Effect of boiling on water mobility, quality and structure characteristics of Mactra veneriformis during hot air drying

Dried clam is a widely consumed marine product, with extended shelf-life and pleasant taste. The drying profiles and moisture distribution of Mactra veneriformis at different temperatures were obtained during hot air drying (HAD) with or without boiling pretreatment using kinetic models and low-field nuclear magnetic resonance (LF-NMR) combined with magnetic resonance imaging (MRI). Quantity analysis showed that boiling pretreatment significantly enhanced drying efficiency from 7.36 ± 0.71 to 4.47 ± 0.68 at 80 °C and Page model was optimal to predict water variation during drying. Moreover, boiled samples dried at 80 °C possessed good rehydration rate (213 ± 16%), texture (Hardness 9.87 ± 0.56, Cohesiveness 0.54 ± 0.06, Springiness 2.55 ± 0.44, Cheswiness 13.63 ± 4.03) and color properties. Structure analysis showed that heating, especially boiling, converted stable and orderly α-helix into β-turn and random coil. Low molecular weight protein was accumulated more in groups with boiling pretreatment than those without boiling. The obtained structure and denatured sarcoplasmic proteins during boiling significantly inhibited the formation of hardened surface and accelerated the drainage of immobilized water during HAD. The results indicate that the boiling pretreatment is essential for drying clams.