Study On The Changes Of Nucleotides And Related Compounds In Minced Litopenaeus Vannamei During Ohmic Heating

The Litopenaeus vannamei（L.vannamei）,is one of the most important commercial farmed species worldwide.Due to its high protein content,low fat content,abundant free amino acids and delicate texture,L.vannamei is one of the most popular seafood products among consumers.Nucleotides and related compounds（NRCs）are important substances in the muscle of shrimps and other aquatic animals.Previous studies focused on the effects of curing on NRCs in meat and ATP degradation during the post-mortem storage of aquatic foodstuffs.However,few studies analysed the content change of NRCs after heating processing for aquatic products.Therefore,it seems necessary to explore the content change of NRCs after heating processing for L.vannamei treated with metal ions,especially ohmic heating treatment.Ohmic heating（OH）,depending on the heat that is generated within the entire sample when an electrical current passes directly through conductive materials performing the cooking process.The main advantages of ohmic heating are rapid and uniform heating,no residual heat transfer after shut-off of the current,a lower capital cost,together with the higher energy conversion efficiency.Therefore,it provides a satisfactory product with minimal changes of structural,nutritional,and organoleptic properties.OH is a developing technology with tremendous potential for the food industry such as preheating,blanching,fermentation,cell disruption,sterilization,extraction,evaporation or dehydration.However,OH has less research on maintaining the flavor of the product.The present study was aimed at understanding the impact of different heating temperatures and different metal ion additives on the changes of NRCs in shrimp mince（L.vannamei）during OH.1.This chapter discusses the feasibility of ohmic heating as the processing mode in minced L.vannamei and determines the relationship between electrical conductivity and frequency,temperature（25,40,55,65,75,85 and 95°C,respectively）,together with metal ion additives(1,5 and 10 mmol/L of Zn²⁺,Cu²⁺,Al³⁺and Fe³⁺,respectively),in order to gain insight into the ohmic heating characteristics of shrimp mince.In the50 Hz-20 kHz range,although the EC and frequency were basically logarithmic,the variation of EC was different in high and low temperature range.The increase in EC was linear with increasing temperature up to 65°C;a non-linear trend was observed at higher temperatures.There was no strong correlation between the EC and the metal ion concentrations.The EC of the minced shrimp treated with Al³⁺and Fe³⁺increased more than of shrimp treated with Zn²⁺and Cu²⁺,and the minced shrimp treated with 10mmol/L Fe³⁺showed the highest electrical conductivity and fastest heating rate.2.There are few studies on ATP degradation pathways of shrimps during OH.Therefore,this chapter examines the effects of the different temperatures（25,40,55,65,75,85 and 95°C,respectively）on the changes of ATP-related products of shrimps and discusses the mechanism of IMP to provide theoretical guidance for shrimp flavor.The results show the ATP degradation pathways in L.vannamei during OH are proposed to be ATP→ADP→AMP→IMP→HxR→Hx（major,>97%）,and ATP→ADP→AMP→Ado→HxR→Hx and ATP→ADP→AMP→Ado→Ad（minor,<3%）.Ado is detected at all temperatures,its concentration is highest at 40,85,and95°C（0.20,0.22,and 0.27μmol/g,respectively）,and below 0.06μmol/g at other temperatures.High temperature（>65°C）is more conducive to the production of AMP,low temperature（<65°C）is more conducive to the production of IMP.At 85°C at high temperatures,it seems to be more conducive to the overall flavor of the shrimp meat.The first kinetic equation and the Arrhenius equation are only applicable to changes in IMP content in minced shrimp during OH（40-75°C）.3.NRCs is directly and indirectly affected by various factors,such as age,gender,migration behavior,species,temperature,treatment and seasonal changes,but little is known about the effect of metal ions on the content of NRCs,especially flavor,in aquatic products during OH.The chapter investigates the changes in ATP and related products of minced shrimp treated with different metal ions.The results show that the bitterness produced by Hx was almost negligible,as its TAV value（<0.08）was<<1,therefore,the optimization of the IMP content was emphasized in the metal-ion-treated minced shrimp.The addition of metal ions greatly increased IMP production,particularly at concentrations of 5 mmol/L Cu²⁺and 10 mmol/L Fe³⁺.The IMP content was more dependent on metal ion content than temperature;thus,the optimum heating temperature was using the predetermined optimum metal ion concentrations.At the high temperature of 85°C,the maximum TAV values of IMP in minced shrimp treated with 5 mmol/L Cu²⁺and 10 mmol/L Fe³⁺were 10.30 and 12.48,respectively.These results indicated that treatment with 10 mmol/L Fe³⁺,which resulted in the maximum electrical conductivity,minimum heating time,and highest IMP concentration,was ideal in terms of the flavor of minced shrimp at the high temperature of 85°C.