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Randolph M. Beaudry

The application of low oxygen through modified atmosphere packaging (MAP) is a technique used successfully to preserve the visual quality of lettuce and some other commodities. The expansion of use of low O2 via MAP to preserve quality of most commodities is limited by technical difficulties achieving target O2 concentrations, adverse physiological responses to low O2, and lack of beneficial responses to low O2. Low O2 often is not used simply because the physiological responses governed by the gas are not limiting quality maintenance. For instance, shelf life may be governed by decay susceptibility, which is largely unaffected by low O2 and may actually be exacerbated by the conditions encountered in hermetically sealed packages. Physiological processes influenced by low O2 and limit storability are discussed. The interdependence of O2 concentration, O2 uptake by the product, and temperature are discussed relative to requirements for packaging films.

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Randolph M. Beaudry

A theoretical model was developed that predicts how volatiles synthesized by fruit accumulate in the fruit interior and the fruit cuticle. Model inputs include temperature, rates of volatile synthesis, solubility of the volatile in the cuticular material, and the permeability of the volatile through the cuticle. The model indicated that the accumulation of volatiles was highly temperature-dependent and dependent upon the nature of the interaction between the volatile and the cuticle. For volatiles whose cuticular permeability declined rapidly with temperature, the concentration in the fruit and fruit cuticle tended to increase with decreasing temperature. This accumulation of volatiles in the fruit and fruit cuticle with decreasing temperature was enhanced by a decrease in the heat of solution (i.e., temperature sensitivity of solubility) and diminished by an increase in the Q10 Of the rate of volatile synthesis (i.e., the temperature sensitivity of the rate of synthesis). The model suggests that storage temperature can influence volatile retention and, hence, the volatile profile.

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Randolph M. Beaudry

Blueberry fruit were sealed in 0.00254 cm (1 mil) thick, 200 cm2 low density polyethylene pouches, which, in turn, were sealed in containers continually purged with gas mixtures containing 0, 20, 40 or 60 kPa CO2 and held at 15C. Sampling the gas composition of the enclosed package permitted accurate determination of O2 uptake, CO2 production and the respiratory quotient (RQ) despite the high background CO2 levels. O2 uptake was minimally affected by the CO2 treatments. CO2 production, however, increased at CO2 partial pressures over 20 kPa, resulting in an elevated RQ at 40 and 60 kPa CO2. Raising the CO2 partial pressure caused the fruit to become more sensitive to lowered O2, raising the O2 partial pressure associated with the RQ breakpoint.

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Rufino Perez and Randolph M. Beaudry

Volatile production is known to change with stages of plant organ development. Research has primarily focused on ripening-related volatiles; however, the potential exists to use volatiles as markers of organ damage and senescence. We have employed gas chromatography/mass spectrometry to establish stages of senescence based on volatile profiles of whole and lightly processed broccoli and carrot. An air-tight chopping apparatus was used as a flow-through chamber system and the exit gas stream analyzed for each commodity with and without tissue disruption. For carrot, isoprenoid pathway volatiles, such as 3-carene, caryophellene, α-caryophellene, and β-pinene, increase with damage and tissue senescence. Similar trends were obtained for broccoli with volatiles characteristic of β-oxidation and shikimic acid pathways. Time and condition-related volatile profile changes will be presented for carrot, broccoli, and strawberry.

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Weimin Deng and Randolph M. Beaudry

Sampling factors that could affect gas chromatograph (GC) response for volatile analysis such as syringe pumping time, injection volume, needle length, temperature, and the type of volatile were investigated. Capillary GC column segments (steel and glass) were installed in gas-tight syringes and used as needles for volatile analysis. Standard stainless-steel needles were also used. Hexylacetate, ethyl-2-methylbutyrate, 6-methyl-5-hepten-2-one, and butanol standard were measured. The number of pumps required to maximize GC response for each needle–volatile combination was determined. Maximal GC response for hexylacetate using standard stainless steel, capillary glass, and capillary steel needles required 10, 20 and 30 pumps, respectively. However, for butanol measurement, the optimal syringe pump number was 5 to 10 for all needle types. The use of a capillary needle resulted in an increase in GC response in the range of 3- to 15-fold relative to a standard stainless steel needle. Injection volume affected GC response in a needle-and volatile-dependent manner. In no case did injection volume vs. GC response extrapolate through origin. The GC response for capillary column needles increased as temperature decreased. Capillary column needles may be useful tools for analysis of volatiles that readily partition into the column coating.

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Weimin Deng and Randolph M. Beaudry

A simple packaging system was developed to simultaneously measure volatile production by plant organs and the permeability of the packaging film to those volatiles. In this system, apple (Malus domestica Borkk cv Golden Delicious) was packaged in low-density polyethylene (LDPE) bag and placed into a glass jar with a low air flow. The package and jar head spaces were sampled for aroma volatile analysis by gas chromatograph. Analysis was by gas chromatography/mass spectrometry. This system allowed at least 10 volatile compounds and their permeabilities to be measured. This system permits volatile production to be measured for products in the package so the product need not be removed from its storage environment. This may be a useful method for determining the dynamic relationship between flavor volatile synthesis and package atmosphere for packaged produce.

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Rufino Perez and Randolph M. Beaudry

Oxygen diffusive resistance of preclimacteric banana flesh is considered to be much lower than skin resistance such that negligible internal gradients in O2 are expected. Therefore, blocking O2 influx and CO2 efflux of banana by sealing 100% of the pores over fractions of one 1/4, 1/2, 3/4, and 7/8 of the surface, should generate an internal modified atmosphere similar to that achieved by using fruit coatings which cover 100% of banana surface but block only a fraction of the pores. Using gas trapping vials to determine internal O2 and CO2 levels, we followed O2 and CO2 behavior along the length of the fruit. Gradients for O2 and CO2 were found indicating sufficient flesh resistance exists to prevent consideration of internal resistances as negligible. Internal gas gradients were linked to ripening in that firmness and greenness were higher at the coated end. These results imply that banana flesh can not be treated according to the hollow sphere models previously suggested.

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Randolph M. Beaudry and Niti Dube

The dynamic physiological processes of CO2 production, O2 uptake and ethylene synthesis for ripening tomato (Lycopersicon esculentum L.) and banana (M usa sp. cv `Valery') fruit were measured using a novel approach. Fruit were sealed in low density polyethylene pouches of known permeability to O2, CO2 and C2H4. The flux of these gases during the climacteric was closely tracked by their respective partial pressure in the headspace of the pouches. Some limitations in application exist due to modification of the atmosphere (primarily O2) within the pouch, however, the system provides some distinct advantages. These include the absence of gas handling equipment, measurement of O2 uptake despite high background levels of O2, measurement of the respiratory quotient, and measurement of low rates of ethylene production. Compared to low-flow, flow-through respirometers, this type of respirometer has the potential to permit the accumulation of several-fold higher levels of some gases due to the property of differential gas permeabilities possessed by polymer films.

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Randolph M. Beaudry and Frank Dennis

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Rufino Perez and Randolph M. Beaudry

We hypothesized that the blocking of O2 influx and CO2 efflux in banana (Musa acuminata) by sealing nearly 100% of the pores over a fraction of the surface would generate a modified internal atmosphere in a manner similar to fruit coatings that cover 100% of the banana surface but only block a fraction of the pores. This hypothesis was based on the observation made by previous workers that the flesh of mature green bananas has insignificant resistance to O2 diffusion relative to the resistance imposed by the skin of the fruit. We modified the O2 diffusion pathway in bananas by covering, beginning at one end, ¼, ½, ¾, and ⅞ of the fruit surface with paraffin, which sealed essentially 100% of the surface where it was applied. Large end-to-end O2 and CO2 gradients developed within coated fruit, relative to the uncoated control, suggesting that the diffusive resistance in the pulp was not insignificant. Since the large gradients of O2 generated caused uneven ripening, using fractional coatings may help analyze gas exchange properties, but it is not suitable for commercially controlling ripening of bananas.