Effect Of Pre-treatment On The Quality Of Frozen Mushrooms And Broccoli

In recent decades, there is a rapid development of frozen food in China. However, the novel blanching technologies have not been applied in the frozen food industry resulting in some disadvantages such as lagging technologies and equipments in frozen industry. In addition, the frozen transportation and marketing of the equipment is not perfect because of the existence of large temperature fluctuations. The freeze-thaw phenomenon of product often occurred, resulting in such as shorter the shelf-life of products, decline in flavor.The objective of this paper is to find a new blanching technology as a substitute of traditional blanching in order to enhance the ability of kill enzymes while the quality of products were maintained well.Firstly, the effect of single microwave blanching and single high-temperature short-time steam blanching on inactivating enzyme activity and quality of mushrooms were investigated. After that, a combined high temperature short time steam and microwave blanching treatment method was chosed to decrease the POD activity. Then the optimal technology conditions in combined blanching process were obtained by orthogonal experiment in terms of peroxidase activaty: the processing time 45 s, steam pressure 0.3 MPa (133°C), material capacity 500 g.Secondly, the effect of the repeated freeze-thaw treatment on quality of frozen mushrooms was studied. The treatment of freeze-thaw cycle accelerate the deterioration of frozen mushrooms quality, with increasing in the freeze-thaw numbers of frozen mushrooms, thawing time shorter, thawing loss has a significant increase. In both sensary and nutrient contents, the samples of microwave combined high-temperature short-time steam are much better than the one of pure high-temperature high-temperature short-time steam at different freeze-thaw cycle times.Thirdly, blanching processing is not suitable applied to blanch some fruits and vegetables. In this article, ozone water as a liquid medium assisted ultrasonic treatment was used to control peroxidase activity of broccoli used as raw materials in order to find suitable non-thermal technology and enlarge the application range of non-thermal technology in the quick-frozen vegetables. The optimal inactivation enzyme technology conditions in ozone-ultrasonic pre-treatment process were obtained by orthogonal experiment in terms of peroxidase activaty: the concentration of ozone water was 6.40 mg/L, the power of ultrasonic was 1200 W, and keep working time was 4.0 min. The results of sensory evaluation show that the quality of the frozen products treated with optimal sterilization technology conditions had been maintained very well. Comparing with blanching, the products treated with combined ultrasound and ozone treatment had better color, less loss of nutrients. Therefore, it can be considered that the quality of frozen broccoli could be better maintained when compared with blanching.