Dielectric properties of sea cucumbers (Stichopus japonicus) and model foods at 915 MHz

Abstract

Short-time microwave (MW) sterilization is a feasible technology to produce high-quality shelf-stable sea cucumbers (SCs) (Stichopus japonicus). Selection of a model food matching the sea cucumbers in dielectric properties (DPs) is one of the most important steps for developing the MW processing. The test results revealed that rehydrated sea cucumber has much lower relative dielectric loss factor (9.73–5.62) than muscle foods, including salmon fillets and sliced beef, which were reported in the literature. The whey protein gel formulations that had been developed in our laboratory as a tool in heating pattern studies for those products are, therefore, not appropriate for sea cucumber. Adding 1.0% gellan powder sharply reduced the amount of whey protein concentrates needed to form firm gels and significantly lowered the dielectric loss factor. The dielectric properties of the sea cucumbers and model food samples with different formulations were measured using a custom-built temperature controlled test cell and an Agilent 4291B impedance analyzer in the temperature range 20–120°C. Based on comparison of the measured dielectric properties and the calculated microwave power penetration depths among the sea cucumbers and model foods, appropriate formulation with whey protein concentration 5%, whey protein isolation 3%, gellan gum 1%, d-ribose 0.5% and water 90.5% was chosen as the model food for the sea cucumbers for the purpose of MW processing development.