title: Critical electric field strengths of onion tissues treated by pulsed electric fields.
abstract: The impact of pulsed electric fields (PEF) on cellular integrity and texture of Ranchero and Sabroso onions (Allium cepa L.) was investigated. Electrical properties, ion leakage rate, texture, and amount of enzymatically formed pyruvate were measured before and after PEF treatment for a range of applied field strengths and number of pulses. Critical electric field strengths or thresholds (E(c)) necessary to initiate membrane rupture were different because dissimilar properties were measured. Measurement of electrical characteristics was the most sensitive method and was used to detect the early stage of plasma membrane breakdown, while pyruvate formation by the enzyme alliinase was used to identify tonoplast membrane breakdown. Our results for 100-μs pulses indicate that breakdown of the plasma membrane occurs above E(c)= 67 V/cm for 10 pulses, but breakdown of the tonoplast membrane is above either E(c)= 200 V/cm for 10 pulses or 133 V/cm for 100 pulses. This disparity in field strength suggests there may be 2 critical electrical field strengths: a lower field strength for plasma membrane breakdown and a higher field strength for tonoplast membrane breakdown. Both critical electric field strengths depended on the number of pulses applied. Application of a single pulse at an electric field up to 333 V/cm had no observable effect on any measured properties, while significant differences were observed for n≥10. The minimum electric field strength required to cause a measurable property change decreased with the number of pulses. The results also suggest that PEF treatment may be more efficient if a higher electric field strength is applied for a fewer pulses.
authors.affiliation: Biological and Agricultural Engineering Graduate Program, Univ. of California Davis, Davis, CA 95616, USA.
authors.forename: Suvaluk
authors.initials: S
authors.lastname: Asavasanti
authors.forename: Seda
authors.initials: S
authors.lastname: Ersus
authors.forename: William
authors.initials: W
authors.lastname: Ristenpart
authors.forename: Pieter
authors.initials: P
authors.lastname: Stroeve
authors.forename: Diane M
authors.initials: DM
authors.lastname: Barrett
mesh_terms: D000465:Algorithms; D013437:Carbon-Sulfur Lyases / Q000378:metabolism; D055598:Chemical Phenomena; D004553:Electric Conductivity; D055664:Electrochemical Techniques / Q000295:instrumentation; D004573:Electrolytes / Q000032:analysis; D005511:Food Handling / Q000295:instrumentation / Q000379:methods*; D006244:Hardness; D007425:Intracellular Membranes / Q000648:ultrastructure; D007700:Kinetics; D055595:Mechanical Phenomena; D019697:Onions / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D015388:Organelles / Q000378:metabolism / Q000648:ultrastructure; D010940:Plant Proteins / Q000378:metabolism; D018517:Plant Roots / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D019289:Pyruvic Acid / Q000378:metabolism; D015203:Reproducibility of Results
chemical_list: D004573:Electrolytes; D010940:Plant Proteins; D019289:Pyruvic Acid; D013437:Carbon-Sulfur Lyases; C019243:alliin lyase