Changes In The Characteristics And Quality Of Squid Fillets Dried By Far Infrared Radiation Assisted Heat Pump

This thesis research investigated the effect of different far infraredradiation intensities on the moisture migration, color kinetics, proximatecompositions, protein quality, thermal and mechanical characters,microstructure and rehydration of squid fillets during far infrared radiation(FIR)-assisted heat pump drying (HPD).Low field nuclear magnetic resonance (NMR) was used to analyzerelaxation time (T2) of different water states in squid fillets. The resultsshowed that the immobilized water (T23) is significantly higher during thedrying process whereas bound water, lipid and their corresponding T21andT22decreased. Moreover, the attenuation degree of immobilized water (T23)was the greatest when treated by HP+8FIR, followed by HP+5FIR andHP+1FIR, while that of HP alone was the smallest.The results on the protein quality value showed that glutamic acid,aspartic acid, lysine, leucine and arginine are the dominant amino acids inall squid fillet samples. The total contents of essential amino acid and non-essential amino acid, total soluble nitrogen, non-protein nitrogen,essential amino acid index, estimated protein efficiency ratio andbiological value were not significantly different among all squid samples.Both fresh and dried fillets were at low levels in total volatile basicnitrogen (TVB-N) and fatty acid oxidation (TBA). The cathepsins B and Lactivity decreased along with increased power supplied to the FIR heater.Drying increased the denaturation enthalpy (ΔH) and temperature (Tmax) ofactin and myosin, but reduced the cathepsins B and L activity comparedwith the fresh squid. L*value of the fillets decreased while a*, b*and△Evalues increased during drying process, which showed acceleration whenFIR power rising. L*value followed the exponential reaction pattern,while△E followed the logarithmic reaction pattern, and both a*and b*followed the line pattern. Electrophoretic profiles showed thedisappearance of6bands (24,57,93,105,121and172kDa), while4bands (30,37,102and154kDa) were appeared. Dried squid muscleexhibited dense and firm microstructure, loss of cell structure and texture,in which the high FIR intensity resulted in more compact and coherentstructure based on SEM and TEM analysis.NMR images illustrated that water penetrates from the periphery tothe central region during rehydration. After60min of rehydration, the HPD samples had high NMR signal intensity, followed by HPD+1FIR,HPD+5FIR and HPD+8FIR. Peleg model was the most suitable fordescribing the rehydration process at all conditions based on theexperimental data. HPD samples presented the highest rehydration ratioand ability, while the lowest rehydration ratio and capacity was found inHPD+8FIR samples.