High pressure (HP) processing has been emerging rapidly as a novel technique for non-thermal preservation of foods. Application of HP processing for shelf life extension of orange juice was the principal objective of the current research. To accomplish this objective, and to establish a scientific basis for HP processing of orange juice, a systemic approach was used which included the evaluation of: (a) HP inactivation kinetics of pectin methyl esterase (PME, the key enzyme in orange juice implicated with respect to quality changes), (b) destruction of spoilage microorganisms and changes in product quality, (c) HP process verification and finally, (d) storage studies on HP treated orange juice. / In preliminary studies, the effect of HP treatment on indigenous microorganisms, texture and color of selected fresh fruits and vegetables were evaluated. Results showed that HP had a significant effect on the destruction of microorganisms. Product texture and color were mildly affected, often resembling the appearance of mildly heat-treated products. / Pressure induced inactivation kinetics of pectin methyl esterase (PME) was investigated at pH 3.7 and 3.2 in freshly squeezed single strength (12.6°Brix) and concentrated (10--40° Brix) orange juice. Results showed a biphasic nature of pressure induced inactivation of PME in both juices. The first phase consisted of rapid change in inactivation of enzyme, designated as instantaneous pressure kill (IPK), due to pulse pressurization, followed by gradual inactivation of enzyme, characterized by a first order rate of inactivation during pressure hold-time. / Combination treatment involving pressure cycle, pressure level and pressure hold-time was then evaluated for inactivation of PME using a response surface methodology. Overall, pressure pulse had a lower effect on inactivation of PME compared to other factors. / Pressure destruction kinetics of Leuconostoc mesenteroides and Saccharomyces cerevisiae the spoilage organisms in orange juice, were then investigated. Pressure destruction kinetics followed the same dual effect behavior, as observed with PME inactivation. IPK effect increased with pressure cycles and was more pronounced with S. cerevisiae that Leu. mesenteroides. / Storage studies of HP treated single strength and concentrated orange juice were conducted at selected temperatures (4, 10 and 20°C). Results showed that treated juice was microbiologically stable from a few days to several weeks depending on type of juice, storage temperature and processing conditions. (Abstract shortened by UMI.)

Thesis (M.Sc.) -- University of Western Sydney, Hawkesbury, 1994. / Thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Food Science, School of Food Sciences, Faculty of Science and Technology, University of Western Sydney, Hawkesbury, 1994. Includes bibliographical references.

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The quality and shelf-life of pressure processed (150, 200 and 250 MPa at 25 and 35&deg / C for 5, 10 and 15 minutes) orange, tomato and carrot juices were compared to fresh and thermally pasteurised (60&deg / C for 5, 10 and 15 minutes and 80&deg / C for 1 minute) juices. Treatments were capable of microbial inhibition of juices to non-detectable levels. The change in ascorbic acid content of HHP treated juices was not statistically significant (p&gt / 0.05). Both heat treatments at 60 and 80&deg / C, displayed a significant loss and induced a decrease in the free radical scavenging activity but was not affected by HHP treatments. Pressurization at 250 MPa at 35&deg / C for 15 minutes and thermal pasteurization at 80&deg / C for 1 minute and stored at 4 and 25&deg / C for shelf-life analysis. HHP treated juices showed a small loss of antioxidants (below 10%) at both storage temperatures whereas the loss is higher (about 30%) in the heat treated juices through shelf life (30 days). The pressurized juices, stored at 25&deg / C, contained ascorbic acid better than heat treated ones after 30 days. The total color changes were minor (&amp / #8710 / E=10) for all pressurized juices but for heat pasteurized samples, higher as a result of insufficient antioxidant activity. The pH of juices was not affected by treatment, storage temperature or time. HHP yielded a better product, regarding the studied parameters of the juices compared to the conventional pasteurization. Therefore, HHP treatment (250 MPa, 35&deg / C for 15 minutes) can be recommended for industrial production of fresh fruit and vegetables.

The effect of refluxing on the aromas of Valencia aqueous orange essences was determined through analysis by GC, MS, Osme, and by a descriptive panel. The strengths and descriptions of volatiles were investigated to determine if differences in essence aroma character and intensity existed. During production, 1 sample was subjected to reflux conditions and contained 16.2% ethanol. The other sample had not been refluxed and contained 6% ethanol. The aroma activity of volatiles was measured by Osme, a method of gas chromatography / olfactometry developed at Oregon State University. The majority of aroma active peaks were found to be present in the reflux and no reflux aqueous orange essence samples. Octanal, linalool, ethyl butanoate and 2 unknowns were the components with strongest aroma activities in both samples. Descriptive analysis was conducted with 7 trained panelists from the Food Science and Technology Department at Oregon State University. Following 12 training sessions, initial testing indicated overall intensity was the major separating attribute of essences. After 6 additional training sessions and adjustment of concentrations to yield essences of approximate equal strength, testing indicated there were no significant differences between samples. Osmegrams, GC FID chromatograms, and descriptive analysis indicated the effect of reflux produced an essence that was more concentrated. Although refluxing concentrated individual volatiles to different levels, character differences other than those associated with concentration were minimal. / Graduation date: 1996

Call number: LD2668 .T4 1957 M70 / Master of Science

Note:

Graduation date: 1939

Graduation date: 1939