通电加热过程中鰤鱼的介电损失率变化

摘要

Dielectric loss rate of white and red muscles of yellowtail fillets were calculated from measured electrical conductivity at frequencies between 50 and 20 000 Hz from 15 to 80 ℃ to provide insights on improving the modeling of continuous ohmic heating (OH) in fish products by LCR (Heinrich Lenz-Capacitor-Resistance).The effects of frequency,temperature,muscle composition (moisture and fat content),muscle and current direction (parallel and series),and muscle membrane on dielectric loss rate were investigated during OH.At 20 kHz,the dielectric loss rate of yellowtail fillets increased with the increase of frequency and temperature.Compared with red muscle,white muscle has a higher dielectric loss rate.The parallel type of yellowtail fillets has a higher dielectric loss rate than the series type.Temperature,fat,moisture contents,and current direction all influenced the dielectric loss rate,especially the muscle membrane which connected fiber has a major influence to both types of muscles.The structure change,protein denaturation and drip loss were also the influence factors during heat processing.Protein denaturation lead to the drip loss,and drip loss rate increased with the increase of temperature.The maximum drip loss was about 14％ when temperature increased to 80 ℃.The membrane is one of the main factors affecting the dielectric loss rate and heating rate during ohmic heating.%为了测定鰤鱼鱼片的介电损失率,通过LCR(heinrich lenz-capacitor-resistance)测试仪直接测定了通电加热过程中鰤鱼鱼片的电导率,并利用电导率计算得到了用于加热(如通电、微波、射频加热等)模拟所需的重要参数-介电损失率,考察了频率(50 ～20 000 Hz)、温度(15 ～ 80℃)、水分及脂肪含量(白色与红色鱼块)、电流方向与鱼块的摆放方式(并联和串联)对鱼片介电损失率的影响.结果表明:介电损失率随频率和温度的增加而增加;脂肪含量少的白色鱼块的介电损失率较脂肪含量多的红色鱼块更高;并联模式的介电损失率较串联模式更高,膜的存在会影响电子的移动,降低电导率,使介电损失率降低.样品结构变化、加热过程中蛋白质变性和汁液损失也是介电损失率变化的影响因素.蛋白质变性导致汁液流失,汁液损失率随着温度的升高而增加,80℃时可达14％左右.鱼片中膜的存在是影响其介电损失率的主要原因之一,也会影响通电加热时的加热速率.