| Pistachio(Pistacia vera L.), walnut, almond and hazelnut are world’s most four famous tree nuts. Pistachio kernels are rich in fat, protein, minerals, vitamins and phytochemicals, with good health care and pharmacological effects. With the consumption of pistachio increases year by year, the price of pistahio increases steadily, which is belong to a precious nut in China. However, the quality loss during storage caused by insect infestation and low value-added products with simple type caused by lack of deep processing has seriously hindered the development of nut industry in China. Therefore, to reduce the quality loss induced by stored-product pests during storage, improve the levels of deep processing, and augment product variety became major problems that need to be studied and solved in nut industry.Kerman pistachio which is the major consumption variety was chosen as the major product to develop radio frequency(RF) disinfestation technology. Then a comprehensive and systematic research on utilization of pistachio nut was carried out. The detailed research contents are as follows:(1) Dielectric properties of the pistachio kernels were measured using an open-ended coaxial-line probe technique at different temperatures, moisture contents and salt levels.(2) A single batch mode RF treatment protocol for insect control in pistachios was developed based on the thermal death kinetics of the targeted insects, optimizing the suitable heating rates, cooling method and heating uniformity, and evaluating the effect of RF disinfestations on the storage stability of pistachios.(3) A continuous RF heating system was used to disinfest pistachios, investigate the heating uniformity, confirm the mortality of insects, and estimate the heating efficiency and throughput of the RF process.(4) Three types of pistachio kernel oil(PKO) were prepared by cold-pressing from raw(RPKO), conventional(CRPKO), and microwave(MRPKO) roasted pistachio kernels. Physicochemical properties, volatile compounds and oxidative stability of extracted oils were determined.(5) Defatted pistachio kernel flour(DPKF) was prepared by cold pressing(partially defatted) and pre-press-solvent extraction(totally defatted) methods both using raw and roasted kernels. The nutritional value, functional properties, bioactivity and microstructure of DPKF were determined.(6) The equilibrium moisture content(EMC) of full fat pistachio kernel flour(FPKF), partially defatted pistachio kernel flour(PDPKF) and totally defatted pistachio kernel flour(TDPKF) was determined using the static gravimetric method. Regression tool of the software SPSS was used to evaluate the fitness of isotherm models for sorption data. The isosteric heats of sorption and monolayer moisture contents were calculated. The main results were described as follows.(1) Both dielectric constant and loss factor of the pistachio kernels decreased with increasing frequency. The rate of decrease was greater at higher moisture levels(>15 %) and lower frequency(<100 MHz). Dielectric loss factor of pistachio kernel samples increased with increasing salty levels, but dielectric constants were not significantly affected. The loss factor of the pistachio kernels was significantly lower than that of insect pests over the RF range, which maybe induced the potential differential heating between pistachios and insects. The largest penetration depth at 27 MHz RF heating was 24 cm, but for 915 MHz MW heating was only 4-6 cm. The large penetration depth indicated that RF heating might be more practical in developing industrial-scale disinfestation treatment for pistachio nuts.(2) Only about 5.5 min were needed to raise the centre temperature of 1.8 kg in-shell and 2.0 kg shelled pistachios to reach 55 °C when using a pilot-scale 27.12 MHz 6 k W RF system in a single batch mode process. RF heating uniformity in both types of pistachios was improved by adding forced hot air, sample movements on the conveyor and a single mixing in the middle of the treatment time. RF treated samples were not significantly different from control samples in quality and storage stability. The RF heating uniformity in continuous process was better than single batch mode process. The continuous RF treatment could cause 100 % mortality of fifth-instar Indianmeal moth in pistachios, and the average energy efficiency of RF system was estimated to be 70 % when heating pistachios at 264.3 kg/h.(3) Both conventional and microwave roasting methods caused an increase in total phenolics content(TPC), antioxidant capacity(AC), peroxide value(PV) and a decrease in levels of total chlorophylls in cold-pressed PKO. Roasting also led to a clear decrease in L* and b* values and increase in a* value. The thermal transition temperatures of the unroasted raw pistachio kernel oil(URPKO) were-47.15 and-19.85 °C for crystallization, and-13.11 and 3.11 °C for melting. However, the thermal transition points, crystallization and melting curves of PKO were not changed significantly after roasting. Roasting treatments can cause pyrazine compounds appeared in PKO, especially for 2-ethyl-5-methyl-pyrazine, 3-ethyl-2,5-dimethyl-pyrazine, and 3,5-diethyl-2-methyl-pyrazine probably play a major role in roasted PKO aromas. Cold-pressed PKO was both highly susceptible to photo-oxidative and auto-oxidation degradation, the oil storage in containers with light-barrier properties, together with the addition of the 0.01 %(w/w) tert-butyl hydroquinone(TBHQ) or 0.02 % ascorbyl palmitate(AP) or 0.07 % rosemary extract(RME), could maintain PKO quality at least up to four months under room temperature condition.(4) The totally defatted pistachio kernel flour(PKF) was found to have higher a* and lower b* values than those corresponding to the full fat and partially defatted PKF. Although the flour obtained from roasted kernels showed no significant differences with unroasted ones in macronutrient compositions, the color was darker than others and the amino acid contents was reduced significantly. Furthermore, the functional properties of PKF did not change significantly after roasting. However, the defatted flours presented significantly higher water adsorption capacity(WAC), oil adsorption capacity(OHC), emulsifying capacity(EC), emulsifying stability(ES), and foaming capacity(FC) than the flours obtained from full fat kernels, especially for totally defatted PKF. The TPC and total flavonoids content(TFC) were highest in partially defatted roasted pistachio kernel flour(PDRPKF), corresponding to 792 mg GAE/100 g and 280.30 mg RE/100 g flour(d.b.), respectively. Also, the PDRPKF showed the highest AC, corresponding to 78.12 and 130.51 μmol Trolox/g flour(d.b.) for DPPH· radical scavenging power and ferric reducing antioxidant power, respectively. The starch granules in PKF were oval in shape with smooth surfaces and approximately 5-15 μm in diameter. Partially defatted flour exhibited large amounts of continuous structure with smooth surfaces surrounding the starch granules and protein clusters compared with a little present in totally defatted flour, which were mainly characterized by the presence of spongy-aspect particles of varied sizes.(5) For full-fat unroasted(FPKF), partially defatted unroasted(PDPKF) and totally defatted unroasted(TDPKF) pistachio kernel flour, the obtained sorption isotherms were of typeⅡ according to brunauer-emmett-teller(BET) classification and its hysteresis cycles can be classified like Type H3 according to International Union of Pure and Applied Chemistry(IUPAC) classification. The EMC values of the TDPKF were higher than those of the PDPKF, and in the PDPKF was higher than those of FPKF at any temperature and aw studied. Smith model gives the best fit to sorption data of FPKF and that for PDPKF and TDPKF, Halsey model is the most appropriate model for fitting well throughout the entire range of aw and temperature. The monolayer moisture content MMC(g/100 g d.b.) calculated by BET model was 2.433 to 3.404 for FPKF, 3.788 to 4.823 for PDPKF, and 4.987 to 6.687 for TDPKF at 15 to 35 °C. At 25 °C and MCs of 2 to 40 %(d.b.), the Qst varied between 74.67 to 44.76, 99.44 to 44.75 and 133.28 to 44.80 k J/mol for FPKF, PDPKF and TDPKF, respectively. It is also worth noticing at the lower MCs between adsorption and desorption processes for all three types of PKF, and the Qst for desorption process was generally greater than that for the adsorption process. |
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