Preparation And Antioxidant Activity Of Oligopeptide From Bighead Carp (Aristichthys Nobilis) By Enzymatic Hydrolysis

Food protein enzymatic hydrolysates, especially the oligopeptides with low molecularweight (<1000Da), may be an ideal source of bioactive peptides with biological propertiessuch as antioxidant capacity, angiotensin converting enzyme (ACE) inhibition, antithrombosisand anti-fatigue, of which the absorption and nutritional value were better than free aminoacids. The bighead carp(Aristichthys nobilis) protein with similar amino acid composition tohuman and rich in essential amino acids could be used as an ideal raw material of proteinhydrolysates. The study was to prepare the bighead carp oligopeptide with high yield andconcentrated molecular weight distribution, in which the optimum process of bighead carphydrolyzed by Alcalase was investigated, and the sensory properties, physicochemical andantioxidant capacity of oligopeptide were also evaluated, which will be of great theoreticaland practical significance for the intensive processing and peptide enzymatic preparation ofChina`s freshwater fisheries development. The main contents were as follows:By investigating the effect of substrate concentrate, pH, temperature, enzyme dosage andhydrolysis time on degree of hydrolysis(DH), the optimum processing technic of bighead carpprotein hydrolyzed by Alcalase was determined: substrate concentrate5.1%, pH9.5,temperature50℃, enzyme dosage0.048AU/g.pr and hydrolysis time120min. Underoptimum conditions, the DH was20.74%and oligopeptides with lower molecular weightsizes (<1,000Da) were more predominant with content of93.56%in hydrolysates satisfyingthe standard of oligopeptide.Three pretreatments, namely ultrasonication (US), microwave (MW) and ultrafinemilling (UM), were used to produce hydrolysate from bighead carp (Aristichthys nobilis) withAlcalase. The hydrolysis efficiency of hydrolysates affected by different pretreatmentmethods mentioned above was investigated. The hydrolysate of sample pretreated by UMexhibited superior hydrolysis efficiency with estimated degree of hydrolysis (DH) of24.22%,protein recovery (PR) of95.76%and oligopeptide yield (OY) of93.37%. Oligopeptides withlower molecular weight sizes (<1,000Da) were predominant in hydrolysates of samples, andthe hydrolysate of sample pretreated by UM had the lowest free amino acid content. Inaddition, the hydrolysis efficiency and antioxidant activity of sample pretreated by UM couldbe kept good even when concentration of substrate was high up to8.5%.The compound enzymatic hydrolysis of bighead carp protein was studied as themolecular weight distribution was not much concentrated. Effect of different enzymecombinations and hydrolysis time was analyzed. The results indicated that Alcalase andFlavourzyme were the best enzyme combinations. Protein was firstly hydrolyzed by Alcalaseunder the optimum conditions, then pH was adjusted to7.0and Flavourzyme was added withthe dosage of30LAPU/g.pr. After90min of hydrolysis, the molecular weight of hydrolysateswas concentrated around300Da.The process of desalination by DA201-C macroporous resin was also studied. Theoptimum flow rate, concentration of ethanol solution was2BV/h and75%, respectively, andthe leakage was at8BV. The desalination rate was92.37%. The sensory properties of oligopeptide dried by spry drying were better than vacuumfreeze-drying product. What`s more, the physicochemical characteristics of bighead carpoligopeptide meet the standards of GB/T22729-2008.The antioxidant activities of bighead carp oligopeptide were evaluated by three differentchemical models in vitro. Results showed that its scavenging activity for DPPH radicals andmetal-chelating activity were0.54and0.35folds stronger than those of GSH`s at the samemolecular concentration (the average molecular weight of bighead carp oligopeptide is about1.63fold of that of GSH).15-25mg/mL bighead carp oligopeptide had the same ability toscavenging ABTS radicals as that of5-10mg/mL GSH.