Antioxidant and Antimicrobial Enhancement by Reaction of Protein Hydrolysates Derived from Shrimp By-Products with Glucosamine

Shrimp cooking juice and shrimp carapaces are interesting sources of protein which are habitually disposed of at large quantities by crustacean industries. In this work, protein obtained from the cooking juice and carapaces of Pacific white shrimp ( Litopenaeus vannamei ) was hydrolyzed by an enzyme extract of Enterococcus faecalis DM19 isolated from raw camel milk. The hydrolysates were afterwards heated separately with glucosamine (GlcN) at 100 °C for 0, 40, 60,120 and 180 min. The reaction was followed by measuring the change in absorbance at 294 and 420 nm and also by fluorescence (λexc = 340 nm; λem = 440 nm). Browning and intermediate products increased with heating time showing a concomitant decrease in free amino groups, while the pH decreased as well. Amino acid analysis showed that the amounts of lysine, arginine, and histidine decreased significantly after heating for 180 min. The infrared spectra suggested the appearance of new molecules after heating, presumably Schiff bases and/or aromatic compounds. The antioxidant and antimicrobial activities of the heated hydrolysates were compared to those of the native hydrolysates. Interestingly, the reducing ferric ion activity was improved 22-fold after conjugation. Meanwhile, both scavenging radical and metal chelating ion activities were increased sevenfold. Besides, the shrimp carapace hydrolysate heated in presence of GlcN exhibited a good antibacterial activity against gram positive and gram negative bacteria. To conclude, protein hydrolysates derived from the shrimp by-products studied in this work could be heated in presence of GlcN at 100 °C and be potentially used as antioxidant and/or antibacterial ingredients for different purposes.