| Ginger (Zingiber officinale Rose.) is one of the "Medicinal and Edible" plants, and rich in nutrients and medicinal composition.Because of its tender skin, high moisture content, short harvest time, the quality of baby ginger declines quickly, this not only affects its processing and utilization seriously, but also affects the development of the industrialization of the production. Low temperature freezing storage is a kind of storage method which can maintain the quality of fruits and vegetables for a long time, and has been widely used in fruit and vegetable industry. By taking the baby ginger from Leshan as raw material, the enzymatic characteristics of polyphenol oxidase (PPO), effect of different color protecting agent on the color of baby ginger, effect of different blanching methods on baby ginger’s physical and chemical quality, the activity of PPO and POD, the freezing law of baby ginger by different freezing temperatures, Quality change rule of baby ginger under -20 ℃ frozen storage condition were studied, the main results of this study were as fellows:Enzymatic characterization of polyphenol oxidase (PPO) from baby ginger was determined using catechol as substrate.The optimal pH and temperature for the enzymatic oxidation were 7.0 and 40 ℃, respectively. The reaction kinetic for PPO-catalyzed browning was in accord with Michaelis-Menten equation, where the Michaelis constant Km and the maximum velocity value Vmax were 14.26 mmol/L and 434.78 U/min, respectively. Thermal inactivation between 65 and 90 ℃ was observed to be biphasic with activation energy of Ea=75.9 kJ/mol. L-cys, ascorbic acid, citric acid and EDTA-2Na inhibited the PPO activity in the order of L-cys>ascorbic-acid>citric acid>EDTA-2Na. Both Cu2+ and Mg2+ could activate the PPO activity, the activation of the Cu2+ was strengthened at high concentration (10 mmol/L), while the activation of Mg2+ decreased. Fe3+、K+、Na+ could activated the PPO activity at low concentration (1 mmol/L), while inhibit it at high concentration (10 mmol/L).Based on the single factor experiment, results were optimized and analyzed by response surface regression. The optimal formula (by mass fraction) was 0.60% citric acid, 0.25% L-cysteine,0.70% Sodium D-isoascorbate,0.65% EDTA-2Na.Boiling water blanching of 60 s gave residual activity of 13.83% and 4.12% for PPO and POD, respectively, microwave blanching(700 W) of 60s 12.35% and5.21%, high temperature short time steam (0.3 MPa) blanching of 30 s10.23%,5.55%. When compared with samples blanched by boiling water and microwave (700 W), high temperature short time steam (0.3MPa) blanching of 30 s had least loss in Vitamine C, gingerol and total soluble sugar content, and degradation in color.When baby ginger was respectively frozen at -60℃,-50℃,-40℃,-30℃, the time of past maximum crystallization (-3.3～15.9℃,-2.9～14.8℃,-2.5～12.4℃,-2.2--9.0℃)was 11.0 min,20.0 min,23.0 min,43.5 min respectively. Frozen at -40 ℃ can past maximum crystallization quickly, save cost and reduce energy consumption.The baby ginger frozen at -40 ℃ storage at -20 ℃.With the extension of storage time, the quality of blanching and color processing baby ginger decreased slowly,and at the end of storage, the loss of Vitamin C was 10.38%, total soluble sugar content 12.98%, gingerol content 5.68%, the direct freezing ginger were 24.53%,21.67%,30.56% respectively. Blanching and color processing can slow down the quality loss of baby ginger during the frozen storage, maintain the quality stable.Microwave thawing can better maintain the ginger hardness(1649.92 g), reduce the drip loss(18.20%). Thawing at room temperature has the greatest impact on the baby ginger quality, the lowest hardness(616.27 g), the highest drip loss(25.51%). After thawing with Room temperature and Water Bath, the color of baby ginger were damaged seriously.Microwave thawing gave the highest total soluble sugar(0.75 g/100g),Vc content(2.57 mg/100g), room temperature thawing the lowest. The thawing method had little effect to the content of gingerol, the gingerol content of baby ginger thawed by different method had not significant difference. Comprehensive factors were considered, microwave thawing can better maintain the original quality ginger. |
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