Low O2 Atmosphere Research Articles

Advantages of Protective Atmosphere Control for No‐Clean Solder Pastes*

Reflow soldering in a controlled O2 atmosphere will lead to practical benefits in the wetting behaviour of solder pastes. The required O2 level and its control depend on the solder paste used and the solderability of the materials to be joined. For a typical application with either fine‐pitch technology, multiple soldering or low residue solder paste, a lack of O2 control can cause soldering problems. Fine‐pitch solder pastes today still do not show an optimum slump behaviour, which is absolutely necessary to avoid bridging between IC leads and to reduce the formation of solder balls during reflow. Using a low O2 atmosphere to reduce these defects can make a difference, but an improved slump behaviour through predrying of the applied solder paste at 50°C or in a low pressure environment will be more effective. Spread of solder is in general better at lower O2 levels, but substantial improvements are only achieved if low residue pastes with low activation levels are reflowed. Even when the low residue paste is compatible with reflow in air, there is still a significant difference found between 20 and 200 ppm O2. Reflow systems which show variations up to 500 ppm in the preheat zones during loading, while maintaining 50ppm in the peak zone, will show non‐wetting or dewetting when a 100 ppm O2 solder paste is used. The visual cleanliness of solder joints is significantly improved at lower O2 levels because the flux residue will be distributed differently over the solder joints. Bridging is initially determined by the slump behaviour of the paste and the alignment of the paste pattern to the pads and the leads, but when the paste of adjacent pads slumps together before reflow, the tendency for the solder to pull back is influenced by the oxygen level. Wetting and spread of the solder on the lands are then an essential factor. All the proven benefits of a low O2 level are not worth the money spent on nitrogen if the consumption necessary to obtain the properly controlled O2 level is very high. When solderability or the solder defect level not an issue the benefits may not represent a value higher than the cost of the nitrogen consumed.

Low-oxygen Atmosphere Increases Fructose 2,6-bisphosphate in Fresh-cut Carrots

This study was undertaken to determine the effect of low-O2 atmosphere on the concentration of fructose 2,6-bisphosphate (Fru-2,6-P2), which can activate the enzyme pyrophosphate-dependent:phosphofructokinase (PPi-PFK) to catalyze the reaction from fructose 6-phosphate to fructose 1,6-bisphosphate (Fru-1,6-P2). Fru-2,6-P2 remained unchanged in carrot (Daucus carota L.) root shreds stored under air, but it increased 3.0- and 5.3-fold at 2% and 0.5% O2 atmosphere, respectively, at 5C, and the increases were almost twice as great at 15C. The concentration of PPi ranged from 17 to 33 nmol·g-1 fresh weight, which is more than sufficient for the PPi-PFK to proceed. Thus, low-O2 atmosphere appeared to hasten glycolysis of carrot shreds by increasing Fru-2,6-P2, which activated PPi-PFK toward glycolysis.

低濃度酸素環境がモモとバナナ果実のエチレン生合成に及ぼす影響

The rates of C2H4 production in peach and banana fruits stored under 3 % O2 decreased by approximately 60% and 50% respectively compared to those stored in air. 1-aminocyclo-propane-1-carboxylic acid (ACC) oxidase activity in both fruits did not change during low O2 and subsequent air storage, when measured in the disks incubated under air condition. Low O2 treatment increased slightly ACC contents in both fruits. However, the increase in ACC content in peaches was much less compared to the calculated increase based on the result of the inhibition in C2H4 production, on the assumption that low O2 atmosphere would not affect the conversion of s-adenosylmethionine (SAM) to ACC. When ACC oxidase activity in excised flesh tissues from peach, banana, cucumber, and eggplant was measured under various O2 concentrations, the activity was distinctly O2-dependent. Our results suggest that inhibition of C2H4 production by shortterm low O2 treatment is mainly due to inhibition of ACC oxidase activity, not due to decrease in amount of the enzyme. The inhibitory effect of low O2 on C2H4 production in peach fruit might be partly due to inhibition of the conversion of SAM to ACC.

Regulation of Glycolytic Metabolism in Fresh-cut Carrots under Low Oxygen Atmosphere

Carrot (Daucus carota L.) shreds were stored under a continuous flow of air or 0.5% and 2% O2 (balance N,) for 9 days at 5 and 15C. The resulting changes in respiration, levels of glycolytic intermediates, and activities of ATP: phosphofructo kinase (ATP-PFK), and PPi: phosphofructokinase (PPi-PFK) were monitored. Carrots under low O atmosphere exhibited an increase in RQ due to a greater reduction in 02 consumption than in CO2 production, and the increase in RQ was greater at 0.5% than at 2% O2 at both temperatures. Fructose 1,6-bisphosphate (F1,6P) accumulated with decreased O2 atmosphere and was 2-fold greater at 0.5% than at 2% O2 atmosphere at both temperatures. The levels of other glycolytic intermediates were not significantly influenced by low O2. The increase in PPi-PFK activity occurred at the same time as F1,6P accumulation. A similar relationship was not found with ATP-PFK. These results suggest that PPi-PFK may be involved in regulation of glycolysis under low O2 atmosphere.

カットニンジンのエチレン処理による苦味発現の誘導ならびに環境ガス組成変更による制御

カットニンジンのエチレン処理による苦味発現の誘導ならびに環境ガス組成変更による制御

Glucosinolates in Broccoli Stored under Controlled Atmosphere

Content of total and individual glucosinolates were determined in, `Marathon' broccoli florets (Brassica olerucea L. var. italica stored 7 days at 10C under air, 0.5% O2, 0.5% O2 + 20% CO2 or 20% CO2 atmosphere, followed by transfer to air for 2 days. `Marathon' broccoli contained glucoraphanin, glucobrassicin, neoglucobrassicin, glucoiberin, 4-methoxyglucobrassicin, progoitrin, glucoalyssin, and gluconasturtiin. The methylssulfinylalkylglucosinolates (glucoiberin and glucoraphanin) and the indol-3-ylmethylglucosinolates (glucobrassicin, neoglucobrassicin and 4-methoxyglucobrassicin) accounted for 78% and 20% of the total content, respectively, in freshly harvested broccoli. CA treatment and storage time had no significant effect on the relative content of these two groups of glucosinolates. Freshly harvested broccoli contained 47 μmol glucosinolate/g dry weight. The total glucosinolate content increased 42% and 21% during 7 days storage under air and 0.5% O2 + 20% CO2, respectively, as compared to freshly harvested broccoli, and decreased 15% in broccoli stored under 20% CO2. Treatment with 20% CO2 in the absence of 0, resulted in visible CO, injury and water soaking of the tissue. Aeration had no significant effect on total glucosinolate content but reduced the glucobrassicin content 35% in broccoli stored 7 days under 0.5% O2 + 20% CO2 or 20% CO2 atmosphere. In contrast, the 4-methoxyglucobrassicin content increased during storage under low O2 atmosphere and increased further after transfer to air.

Low-oxygen-induced Poststorage Suppression of Bell Pepper Fruit Respiration and Mitochondrial Oxidative Activity

Bell pepper (Capsicum annum var. Jupiter) fruit were exposed to 1.5% O2 for 1 to 5 days at 20C to examine whether the low-O2-induced poststorage respiratory suppression (PRS) in whole fruit could be due to limitations in mitochondrial oxidative capacity. Mitochondrial oxidative capacity was not affected after storing bell peppers for 1 day in 1.5 % O2. Extending the storage period from 1 to 5 days in 1.5 % 0, resulted in PRS of CO2 production for about 55 hours after transfer to air, and a marked reduction in the oxidative capacity of isolated mitochondria. Mitochondrial activity was suppressed for 10 hours after transfer to air but, within 24 hours, bad recovered to values comparable to those of mitochondria from fruit stored continuously in air. Storing bell peppers in 1.5% O2 for 5 days resulted in a reduction in the respiratory control (RC), while ADP/O ratios were not affected. The reduction was temporary since the RC attained normal activity after returning bell peppers to air. Cyanide-sensitive cytochrome and CN-insensitive pathways were suppressed after storing fruit in 1.5 % O2 for 5 days. After returning fruit from a low-O2 atmosphere to air, the alternative pathway recovered at a greater rate than the cytochrome pathway.

Changes in the Respiratory Activity of Papaya Fruit Following Storage in Low-oxygen Atmosphere

Controlled-atmosphere (CA) storage of fruits employing low O2 and/or elevated CO2 have been used to reduce respiration and other associated metabolic activities. Papaya fruit cv. Eksofika were exposed to 2%, 5%, and 21% (air) O2 for 4 weeks at 12C. The CO2 production rates of fruit previously stored in 2% and 5% O2 were suppressed during storage, but increased upon transfer to air at 20C. Carbon dioxide production rates of low-oxygen stored fruits were slightly lower than the air-stored fruit during transfer to air, indicating a slight residual effect of low O2 on the respiratory activity of the fruit. This was highly evident in fruit stored in 2% O2 for 4 weeks. Ethylene production rates were not affected by prior storage of fruit in low-O2 atmosphere. Anaerobic metabolism did not occur in fruit stored in 2% O2 for 4 weeks, as evidenced by the RQ values close to unity and the absence of ethanol from the headspace of the respired gas. The total sugar content of ripe fruit at color score 5, previously stored in low-O2 atmosphere for 4 weeks, were not significantly different from the air-stored fruit.

Controlled-atmosphere Storage of Shredded Carrots

Quality and physiology of carrot shreds were monitored during storage in air, low O2 (0.5%, 1%, and 2%), or high CO2 (3%, 6%, and 10%) at 0, 5, and 10C to evaluate the response to controlled-atmosphere (CA) storage. Oxygen uptake and CO2 production from respiration were reduced under low-O2 or high-CO2 atmosphere, the reduction being greater at lower O2 and higher CO2 levels. The respiratory quotient was about 1 with samples in air, more than 1 in low-O2, and less than 1 in high-CO2 atmosphere during storage at all temperatures. No differences were found in ethylene production, which were less than 0.2 μl·kg–1·h–1 with all samples. The CA containing 0.5% O2 and 10% CO2 reduced weight loss and formation of white-colored tissue and decreased pH, but did not affect microbial count and texture at all temperatures. Off-odor and black root rot were not detected in both CA and air atmospheres.

Elevated CO2 and/or Low O2 Atmospheres Influence ACC Synthase and ACC Oxidase during Long-term Storage of `Golden Delicious' Apple Fruit

The objective of this study was to compare and contrast the mode of action by which elevated carbon dioxide and/or reduced oxygen atmospheres inhibit ethylene biosynthesis. `Golden Delicious' apple fruit were placed at 0C in one of the following four atmospheres: 1) air; 2) air + 5% CO2; 3) 2% O2 + 98% N2; or 4) 2% O2 + 5% CO2 + 93% N2 and then sampled monthly for 4 months. Ethylene biosynthesis rates and in vitro ACC synthase activities were closely correlated in all treatments. In vitro ACC synthase activity and ethylene biosynthesis rates were lowest in fruit treated with 5% CO2 + 2% O2, while air-treated fruit had the highest ethylene biosynthesis rate and in vitro ACC synthase activity. Fruit treated with air + 5% CO2, or 2% O2 + 98% N2, had intermediate ethylene and in vitro ACC synthase activities. In vitro ACC oxidase was significantly different among treatments, but not as closely correlated with the ethylene biosynthesis rate as in vitro ACC synthase activity. Western blot analysis of the ACC oxidase protein was performed to determine if activity differences among treatments were correlated with the amount of enzyme present in vivo. ACC synthase and ACC oxidase mRNA transcript of abundance was determined via Northern blot analysis. Results will be discussed regarding how ethylene biosynthesis is inhibited at the molecular level by elevated CO2 and/or reduced O2.

DETERMINING THE EXTINCTION POINT OF SPINACH CULTIVARS FOR STORAGE IN LOW-OXYGEN ATMOSPHERE

The extinction point (EP) of spinach cultivars was determined to identify the minimum O2 concentration that can be used for modified-atmosphere storage of spinach. EP was based on respiratory quotient (RQ) and appearance quality during storage. Oxygen consumption decreased as O2 concentration was lowered from 2.0% to 0.1%; whereas CO2 production decreased as O2 concentration was lowered from 2.0% to 0.5%, but not below 0.5%. The RQ was close to 1 in oxygen atmospheres of 2.0% to 0.4% and exceeded 1 at 0.2% or less. No alcohol production was noted at 0.2% or less O2, but deterioration of leaves occurred at these low-O2 atmospheres. Since the EP is slightly below 0.4% O2, the concentration of O2, should not be allowed to go below 0.5% for successful modified-atmosphere storage of spinach.

Prestorage Low-oxygen Atmosphere Treatment Reduces Chilling Injury Symptoms in `Fuerte' Avocado Fruit

Prestorage treatment of avocado fruit (Persea americana Mill. cv. Fuerte) with a low-O2 atmosphere (3% O2 + 97% N2) for 24 hours at 17C, significantly reduced chilling injury (CI) symptoms after storage at 2C for 3 weeks. Fruit softening was also delayed by this treatment. The treated fruit had lower respiration and ethylene production rates during storage at 2C and subsequently at 17C. Electrolyte leakage was significantly lower in peel disks from treated fruit. Reducing power, expressed as total sulfhydryl groups, was higher in the peel and pulp of low-O2-treated fruit. The amount of peel chlorophyll was inversely correlated with the severity of CI symptoms.

CONTROLLED ATMOSPHERIC ENVIRONMENTS AND THEIR EFFECTS ON APHIDS AND WESTERN FLOWER THRIPS ON FLORAL PRODUCTS

Shipments of floral products to Pacific rim markets must meet stringent pest-free requirements. Conventional fumigation methods with methyl bromide will soon become unavailable. Studies show that controlled atmosphere (CA) environments can offer effective insect control. Currently, CA overseas marine shipping is occuring with fresh fruits and vegetables. These shipments use microprocessors to precisely control O2, CO2, temperature and relative humidity. This study is evaluating similar commercial shipments with fresh flowers and foliage under low temperature and low O2 and high CO2 atmospheres. Preliminary results with shipments conducted by TransFresh to Guam indicate that properly maintained CA shipments of 0.5 % O2 kill insects and that flowers in properly maintained atmospheres can withstand 14 days of marine shipment with minimum effect on post-harvest life. Adequate regulation of CA storage during transit seems to be the primary limitation to the expansion of floral markets using this method of shipment.

920 PB 461 CONTROLLED ATMOSPHERE AFFECT STORAGE QUALITY OF ZUCCHINI SQUASH SLICES

Physiology and quality of CaCl2 treated or nontreated `Elite' zucchini squash slices were monitored during storage in air, low O2 (0.25, 0.5 and 1%) or high CO2 (3, 6, and 10%) atmosphere at 10C. O2 consumption and CO2 production were reduced under low O2 and high CO2 atmospheres and the reduction was greater with low O2. C2H4 production was reduced with low O2 and initially with high CO2. After day 2 or 4, C2H4 production under high CO2 increased with the increase being greater at the lower CO2 level. The amount and severity of injury/decay were less under low O2 and high CO2 than air atmosphere. Slices stored under 0.25% O2 atmosphere had less weight loss and injury/decay and greater shear force and ascorbic acid content than those held in air atmosphere. Microbial count, pH, and color were affected by the low O2 only on the last day. CaCl2 had no additive effect.

Tolerance and Responses of Harvested Mango to Insecticidal Low-oxygen Atmospheres

`Keitt' mangoes (Mangifera indica L.) were stored for 0 to 5 days at 20C in a continuous flow of an insecticidal low-O2 atmosphere (0.2% to to 0.3%, balance N2). Fruit were evaluated every day after exposure to a low-O2 atmosphere and again after being held in air at 20C for 5 days. There was no fruit injury, organoleptic fruit quality was not lowered due to the low-O2 atmosphere, and fruit ripened normally. These results indicate that applying low-O2 atmospheres postharvest can be used to control insects in mangoes.

External and Internal Factors Influence Fruit Tolerance to Low-oxygen Atmospheres

Fruits of `Bing' cherry (Prunus avium L.), `Red Jim' nectarine (Prunuspersica L.), `Angeleno' plum (Prunus salicina, L.), `Yellow Newtown' and `Granny Smith' apples (Malus domestica Borkh.), and `20th Century' pear (Pyrus serotina L.) were treated with 0.25% or 0.02% O2 (balance N2) at 0, 5, or 10C to study the effects of these insecticidal low-O2 atmospheres on their postharvest physiology and quality attributes. Development of alcoholic off-flavor was associated with ethanol accumulation, which was the most common and important detrimental effect that limited fruit tolerance to low O2. Relatively higher storage temperature (T), higher respiration rate (R), and greater resistance to gas diffusion (r) enhanced while relatively higher O2 concentration (C) and higher soluble solids concentration (SSC) reduced off-flavor development. Using a SAS computer program to do multiple regression analysis with T, C, R, r, and SSC as variables, models were developed for prediction of fruit tolerance to insecticidal low-O, atmospheres. Comparison of fruit tolerances and published information on the times required to completely kill specific insects by O2 levels at or below 1% suggests that low-O2 atmospheres have a good potential for use as postharvest quarantine treatments for some fruits.

Effect of modification of storage atmosphere on phospholipids and ultrastructure of cauliflower mitochondria

Differences in mitochondrial membrane composition and ultrastructure were studied after storage of cauliflower (Brassica oleracea, L., Botrytis group) for 5 days at 25°C in air or under controlled atmospheres: 3% O2, 21% O2+ 15% CO2 or 3% O2+ 15% CO2. In air, postharvest senescence involved a 20% decrease in mitochondrial phospholipid content. A large reduction in the relative abundance of phosphati-dylcholine (PC) and in the degree of unsaturation of PC and phosphatidyl ethanolamine (PE) was observed. However, the degree of unsaturation increased in cardiolipin (CL). Storage under 3% O2 did not prevent phospholipid breakdown. Low O2 prevented the relative decrease in PC observed during storage in air and the loss of linoleic acid from PC, but not from PE. This relative protection offered by the low O2 atmosphere was lost under 3% O2+ 15% CO2. The high CO2 atmospheres caused twice as much loss in phospholipids as that observed during storage in air. Extensive loss of mitochondrial protein, a marked decrease in phospholipid to protein ratio, and electron micrograph observations suggest structural alterations in the presence of high CO2.

Physiology and Prediction of Fruit Tolerance to Low-oxygen Atmospheres

Fruits of `Granny Smith' and `Yellow Newtown' apples (Malus domestica Borkh), `20th Century' pear (Pyrus serotina L.), and `Angeleno' plum (Prunus domestica L.) were kept in air and in 0.25% or 0.02% O2 at 0, 5, or 10C for 3, 7, 14, 25, or 35 days to study the effects of low-O2 atmospheres on their postharvest physiology and quality attributes. Soluble solids content (SSC), pH, and external appearance were not significantly influenced, but resistance to CO2 diffusion was increased by the low-O2 treatments. Exposures to the low-O2 atmospheres inhibited ripening, including reduction in ethylene production rate, retardation of skin color changes and flesh softening, and maintenance of titratable acidity. The most important detrimental effect of the low-O2 treatments was development of an alcoholic off-flavor that had a logarithmic relation with ethanol content of the fruits. The ethanol content causing slight off-flavor (Eo) increased with SSC of the commodity at the ripe stage, and it could be estimated using the following formula: (Log Eo)/SSC = 0.228. Using SSC of ripe fruits and average ethanol accumulation rate per day (VE) from each low-O2 treatment, the tolerance limit (Tl) of fruits to low-O2 atmospheres could be predicted as follows: Tl = Eo/VE = (100.228SSC)/VE.

INTERACTION BETWEEN SOLUBLE SOLIDS AND ETHANOL IN DETERMINING FLAVOR AND TOLERANCE OF FRUITS TO LOW OXYGEN ATMOSPHERES

Selected cultivars of several fruit species were exposed to 0.25% or 0.02% O2 at 0, 5, or 10C for short durations to investigate the potential of these treatments as quarantine procedures for postharvest insect control. Beneficial effects of such low O2 treatments included inhibition or delay of ripening processes as indicated by reduction in respiration and ethylene production rates, retardation of skin color changes and flesh softening, and maintenance of titratable acidity. While appearance was not adversely influenced by the short-term low O2 treatments, the development of alcoholic off-flavor was the most important detrimental effect, which limited the tolerance of fresh fruits to low-O2 atmospheres. Ethanol content and flavor score of the fruits had a logarithmic relationship. The threshold ethanol concentration associated with off-flavor detection (EO) increased with SSC of the commodity at the ripe stage, and it could be estimated using the following formula (Log EO)/SSC = 0.228. Using SSC of ripe fruits and average ethanol accumulation rate per day (V) from each low O2 treatment, the tolerance limit (Tl) of fruits to low O atmospheres could be predicted as follows: Tl = EO/E = 1 00.228 SSC2/V.E

THE TOLERANCE OF MANGO TO INSECTICIDAL OXYGEN ATMOSPHERE

Mango fruits (cv Keitt) were exposed to a continuous flow of low O2 atmosphere of 0.1 to 0.2% (balance is N2) for 0 to 5 days at 20°C. Fruits were evaluated every day after exposure to low O2 atmosphere, and again after 5 days in air at 20°C. A sensory evaluation test was conducted after 15 days from the initiation of the experiment. The low O2 atmosphere reduced the activity of the enzymes malic dehydrogenase and isocitric dehydrogenase but did not affect the activity of α- Ketoglutarate dehydrogenase. However, there was no indication of any fruit injury nor any detrimental organoleptic changes due to the low O2 atmosphere. These results suggest the possibility of the application of very low O2 atmosphere for postharvest insect control in mango.