Functional Properties Of Scallop Patinopecten Yessoensis Gonad Hydrolysate And Its Derivatives

In recent years, the amount of processed scallop products increased with the enlargementof coastal acquculture in China. During the processing of adductor muscle product, a largequantity of byproducts such as shells, mid-gut gland, mantle lobe, gonad （ovary and testis）,accounting for about70%of the scallop body, are produced and underutilized. Scallop gonadcontained protein at a high level, which can be used as good resources for preparation ofprotein hydrolysate or bioactive peptides.Taking scallop Patinopecten yessoensis gonad as research object, this dissertationassayed the chemical composition of scallop Patinopecten yessoensis gonad （male and female,respectively）, and a pilot study on hydrolysis effects and functional properties of proteinhydrolysate derived from scallop Patinopecten yessoensis gonad （male and female,respectively） was conducted. On one hand, antioxidant activity and functional properties ofscallop Patinopecten yessoensis gonad hydrolysates were investigated, and antioxidantpeptides was also isolated and identified from the gonad hydrolysate. On the other hand, thederivatives of Patinopecten yessoensis gonad hydrolysates through modification of maillardreaction and calcium chelating were prepared and its functional characterizations wereinvestigated. The main research contents and results were as follows:（1） The proximate composition indicated that the crude protein contents （on dry basis） ofscallop Patinopecten yessoensis gonad were62.89±0.87%（female gonad） and81.66±0.03%（male gonad）, respectively. The scallop Patinopecten yessoensis gonad homogenates atprotein concentration of4%were treated with the denaturated（100℃,10min） andnon-denaturated （control） groups, then subjected to enzymatic hydrolysis with commercialneutrase at50℃for180min, respectively. After this, scallop female gonad hydrolysates（SFGHs） and male gonad hydrolysates （SMGHs） were obtained. The results showed thatscallop female gonad（SFG） can be effectively hydrolyzed by neutrase, while scallop malegonad（SMG） was insensitive to neutrase, for the SMGHs exhibited gelation-like properties.The yield of peptides and degree of hydrolysis were higher than control for SFG and SMGafter neutrase hydrolysis by the denaturing pretreatment. Compared with control, the yield of peptides and degree of hydrolysis of SFG after neutrase hydrolysis were increased by94.78%and36.16%, respectively, by denaturing treatment. SFGHs were separated by Sephadex G-25gel filtration chromatography, and the results suggested that the fractions in SFGHs wereconcentrated by denaturing treatment, and with reducing power. The molecular massdistribution of SFGHs with denaturing pretreatment ranged from250to5000Da, accountingfor74.78%of the total, by HPLC. Therefore, SFG could be effectively hydrolyzed usingneutrase in combination with denaturing treatment, and peptides with antioxidant activitycould be isolated through SFGHs.（2） As for the gelation-like protein hydrolysate from neutrase-hydrolyzed scallop malegonad （SMGHs）, the functional properties of SMGHs with different degree of hydrolysis （DH）were investigated. The results showed that hydrolysis with neutrase improved the gelationproperty, solubility, water holding capacity （WHC）, oil holding capacity （OHC） and surfacehydrophobicity （SH）, but not foaming capacity （FC） of SMG. The SMGHs at high DH（11.86%） showed better gelation property and solubility than that at low DH （4.94⁷.53%）.However, the maximum values of WHC, OHC and SH of SMGHs were found at DH of4.94%, significantly higher than （p<0.05） or equivalent to （p>0.05） that of soy protein isolate（SPI） for WHC and OHC. Emulsifying capacity of SMGH is independent of DH, butrestricted by pH environment. The emulsifying activity index （EAI） of all SMGH wassignificantly higher than that of SPI in pH5（p<0.05）, and slightly higher than or equivalent tothat of SPI in pH7. Meanwhile, SMG and SMGHs were abundant in glycine, lysine, alanine,glutamic acid and aspartic acid, containing all the essential amino acids （41.63%⁴2.90%ofthe total amino acids）. These results imply that SMGHs might be utilized as multifunctionaland nutritive ingredients in food industry.（3） SMGHs chiefly consisted of peptides both below1,000Da （46.86%） and above10,000Da （30.30%）, and showed a porous, three-dimensional network observed by scanningelectron microscopy. The gelation properties of SMGHs were studied by texture analyzer, andcompared with several commercial hydrocolloids. The results showed that SMGHs exhibitedfirmness of40.49±1.96g, consistency of479.02±37.04g·sec and cohesiveness of23.69±1.92g, which were similar with that of1.0%¹.5%guar gum,1.5%carrageenan,1.0%².0%xanthan gum and0.5%¹.5%gelatin. These results suggest that the fine gelation properties ofSMGH could be used as replacement of guar, gelatin, xanthan gum and carrageenan undercertain conditions, which may act as thickening and gelation agents in food systems.（4） To further understand the gelation mechanism of SMGHs, we investigated the effectof various chemicals on molecular forces of the gel network of SMGHs, by monitoringchanges of gel properties. The results showed that addition of urea, and propylene glycol （PG） decreased the gel strength of SMGHs with the increase of concentration, and only a veryweak gelation was observed when the concentration of urea reached8M. The overall gelproperties of SMGHs were improved in the presence of0.3M NaCl, KCl, CH₃COONa andNaSCN （p<0.05）. However, elevated salt concentration led to decreased gel properties ofSMGHs, especially the inhibiting effect of NaSCN at3M. In addition, inclusion ofdithiothreitol （DTT）,2-mercaptoethanol （2-ME）, and N-ethylmaleimide （NEM） alsodiminished the gel properties at high concentration （p<0.05）, but not severely, and theiraddition did not change the gelation-like profiles of SMGHs. These results suggest that the gelnetwork of SMGHs was primarily maintained by hydrophobic and electrostatic interactions.（5） Scallop Patinopecten yessoensis female gonad hydrolysates （SFGHs） possessed highantioxidant activity. The IC₅₀value for DPPH radical scavenging activity was9.44mg/mL,IC₅₀value for Fe²⁺-chelating activity was0.94mg/mL and AC_0.5value for reducing powerwas5.88mg/mL. SFGHs was fractionated into six fractions by Sephadex G-25gel filtrationchromatography, Number4（F4） fraction exhibited highest DPPH radical scavenging activity.The F4fraction was analyzed by mass spectrography, two oligopeptides were identified asHis-Met-Ser-Tyr （P1） and Pro-Glu-Ala-Ser-Tyr （P2）. After synthesis, both P1and P2showedcertain dose-DPPH radical scavenging activity relationships（30mM:54.03±3.95%and50.27±1.36%, respectively）, but weaker than contro（20mM BHA）. Besides, both P1and P2exibited strong protective effects against hydroxyl radical induced DNA oxidative damage.（6） Antioxidant activity of maillard reaction products （MRPs） of scallop Patinopectenyessoensis female gonad hydrolysate（SFGHs）-sugar model system were investigated. Theresults showed that the optimum conditions for SFGHs maillard reaction were ribose, pH8.0,and peptide to sugar mass ratio1:2, reaction time4⁶h, temperature80¹00℃. The MRPswere prepared under these conditions at95℃. The IC₅₀value of SFGHs-MRPs for DPPHradical scavenging activity was49.55μg/mL, and The AC_0.5for reducing power was34.34μg/mL, which were190.51and171.23times as for SFGHs, respectively. SFGHs-MRPs （32μg/mL or above） also showed good protective effect against hydroxyl radical induced DNAoxidative damage.During the process of SFGHs-ribose maillard reaction, the pH value of the model systemdeclined, and pH reduction was more obvious when the temperature was higher or thereaction time was longer. The UV absorbance, browning extent, fluorescence intensity, andantioxidant activity of the system were growing. The increasing seemed obvious when thetemperature was higher or the reaction time was longer. Correlation analysis showed thatnegative correlation between UV absorbance, browning extent, fluorescence intensity, DPPHradical scavenging activity, and reducing power of the system against pH were observed, while the correlation of other indexes were significantly positive（p<0.01）.（7） In order to optimize the preparation conditions of scallop （Patinopecten yessoensis）gonad hydrolysate-Ca²⁺complex, on the basis of single factor experiments, a quadratic centralrotary combination design of response surface methodology was used to analyze the influenceof pH, time, temperature, and mass ratio of peptide to calcium on the yield of peptide-Ca²⁺complex. The results showed that the optimum parameters for peptide-Ca²⁺chelating were pH8.0,22min,64.8℃, and peptide to calcium ratio of3.4:1. Under these conditions, thepredicted yield was6.75%, the actual yield was6.81%, and the complex contained6.67±0.11%nitrogen and9.75±0.17%calcium. Infrared spectroscopic study showed that bothamino and carboxyl groups are involved in the complex. Calcium dialyzability of the complexafter in vitro digestion was41.86±2.33%, but showed no difference with control （p>0.05）.Therefore, scallop （Patinopecten yessoensis） gonad hydrolysate-Ca²⁺complex might havegood calcium bioavailability.