Shelf life and quality changes during storage of high pressure treated orange juice

摘要

The effect of high pressure (HP) treatment and subsequent storage at 4, 10 and 20℃ on the natural microflora, enzymatic activity and quality attributes of single strength orange juice was investigated. HP treatment of orange juice at pH 3.7 and 3.2 at 400 MPa comprised of a single cycle (1-cycle) pressure pulse (with a short hold time of 2 min). The juice atpH 3.7 was also treated with a 3-cycle pressure pulse which involved three 1-cylce pulses in succession. Test samples were analyzed for microbial growth, enzymatic and quality changes at 3, 7 and 14 day intervals at 20, 10 and 4℃, respectively. The quality attributes tested were "Brix, titrable acidity, Brix/acid ratio, cloud, browning index, color (L and a values) and the viscosity of juice. Rate constants of each attribute were evaluated based on a zero order model. Results indicated that the natural microflora in treated juice was below detectable limits during the early periods of storage. Subsequently, however, the microorganisms followed conventional temperature dependent growth kinetics. There was no growth of lactic acid bacteria in any of the pressure treated samples. The residual pectin methyl esterase activity decreased slowly during the storage reaching a steady state low value. In general, changes in quality attributes were minimal. Although some changes in L and a values were noticed during storage, the overall acceptability of color was not significantly affected. Pressure treated orange juice at its natural pH (3.7), was found to have a better flavor compared to the acidified juice (pH 3.2) due mainly to the associated sour flavor. Observed sensory changes in pressure treated juices were not caused by microbiological growth, but by alterations in the chemical and volatile composition of juice. The shelf life of 3-cycle pressure treated orange juice at pH 3.7 ranged from 21 days at 10℃ to 56 days at 4℃. Storage temperature had a significant influence on microbial growth, enzymatic activity and changes in quality factors.