7 min, respectively. The z (thermal resistance) values for FCV-F9, MNV-1, and HAV were 11.3 ± 2.1°C, 11.0 ± 1.6°C, and 13.4 ± 2.6°C, respectively, using the Weibull model. The z values using the first-order model were 11.9 ± 1.0°C, 10.9 ± 1.3°C, and 12.8 ± 1.7°C for FCV-F9, MNV-1, and HAV, respectively. For the Weibull model, estimated activation energies for FCV-F9, MNV-1, and HAV were 214 ± 28, 242 ± 36, and 154 ± 19 kJ/mole, respectively, while the calculated activation energies for the first-order model were 181 ± 16, 196 ± 5, and 167 ± 9 kJ/mole, respectively. Precise information on the thermal inactivation of HNoV surrogates and HAV in turkey deli meat was generated. This provided calculations of parameters for more-reliable thermal processes to inactivate viruses in contaminated presliced ready-to-eat deli meats and thus to reduce the risk of foodborne illness outbreaks.