Ohmic Heating Behaviour and Rheological Properties of Ice Cream Mixes

Development and investigation of ultrasound-assisted pulsed ohmic heating for inactivation of foodborne pathogens in milk with different fat content

The central objective of this research was to develop an ultrasound-assisted pulsed ohmic heating (POH) system for inactivation of food-borne pathogens in phosphate buffered saline (PBS) and milk with 0-3.6% fat and investigate its bactericidal effect. Combining ultrasound with POH did not significantly affect the temperature profile of samples. Both POH alone and ultrasound-assisted POH took 120 s to heat PBS 60℃. Milk with 0, 1, and 3.6% fat was heated to 60℃ by POH alone and ultrasound-assisted POH after 335, 475, and 525 s, respectively. This is because the electrical conductivity of the samples was the same for POH alone and ultrasound-assisted POH. Despite identical temperature profiles, ultrasound-assisted POH exerted a synergistic effect on the reduction of Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes, and Staphylococcus aureus. In particular, the inactivation level of S. Typhimurium in PBS subjected to ultrasound-assisted POH treatment for 120 s corresponding to a treatment temperature of 60℃ was 3.73 log units higher than the sum of each treatment alone. A propidium iodide assay, intracellular protein measurements, and scanning electron microscopy revealed that ultrasound-assisted POH treatment provoked lethal cell membrane damage and leakage of intracellular proteins. Meanwhile, fat in milk reduced the efficacy of the bacterial inactivation of the ultrasound-assisted POH system due to its low electrical conductivity and sonoprotective effect. After ultrasound-assisted POH treatment at 60℃, there were no significant differences (P > 0.05) in the pH, color, and apparent viscosity of milk between the untreated and treated group.

Use of ohmic heating as an alternative method for cooking pasta

BACKGROUND

In this study, the alternative method of ohmic heating (OH) was applied to investigate its potential usage in the cooking process for pasta and its comparison with the conventional method. For this purpose, OH was operated at four different voltage gradients (10, 20, 30, 40 V cm^-1 ). The electrical conductivity of pasta σ (S m^-1 ) was calculated for the temperature range 22-95 °C and a three-phase linear relation between σ and temperature was determined.

RESULTS

According to the results, the energy consumption of the OH system and cooking time were lower than the conventional method. Energy conservation was about 73.7% at 40 V cm^-1 and increased up to 90.4% (at 10 V cm^-1 ) with lower voltage gradients. Total cooking time, cooking loss, water absorption, degree of gelatinization, volume uptake, energy consumption and sensorial properties were investigated. No significant differences between the results of samples cooked with the conventional method and OH at 30-40 V cm^-1 were found in terms of starch gelatinization degree, volume change, water absorption, and sensorial analysis (P > 0.05).

CONCLUSION

These results revealed that OH did not cause any negative effects on the quality parameters of pasta samples, and positive effects were observed on energy and time saving. © 2021 Society of Chemical Industry.

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.