Concentration-dependent suppressive effect of shrimp head protein hydrolysate on dehydration-induced denaturation of lizardfish myofibrils.

To utilize fishery waste products as functional food material, the shrimp head protein hydrolysate (SHPH) was produced from three species of shrimp wastes, Northern pink shrimp, Endeavour shrimp and black tiger shrimp, by enzymatic hydrolysis. The SHPH was used as a natural food preservative by adding to lizardfish myofibrils at concentrations ranging from 2.5% to 10%. Their effects on the state of water and the denaturation of myofibrils during dehydration were evaluated. The amount of monolayer and multilayer water in myofibrils containing SHPH were higher than those without SHPH (control). DSC analyses revealed that the amount of unfrozen water increased significantly after addition of SHPH. The Ca-ATPase inactivation rate of myofibrils containing SHPH decreased during dehydration while 5-7.5% concentrations of SHPH exhibited optimum effect regardless of the species. The results implicated that SHPH can be used as an alternative food preservative for suppressive the dehydration-induced denaturation of myofibrils.

Extracellular prolyl endoprotease from Aspergillus niger and its use in the debittering of protein hydrolysates.

The observation that the bitterest peptides from casein hydrolysates contain several proline residues led us to hypothesize that a proline-specific protease would be instrumental in debittering such peptides. To identify the desired proline-specific activity, a microbiological screening was carried out in which the chromogenic peptide benzyloxycarbonyl-glycine-proline-p-nitroanilide (Z-Gly-Pro-pNA) was used as the substrate. An Aspergillus niger (A. niger) strain was identified that produces an extracellular proline-specific protease with an acidic pH optimum. On the basis of sequence similarities, we conclude that the A. niger-derived enzyme probably belongs to the S28 family of clan SC of serine proteases rather than the S9 family to which prolyl oligopeptidases belong. Incubating the overexpressed and purified enzyme with bitter casein hydrolysates showed a major debittering effect. Reversed phase HPLC analysis revealed that this debittering effect is accompanied by a significant reduction of the number of hydrophobic peptides present.

Transcriptomic and peptidomic analysis of protein hydrolysates from the white shrimp (L. vannamei).

An RNAseq approach associated to mass spectrometry was conducted to assess the composition, molecular mass distribution and primary sequence of hydrolytic peptides issued from hydrolysates of white shrimp (Litopenaeus vannamei) by-products. High performance size exclusion chromatography (HPSEC) analyses indicated that 69.2% of the 214-nm-absorbing components had apparent molecular masses below 1000 Da, and 88.3% below 2000 Da. OFFGEL-nLC-MALDI-TOF/TOF and nLC-ESI-MS/MS analyses led to the identification of 808 peptides based on the NCBI EST databank (161,397 entries) completed by the new L. vannamei databank (58,508 entries) that we created from the RNAs of tissues used for hydrolysate production. Whereas most of hydrolytic peptides have a MW below 2000 Da, preliminary investigations of antimicrobial properties revealed three antibacterial fractions that demonstrate functional activities. The abundance of small peptides as well as the biological activities detected could imply very interesting applications for shrimp hydrolysate in the field of aquaculture feeding.

Silk fibroin hydrolysate exerts an anti-diabetic effect by increasing pancreatic ß cell mass in C57BL/KsJ-db/db mice.

Components of silk including silk fibroin have long been used as anti-diabetic remedies in oriental medicine. However, detailed mechanisms underlying these antidiabetic effects remain unclear. In this study, we examined the anti-diabetic activity of silk fibroin hydrolysate (SFH) in C57BL/KsJ db/db (db/db) mice, a well-known animal model of non-insulin dependent diabetes mellitus. When the db/db mice were administered SFH in drinking water for 6 weeks, hyperglycemia in the animals gradually disappeared and the level of glycosylated hemoglobin decreased, indicating that SFH plays important role in reducing the symptoms of diabetes. In addition, SFH-treated db/db mice exhibited improved glucose tolerance with increased plasma insulin levels. Immunohistochemical and morphological analyses showed that SFH up-regulated insulin production by increasing pancreatic ß cell mass in the mice. In summary, our results suggest that SFH exerts anti-diabetic effects by increasing pancreatic ß cell mass in a non-insulin dependent diabetes mellitus mouse model.