The Effect Of Ultra High Pressure On The Quality Of Fresh Orange Juice

The effect of ultra high pressure (UHP) treatment on microorganism, enzyme, physicochemical properties and aroma in fresh orange were investigated, in order to provide the theory date for developing quality of orange juice. Results are as follows.1. The variation law of total number in colonies, activity of PME and POD were investigated under different processing pressure and processing time. The results show that UHP can significantly reduce the total number of colonies in orange juice, commercial sterilization is achieved under 400Mpa pressure for 15min, with logarithm reducing to 0.954. Sterilizing effect under 500Mpa for 15min is better than that treated by thermal sterilization. With the pressure increase, activity of PME and POD firstly increased and then decreased. The activity of PME and POD can slightly activate at the range from 0 to 200MPa, top to 105.21±1.55% and 103.41±1.23%. when the pressure was higher than 400MPa, the activity of two enzymes were significantly decreased (P<0.05), relative residues activity reduced to 12.42±1.49% and 70.31±0.58% under 600MPa pressure.Under 400Mpa processing, with constant time become longer, the total number of colonies and activity of PME and POD are more significantly decreased (P<0.05), the inactivity effect of PME and POD is significant (P<0.05). While pressure time is longer than 15min, the three changes turn to stabilize.2. The effect of processing pressure, processing time and processing capacity on the color of orange juice were investigated based on the single factor and orthogonal experiments. Study shows that the pressure significantly changed the color parameters, including lightness value (L*), red-green value (a*) and yellow-blue value (b*) (P<0.05), expressed as L*, b* increased while a* decreased. Under 200MPa,300MPa and 400MPa processing, the chromatic difference (ΔE*) interaction is not significant (P>0.05), compared to heat treatment,UHP treatment is more conducive to maintaining the original color of orange juice. The orthogonal experiment results show that processing pressure, processing time and processing capacity have significant effect on ΔE* (P<0.05), the order is processing pressure> processing time> processing capacity. The optimal parameters are 400MPa pressure for 18min, processing 35mL once.3. The effect of UHP treatment on physicochemical properties such as total acid, total sugars, total polyphenols and soluble solids is not significant (P>0.05), with the increase of processing pressure and processing time, vitamin C in orange juice gradually reduced, amino acid nitrogen content increased significantly (P<0.05), under 500MP pressure for 15min treatment, the retention rate of vitamin C is 92.71%, the growth rate of amino acid nitrogen is 19.89%. Compared to heat treatment, UHP treatment is more conducive to the stability of physicochemical properties.Under 400MPa pressure, time change have little effect on physicochemical properties after 15min.4. Contrast to the quality stability of ultra-high pressure treated orange juice under different storage temperatures, results show that total number of colonies increased during storage and positively correlated with storage temperature. The total number of colonies in orange juice treated by 400MPa for 15min can meet the commercial sterility requirements during 30days at -4℃or 20days at 4℃. At the temperature of-4℃,4℃and 25℃, trend of color changes are the same. L* and b* increased during storage time, while a* decreased. The the retention rate of vitamin C were 93.1% and 86.2% after 30-day srorage period at -4℃and 4℃. Low temperature is conducive to the stability of color and significantly reduce the Vc loss (P<0.05)。5. The effect of UHP treatment on the mainaroma constituents in orange juice was studied using SDE and GC-MS. Under 400MPa pressure for 15min processing,8 kinds of aroma component disappeared, other 7 kinds of aroma component appeared,40 kinds of aroma component in total. Comparison results show that main types of aroma compositions were unchaged after treatment, but contents were not. Content of Olefins, ketones, aldehydes decrease 11.49μg/mL,0.63μg/mL and 0.85,ug/mL, while alcohols and esters increase 0.80μg/mL and 0.85μg/mL. The main aroma components such as valencia orange ene, limonene, ethyl butyrate, ethyl caproate and grapefruit ketones are decreased, with remain rate of 71.07%,42.11%,82.74% respectively. On the contrary, a-terpinene alcohol and furfural are increased by 81.33% and 37.5%. Compared to heat treatment at 90℃for lmin, UHP treatment is more conducive to maintaining the natural aroma component of orange juice.