| In this paper, the natural spoilage bacteria from crab (Portunus trituberculatus)and squid (Dosidicus gigas) were used as indicative strains. Three natural seasonings,including onion, ginger and garlic, as well as one kind of vinegar without addition ofpreservative, were used as materials to determine their antibacterial activities, andthereafter to prepare one kind of seasoning antibacterial agent. This agent caneffectively prolong the storage period for crab and squid at4℃. The main researchcontents are included as following:(1) Antibacterial activity of natural seasonings onspoilage bacteria from crab and squid;(2) Optimization of the antibacterial formula ofnatural seasonings;(3) Preservative activity of natural antibacterial agents on crab andsquid;(4) Microencapsulation of natural flavoring antibacterial agent.Results showed that the water-soluble and alcohol-soluble garlic extracts andvinegar displayed strong antibacterial activities on crab and squid spoilage bacteria.The alcohol-soluble ginger extracts demonstrated antibacterial activity. While theinhibiting activity of onion extracts including water-soluble and alcohol-soluble wasnot obviously observed. The minimum bactericidal concentration (MBC) andminimum inhibitory concentration (MIC) of garlic water-soluble extracts on crab andsquid spoilage bacteria were the raw extracts and4fold dilutions of raw ones,respectively. By comparison, the MBC and MIC of vinegar on crab and squidspoilage bacteria were16fold and32fold dilutions, respectively. In addition, theantibacterial activity of garlic water-soluble extracts was decreased with increasedheating temperature (ranged from60to100℃) and prolonged heating time (rangedfrom10to40min). However, the inhibition zone diameter of vinegar wassignificantly increased when heated at over70℃for more than30min. The pHvalues of heated vinegar were in the range of3.60-3.80, whereas the contents ofreduce sugar and free amino acids were increased for the enhanced antibacterialactivity of heated vinegar.Considering the antibacterial activity, flavoring and potential application for thenatural seasonings, garlic and ginger water-soluble extracts and vinegar were used to optimize the compound formula of antibacterial agents. Results showed thecompound solution showed different antibacterial activities. When the relative contentof vinegar was25.0-50.0%and ginger and garlic water-soluble extracts was20.0-50.0%, the antibacterial inhibition zone of compound solution on crab spoilagebacteria ranged from19.4to22.3mm. By comparison, the antibacterial inhibitionzone of compound solution on squid spoilage bacteria ranged from18.7to20.1mm,which had the relative contents of16.6%to57.3%for vinegar,14.3%to40.0%forginger water-soluble extract and20.0%to66.6%for garlic water-soluble extract. Theoptimized formula of antibacterial agent inhibiting crab spoilage bacteria wascomposed of50%vinegar,14%ginger water-soluble extract and20%garlicwater-soluble extract, respectively. The antibacterial inhibiting zone of the optimizedantibacterial compound solution was25.3mm, which was close to the predictedinhibiting zone of24.9mm. Similarly, the optimized formula of antibacterial agent forsquid spoilage bacteria was50%vinegar,14%ginger water-soluble extract and29.9%garlic water-soluble extract using the response surface method. The actual inhibitingzone of optimized compound solution on squid spoilage bacteria was23.6mm, whichwas slightly higher than the predicted inhibiting zone of22.1mm.After immersed in the natural antibacterial seasoning solutions at20℃for30min, the diced or sliced crab or squid were packaged at atmospheric and stored at4℃.The property of sensory valuation, total numbers of bacteria colony and changes ofTVB-N values and color of the control and treated samples were determined everythree days. Results showed that the control samples of crab were spoilage at the timeof4days. The meats were foul, without luster and elasticity. The total numbers ofbacteria colony was5.57×105CFU/g exceeding the standard. In addition, the TVB-Nvalue was26.35mg/100g close to the critical value of30mg/100g. In contrast, thetreated crab samples with natural seasonings demonstrated no significant sensoryproperty. The total numbers of bacteria colony was4.65×105CFU/g. The TVB-Nvalue was30.93mg/100g, which was slightly higher than the critical value ofstandard. Furthermore, the sensory changes of squid were similar to those of crab samples after stored at4℃for6days. The control squid samples had foul smells andover standard total numbers of bacteria colony (>105CFU/g) and TVB-N values (>30mg/100g). By comparison, the squid samples treated with natural seasonings had nosignificant spoilage smells, whereas the total numbers of bacteria colony and TVB-Nvalues were close to the critical values of105CFU/g and30mg/100g, respectively, atthe time of16days. Moreover, the values of color changed dramatically. So, thesuitable storage periods for diced or sliced crab or squid treated with naturalantibacterial seasonings were prolonged to4days and10days, respectively,compared with their control samples.Beta cyclodextrin and sodium alginate were used to microencapsule theantibacterial seasoning agents. Results displayed that the β-cyclodextrin entrapmentrate was31.7%for antibacterial seasoning agents with inhibition of crab spoilagebacteria. This was slightly higher than that for inhibition of squid spoilage bacteria(28.6%). In addition, the best spherical orifice granulation of the microencapsule wasobtained when the concentrations of sodium alginate and CaCl2were30g/L and20g/L, respectively. The entrapment rates for antibacterial seasonings with inhibition ofcrab and squid spoilage bacteria were68.47%and63.57%, respectively. Theinhibiting zones of β-cyclodextrin microencapsules with concentration of1g/mLwere26.4mm for crab spoilage bacteria and25.3mm for squid spoilage bacteria. Bycomparison, the antibacterial activity of sodium alginate microencapsule was weakerthan that of β-cyclodextrin microencapsule. At the concentration of1g/mL, theinhibiting zones were11.9mm for crab spoilage bacteria and15.3mm for squidspoilage bacteria. |
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