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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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Eric Young

During natural leaf abscission, 2-year-old potted apple trees (Malus domestica Borkh. cv. MM.111 EMLA) were placed in a room at 6C for chilling [0,600, 900, or 1400 chilling units (CU)]. After each chilling treatment, respiration of shoot segments was measured as CO2 evolved and O2 consumed at 22C in several O2 concentrations. Respiration increased with oxygen concentration after all CU treatments. Carbon dioxide evolved at the several O2 levels did not show a pattern related to CU, but O2 consumed decreased at a decreasing rate with additional CU. Respiratory quotient was <1 at 0 and 600 CU and equal to 1 at 900 and 1400 CU, indicating a possible shift in respiratory substrate with chilling.

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Eric Young

During natural leaf abscission, two-year-old, potted apple trees (Malus domestica cv. MM.111 EMLA) were placed in a cold room at 6C for chilling. At 0, 600, 900, and 1400 chilling hours (CH), ten trees were removed and terminal shoots cut into four 15 cm sections. These sections were randomly placed in forty 10 1 test tubes at 20C and subjected to ten oxygen levels from 0.5 to 21% O2 with four reps each by flushing tubes with mixtures of air and nitrogen prior to sealing. Tubes remained sealed for 4 hr then reflushed and resealed for another 4 hr after which 1 ml gas samples were drawn and CO2 and O2 levels measured on a gas chromatograph. Respiration decreased with oxygen level at all CH. CO2 evolved did not show a pattern related to oxygen level, but O2 consumed decreased at a decreasing rate with additional CH. Respiratory quotient was below one at 0 and 600 CH and equal to one at 900 and 1400 CH, indicating a possible shift in respiration substrate with chilling.

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Randolph M. Beaudry, Arthur C. Cameron, Ahmad Shirazi and Diana L. Dostal-Lange

Abbreviations: CA, controlled atmosphere; LDPE, low-density polyethylene; MAP, modified-atmosphere packaging; RQ, respiratory quotient. 1 Present address: Dept. of Food Science and Human Nutrition, Michigan State Univ., East Lansing, MI 48824

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Edna Pesis and Rosa Marinansky

Abbreviations: AA, acetaldehyde; RQ, respiratory quotient; TSS, total soluble solids content. Supported by grant no. 1-900-85 from BARD, the U.S.-Israel Binational Agricultural Research and Development Fund. Contribution from the Agr. Res

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Dennis W. Joles, Arthur C. Cameron, Ahmad Shirazi, Peter D. Petracek and Randolph M. Beaudry

`Heritage' raspberries (Rubus idaeus L.) were sealed in low-density polyethylene packages and stored at 0, 10, and 20C during Fall 1990 and 1991 to study respiratory responses under modified atmospheres. A range of steady-state O2 and CO2 partial pressures were achieved by varying fruit weight in packages of a specific surface area and film thickness. Film permeability to O2 and CO2 was measured and combined with surface area and film thickness to estimate total package permeability. Rates of O2 uptake and CO2 production and respiratory quotient (RQ) were calculated using steady-state O2 and CO2 partial pressures, total package permeability, and fruit weight. The O2 uptake rate decreased with decreasing O2 partial pressure over the range of partial pressure studied. The Michaelis-Menten equation was used to model O2 uptake as a function of O2 partial pressure and temperature. The apparent Km(K½) remained constant (5.6 kPa O2 with temperature, while Q10 was estimated to be 1.9. RQ was modeled as a function of O2 partial pressure and temperature. Headspace ethanol increased at RQs >1.3 to 1.5. Based on RQ, ethanol production, and flavor, we recommend that raspberries be stored at O2 levels above 4 kPa at 0C, 6 kPa at 10C, and 8 kPa at 20C. Steady-state CO2 partial pressures of 3 to 17 kPa had little or no effect on O2 uptake or headspace ethanol partial pressures at 20C.

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M. Helena Gomes, Randolph M. Beaudry and Domingos P.F. Almeida

Eq. [2] using steady-state O 2 and CO 2 partial pressures, package permeability, and fruit weight ( Beaudry et al., 1992 ; Lakakul et al., 1999 ). Respiratory quotients ( ) for aerobic respiration were computed from the calculated respiration rates

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Jennifer R. DeEll and Geoffrey B. Lum

.M. 2016 A novel type of dynamic controlled atmosphere storage based on the respiratory quotient (RQ-DCA) Postharvest Biol. Technol. 115 91 102 Blanpied, G.D. Silsby, K.J. 1992 Predicting harvest date windows for apples. Inform. Bul. 221. Cornell Coop. Ext

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Christopher D. Gran and Randolph M. Beaudry

The oxygen partial pressure associated with the respiratory quotient (RQ) breakpoint (ie., lower oxygen limit) was determined for fruits of several apple cultivars stored at 0°C. Fruits were sealed in low density polyethylene pouches of various thicknesses and known permeability to determine O2 uptake, CO2 production, and respiratory quotients (RQ) at various O2 partial pressures. There were differences in the shape of O2 uptake versus steady state O2 curves between cultivars. While some cultivars showed steady declines in respiration rate from 8 kPa O2 to < 1 kPa, other cultivars showed no decline in respiration until O2 levels fell below 3 to 4 kPa. Fruits having elevated RQ values had greater levels of headspace ethanol in the polyethylene pouches, which confirmed anaerobic respiration. The lower oxygen limit ranged from a low of approximately 0.75 kPa for cultivars Northern Spy and Law Rome to high of 1.5 kPa for McIntosh.

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Arthur C. Cameron, Randolph M. Beaudry, Nigel H. Banks and Mark V. Yelanich

Abbreviations: MA, modified atmosphere; LDPE, low-density polyethylene; RQ, respiratory quotient. 1 Dept. of Plant Science, Massey Univ., Palmerston North, New Zealand. Mention of a trademark, proprietary product, or vendor does not constitute a