Abstract
We aimed to explore the differences of thermal behaviors between insoluble collagen fibrils (ICFs) and pepsin-solubilized collagens (PSCs) from sea cucumber Stichopus japonicus. The unfolding/refolding sequences of secondary structures of ICFs and PSCs during the heating and cooling cycle (5 → 70 → 5 °C) were identified by Fourier transform infrared spectrometry combined with curve-fitting and 2D correlation techniques. ICFs showed a higher proportion of α-helical structures and higher thermostability than PSCs, and thus had more-stable triple helical structures. The sequences of changes affecting the secondary structures during heating were essentially the same between ICFs and PSCs. In all cases, α-helix structure was the most important conformation and it disappeared to form a β-sheet structure. In the cooling cycle, ICFs showed a partially refolding ability, and the proportion of β-sheet structure rose before the increasing proportion of α-helix structure. PSCs did not obviously refold during the cooling stage.
Highlights
The body walls of the sea cucumber Stichopus japonicus are enjoyed in Japan and China as a highly-priced delicacy, owing to their unique elasticity and palatability [1]
Fourier transform infrared spectroscopy (FTIR) combined with curve-fitting was used to analyze the secondary structures of insoluble collagen fibrils (ICFs) and pepsin-solubilized collagens (PSCs)
ICFs showed a higher proportion of α-helical structure than PSCs
Summary
The body walls of the sea cucumber Stichopus japonicus are enjoyed in Japan and China as a highly-priced delicacy, owing to their unique elasticity and palatability [1]. The dermis of the body wall is a typical connective tissue with mutable mechanical properties that rapidly changes in response to various stimuli [2]. Insoluble collagen fibrils (ICFs), the most abundant structural element in the dermis, account for about 70% of the total body wall proteins and are arranged into interwoven bundles [1,4]. The structural and rheological changes observed during cooking are due to denaturation and gelatination of collagen [5,6]. The unique textural properties of cooked sea cucumber are most probably attributable to the thermal denaturation of ICFs [1]
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