| Pumpkin?Cucurbita pepo L.?seed production is gradually increasing in China.The development and utilization of pumpkin seed oil attracts more and more attention in recent years.Drying is a vital pretreatment process in the pumpkin seed oil extracting techniques.The drying parameters have an important influence on the functional quality of pumpkin seed oil.The objectives of this study are to analyze the heat and mass transfer in pumpkin seed during hot-air and rotary drying processes,and to investigate the effects of drying processes on the physicochemical properties of pumpkin seed,oil yield and the functional quality of oil.The results of this study can provide certain references and advices for the optimization of oil extracting processes of pumpkin seed and other oil seed.The moisture content of pumpkin seed during hot-air drying?50,60 and 70??and rotary drying?140,150 and 160??processes were recorded and analyzed based on drying tests and computer simulation technique.Drying kinetic models were developed based on the experimental data.The Lewis model and the Page model provided the best goodness of fit for hot-air and rotary drying,respectively.The effective moisture diffusivity ranged from 1.79×10-10-4.13×10-10m/s for hot-air drying and 5.00×10-9-9.34×10-9m/s for rotary drying.The activation energy was 38.37 kJ/mol for hot-air drying and 52.69 kJ/mol for rotary drying.The effects of hot-air and rotary drying processes on the physicochemical properties of pumpkin seed were evaluated.Hot-air dried seed had higher content of crude protein and crude fat than rotary dried seed.The hardness of hot-air dried seed was enhanced with the increase of drying temperature.During rotary drying,the seed hardness and the density were both decreased as the drying temperature raised.Compared with the rotary dried seed,hot-air dried seed were thinner and harder,and had a higher density.With the use of scanning electron microscope?SEM?,compact and intact cellular structures were observed in hot-air dried seed.By contrast,roasted seed presented loosen and porous cellular structures.The cell damaging rate was increased as the temperature raised for both hot-air and rotary drying.Hot-air dried seed resulted in a higher oil yield?47.75%-48.92%?than rotary dried seed?41.67%-46.20%?.The functional quality of pumpkin seed oil made from different drying processes was analyzed.The drying temperature significantly affected the content of bio activators,Oxygen Radical Absorbance Capacity?ORAC?,peroxide value and oil color.Pumpkin seed oil produced at 50??hot-air drying?and 140??rotary drying?had a better quality than those produced at the other tested temperatures.Oil extracted from hot-air dried seed had a higher content of bio activators and lower peroxide value and acid value than that from roasted seed.Oil produced by hot-air drying and mechanical pressing process had a great potential for promotion and use because of its high nutritive value,functionality and antioxidant ability.The storage stability of pumpkin seed oil was studied based on the storage tests?20 and 30?,with and without light?and kinetic analysis.The contents of total phenolic,phenolic profile and color in hot-air dried seed oil and rotary dried seed oil were not significantly different regardless of the storage conditions.The content of Vitamin E and carotenoid,and the ORAC values of both kinds of pumpkin seed oils were decreased as the storage time extended,especially when the oils were stored at 30? with light on.The changes of vitamin E,carotenoid and ORAC belong to energy-requiring reactions because their activation energy were greater than zero.The higher activation energy at low storage temperature?20 °C?without light indicated that the quality of pumpkin seed oil was more stable under these storage conditions.Oil made from hot-air dried seed had a better storage stability compared with oil from roasted seed. |
PDF Full Text Request