Effect of a mango film on quality of whole and minimally processed mangoes

Available online at www.sciencedirect.com

Postharvest Biology and Technology 47 (2008) 407–415

Effect of a mango film on quality of whole and minimally processed mangoes Rungsinee Sothornvit ∗ , Patratip Rodsamran Department of Food Engineering, Faculty of Engineering at Kamphaengsaen, Kasetsart University, Kamphaengsaen Campus, Nakhonpathom 73140, Thailand Received 8 November 2006; accepted 8 August 2007

Abstract Ripe mango fruit tissue offers the possibility to form edible films and coatings, thus extending fruit shelf-life. The effect of a mango edible film and storage conditions on fresh mango quality and shelf-life was determined. A mango film provided a good oxygen barrier with sufficient mechanical properties to wrap whole and minimally processed mangoes. The film reduced weight loss and extended the ripening period of whole fresh mangoes. The shelf-life of unwrapped minimally processed mangoes kept in cellophane bags at room temperature (30 ◦ C) and cold storage (5 ◦ C) were 2 and 4 days, respectively. When the minimally processed mangoes were wrapped in a mango film and kept in cellophane bags, the shelf-life was extended to 5 and 6 days, when stored at 30 and 5 ◦ C, respectively. The highly hydrophilic character of the mango film meant solubility of the film limited its application. However, this opens further research to improve mango films for use with frozen and dried foods. © 2007 Elsevier B.V. All rights reserved. Keywords: Mango; Edible films; Minimally processed mango; Quality

1. Introduction Mango fruit are climacteric and ripen rapidly after harvest. During the harvest season, high production and perishability of tropical fruit such as mango results in substantial postharvest losses and environmental waste. Growing consumer demand for healthy and fresh fruit, including minimally processed fruit, is a current driving force in the market. Production of mango as a fresh-cut product opens another possibility for their commercialization. However, minimally processed fruit are subject to undesirable physiological changes such as color, texture, aroma, and overall appearance that cause a reduction in fruit shelf-life (Bolin and Huxsoll, 1989; Wong et al., 1994). Edible films and coatings have a potential to extend the shelf-life and quality of foods by preventing changes in aroma, taste, texture and appearance (Arvanitoyannis, 1999; Tharanathan, 2003). Studies of edible films and coatings show potential for some fruit; for example, whey protein coatings for apples (Cisneros-Zevallos and Krochta, 2003a,b), potato starch-based edible coatings on guava (Quezada Gallo et al.,

∗

Corresponding author. Tel.: +66 34281098; fax: +66 34351404. E-mail address: [email protected] (R. Sothornvit).

0925-5214/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2007.08.005

2003), hydroxypropyl methylcellulose-lipid edible composite coatings on plum (Perez-Gago et al., 2003), whey protein- and hydroxypropyl methylcellulose-based edible composite coatings on fresh-cut apples (Perez-Gago et al., 2005), and wheat gluten-based films and coatings on refrigerated strawberries (Tanada-Palmu and Grosso, 2005). Recently, fruit and vegetable purees, for example, peach, strawberry, apricot, apple, pear, carrot and broccoli, have been shown to be of use as alternative components of edible films (McHugh et al., 1996; McHugh and Olsen, 2004). These films under certain relative humidity (RH) and temperature conditions have been shown to be good barriers to gas diffusion but poor barriers to water vapor diffusion. These properties of edible films translate into an effective semi-permeable barrier to the respiratory gases (carbon dioxide and oxygen), creating a modified atmosphere (MA) when applied to fruit and vegetables (Baldwin, 1994). MA slows down respiration, metabolism and retards ethylene production, and application of films formed by fruit purees of the same freshcut product might benefit both quality and shelf-life, without affecting flavor. McHugh and Senesi (2000) observed a significant reduction in moisture loss and browning in fresh-cut apples when samples were wrapped in apple puree films containing beeswax, pectin, glycerol, ascorbic acid and citric acid. There is one study on fresh-cut mango using edible coatings

408

R. Sothornvit, P. Rodsamran / Postharvest Biology and Technology 47 (2008) 407–415

made of carboxymethycellulose, starch, chitosan, and whey protein with other ingredients. Fresh-cut mangoes coated with carboxymethycellulose containing maltodextrin presented the highest scores for visual quality and flavor (Plotto et al., 2004). Mango contains high levels of carbohydrate, protein and fat, which are the main components for edible films (Lakshminarayana, 1980; Han and Gennadios, 2005). Mango films might therefore be an alternative natural wrapping for maintaining quality and shelf-life of whole and fresh-cut mango. However, there has been no research on mango puree films and their application on whole and minimally processed mangoes. Therefore, the objectives of this study were to form a mango film and determine its water and oxygen barriers and mechanical properties and to apply the film as a wrapper on whole and minimally processed mangoes to maintain their quality and shelf-life.

the ASTM E96 (McHugh et al., 1993). Films selected without defects and pinholes were cut and sealed to the cup base previously filled with 7 ml distilled water. The cup was then placed into a cabinet at 27 ± 3 ◦ C and 50 ± 2% relative humidity maintained with a desiccant (silica gel) and 2.80 ± 0.25 m/s air velocity over the film. A temperature-RH meter (model DM760) was used to monitor the conditions inside the chamber. Once the film came into equilibrium with the cup and cabinet conditions, steady-state moisture transfer was obtained. Weights were taken at 2 h intervals. The WVP of the films was calculated by multiplying the water vapor transmission rate (WVTR) by the film thickness and dividing by the water vapor partial pressure difference across the films. WVTR × thickness WVP = (pA1 − pA2 )

2. Materials and methods

where pA1 and pA2 are the water vapor partial pressures inside and outside the cup, respectively.

2.1. Materials

2.6. Oxygen permeability determination

Ripe mangoes (Mangifera indica L.) cv. Namdok Mai, obtained from the local market in Nakhonpathom province (Thailand) were selected and cleaned to form mango puree to make the films and later use as minimally processed mangoes for coated samples. Green or unripe whole mangoes were used for coating applications.

Oxygen permeability (OP) of mango films was measured at 25 ± 2 ◦ C and 55 ± 5% RH using an Oxygen Permeation Analyzer (Model 8500, Illinois Instruments). A film was greased at the rim and placed on the sample chamber with an exposed testing area of 100 cm2 . Nitrogen gas flowed on one side and pure oxygen gas flowed on the other under the above conditions. The oxygen transmission rate (OTR) was recorded to calculate OP by multiplying OTR by the film thickness and dividing by the oxygen partial pressure difference (P) according to the following equation:

2.2. Film formation Ripe mangoes were washed, peeled, cut into pieces, and pulped to a mango puree by hand, followed by sieving. The puree (19% soluble solid content) was degassed and 20 g poured into 15 cm diameter high density polyethylene plates, and dried at 50 ◦ C for 12 h until a dried film was formed. Twenty replicates of films were used to determine each film property. 2.3. Film thickness Film thickness was measured with a micrometer (No. 7326, Mitutoyo Manufacturing, Japan) to the nearest 0.0001 in (0.00254 mm) around the film testing area at five random positions. An average value of film thickness was obtained for each film replicate. 2.4. Moisture content and water activity analyses The moisture content of mango films was determined using a Sartorius MA40 moisture meter (Sartorius, Inc., Goettingen, Germany). The water activity was determined using an AquaLab Model CX3TE water activity meter (Decagon Devices, Inc., Pullman, WA) at 25 ± 1 ◦ C. 2.5. Water vapor permeability determination Water vapor permeability (WVP) of mango films was determined by the gravimetric modified cup method according to

OP =

OTR × thickness . P

2.7. Mechanical properties Tensile strength (TS), elastic modulus (EM) and elongation (E) of films were measured according to the ASTM standard D882-97 using an Instron Universal Testing Machine model 5569 with a 50 N load cell. Film specimens were cut as a rectangular center, 10 mm wide and 100 mm long, flaring to 25 mm × 30 mm grip areas on both ends and then preconditioned at 23 ± 2 ◦ C and 50 ± 5% RH for at least 40 h. The test was performed at 23 ± 2 ◦ C and 50 ± 5% RH. The initial gauge separation and the crosshead speed were set to 100 mm and 50 mm/min, respectively. 2.8. Coating application 2.8.1. Whole mangoes Raw green whole mangoes (cv. Namdok Mai) were wrapped with mango film and compared with unwrapped mangoes. Each wrapped and unwrapped mango was packed in polypropylene bags (OP = 1490 cm3 ␮m/m2 d kPa, at 30 ◦ C) and stored either 30 ± 2 ◦ C or 10 ± 2 ◦ C. Nine fruits per treatment were used to determine each quality parameter. Quality assessment was

R. Sothornvit, P. Rodsamran / Postharvest Biology and Technology 47 (2008) 407–415

done at 2-day intervals until the fruit ripened and showed an acceptable color for market demand (L* = 74.30, a* = −9.33 and b* = +34.02).

409

5 mm depth using a Universal testing machine with a 500 N load cell (LLOYD, model LR 5K). 2.13. Oxygen and carbon dioxide concentrations

2.8.2. Minimally processed mangoes Ripe whole mangoes were cleaned with tap water, peeled, and cut into rectangular pieces (approximately 15 mm × 25 mm × 15 mm). The samples were processed in a temperature controlled room at 10 ◦ C, previously sanitized to avoid initial contamination of the samples. Six pieces per treatment were used to determine each quality parameter. The samples were placed in cellophane bags (20 ␮m thickness and OP = 108 cm3 ␮m/m2 d kPa, at 20 ◦ C, 85% RH) and the bags were sealed with a heat sealing machine. Finally, samples were stored at 30 ± 2 ◦ C or 5 ± 2 ◦ C and evaluated for quality each day. We compared storage under cold temperature conditions as normal practice for fruit and vegetable products (5 ◦ C for fresh-cut mango and 10 ◦ C for whole mango) and storage at room temperature simulating commercial conditions in Thailand (30 ◦ C). 2.9. Weight loss determination of whole mangoes Weight loss was measured every 2 days by weighing whole mangoes without the wrap. The edible film that wrapped the whole mangoes was removed, then the mangoes were cleaned and dried before weighing. Measurements were in triplicates and the results were expressed as the percentage loss of initial weight. 2.10. Colorimetric measurements of whole mangoes Color measurements were made with a Minolta (Model CR300, Ramsey, NY, USA) on the flesh of whole mango using the CIELAB color parameters, L*, a*, and b*. A standard white calibration plate was employed to calibrate the equipment. Each measurement was taken at the top and bottom on the flesh of each peeled whole mango. Comparison of color with market acceptance of flesh ripe mangoes (L* = 74.30, a* = −9.33 and b* = +34.02) was used to determine the ripening of whole mangoes. Color was measured every 2 days until ripening or deterioration. 2.11. Soluble solids measurements of whole mangoes Soluble solids measurements were performed using a portable hand-held refractometer (Model N32, Bellevae, WA, USA).

Oxygen and carbon dioxide concentrations in the package were determined using an oxygen/carbon dioxide analyzer (Quantek Instruments, model 902D). The needle was plunged into the package. The pump was electronically timed to draw in the amount of sample required for the analysis, and then turn itself off after the pre-set sampling time (5–10 s). Three replications were done to determine oxygen and carbon dioxide concentrations inside the package. 2.14. Ethanol concentration analysis Ethanol concentration in the package was determined using a gas chromatograph (GC, Hewlett Packard, model 6890) with a flame ionization detector and a capillary column, model HPFFAP polyethylene glycol TPA, 25 m length, 0.32 mm diameter, 0.50 ␮m film thickness. Helium was used as a carrier gas at 28 cm/s velocity. The injector, oven and detector temperatures were 210, 60 and 210 ◦ C, respectively. A sample of 1 ␮L was injected into the GC. A series of standard ethanol concentrations were used to determine the ethanol concentration. ChemStation version A05.0X software was utilized. Three replications were used to determine ethanol concentrations. 2.15. Sensory evaluation of minimally processed mangoes The shelf-life of minimally processed mangoes was determined by sensory evaluations using a descriptive test (3-point scale), where 1 = fresh-like, 2 = acceptable, and 3 = completely deteriorated. Six semi-trained panelists were chosen to determine the mango quality aspects such as aroma/flavor, color, translucency and overall visual appearance of the given sample. At the beginning of each session, fresh mango was presented to the judges as a calibration for the “fresh-like mango” attribute before they rated all the attributes of the minimally processed samples during storage. The sample was coded, presented in random order and the judges scored each sample as it was received in each plastic bag. Minimally processed mangoes were kept in cellophane bags which were opaque; therefore, browning (color change) and internal appearance (translucency) could not be observed as initial indicators for rejection. The judges evaluated the general visual appearance without taste. Thus, our protocol for determining the shelf-life of minimally processed mangoes was based on the aroma (off-flavor) attribute followed by color and visual appearance, respectively. 2.16. Statistical analyses

2.12. Firmness measurements of minimally processed mangoes Firmness was determined by measuring the force required for a 2 mm diameter probe to penetrate the fresh-cut surface, held perpendicular to the probe at 10 mm/min compression speed and

A completely randomized experimental design was used to study coating method and storage temperature factors. SPSS for Windows software program, Release 9.0.0 (SPSS Inc., 1999) was utilized to calculate analysis of variance (ANOVA) using the general linear models procedure. Duncan’s multiple range

410

R. Sothornvit, P. Rodsamran / Postharvest Biology and Technology 47 (2008) 407–415

Table 1 Water vapor permeability (WVP) of fruit films Film type Mango puree (this study) Peach pureea Apricot pureea Apple pureea Pear pureea a

Table 2 Oxygen permeability (OP) of fruit and polymer films

WVP (g mm/m2 d kPa)

Test conditions

Film type

213.2 100.4 103.0 140.1 186.6

27 ◦ C,

Mango puree (this study) Calcium-crosslinked peach pureea Methyl celluloseb (MC) Denatured whey protein isolatec (WPI) Native WPIc High density polyethylened Low density polyethylened

50%RH 25 ◦ C, 80%RH 27 ◦ C, 80%RH 27 ◦ C, 76%RH 27 ◦ C, 74%RH

The data are from McHugh et al. (1996).

test was used to determine significant differences between treatments at 95% confidence interval. 3. Results and discussion 3.1. Mango film properties Pure mango films were transparent and flexible and possessed a yellowish color and mango flavor. The average thickness of the films was 0.17 ± 0.02 mm. The moisture contents and water activity (aW ) were 7.96 ± 1.22% and 0.52 ± 0.03, respectively. These low moisture contents and intermediate aW s suggest that they would be reasonably stable against microbial growth under dry conditions. However, studies on the relationship between moisture content and aW are needed to fully develop the sorption isotherms. We also found that the film can be stored at 30 ◦ C without sugar crystallization for up to 3 months. This result showed the potential of applying mango film as a wrapper for food products such as frozen and dried foods, reducing many layers of plastic laminated packaging requirements and providing nutritional value for food products. Tables 1 and 2 show the WVP and OP of the films, and compare the results with other edible and synthetic films. The WVP of the mango film was higher than that of other fruit puree films (Table 1). This might be due to the higher aW of the ripe mango used to form films compared to the aW of peach film (aW = 0.43) (McHugh et al., 1996). The addition of lipids to a mango film might improve the water barrier, and should be looked at in future studies. Nonetheless, the mango film exhibited a lower OP than a calcium-crosslinked peach film, a whey protein isolate (WPI) film and especially high and low density polyethylene films, but had higher a OP than methylcellulose film (Table 2). Both the WVP and OP of mango films suggest that their use would be

OP (cm3 (m/m2 d kPa)

Test conditions

41.2 69.6

27 ◦ C, 50%RH 23 ◦ C, 58%RH

6.8 59

25 ◦ C, 0%RH 23 ◦ C, 50%RH

78 427 1870

23 ◦ C, 50%RH 23 ◦ C, 50%RH 23 ◦ C, 50%RH

a,b,c,d The

data are from McHugh et al. (1996), Ayranci and Tunc (2003), PerezGago and Krochta (2001) and Salame (1986), respectively.

appropriate for dry foods, and foods which are susceptible to oxidation at low to intermediate aW . McHugh et al. (1996) also suggested that fruit puree films could wrap whole fruit to improve quality. In this work, we applied the mango films on whole and minimally processed mangoes to determine their potential; like other edible films, mango films can control mass transfer. In order to wrap fruit with edible coatings, the mechanical properties of the film should be appropriate to avoid cracking during manipulation and storage. Table 3 shows the mechanical properties of puree films with and without plasticizers and compares the properties with other edible films. Mango and other fruit puree films without added glycerol as a plasticizer showed higher elastic modulus (EM), lower tensile strength (TS) and elongation (%E) than those films made of fruit starch and plasticized with glycerol. The fruit puree can form stand-alone films without addition of plasticizers, whereas fruit starch requires a certain amount of plasticizer to form flexible films. The different composition between fruit puree and fruit starch may take into account these differences. We hypothesized that the types of carbohydrate such as total sugars, fructose and sucrose in fruit purees might play an important role in providing more flexibility, but less strength and stretchability of films than where the main component was starch, as in fruit starch. 3.2. Fruit properties and responses of whole mangoes Increase in weight loss during storage was expected due to transpiration in all treatments (Fig. 1). Cold temperature (CT) storage reduced weight loss of mangoes better than room temper-

Table 3 Mechanical properties of fruit and vegetable films Film type

TS (MPa)

EM (MPa)

E (%)

Test conditions

Mango puree (this study) Banana starcha (50% glycerol) Mango starcha (50% glycerol) Apple pureeb (0% glycerol) Peach pureeb (0% glycerol) Carrot pureeb (0% glycerol) Broccoli pureeb (0% glycerol)

1.2 25 19 0.7 1.8 5.3 7.1

8.3 1.6 1.4 4.4 5.9 208.9 421.5

18.5 40 30 11.8 23 7.3 4.1

23 ◦ C, 50%RH – – 25 ◦ C, 53%RH 25 ◦ C, 53%RH 25 ◦ C, 53%RH 25 ◦ C, 53%RH

a,b The

data are from Romero-Bastida et al. (2005) and McHugh and Olsen (2004), respectively.

R. Sothornvit, P. Rodsamran / Postharvest Biology and Technology 47 (2008) 407–415

Fig. 1. Effect of mango film and storage temperature on weight loss of whole mangoes during storage. Error bars show standard deviations. UR and WR stand for unwrapped and wrapped whole mangoes at room temperature (30 ◦ C), respectively. UC and WC stand for unwrapped and wrapped whole mangoes at cold temperature (10 ◦ C), respectively.

ature (RT) storage. Wrapping whole mangoes with mango film significantly reduced weight loss around 5% and 10% (p ≤ 0.05) at both RT and CT. A similar effect was observed by TanadaPalmu and Grosso (2005) with strawberries wrapped with gluten film. The mango wrapper possessed an intermediate WVP, and therefore, wrapping provided an additional moisture barrier for whole mangoes. Whole mangoes were selected at the mature green peel stage with white and hard flesh and stored until they ripened with optimum quality at the yellow peel stage with yellow and soft flesh. The ripe stage with unwrapped whole mangoes was reached after 7 and 18 days at RT and CT, respectively. In contrast, wrapped whole mangoes at RT (WR) showed an increase in solubility of the mango film after day 2 of storage. However, after removing the film and drying the mangoes, flesh and peel of whole mangoes were observed to be normal. Afterwards, mold grew on the mango wrapper but normal peel and soft flesh of mangoes were observed with off-flavors, due to fermentation after day 4 of storage. Abnormal peel coloration started at day 7 and covered the whole mango at day 9 during storage. The high sugar contents of the mango wrapper and high respiration of the fruit stored inside the polypropylene bag caused anaerobic fermentation and provided alcohol flavors at high storage temperatures. Furthermore, the anaerobic fermentation was stimulated by the strong oxygen barrier of the coating causing low oxygen levels (Cisneros-Zevallos and Krochta, 2003a). Coatings generally modify the internal atmosphere of fruit and vegetables, and a possible explanation for internal modified atmospheres would be the mixing of gases between the gap of wrapping and the fruit surface (Banks et al., 1993). Therefore, coating thickness and permeability are the keys to potential application of wrappers to achieve appropriate internal modified atmospheres. However, wrapped whole mangoes in cold storage (WC) did not show any solubility of the film at the beginning of storage. Nonetheless, mold grew on them by day 11, but after removing the film, normal peel was still observed up until day 14 of storage. Therefore, the cold storage temperature helped delay respiration and transpiration of both mango and mold growth. Total soluble solids (SS) of mangoes significantly (p ≤ 0.05) increased with storage time in all treatments. At the unripe/ immature stage, wrapping and storage temperature did not show

411

Fig. 2. Effect of mango film and storage temperature on soluble solids of whole mangoes during storage. Error bars show standard deviations. UR and WR stand for unwrapped and wrapped whole mangoes at room temperature (30 ◦ C), respectively. UC and WC stand for unwrapped and wrapped whole mangoes at cold temperature (10 ◦ C), respectively.

any significant difference (p > 0.05) in SS (Fig. 2). SS increased during storage due to the change of starch to sugar by amylase (Arpaia et al., 1985). SS increased rapidly after day 4 in unwrapped mangoes at RT (UR) during storage, and this could be attributed to fruit ripening. On the other hand, SS changed very little in wrapped mangoes at RT (WR), suggesting a delay in ripening under these conditions. The same behavior was observed in wrapped mangoes at CT (WC), but SS increased suddenly after day 14 in unwrapped mangoes at CT (UC). During the ripening period, storage temperature was the significant factor (p ≤ 0.05) in SS changes. High temperature caused a rapid change, presumably because of higher enzyme activity and a more rapid conversion of starch to sugar. A slow change of SS indicates an extension of shelf-life (Fuchs et al., 1980). This was also found in the cellulose-based polysaccharide commercial coating on mangoes which showed a delay of ripening (Baldwin et al., 1999). Mango ripening can also be observed by changes in flesh color. Flesh color changed during storage (Fig. 3), with the L* value of the flesh being significantly higher (p ≤ 0.05) at CT, compared to RT. Unwrapped and wrapped mangoes showed significant (p ≤ 0.05) differences in L* and a* values during storage. The b* value was used as the main indicator for flesh color change, with the b* value (+34.02) of acceptable ripe flesh mango as a standard. The b* value also increased significantly (p ≤ 0.05) during storage. Wrapping and storage temperature did not change the b* value up to day 4 of storage. RT increased the b* value independent of wrapping from day 7 during storage. The ripe stage was only observed in unwrapped mangoes, whereas, wrapped mangoes showed abnormal peel coloration prior to ripening. The standard b* value was reached more rapidly at RT than at CT. This was also observed in a previous study, where temperature had more effect on color development of the peel and flesh of mangoes than a plastic film wrap (Ketsa and Raksritong, 1992). 3.3. Firmness of minimally processed mangoes As expected, regardless of wrapping and storage temperature, firmness of minimally processed mangoes decreased significantly (p ≤ 0.05) during storage (Fig. 4). Firmness loss in

412

R. Sothornvit, P. Rodsamran / Postharvest Biology and Technology 47 (2008) 407–415

Fig. 4. Effect of mango film and storage temperature on firmness of minimally processed mangoes during storage until rejection from panelists. Error bars show standard deviations. UR and WR stand for unwrapped and wrapped minimally processed mangoes at room temperature (30 ◦ C), respectively. UC and WC stand for unwrapped and wrapped minimally processed mangoes at cold temperature storage (5 ◦ C), respectively.

3.4. Oxygen, carbon dioxide and ethanol concentrations

Fig. 3. Effect of mango film and storage temperature on color L (A), a (B) and b (C) of whole mangoes during storage. Error bars show standard deviations. UR and WR stand for unwrapped and wrapped whole mangoes at room temperature (30 ◦ C), respectively. UC and WC stand for unwrapped and wrapped whole mangoes at cold temperature (10 ◦ C), respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)

mangoes has been attributed to the action of polygalacturonase and pectinesterase on the solubilization of pectic substrates (Lakshminarayana, 1980). The soft texture of fruit and vegetables is due to many factors such as the loss in cell turgor pressure, vascular air and the degradation of cell wall constituents and polysaccharides. We also hypothesized that solubility of the hydrophilic mango film might cause diffusion of water to the fruit flesh, resulting in a soggy texture (lower firmness). Thus, wrapped mangoes were softer than unwrapped. Carboxymethylcellulose coatings on fresh-cut mangoes also did not maintain mango firmness (Plotto et al., 2004). Improvement of the water barrier of the mango wrapper by adding lipid in the film formulation could help maintain mango texture during storage.

Increasing storage time decreased O2 concentrations and increased CO2 concentrations inside the plastic bags (Fig. 5). Low O2 and high CO2 concentrations slow down respiration and retard ethylene production and therefore ripening (Kader, 1986). During storage of mangoes, high levels of CO2 caused an abnormal, grayish, epidermal color, inhibition of normal aroma development and appearance of off-flavors. Low levels of O2 resulted in abnormal color development and increased ethanol production. In this study, no significant differences in gas concentrations were observed between wrapped and unwrapped minimally processed mango tissue. Ethanol contents of minimally processed mango were similar for all treatments at the start of the experiment (3.32 ± 0.96 mg/kg). However, temperature showed a significant effect on ethanol content and off-flavors at the end of shelf-life. Higher temperature storage induced higher ethanol contents in the package (Fig. 6). No effect of film application

Fig. 5. Effect of mango film and storage temperature on O2 and CO2 concentrations of minimally processed mangoes inside the package during storage. Error bars show standard deviations. UR and WR stand for unwrapped and wrapped minimally processed mangoes at room temperature (30 ◦ C), respectively. UC and WC stand for unwrapped and wrapped minimally processed mangoes at cold temperature storage (5 ◦ C), respectively.

R. Sothornvit, P. Rodsamran / Postharvest Biology and Technology 47 (2008) 407–415

413

Fig. 6. Effect of mango film and storage temperature on ethanol concentration of minimally processed mangoes inside the package at the end of shelf-life. Error bars show standard deviations. UR and WR stand for unwrapped and wrapped minimally processed mangoes at room temperature (30 ◦ C), respectively. UC and WC stand for unwrapped and wrapped minimally processed mangoes at cold temperature storage (5 ◦ C), respectively.

was observed at CT (5 ◦ C). Nonetheless, wrapped mango had greater ethanol contents than unwrapped at RT (30 ◦ C). The offflavors might partially be due to the cellophane bag but when comparing the OP of cellophane and the mango film, we found that the OP of the mango film (41.2 cm3 ␮m/m2 d kPa) was lower than that of cellophane (108 cm3 ␮m/m2 d kPa). Therefore, the contribution to off-flavors might be due to the good oxygen barrier of the mango wrapper which enhanced anaerobic conditions.

3.5. Sensory aspects of minimally processed mangoes Storage time and temperature significantly (p ≤ 0.05) affected fresh mango flavor and panelists detected off-flavors as the main quality attribute affecting flavor. RT storage stimulated off-flavors faster than storage at CT (Fig. 7). Off-flavors were from anaerobic respiration which produced and released alcohol and acetaldehyde. Low temperature storage usually lowers respiration rates and reduces off-flavors, and wrapping had

Fig. 7. Effect of mango film and storage temperature on off-flavors (A), color (B), translucency (C) and visual quality (D) (3-point scale Descriptive test) of minimally processed mangoes during storage time until rejection from panelists. Error bars show standard deviations. UR and WR stand for unwrapped and wrapped minimally processed mangoes at room temperature (30 ◦ C), respectively. UC and WC stand for unwrapped and wrapped minimally processed mangoes at cold temperature storage (5 ◦ C), respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)

414

R. Sothornvit, P. Rodsamran / Postharvest Biology and Technology 47 (2008) 407–415

no effect on fresh mango flavor. This finding was similar to the result of gluten-based and composite coatings on strawberries, which also were not different from the controls (Tanada-Palmu and Grosso, 2005). We also checked the O2 and CO2 concentrations inside the plastic bags and found a decrease in O2 and an increase in CO2 concentrations during storage (Fig. 5). Moreover, we detected higher ethanol concentrations at RT than CT (Fig. 6). This could indicate development of off-flavors during storage. However, the benefit of the mango film over the use of other polymer coatings on fresh mango is the use of the same material, which leads to better acceptance by consumers. It was also found that storage time and temperature had significant (p ≤ 0.05) effects on color, translucency and overall acceptability of fresh mangoes (Fig. 5). Increasing storage time and temperature increased the scores given to these attributes, whereas wrapping did not show any significant effect on them (p > 0.05). Color change was observed on the surface of fresh mangoes due to enzymatic browning. Cutting allows polyphenoloxidase to come in contact with phenolic compounds and O2 , and leads to tissue browning. Generally, coatings or films reduce exposure of fruit and vegetables to O2 and reduce fruit browning, as shown in whey protein coated or hydroxypropyl methylcellulose-based fresh-cut apples (Perez-Gago et al., 2005, 2006). We expected that wrapping fresh mangoes would reduce browning because of the strong oxygen barrier of the mango film, but this did not occur. Nevertheless, wrapping together with cold storage extended the shelf-life of fresh mangoes by 1 day compared to cold storage alone. Generally, minimally processed mangoes in a polystyrene tray and covered with plastic film in the market have 2–3 days of shelf-life at CT. Using the mango film can extend this to 5–6 days. This result is comparable to use of low methoxy pectin coated fresh-cut mango (Fardiaz et al., 2000). Cold storage also retards enzymatic browning. Wrapping extended fresh mango shelf-life at RT for 2 days comparing to unwrapped mango. Translucency of mango also developed during storage. Regardless of wrapping, translucency of mango flesh at RT was higher than that at CT. The visual appearance of UC mangoes was rated higher than for WC. This might be due to the occurrence of chilling injury of mango flesh at cold temperatures and the hydrophilic character of the mango film during storage. However, there is an opportunity to increase water resistance by including lipids, and to reduce browning by incorporating antioxidants in order to make mango films more suitable for maintaining fruit and vegetable quality. Acknowledgements The authors thank the Postgraduate Education and Research Development Project in Post harvest Technology (Thailand) and the Graduate School Kasetsart University (Thailand) for the financial support through out this research. References Arpaia, M.L., Mitchell, F.G., Kader, A.A., Mayer, G., 1985. Effects of 2% O2 and varying concentrations of CO2 with or without C2 H4 on

the storage performance of kiwifruit. J. Am. Soc. Hortic. Sci. 110, 200–203. Arvanitoyannis, I., 1999. Totally and partially biodegradable polymer blends based on natural and synthetic macromolecules: preparation, physical properties and potential as food packaging material. J. Macromol. Sci. 39, 205–271. Ayranci, E., Tunc, S., 2003. A method for the measurement of oxygen permeability and the development of edible films to reduce the rate of oxidative reactions in fresh foods. Food Chem. 80, 423–431. Baldwin, E.A., 1994. Edible coatings for fresh fruits and vegetables: past, present, and future. In: Krochta, J.M., Baldwin, E.A., Nisperos-Carriedo, M.O. (Eds.), Edible Coatings and Films to Improve Food Quality. Technomic Publishing Company, Inc., Lancaster, Pennsylvania, pp. 25–64. Baldwin, E.A., Burns, J.K., Kazokas, W., Hagenmaier, R.D., Bender, R.J., Pesis, E., 1999. Effect of two edible coatings with different permeability characteristics on mango (Mangifera indica L.) ripening during storage. Postharvest Biol. Technol. 17, 215–226. Banks, N., Dadxie, B., Cleland, D., 1993. Reducing gas exchange of fruits with surface coatings. Postharvest Biol. Technol. 3, 269–284. Bolin, H.R., Huxsoll, C.C., 1989. Storage stability of minimally processed fruit. J. Food Process Preserv. 13, 281–292. Cisneros-Zevallos, L., Krochta, J.M., 2003a. Whey protein coatings for fresh fruits and relative humidity effects. J. Food Sci. 68, 176–181. Cisneros-Zevallos, L., Krochta, J.M., 2003b. Dependence of coating thickness on viscosity of coating solution applied to fruits and vegetables by dipping method. J. Food Sci. 68, 503–510. Fardiaz, D., Setiasih, I.S., Purwadaria, H.K., Apriyantono, A., 2000. Quantitative descriptive analysis and volatile component analysis of minimally processed ‘Arumanis’ mango coated with edible film. In: Johnson, G.I., To, L.V., Duc, N.D., Webb, M.C. (Eds.), Proceedings of the ACIAR 100. Institute Pertanian Bogor, Indonesia, pp. 196–200. Fuchs, Y., Pesis, E., Zauberman, G., 1980. Change in amylase activity, starch and sugar content in mango fruit pulp. Sci. Hortic. 13, 155–160. Han, J.H., Gennadios, A., 2005. Edible films and coatings: a review. In: Han, J.H. (Ed.), Innovations in Food Packaging. Elsevier Applied Science Publishing Co., London, pp. 239–262. Kader, A.A., 1986. Biochemical and physical basis of effects of controlled and modified atmospheres on fruits and vegetables. Food Technol. 40, 99–104. Ketsa, S., Raksritong, T., 1992. Effect of PVE film wrapping and temperature on storage life and quality of ’Nam Dok Mai’ mango fruits on ripening. Acta Hortic. 321, 756–763. Lakshminarayana, S., 1980. Mango. In: Nagy, S., Shaw, P.E. (Eds.), Tropical and Subtropical Fruits. AVI Publishing, Inc., Westport, Connecticut, pp. 184–257. McHugh, T.H., Avena-Bustillas, R., Krochta, J.M., 1993. Hydrophilic edible films: modified procedure for water vapor permeability and explanation of thickness effects. J. Food Sci. 58, 889–903. McHugh, T.H., Huxsoll, C.C., Krochta, J.M., 1996. Permeability properties of fruit puree edible films. J. Food Sci. 61, 88–91. McHugh, T.H., Senesi, E., 2000. Apple wraps: a novel method to improve the quality and extend the shelf-life of fresh-cut apples. J. Food Sci. 65, 480–485. McHugh, T.H., Olsen, C.W., 2004. Tensile properties of fruit and vegetable edible films. U.S.–Jpn. Cooper. Program Nat. Res., 104–108. Perez-Gago, M.B., Krochta, J.M., 2001. Denaturation time and temperature effects on solubility, tensile properties, and oxygen permeability of whey protein edible films. J. Food Sci. 66, 705–710. Perez-Gago, M.B., Rojas, C., del Rio, M.A., 2003. Effect of hydroxypropyl methylcellulose-lipid edible composite coatings on plum (cv. Autumn giant) quality during storage. J. Food Sci. 68, 879–883. Perez-Gago, M.B., Serra, M., Alonso, M., Mateos, M., del Rio, M.A., 2005. Effect of whey protein- and hydroxypropyl methylcellulose-based edible composite coatings on color change of fresh-cut apple. Postharvest Biol. Technol. 36, 77–85. Perez-Gago, M.B., Serra, M., del Rio, M.A., 2006. Color change of fresh-cut apples coated with whey protein concentrate-based edible coatings. Postharvest Biol. Technol. 39, 84–92.

R. Sothornvit, P. Rodsamran / Postharvest Biology and Technology 47 (2008) 407–415 Plotto, A., Goodner, K.L., Baldwin, E.A., 2004. Effect of polysaccharide coatings on quality of fresh cut mangoes (Mangifera indica). Proc. Fla. State Hortic. Soc. 117, 382–388. Quezada Gallo, J.A., Diaz Amaro, M.R., Gutierrez Cabrera, D.M.B., Castaneda Alvarez, M.A., Debeaufort, F., Voilley, A., 2003. Application of edible coatings to improve shelf-life of Mexican guava. Acta Hortic. 599, 589–594. Romero-Bastida, C.A., Bello-Perez, L.A., Garcia, M.A., Martino, M.N., Solorza-Feria, J., Zaritzky, N.E., 2005. Physicochemical and microstructural characterization of films prepared by thermal and cold gelatinization from non-conventional sources of starches. Carbohydr. Polym., 235–244. Salame, M., 1986. Barrier polymers. In: Bakker, M. (Ed.), The Wiley Encyclopedia of Packaging Technology. John Wiley & Sons, New York, pp. 48–54.

415

SPSS 1999. SPSS for Windows Release 9.0.0. SPSS Inc. Chicago, IL. Tanada-Palmu, P.S., Grosso, C.R.F., 2005. Effect of edible wheat gluten-based films and coatings on refrigerated strawberry (Fragaria ananassa) quality. Postharvest Biol. Technol. 36, 199–208. Tharanathan, R.N., 2003. Biodegradable films and composite coatings: past, present and future. Food Sci. Technol. 14, 71–78. Wong, D.W.S., Camirand, W.M., Pavlath, A.E., 1994. Development of edible coatings for minimally processed fruits and vegetables. In: Krochta, J.M., Baldwin, E.A., Nisperos-Carriedo, M.O. (Eds.), Edible Coatings and Films to Improve Food Quality. Technomic Publishing Company, Pennsylvania, pp. 65–82.