Quality and Stability of Shelf-Stable Pulp-Rich Fruit Juice
Tart cherries, Concord grapes, and apples are known for their health benefits due to high phenolic content and antioxidant capacity. Apples are also a rich source of fiber, helping to reduce the risk of some types of cancer. However, current juice processing leads to significant losses of these compounds through degradation heating and poor extraction from fruit. Pomace, a byproduct of pressing, is a rich source of total phenols, antioxidants, and dietary fiber. Therefore, alternative processing approaches which promote the preservation of these compounds are essential. Our objective was to develop pulpy juices from tart cherries, Concord grapes, and apples with maximum retention of fruit components and to evaluate storage quality of pulpy juices against clear juices. The following fruits were used in this study: Concord grape; tart cherry cv. Balaton and Montmorency; three varieties of red apple: Cortland, Empire, and McIntosh; and one variety of yellow apple: Golden Delicious. Fruits were harvested from the New York State Agricultural Experiment Station Orchards, Geneva, NY during the 2007 harvesting season. Juices were processed as clarified/clear (depectinased) and pulpy. A turbo extractor with two screen sizes, and a high shear mixer, were employed in pulpy tart cherry and Concord grape juice processing. A turbo extractor was used with or without a blanching and/or enzymatic treatment in pulpy apples juice processing. Juices were pasteurized by hot-filling at 85?C in 10-oz glass bottles. Whole fruit and juices were analyzed for pH, acidity, soluble solids, and dry and pectin content. Juice viscosity was also measured. Shelf-life studies at 18?C were conducted at 0, 12, and 24 weeks to determine changes over time in color, percent settled solids, turbidity, total phenolics content, antioxidant capacity, anthocyanin content and polymeric color (only in tart cherry and Concord grape). Total phenolic and anthocyanin content, antioxidant capacity, and percent polymeric color in whole fruits were also measured in extracts prepared by methanol extraction of freeze-dried powdered fruit. Sensory evaluations were conducted at 0 and 24 weeks to determine an acceptance of color, flavor, mouthfeel, and overall acceptability using a 7-point hedonic scale. The ranking test was used for flavor intensity and preference. Pulpy juices had higher phenolic and anthocyanin content, and antioxidant capacity than clear juices of the same fruit type; the content was comparable to that of whole fruits. These compounds in pulpy juices were 73 to 87% of whole tart cherry, 95 to 100% of whole Concord grapes, and 60 to 100% of whole apples. The percent loss over time of these compounds was similar in clear and pulpy juices from tart cherry and Concord grapes; however, the content in pulpy tart cherry juices was 13 to 41% higher than that of clear juices, and 50 to 134% higher in Concord grape juices. Even though the percent loss of total phenols and antioxidant capacity over 24 weeks in clear apple juices was lower (0 to 11%) than that of pulpy juices (6 to 22%), pulpy juices had 1.7 to 3.6 times higher total amounts of these compounds than clear juices. Dry content of pulpy juices were 0.3 to 11.8% higher than clear juices. Pectin content of pulpy juices was comparable to that of whole fruits. There was almost no pectin in clear juices. Pulpy juices represented a rich source of soluble fiber and one serving contained 0.7 to 11.6 g pectin. Sensory evaluation confirmed that overall acceptability and preference of pulpy juices were as equally acceptable as clear juices at 0 weeks storage but was lower at 24 weeks. However, pulpy juices were rated positively in all attributes and thus were acceptable from a consumer view point. Pulpy juices could be a healthy shelf-stable fruit juice product if the processing is optimized.
Dr. Olga Padilla-Zakour, Dr. Edward McLaughlin
Pulpy juices; Tart cherries; Apples; Concord grapes
dissertation or thesis