Study On Polyphenol Oxidase And Development Of Vacuum Freeze Drying Product Of Apricot

Apricot is a kind of fruit with unique flavor and rich nutrition,which is deeply loved by people.Because of its easy decay,apricots are still mainly fresh food.The type and scale of apricot deep processing products are very limited,and most of them are dry products,with low added value.In this paper,the properties of polyphenol oxidase（PPO）of Huangjin Apricot andWanhong Apricot were studied firstly,and then the key technology of vacuum freeze-drying of apricot was determined,and the freeze-drying products of apricot were developed.The results were as follows:PPO was extracted by cold acetone,and the kinetics equation of enzymatic reaction of apricot PPO was determined with catechol as substrate.The kinetics equation of PPO enzymatic reaction of Huangjin Apricot was 1/[V]=7.39×10^-4/[S]+0.006（R²=0.997）,V_maxax was166 U/min,and K_m（Michaelis constant）was 0.114 mol/L.The kinetics equation of PPO enzymatic reaction of Wanhong Apricot was 1/[V]=4.25×10^-4/[S]+0.010（R²=0.998）,V_maxax was100 U/min,and K_m was 0.042 mol/L.PPO of Wanhong Apricot has stronger affinity for catechol than that of Huangjin Apricot.The optimum pH of PPO for Huangjin Apricot and Wanhong Apricot was 5.5,and the optimum reaction temperature was 30 C.Ascorbic acid,sodium bisulfite,L-cysteine and citric acid had inhibitory effects on PPO of Huangjin Apricot,IC₅₀0 was 23.9 mmol/L,9.9mmol/L,9.5 mmmol/L and 8.6 mmol/L,respectively.Ascorbic acid,citric acid and sodium bisulfite had inhibitory effects on PPO of Wanhong apricot,IC₅₀0 was 37.3 mmol/L,7.1 mmol/L and 6.5 mmol/L,respectively.Cu²⁺,Mg²⁺and Na⁺could promote PPO activity of Huangjin Apricot,Fe³⁺could inhibit it,while Mn²⁺and Ca²⁺had no significant effect.Fe³⁺,Cu²⁺,Mn²⁺,Mg²⁺and Na⁺could promote PPO activity of Wanhong Apricot,but Ca²⁺could inhibit it.The results of single factor experiments showed that L-cysteine（6 mmol/L）and ascorbic acid（20 mmol/L）were the color protectors of Huangjin Apricot and Wanhong Apricot in vacuum freeze-drying.Wanhong apricot should be immersed in 14%sucrose solution for 15minutes to improve its taste.The vacuum freeze-drying process is-40℃（4 h）→-30℃（4h）→-20℃（2 h）→-10℃（1 h）→0℃（1 h）→10℃（1 h）→20℃（1 h）→30℃（2 h）→40℃（15 h）.The vacuum freeze-drying products of apricot obtained by pretreatment,color protection,（sugar-in）,vacuum freeze-drying and vacuum packaging are bright in color,good in shape,crisp in taste.The moisture content of Huangjin Apricot and Wanhong Apricot was2.5%and 3.2%respectively,which met the requirements of GB/T 23787-2009.