Effect Of High Pressure Treatment On Aromatic Amino Acids And Dielectric Properties Of Cheddar Cheese

The influences of hydristatic high pressure treat ments and pressure holding times on the physical and chemical properties, TPA properties, dielectric properties, ripening indexes and contents of amonia acids were tested. The hydrostatic high pressures exited on the cheese samples were 200MPa、400MPa、600MPa respectively, and the pressure holding times were 5min and 15min respectively for each pressure. The cheese samples that untreated by hydrostatic high pressure was taken as a control group. The ripening temperature of all the cheese samples was 6℃. In the mean time, the relationship between the dielectric property and content of amonia acids was analysised. The results showed as following.(1) With the extension of the ripening time of the cheese samples, the contents of phenylalanine, tyrosine and tryptophan had a rising trend before 30d and that of all the samples showed a downward trend after 30d, The variance analysis showed that the effect of hydrostatic high pressure treatments and pressure holding time on the contents changes of phenylalanine, tyrosine and tryptophan was not evident by comparing with the control group.(2) For the cheese samples on the ripening times of 7d,30d and 90d, the relative dielectric constants of the hydrostatic pressure treatment group were significantly higher that of the control group and the relative dielectric constant for the 400MPa treatment sample were higher than that of 200MPa and 600MPa treatments. The dielectric loss factors for both control group and the treatment group decreased with the extension of the ripening time. High pressure treatment had no significant effect on the dielectric loss factor. Conductivity was not dependent on high pressure treatment.(3) Range analysis showed that the influence order of ripening time, hydrostatic high pressure treatment and pressure holding time on dielectric properties was that the ripening time> hydrostatic high pressure treatment pressure> holding time.(4) Compared with the control group, the hardness, cohesiveness and elasticity of the samples were decreased for group of high pressure treatment.(5) The ripening indexes (12% TCA-SN/TN) of the control group and the treatment group increased during ripening. The Increase amplitude of the ripening indexes were steep before 30d and the increase amplitude of the ripening indexes were gentle during 30d-90d. The ripening index (12% TCA-SN/TN) of the cheese samples for the hydrostatic high pressure treatment group was higher than that of control group.(6) With the extension of cheese ripening period, fat content in dry matter (FDM) for the groups both control and treatment showed a decreasing trend. During the ripening period, the lowest fat reduction rate of the treatment group was 7.5%, the highest was 15.07%. The fat reduction rate of the hydrostatic high pressure treatment group was higher than that 6.23% for the control group.(7) The relationship between the relative dielectric constant and the content of aromatic amino acid could be expressed by the polynomial equation Y=A*X4+B*X3+ C* X2+D*X+E, the correlation coefficient was above 0.6.