Research Of Rapid And Non-destructive Determination For Quality Of Prawns Based On Nuclear Magnetic Resonance Technology

Prawns have become an integral part of the nutrients in the diet of people in our country.Prawns are popular in foreign markets and play an important role in the aquatic economy,owing to its tissues'soft,fresh,protein,various trace elements and vitamins.With the rapid development of transportation,prawns are frequently transported to inland or overseas for sales.However,the quality,such as taste,nutrition,etc.,might be affected at micro-organisms and storage processes.The aforementioned problems even do harm to human body.The main problems that can adversely affect the quality of prawns during storage can be concluded as preservation,processing,adulteration and etc.These problems possible impact on the prawns'quality:muscle and sensory,freshness and adulteration.Therefore,rapid risk assessment of prawns is of great importance.Nuclear magnetic resonance?NMR?technology is one of the most common investigative techniques of modern food assessments.There are two branches in this technique,including nuclear magnetic resonance spectroscopy?NMR?and magnetic resonance imaging?MRI?.NMR,one of the rapid and non-destructive determination,plays an essential role in food science,chemistry and biology because of its fastness,non-destructiveness,non-pretreatment and non-pollution.There is a significant relationship between the moisture and quality of food,which can be attributed to the following reasons:?1?moisture is one of the greatly important reasons of food spoilage.So controlling the moisture content is important to food quality and shelf life;?2?moisture in food results in protein denaturation and enzymatic reaction;?3?it is an important factor of decisive characteristics of food rheology.Therefore,the water in food is indispensable to food quality.Nevertheless,LF-NMR studies on water distribution and migration are extensive,which can be used to establish a rapid and nondestructive method to assess the prawns'quality by simulating the daily storage of prawns.The assessment method includes ice preservation,cooking processing and adulteration,which is applied to the food quality and safety.The main contents and results of this study are as follows:1.Analysis of moisture changing of prawns via ice preservationA preliminary method has been established that can evaluate the quality of prawns during the ice preservation based on the LF-NMR technology.The moisture changing of prawns includes three aspects.The bound water combing with proteins are partly transferred to intermediate water,which caused prawns'tissues fleshy rough and loose;The intermediate water of myofibrils have a maximum loss,so that the water holding capacity decreased significantly which makes prawns lost the fresh taste;The proportion of free water increased,which indicated the cell water is easyer to loss.In while water loss seriously affect the hardness of the shrimp meat.The sixth day during the ice preservation was the turning point of the decreased quality of prawns.2.Analysis of moisture changing during heating processA preliminary method has been established that can evaluate the quality of prawns during the heating based on the LF-NMR technology.The moisture changing of prawns includes the bound water,intermediate water and free water.The three water types are more relaxation,which had not been transferred but only part of the bound water were transferred to the intermediate water.It shows that the binding degree with protein is reduced obviously.In while the water holding capacity of myofibrils were only relaxed,which is attributed to the good quality of fresh prawns and high water holding capacity.The changes of water state affects the texture of prawns,including increasing of the hardness,chewiness,springiness and cohesiveness,which makes prawns rougher and harder.The best time for heating of prawns is 5⁶ min.3.Identification and differentiation of adulterated prawnsWe firstly proposed an effective method to authenticate the hydrocolloids adulterated prawns via NMR technology.The LF-NMR T₂ relaxation measurement of the adulterated prawns revealed the injection of hydrocolloid at the molecular level.Furthermore,the accurate location of injected hydrocolloids in prawns were visualized by LF-MRI,and four regions including head,tail,paw and back can be used for the target sites for screening adulterated prawns.Therefore,LF-NMR and MRI combined with PCA provide unique insights into the monitoring of food adulteration.