Influence Of Cold Plasma Treatment On Flavor Quality Of Dried Meat Products

Dried pork product is very popular in China.It has a long history and is well received because of its taste,nutrition and portability.Curing is a key processing step of Chinese dried meat product.The traditional methods of curing is performed by rubbing the curing mixture(mainly sodium chloride,nitrate and/or nitrite,sugars and spices)on the surface of meat or by soaking the meat in the brine solution.Nitrosamines and biogenic amines problems will occur during the process of curing and ripening.Cold plasma is considered as a new environmental protection technology because it does not produce residues or toxic molecules.Since plasma can produce reactive substances such as ultraviolet light,electrons,positive and negative ions,atoms,reactive oxygen species(ROS)and reactive nitrogen species(RNS),it is often used to replace heat treatment for food sterilization,preservation and modification.Nitric acid and nitrite can be produced by liquid matrix treated with cold plasma.The plasma activated water(PAW)containing nitric acid and nitrite can be produced by treating water with high voltage electric field plasma,which contains many reactive substances and has been proved with good cold sterilization effect.According to this characteristic,the aims of this study was to investigate the effects of cold plasma treatment on the flavor quality of dried meat products and explore the application of cold plasma as a new technology in dried meat products.Our results will provide theoretical basis and experimental guidance for the development of novel meat products and meat protein products.The main research contents and results are as follows:1.Effect of plasma-activated water as a curing processing on biogenic amines and nitrosamines of dried meat productThe application of dielectric barrier discharge cold plasma(DBD-CP)-treated water as a novel curing process for manufacturing dried meat product was investigated.Samples were treated by direct treatment with output voltages of 50,60 and 70 kV respectively.The PAW was refrigerated for 2 h at 4℃ refrigerator after being prepared,then added NaCl in PAW solution and pure water to made marinated solutions of 6%NaCl.Pork loins were marinated in control or PAW brine at 4℃ for 24 h and then dry-ripened for 15 days to made dried pork loin products.The formation and alteration of nitrosamine and biological amines contents,reactive oxygen species(ROS)and reactive nitrogen species(RNS)of dried pork loin were determined.The results showed that PAW treated for 3 min had the alkaline environment and a higher nitrite content than that of the other treatment time,the ultimate nitrite concentration of 50,60 and 70 kV treatments were 115.6 mg/Kg,158.9 mg/kg and 221.5 mg/kg respectively.OES showed that PAW was rich in ROS and RNS.RNS is critical to the formation of nitrite and nitrate,the nitrite residues of 50,60 and 70 kV treatments were 8.12,10.11 and 15.24 mg/kg,respectively,all values are below 20 mg/kg.PAW could lower the pH under the 6,the lower pH value could lead to the transformation of nitrite into the nitrous acid and NO,maintained the residue of nitrite within the safe range.Under the 50,60 and 70 kV treatments,the a*value of PAW marinated samples were 28%,34%and 42%higher,respectively than control.The analysis of GC-MS/MS also showed that N-nitrosome content beyond the dectection limit.As ROS could limit the growth of microbes so that limited the formation of biogenic amines of samples.With the increase of treatment voltage,all biogenic amines content lowering gradually,especially the cadaverine and spermine.The lowering conten of cadaverine are 8.21%,11.29%and 19.49%,respectively and that of spermine are 9.64%,16.54%and 27.56%.So,conclusion could be draw that PAW cuirng processing is a safe,manipulatable novel proscessing method.2.Effect of plasma-activated water as a curing processing on oxidation and proteolysis of dried meat productStudy the effects of PAW brine on proteolysis,oxidation of dried pork product by analysis of total sulfhydryl groups and carbonyl contents,sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE),free amino acids(FAAs)contents and TEM,TABARS value of samples.The results showed that TBARS value of 60 kV and 70 kV treatments were significantly lower than those of 50kV treatment.Nitrite itself is a good lipid oxidation inhibition stuff,which indicated that high voltage treatment could improve the oxidation stability of meat products and the degree of lipid oxidation of meat products were below the 0.5mg MDA/kg.FAAs results showed that,compared with traditional methods,PAW treated sample had no bad taste.As the increse of treatment voltage,the increas of essential amino acid of 60 and 70 kV treatment were 160.65%and 164.4%,respectively.Moreover,the sulfur-containing amino acids(Cys and Met)in 60 and 70 kV treatments increased significantly,which could promote the production of sulfur-containing volatiles and improved the flavor of products.With the analysis of SDS-PAGE and TEM,the degradation of troponin T and desmin have been found during the high voltage treatment.The attack of ·OH produced during the PAW treatment on peptide chain lead to those degradation,but PAW produced by 50 kV resulted in the assemble of protein.The carbonyl contents of 50,60 and 70 kV increased 0.71,1.52 and 2.37 nmol/mg than control and sulfhydryl content decreased 10.34%,13.79%and 24.14%respectivley,which showed that PAW treatment could lead to protein oxidation by the decreasing content of total sulfhydryl groups.3.Effect of plasma-activated water as a curing processing on volatile compounds of dried meat productThe volatile flavor compounds in different treatment groups were identified by solid phase microextraction(SPME)-gas chromatography-mass spectrometry(GC/MS)combined with electronic nose technology.Combined the principal components analysis(PCA)with load analysis(LOA),the contribution rate of each principal components were quantified to better distinguish the flavors of samples with different treatments.The results showed that the relative resistivity values(G/G0)of S7(sulfide)and S9(aromatic component)were higher than that of other sensors in the determination of sample volatile odor,as the remarkable increase of sulfur-containing amino acid contents lead to the production of sulfur-containing volatile compounds of treatment groups,showed that protein oxidation was crucial to lead the differences of sensory quality of samples.The contribution rate of PCA beyond 85%proved E-nose could differ different flavour of samples effectively,the results of PCA and LOA also showed that it worked well related to the flavour differentiation.The signal intensities of S1,S3 and S5 sensors in 60 kV treatment group were significantly higher than those in other treatment groups,indicating that the intensities of aromatic,alkane and olefin flavor compounds in 60 kV treatment increased significantly.The signal of S 8 and S9 sensors was significantly lower than that of other groups,showed that the content of ethanol and sulfur-compounds decreased.The volatile flavors of different treatment samples were identified by GC/MS,54 kind of volatile compounds were identified which included 10 aldehyde,5 ester,5 alcohol,6 acetone,1 acid and 27 alkane.The results showed that 3-methyl butanol,1-hexanol,1-heptanol,2,3-octanedione and 2,3-hydroxybutanone could only been found in PAW treatments,and 2 ester compounds gained in PAW treatments.Also,the contents of lipid oxidation related volatile compounds(1-octene-3-ol,nonanal,benzaldehyde,2-heptanone and 2-nonone)in PAW treatments were significantly lower than those in control,which was consistent with the previous results.However,the content of hexanal increased,which could be due to the difference in origins of hexanal and MDA,and the different formation rates.The increase of trimethyl butyraldehyde,trimethyl butanol,phenylacetaldehyde and indole in PAW treatments was closely related to the increase of leucine,isoleucine,phenylalanine and tryptophan,respectively.In sensory evaluation,except for the 50kV treatment group,the score of sample color cured with PAW was significantly higher than that of the control,which illustrated that PAW treatment gave the product better curing color.4.Effects of dielectric barrier discharge cold plasma treatment on the structure and functional properties of myofibrillar protein and its correlation with flavorMyofibrillary protein(MP)from dried meat product was directly treated with DBD-CP.The influence of DBD-CP treatment on the structural changes and functional properties of MP were studied.MP were treated with DBD-CP at 0,50,60 and 70 kV for 180 s to monitor the emulsifying property and binding ability with aroma compounds such as 3-methyl-butanal,2-methyl-butanal,nonanal,heptanal and octanal;analyzed microstructure,primary and secondary structure changes,surface hydrophobicity and average particle size of MP using GC-MS,SDS-PAGE,scanning electron microscope(SEM)and FTIR spectroscopy,FTIR spectroscopy revealed that with the increasing treatment voltage,the α-helices structure decreased 20.73%,26.71%and 45.32%,respectively,while the portion of β-sheets increased 7.78%,10.87%and 15.41%,random coils increased 6.50%,19.38%and 28.23%,respectively.The unwinding of the α-helix structure accompanied with the increase of β-sheets content suggested that DBD-CP induced partial unfolding of proteins which exposed the previously buried sites within the proteins.Compared to the control,the EAI of 60 and 70 kV treatments increased 26.67%and 66.67%,respectively;the ESI of them increased 23.12%and 54.21%respectively,which indicated that high voltage level could promote the interaction between MP and oil,also increase the binding ability of MP to lipid flavor compounds.With the increasing treatment intensity,the concentration of free amino acids increased significantly(P<0.05),including hydrophobic amino acids,suggested that DBD-CP treatment could increase the proteolysis of proteins and also could increase the hydrophobicity of protein surface(P<0.05)proved by the increasing of S0-ANS after DBD-CP treatment.But,the hydrophobicity of 50 kV treatment was lower than that of control.SEM analysis showed that 50 kV treatment caused protein refolding and reaggregation,which prevented non-polar amino acids from being exposed to protein surface.The decrease of surface hydrophobicity could reduce the binding sites of aroma compounds and reduce the binding capacity of aldehydes.However,the wrinkle surface produced by high voltage treatment could improve the surface hydrophobicity and enhance binding ability with aroma compounds.The enhancement of MP flavor binding ability can retain the flavor compounds in meat products for a longer time and prevent the loss of volatile compounds.