| In this study, the effect of high pressure treatment and Ultra High Temperature treatment to total bacterial count, endoenzymes activity, protein secondary structure, aroma rheological property,color and physicochemical indexes of quality were investigated. The main conclusions were summarized as follows:(1) The total number of colonies were reduced significantly in watermelon juice by UHP treatments.Enhance the pressure to more than 200MPa could achieve the commercial sterile conditions (Ig2 CFU/mL),and the total number of colonies were less than UHT treatment lg1.64 CFU/mL. When treated under 400 MPa and 600 MPa the total number of colonies were 1g1.43 and 1g1.64 CFU/mL respectively. The results show that the pressure is the key factors influencing the bacteria survive or not, and coordinated with ultra high temperature time can strengthen the sterilization effect.(2) The PPO and PME activity in watermelon juice of UHP and UHT treatments were significantly decreased (p< 0.05),400 Mpa,30? and 20 min of UHP treatment PPO and PME activity reduced to 78.8% and 64.0% respectively in watermelon juice,which had no significant difference with UHT treatment. Higher pressure, higher thermal synergy, increase pressure batch number resulted more enzyme inactivated.When treated under 400Mpa,20min, the synergy of 60?,PPO and PME activity were 69.6%, 48.6% respectively.(3) The UHP and UHT treatments changed the protein secondary structure in watermelon juice. Higher pressure, higher thermal synergy UHP, increase pressure batch number resulted more changes of the secondary structure of watermelon juice. The influence of UHP treatment secondary structure is greater than the UHT treatment. UHP treatment on watermelon juice secondary structure is greater than the influence of UHT treatmentThe relative contents of ?-helix was reduced by 31.64%(p< 0.05) under 600MPa treatment;?-sheet,?-turn had no significant change in 200-400Mpa, and 600Mpa increased by 8.86% and 6.92% respectively, reduced,;?-sheet or ?-turn inceased, random coil had no significant change by UHP treatment,the relative contents of ?-helix in watermelon juice turned to ?-sheet or ?-turn. Higher pressure, higher thermal synergy UHP, increase pressure batch number resulted more changes of the secondary structure of watermelon juice proein.(4) The apparent viscosity decreased with the shear rate by the UHP and UHT treatments, indicated the watermelon juices were pseudoplastic fluid type. Higher pressure, higher thermal synergy UH P, and increase batch number, the apparent viscosity and G'increased,well the viscosity of UHT treatments decreased.400,600 Mpa, the G "increased by 27.2% and 53.3% respectively. UHP treatment weakened against the G', and reinforcement on G" watermelon juice system by elastic fluid into a viscous fluid.400 Mpa,20 min,30? treatment can not only ensure commercial aseptic conditions, and make the watermelon juice taste more smooth, sensory quality is better than UHT treatment.(5) The effect of UHP treatment on volatile substances in watermelon juice were smaller than UHT treatment, which can better maintain the characteristics aroma components of watermelon juice.The percentage of aldehyde by UHP treatment in watermelon juice increased lead to melon flavor characteristics more full-bodied, esters, acids, alcohols, ketones, alkanes maintained better compared with control group. However, the volatile substances of UHT were obviously changed. UHT processing material percentage increased by 25.9%, the amyl butyrate percentage increased by 80.4%,ketone sharply reduced 59.5% alcohol by 80.1%.400 MPa,30?,20 min,the volatile substances in watermelon juice minimal impact, and the volatile substances has more advantages than UHT. The Percentage and the actual content of 2,6-dimethyl-5-heptene aldehyde were increased by UHP processing, and under 400-600 Mpa the percentage of nonyl aldehyde increased by 23.4%?52.7%, More rich melon flavor, and the percentage composition of UHT on nonyl aldehyde reduced by 59.2%, flavor was not harmonious.The main characteristics under 400 MPa,30?,20 min of ion abundance compared with UHT treatment was small, similiar to untreated watermelon juice by the electronic nose. However,the UHT treatment volatile substances of watermelon juice obviously changed,the flavor of the UHT treatments was not harmonious.(6) UHP treatment can well maintain the nutrients, color and other qualities of watermelon juice.The content of lycopene was not changed, well, UHT processing was significantly decreased by 29.53%(P< 0.05).The L* value increased by 3.7% (p< 0.05), a*, b* value and ?E had no significant change by 400 Mpa. L* value, a* values decreased 4.4% and 38.6% respectively, ?E was 2.65, showed that color of watermelon juice to a dark, red degrees declined dramatically.UHT treatment can better maintain the titratable acid, soluble solid content, pH value and the degree of Browning, and UHT processing titratable acid content was reduced by 5.64%(p<0.05), Browning degree significantly increased by 40.6%(p<0.05).(7) Low temperature (4?) combined with ultra-high pressure treatment can prolong the shelf life of watermelon juice, storaged in line with the juice business sterile conditions after 16 weeks, shelf life of UHT processing was Short.UHP treatment watermelon juice in the storage period can be better to keep the color, soluble solids content, titratable acid, etc. Different processing of watermelon juice can separated by lectronic tongue,400Mpa,30?,20 min treatment group can better keep the watermelon juice original flavor, UHT treatment group watermelon juice taste changes greatly. According to the national standard method, slected shelf period of watermelon juice using preference ordering inspection, showed that the sensory evaluation member prefer 400 Mpa,30?,20 min of watermelon juice processing group, and then UHT watermelon juice which has significant difference (p< 0.05). |
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