Study of effect Rosmarinus officinalis oil and nisin on the growth of Streptococcus iniae in lab conditions and fillets of rainbow trout (Oncorhynchus mykiss)

Fish are an important part of a healthy diet since they contain high quality protein,but typically present a low fat percent when compared to other meats. Fish is anextremely perishable food commodity. On the other hand, food borne diseases arestill a major problem in the world, even in well-developed countries. Theincreasing incidence of food borne diseases coupled with the resultant social andeconomic implications means there is a constant striving to produce safer food andto develop new antimicrobial agents concerns over the safety of some chemicalpreservatives and negative consumer reactions to preservatives they perceive aschemical and artificial, have prompted on increased interest in more ‘‘naturalgreen’’alternatives for the maintenance or extension of product shelf-life.Particular interest has focused on the potential applications of plant essential oils.However, to establish the usefulness of natural antimicrobial preservatives, theymust be evaluated alone and in combination with other preservation factors todetermine whether there are synergistic effects and multiple hurdles can be devised.In this study, were evaluated the effects of different concentrations of Rosmarinusofficinalis and nisin and storage time (15 days) on growth of Streptococcus iniaeGQ850377 in a lab conditions and a food model system (fillets of rainbow trout) in4 and 8 °C. In addition, we also studied multi factorial effects of four differentconcentration of rosemary, three different concentrations of nisin, two differentlevels of pH in 3 temperature 4,15 and 37 °C on log% of S.iniae during 43 days inBHI broth.The results on growth of S. iniae were evaluated using SPSS 20.0 statisticalsoftware and analyzed the logarithm of total count of the bacterial by Tukey Test.Results were considered statistically significant when P<0.05.MIC and MBC values of rosemary and nisin were 0.03, 0.075 % and 5, 40 μg/mL,respectively. The growth of S. iniae was effected significantly (P<0.05) byrosemary and nisin and also combination of rosemary and nisin in 4 and 8 °C.Samples treated with 0.135 and 0.405 % of rosemary showed a significant decreaseon the growth of the bacteria compared with control sample(P<0.05). The most١٤٦inhibitory effects were seen in samples treated with 0.135 and 0.405% of rosemaryuntil 9 days after storage.Also, the synergism effects of rosemary and nisin on the growth rate of bacteriawas significant (P<0.05) compared with untreated samples and samples treatedwith the rosemary or nisin, only. Synergistic effects was observed at concentrationof 0.405% rosemary and 0.75 μg/mL nisin in both temprature.Results of this study showed that different concentration of rosemary a significantinhibitory effect (P<0.05) on log% of S. iniae, in BHI broth in pH 5.5 and 7 in 4,15and 37 °C during 43 days.In concentration of 0% rosemary (control) in pH 5.5 and 7 and 37°C, log% were1.099 and 3.15, whereas in concentration of 0.015% rosemary were -4/241 and1.454, respectively.The use of essential oils may improve food safety and overall microbial quality. Ifessential oils were to be more widely applied as antibacterials in foods, theorganoleptic impact would be important. In addition, it is recommended to applyessential oils or their compounds as part of a hurdle system and to use it as anantimicrobial component along with other preservation techniques. Thus essentialof R. officinalis with high antibacterial activity selected in this study could be apotential source for inhibitory substances against some food-borne pathogens andthey may be candidates for using in foods or food-processing systems.

Bibliographic Details

Main Author:	Roomiani, Laleh
Format:	thesis biblioteca
Language:	Persian
Published:	Islamic Azad University, Science and Research Branch, Tehran, Fisheries 2012
Subjects:	Aquaculture, Fisheries,
Online Access:	http://hdl.handle.net/1834/34407
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