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United States Department of Agriculture

Agricultural Research Service

Research Project: Postharvest Sensory, Processing and Packaging of Catfish

Location: Food Processing and Sensory Quality Research

2012 Annual Report


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:
California-grown pomegranate cultivars were selected from the Agricultural Research Service (ARS) germplasm repository to represent high versus low quality characteristics. Aroma volatiles were analyzed in freshly pressed juices from several cultivars. Based upon color, ellagic acid content, and bitterness/astringency, several cultivars are not suitable for juice; however, they served to deliver sensory and analytical databases to calibrate future experiments.

Several locally grown blueberry varieties and California pomegranate cultivars were analyzed by gas chromatograph-mass spectrometry to determine their volatile profiles. We have identified substantially different volatile profiles between southern highbush and rabbiteye blueberry types. Differences positively correlated with desirable sensory attributes may guide variety selection for juice production.

Not-from-concentrate pomegranate juice was prepared by hydraulic pressing, ultra-filtration, and pasteurization. Processing stages were used to compare compositional and quality differences. Juice stability during storage was also evaluated. Volatile compounds have been identified in these juices. Juices from whole pressed fruit, ultra-filtration, and in-house pasteurization had very similar volatile profiles, with 32 compounds recovered; however, commercial concentrates and our own in-house ARS concentrate had only nine compounds. Loss of several flavor/aroma compounds occurred in commercial concentrates compared against freshly produced, not-from concentrate juices.

Differences in the recovery and quality of blueberry juice with different processing regimes were studied in selected varieties of rabbiteye and southern highbush blueberries. Fruit was pressed immediately after harvest/freezing, and by making a mash with heat and heat plus commercial pectinase enzymes. Commercial pectinases used in heated mashes ameliorated gelling and increased percentage juice recovery.

Several local rabbiteye and southern highbush blueberry varieties were harvested twice during the season and stored frozen to evaluate quality and chemical differences in hand-pressed juice. Blueberry juice, pomace, and skins were analyzed for polyphenolics, anthocyanins, anthocyanidins, oxygen radical absorbance capacity, and total phenolics. A detailed gas chromatography-olfactometry-mass spectrometry appraisal is under way to differentiate blueberry types for volatiles and human described aroma attributes.


4.Accomplishments
1. Not-from-concentrate, pomegranate juice pasteurization. Standard production of pomegranate juice is to produce a concentrate, which is stored, and later diluted out to produce commercial juices. Researchers at the Agricultural Research Service, New Orleans, Louisiana, produced a not-from-concentrate juice prepared from pomegranates by hydraulic pressing, followed by ultra-filtration and high-temperature short-time pasteurization, using commercial-like pilot-plant equipment. Reducing processing abuse, i.e., heat and concentration steps, retained more low-molecular-weight flavor volatile compounds compared with commercial juices. Further analysis will guide processing technologies to protect desirable compounds during juice production, while ameliorating undesirable flavor/aroma changes. Smaller or start-up companies entering the pomegranate juice arena may benefit from initially delivering consumers not-from-concentrate product because it may be perceived as superior to most juices marketed that are produced from concentrates.

2. Blueberry aroma/flavor compounds identified. Researchers at the Agricultural Research Service, New Orleans, Louisiana, used gas chromatography-olfactometry data from blueberries with gas chromatograph-mass spectrometry data to identify volatile compounds associated with blueberry aroma. In addition to cis-3-hexenal and linalool (previously reported), the terpenoids fenchone, geraniol, and carene were found to enhance blueberry aroma. These compounds singularly possess pungent, floral-like aromas, but when present in juice, served to enhance the overall blueberry aroma. Selecting blueberry varieties possessing these compounds and maintaining them through pasteurization could improve consumer acceptability of blueberry juices, leading to further demand and increased production.

3. Sensory evaluation and correlation to quality parameters in blueberry. Several local rabbiteye and southern highbush blueberry varieties were harvested twice during the season, frozen, then thawed and pressed into juice to evaluate quality and chemical differences. Scientists at the Agricultural Research Service, New Orleans, Louisiana, studied the effect of sugars, acids, and polyphenols on basic tastes of sweet, sour and bitter, and mouth feels of astringency, tooth-etch, tongue tingle, tongue numbing, and throat burn. Total anthocyanins slightly correlated with sweet taste and did not correlate with bitter or astringency. Glucose and oxalic acid were highly correlated with sweet taste and negatively correlated with bitter taste. Quinic acid (highest in these blueberries) was negatively correlated with sweet, whereas, citric acid was positively correlated with sweet taste. Tooth-etch and astringency were highly correlated, and tongue burn and sour taste were highly correlated. The interactions between sugars and acids was found to significantly impact the perception of sweet, sour, bitter and astringent, as well as some other mouth feels. Historically, low molecular weight acids and phenolic compounds have been ascribed to confer bitterness, whereas, high molecular weight polymeric phenols confer astringency. Hence, these data appear to reflect more potential bitterness issues, whereas, forthcoming data on higher molecular weight polyphenolics and anthocyanins, plus tannins, might confirm that the astringency is due to complex chemical interactions and polyphenolic changes occurring in situ.

4. Blueberry juice recovery in local varieties using various processing regimes. Commercially harvested blueberry varieties on many farms are commonly combined and sold as co-mingled products. In the southeast, newer southern highbush varieties are replacing rabbiteye varieties. Researchers at the Agricultural Research Service, New Orleans, Louisiana, investigated differences in juice recovery by various processing regimes, including native fresh presses versus heated mashes in typical mixed varieties grown in Mississippi. Fruit was pressed immediately after harvest/freezing, and by making a mash with heat and heat plus commercial pectinase enzymes. Percent juice recovery, rapid quality and chemical appraisals, and processing ease will dictate the direction for future in-house pilot plant juice experiments. Preliminary data indicates that a heated mash followed by commercial pectinase enzymes delivers the highest juice recovery and has no gelling problems. Furthermore, the newer southern highbush varieties tested had superior informal taste and sweetness compared with older rabbiteye varieties. This is good information supporting local grower’s decisions to convert several fields over to the earlier bearing southern highbush varieties, which are more competitively priced on the National market.


Review Publications
Amaro, A.L., Beaulieu, J.C., Grimm, C.C., Stein, R.E., Almeida, D.P. 2011. Effect of oxygen on aroma volatiles and quality of fresh-cut cantaloupe and honeydew melons. Food Chemistry. 130(1):49-57.

Beaulieu, J.C., Ingber, B.F., Lea, J.M. 2011. Physiological, volatile, and SEM surface effects resulting from cutting and dipping treatments in cantaloupe. Journal of Food Science. 76(7):S415-S422.

Bett Garber, K.L., Lea, J.M., Champagne, E.T., Mcclung, A.M. 2012. Whole grain rice flavor asssociated with assorted bran colors. Journal of Sensory Studies. 27:78-86.

Last Modified: 9/22/2014
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