Sterilization of liquid foods by pulsed electric fields–an innovative ultra-high temperature process

Abstract

The intention of this study was to investigate the inactivation of endospores by a combined thermal and pulsed electric field (PEF) treatment. Therefore, self-cultivated spores of Bacillus subtilis and commercial Geobacillus stearothermophilus spores with certified heat resistance were utilized. Spores of both strains were suspended in saline water (5.3 mS cm−1), skim milk (0.3% fat; 5.3 mS cm−1) and fresh prepared carrot juice (7.73 mS cm−1). The combination of moderate preheating (70–90°C) and an insulated PEF-chamber, combined with a holding tube (65 cm) and a heat exchanger for cooling, enabled a rapid heat up to 105–140°C (measured above the PEF chamber) within 92.2–368.9 μs. To compare the PEF process with a pure thermal inactivation, each spore suspension was heat treated in thin glass capillaries and D-values from 90 to 130°C and its corresponding z-values were calculated. For a comparison of the inactivation data, F-values for the temperature fields of both processes were calculated by using computational fluid dynamics (CFD). A preheating of saline water to 70°C with a flow rate of 5 l h−1, a frequency of 150 Hz and an energy input of 226.5 kJ kg−1, resulted in a measured outlet temperature of 117°C and a 4.67 log10 inactivation of B. subtilis. The thermal process with identical F-value caused only a 3.71 log10 inactivation. This synergism of moderate preheating and PEF was even more pronounced for G. stearothermophilus spores in saline water. A preheating to 95°C and an energy input of 144 kJ kg−1 resulted in an outlet temperature of 126°C and a 3.28 log10 inactivation, whereas nearly no inactivation (0.2 log10) was achieved during the thermal treatment. Hence, the PEF technology was evaluated as an alternative ultra-high temperature process. However, for an industrial scale application of this process for sterilization, optimization of the treatment chamber design is needed to reduce the occurring inhomogeneous temperature fields.

Bacillus Spores in the Food Industry: A Review on Resistance and Response to Novel Inactivation Technologies

“…PEF treatment at 195 kJ/kg in association with heat 133 °C has been reported to give a 4‐log reduction of B. subtilis spores, which could be separated into 1.15‐log reduction by heat and 3.2‐log reduction by PEF by modeling (Siemer and others ). A 5‐log inactivation of B. subtilis spores in milk was reported by preheating the milk to 95 °C, followed by PEF (130 kJ/kg) accompanied with an increase of temperature of the product to 120 °C (Reineke and others ). A 3‐log reduction in B. cereus spores was achieved with a field intensity of 35 kV/cm combined with a thermal treatment (50 °C) in skim milk, and a 6‐log reduction was observed at 65 and 75 °C (Bermúdez‐Aguirre and others ).…”

Simultaneous Impact of High Pressures and Pulsed Electric field on Saccharomyces cerevisiae Model System

“…Depending on the product, electric field intensity and the total duration of pulses the number of microorganisms can decrease from 2 to 5 decades [10][11][12][13]. For PEF method the post-process increase of temperature, reaching even 40 K, is reported [12][13][14].…”

“…It is notable that for PEF treatment some degree of denaturation and loss of microorganisms is reported, what may be considered as a possible aftermath of short-time local thermal pasteurization. The extensive resume of recent advances for HPP and PEF methods can be found in references [1][2][3][4][10][11][12][13][14][15][16]. This report presents studies focusing on the simultaneous impact of HPP + PEF on Saccharomyces cerevisiae model system.…”

Advances in the Value Addition to Foods-recent Trends

“…The novel and emerging food processing technologies for value addition are the following: High Pressure Processing for salads and ready meals 7 , pulsed electric field processing for liquid foods and beverages 8 , high intensity electric field pulses on solid foods 9 , enzymatic inactivation by pulsed electric fields 10 , etc. are considered to be thermal at the same time the thermal abuse is low.…”