Study On Color Protection And Brittleness-keeping Process Of Vacuum Freeze-dried Fiddlehead And Its Physic-chemical Characteristics

Fiddlehead, as a traditional export product, has a good reputation of king of mountain vegetables, with unique flavor and smooth taste, which has high edible and medicinal effects. In this paper, the fresh fiddlehead of Hunan is used as raw material, it is known that fiddlehead is usually plucked not long after sprouting, with strong seasonality, while the weather is hot and humid at this time of year, and fiddlehead would turn browning,ageing,inedible easily, which result in serious waste of resources. In this passage, to make full use of such wild resource, the green-maintaining process was discussed, by using different color protection solutions and different concentrations, and by blanching,dipping at normal temperature and vacuum infiltration etc. According to the experiment, the optimum complex liquid for color protection is as follow: zinc glaciate 3.5 mg/L,zinc lactate 50 mg/L,sodium bicarbonate 300 mg/L,sodium sulfite 300 mg/L,zinc acetate 250 mg/L. And the optimum complex liquid for brittleness-keeping agent is:calcium lactate 100 mg/L,calcium chloride 50 mg/L and magnesium chloride 150 mg/L. The optimum proportion of color protection solution and brittleness-keeping agent is 1:2. Processed by the complex liquid above, the presidium aquiline is brilliant in color, tastes clear and melodious, and the natural flavor of fiddlehead is well maintained.The water content of fresh fiddlehead, influenced by the climate, reaches up to 92%, and it's exterior appearance and quality would turn bad about two days after being plucked. To prolong shelf life and maintain exterior appearance, vacuum freeze-drying was applied to dry fiddlehead, and drying parameters was optimized by three factors and three levels response surface methodology. The quadratic regression model that reflects the relations among heating temperature,pressure in hothouse,thickness of material and drying time on the process of fiddlehead vacuum freeze-drying, significance test and analysis of variance proved that this model was reasonable and reliable, with high degree of fitting, could predict the drying time precisely. According to the experiment, the optimum condition for fiddlehead vacuum drying was proved and curtained as follows:freezing temperature 1.5℃/min; finishing temperature-25℃-27℃; freezing time 90 min; shelf board heating temperature, while vacuum drying,42℃; pressure in hothouse 48 Pa; thickness of material 14.5 mm, by which the energy consumption could be cut down effectively, enhancing economic benefits.Comparison and analysis of the physical and chemical characters between freeze-dried and heat-dried fiddlehead, about the difference in rehydration,water activity etc., were made, including the comparison about the nutrient elements and the loss with fresh fiddlehead.Results showed that vacuum freeze-drying could kept the fresh color and structural state, with the flavor and aroma of fiddlehead, while the color turned brown, the tissue became compactness and the aroma became weaker; vacuum freeze-dried fiddlehead was high in drying rate and low in water activity, compared with hot-air drying, so it had high preserving rate; the resorting of vacuum freeze-dried fiddlehead was high in 91.8%, it could maintain the color, aroma, flavor, structure and taste, however the resorting of hot-air dried fiddlehead was only 77% after heating, and only the aroma remained; Compared with hot-air dried fiddlehead, the preserving rate of nutrition components amino acid, VC,VE and carotene of freeze-dried fiddlehead increased by 10%, 63.4%, 61%, 7.7% respectively.