FORCED-AIR COOLING AFTER AIR-SHIPMENT DELAYS ASPARAGUS DETERIORATION

FORCED-AIR COOLING AFTER AIR-SHIPMENT DELAYS ASPARAGUS DETERIORATION

E. LAURIN. M.C.N. NUNES' and J-P. EMOND

Air Cargo TranspoRation Research Group Universiiy Lava1

FSAA - Pavillon Paul-Comtois Depamnent of Soils and Agrifood Eng.

Quebec, GIK 7P4 CaMda

Accepted for Publication January 12, 2002

ABSTRACT

Asparagus (cv. Locullus) was stored at 20C for 20 h to simulate time delays and temperature typically encountered during air-shipment operations. After that period, asparagus were immediately forced-air cooled at I C, or room cooled at IC or IOC, or stored at 20C to simulate diferent facility conditions usually available at the airports. The objective of this work was to detennine which cooling method should be applied to limit the degradation of asparagus after a temperature abuse during ground and in-flight operations. Forced-air cooled asparagus gained in average one to three days of sherf-life when compared to room cooled asparagus at 1 C and 1 OC, and five to seven days when compared with asparagus stored at 20C. Results from this study illustrate that whenever a load of warm asparagus am'ves to the airport facilities a forced-air cooling treatment at IC may be applied to delay product deterioration without causing chilling injury symptoms.

INTRODUCTION

In the past five years, the volume of all perishables transported by air, including fruits and vegetables, increased 10 to 12% per year (Stera 1999). Even if the horticultural crops comprise a big part of this market, air transportation still represents a break in the cold chain of perishable handling. The major cause for this rupture is the temperature abuse during flight and ground operations. For example, for a national flight in the United States, perishables leaving Miami airport need to be delivered 3-4 h prior to flight departure, and for an

' Contact author. M. Cecilia N. Nunes, University Laval. FSAA - Pavillon Paul Comtois, Department of Soils and Agrifood Eng., Quebec, CANADA G1K 7P4. TEL: (418) 656-2131. ext. 2656; FAX: (418) 656-3723; Email:[email protected].

Journal of Food Quality 26 (2003) 43-54. Alf Rights Reserved. "Copyright 2003 by Food & Nutrition Press, Inc., Trumbull. Connecticut. 43

44 E. LAURIN. M.C.N. NUN= and J-P. EMOND

international flight, 6 h before departure are required (Villeneuve e? al. 1999). These delays are necessary to the normal ground operations. However, during these periods, perishables are often exposed to temperatures that do not correspond to their optimal, since most of the ground operations are performed at ambient temperatures that may vary from -40 to +5OC (Stera 1999). Several studies also reveal that temperatures during loading, flight and unloading do not correspond to the optimal temperature required by most of the commodities (Emond et al. 1999; Bollen e? al. 1998; Akinaga and Kohda 1992; Sharp 1989). For example, Downs (1985) reported that the temperature inside the cargo holds of an aircraft transporting perishables from New Zealand could be as high as 25C. Later Emond e? al. (1999) confirmed that the temperature inside a Boeing 747-400 combi varies depending on the location of the cargo inside the aircraft, at the center of the Aft lower hold, the warmest place, the temperature easily reaches 28 to 32C. Thus, upon arrival to their final destination perishables may have reached very high temperatures, due to the accumulated heat inside the cargo containers.

Asparagus is one of the vegetables most often transported by air and responsible for claim (Nunes and Emond 1999). However, temperature abuse that occurs during air shipment of asparagus often result in loss of quality (Graemer et al. 1987). Bollen ez al. (1998) reported that temperature of asparagus, on a trip from New Zealand to Japan with a transit at Singapore airport, might be as high as 24C. This temperature is too high compared to an optimum of 2C. usually recommended for long term storage of asparagus. Thus, temperature abuse leads to loss of quality and sometimes to rejection of the whole load of asparagus upon arrival. In addition, temperature fluctuations during handling operations may lead to water condensation on the surface of the spears, which may promote pathogen growth. Another problem that might also occur during storage of asparagus is the development of chilling injury symptoms such as flaccidity of the spear, loss of sheen and glossiness and graying of the tips, as that may be present if stored for more than 10 days at temperatures lower than 2C (Perkins-Veazie e? al. 1993; Hardenburg e? al. 1986). Thus, confusion may take place when deciding where to place such products since most often the airport facilities have only 0 to lC, 1OC or 20C temperatures available.

There was no data available in the literature regarding the best procedure to use in order to avoid major quality losses of horticultural products transported or maintained under nonoptimum temperatures. More specifically, when a shipment of fruits or vegetables transported under high temperatures arrives to the airport facilities, two main issues often arise. The first issue, that is often overlooked, is what temperature should be selected to place the perishables. The second issue is the benefit of using any kind of rapid cooling procedure to slow down product deterioration.

FORCED-AIR COOLING AFTER AIR-SHIPMENT OF ASPARAGUS 45

The objectives of this study were: (1) to determine which cooling method should be used after temperature abuse during air shipment of asparagus. (2) to evaluate the effect of the available temperatures at the airport facilities on the quality of asparagus.

MATERIALS AND METHODS

Rant Material and Storage Condition

“Locullus” asparagus was obtained from a commercial field near Mirabel, Quebec, Canada. After cleaning, the asparagus was classified by size. trimmed and packed in boxes of 9 kg each. Two replicated experiments were conducted during the 2000 summer season. The asparagus was harvested June 5 and 8 at 7:OO am. The field temperature at that time was about 4C and 7C for the first and second harvest, respectively. The warmest temperature recorded 24 h prior to harvest was 13C and 19C for the first and second harvest, respectively. After harvesting, the asparagus was transported with minimal delay to the laboratory at Mirabel fret cargo airport.

Thirty asparagus spears per treatment were selected for uniformity of color, size and freedom from defects. In order to avoid major water loss during storage, groups of 10 asparagus (a total of 30 spears per treatment) were placed in 1 L transparent plastic containers. After conditioning for about 5 h in a cold room at 1C f 0.2C and 85-9076 RH, the plastic containers were covered with a perforated plastic film SM60 (Cryovac, Montreal, Canada) with a thickness of 39 pm in order to assure a relative humidity inside the container near saturation. The asparagus was then stored 20 h at 20C f 2C and 60-70% RH to simulate time delays and temperature abuse during flight and ground operations.

Three containers of 10 spears each were immediately forced-air cooled at 1C f 0.2C. or placed in cold room at 1C 5 0.2C and 85-9096 RH. 1OC f 1C and 95-1001 RH or stored at 20C f 2C and 60-70% RH to simulate the conditions often encountered in the airport facilities. Forced-air cooling was performed at a flow rate of 2 L- s-l. kg’ in a cold room at 1C f 0.2C, and the airflow was perpendicular to the products. Forced-air was completed when spear temperature reached approximately 2C, which corresponded to 718 cooling temperature. After precooling, the asparagus samples remained at 1C f 0.2C and 85-902 RH. All the samples were stored in commercial cold room and exposed to artificial light during normal handling operations (approximately 10 h per day). A sample stored continuously at 1C k 0.2C and 8540% RH (no warming up) was used as a control.

46 E. LAURIN. M.C.N. NUNES and J-P. EMOND

The temperature inside the plastic containers was monitored throughout the storage period with Stow Away@ XTI02 temperature loggers (-5C to 37C) (Onset Computer Corp., Pocasset, MA). Relative humidity was monitored using Stow Away@ RH loggers (10 to 95% RH) (Onset Computer Corp., Pocasset, MA). Quality characteristics of asparagus were evaluated at harvest, after the simulation of air-shipment, after the cooling treatment, and during a 15-day storage period.

Weight Loss

Weight of 30 individual asparagus spears per treatment was taken using a precision scale with an accuracy of f 0.01 g (Acculab Model LT-3200, Acculab-Sartorius Co., Goettingen, Germany). Weight loss was then calculated from the weight of the spears measured at harvest, after the simulation of air- shipment, after the cooling treatment, and after 7 and 15 days of storage.

Visual Quality

Visual quality was evaluated by the same trained person using a modified rating scale by Graemer ez al. (1987) where 1 = fresh from the field, 3 = slight wilting, very slight wrinkle of the stem, 5 = browning of the stem bracts, moderate wilting, and feathering, 7 = soft rots starting, browning of spears, severe wilting and feathering, 9 = extensive rotting, stem collapse, extreme bud wilting, browning and feathering. A visual rate of five was considered the maximum limit of acceptability for the marketplace. Visual quality of asparagus was evaluated at harvest, after the simulation of air-shipment, after the cooling treatment, and daily during a 15-day storage period.

Firmness

Firmness was measured on the central part of a 10 mm height section of asparagus, using a Texture Analyzer (Model TA-XT2, Stable Micro Systems, Texture Technologies Corp., Scarsdale, NY). The asparagus section was obtained by cutting at 10 cm distance from the basal part of each spear. A 25-kg cell load was used for firmness determination of the asparagus spears. Crosshead speed was 0.8 mm- s-'. A 3 mm diameter convex tip probe was used. In order to avoid differences in f m e s s due to temperature, asparagus were removed from cold storage and allowed to warm up to 20C for 4 h. Since the penetration force is affected by the diameter of the spears, firmness was calculated as following: Force (N) divided by the diameter of the section (mm). The results were expressed in Newtodmm. Firmness of asparagus was measured at harvest, after the simulation of air-shipment, after the cooling treatment, and after 7 and 15 days of storage.

FORCED-AIR COOLING AFTER AIRSHIPMENT OF ASPARAGUS 41

Fiber Content

Fiber content (FC) was determined using a modified blender method (Sosa- Coronel m al. 1976; Siomos et al. 1995). Asparagus were weighed, boiled for 15 min, immerged in 200 mL of water for 2 min and blended for 1 min. The mixture was then filtered through a 30-mesh screen to separate fiber from the remaining mixture and transferred to a preweighed container. After the separation the fibers were dried for 12 h at a temperature around 1OOC. Fiber content of asparagus was calculated from the difference between the total weight of asparagus before and after the separation of fibers. Fiber content of asparagus was measured at harvest, after the simulation of air-shipment, after the cooling treatment, and after 7 and 15 days of storage.

Statistical Analysis

The treatments were arranged in a factorial design consisting of 2 harvests x 5 temperature treatments (control, forced-air cooling, room cooling at 1, 10 or 20C) x 4-storage times (1, 2, 7 and 15) x 3 replicates samples of 10 asparagus, plus three additional samples for time zero. The Statistical Analysis System computer package (SAS Institute 1982) was used for analysis of data from these experiments. Initial analysis of the data for the combined harvests by analysis of variance (ANOVA) indicated a significant harvest effect. Subsequent- ly, data for the different harvests were analyzed separately. Significant differences between the cooling treatments were detected using the Least Significant Differences (LSD) at the 5% level of significance.

RESULTS AND DISCUSSION

Weight Loss

According to Robinson ef al. (1975). when the initial weight of asparagus is reduced by 8% or more due to the loss of moisture the spears are considered unmarketable. Therefore, asparagus from the two harvests kept at 20C attained the maximum acceptable weight loss after two days, which corresponds to the period of time after the cooling treatment (Table 1). However, after the cooling treatment there was no significant difference between the weight loss of asparagus from the forced-air and room cooling treatments. Weight loss of spears from the room cooling treatment at 1C or 1OC was no longer acceptable after seven days while weight loss of asparagus from the control and forced-air cooling treatment was still acceptable beyond that time. Past 15 days all the asparagus had already reached more than 8 X weight loss, regardless the harvest or temperature treatment. Overall, following air-shipment the forced-air cooling

48 E. LAURIN, M.C.N. NUNES and J-P. EMOND

treatment contributed to a lower weight loss of asparagus for at least seven days when compared with the other temperature treatments.

TABLE 1. EFFECTS OF AIRSHIPMENT OPERATIONS ON QUALITY CHARACTERISTICS OF ASPARAGUS FROM THE FIRST HARVEST AFTER COOLING AND STORAGE FOR

ONE OR TWO WEEKS AT 1.10 AND 2OC'

Temperature Treatments Weight Loss (96) Firmness (Nlmm) Fiber Content (96)

A f harvesf 0.00 0.8 2.4

After simulation of air-shipmenf (20 h at 20C)

Control at 1C Forced-air cooling at 1C Room cooling at 1C Room cooling at 1OC Storage at 20C


Control at 1C Forced-air cooling at 1C Room cooling at 1C

Room cooling at 1OC Storage at 20C


0.68 b 0.79 a 3.34 a 0.79 a 3.34 a 0.79 a 3.45 a 0.80 a

3.84 a 0.77 a

After fhe cooling treafment 1.19 c 0.83 a 4.14 b 0.89 a 4.38 b 0.81 a 4.53 b 0.90 a 8.96 a 0.89 a

After seven days 4.28 c 0.91 a 6.92 bc 0.84 a 8.60 b 0.83 a 8.67 b 0.84 a 33.40 a 0.63 b

After I5 days

9.75 b 0.93 a 11.19 a 0.89 a 12.82 a 0.76 b 13.56 a 0.48 c Decayed Decayed

2.69 a 2.99 a 3.00 a 3.00 a 3.00 a

2.34 a 2.69 a 3.17 a 2.95 a 2.49 a

2.59 ab 2.33 ab 2.88 ab 2.27 b 3.78 a

2.13 c 2.22 c 2.62 b 3.07 a

Decayed

a Data are means of 30 individual spears replicates. Significant differences between cooling treatments within each storage time determined by Least Significant Difference (LSD). P = 0.05.


Visual Quality

Asparagus from the first harvest stored continuously at 1C maintained a good visual quality during 15 days of storage, while those from the forced-air and room cooling treatments at 1C or lOC, and storage at 20C reached the maximum acceptable visual quality after approximately 11, 10. 11.5 and 5.5 days of storage, respectively (Fig. 1A). After seven days, asparagus from the room cooling treatment at 1C had a better visual quality when compared with those from the forced-air or room cooling at 1OC. However, after 15 days asparagus from the forced-air treatment had a better visual quality than those from the room cooling treatments.

For the second harvest, asparagus from the control treatment reached their limit of acceptability after 13 days (Fig. 1B). Whereas asparagus from the forced-air and room cooling treatments at 1C or lOC, and storage at 20C maintained an acceptable visual quality after 11. 10. 10.5 and 5 days, respectively. As for the first harvest, after seven days, asparagus from the room cooling treatment at 1C had a better visual quality when compared with those from the forced-air or room cooling at 1OC. There was no significant difference in the visual quality of asparagus from the forced-air, room cooling at 1C or 1OC after 15 days in storage. No symptoms of chilling injury were observed in asparagus stored continuously at 1C neither in those from the forced-air nor room cooling treatment at 1C.

Firmness

Firmness of asparagus from the first harvest did not significantly change after the air-shipment or cooling treatments (Table 1). After seven days there was no significant difference in firmness of the asparagus between the control, forced-air and room cooling treatments at 1C or 1OC. After 15 days, asparagus from the control and forced-air cooling treatment had the highest firmness compared with the room cooling treatments.

For the second harvest, firmness of the asparagus increased after the simulation of air-shipment but remained quite stable after the cooling treatment (Table 2). As for the first harvest, after seven days there was no significant difference in firmness of the asparagus between the control, forced-air and room cooling treatments at 1C or 1OC. After 15 days there was no significant difference in the firmness of asparagus from the control and forced-air cooling treatment. However, after that time a significant decrease in the firmness of asparagus was observed for the room cooling treatment at 1OC. Decrease in firmness was mostly due to the softening of asparagus tissues and increased loss of moisture during storage at higher temperatures.


3 E

- - - m - - Control - Forced air - 1C + 1OC - 20C 9.0 1

7.0

5.0

3.0

1 .o 9.0

7.0

5.0

3.0

1 .o

/Trn i .................. i

.....................

0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 Storage time (days)

FIG. 1. EFFECTS OF AIR-SHIPMENT OPERATIONS ON VISUAL QUALlTY OF ASPARAGUS FROM THE FIRST (A) AND SECOND (B) HARVEST AFTER

COOLING AND STORAGE FOR ONE OR TWO WEEKS AT 1.10 AND 20C' Day one corresponds to simulation of air-shipment; Day 2 corresponds to cooling treatment.


TABLE 2.

ASPARAGUS FROM THE SECOND HARVEST A€TER COOLING AND STORAGE FOR ONE OR TWO WEEKS AT 1.10 AND 2oc'

EFFECTS OF AIR-SHIPMENT OPERATIONS ON QUALITY CHARACTERISTICS OF

Temperature Treatments Weight Loss (W) Firmness (Nlmm) Fiber Content (46)

At harvest 0.00 0.66 0.9

After simulation of air-shipment (20 h at 20C)

Control at 1C 0.82 b 0.85 a 2.32 b Forced-air cooling at IC 3.82 a 0.92 a 2.90 a Room cooling at 1C 4.00 a 0.92 a 2.90 a Room cooling at 1OC 4.40 a 0.92 a 2.90 a Storage at 20C 3.22 a 0.94 a 2.90 a

After the cooling ireatment Control at 1C 1.20 c 0.86 b 2.39 c Forced-air cooling at 1C 4.14 b 0.98 ab 2.70 c Room cooling at 1C 4.54 b 0.97 ab 2.79 bc Room cooling at 1OC 4.60 b 0.99 ab 3.15 b Storage at 20C 8.63 a 1.05 a 3.52 a

Control at 1C 4.28 d 0.70 a 2.18 c Forced-air cooling at 1C 7.60 c 0.75 a 2.69 bc Room cooling at 1C 10.28 b 0.75 a 2.72 b Room cooling at 1OC 11.08 b 0.80 a 2.71 b Storage at 20C 33.41 a 0.89 b 3.70 a

After seven days

After I S dqvs Control at 1C 11.19 a 0.87 b 2.31 c Forced-air cooling at 1C 11.66 a 0.85 b 2.63 bc Room cooling at 1C 12.82 a 0.95 a 3.05 ab Room cooling at 1OC 13.56 a 0.44 c 3.24 a Storage at 20C Decayed Decayed Decayed

a Data are means of 30 individual spears replicates. Significant differences between cooling treatments within each storage time determined by Least Significant Difference (LSD), P = 0.05.

Fiber Content

The initial fiber content (FC) of the asparagus was higher in the first harvest when compared with the second harvest (Tables 1 and 2). The preharvest growth


rate of asparagus might explain the differences between harvests regarding the fiber content of the spears. Lipton (1990) reported that cold weather slows down the preharvest growth of asparagus. Herner’s research (1990) revealed that lower temperatures cause less stem elongation but do not affect fiber development. In the present study, asparagus from the first harvest came from a cooler harvest and had a higher FC than those from the second harvest that came from a warmer harvest.

Fiber content of asparagus increased regardless of the temperature treatment. This fact might be explained by the faster increase in FC of asparagus often observed during the first 24 h after harvest (Chang 1987). After seven days, FC of asparagus stored at 20C significantly increased when compared with the other treatments. The lignification of the fibers, which is responsible for toughening of the spears, is due to the enzyme phenylalanine-ammonia-lyase. The lignification activity is enhanced by light and temperature (Chang 1987). In fact, Chen et al. (1980) reported that after exposure at 26C for 48 h, light-enhanced activity induces an increase of 21% of lignified cells and the effect of light is even more effective at temperatures around 5C. Lipton (1990) reported that the rate of FC development is fairly constant in the entire spear when stored between OC and 13C, but increases with a temperature raise. After 15 days there was no significant difference in FC of asparagus from the control and the forced-air cooling for both harvests. Results from the present study suggested that the forced-air as well as the room cooling treatment at 1C might inhibit the lignification of the spears and limited the increase in FC of the spears after seven days in storage, when compared with room cooling at 1OC and storage at 20c.

The differences between firmness and FC of the asparagus might be explained by the fact that the lignified pericyclic fibers that are responsible for toughing of the spears are predominantly developed in the external sides of the spear (Lipton 1990). Consequently, the middle part of the section. used to measure the firmness of the asparagus, possibly contained little lignified pericyclic fibers. According to Lipton (1990) FC is a more accurate measure- ment of toughening in asparagus than firmness since the diameter, weight, length and turgidity of the spear may affect the latter.

CONCLUSIONS

Temperature abuses occurring during air-shipment reduces the shelf-life of asparagus. The use of forced-air cooling after air-shipment can extend the shelf- life of asparagus for at least seven days, by reducing the loss of moisture and maintaining a better firmness and texture and by limiting the increase of fiber content. Forced-air cooled asparagus gained on average one to three days of


shelf-life when compaFed with room cooled asparagus at 1C and 1OC. and five to seven days when compared with asparagus stored at 2OC. Results from the present study showed that when a load of asparagus suffering from temperature abuse arrives at the airport facilities, a forced-air cooling treatment at 1C may be applied in order to delay further product deterioration without causing chilling injury. Although forced-air cooling provides a good solution to extend the shelf- life of temperature-abused asparagus, further research needs to be performed on real time shipment and containers.

ACKNOWLEDGMENTS

The authors wish to thank Perisco Inc., at the Montreal International Airport, Quebec. Canada by funding this research project. The authors are also thankful to Marjorie LePrince and Sharon Dea for their assistance in the laboratory work.

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FORCED-AIR COOLING AFTER AIR-SHIPMENT DELAYS ASPARAGUS DETERIORATION

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