Effects of High Hydrostatic Pressure and Thermal Processing on the Antioxidant and Sensory Characteristics of Blueberry Juice

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Title: Effects of High Hydrostatic Pressure and Thermal Processing on the Antioxidant and Sensory Characteristics of Blueberry Juice
Author: Leavens, Je'Velle Bonique
Advisors: Dr. Leon Boyd, Committee Chair
Dr. MaryAnne Drake, Committee Member
Dr. Brian Farkas, Committee Member
Abstract: Blueberries are recognized for their potential health benefits and high antioxidant levels. Increased dietary consumption of blueberry products may reduce risk factors associated with cancer, heart disease, and other degenerative diseases. Blueberries are often processed into juices or wines. However during blueberry processing, the levels of antioxidants may be altered resulting in a change in antioxidant and sensory qualities. Due to the high antioxidant levels found in blueberries, blueberry processors are seeking effective processing techniques such as High Hydrostatic Pressure (HHP) to further optimize the amount of antioxidants retained in the final product. Therefore, the objectives of this study were to determine the effects of different processing techniques on the antioxidant properties of blueberry juice and consumer acceptability of blueberry juices developed from selective processing techniques (i.e. cold processing versus hot processing). Individually quick frozen Croatan blueberries were treated with enzyme (Rapidase TM) and pressed at 22oC, 43oC and 75oC, followed by further pasteurization of the initial cold press and hot pressed (43oC) juices at 75oC. In addition, trial studies were conducted using HHP processing at 400 MPa for 10 min, 20 min, and 30 min holding times. Antioxidant levels were measured by changes in total anthocyanins, total phenols, and Oxygen Radical Absorbance Capacity (ORAC) values. Results indicated the hot-pressed juice (75oC) was significantly higher in antioxidant activity compared to the hot-pressed juice (43oC) followed by the cold-pressed juice (22oC). Addition of heat to the cold and hot-pressed juices caused an increase in the overall antioxidant activity. However, juice samples pressed at 75oC resulted in the greatest levels of total anthocyanins, phenols, and antioxidant capacity. There was a substantial amount of anthocyanins and phenolics recovered in the blueberry juice processed using HHP. The HHP30min resulted in a higher antioxidant activity than the HHP20min with the HHP10min exhibiting the lowest antioxidant activity. In comparison to thermal processing, there were no significant differences between the hot pressed juice (43oC) and the pressurized treatments at 20 min and 30 min holding times. Overall, equivalent antioxidant activity was achieved between the HHP20min and the hot pressed juiced (43oC), with a similar ORAC value for the HHP30min. These results suggest that selective processing can be used to improve the antioxidant yield in blueberry juice. Though the addition of heat to the juices resulted in the highest levels of antioxidant activity, the application of greater levels of HHP may be an effective non-thermal processing technique to maximize antioxidant activity while minimizing sensory loss during blueberry juice processing. Evaluation of heat treated blueberry juices by consumers (n=79) was based on the following attributes: overall acceptability, blueberry flavor intensity, blueberry flavor liking, sweetness intensity, sweetness liking, overall flavor liking, overall acceptability and overall appearance liking. Results from the consumer acceptability test indicated the juice extracted at 75oC and 43oC was more readily accepted by consumers than the cold- pressed juice with mean hedonic ratings of 6.33, 6.05, and 4.78, respectively. Overall, the thermally processed blueberry juices yielded a product with relatively high levels of antioxidants with a deep rich blue-purplish color that was appealing to consumers.
Date: 2007-12-08
Degree: MS
Discipline: Food Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/684

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