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P. Chowdary Talasila, Arthur C. Cameron, and Randolph M. Beaudry

In modified-atmosphere (MA) packaging of fruits and vegetables, there is a risk of generation of excessively low, injurious O2 levels due to improper package design, temperature abuse, and/or product respiration rate variation. When exposed to injurious O2 levels, product quality deteriorates and off-flavors develop. Also, there is increased production of ethanol and other fermentative volatiles. For blueberries, off-flavors were positively correlated with tissue ethanol level when the product was exposed to a range of O2 partial pressures (0 to 18 kPa) and temperatures (0 to 25C). A biosensor that measures ethanol level in package headspace will be useful for easy identification of the packages containing injured products. Biosensors that measure ethanol in aqueous solutions by a color change reaction are commercially available. We have found a positive correlation between the color (hue) of the sensor and headspace ethanol levels in packages containing cut broccoli at 22C. The utility of the biosensor in quality assurance (QA) based on the identification of low-O2 injury of the packaged products will be discussed.

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Ruomwadee Lakakul, Randolph M. Beaudry, and Ruben J. Hernandez

Reduced O2 and elevated CO2 atmospheres have the potential to control browning, decay and texture changes in sliced apples. Modified-atmosphere packaging (MAP) was used as a tool for obtaining respiratory data needed to calculate permeability characteristics of packaging films that will obtain and maintain target gas levels in the package headspace at 0, 5, 10 and 15C. Respiratory data collected for sliced apple fruit include the K1/2 (the O2 level at the half-maximal respiratory rate), RRO2max (the maximal respiratory rate) and the Lower O2 limit for aerobic respiration. The K1/2 and RRO2max appeared to increase exponentially with temperature. The lower O2 limit was approximately 0.1, 0.2, 0.3 and 0.35 kPa at 0, 5, 10 and 15C, respectively. Permeability characteristics needed for various storage strategies were calculated based on these data.

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Rufino Perez, John Linz, Matt Rasick, and Randolph M. Beaudry

Minimally processed fruits and vegetables, by virtue of cell disruption resulting from processing and handling, can encourage the growth of microorganisms. There is potential for identification of microorganisms and characterization of microbial products and constituents in food, based on volatile profile analysis. We have prepared a flow-through system to grow several bacteria including E. coli 25922-ATCC and E. coli 0157:H7 and monitored the volatile profiles under conditions similar to those experienced by minimally processed fruits and vegetables during marketing conditions. Specific volatiles have been identified that may have potential to serve as signature-type volatiles in accurate automated quality control systems. For example, indole and a number of short-chain fatty acids are produced in copious amount by E. coli 25922-ATCC, but are not constituent of broccoli or carrot aroma profiles. The data suggest that specific volatiles may serve as “markers” for bacterial presence.

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Jun Song, Weimin Deng, Randolph M. Beaudry, and Paul R. Armstrong

Trends in chlorophyll fluorescence for `Starking Delicious', `Golden Delicious' and `Law Rome' apple (Malus ×domestica Borkh.) fruit were examined during the harvest season, during refrigerated-air (RA) storage at 0 °C, following RA and controlled-atmosphere (CA) storage, and during a poststorage holding period at 22 °C. Fluorescence parameters of minimal fluorescence (Fo), maximal fluorescence (Fm), and quantum yield [(Fm-Fo)/Fm, otherwise denoted as Fv/Fm] were measured. During `Starking Delicious' fruit maturation and ripening, Fv/Fm declined with time, with the rate of decline increasing after the ethylene climacteric. During RA storage, all fluorescence parameters remained constant for approximately 2 weeks, then steadily declined with time for `Starking Delicious' fruit. Superficial scald was detected after Fv/Fm had declined from an initial value of 0.78 to ≈0.7. Fv/Fm was consistently higher for CA-stored fruits than for RA-stored fruits. We were able to resegregate combined populations of “high-quality” (CA) and “low-quality” (RA) `Law Rome' fruit with 75% accuracy using a threshold Fv/Fm value of 0.685, with only 5% RA-stored fruit incorrectly identified as being of high quality. During a poststorage holding period, Fo, Fm, and Fv/Fm correlated well with firmness for `Starking Delicious', but not for `Golden Delicious' fruit, which were already soft. Fo and Fm were linearly correlated with hue angle for 'Golden Delicious' fruit, decreasing as yellowness increased. The accuracy, speed of assessment, and light-based nature of fluorescence suggests that it may have some practical use as a criterion to assist in sorting apple or other chlorophyll-containing fruit or vegetables on commercial packing lines.

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Michael Wendorf, Nazir A. Mir, and Randolph M. Beaudry

Broccoli tissue, ranging in weight from 7 to 21 g, was sealed in packages made from low-density polyethylene (LDPE) of various thickness and permeability to establish a range of O2 levels in the package headspace. A pouch containing either hydrogen peroxide (H2O2) or water as a control was also sealed in the package. For packages that developed anaerobic atmospheres, inclusion of H2O2 permitted the maintenance of aerobic conditions for up to 3 days at ambient room temperature. These results suggest that the plant tissue is able to actively metabolize the H2O2 vapor to generate O2, which will prevent the development of low-O2 conditions in packaged produce, even under conditions of elevated storage temperature.

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Nazir Mir, Michael Wendorf, Rufino Perez, and Randolph M. Beaudry

The relationship between chlorophyll fluorescence of `Cortland', `Redchief Delicious', and `Empire' apple (Malus ×domestica Borkh.) fruit and the development of superficial scald was studied during 120 days of refrigerated air (RA) storage at 0 °C and during 7 days of poststorage holding at 22 °C. Minimal fluorescence (Fo), maximal fluorescence (Fm), photochemical efficiency (Fv/Fm, where Fv=Fm=Fo) and coefficient of photochemical fluorescence quenching (qp) were measured. During storage, while Fv/Fm and Fm declined in `Cortland' and `Redchief Delicious' fruit over time, these two measures of chlorophyll fluorescence remained stable in `Empire' fruit. Of the three cultivars, only `Empire' is resistant to and did not develop superficial scald. A decline in Fv/Fm preceded scald development in `Cortland' and `Redchief Delicious' fruit. After 30 days of storage, qp began to decrease in fruit from all three cultivars. Prestorage diphenylamine (DPA) application had no effect on Fv/Fm, Fo, and Fm and only marginally improved maintenance of qp, but completely prevented the development of superficial scald. Poststorage holding at 22 °C accelerated the rate of change in most fluorescence measurements. The decline in the Fv/Fm ratio and/or qp with storage time may be in response to senescence-related factors that also enhance scald susceptibility, however, Fv/Fm does not appear to be directly related to superficial scald susceptibility per se.

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Mauricio A. Cañoles, Randolph M. Beaudry, Chuanyou Li, and Gregg Howe

Six-carbon aldehydes and alcohols formed by tomato (Lycopersicon esculentum Mill.) leaf and fruit tissue following disruption are believed to be derived from the degradation of lipids and free fatty acids. Collectively, these C-6 volatiles comprise some of the most important aroma impact compounds. If fatty acids are the primary source of tomato volatiles, then an alteration in the fatty acid composition such as that caused by a mutation in the chloroplastic omega-3-fatty acid desaturase (ω-3 FAD), referred to as LeFAD7, found in the mutant line of `Castlemart' termed Lefad7, would be reflected in the volatile profile of disrupted leaf and fruit tissue. Leaves and fruit of the Lefad7 mutant had ≈10% to 15% of the linolenic acid (18:3) levels and about 1.5- to 3-fold higher linoleic acid (18:2) levels found in the parent line. Production of unsaturated C-6 aldehydes Z-3-hexenal, Z-3-hexenol, and E-2-hexenal and the alcohol Z-3-hexenol derived from 18:3 was markedly reduced in disrupted leaf and fruit tissue of the Lefad7 mutant line. Conversely, the production of the saturated C-6 aldehyde hexanal and its alcohol, hexanol, were markedly higher in the mutant line. The shift in the volatile profile brought about by the loss of chloroplastic FAD activity in the Lefad7 line was detected by sensory panels at high significance levels (P < 0.0005) and detrimentally affected fruit sensory quality. The ratios and amounts of C-6 saturated and unsaturated aldehydes and alcohols produced by tomato were dependent on substrate levels, suggesting that practices that alter the content of linoleic and linolenic acids or change their ratios can influence tomato flavor.

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Sastry S. Jayanty, Mauricio Cañoles, and Randolph M. Beaudry

We studied the dose-response of `Redchief Delicious' apple [Malus sylvestris (L) Mill. var. domestica (Borkh.) Mansf.] fruit to repeated (weekly) dosages of 0.0, 0.02, 0.1, and 1.0 μL·L-1 1-methylcyclopropene (1-MCP) by measuring fruit firmness and chlorophyll fluorescence throughout an extended storage period at 0, 5, 10, 15, and 20 °C. The rate of firmness loss for nontreated fruit increased with increasing temperature. 1-MCP applied at concentrations of 0.1 and 1.0 μL·L-1 slowed firmness loss. The 1-MCP dose-response curve for the rate of firmness loss was essentially the same for all five temperatures. A concentration of 1.0 μL·L-1 1-MCP prevented firmness loss at all temperatures for the duration of the study; however, after holding fruit for an additional 7 days at room temperature, the fruit stored at 10 °C softened with increasing storage duration, whereas fruit at stored at higher and lower temperatures did not. The influence of 1-MCP on chlorophyll fluorescence (Fo and Fm) was markedly affected by temperature; Fo increased during storage at higher storage temperatures and this increase was enhanced by 1-MCP. Conversely, Fm decreased during storage and the rate of decline was much greater at the higher storage temperatures; the rate of decline was reduced by 1-MCP, but only at the higher storage temperatures. Photochemical efficiency (Fv/Fm) of nontreated fruit declined with time for all storage temperatures. Treatment with 0.1 and 1.0 μL·L-1 1-MCP only marginally reduced the rate of decline of photochemical efficiency. Sample loss due to decay increased with temperature, but was reduced by 1-MCP at all temperatures.

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Jun Song, Rujida Leepipattanawit, Weimin Deng, and Randolph M. Beaudry

Hexanal vapor inhibited hyphae growth of Penicillium expansum and Botrytis cinerea on potato dextrose agar (PDA) and on apple (Malus domestica Borkh.) slices. After 48 hours exposure to 4.1 μmol·L-1 (100 ppm) hexanal, the hyphae growth of both fungi was about 50% that of untreated controls. At a concentration of 10.3 μmol·L-1 (250 ppm), neither fungus grew during the treatment period, however, some growth of both fungi occurred 120 hours after treatment. At concentrations of hexanal vapor of 18.6 μmol·L-1 (450 ppm) or more, the growth of both fungi ceased and the organisms were apparently killed, neither showing regrowth when moved to air. When fungi were allowed to germinate and grow for 48 hours in hexanal-free air, a subsequent 48-hour exposure to 10.3 μmol·L-1 hexanal slowed colony growth relative to controls for several days and a 48-hour exposure to 18.6 μmol·L-1 stopped growth completely. Concentrations of hexanal that inhibited fungal growth on PDA also retarded decay lesion development on `Golden Delicious' and on `Jonagold' apple slices. Hexanal was actively converted to aroma volatiles in `Jonagold' and `Golden Delicious' apple slices, with hexanol and hexylacetate production strongly enhanced after 20 to 30 hours treatment. A small amount of butylhexanoate and hexylhexanoate production was also noted. Within 16 hours after treatment, no hexanal could be detected emanating from treated fruit. Since hexanal was metabolized to aroma-related volatiles by the fruit slices, the possibility of hexanal being an essentially residue-less antifungal agent seems likely. The possibility of developing a system for treating apple slices with hexanal in modified-atmosphere packages was also examined. The permeability of low-density polyethylene (LDPE) film to hexanal and hexylacetate was, respectively, about 500- and 1000-fold higher than LDPE permeability to O2. The permeability of both compounds increased exponentially with temperature, with hexanal permeability increased 6-fold while hexylacetate increased only 2.5-fold between 0 and 30 °C.

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Jennifer M. Evans, Veronica A. Vallejo, Randolph M. Beaudry, and Ryan M. Warner

The biosynthesis of steviol glycosides is affected by both genetic and environmental factors. To evaluate the influence of total daily solar radiation or daily light integral (DLI) under long-day conditions on steviol glycoside concentration, we grew Stevia rebaudiana under ambient irradiance or varying levels of shading at different times of the year in both greenhouse and field environments, resulting in DLIs ranging from 3.55 to 20.31 mol·m−2·d−1 in the greenhouse and 10.32 to 39.7 mol·m−2·d−1 in the field. Total steviol glycoside concentration of selected leaves from greenhouse-grown plants increased as DLI increased up to ca. 10 mol·m−2·d−1, remaining constant with further increases in DLI, and was similar across the range of DLIs evaluated in the field. DLI influenced both the concentration and the relative proportions of specific steviol glycosides. Rebaudioside A concentration increased as DLI increased from 3.55 to 8.53 mol·m−2·d−1, remaining similar with further increases in DLI. Rebaudioside D and stevioside concentration of selected leaves from field-grown plants decreased by 22% and 13%, respectively, as DLI increased from 10.32 to 39.7 mol·m−2·d−1, while rebaudioside A and M concentrations remained similar across this DLI range. Collectively, these results indicate that the greatest influence of DLI on steviol glycoside concentration occurs under relatively low DLIs (<10 mol·m−2·d−1). However, higher DLIs can significantly affect the synthesis of minor glycosides of increasing commercial importance including rebaudioside D.