| NFC orange juice is popular among consumers because of its unique flavor,color and rich nutrients.In recent years,more and more consumers begin to pay attention to the taste problem of NFC orange juice.Therefore,the development of orange juice with different tastes to cater to consumers with different taste preferences has a broad industrial development prospect and significance.Rheological properties are an important index to evaluate the taste of NFC orange juice,including viscosity,viscoelasticity,stick slip,etc.It can reflect the taste quality of orange juice in the tactile aspect.The research of orange juice with different rheological properties can provide theoretical basis for the taste improvement,processing,production and quality management of orange juice.High pressure homogenization(HPH)treatment and high pressure processing(HPP)treatment are common non-thermal processing methods at present.Both of them can change the rheological properties of orange juice.In addition,HPH treatment can effectively improve the stability of orange juice,and HPP treatment can play a bactericidal role.Therefore,the combined treatment method of HPH-HPP was adopted for NFC orange juice in order to provide an orange juice product with good taste and stable storage,and to explore the effects of different treatment parameters on the taste of orange juice.The main research contents and conclusions are as follows:(1)Homogenizing pressures(20,40,60,80,100 MPa),injection temperatures(4,25,50℃),and cycles(1,2,3 times)were selected as variables for HPH treatment.After20～100 MPa HPH treatment,the flow coefficient of orange juice increased by19.9%～76.1%,the viscosity coefficient k decreased by 22.9%～77.1%,and the apparent viscosity decreased by 5.40%～74.1%.The storage modulus G’and loss modulus G’’decreased gradually,the critical gel point of orange juice moved forward gradually,and the viscoelasticity decreased.When injected at 4℃,25℃and 50℃,k value decreased by60.0%,45.7%and 48.6%,n value increased by 85.1%,59.0%and 64.9%,and apparent viscosity decreased by 81.4%,42.5%and 54.3%,respectively.The critical cementing points are 1.74 rad/s,4.52 rad/s and 2.81 rad/s,respectively.After 1 to 3 times of homogenization,the k value of orange juice decreased by 45.7%～68.6%and the n value increased by 59.0%～80.5%.The apparent viscosity decreased by 42.5%～79.7%,and the critical gel point was 4.52 rad/s～1.74 rad/s.The taste of HPH orange juice changed greatly with temperature when it was lower than 25℃,but changed little with temperature when it was higher than 25℃.The HPH orange juice treated at 60 MPa and 25℃for three times showed the strongest resistance to external forces and the best taste.(2)After HPH treatment,the average particle size of orange juice decreased by20.0%～94.5%,and the average diameter of solute particles decreased by 5.0%～20.0%under scanning electron microscope(SEM).The Zeta potential increased by11.5%～87.8%,and the system was more stable.M_w of cellulose in orange juice and soluble dietary fiber(SDF)in pectin decreased by 1.5%～21.9%and 9.1%～76.4%respectively.The enzyme activity of PPO,POD and PME decreased by 24.3%～98.2%,50.4%～98.5%and 10.9%～59.4%,respectively.The results of FTIR analysis showed that HPH treatment could break the carbon skeleton of SDF,reduce the carbon chain length of solute and the degree of methyl esterification(DM)of pectin to reduce the M_w of SDF.The L value and b value of orange juice decreased,while a value increased,and the color of orange juice was brighter.All the results showed that the HPH orange juice treated at60 MPa and 25℃for three times had good taste.(3)On the basis of three cycles of HPH treatment at 60 MPa and 25℃,different pressures(450,475,500,525,550,575,600 MPa)and different times(5,10,15,20,30min)were selected as variables for HPP treatment.After 450～600 MPa treatment,k value decreased by 23.4%～81.9%,n value increased by 12.3%～127.3%,and apparent viscosity decreased by 18.1%～69.8%.However,after 5～30 min treatment,k value decreased by81.8%～85.1%,n value increased by 115.3%～140.4%,and apparent viscosity decreased by 61.8%～88.0%.G’<G",and both of them showed a decreasing trend,and the viscoelasticity decreased.The temperature scanning changes little,and the inflection point appears at 25℃.The time scanning results showed that the HPP orange juice treated at 600 MPa for 10min had stability and taste.(4)After HPP treatment with different parameters,the particle size distribution range of HPH orange juice was reduced,and the average particle size was reduced by16.5%～72.3%.The average diameter of solute particles decreased to 20.0%～80.0%under scanning electron microscope(SEM).Zeta potential increased by 10.7%～44.3%,respectively,and the system reached the metastable state.Cellulose and M_w in orange juice were decreased by 17.6%～54.4%and 53.0%～59.4%,respectively.M_w of SDF was decreased by 34.6%～95.7%and 95.5%～96.5%.PPO was basically inactivated,POD decreased by 18.8%～87.5%,PME enzyme activity decreased by 14.4%～30.4%.The L value and b value of HPP orange juice decreased,while a value increased,and the color of HPP orange juice was brighter.FTIR analysis results show that HPP treatment can not only reduce the M_w of solute molecules,but also change the molecular structure and internal hydrogen bonding of solute,resulting in the change of rheological properties.This may be due to the demethylation reaction and the dispersion of multiple entangled pectin molecules by HPP.(5)The orange juice treated by HPH-HPP was stored at 4℃for 3 months,and compared with the orange juice treated by thermal sterilization(TP).The results showed that the fluidity of HPH-HPP orange juice and TP orange juice was gradually enhanced.During 0～3 months,k value decreased by 8.0%～39.4%and 17.8%～49.1%,respectively,and n value increased by 8.5%～31.1%and 9.0%～27.6%,respectively.The apparent viscosity decreased by 20.6%～64.8%and 11.5%～59.3%,respectively.G’<G"and showed a decreasing trend,and the viscoelasticity of orange juice decreased.The effect of temperature on both HPH-HPP and TP orange juice remained unchanged,and the stability gradually decreased.(6)Within 3 months,the L and a values of HPH-HPP and TP orange juice increased,while the b values decreased,and the color of HPH-HPP orange juice gradually darkened.Compared with TP orange juice,the activities of PME enzyme,POD enzyme and PPO enzyme of HPH-HPP orange juice were about 4 times,2～3 times and 12～15 times,but the activities of PPO and POD enzyme of both orange juice and HPH-HPP orange juice were almost completely inactivated.The contents of TSS,TA and vitamin C remained unchanged.Among them,the TA content of TP orange juice is about 87.0%of that of HPP orange juice,and the vitamin C content is about 1/3 of that of HPP orange juice,which is due to the decomposition of some organic acids and vitamin C caused by orange juice in the process of thermal processing.However,the vitamin C content of HPP orange juice decreased by about 2.0%in the first 0.5 months,which was due to the oxidation of vitamin C by air in the orange juice. |
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