No abstract

The sensory texture of sea cucumber (Apostichopus japonicus) was dramatically affected by heat treatment. In this study, sea cucumbers were heated under different thermal conditions (HSC), and divided into five groups (HSC-80, HSC-90, HSC-100, HSC-110, and HSC-120) according to the heating temperature (from 80 to 120°C). The changes in texture, moisture, gel structure, and biochemical parameters of the HSC were investigated. With increasing heating time (from 10 to 80 min), the hardness and gel structure changed slightly, and the water activity decreased as the proportion of T 21 increased by 133.33, 55.56, and 59.09% in the HSC-80, HSC-90, and HSC-100 groups, respectively. This indicated that moderate heating conditions (below 100°C) caused gelation of sea cucumbers in HSC-80, HSC-90, and HSC-100 groups. However, as the water activity increased, the hardness declined rapidly by 2.56 and 2.7% in the HSC-110 and HSC-120 groups, with heating time increased from 10 to 80 min. Meanwhile, free hydroxyproline and ammonia nitrogen contents increased by 81.24 and 63.16% in the HSC-110 group; and by 63.09 and 54.99% in the HSC-120 group, as the gel structure of the sea cucumbers decomposed in these two groups. These results demonstrated that, severe heat treatment (above 100°C) destroyed the chemical bonds, triggered the disintegration of collagen fibers and the gel structure of sea cucumbers, and transformed the migration and distribution of moisture, finally causing the deterioration of the sensory texture of the sea cucumbers.

HSC (sea cucumbers treated by high pressure steam) were easy to degrade during storage, even if microorganism and endogenous enzyme were inactivated. To explore the softening mechanism of HSC, packaged samples were stored at 37C for 33 days. The hardness value decreased sharply from 374.60 to 35.00 gf in 33 days, as well as springiness, cohesiveness, chewiness and restorability. The proportion of transverse relaxation time (T23) increased from 0.841 to 0.917 in 24 days, indicating that the proportion of free water ascended significantly. Nuclear magnetic resonance images showed that part of bound water in body wall transformed into free water in 18 days. Collagen fibers were broken in 27 days as Van Gieson stained images showed. Ammonia nitrogen and ε-amino group increased significantly, and free hydroxyproline level also increased from 8.33 to 24.12 μg/g, indicating the degradation of HSC. Therefore, softening of HSC may be caused by moisture migration, break of collagen fiber and degradation of collagen. PRACTICAL APPLICATIONSHigh pressure steam treatment can inactivate microorganisms and enzymes without affecting the flavor and nutrition of sea cucumbers. However, sea cucumbers treated with high pressure steam (HSC) can also degrade after being stored for several days. This restricts the development of sea cucumber products. Therefore, it is important to study the nonenzymatic softening mechanism of HSC during storage. This will be a basis for the study in resolving the autolysis of sea cucumbers.