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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Citrus and Other Subtropical Products Research » Research » Research Project #423290


Location: Citrus and Other Subtropical Products Research

2013 Annual Report

1a. Objectives (from AD-416):
1. To identify the compounds responsible for off flavors in juice and pulp provided by Coca Cola/Minute Maid. 2. To understand the mechanisms of formation of responsible contaminants by conducting experiments that simulate conditions that are favorable for the development of off-flavors.

1b. Approach (from AD-416):
Samples of defective and normal juice/pulp will be obtained from the industry and analyzed by gas chromatography-olfactometry (GC-O) and a trained sensory evaluation panel. Compounds that are present in the defective juice but not in the normal juice will be identified and quantified using gas chromatography-mass spectrometry (GC-MS) and gas chromatography-pulsed flame photometric detector (GC-PFPD). If warranted by panel evaluations, analysis of non-volatile flavor compounds will also be conducted using liquid chromatography (LC) and liquid chromatography-mass spectrometry (LC-MS). Confirmation of contribution of target compounds to off-flavor will be done by spiking normal orange juice with food grade compound(s) of interest and presented to panelists. Once the compounds that cause off-odor or off-taste are identified and quantified, then experiments will be set up to mimic temperature abuse and/or microbial contamination, and oxidation and the product re-evaluated compared to a control product stored under ideal conditions. This information will be useful to industry to understand which conditions of shipping and storing pulp products result in off-flavors so that these conditions can be avoided, or monitored allowing prediction of product quality. This should result in less product loss due to flavor quality problems, benefitting the industry as a whole.

3. Progress Report:
This project is related to Objective 1 of this in-house project: Evaluate the effect of genetics on microbial and composition of flavor and healthful compounds sugars, acids, volatiles, carotenoids, total phenolics, pectin and fiber -in citrus, tomato, and subtropical-bred small fruit breeding lines and Objective 2: Relate chemical composition to sensory flavor and pathogen resistance data from Objective 1 to determine which compounds are important for flavor or have antimicrobial properties. Pulp samples provided by the industry were analyzed by gas chromatography (GC), mass spectrometry (MS) and olfactometry (O), and also by sensory evaluation using expert panelists. Off flavored samples were described as moldy, chemical (oxidized), spicy, woody and clove-like,in contrast with control samples that had typical orange, sweet and fruity favor. Off flavor in samples was identified to be mostly due to large amounts of p-vinylguaiacol (PVG) and a reduction of the typical orange volatiles. PVG was described as vanilla, cinnamon, rotten fruit by GC-O. Heptanal and two unknown odor compounds were greater in the off favored samples than in the control, with descriptors of plastic, green, fatty. On the other hand, control samples had larger amount of typical orange juice compounds such as linalool (floral), decanal (citrus), beta-myrcene (metallic), ethyl hexanoate (fruity, citrus), 1-octen-3-one (floral, green, mushroom),(E)-p-2, 8-menthadien-1-ol (green, fresh, foral), decanal (citrus), carvone (mint), beta-damascenone (fruity, apple) and beta-ionone (violet). Quantification of PVG in the off-flavored pulp was 842 ppb, in contrast with less than 30 ppb in normal samples. Microbial analysis of samples revealed no initial microbial growth in off-flavored samples. However, control samples stored at 10 °C for 2 weeks or more had a red yeast growing, Rhodotorula rubra. This yeast has potential to convert ferulic acid to PVG. Experiments are in progress to confirm the source of PVG in off-flavored samples, by inoculating sterile orange pulp with R. Rubra, and storing at 10 °C for several weeks.

4. Accomplishments