The objectives of this research were to isolate chitinolytic bacteria from shrimp rusip (an Indonesian traditional fermented shrimp product), identify bacterial isolates showing high chitinolytic activity, and determine the chitinolytic activity of these isolates. There were 44 chitinolytic bacteria isolated from shrimp rusip: 39 isolates of Gram-positive bacteria and 5 isolates of Gram-negative bacteria. The quantitative method we used to evaluate chitin-degrading enzyme activity measured the amount of N-acetylglucosamine produced from the reaction of crude enzyme and colloidal chitin. Seven isolates showing highest chitinolytic activity were Bacillus cereus

Highlight Research Snakehead fish head possess high protein content and potential to be used as materials for protein hydrolysate Snakehead fish head protein hydrolysis optimum condition were determined Snakehead fish head hydrolysate protein antioxidant activity were analyzed Snakehead fish head is potential to be used as materials for fish protein hydrolysate   Abstract There is concern regarding the use of synthetic antioxidants which spurred the yearly increase of natural antioxidants to substitute synthetic ones. Fish protein hydrolysate (FPH), which has been reported to have potent antioxidant properties, could be utilized to solve this problem. This study aimed to utilize the by-product of snakehead fish (head) and determine the optimum hydrolysis conditions to obtain FPH with antioxidant activity. Two parameters were tested during the hydrolysis process: enzyme concentration (papain enzyme) and hydrolysis time. The optimum condition was evaluated by measuring dissolved protein, hydrolysis degree (DH), and antioxidant activity, including DPPH, ABTS, and FRAP. The optimal hydrolysis conditions were 5% enzyme concentration and 6 h of hydrolysis time at 55°C and pH 7.0. The DPPH, ABTS, and FRAP antioxidant activities were 50.70%, 66.67%, and 1.35 M Tr/mg, respectively. Based on the antioxidant activity, Snakehead fish head has the potential as a source of natural antioxidants.

The toxicity caused by high histamine content produced by histamine-producing bacteria (HPB) during the fermentation of scombridae fish group based fermented fish products is still a problem that requires a solution. This study aims to explore the potential of secondary metabolites in the form of cell free supernatant (CFS) produced by lactic acid bacteria (LAB) as antibacterial agents against HPB. The LAB was isolated from the fermented fishery products named bekasan, cincalok and fish sauce using MRS-Agar and fermented on MRS-broth for 48 hours. CFS was collected by centrifugation at 15,000 x g for 15 minutes, followed by heating at 100oC for 3 minutes and pH neutralization with 0.1N NaOH. Antimicrobial activity of CFS then tested on HFB namely Morganella morganii TK7, Citrobacter freundii CK1, and Klebsiella sp. CK13.2 (collection of the Laboratory of Fisheries Product Quality and Safety, Department of Fisheries UGM) using the macrodilution method. Isolation of LAB from all three products successfully isolated 34 isolates. The results of the antibacterial activity showed that 4 isolates namely GMCN 1.12, GMBK 2.6, GMBK 2.7, dan GMKI 2.1 were able to inhibit HFB growth more than 70%. The highest activity was shown by GMBK 2.7 which inhibits 98% against Morganella morganii TK7, 99% against Citrobacter freundii CK1, and 84% against Klebsiella sp. CK13.2. The antimicrobial activity was reduced after proteolytic enzymes were added suggesting that the bioactive compound came from peptide-based substances like bacteriocin.

N‐acetylglucosamine (NAG) is the monomer product of chitin, which has been widely used as a bioactive com‐ pound in applications such as anti‐tumor, anti‐microbial, and antioxidant activities. In production, biological processes using enzymes are preferable to chemicals due to environmental issues. This study aims to determine the activity, purity level, and molecular weight of purified chitinase from Micromonospora sp. AR17 determines the concentration of NAG produced by purified chitinase that has been characterized. Chitinase was produced by fermentation in colloidal chitin broth at 40 °C, pH 7, for 7 days, while chitinase activity was checked every 24 h. The optimal fermentation time was used to produce chitinase for a further purification step. Enzyme purification was carried out by ultrafiltration, ammonium sulfate precipitation, ion exchange chromatography (Q Sepharose Fast Flow), and gel filtration (Sephacryl S‐300). The purified enzyme was then char‐ acterized for optimum time, pH, and temperature to produce NAG. The results suggested that the fourth day was the optimal time for chitinase production, with chitinase activity of 0.0040 U/mL and a NAG concentration of 7.62 µg/mL. The purifica‐ tion step successfully increased the purity by 6.82 times with chitinase‐specific activity at 1.4648 U/mg. Production of NAG with purified chitinase produced a NAG concentration of 32.472 µg/mL with an incubation time of 30 min at 40 °C and pH 7.

Streptomyces is a Gram-positive bacteria that produces the largest secondary metabolite compounds. The results of whole-genome sequence analysis showed that Streptomyces can carry more than 30 Biosynthetic Gene Clusters (BGC) encoding secondary metabolites that have the potential to be explored in the exploration for new bioactive compounds. However, not all BGC can be expressed in the laboratory scale and requires a specific activation method. This study aims to explore the potential of chitosan as an elicitor compound to activate and or increase the antibacterial activity of Streptomyces sp. GMR-22 was tested against histamine-producing bacteria (HPB) Morganella morganii TK7 and Citrobacter freundii CK1. Chitosan was added to the fermentation medium with the final concentration of 250, 500, and 750 µg/ml while without the addition of chitosan used as control. Fermentation was carried out for 10 days at room temperature, with constant agitation 200 rpm. The supernatant was separated by centrifugation at 3500 rpm for 15 minutes, then fractionation with ethyl acetate, concentrated by vacuum rotary evaporator, and freeze-dried. The test for antibacterial activity was carried out by the microdilution method with an extract concentration of 100 mg/ml. The test results of the microdilution method showed that the addition of chitosan successfully increases the antibacterial activity with the highest activity shown by the water fraction of 250 µg/ml addition of chitosan which effective in inhibiting the growth of Morganella morganii TK7 and Citrobacter freundii CK1 by 97,29% and 97,92% respectively.