EFFECT OF FILM PERFORATION ON THE QUALITY OF INDIVIDUALLY SEAL PACKAGED TOMATOES

EFFECT OF FILM PERFORATION ON THE QUALITY OF INDIVIDUALLY SEAL PACKAGED TOMATOES

JOHN D. FLOROS’ and MANJEET S. CHINNAN’

Accepted for Publication April 18, 1990

ABSTRACT

Freshly harvested, ethylene treated, mature green tomatoes (Lycopersicon esculentum Mill. cv. ‘Flora-Dade’) were individually packaged in heat-shrinkable perforated films and stored at 21°C and 55% RH. The degree of film perforation (exposed surface area, A ) was varied as 0, I .4, 4.5, I1 and loo%, with the hole diameter, D, being constant at 8 mm or D was varied as 0.7, 4, 8 and 16 mm, while A was kept constant at 11%. Films with A = 0 or 1.4% drastically reduced weight loss and tissue softening resulting in tomatoes of good eating quality and bright red color. Off-flavor was detected when films with D = 0.7 mm were used. Large size holes (D = 16 mm) allowed free gas exchange between the fruit and the environment. Results indicated that fruits transpire throughout the entire skin surface area, but respire primarily through the stem scar.

INTRODUCTION

Individual seal packaging (ISP) has been developed during the last decade as a method for extending the shelf life of fruits and vegetables. It creates a water saturated atmosphere around the fruit which reduces water loss and shrinkage. This technique has been used as an alternative to the traditional refrigerated storage of fresh produce or to the more sophisticated controlled atmosphere storage, which are both quite expensive and require high capital investment (Ben-Yehoshua et al. 1979; Ben-Yehoshua et al. 1983; Anzueto and Rizvi 1985; Yang et al. 1987). However, certain limitations apply (Ben-Yehoshua 1985; Hulbert and Bhowmik 1987) such as production of off-flavors caused by poor gas exchange (Risse et al. 1985; Risse 1987), and greatly enhanced decay and spoilage due to the phytotoxic microatmosphere which may develop around the enclosed fruit, i.e., low 0, and excessive CO, and C,H,. ISP has also been

‘Formerly with the University of Georgia, now with the Department of Food Science, Purdue University, West Lafayette, IN 47907 Author to whom all correspondence should be sent. 2Department of Food Science and Technology, University of Georgia, Griffin, GA 30223-1797

Journal of Food Quality 13 (1990) 317-329. All Rights Reserved. 0 Copyright 1990 by Food & Nutrition Press, Inc., Trumbull, Connecticut. 317

318 JOHN D. FLOROS and MANJEET S. CHINNAN

referred to as individual shrink wrapping, shrink wrapping and unipacking in the literature.

The present study was undertaken in an attempt to introduce perforation in the packaging film as a means of retaining the positive effects of ISP (reduced water loss and shrinkage of the product. ease of storage, transportation and handling, and economy), but reducing the negative effects (off-flavors, decay, and spoilage). The objective was to determine the effect of film perforation on selected physiological responses and the overall quality of individually packaged tomatoes in heat-shrinkable polymeric films.

MATERIALS AND METHODS

Individual Seal-Packaging (ISP) Treatment Freshly harvested, mature green tomatoes, grown in Florida and commercially

treated with ethylene for 14 h, were sorted for size uniformity (diameter 7 t 1 cm, and weight 145 k 15 glfruit) and absence of physical and microbial damage. They were divided into 10 groups with 10 to 20 fruits per group. Each group of tomatoes was subjected to a different treatment. Cryovac D-955@ film, 19 p,m (0.75 mil) thick, obtained from the Cryovac Division of W. R. Grace & Co. (Duncan, SC) , was used in all individual seal packaging treatments. Films were perforated prior to seal packaging by drilling varying size and number of holes through the film. Two experiments called I and I1 were designed. In experiment I the hole diameter D was kept constant (8 mm), whereas the percent perforation area, A, was varied (0.0, 1.4, 4.5 and 11% of the film surface). In experiment I1 the exposed surface area, A , was kept constant at 11%, whereas the hole diameter, D, was varied (0.7, 4, 8 and 16 mm). Sealing was performed using a Bestronic sealer, Model 1913 (GSM (Eiessler, Florham Park, NJ) and by passing the fruits through a Bestronic shrink-wrapping tunnel (Model T14- 8-D) for 5.2 ? 0.1 s at operating temperature of 400°C. At times, if the shrinkage of the film was not satisfactory, a hot-air-gun was used, after the tunnel treatment, to improve the wrapping quality and shrink the film smoothly against the tomato surface. A group of fruits was shrink-wrapped in nonperforated film but im- mediately after the shrink-wrapping the film was removed. This treatment (here- after referred to as the reference group) was included to study the effect of heat on the fruits and to compare with the control fruits which did not undergo any treatment. After shrink wrapping, tomatoes were stored at 21"C, 55% RH and measurements were performed every 3-4 days (twice a week).

Weight

The weight of 10-20 fruits (depending upon treatment) was recorded with an accuracy of ?0.01 g using a Sartorius GMBH balance, Model 1264 MP (Got- tingen, W . Germany) and the rate of weight loss was calculated as g/kg-day.

PERFORATED FILMS FOR ISP TOMATOES 319

Color

At each sampling day the color of six tomatoes (the same throughout the experiment) from each treatment group was determined using a Gardner color- imeter, Model XL-845 (Pacific Scientific, Bethesda, MD). Color values were obtained by averaging instrument readings at four points on the circumference of the fruit, each approximately 90” apart, and one on the blossom end. The light red Gardner Reflectance Standard plaque (L = 74.7, a = +23.5, b = + 10.7) was used as a reference to standardize the instrument.

Firmness

A nondestructive deformation test, adapted from Bourne (1982), was used to evaluate fruit firmness. An Instron Model 1122 (Canton, MA) mounted with a 25.8 sq cm (4 sq in.) compression anvil (Assembly No. A372-19) was employed for firmness tests. Force readings at 2% deformation were recorded at two points (90” apart) for each tomato. The tomato diameter at these points was measured using vernier calipers with an accuracy of 0.1 mm, while the Instron was operated at 1 mdmin crosshead speed and 50 mdmin chart speed. Firmness tests were performed on five tomatoes from each treatment and the same group of tomatoes were used throughout the experiment.

Ethylene and Carbon Dioxide Evolution Rates

C,H, and CO, evolution rates were measured on four tomatoes taken from each treatment. Fruits were placed into glass containers of known volume (0.8 L net) and sealed for 2 to 4 h. Gas samples from the headspace were analyzed for ethylene using a Varian Gas Chromatograph, Model 3400 (Palo Alto, CA) equipped with hydrogen flame ionization detector and a 65 cm long aluminum column packed with aluminum oxide. The flow rate of the carrier gas (NJ was 25 mL/min, and the column, injector and detector temperatures were 90, 100 and 250”C, respectively. Carbon dioxide was measured with a Hewlett-Packard Gas Chromatograph, Model 5790A (Avondale, PA) equipped with a thermal conductivity detector and a CTR-I column (Alltech Associates, Deerfield, IL). The flow rate of the carrier gas (He) was 100 mL/min, and the column, injector and detector temperatures were 33, 100 and 250”C, respectively. Reported values represent the average of four tomatoes.

Sensory Attributes

Packaged and control fruits were evaluated for off-flavor and taste (eating quality) after three weeks of storage. A sensory panel of ten semi-trained panelists ranked the fruits by placing a vertical mark on a 100 mm horizontal scale. The scale was marked at 0, 50 and 100 mm to indicate “weak,” “moderate” and


“strong” for off-flavor, or “dislike very much,” “neither like nor dislike” and “like very much” for taste. Each panelist was provided with one quarter of a tomato (sliced) from each treatment. Samples were served at ambient temperature and under normal illumination.

Data Analysis

Firmness. A typical force-deformation behavior is shown in Fig. lA , which was obtained when control or reference fruits were tested. The force (F,) was measured at d = 2% deformation. At times, when fruits with films were com- pressed, irregularities were encountered, which produced a “tail” (Fig. 1B) or a “jump” (Fig. 1C) at the low force end of the curve. Such phenomena represent the deformation of the film (Fig. 1B) or a “slipping out” of the film during compression (Fig. 1C) and can introduce large errors in measuring force values at some specified deformation d (compare F, and F, in Fig. IB and 1C with F, in Fig. 1A). Therefore, a correction was applied as suggested by Bourne (1982). The linear part of the force-deformation curve was extrapolated (Fig. 18 and 1C) and the deformation (d) was measured from the point of its intersection with the x-axis.

Statistical Analysis. The procedures of General Linear Models (GLM), analysis of variance and Duncan’s Multiple Range Test of the Statistical Analysis

Distance FIG. 1. A TYPICAL FORCE-DEFORMATION CURVE (A) WITH

THE FORCE F, MEASURED AT DEFORMATION d = 2% Irregularities encountered during Compression as a “tail” due to film deformation (B) or as a

“jump” due to film slipping out of position (C). Correction of irregularities by extrapolation of the linear part to locate the actual starting point (B and C). and measure F, instead of Fb or F,.

32 I PERFORATED FILMS FOR ISP TOMATOES

Systems (SAS 1985) were used for regression analysis and determination of differences among groups.

RESULTS

Weight Loss

Moisture loss due to transpiration during storage was observed for all fruits. Control fruits lost more than 5% of their initial weight after three weeks of storage (Fig. 2) , exhibiting no significant difference from the reference group. This observation indicates that the heat treatment during shrink wrapping did not affect the transpiration of the fruit. Weight loss for the fully seal-packaged tomatoes was less than 0.5% of their initial weight after three weeks of storage, indicating that packaging reduced moisture loss more than 90%. Tomatoes packaged in films with constant hole diameter (D = 8 mm) and varying degree of perforation had intermediate moisture losses with values between those of control and completely covered fruits (Fig. 2A).

When fruits were packaged in films with constant degree of perforation (A = 1 l%), but varying hole size, greater moisture loss was generally observed when films with hole size smaller than 16 mm were used (Fig. 2B). Fruits packaged in film of D = 16 mm exhibited the least weight loss (2.5% after

0 2 4 6 8 10 12 14 16 18 20 22 94 -

0 2 4 6 8 10 12 14 16 18 2 0 2 2

rime (days) Time (days)

FIG. 2. (A) CHANGES IN WEIGHT DUE TO MOISTURE LOSS DURING STORAGE OF TOMATOES PACKAGED IN FILMS WITH VARYING DEGREE OF PERFORATION AND CONSTANT HOLE DIAMETER (D = 8 mm); (B) CHANGES IN WEIGHT DUE TO

MOISTURE LOSS DURING STORAGE OF TOMATOES PACKAGED IN FILMS WITH VARYING HOLE DIAMETER, AND CONSTANT DEGREE OF PERFORATION (A = 1 1 % )


three weeks of storage). Fruits packaged in film of D = 0 . 4 , 4 or 8 mm exhibited similar weight loss (about 4 9 after three weeks of storage).

Firmness

The firmness of tomatoes declined during the three weeks of storage with the groups of 0 and 1 . 4 9 perforation maintaining higher firmness values than the rest (Fig. 3A). During the first week of storage, however, no significant (P > 0.05) differences were detected among treatments with varying degree of perforation. For the next two weeks of storage, the groups with 0 and 1.4% perforation were significantly (P > 0.05) firmer than the control and reference groups. No significant differences were detected among treatments with varying hole diameter, but there was a tendency for higher retention of texture values (Fig. 3Bj when films with large holes were used (D = 8 mm, 16 mm).

Ethylene and Carbon Dioxide Evolution Rates

All treatments. except 0 and I .4% perforation, had similar ethylene evolution rates. The rate of evolution peaked after one week of storage with a rapid reduction thereafter (Figs. 4A and 4B). The 0 and 1.4% perforation treatments, however. exhibited no sharp peaks but rather a gradual increase and decrease

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FIG 3. (A) CHANGES IN FIRMNESS DURING STORAGE OF TOMATOES PACKAGED IN FILMS WITH VARYING DEGREE OF PERFORATION AND CONSTANT HOLE DIAMETER (D = 8 mm): (9) CHANGES OF FIRMNESS

DURING STORAGE OF TOMATOES PACKAGED IN FILMS WITH VARYING HOLE DIAMETER AND CONSTANT DEGREE OF PERFORATION (A = 11%)

PERFORATED FILMS FOR ISP TOMATOES

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FIG. 4. (A) ETHYLENE EVOLUTION RATES OF TOMATOES PACKAGED IN FILMS WITH VARYING DEGREE OF PERFORATION AND CONSTANT HOLE DIAMETER (D = 8 mm); (B) ETHYLENE EVOLUTION RATES OF TOMATOES PACKAGED IN FILMS WITH VARYING HOLE DIAMETER

AND CONSTANT DEGREE OF PERFORATION (A = 1 1 %)

of ethylene production (Fig. 4A). They had significantly lower ethylene production than the rest during the first few days of storage, but after two weeks no significant differences were detected.

The CO, evolution rates of 0 and 1.4% perforation treatments were significantly lower than the rest at the beginning of the experiment (Fig. 5A), but after two weeks of storage no statistically significant differences existed. The 16 mm hole size treatment retained higher values than all other treatments up to three weeks of storage (Fig. 5B).

Color Development

Packaging of fruits in polymeric film without perforation (0%) delayed color development during the first week of storage (Fig. 6 ) compared to the control and reference treatments. In contrast, packaging in films with perforation enhanced red color development from the first day of storage. After two weeks of storage, individually seal packaged fruits (in perforated or nonperforated films) had developed brighter and redder color than the control groups. No significant differences were observed between the control and reference treatments. All the fruits packaged in perforated films with varying hole size had essentially the same behavior as those packaged in films with 1.4, 4.5 or 11% perforation.

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Sensory Attributes

All groups had some off-flavor after three weeks of storage. The control group had the lowest value, but it was statistically different only from the 0.7 rnm hole size treatment, which had the highest value (Fig. 7). No significant differences (P > 0.05) were recorded in taste ratings, even though the 0.7 mm hole size treatment was ranked lowest.

DISCUSSION

Individual seal packaging (ISP) of tomatoes reduced moisture loss by more than 90% after three weeks of storage. Similar results were reported for citrus fruits by Ben-Yehoshua et af. (1985). When tomatoes were packaged in perforated films the weight loss increased as the degree of perforation increased

326

65

JOHN D. FLOROS and MANJEET S . CHINNAN

Taste - Off-Flavor

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FIG. 7 . SENSORY AlTRIBUTES OF TOMATOES AFTER THREE WEEKS OF STORAGE

(Fig. 2A). A significant relationship (R' = 0.953) between the rate of weight loss and the degree of perforation (Fig. 8) was derived, which had the following exponential form:

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This observation indicates that significant water transport takes place through the entire surface of the fruit and not just through the stem scar. In previous investigations (Albrigo 1972) it has been reported that the epicuticular wax, which covers the surface of fruits and vegetables, reduces but does not eliminate the movement of water through the skin. Similarly, Ben-Yehoshua et af. (1985) suggested that water moves through a liquid aqueous phase in the cuticle, which in turn supports the idea of water transport throughout the entire skin surface area of the fruit. A possible mechanism of the water movement through the skin is Fickian diffusion.


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Texture results indicate that only treatments A-0 and A-1.4, which had higher firmness values, delayed the physiological deterioration and noticeably affected the shelf life of tomatoes. In a sensory evaluation study, Resurreccion and Shewfelt (1985) reported that firmness was one of the principal factors associated with the quality of tomatoes. Yang et al. (1987) also reported that seal-packaging prolonged the ripening period of tomatoes, while Anzueto and Rizvi (1985) noted that individual packaging in heat-shrinkable co-polymeric films extended the shelf-life of apples. In the later study (Anzueto and Rizvi 1985), the excessive water loss from control apples (nonpackaged) caused the flesh to become spongy and dry. Therefore, an increase in firmness occurred after 4 weeks of storage. In tomatoes such a phenomenon was not observed. Enzymatic softening and microbial deterioration occurred well before that stage.

The lower CO, and C,H, evolution rates of treatments with 0% and 1.4% exposed surface area, compared with the other groups, were probably associated with the respiratory rate of the fruits. The lower rate of ethylene evolution is in agreement with reports for lower internal ethylene content in sealed fruits (Ben- Yehoshua er al. 1979). The lower carbon dioxide evolution rate could also be attributed to lower internal concentration, since it has been found that the dif- fusivities of C,H, and C,D2 are similar (Burg and Burg 1965). Ben-Yehoshua et al. (1979) reported that the CO, and 0, content in the internal atmosphere of sealed and control fruits were similar, and that low CO, production is most likely due not to the restriction of CO, movement (polyethylene is a gas permeable film), but rather due to lower water stress (polyethylene is a good water vapor


barrier). The low evolution rates of COz and C,H, for fruits with 0% and 1.4% exposed surface area could also be explained because these fruits had their stem scar covered. Cameron and Yang (1982) reported that 97% of the gas exchange in tomatoes occurs through the stem scar, while Ben-Yehoshua et al. (1985) suggested that in citrus fruits gases move through stomata.

Sensory evaluation results suggested that the use of perforated films with small holes (D < 1 mm) is not a good practice for packaging tomatoes. The highly detectable off-flavor and the low taste profile of treatment 0-0.7 may possibly be attributed to the hot air-gun heat treatment given to this group for improvement of shrinkage. Heat may have penetrated the film and affected the physiological state of the fruit. Control fruits developed very little off-flavor and taste ratings were statistically similar to other treatments, but tissue softening and physiological deterioration were noticeable after two weeks of storage. The fully covered tomatoes did not exhibit significant off-flavor, developed good taste and bright red color.

CONCLUSIONS

Combining the results reported here for moisture loss, tissue softening, gas exchange and sensory quality for tomatoes packaged in perforated or non-perforated polymeric films the following conclusions can be stated: Water moves throughout the entire surface of the tomato and not only through the stem scar as gases do. Packaging of tomatoes in nonperforated films reduces the weight loss more than 90% compared to nonpackaged fruits. Packaging in nonperforated films or films with a small degree of perforation (A < 2%) would result in higher firmness values and retain good tissue texture for over three weeks. Small degree of perforation (A < 2%) combined with large size hole(s) ( D = 2 cm), especially if they leave the stem scar free, could allow free gas exchange, limit water loss and maintain firmness. This might lead to products with low off-flavor and good taste profiles. The role of stem scar in transpiration, respiration and shelf-life extension of tomatoes is very important and needs further investigation.

REFERENCES

ALBRIGO, L. G . 1972. Distribution of stomata and epicuticular wax on oranges as related to stem end rind breakdown and water loss. J . Amer. SOC. Hort. Sci. 97, 22&223.

ANZUETO, C . R. and RIZVI, S . S . H . 1985. Individual packaging of apples for shelf life extension. J. Food Sci. 50, 897-900.

BEN-YEHOSHUA, S. 1985. Individual seal-packaging of fruits and vegetables in plastic film-A new postharvest technique. HortScience 20, 32-37.


BEN-YEHOSHUA, S . , BURG, S. P. and YOUNG, R. 1985. Resistance of citrus fruit to mass transport of water vapor and other gases. Plant Physiol. 79, 1048-1053.

BEN-YEHOSHUA, S . , KOBILER, I. and SHAPIRO, B. 1979. Some physiological effects of delaying deterioration of citrus fruits by individual seal packaging in high density polyethylene film. J. Amer. SOC. Hort. Sci. 104,

BEN-YEHOSHUA, S . , SHAPIRO, B., CHEN, Z. E. and LURIE, S. 1983. Mode of action of plastic film in extending life of lemon and bell pepper fruits by alleviation of water stress. Plant Physiol. 73, 87-93.

BOURNE, M. C. 1982. Food Texture and Viscosity: Concept and Measurement. Academic Press, New York.

BURG, S. P. and BURG, E. A. 1965. Gas exchange in fruits. Physiol. Plant. 18, 870-884.

CAMERON, A. C. and YANG, S. F. 1982. A simple method for the determination of resistance to gas diffusion in plant organs. Plant Physiol. 70, 21- 23.

HULBERT, G. J. and BHOWMIK, S. R. 1987. Quality of fungicide treated and individually shrink-wrapped tomatoes. J. Food Sci. 52, 1293-1297, 1329.

RESURRECTION, A. V. A. and SHEWFELT, R. L. 1985. Relationship between sensory attributes and objective measurement of postharvest quality of tomatoes. J. Food Sci. 50, 1242-1245.

RISSE, L. A. 1987. Film wrapping fresh produce. ASAE Paper No. 87-6006, St. Joseph, MI.

RISSE, L. A., MILLER, W. R. and BEN-YEHOSHUA, S. 1985. Weight loss, firmness, colour and decay development of individually film-wrapped tomatoes. Trop. Sci. 25, 117-121.

868-872.

SAS. 1985. SAS User’s Guide: Slaristics. SAS Institute, Cary, NC. YANG, C. C., BRENNAN, P., CHINNAN, M. S. and SHEWFELT, R. L.

1987. Characterization of tomato ripening process as influenced by individual seal-packaging. J. Food Qual. 10, 21-33.

EFFECT OF FILM PERFORATION ON THE QUALITY OF INDIVIDUALLY SEAL PACKAGED TOMATOES

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