ID: 2235

• Title:
  Estimation of thermal impact during pulsed electric field (PEF) inactivation of Lactiplantibacillus plantarum strains in oat-based milk alternative
  
  Authors:
  

  Thamsuaidee, Arisa - Elea Technology GmbH,Quakenbrueck, DE & National and Kapodistrian University of Athens, Athens, GR
  Schaefer, Eva - Hochschule Biberach, Biberach an der Riss, DE
  Siemer, Claudia - Elea Technology GmbH,Quakenbrueck, DE
  Valdramidis, Vasilis - National and Kapodistrian University of Athens, Athens, GR
  

  
  
  Abstract:
  Background and objectives: Pulsed electric field (PEF) technology is proposed as a mild preservation technique for extending the shelf life of plant-based dairy alternatives. It is known that the microbial inactivation mechanism of PEF is based on electroporation, but the colinear treatment chamber could also contribute to a partial thermal effect resulting from the generated ohmic heating. The current study aimed to quantify the microbial resistance of two model strains of L. plantarum, and to estimate the contribution of the thermal effect on the processing of oat-based beverage.
  
  Materials and methods: Oat-based beverage was inoculated with L. plantarum strains ATCC 8014 and WCFS1. The samples were processed with a continuous PEF system fitted with a colinear chamber comprising of two treatment zones, both with an electrode gap of 1 cm. The applied electric field strength varied between 10 – 24 kV/cm, and the specific energy input between 20 - 120 kJ/L. The overall inactivation levels were assessed via colony enumeration on MRS medium.
  
  The temperature-time profile during PEF was established by splitting the process into 1) warming, 2) treatment zone, and 3) cooling phases. A theoretical numerical approach was used to simulate the warming phase as the sample entered the treatment chamber at an inlet temperature of 35°C. The temperatures inside the PEF treatment zone and during cooling were measured by fibre optic sensors.
  
  In a separate experiment, the microbial thermal resistance of each microorganism was determined by the glass capillary method. Integration of the microbial thermal resistance data and the temperature-time profile enabled an estimation of the total thermal impact on the studied microorganisms. The effect of electroporation can subsequently be quantified by subtracting the thermal effect from the overall observed microbial inactivation.
  
  Results: The kinetic data clearly demonstrated that PEF was able to achieve at least 5 log reduction of both studied strains in the oat beverage matrix. Under all treatment conditions, L. plantarum WCFS1 was found to be more resistant than L. plantarum ATCC 8014, suggesting higher resistance of the strain WCFS1 to both thermal and electroporation impacts. The electroporation effect was evident when higher microbial inactivation levels were achieved with increasing electric field strengths. On the other hand, temperature measurement in the PEF treatment zones confirmed the presence of hot spots. In particular, at increasing specific energy input levels, there was significant contribution of temperature to the total observed inactivation.
  
  Conclusions: PEF proved to be a promising technology for microbial decontamination in plant-based beverages. It is important to define the target pertinent microorganisms, as difference in resistance can be observed even within the same species. Additionally, depending on the equipment design and selected treatment parameter combinations, microbial inactivation may be based nearly solely on the thermal effect. Optimization of the process and industrial equipment setup should aim to maximize microbial inactivation while minimizing the potential impact of high temperature on the product nutritional value and organoleptic quality.
  
  
  
  Keywords:
  
  
  Refs:
  
  
  Topic 1:
  10. Food safety and food preservation
  
  Topic 2:
  3. Modelling and simulation of exposures and effects