Study On Near-Freezing Point Storage Technology And Basis For Comprehensive Utilization Of Chilgoza Pine Nut

Chilgoza pine nut (Pinus gerardiana W.) is the edible seed of Himalayan bungeana. It contains rich protein、oil、vitamins、minerals and dietary fiber, and is favored by people for its special amino acids composition and high content of unsaturated fatty acids. The consumption of chilgoza pine nut has been increasing year by year.As pine nut contains high amount of fats and unsaturated fatty acids it is prone to hydrolytic and oxidative rancidity which led to losses of nutritional and sensory quality in storage. Therefore, the reduction of the loss induced by fat rancidity during storage and extention of the shelf-life of pine nut have been paid much attention by researchers as well as business operators.In our project, Chilgoza pine nut was chosen as the major subject to develop near-freezing point storage technology. Then a comprehensive and systematic research on utilization of pine nut, including protein isolatess protein hydrolysates、oil was carried out. The objective of this study was to provide basis for exploitation of Chilgoza pine nut. The major sudy topics include:(1) Changes in quality and sensory attributes of moisture conditioned Chilgoza pine nut under near-freezing point storage;(2) Ultrastructure and lipid quality changes in low-moisture Chilgoza pine nut during near-freezing point storage;(3) Functional properties of Chilgoza pine nut protein prepared by ultrasonic-assisted ultrafiltration extraction process;(4) Functional properties and bioactivities of Chilgoza pine nut protein isolates and its enzymatic hydrolysates;(5) Influence of kernel roasting on bioactive components and oxidative stability of Chilgoza pine nut oil.The main research findings were summarized as follows:1. Free fatty acid content and peroxide value of the pine nuts increased in the whole12months storage, while sensory quality decreased. Low-moisture nuts had lower respiration, free fatty acid content and peroxide value. Nuts stored at-3℃had less visible mold infection and browning percentage than at-1℃. Low-moisture treatment exerted a slight negative effect on texture, but had significant preservative effects on color, odor and taste during storage. Integration of low-moisture conditioning and near-freezing point storage technology can be a promising non-chemical way for maintaining the postharvest quality and extending shelf-life of pine nuts. 2. Low-moisture treatment helped in maintaining cell integrity and improving the storage stability. The hydrolysis of lipids was delayed in low-moisture pine nuts, resulted a significant inhibition of free fatty acids accumulation in pine nuts. Low-moisture pine nuts also demonstrated lower peroxide value and TBARS value as compared with control pine nuts. Transmission electron microscopy (TEM) revealed that low-moisture treatment maintained the integrity of the cell, deferring the degradation of plasmalemma and protected the internal lipid droplet. Low-moisture treatment better preserved antioxidant components including total phenolics and Vitamin E, and reduced the activities of lipase and lipoxygenase in pine nuts, retarded the senescence and the deterioration of lipid quality.3. The extraction efficiency and functional properties of pine nut protein were significantly improved by the ultrasonic-assisted extraction and ultrafiltration method. The optimum extraction conditions were as follows:ultrasonic temperature43℃, pH value9, ultrasonic power400W, ultrasonic treatment time38min, solid/liquid ratio1:35. The extraction efficiency was77.94%under the optimized extraction conditions. Functional properties (bulk density, emulsifying capacity, foaming capacity and foam stability) of pine nut protein obtained by ultrafiltration were found to be better than traditionally extracted pine nut protein and some of other plant proteins. The results of this study indicated pine nut protein as an available plant protein source could be widely applied in food industry.4. The solubility of PPH significantly increased (p<0.05) with the increase of the DH, while the foaming capacity of PPH was only improved at a low DH. However, enzymatic hydrolysis reduced the emulsifying capacity of PPH. The DPPH radical scavenging and inhibition of linoleic acid oxidation activities of PPH were significantly improved by a low DH (5%) compared with those of PPH with a higher DH and the original PPI (p<0.05). The reducing power of PPH at all DH decreased in comparison to that of the original PPI. The ACE inhibitory activity of PPH increased (p<0.05) with the DH. These results revealed that a low degree of enzymatic hydrolysis was appropriate to obtain PPH with improved functional properties and good antioxidant activities, while a high degree of hydrolysis was essential to obtain highly potent ACE inhibitory peptides from PPI, the control of the DH may be an effective strategy to modify specific functional and bioactive properties of PPH.5. Oil extracted from kernels roasted for30min demonstrated the highest oxidative stability. The browning index which indicates extent of Maillard reaction significantly (p<0.05) increased with roasting. Compared to samples from unroasted kernels, roasting was found to cause an increase in total phenolics and a reduction in the level of total tocopherols. Total carotenoids and total chlorophylls were also reduced by roasting and almost completely diminished in heaver roasting conditions. The highest radical scavenging capacity was detected in oil sample from kernels roasted for30min. The improvement of oxidative stability and antioxidant capacity is possibly resulted from the combined action of the neo-formed Maillard reaction products, increased total phenolics and other remaining bioactive components.