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Mar 22, 2010 - Lougheed (1964) reported that spears stored in 15% CO2 lacked flavour. Effective insect control requires subjecting asparagus to high CO2 ...
New Zealand Journal of Crop and Horticultural Science

ISSN: 0114-0671 (Print) 1175-8783 (Online) Journal homepage: http://www.tandfonline.com/loi/tnzc20

Effects of treatment with elevated carbon dioxide levels on the sensory quality of asparagus Virginia K. Corrigan & Alan Carpenter To cite this article: Virginia K. Corrigan & Alan Carpenter (1993) Effects of treatment with elevated carbon dioxide levels on the sensory quality of asparagus, New Zealand Journal of Crop and Horticultural Science, 21:4, 349-357, DOI: 10.1080/01140671.1993.9513793 To link to this article: http://dx.doi.org/10.1080/01140671.1993.9513793

Published online: 22 Mar 2010.

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New Zealand Journal of Crop and Horticultural Science, 1993, Vol. 21: 349-357 0114-0671/93/2104-0349 $2.50/0 © The Royal Society of New Zealand 1993

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Effects of treatment with elevated carbon dioxide levels on the sensory quality of asparagus

VIRGINIA K. CORRIGAN ALAN CARPENTER New Zealand Institute for Crop & Food Research Limited Levin Research Centre Private Bag 4005 Levin, New Zealand Abstract Asparagus spears (Asparagus officinalis L. cv. Limbras 10) were stored for 3-5 days in atmospheres containing between 40 and 90% carbon dioxide (CO2) to evaluate the effect of insecticidal CO2 atmospheres on sensory quality based on sensory panel ratings of characteristic asparagus flavour, offflavours, flavour acceptability, andoverall acceptability. Sensory quality of spears after 4 days storage in 60% CO2 was similar to air-stored spears but 5 days storage caused deterioration in the CO2-stored spears relative to the air-stored spears. Using higher CO2 levels than this for shorter storage times resulted in spears with CO2 injury and poor sensory quality. Spear quality deteriorated with shelf period but previous CO2 treatment did not affect the rate of deterioration. Storing spears at 5°C in 60% CO 2 or 0°C in air gave consistently higher (lower for off-flavours) sensory quality ratings for all characteristics assessed than vice versa. Thick spears had more flavour and were more acceptable than thin spears. Thick spears had more flavour than thin spears when stored in CO2, but thin spears had more flavour when stored in air than in CO2. In 60% CO2, spears stored dry had a more acceptable flavour and were more acceptable overall (where panellists considered aspects such as flavour, texture, and off-flavours in the overall rating) than those stored

H93021 Received 31 March 1993; accepted 16 September 1993

with their butts in water. Spears stored in air with their butts in water had a more acceptable flavour and were more acceptable overall, spears stored with their butts in water had less characteristic asparagus flavour than those stored dry. High levels of CO2 could be used as a disinfestation treatment of fresh asparagus spears without significant effect on spear quality (compared to spears stored in air under similar conditions) providing levels >60% CO2 are not used, and storage time in the atmosphere is kept to 4 days or less. Keywords asparagus; sensory quality; Asparagus officinalis L.; carbon dioxide INTRODUCTION Healthy living and good nutrition are important to the consumer in today's society. The emphasis on "clean", "green" food has prompted an increasing concern over the use of chemicals and pesticides in food crop production (MAFF 1987;EFRC 1988; Henley Centre 1989; Maddy 1989). Sales of organically grown produce are increasing and attract premiums of up to 50% (e.g., Boyle et al. 1981; Werner 1984; EFRC1988). Current quarantine treatments such as methyl bromide may become unacceptable, but quarantine pests must be controlled if produce is to be exported. Japan is the major market for New Zealand's fresh asparagus exports. Asparagus infested with thrips or aphids is fumigated with methyl bromide or hydrogen cyanide on arrival in Japan. The warm conditions used for fumigation plus the phytotoxic effects of the fumigant may cause flavour loss and off-flavour development in asparagus, without any visible damage. Respiration rate and ethylene production increase in fumigated spears, accelerating senescence (Beeveretal. 1985). Standard controlled atmosphere storage usually uses atmospheres containing up to 10% CO2 and from 2 to 10% O2. This may not be a practical method of disinfestation as up to 18 days storage in 7%O2:8% CO2 are needed to kill 80% of thrips and aphids (Lill & van der Mespel 1986), and this is close to the

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maximum postharvest shelf life of asparagus, leaving no room for error such as delays in transport. What is needed is a rapid disinfestation method that fits in with the postharvest life of the crop. Treating asparagus with very high CO2 levels (40-90%) for relatively short periods can successfully kill aphids and thrips (A. Carpenter unpubl. data) and the short treatment time means that spears could be treated before export. The advantage of high CO2 levels is their effectiveness at 0°C compared to methyl bromide and dichlorvos fumigation which require product warming, but the effects of high CO2 levels on sensory quality of asparagus have not been investigated. The storage life and quality of a range of horticultural products can be improved by short-term exposure to high CO2 levels (Wills & Wimalasiri 1979). Reported effects on asparagus quality vary. Thornton (1931) found CO2 levels above 12% caused spear injury such as pitting, whereas levels between 50 and 80% caused browning of the spear bracts. In contrast Isenberg (1979) states that "Asparagus is one vegetable that appears to have enhanced edible quality if subjected to controlled atmosphere treatment". He attributes this to the retardation of morphological spear development. Controlled atmosphere storage of horticultural produce helps maintain quality of horticultural produce by inhibiting respiratory enzyme systems (Siriphanich & Kader 1986), decreasing oxygen uptake (Lee 1981), and retarding colour loss (Wang et al. 1971; Isenberg 1979; Wills & Wimalasiri 1979). In asparagus the onset of softening is delayed (Wills & Wimalasiri 1979) and bracts open more slowly so spears are less susceptible to fungal attack (Isenberg 1979) and soft rot infections (Lipton 1957; Lee 1981). Treated spears are more tender than air-stored asparagus (Lipton 1960; Lee 1981). Brooks et al. (1936) report 48 h storage in 25-30% CO2 or 24 h storage in >40% CO2 caused an objectionable flavour in some spears and Lipton (1965) found 7 days storage in 20-39% CO2 caused severe spear damage. Franklin et al. (1960) found little taste difference between spears stored for 7-14 days in 15% CO 2 and airstored spears. Lougheed (1964) reported that spears stored in 15% CO2 lacked flavour. Effective insect control requires subjecting asparagus to high CO2 levels. If this is to be a practical control method the spears must remain undamaged and retain good appearance, flavour, and aroma. Most of the literature describes the effects of much lower CO2 concentrations than those proposed for insect control. In this report we evaluated the sensory quality of asparagus spears treated with high CO2 levels under a range of storage conditions.

MATERIALS AND METHODS Plant material Asparagus spears (Asparagus officinalis L. cv. Limbras 10) were hand harvested on the morning of treatment, from beds at the Levin Research Centre, Levin, New Zealand. Straight, undamaged spears with unopened bracts were selected, consistent with fresh export specifications (Franklin 1990), and trimmed to 180 mm. Butt diameters were between 12 and 18 mm unless otherwise specified. Treatment conditions Bundles of 20 freshly picked unwashed spears were secured with a rubber band and placed upright in 1 litre glass jars covered with paper tissues. Two jars of spears per treatment were stored in an airtight galvanised metal container at 0°C with the experimental gas mixtures delivered by a flow-through system at 200 ml/min for a treatment period of 3-5 days. Gases were mixed and supplied by New Zealand Industrial Gases (NZIG) Special Gases in G size cylinders as a Beta standard laboratory gas. Gas mixtures consisted of O2 and CO2 in the required proportions with the balance made up of nitrogen, and were tested and certified by the NZIG laboratory which has TELARC registration. Following the treatment time, spears were held uncovered at 20°C in a room continuously illuminated by Osram cool white fluorescent tubes for a shelf period of 1-3 days to simulate marketplace conditions. The term "storage" refers only to time spent in the treatment atmospheres, the term "shelf period" is used for time spent at 20°C. The first three experiments assessed the effects of 3-5 days storage at between 40 and 90% CO2 followed by a 1-3-day shelf period. Four subsequent experiments examined the effects of a range of storage methods on spear quality. These were the response of thick or thin diameter spears to CO2, effect of previous CO2 storage on shelf life performance (assessed 1 and 3 days after treatment), storing spears lying flat or standing in jars with their butts in water, and effect of storage temperature in the CO2 (using 0 or 5°C) (Table 1). Air-stored spears were included as controls in all trials and fresh spears were included as controls in the first three panels to look at the speed of spear deterioration after harvest. Evaluation Spears were held at 20°C until immediately before evaluation. All spears from a treatment were combined and the top 5 cm of each spear tip (referred to as the

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Corrigan & Carpenter—Sensory quality of asparagus sample) was used for panellist assessments. Changes in the chemical composition of the spear (e.g., amino acids and carbohydrates) occur most rapidly in the tips (Lill et al. 1990) because of the higher respiration rate of spear tips (Saltveit & Kasmire 1985). Samples were wrapped in Gladwrap® cling film and cooked at full power for 60 sec/100 g in a 680 W Sanyo "Wizard" automatic microwave oven. They were left to stand on a bench at ambient temperature in the cooking container for twice the cooking time to complete the cooking process. Samples (one spear tip per treatment, with a maximum of five spear tips per assessment) were served up immediately following standing time on a white plate and assessed while warm. They were presented in randomised order with a three digit random number code. Red lighting was used to help mask any possible colour differences. Rinsing water at room temperature was provided and panellists were instructed to rinse between samples or not as they wished, but to be consistent. Sensory panels consisting of 12-18 members were used on seven occasions to investigate the effects of the treatments discussed. Panellists were staff members from the Levin Research Centre who had some previous experience in assessing horticultural produce, including asparagus. Each panellist rated one sample from each treatment (with a maximum of five samples) on four attributes in one session—characteristic asparagus flavour, off-flavour intensity (an overall rating including such possible offflavours as bitterness, sourness, and "old flavour"), flavour acceptability, and overall acceptability (Beever et al. 1985). Panellists marked a 160 mm linear unstructured scale (anchored 5 mm from each end with a vertical mark) to indicate the intensity of the sample characteristics. Scores were allocated by

351 measuring the distance of the marked point (in mm) from the left-hand anchor point of the scale; thus, 0 = the least and 150 = the greatest intensity of any sample characteristic. An acceptability scale was included to give panellists a chance to give an overall rating that may also take into account aspects not asked for elsewhere. Analysis Results from each experiment were examined using analysis of variance (PROC ANOVA) (SAS Institute Inc. 1987). Direct comparison between results from the different experiments cannot be made because of variations in sensory panel composition, differing lengths of spear storage time, and different spear harvest dates. Differences between treatment means were tested for significance by least significance difference (LSD) procedures. Significance levels of the treatment effects are stated in the text. A P value of P < 0.05 was used to establish significance, however, all probability levels are listed in the tables to allow readers to examine trends in the data.

RESULTS The first three experiments were run to determine the effects of CO2 level and length of storage (in the treatment atmosphere) on the sensory quality of asparagus, and thus establish the most suitable CO2 level to use in subsequent experiments. Results are presented in Table 2. The next four experiments looked at a range of treatment conditions used in conjunction with the treatment atmospheres and results are presented in Tables 3-6.

Table 1 Treatment conditions of controlled atmosphere stored asparagus spears. (Unless otherwise stated, spears were stored at 0°C, standing upright in glass jars, and spear size was consistent with export standards.) Experiment

Storage period (days)

Shelf period (days)

Storage treatments

2 1 2 2

Fresh spear Fresh spear Fresh spear Air or 60% CO2

1 3 2

Air or 60% CO2 Air or 60% CO 2 Air or 60% CO2

2

Air stored 60% CO2 80% CO2 Air stored 60% CO2 80% CO2 90% CO2 Air stored 40% CO2 60% CO2 Thick spears (17-23 mm diam.) Thin spears (9-12 mm diam.) Measured 180 mm from tip Spears assessed after 1 and 3 days shelf period following treatment Stored standing, butts in 2 cm water Stored dry, lying flat Stored at 0°C during treatment Stored at 5°C during treatment

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New Zealand Journal of Crop and Horticultural Science, 1993, Vol. 21 Table 2 Effect of CO 2 concentration and storage time on asparagus quality. (NS = not significant.) Sensory panel ratinga Characteristic asparagus flavour

Storage treatment

Flavour acceptability

Overall acceptability

Effect of storage in 60% CO2 or 80% CO2 atmospheres (4 days storage + 2 days shelf period ) 85.9 47.3 94.0 86.1 72.9 57.9 64.7 61.5 71.1 62.4 62.5 66.5 65.9 84.3 49.2 53.1

Experiment 1 Fresh Air-stored 60% CO2 80% CO2 Atmosphere effect F test probability LSD P = 0.05

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Offflavours

0.12 NS

0.03 24.8

0.0003 19.9

0.05 23.7

Effect of shorter storage time (3 days + 1 day shelf period) and higher CO2 levels 79.8 50.9 82.3 79.5 79.8 70.5 58.4 60.1 84.8 80.7 58.2 57.7 49.2 63.5 73.1 52.9 59.0 99.1 45.2 45.4

Experiment 2 Fresh Air-stored 60% CO2 80% CO2 90% CO2 Atmosphere effect F test probability LSD P = 0.05

0.03 18.8

0.02 27.0

0.01 21.9

0.06 23.2

Effect of lower CO2 level and longer storage time (5 days + 2 days shelf period) 92.5 23.7 100.9 107.8 68.2 71.7 52.3 57.5 78.7 62.4 47.3 46.1 97.1 34.4 35.2 47.5

Experiment 3 Fresh Air-stored 40% CO2 60% CO 2 Atmosphere effect F test probability LSD P = 0.05

0.0004 19.8

0.0001 23.0

0.0001 20.7

0.0001 17.5

a

Ratings are mean values from all participating panellists.

Table 3 Effect of spear diameter on response to high CO2 after 3 days storage and 2 days shelf period. Thick spears measured between 17 and 23 mm, and thin spears between 9 and 12 mm in diameter measured 180 mm from the spear tip. Sensory panel ratings'1

Spear size:

Characteristic asparagus flavour Thick Thin

Offflavours Thick Thin

85.9 94.9

60.3 60.1

Air-stored 60% CO2 F test probabilities Spear size effect Atmosphere effect LSD P = 0.05 Spear size by atmosphere interaction effect a

76.7 72.9

0.04 0.73 14.9 0.39

51.3 62.0 0.72 0.59 _ 0.58

Ratings are mean values from all participating panellists.

Flavour acceptability Thick Thin 68.9 82.8 0.16 0.97 _ 0.11

70.7 57.4

Overall acceptability Thick Thin 71.4 81.5

69.0 56.4

0.11 0.88 _ 0.18

Corrigan & Carpenter—Sensory quality of asparagus

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Table 4 Effect of high CO2 storage on asparagus quality as shelf period is extended from 1 to 3 days. Spears in all treatments were stored for 3 days. (NS = not significant.) Sensory panel ratings'1

Shelf period (days): Air-stored 60% CO2

Characteristic asparagus flavour 1 3 97.6 90.8

80.2 81.5

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F test probability Shelf period effect 0.08 Storage atmosphere effect 0.71 LSD P = 0.05 NS Shelf period by 0.59 atmosphere interaction effect

Offflavours 1 3 56.5 45.6

65.2 71.9

0.13 0.71 NS 0.45

Flavour acceptability 1 3 82.5 77.8

53.1 60.0

0.02 0.71 20.4 0.57

Overall acceptability 1 3 84.1 70.5

53.3 67.2

0.02 0.91 NS 0.18

a

Ratings are mean values from all participating panellists.

Table 5 Effect of storage method and high CO2 treatments on asparagus quality. Spears were either stored standing with butts in 2 cm of water (wet) or lying flat with the butts exposed (dry). Spears in all treatments were stored for 3 days and assessed after 2 days shelf period. (NS = not significant.) Sensory panel ratings11 Characteristic asparagus flavour Storage technique: Dry Wet Air-stored 60% CO2

88.8 91.1

82.8 66.3

F test probabilities Storage method effect 0.01 Storage atmosphere effect 0.24 LSD P = 0.05 12.1 Storage method by 0.12 atmosphere interaction effect LSD P = 0.05 LS

Offflavours Dry Wet 44.8 54.8

43.0 67.4

Flavour acceptability Dry Wet 56.5 74.4

0.54 0.06 NS 0.42 NS

70.6 52.0

Overall acceptability Dry Wet 59.9 75.0

0.60 0.97 NS 0.02

69.4 53.1 0.60 0.94 LS 0.06

22.5

LS

a

Ratings are mean values from all participating panellists.

Table 6 Effect of storage temperature and high CO2 on asparagus quality. Spears in all treatments were stored for 3 days and assessed after a shelf period of 2 days. (NS = not significant.) Sensory Panel Ratings'1 Characteristic asparagus flavour Storage temperature: 0°C 5°C Air-stored 60% CO2

97.6 85.6

91.7 92.7

F test probabilities Storage temperature effect 0.94 Storage atmosphere effect 0.46 Temperature by 0.38 atmosphere interaction effect LSD P = 0.05 NS a

Offflavours 0°C 5°C 42.4 55.9

69.9 46.8

0.33 0.61 0.06 NS

Ratings are mean values from all participating panellists.

Flavour acceptability 0°C 5°C 90.3 63.0

59.7 79.8 0.42 0.67 0.008

2422

Overall acceptability 0°C 5°C 89.1 61.8

63.1 77.9 0.54 0.44 0.01

23.1

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Experiment 1 Effect of storage in 60% CO2 or 80% CO2 atmospheres (4 days storage + 2 days shelf period). After 4 days storage and 2 days shelf period, storage atmospheres caused no significant differences in characteristic asparagus flavour, off-flavours, flavour acceptability, or overall acceptability between treated or air-stored spears. However, fresh spears had a significantly more acceptable flavour than spears from all other treatments (P = 0.0003) and lower offflavour ratings (P = 0.03) than the air-stored or 80% CC>2-stored spears and were significantly more acceptable overall than spears stored in air or 80% CO2 (P = 0.05) (Table 2). Spears stored in 60% CO 2 were not significantly different in off-flavours to spears from any other treatments including fresh spears. Experiment 2 Effect of shorter storage time (3 days + 1 day shelf period) and higher CO2 levels. There were no significant differences between spears stored in air and 60% CO2, but the spears stored in 60% CO2 had significantly more characteristic asparagus flavour (P = 0.03) than the spears stored in 80 and 90% CO2 (Table 2). The spears stored in 90% CO2 had significantly higher off-flavour ratings than the airstored and fresh spears (P - 0.02), but the spears stored in 60% CO2 were not significantly different to other treatments except fresh spears. There were no significant differences between the treatments for flavour acceptability and overall acceptability. Fresh spears had the most acceptable flavour (P - 0.01) and showed a trend of greater overall acceptability than spears stored in 80 or 90% CO2 (P = 0.06). Experiment 3 Effect of lower CO2 level and longer storage time (5 days + 2 days shelf period). Spears stored in 40% CO 2 were not significantly different from those stored in air or 60% CO2 in any of the attributes rated (Table 2). Air-stored spears rated significantly higher for characteristic asparagus flavour and overall acceptability and significantly lower for off-flavours than spears stored in 60% CO2. All stored spears rated significantly lower than fresh spears for characteristic asparagus flavour (P = 0.0004), flavour acceptability (P = 0.0001), and overall acceptability (P = 0.0001) and had significantly higher off-flavour ratings (P = 0.0001) (Table 2).

Experiment 4 Effect of spear diameter on response to storage in 60% CO2 (Table 3). Thick spears had significantly more characteristic asparagus flavour than thin spears. There were no significant differences in off-flavours and flavour acceptability. There was a trend towards higher flavour acceptability and overall acceptability ratings for thick spears stored in 60% CO2 compared to all other spears whereas thin spears stored in 60% CO2 rated lower than other spears for the same attributes. Experiment 5 Effect of storage in 60% CO2 storage on subsequent shelf quality of asparagus spears (Table 4). Flavour acceptability of both air-stored and 60% CO2stored spears decreased between 1 and 3 days shelf period(P-0.02) with trends of decreasing characteristic asparagus flavour (P = 0.08) and overall acceptability (P - 0.10). Off-flavour ratings for spears stored in CO2 showed a much larger increase after the shelf period than did ratings for the air stored spears but this storage atmosphere by shelf period interaction was not significant. Otherwise previous CO2 storage did not affect subsequent spear quality. Experiment 6 Effect of storage method and 60% CO2 levels on asparagus quality (Table 5). Dry stored spears had significantly more characteristic asparagus flavour than those stored standing in water (P = 0.01) which was mainly because of high ratings for the 60% CO2-stored spears which were stored dry, and the low ratings for the 60% CO2-stored spears which were stored standing in water. The storage method by storage atmosphere interaction was not significant (P = 0.12) however, as the ratings for the air-stored spears remained relatively unchanged. Spears stored in CO2 showed a trend towards higher offflavour ratings than air-stored spears (P - 0.06) which was again mainly the result of higher ratings for wet CO2-stored spears compared to the CO2 dry-stored spears. There was no significant effect of storage method or atmosphere on flavour acceptability or overall acceptability. There was a significant CO2 concentration by storage method interaction for flavour acceptability (P = 0.02) and a trend for overall acceptability (P = 0.06). Spears stored dry in CO2 had a more acceptable flavour and higher overall acceptability ratings than those stored in water. Spears stored in air with water had higher characteristic asparagus flavour ratings than those stored in air without water.

Corrigan & Carpenter—Sensory quality of asparagus Experiment 7 Effects of storage temperature and 60% CO2 (Table 6). Storage temperature alone did not have a significant effect on spear quality. Spears stored in air at 0°C had a significantly more acceptable flavour (P = 0.008) and were significantly more acceptable overall (P = 0.01) than those stored in CO2 at 0°C or air at 5°C. Spears stored in 60% CO2 at 5°C or in air at 0°C showed a trend of lower off-flavour ratings than spears stored at 5°C in air or in 60% CO2 at 0°C (P = 0.06).

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DISCUSSION High CO2 disinfestation offers an alternative to current disinfestation practices, and does not adversely affect sensory quality of the stored spears if the right combinations of storage time and treatment conditions are used, and may help maintain the sensory quality of the stored spears. Standard controlled atmosphere storage generally uses CO2 levels of up to 10 or 15% CO2 (Kader 1989). Levels higher than this have been reported to be damaging to a wide range of produce including asparagus, but storage times were longer than used here, and were often used in combination with low oxygen (e.g., Weichmann 1986). Ratings for fresh spears were (with one exception) higher (lower for off-flavours) than ratings for the treated spears, but there was generally little difference between ratings for air-stored or CO2-stored spears. Spears stored for either 3 and 4 days in 60% CO2 or in air had similar sensory quality ratings. Spears stored for 4 days in 80% CO2 were not significantly different from those stored in air or 60% CO2 for flavour acceptability and overall acceptability, but had significantly higher offflavour ratings, and showed typical signs of CO2 injury, mainly shrunken surfaces and pitting (Lipton 1965). Decreasing storage time to 3 days decreased off-flavour ratings in the spears stored in 80% CO2 but other ratings were still poor and spears showed CO2 damage. The overall quality of spears stored in 90% CO2 was very poor both in visual appearance and sensory ratings. Five days storage in 60% CO2 was too long, and spears were of significantly lower quality than spears stored in air for the same length of time. The spears stored in 40% CO2 were not significantly different from spears stored in air or 60% CO2 but all treatments were inferior in quality to fresh spears. The low quality ratings, however, make the 5-day storage treatment unacceptable. CO2 injury to asparagus spears has been previously shown to increase with the length of storage time in the gas (e.g., Lipton 1965) and this is

355 supported by these findings. Spears from all storage treatments were significantly less acceptable than the fresh spears for the attributes rated. Fresh spear ratings were considerably higher than those given by previous panels, probably in contrast to the poorer quality of the treated spears at this panel. This effect remains when data from only the 11 panellists who attended all three panels are analysed and compared (results not shown here). This contrast effect has been widely documented and discussed, for example see Amerine et al. (1965). Treatment with 60% CO2 did not affect the shelf quality of asparagus spears although ratings for characteristic asparagus flavour, flavour acceptability, and overall acceptability dropped less in spears stored in 60% CO2 than for the air-stored spears. Off-flavours increased more in the CO2-stored spears (Table 4). This is consistent with King et al. (1986) who found that standard controlled atmosphere storage did not significantly extend the shelf period of asparagus. Spears were best stored at 5°C in 60% CO2 or at 0°C in air. In contrast, spears stored in 60% CO2 at 0°C had lower flavour and acceptability ratings and higher off-flavour ratings than those stored at 5°C in 60% CO2. Controlled atmosphere storage increases susceptibility to chilling injury (Isenberg 1979) which may become apparent only after a shelf period (Lipton 1965), causing flavour loss or off-flavour development. Spears stored at 0°C in air for 3 days had lower offflavours, a more acceptable flavour, and were more acceptable overall than those stored at 5°C in air. The spears stored in CO2 showed a trend towards higher flavour and acceptability ratings and lower off-flavour ratings when stored at 5°C than 0°C. Although the ratings at the two storage temperatures for the CO2 stored spears are not significantly different at P < 0.05, the higher storage temperatures appear to be a better choice for maintaining sensory quality when using high levels of CO2 for disinfestation. Thick spears had more flavour and showed a trend of greater overall acceptability than thin spears. Thick spears stored in 60% CO2 had higher flavour acceptability ratings than thin spears stored in 60% CO2. Although this was not significant at P < 0.05 the probability level of P = 0.11 indicates there is a trend here. Differences in ratings between the air-stored thick and thin spears were very small in comparison. Spear length has a significant effect on spear composition (Hyde & Shewfelt 1958; Shewfelt & Mohr 1960) and on rate of changes in composition during storage (Saltveit & Kasmire 1985). It is therefore reasonable to expect spear diameter may have an effect, on response to storage conditions. Standing spears in water during 60% CO2 storage decreased quality. Ratings for off-flavours were higher

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and ratings for characteristic asparagus flavour, flavour acceptability, and overall acceptability were lower than spears from all other treatments. Flavour acceptability ratings and to a lesser extent overall acceptability ratings were higher in air-stored spears standing in water during treatment than for those stored dry (Table 5). Spears stored in water have been shown to increase in length and weight, mainly as a result of water uptake and increased cell size. The effect is increased by elevated CO2 levels (Brennan 1958; Lougheed & Franklin 1965) which may have stimulated cell division (Lougheed 1964). Lower quality ratings may be caused by dilution of flavour components or by production of metabolic byproducts stimulated by the combined effects of water storage and CO2 level. The pH of the standing water was not measured, but may have become acidic in the CO2 storage treatment as a result of dissolved CC>2This could have contributed to off-flavour development and flavour loss in the CO2-stored spears as spears cooked in a slightly acidic solution develop offflavours (Corrigan unpubl. data). Further work needs to be done on the quality of spears that have been kept in cold storage for 1-2 weeks after the high CO2 storage treatment, then held for a shelf period to study spear quality under conditions closer to those likely to be encountered in the marketplace.

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