Identification and characterisation of a novel heptapeptide mackerel by-product hydrolysate, and its potential as a functional fertiliser component.

Functional fertilisers for hydroponics are in great demand. Herein, we isolated peptides from mackerel by-products, a valuable source of bioactive peptides. The pellet-phase fraction obtained after cold-acetone extraction exhibited plant growth-promoting activity in wheat hydroponics, and the presumed peptides were determined to be ≤ 1 kDa based on molecular weight cut-off and tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Size exclusion chromatography and matrix-assisted laser desorption ionisation time of flight mass spectrometry analysis were employed for peptide purification and identification. Finally, two peptides were identified, both with linear structures, consisting of amino acid sequences TCGGQGR and KEAGAFIDR. At 1 mg/mL, the heptapeptide performed better than the nonapeptide in terms of wheat growth and health, but neither peptide exhibited antimicrobial activity. Only the heptapeptide displayed significant antioxidant activity, and this activity bioaccumulated in wheat leaves after 7 days of hydroponic growth. The heptapeptide did not match any known metabolites in PepBank, BIOPEP, UniProt or METLIN databases, and is therefore a novel peptide with potential as a functional fertiliser component.

Recovery of antioxidant and antimicrobial peptides through the reutilization of Nile perch wastewater by biodegradation using two Bacillus species.

Nile perch wastewater was biodegraded using two Bacillus species to recover bioactive substances to enhance its reutilization value. The two Bacillus species successfully produced low-molecular-weight substances with a 47.8% degree of hydrolysis. The antioxidant activities of the Nile perch wastewater increased as the biodegradation proceeded, and the culture supernatant exhibited the highest DPPH (80.1%), ABTS (93.1%) and Fe2+ chelating (88.5%) antioxidant activities at 60 h. The antioxidant potential of the biodegraded Nile perch wastewater was found to be higher than those of other fish hydrolysates. Moreover, the biodegraded Nile perch wastewater exhibited effective antimicrobial activity against Vibrio vulnificus, exhibiting a minimal inhibitory concentration of 585 µg mL-1. Two-dimensional thin layer chromatography analysis revealed the specific amino acids responsible for the antioxidant activity, and molecular-weight cut-off ultrafiltration revealed that the <2-kDa fraction exhibited the highest antioxidant activity with the lowest IC50 values (0.43 and 0.22 mg mL-1 for DPPH and ABTS antioxidant activities, respectively). This is the first report of the reutilization of Nile perch wastewater as a natural antioxidant and antimicrobial ingredient for nutraceuticals.

Biodegraded mackerel wastewater selectively inhibits harmful algal blooms.

Functional substances from mackerel wastewater were biodegraded and tested for inhibitory activity against harmful algal blooms (HABs) that are detrimental to aquaculture. The supernatant from a 48 h culture of mackerel wastewater had a half-maximal inhibitory concentration of 0.54-0.68 mg/ml for the three tested HAB organisms (Heterocapsa triquetra, Alexandrium fundyense and Prorocentrum minimum). This inhibitory effect was not observed form 48-h biodegraded nutrient broth culture supernatant, indicating inhibitory substances did not originate from bacterial metabolites. Rough estimation of molecular weight using ultrafiltration indicated that the inhibitory substance was less than 2 kDa, and it did not inhibit the non-HAB organism (Skeletonema costatum), which is essential for preserving marine ecosystems in real-world applications. Furthermore, this inhibitory effect against HABs was not observed for biodegraded culture supernatants of other protein sources (skim milk and okara), indicating that the inhibitory substances were derived from a particular source present only in raw mackerel wastewater. To the best of our knowledge, this is the first report describing the selective inhibitory effects of the culture supernatant of mackerel wastewater against HABs.

The high reutilization value potential of high-salinity anchovy fishmeal wastewater through microbial degradation.

To provide an option for the reutilization of high-salinity anchovy fishmeal wastewater (FMW), generated during the anchovy fishmeal manufacturing processes, its potential for biodegradation was assessed in 1-l five-neck flasks using a halotolerant and proteolytic microbial consortium. During the first 41 h of biodegradation, the pH, DO, ORP, and dry-sludge weight decreased as the total cell number of the microbial consortium increased steadily; the COD(Cr)/TN ratios remained between 4.0 and 5.5, respectively, indicating the stable metabolic degradation of organic matter. The ORP tended to increase after 41 h, and the unpleasant fishy smell disappeared once positive ORP values were achieved. The removal percentages of COD(Cr) and TN were 59.0 and 54.4%, respectively, and the dry-sludge weight decreased from 115.5 to 68.0 g, with a degradation rate of 0.59 g h(-1), during the 80 h experiment. The supernatant from the culture of the anchovy FMW at 70 h (culture supernatant) was phytotoxin-free, and the level of total amino acids was 8.04 g 100 g(-1), comparable to that of commercial fertilizers. In hydroponic cultures containing red bean and barley, the culture supernatant demonstrated a good fertilizing ability. The culture supernatant also exhibited a high degree of antioxidant activity, with a 52.3% hydroxyl radical-scavenging activity and 0.16 reducing power (at OD 700 nm). Moreover, the culture supernatant inhibited DNA damage from hydroxyl radicals, enhancing the reutilization value of anchovy FMW. This report presents the first description of high-salinity anchovy FMW possessing a high reutilization value potential both for agriculture and medicine.