1a. Objectives (from AD-416)
Objective 1: Determine the correlative relationships between chemical composition and descriptive sensory scores to establish the levels of polyphenols (flavonoids, tannins, lignins, anthocyanins) relative to key flavor and taste compounds in model fruit juices that result in low to high ratings for astringency, bitterness, and other undesirable flavor attributes. Objective 2: Determine the effects of processing technologies on relative amounts of polyphenolic and key flavor compounds and resulting impact on the sensory profiles for juices, concentrates, and puree/fruit smoothie type products. Objective 3: Using the results of Objectives 1 and 2, develop means (e.g. complexation, masking, concentration, blending, buffering agents, encapsulating agents) to amplify positive flavor attributes and decrease astringency and bitter flavors in juices/beverages prepared from phytonutrient-rich fruits without adversely affecting phytonutrient content, solubility, stability, or phytonutrient bioavailability.
1b. Approach (from AD-416)
In Objective 1, baseline benchmarks will be established for high to low levels of sensory attributes in regards to total and selected monomeric and polymeric polyphenol content in single-strength blueberry and pomegranate juices prepared from commercial concentrates that have been diluted to Code of Federal Regulations (CFR) minimum and/or commercial °Brix standards. Flavor intensities will be related to the concentrations of polyphenol compounds, sugars, acids, and key flavor compounds. In Objective 2, changes in °Brix, acidity, color, total phenolic and key polyphenolic compound contents, antioxidant capacity, and sensory profiles of model, single-strength blueberry and pomegranate juices will be assessed at the juice processing stages (control points). Processing conditions will be altered at stages to improve the flavor profiles of juices, purées, and functional beverages without adversely affecting phytonutrient content, solubility, stability, or bioavailability. In Objective 3, further optimization of flavor and phytonutrient content/bioavailability will be achieved by incorporating into the processing scheme, novel physical and chemical means, and via varietal selection and blending.
3. Progress Report
Gas chromatograph-mass spectrometry was used to identify semi-volatile and volatile flavor and aroma compounds in rabbiteye blueberries and pomegranates. The identity of these components was confirmed with standards. Domestic and imported pomegranate juices pressed from arils (i.e., seed casings and fruit pulp separated from the peel) and whole fruit were characterized for aroma and flavor compounds. A popular U.S. grown cultivar (Wonderful) was used for this analysis. Several pomegranate cultivars were collected from the Agricultural Research Service germplasm collection in Davis, CA, and characterized for sweetness and astringency extremes. Based on a preliminary sensory evaluation, specific pomegranate cultivars were chosen to use for juice flavor research in the 2011 season. A blueberry lexicon (i.e., a library of terms and descriptors that are used to describe flavors and aromas) was developed and panelists were trained to use the lexicon on commercially bottled 100% blueberry juice and fresh squeezed blueberry juice. A number of analytical techniques were developed to support juice flavor and antioxidant retention. Two chromatographic methods were developed and refined to analyze blueberry and pomegranate juices for anthocyanins, anthocyanidins, polyphenolics and their various sugar residues in both native glycosylated form (i.e., with attached sugars) and nonglycosylated form (hydrolyzed to release the sugars). For nonglycosylated samples, the identities of the sugars were also determined. In addition, a liquid chromatographic-mass spectrometry method was refined to analyze organic acids in these juices. These components likely affect juice acidity, and confer other flavor attributes. In continuing work, several local rabbiteye blueberry varieties were harvested and frozen to begin evaluating various processing regimes. Methods to be tested include cold and hot press extraction, extraction with and without enzymes, and ultrafiltration. These juices will be assayed for polyphenolics components that have antioxidant properties and quality changes. To better assess changes their antioxidant potential, a standard oxygen radical absorbance capacity apparatus and method were adapted for the analysis of fruit juices. Evaluation of these properties will continue into next year. Whole pomegranate fruit were surface blanched, pressed on pilot plant equipment and batch pasteurized to assess flavor compounds, quality (soluble solids, color, organic acids) and polyphenolics changes. Blanching or batch pasteurization reduced juice color and organic acidity but increased titratable (net) acidity. Blanching reduced several volatile aldehyde and alcohol components slightly, whereas pasteurization significantly reduced aldehydes and terpenes that might be flavor-important, but increased alcohols and ketones that might confer undesirable flavors. After 28 days of storage, juice terpenes were almost completely lost and alcohols were increased in pasteurized juice.
1. Industry-oriented research on critical flavor issues in standard pomegranate juice. According to industry representatives, pomegranate juice might have off flavors and poor long-term shelf-life stability due to aerobic yeast and mold organisms on the fruit surface and inside the floral cavity (calyx) during pressing of the whole fruit. Subsequently ARS researchers at New Orleans, Louisiana, surface blanched whole pomegranate fruit, pressed fruit on pilot plant equipment and batch pasteurized juice to assess quality changes. Blanching and batch pasteurization reduced color and acidity but increased titratable acidity. Pasteurization reduced aldehydes and terpenes, and alcohols and ketones that might confer undesirable flavors increased. These results were expected. However, blanching had nominal effects on volatile compounds that might be flavor-important. Preliminary results indicate that preblanching fruit has little effects on the quality of juices but, further microbial analysis is warranted to determine if shelf-life is improved. If off-flavors can be reduced and oxidative flavors minimized, then these processing treatments might allow for creation of new shelf-stable, not-from-concentrate fresh juices.
2. Development of flavor and aroma volatile libraries for pomegranates and blueberries. Only recent reports have identified some flavor compounds in pomegranates. Likewise flavor compounds have not been extensively examined in rabbiteye blueberry since the 1970-80’s. Using gas chromatographic techniques, Agricultural Research Service researchers at New Orleans, Louisiana, determined the semi-volatile and volatile components of these fruits that contribute to flavor and aroma from a variety of fruit tissue types and cultivars. These libraries will be used to better assess changes in flavor and aroma of processed juices that occur during processing and storage.
3. A blueberry sensory lexicon was developed. In order to fill a void in the analysis of blueberry flavor, ARS researchers at New Orleans, Louisiana, developed a blueberry descriptive flavor lexicon and a sensory panel was trained on the lexicon in order to better compare and evaluate juice properties. The lexicon will ultimately allow researchers to associate or correlate quality attributes with changes in polyphenolics and acid levels and will enable better evaluation of juice processing and storage conditions.
Bett Garber, K.L., Greene, J., Lamikanra, O., Ingram, D., Watson, M.A. 2010. Effect of storage temperature variations on sensory quality of fresh-cut cantaloupe melon. Journal of Food Quality. 34:19-29.