Abstract
Hagfish slime is an ultra dilute, elastic and cohesive hydrogel that deploys within milliseconds in cold seawater from a glandularly secreted exudate. The slime is made of long keratin-like fibers and mucin-like glycoproteins that span a network which entraps water and acts as a defense mechanism against predators. Unlike other hydrogels, the slime only confines water physically and is very susceptible to mechanical stress, which makes it unsuitable for many processing operations and potential applications. Despite its huge potential, little work has been done to improve and functionalize the properties of this hydrogel. To address this shortcoming, hagfish exudate was mixed with a soy protein isolate suspension (4% w/v) and with a soy emulsion (commercial soy milk) to form a more stable structure and combine the functionalities of a suspension and emulsion with those of the hydrogel. Hagfish exudate interacted strongly with the soy systems, showing a markedly increased viscoelasticity and water retention. Hagfish mucin was found to induce a depletion and bridging mechanism, which caused the emulsion and suspension to flocculate, making “soy slime”, a cohesive and cold-set emulsion- and particle gel. The flocculation network increases viscoelasticity and substantially contributes to liquid retention by entrapping liquid in the additional confinements between aggregated particles and protein fibers. Because the mucin-induced flocculation resembles the salt- or acid-induced flocculation in tofu curd production, the soy slime was cooked for comparison. The cooked soy slime was similar to conventional cooked tofu, but possessed a long-range cohesiveness from the fibers. The fibrous, cold-set, and curd-like structure of the soy slime represents a novel way for a cold coagulation and fiber incorporation into a suspension or emulsion. This mechanism could be used to efficiently gel functionalized emulsions or produce novel tofu-like structured food products.
Highlights
The marine hagfish produces record-breaking amounts of slime when provoked or attacked
Exudate stabilized in citrate/PIPES buffer allows a separation of the mucin vesicles from the thread skeins and the investigation of the influence of the hagfish mucin on the soy systems alone
These results suggest a fundamental change in the microstructure for soy protein isolate (SPI) gelled with hagfish exudate
Summary
The marine hagfish produces record-breaking amounts of slime when provoked or attacked. The fibers are made of intermediate filaments (IFs) and are phylogenetically related to type II keratins [5] In their native form they are coiled-coil type of proteins and undergo a so called α to β transition when subjected to deformation, leading to substantially improved mechanical properties [6]. This α to β transition appears to be a hallmark of IFs-like proteins [7], imparting hagfish fibers mechanical properties similar to spider silk but exceeding their processing possibilities and bio-physical properties [8]
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