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Lemongrass essential oil incorporated into alginate-based edible coating for shelf-life extension and quality retention of fresh-cut pineapple
Postharvest Biology and Technology 88 (2014) 1–7
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Lemongrass essential oil incorporated into alginate-based edible coating for shelf-life extension and quality retention of fresh-cut pineapple Nima Azarakhsh a , Azizah Osman a,∗ , Hasanah Mohd Ghazali a , Chin Ping Tan b , Noranizan Mohd Adzahan b a b
Department of Food Science, Faculty of Food Science and Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia Department of Food Technology, Faculty of Food Science and Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
a r t i c l e
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Article history: Received 17 June 2013 Accepted 17 September 2013 Keywords: Pineapple Fresh-cut Edible coating Alginate Lemongrass Essential oil
a b s t r a c t The effects of different concentrations (0.1%, 0.3% and 0.5%, w/v) of lemongrass essential oil incorporated into an alginate-based [sodium alginate 1.29% (w/v), glycerol 1.16% (w/v) and sunflower oil 0.025% (w/v)] edible coating on the respiration rate, physico-chemical properties, and microbiological and sensory quality of fresh-cut pineapple during 16 days of storage (10 ± 1 ◦ C, 65 ± 10% RH) were evaluated. Coated fresh-cut pineapple without lemongrass and uncoated fresh-cut pineapple were stored under the same conditions and served as the controls. The results show that yeast and mould counts and total plate counts of coated samples containing 0.3 and 0.5% (w/v) lemongrass were significantly (p < 0.05) lower than other samples. However, the incorporation of 0.5% (w/v) lemongrass in coating formulation significantly (p < 0.05) decreased the firmness and sensory scores (taste, texture and overall acceptability) of fresh-cut pineapples. Therefore, the results indicate that an alginate-based edible coating formulation incorporated with 0.3% (w/v) lemongrass has potential to extend the shelf-life and maintain quality of fresh-cut pineapple. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Fresh pineapple possesses a thick inedible peel and a large crown which takes up storage space and results in higher transportation cost (James and Ngarmsak, 2010). Value addition by processing into a ready-to-eat product is an attractive alternative since consumers will spend less time on food preparation (Rocculi et al., 2009). However, fruit peeling and cutting increase metabolic activities such as respiration rate and delocalisation of enzymes and substrates leading to quality deterioration such as browning, softening, off-flavour and microbial growth, resulting in a short shelf life (Montero-Calderón et al., 2008). Edible coatings are thin layers of edible material (protein, polysaccharide and lipid) which form directly on the surface of fresh-cut fruit (González-Aguilar et al., 2010). Edible coatings have potential to provide a selective barrier to moisture, carbon dioxide and oxygen, improve mechanical and textural properties, prevent flavour loss, and act as a carrier for different food additives (Tapia et al., 2008). Several studies have been done to determine the effects
∗ Corresponding author. Tel.: +603 8946 8373; fax: +603 8942 3552. E-mail addresses: [email protected], [email protected] (A. Osman). 0925-5214/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.postharvbio.2013.09.004
of edible coatings on fresh-cut fruit such as mango (Chien et al., 2007), papaya (Tapia et al., 2008; Brasil et al., 2012), pear (Oms-Oliu et al., 2008), banana (Bico et al., 2009) and pineapple (MonteroCalderón et al., 2008; Bierhals et al., 2011; Azarakhsh et al., 2012; Mantilla et al., 2013). The incorporation of antimicrobial agents in edible coatings may widen the functionality of coatings in protecting the freshcut fruit from microbial spoilage and thus extend their shelf-life (Raybaudi-Massilia et al., 2008). Recently, essential oils have gained considerable interest as alternatives to chemical preservatives (Mastromatteo et al., 2011). Lemongrass (Cymbopogon citratus) is a tall perennial grass, widely cultivated in warm tropical and subtropical regions (Naik et al., 2010). Lemongrass essential oil has antimicrobial activity against a diverse range of microorganisms including moulds, yeasts and gram positive and gram negative bacteria (Naik et al., 2010). Few studies have been done to determine the effects of lemongrass essential oil incorporated into edible coatings for fresh-cut fruit; examples include melon (RaybaudiMassilia et al., 2008) and apple (Rojas-Graü et al., 2007). However, no published data have been reported on the effects of incorporation of lemongrass essential oil in edible coatings for fresh-cut pineapple. Thus, the objective of this study was to evaluate the effects of different concentrations of lemongrass essential oil incorporated
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into an alginate-based edible coating on the respiration rate, physico-chemical properties, and microbiological and sensory quality of fresh-cut pineapple during low temperature storage. 2. Materials and methods 2.1. Materials Fresh pineapples (Ananas comosus cv. Josapine) were purchased from Pasar Borong Selangor, Malaysia. Pineapple fruit of regular shape and uniform size without any defect were selected. Fruit at maturity stage 5 (about 50% of eyes were orange-yellow, half ripe fruit) were used. The stage of maturity was determined based on the Malaysian standard by Federal Agricultural Marketing Authority (FAMA) (Shamsudin et al., 2009). Food grade sodium alginate (Chemtron Sdn Bhd., Kuala Lumpur, Malaysia) was used as a polysaccharide-based edible coating. Glycerol (Sigma–Aldrich, Steinheim, Germany) was applied as a plasticiser. Sunflower oil (Sigma–Aldrich, Argentina) was added as an emulsifier and lipid source. Calcium chloride (Sigma–Aldrich, Steinheim, Germany) was used for gel forming and cross-linking reactions. Ascorbic acid (Sigma–Aldrich, Steinheim, Germany) and citric acid (Sigma–Aldrich, Steinheim, Germany) were used as antibrowning agents. Food grade lemongrass essential oil obtained by steam distillation was purchased from Chemtron Biotechnology Sdn Bhd. (Kuala Lumpur, Malaysia) and used as a natural antimicrobial agent in the alginate-based edible coating formulation. 2.2. Preparation of samples and edible coating formulations Pineapples, all containers, cutting board, knives and other utensils that would be in contact with pineapple were washed and sanitised with 0.1% (w/v) sodium hypochlorite solution. After washing, the pineapples were peeled manually and cut with a sharp knife into cubes of 2 cm (Rocculi et al., 2009). An optimised alginate-based edible coating formulation was used, based on our previous study (Azarakhsh et al., 2012) and prepared by dissolving sodium alginate 1.29% (w/v) powder in distilled water while heating with stirring on a hot plate at 70 ◦ C until the mixture became clear. Glycerol 1.16% (w/v) was then added to the formulation, then 0.025% (w/v) of sunflower oil. Different concentrations (0.1%, 0.3% and 0.5%, w/v) of lemongrass essential oil were then incorporated into the alginate-based edible coating formulation. The overall volume for each formulation was 500 mL and this included alginate, glycerol, sunflower oil, lemongrass with the remainder distilled water. All formulations were mixed in an homogeniser (Ultra-Turax T25, Janke and Kunkle, IKaLabortechnik, Breisgau, Germany) for 5 min at 24,500 rpm to form emulsions and then degassed under vacuum. For a cross-linking reaction necessary for gel formation, a 2% (w/v) calcium chloride solution that contained 1% (w/v) ascorbic acid and 1% (w/v) citric acid was prepared. 2.3. Coating treatment and storage of cut fruit The pineapple cubes were dipped in the alginate-based formulations for 2 min and excess coating materials were allowed to drip off. The pineapple cubes were then dipped in calcium chloride solution for 2 min. The samples were then air-dried at ambient temperature (26 ± 1 ◦ C) for 1 h. Once coated, the samples were packed in polystyrene trays (10 cubes in each tray) and wrapped with PVC film and then stored at 10 ± 1 ◦ C (GonzálezAguilar et al., 2004), 65 ± 10% RH for 16 days. Coated fresh-cut pineapple without lemongrass and uncoated fresh-cut pineapple were similarly packed and stored in the same conditions and served
as controls. Determinations of respiration rate, weight loss, firmness, colour (L value, chroma, hue angle) and microbial analysis were carried out at 4 day intervals. Evaluation of sensory and morphological properties was carried out after 8 days of storage. 2.4. Determination of respiration rate, weight loss, firmness and colour Respiration rate was determined using an O2 /CO2 gas analyser (Mocon Inc., USA) during 16 days of storage. Approximately 10 g of coated or uncoated pineapple cubes were placed in 200 mL glass jars and incubated at 10 ± 1 ◦ C for 1 h. The glass jars had a rubber septum and air-tight screw caps for headspace sampling. The calculation of respiration rate was based on the production of carbon dioxide (mg CO2 /kg h) (Bhande et al., 2008). Weight loss of pineapple cubes was determined by comparing the weights of samples during 16 days of storage with initial weights by using a digital balance (Presica 4000C, Zurich, Switzerland) and expressing the results as a percentage (Chien et al., 2007). Firmness of the cubes was evaluated during 16 days of storage with a texture analyser (TAXT2i, Stable Micro System Ltd, England). Penetration tests using a 2 mm diameter stainless steel cylindrical probe, 5 kg load cell and 0.5 mm s−1 test speed were employed. The maximum peak measured during the test was taken as firmness (Rocculi et al., 2009). Colour changes of pineapple cubes during 16 days of storage were evaluated using a Minolta CR-300 chroma meter (Konica Minolta Sensing, Inc., Japan). The instrument was calibrated using a standard white plate. The L value (lightness), C (chroma) and h◦ (hue angle) were determined for coated and uncoated samples (Antoniolli et al., 2006). 2.5. Microbiological analysis Total plate counts (TPC) and yeast and mould counts were carried out for microbiological analysis of coated and uncoated fresh-cut pineapple during 16 days of storage (Yousef and Carlstrom, 2003). Total plate counts were determined using the pour plate method and Plate Count Agar (PCA) (Merck, Darmstadt, Germany) as medium. The plates were incubated at 35 ◦ C for 2 days. Yeast and mould counts were determined using the spread plate method and Dichloran Rose-Bengal Chloramphenicol Agar (Merck, Darmstadt, Germany) was used as specific medium for yeast and mould (Olivas et al., 2007). All microbiological analysis was carried out in triplicate and the results were expressed as log10 colony forming units per grams (log10 CFU/g). 2.6. Sensory analysis Sensory characteristics of pineapple cubes were determined after 8 days of storage by regular pineapple consumers. Thirty individuals aged between 20 and 50 year old who like and eat pineapple frequently were recruited among students and staff of the Faculty of Food Science and Technology, Universiti Putra Malaysia. The male/female proportion of the assessors was equal. The assessors evaluated the colour, appearance, odour, taste, texture and overall acceptability of the samples based on a 9-point hedonic scale (Peryam and Pilgrim, 1957). Sensory tests were carried out in a sensory lab equipped with individual sensory booths in a morning session. The assessors used water and unsalted crackers as palate cleansers between samples. The rest time between samples was 1 min. The samples were presented in plastic containers at ambient temperature (26 ± 1 ◦ C) and codified with three-digit number codes. The order of sample presentation
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was randomised and balanced among assessors. The assessors recorded their responses on paper scorecards. 2.7. Morphological properties The microstructure of coated and uncoated samples were analysed using an environmental scanning electron microscope (ESEM) (Philips XL30 ESEM, Netherlands). For sample preparation, selected coated and uncoated pineapple cubes were cut into 1 cm3 cubes. Then, the cubes were placed in separate vials (5 mL) and fixed in 4% glutaraldehyde for 2 days at 4 ◦ C. After that, the cubes were washed with 0.1 M sodium cacodylate buffer pH 7 (3 times, 30 min each). Then, the cubes were post-fixed in 1% osmium tetroxide for 2 h at 4 ◦ C. The cubes were washed again with 0.1 M sodium cacodylate buffer pH 7 (3 times, 30 min each). Then a series of acetone of different concentrations (35%, 50%, 75%, 95% and 100%) were used to dehydrate the samples. After that, the cubes were transferred into a specimen basket and placed in a critical point dryer (Bal-Tec CPD 030, Kettleshulme, UK) with a flow of CO2 for about 30 min. Finally, the cubes were mounted onto metal stubs and coated with Au/Pd using a sputter coater (Bal-Tec Csd 005, Kettleshulme, UK) and observed with an environmental scanning electron microscope (using an accelerating voltage of 20 kV).
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2.8. Statistical analysis One-way analysis of variance (ANOVA) was performed to compare mean values with Tukey’s test for different coatings and control samples. In addition, for analysis of sensory data, a twoway ANOVA using the samples and assessors as factors was used. Differences were considered to be significant when the p-values were less than 0.05. The experiments and/or measurements were done in triplicates. 3. Results and discussion 3.1. Respiration rate Respiration rate is one of the major factors contributing to postharvest losses of fruit (Bhande et al., 2008). Results obtained in this study show that the respiration rates of all coated samples (with and without lemongrass) were significantly (p < 0.05) lower than that of uncoated samples during 16 days of storage at 10 ◦ C (Fig. 1A). Edible coatings have potential to decrease the respiration rate of fresh-cut fruit (Olivas and Barbosa-Cánovas, 2005). This may be associated with creating an internal modified atmosphere and decreasing the interchange of carbon dioxide and oxygen between environment and coated fruit (Olivas and Barbosa-Cánovas, 2005; González-Aguilar et al., 2010). Results obtained in this study also show that the respiration rates of coated samples incorporated with all concentrations of lemongrass were significantly (p < 0.05) lower than with coated samples without lemongrass after 8 days of storage (Fig. 1A). According to Raybaudi-Massilia et al. (2008), the incorporation of lemongrass into an alginate-based coating caused minor carbon
Fig. 1. Effect of different concentrations of lemongrass essential oil incorporated into alginate-based edible coating on (A) respiration rate, (B) weight loss and (C) firmness of fresh-cut pineapple during 16 days of storage at 10 ± 1 ◦ C; 65 ± 10% RH. Means with the same letters (lowercase: amongst different treatments for the same time; uppercase: for the same treatment during different storage times) are not significantly different according to Tukey’s test (p > 0.05). EC = alginate-based edible coating; Lg = lemongrass.
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dioxide production and oxygen consumption because of the antimicrobial effects of lemongrass and the lipophilic nature of this essential oil, which possibly increased the resistance of the coating to gas diffusion. 3.2. Weight loss Fresh-cut fruit are highly susceptible to weight loss (Watada and Qi, 1999). Therefore, evaluating weight loss is very important for fresh-cut fruit during storage. Results obtained in this study indicated that weight loss significantly (p < 0.05) increased for all samples during 16 days of storage at 10 ◦ C (Fig. 1B). The weight loss of all coated samples (with and without lemongrass) was significantly (p < 0.05) lower than for the uncoated samples. Adding sunflower oil to the coating formulations as a lipid source could be responsible for lower weight loss in coated samples (Tapia et al., 2008). In addition, alginate-based coatings can act sacrificially, with moisture lost from the coating before it is lost from the food (Lacroix and Tien, 2005). In the present study, no significant (p > 0.05) differences were found between the weight loss of coated samples incorporated with or without lemongrass. In addition, no significant (p > 0.05) differences in weight loss were observed among coated samples with different concentrations of lemongrass (Fig. 1B). Rojas-Graü et al. (2007) observed that the incorporation of lemongrass into alginate-apple puree edible film did not significantly (p > 0.05) affect water vapor permeability. They noted that it could be related to the main components of this essential oil, which is not lipid and mostly contains terpene-like compounds. 3.3. Firmness Tissue softening is one of the major problems that limit the shelf-life of fresh-cut fruit (Toivonen and Brummell, 2008), and firmness is an important factor that influences the consumer acceptability of these products (Rojas-Graü et al., 2008). Results obtained in this study showed that the coated samples could significantly (p < 0.05) maintain the firmness as compared to uncoated samples during 16 days of
storage at 10 ◦ C (Fig. 1C). The firmness of uncoated samples was significantly (p < 0.05) lower than in all coated samples (day 8, 12 and 16) (Fig. 1C). It could be due to lower weight loss of coated samples and beneficial effects of calcium chloride on firmness retention of fresh-cut fruit. In this study, incorporation of (0.1 and 0.3%, w/v) lemongrass into alginate-based coating formulation did not have any significant (p > 0.05) effect on firmness. However, the coating formulations with a high concentration (0.5%, w/v) of lemongrass significantly (p < 0.05) decreased firmness (Fig. 1C). Results obtained in the present study were in agreement with Raybaudi-Massilia et al. (2008) who studied the effects of an alginate-based coating on firmness of fresh-cut melon. They reported that calcium chloride was effective in maintaining firmness of coated samples. However, the coating formulations with a high concentration (0.7%) of lemongrass significantly (p < 0.05) decreased the firmness of samples due to the action of lemongrass over the cell tissues which possibly undergo structural changes. They noted that lemongrass essential oil has active compounds such as citral, and secondary compounds such as geraniol, which have a synergistic effect with active compounds and could be related to firmness changes in fresh-cut melon. 3.4. Colour Colour change is one of the most important changes in fresh-cut fruit during storage which directly affects perception of quality by customers (Olivas and Barbosa-Cánovas, 2005). Colour parameters namely, L value, chroma and hue angle, of coated and uncoated fresh-cut pineapples during 16 days of storage at 10 ◦ C are shown in Fig. 2A–C. Results indicated that all coated samples (with and without lemongrass) were significantly (p < 0.05) effective in maintaining these values as compared to uncoated samples. It could be related to added ascorbic acid and citric acid in the coating formulations. These acids function as antibrowning agents. González-Aguilar et al. (2004) studied the colour changes of fresh-cut pineapple treated with antibrowning agents during 16 days storage at 10 ◦ C. They reported that the antibrowning agents (isoascorbic acid, ascorbic acid or acetyl cysteine)
Fig. 2. Effect of different concentrations of lemongrass essential oil incorporated into alginate-based edible coating on (A) L value, (B) chroma and (C) hue angle of fresh-cut pineapple during 16 days of storage at 10 ± 1 ◦ C; 65 ± 10% RH. Means with the same letters (lowercase: amongst different treatments for the same time; uppercase: for the same treatment during different storage times) are not significantly different according to Tukey’s test (p > 0.05). EC = alginate-based edible coating; Lg = lemongrass.
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Fig. 3. Effect of different concentrations of lemongrass essential oil incorporated into alginate-based edible coating on (A) total plate counts and (B) yeast and mould counts of fresh-cut pineapple during 16 days of storage at 10 ± 1 ◦ C; 65 ± 10% RH. Means with the same letters (lowercase: amongst different treatments for the same time; uppercase: for the same treatment during different storage times) are not significantly different according to Tukey’s test (p > 0.05). EC = alginate-based edible coating; Lg = lemongrass.
significantly (p < 0.05) reduced changes in L and b values as compared to the control. Moline et al. (1999) found that the combination of citric acid and ascorbic acid was effective in reducing the browning of fresh-cut banana. 3.5. Microbiological analysis Fresh-cut fruit have a large area of cut surface with high moisture conditions and a rich source of nutrients, which provides a good environment for growth of microorganisms (Olivas and Barbosa-Cánovas, 2005; Oms-Oliu et al., 2010). Results obtained in this study showed that total plate counts (TPC) and yeast and mould counts increased significantly (p < 0.05) during storage for all treatments (Fig. 3). There was no significant (p > 0.05) difference between the TPC for alginate-based coating without a natural antimicrobial agent (lemongrass) and uncoated samples at the same storage time (similar results were observed for yeast and mould counts). The incorporation of lemongrass in the alginate-based coating formulation significantly (p < 0.05) reduced the TPC and yeast and mould counts of coated samples during storage. Among different concentrations (0.1%, 0.3%, 0.5%, w/v) of lemongrass, 0.3 and 0.5% (w/v) were more effective than 0.1% (w/v) in reducing the TPC and yeast and mould counts (Fig. 3). Rojas-Graü et al. (2007) who studied the effects of lemongrass incorporated into alginate-based edible coating for fresh-cut apple reported that this coating significantly (p < 0.05) reduced the microbial growth of fresh-cut apple during storage. According to the Institute of Food Science and Technology (IFST), 106 CFU/g is considered the limit of acceptance of fruit-based products during the study of shelf-life (Bierhals et al., 2011). In this study, TPC and yeast and mould counts for uncoated and coated samples without lemongrass reached 106 CFU/g at day 8 of storage at 10 ◦ C. However, addition of lemongrass increased the shelf-life. TPC and yeast and mould counts for coated samples with 0.3% and 0.5% (w/v) lemongrass reached 106 CFU/g after 12 and 16 days, respectively (Fig. 3). Several studies have been done to extend the shelf-life of fresh-cut pineapple during cold storage. Mantilla et al. (2013) studied the effects of multilayered edible coating with a microencapsulated antimicrobial complex (betacyclodextrin and trans-cinnamaldehyde) on quality and shelf-life. They reported that trans-cinnamaldehyde affects the pineapple flavour. However, the application of this antimicrobial coating extended the shelf-life of samples to 15 days at 4 ◦ C by inhibiting microbial growth. Wu et al. (2012) studied the effects of high pressure argon treatment to maintain the quality of fresh-cut pineapple during cold storage. They reported that the application of high pressure argon treatment extended the shelf-life of samples to 18 days during storage in modified atmosphere packaging at 4 ◦ C as compared to the control (only 12 days). Bierhals et al. (2011) studied the effects of cassava starch coating on quality and shelf-life of fresh-cut pineapple. They found that this coating did not increase the shelf life due to the higher microbial growth in coated samples as compared to uncoated samples. They reported that the shelf life of coated and uncoated samples stored at 5 ◦ C were 7 and 8 days, respectively. Torri et al. (2010) evaluated the shelf-life of fresh-cut pineapple by using an electronic nose. They reported that the shelf-life was about 5 days at 4 ◦ C, 2 days at 7.6 ◦ C and 1 day at 16 ◦ C. Egidio et al. (2009) evaluated the shelf-life of
fresh-cut pineapple using infrared spectroscopy and microbiological analysis. They reported that the microbial shelf-life in their study was 8–10 days at 5.3 ◦ C, 4–5 days at 8.6 ◦ C and about 2 days at 15.8 ◦ C. In the present study, the incorporation of 0.3% and 0.5% (w/v) lemongrass in the coating formulation extended the microbial shelf life of fresh-cut pineapple to 12 and 16 days, respectively. 3.6. Sensory analysis Edible coatings are usually consumed with coated fresh-cut fruit (Rojas-Graü et al., 2009). Therefore, sensory analysis is very important, especially for coatings incorporated with active components such as antimicrobial agents. These components may impact on the sensory attributes such as taste and odour of coated fruit (Zhao and McDanie, 2005). In the present study, sensory evaluation based on colour, appearance, odour, taste, texture and overall acceptability scores of coated and uncoated samples was carried out after 8 days of storage at 10 ◦ C (Fig. 4), because at this time uncoated samples reached the limit of acceptance (106 CFU/g). The results obtained indicated that coated samples had significantly (p < 0.05) higher scores as compared to uncoated samples. The incorporation of (0.1 and 0.3%, w/v) lemongrass into alginate-based coating formulation did not have any significant (p > 0.05) effect on sensory attributes of coated samples and lemongrass odour and taste were not detected by assessors at these concentrations. However, incorporation of 0.5% (w/v) lemongrass affected the sensory attributes of coated samples. Taste evaluation showed that 0.5% (w/v) lemongrass had a negative (p < 0.05) effect on taste scores (below 5). In addition, samples containing 0.5% (w/v) lemongrass had a negative (p < 0.05) effect on texture score (below 6) (Fig. 4). The incorporation of 0.5% lemongrass negatively affected the overall acceptability of samples where its score decreased by two points (about 5) when compared to other coated samples (about 7). Results obtained in the present study were in agreement with those of RaybaudiMassilia et al. (2008), who studied the effects of alginate-based edible coating as a carrier of lemongrass on sensory characteristics of fresh-cut melon. They observed that the firmness score was significantly (p < 0.05) reduced by incorporation of 0.7% lemongrass in coating formulation. In addition, Rojas-Graü et al. (2007) studied the effects of lemongrass incorporated into apple puree-alginate edible coating on sensory characteristics of fresh-cut apple. They reported that lemongrass (1.0 and 1.5%, w/w) had a negative effect on texture of coated fresh-cut apples. 3.7. Morphological properties Images from scanning electron microscopy (SEM) of fresh-cut pineapple (day 0) and uncoated and coated samples incorporated with 0.3% (w/v) lemongrass after 8 days of storage at 10 ◦ C, are shown in Fig. 5. SEM images demonstrated that the cell walls of coated fresh-cut pineapple had an appearance almost similar to those of fresh pineapple, while more cell wall disruption and high microbial growth was observed in stored uncoated samples (Fig. 5). Results obtained in the present study were in agreement with those of Quiles et al. (2007) who studied the effect of calcium propionate on the microstructure of fresh-cut apples using SEM. After 1 week of
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Fig. 4. Effect of different concentrations of lemongrass essential oil incorporated into alginate-based edible coating on sensory characteristics of fresh-cut pineapple after 8 days storage at 10 ± 1 ◦ C; 65 ± 10% RH. Means with the same letters are not significantly different according to Tukey’s test (p > 0.05). EC = alginate-based edible coating; Lg = lemongrass.
Fig. 5. Scanning electron microscopy images of (A) fresh-cut pineapple at Day 0, (B) coated fresh-cut pineapple with 0.3% (w/v) lemongrass, (C) and (D) uncoated fresh-cut pineapple after 8 days of storage at 10 ± 1 ◦ C; 65 ± 10% RH.
N. Azarakhsh et al. / Postharvest Biology and Technology 88 (2014) 1–7 storage, they observed that the cell walls of samples treated with calcium propionate maintained the integrity and uniformity as compared to untreated fresh-cut apples. They suggested that the ionic bounds formed between pectic polymers and calcium maintained the cell wall strength.
4. Conclusions Results obtained in this study showed that among all formulations, the alginate-based edible coating incorporated with 0.3% (w/v) lemongrass significantly (p < 0.05) reduced respiration rate, weight loss, TPC, yeast and mould counts while maintained the firmness, colour, sensory characteristics and morphological properties of fresh-cut pineapple during low temperature storage. Thus, it can be concluded that alginate-based edible coating formulation incorporated with 0.3% (w/v) lemongrass has potential to extend the shelf-life and maintain the quality of fresh-cut pineapple. References Antoniolli, L.R., Benedetti, B.C., Sigrist, J.M., Souza Filho, M.M., Alves, R.E., 2006. Metabolic activity of fresh-cut ‘Perola’ pineapple as affected by cut shape and temperature. Braz. J. Plant Physiol. 18, 413–417. Azarakhsh, N., Osman, A., Ghazali, H.M., Tan, C.P., Mohd Adzahan, N., 2012. Optimization of alginate and gellan-based edible coating formulations for fresh-cut pineapples. Int. Food Res. J. 19, 279–285. Bhande, S.D., Ravindra, M.R., Goswami, T.K., 2008. Respiration rate of banana fruit under aerobic conditions at different storage temperatures. J. Food Eng. 87, 116–123. Bico, S.L.S., Raposo, M.F.J., Morais, R.M.S.C., Morais, A.M.M.B., 2009. Combined effects of chemical dip and/or carrageenan coating and/or controlled atmosphere on quality of fresh-cut banana. Food Control 20, 508–514. Bierhals, V.S., Chiumarelli, M., Hubinger, M.D., 2011. Effect of cassava starch coating on quality and shelf life of fresh-cut pineapple (Ananas Comosus L Merril cv “P’erola”). J. Food Sci. 76, 62–72. Brasil, I.M., Gomes, C., Puerta-Gomez, A., Castell-Perez, M.E., Moreira, R.G., 2012. Polysaccharide-based multilayered antimicrobial edible coating enhances quality of fresh-cut papaya. Food Sci.Technol. 47, 39–45. Chien, P.J., Sheu, F., Yang, F.H., 2007. Effects of edible chitosan coating on quality and shelf life of sliced mango fruit. J. Food Eng. 78, 225–229. Egidio, V.D., Sinelli, N., Limbo, S., Torri, L., Franzetti, L., Casiraghi, E., 2009. Evaluation of shelf-life of fresh-cut pineapple using FT-NIR and FT-IR spectroscopy. Postharvest Biol. Technol. 54, 87–92. González-Aguilar, G.A., Ayala-Zavala, G.F., Olivas, G.I., de la Rosa, L.A., AlvarezParrilla, E., 2010. Preserving quality of fresh-cut products using safe technologies. J. Consum. Prot. Food Saf. 5, 65–72. González-Aguilar, G.A., Ruiz-Cruz, S., Cruz-Valenzuela, R., Rodríguez-Félix, A., Wang, C.Y., 2004. Physiological and quality changes of fresh-cut pineapple treated with antibrowning agents. Food Sci. Technol. 37, 369–376. James, J.B., Ngarmsak, T., 2010. In: Rolle, R.S. (Ed.), Processing of Fresh-cut Tropical Fruits and Vegetables: A Technical Guide. RAP Publication 2010/16 FAO, Bangkok, pp. 1–86. Lacroix, M., Tien, C.L., 2005. Edible films and coatings from non-starch polysaccharides. In: Han, J.H. (Ed.), Innovations in Food Packaging. Elsevier Academic Press, London, pp. 338–361. Mantilla, N., Castell-Perez, M.E., Gomes, C., Moreira, R.G., 2013. Multilayered antimicrobial edible coating and its effect on quality and shelf-life of fresh-cut pineapple (Ananas comosus). LWT-Food Sci. Technol. 51, 37–43.
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Mastromatteo, M., Mastromatteo, M., Conte, A., Del Nobile, M.A., 2011. Combined effect of active coating and MAP to prolong the shelf life of minimally processed kiwifruit (Actinidia deliciosa cv Hayward). Food Res. Int. 44, 1224–1230. Moline, H.E., Buta, J.G., Newman, I.M., 1999. Prevention of browning of banana slices using natural products and their derivatives. J. Food Qual. 22, 499–511. Montero-Calderón, M., Rojas-Graü, M.A., Martín-Belloso, O., 2008. Effect of packaging conditions on quality and shelf-life of fresh-cut pineapple (Ananas comosus). Postharvest Biol. Technol. 50, 182–189. Naik, M.I., Fomda, B.A., Jaykumar, E., Bhat, J.A., 2010. Antibacterial activity of lemongrass (Cymbopogon citratus) oil against some selected pathogenic bacterias. Asian Pac. J. Trop. Med. 3 (7), 535–538. Olivas, G.I., Barbosa-Cánovas, G.V., 2005. Edible coatings for fresh-cut fruits. Crit. Rev. Food Sci. Nutr. 45, 657–670. Olivas, G.I., Mattinson, D.S., Barbosa-Cánovas, G.V., 2007. Alginate coatings for preservation of minimally processed ‘Gala’ apples. Postharvest Biol. Technol. 45, 89–96. Oms-Oliu, G., Rojas-Graü, M.A., González, L.A., Varela, P., Soliva-Fortuny, R., Hernando, M.I., Munuera, I.P., Fiszman, S., Martín-Belloso, O., 2010. Recent approaches using chemical treatments to preserve quality of fresh-cut fruit. Postharvest Biol. Technol. 57, 139–148. Oms-Oliu, G., Soliva-Fortuny, R., Martín-Belloso, O., 2008. Edible coatings with antibrowning agents to maintain sensory quality and antioxidant properties of fresh-cut pears. Postharvest Biol. Technol. 50, 87–94. Peryam, D.R., Pilgrim, F.J., 1957. Hedonic scale method of measuring food preferences. Food Technol. 11, 9–14. Quiles, A., Hernando, I., Pe rez-Munuera, I., Lluch, M.A., 2007. Effect of calcium propionate on the microstructure and pectin methy-lesterase activity in the parenchyma of fresh-cut Fuji apples. J. Sci. Food Agric. 87, 511–515. Raybaudi-Massilia, R.M., Mosqueda-Melgar, J., Martín-Belloso, O., 2008. Edible alginate-based coating as carrier of antimicrobials to improve shelf-life and safety of fresh-cut melon. Int. J. Food Microbiol. 121, 313–327. Rocculi, R., Cocci, E., Romani, S., Sacchetti, G., Dalla Rosa, M., 2009. Effect of 1MCP treatment and N2 O MAP on physiological and quality changes of fresh-cut pineapple. Postharvest Biol. Technol. 51, 371–377. Rojas-Graü, M.A., Raybaudi-Massilia, R.M., Soliva-Fortuny, R.C., Avena-Bustillos, R.J., McHugh, T.H., Martín-Belloso, O., 2007. Apple puree-alginate edible coating as carrier of antimicrobial agents to prolong shelf-life of fresh-cut apples. Postharvest Biol. Technol. 45, 254–264. Rojas-Graü, M.A., Soliva-Fortuny, R., Martín-Belloso, O., 2009. Edible coatings to incorporate active ingredients to fresh-cut fruits. Trends Food Sci. Technol. 20, 438–447. Rojas-Graü, M.A., Tapia, M.S., Martín-Belloso, O., 2008. Using polysaccharide-based edible coatings to maintain quality of fresh-cut Fuji apples. Food Sci. Technol. 41, 139–147. Shamsudin, R., Daud, W.R.W., Takrif, M.S., Hassan, O., 2009. Physico-mechanical properties of the Josapine pineapple fruits. Pertanika J. Sci. Technol. 17, 17–23. Tapia, M.S., Rojas-Graü, M.A., Carmona, A., Rodríguez, F.J., Soliva-Fortuny, R., MartínBelloso, O., 2008. Use of alginate- and gellan-based coatings for improving barrier, texture and nutritional properties of fresh-cut papaya. Food Hydrocoll. 22, 1493–1503. Toivonen, P.M.A., Brummell, D.A., 2008. Biochemical bases of appearance and texture changes in fresh-cut fruit and vegetables. Postharvest Biol. Technol. 48, 1–14. Torri, L., Sinelli, N., Limbo, S., 2010. Shelf life evaluation of fresh-cut pineapple by using an electronic nose. Postharvest Biol. Technol. 56, 239–245. Watada, A.E., Qi, L., 1999. Quality of fresh-cut produce. Postharvest Biol. Technol. 15, 201–205. Wu, Z.S., Zhang, M., Adhikari, B., 2012. Application of high pressure argon treatment to maintain quality of fresh-cut pineapples during cold storage. J. Food Eng. 110, 395–404. Yousef, A.E., Carlstrom, C., 2003. Food Microbiology a Laboratory Manual. WileyInterscience, New Jersey. Zhao, Y., McDanie, M., 2005. Sensory quality of foods associated with edible film and coating systems and extension. In: Han, J.H. (Ed.), Innovations in Food Packaging. Elsevier Academic Press, London, pp. 434–453.
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Lemongrass essential oil incorporated into alginate-based edible coating for shelf-life extension and quality retention of fresh-cut pineapple Nima Azarakhsh a , Azizah Osman a,∗ , Hasanah Mohd Ghazali a , Chin Ping Tan b , Noranizan Mohd Adzahan b a b
Department of Food Science, Faculty of Food Science and Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia Department of Food Technology, Faculty of Food Science and Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
a r t i c l e
i n f o
Article history: Received 17 June 2013 Accepted 17 September 2013 Keywords: Pineapple Fresh-cut Edible coating Alginate Lemongrass Essential oil
a b s t r a c t The effects of different concentrations (0.1%, 0.3% and 0.5%, w/v) of lemongrass essential oil incorporated into an alginate-based [sodium alginate 1.29% (w/v), glycerol 1.16% (w/v) and sunflower oil 0.025% (w/v)] edible coating on the respiration rate, physico-chemical properties, and microbiological and sensory quality of fresh-cut pineapple during 16 days of storage (10 ± 1 ◦ C, 65 ± 10% RH) were evaluated. Coated fresh-cut pineapple without lemongrass and uncoated fresh-cut pineapple were stored under the same conditions and served as the controls. The results show that yeast and mould counts and total plate counts of coated samples containing 0.3 and 0.5% (w/v) lemongrass were significantly (p < 0.05) lower than other samples. However, the incorporation of 0.5% (w/v) lemongrass in coating formulation significantly (p < 0.05) decreased the firmness and sensory scores (taste, texture and overall acceptability) of fresh-cut pineapples. Therefore, the results indicate that an alginate-based edible coating formulation incorporated with 0.3% (w/v) lemongrass has potential to extend the shelf-life and maintain quality of fresh-cut pineapple. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Fresh pineapple possesses a thick inedible peel and a large crown which takes up storage space and results in higher transportation cost (James and Ngarmsak, 2010). Value addition by processing into a ready-to-eat product is an attractive alternative since consumers will spend less time on food preparation (Rocculi et al., 2009). However, fruit peeling and cutting increase metabolic activities such as respiration rate and delocalisation of enzymes and substrates leading to quality deterioration such as browning, softening, off-flavour and microbial growth, resulting in a short shelf life (Montero-Calderón et al., 2008). Edible coatings are thin layers of edible material (protein, polysaccharide and lipid) which form directly on the surface of fresh-cut fruit (González-Aguilar et al., 2010). Edible coatings have potential to provide a selective barrier to moisture, carbon dioxide and oxygen, improve mechanical and textural properties, prevent flavour loss, and act as a carrier for different food additives (Tapia et al., 2008). Several studies have been done to determine the effects
∗ Corresponding author. Tel.: +603 8946 8373; fax: +603 8942 3552. E-mail addresses: [email protected], [email protected] (A. Osman). 0925-5214/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.postharvbio.2013.09.004
of edible coatings on fresh-cut fruit such as mango (Chien et al., 2007), papaya (Tapia et al., 2008; Brasil et al., 2012), pear (Oms-Oliu et al., 2008), banana (Bico et al., 2009) and pineapple (MonteroCalderón et al., 2008; Bierhals et al., 2011; Azarakhsh et al., 2012; Mantilla et al., 2013). The incorporation of antimicrobial agents in edible coatings may widen the functionality of coatings in protecting the freshcut fruit from microbial spoilage and thus extend their shelf-life (Raybaudi-Massilia et al., 2008). Recently, essential oils have gained considerable interest as alternatives to chemical preservatives (Mastromatteo et al., 2011). Lemongrass (Cymbopogon citratus) is a tall perennial grass, widely cultivated in warm tropical and subtropical regions (Naik et al., 2010). Lemongrass essential oil has antimicrobial activity against a diverse range of microorganisms including moulds, yeasts and gram positive and gram negative bacteria (Naik et al., 2010). Few studies have been done to determine the effects of lemongrass essential oil incorporated into edible coatings for fresh-cut fruit; examples include melon (RaybaudiMassilia et al., 2008) and apple (Rojas-Graü et al., 2007). However, no published data have been reported on the effects of incorporation of lemongrass essential oil in edible coatings for fresh-cut pineapple. Thus, the objective of this study was to evaluate the effects of different concentrations of lemongrass essential oil incorporated
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into an alginate-based edible coating on the respiration rate, physico-chemical properties, and microbiological and sensory quality of fresh-cut pineapple during low temperature storage. 2. Materials and methods 2.1. Materials Fresh pineapples (Ananas comosus cv. Josapine) were purchased from Pasar Borong Selangor, Malaysia. Pineapple fruit of regular shape and uniform size without any defect were selected. Fruit at maturity stage 5 (about 50% of eyes were orange-yellow, half ripe fruit) were used. The stage of maturity was determined based on the Malaysian standard by Federal Agricultural Marketing Authority (FAMA) (Shamsudin et al., 2009). Food grade sodium alginate (Chemtron Sdn Bhd., Kuala Lumpur, Malaysia) was used as a polysaccharide-based edible coating. Glycerol (Sigma–Aldrich, Steinheim, Germany) was applied as a plasticiser. Sunflower oil (Sigma–Aldrich, Argentina) was added as an emulsifier and lipid source. Calcium chloride (Sigma–Aldrich, Steinheim, Germany) was used for gel forming and cross-linking reactions. Ascorbic acid (Sigma–Aldrich, Steinheim, Germany) and citric acid (Sigma–Aldrich, Steinheim, Germany) were used as antibrowning agents. Food grade lemongrass essential oil obtained by steam distillation was purchased from Chemtron Biotechnology Sdn Bhd. (Kuala Lumpur, Malaysia) and used as a natural antimicrobial agent in the alginate-based edible coating formulation. 2.2. Preparation of samples and edible coating formulations Pineapples, all containers, cutting board, knives and other utensils that would be in contact with pineapple were washed and sanitised with 0.1% (w/v) sodium hypochlorite solution. After washing, the pineapples were peeled manually and cut with a sharp knife into cubes of 2 cm (Rocculi et al., 2009). An optimised alginate-based edible coating formulation was used, based on our previous study (Azarakhsh et al., 2012) and prepared by dissolving sodium alginate 1.29% (w/v) powder in distilled water while heating with stirring on a hot plate at 70 ◦ C until the mixture became clear. Glycerol 1.16% (w/v) was then added to the formulation, then 0.025% (w/v) of sunflower oil. Different concentrations (0.1%, 0.3% and 0.5%, w/v) of lemongrass essential oil were then incorporated into the alginate-based edible coating formulation. The overall volume for each formulation was 500 mL and this included alginate, glycerol, sunflower oil, lemongrass with the remainder distilled water. All formulations were mixed in an homogeniser (Ultra-Turax T25, Janke and Kunkle, IKaLabortechnik, Breisgau, Germany) for 5 min at 24,500 rpm to form emulsions and then degassed under vacuum. For a cross-linking reaction necessary for gel formation, a 2% (w/v) calcium chloride solution that contained 1% (w/v) ascorbic acid and 1% (w/v) citric acid was prepared. 2.3. Coating treatment and storage of cut fruit The pineapple cubes were dipped in the alginate-based formulations for 2 min and excess coating materials were allowed to drip off. The pineapple cubes were then dipped in calcium chloride solution for 2 min. The samples were then air-dried at ambient temperature (26 ± 1 ◦ C) for 1 h. Once coated, the samples were packed in polystyrene trays (10 cubes in each tray) and wrapped with PVC film and then stored at 10 ± 1 ◦ C (GonzálezAguilar et al., 2004), 65 ± 10% RH for 16 days. Coated fresh-cut pineapple without lemongrass and uncoated fresh-cut pineapple were similarly packed and stored in the same conditions and served
as controls. Determinations of respiration rate, weight loss, firmness, colour (L value, chroma, hue angle) and microbial analysis were carried out at 4 day intervals. Evaluation of sensory and morphological properties was carried out after 8 days of storage. 2.4. Determination of respiration rate, weight loss, firmness and colour Respiration rate was determined using an O2 /CO2 gas analyser (Mocon Inc., USA) during 16 days of storage. Approximately 10 g of coated or uncoated pineapple cubes were placed in 200 mL glass jars and incubated at 10 ± 1 ◦ C for 1 h. The glass jars had a rubber septum and air-tight screw caps for headspace sampling. The calculation of respiration rate was based on the production of carbon dioxide (mg CO2 /kg h) (Bhande et al., 2008). Weight loss of pineapple cubes was determined by comparing the weights of samples during 16 days of storage with initial weights by using a digital balance (Presica 4000C, Zurich, Switzerland) and expressing the results as a percentage (Chien et al., 2007). Firmness of the cubes was evaluated during 16 days of storage with a texture analyser (TAXT2i, Stable Micro System Ltd, England). Penetration tests using a 2 mm diameter stainless steel cylindrical probe, 5 kg load cell and 0.5 mm s−1 test speed were employed. The maximum peak measured during the test was taken as firmness (Rocculi et al., 2009). Colour changes of pineapple cubes during 16 days of storage were evaluated using a Minolta CR-300 chroma meter (Konica Minolta Sensing, Inc., Japan). The instrument was calibrated using a standard white plate. The L value (lightness), C (chroma) and h◦ (hue angle) were determined for coated and uncoated samples (Antoniolli et al., 2006). 2.5. Microbiological analysis Total plate counts (TPC) and yeast and mould counts were carried out for microbiological analysis of coated and uncoated fresh-cut pineapple during 16 days of storage (Yousef and Carlstrom, 2003). Total plate counts were determined using the pour plate method and Plate Count Agar (PCA) (Merck, Darmstadt, Germany) as medium. The plates were incubated at 35 ◦ C for 2 days. Yeast and mould counts were determined using the spread plate method and Dichloran Rose-Bengal Chloramphenicol Agar (Merck, Darmstadt, Germany) was used as specific medium for yeast and mould (Olivas et al., 2007). All microbiological analysis was carried out in triplicate and the results were expressed as log10 colony forming units per grams (log10 CFU/g). 2.6. Sensory analysis Sensory characteristics of pineapple cubes were determined after 8 days of storage by regular pineapple consumers. Thirty individuals aged between 20 and 50 year old who like and eat pineapple frequently were recruited among students and staff of the Faculty of Food Science and Technology, Universiti Putra Malaysia. The male/female proportion of the assessors was equal. The assessors evaluated the colour, appearance, odour, taste, texture and overall acceptability of the samples based on a 9-point hedonic scale (Peryam and Pilgrim, 1957). Sensory tests were carried out in a sensory lab equipped with individual sensory booths in a morning session. The assessors used water and unsalted crackers as palate cleansers between samples. The rest time between samples was 1 min. The samples were presented in plastic containers at ambient temperature (26 ± 1 ◦ C) and codified with three-digit number codes. The order of sample presentation
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was randomised and balanced among assessors. The assessors recorded their responses on paper scorecards. 2.7. Morphological properties The microstructure of coated and uncoated samples were analysed using an environmental scanning electron microscope (ESEM) (Philips XL30 ESEM, Netherlands). For sample preparation, selected coated and uncoated pineapple cubes were cut into 1 cm3 cubes. Then, the cubes were placed in separate vials (5 mL) and fixed in 4% glutaraldehyde for 2 days at 4 ◦ C. After that, the cubes were washed with 0.1 M sodium cacodylate buffer pH 7 (3 times, 30 min each). Then, the cubes were post-fixed in 1% osmium tetroxide for 2 h at 4 ◦ C. The cubes were washed again with 0.1 M sodium cacodylate buffer pH 7 (3 times, 30 min each). Then a series of acetone of different concentrations (35%, 50%, 75%, 95% and 100%) were used to dehydrate the samples. After that, the cubes were transferred into a specimen basket and placed in a critical point dryer (Bal-Tec CPD 030, Kettleshulme, UK) with a flow of CO2 for about 30 min. Finally, the cubes were mounted onto metal stubs and coated with Au/Pd using a sputter coater (Bal-Tec Csd 005, Kettleshulme, UK) and observed with an environmental scanning electron microscope (using an accelerating voltage of 20 kV).
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2.8. Statistical analysis One-way analysis of variance (ANOVA) was performed to compare mean values with Tukey’s test for different coatings and control samples. In addition, for analysis of sensory data, a twoway ANOVA using the samples and assessors as factors was used. Differences were considered to be significant when the p-values were less than 0.05. The experiments and/or measurements were done in triplicates. 3. Results and discussion 3.1. Respiration rate Respiration rate is one of the major factors contributing to postharvest losses of fruit (Bhande et al., 2008). Results obtained in this study show that the respiration rates of all coated samples (with and without lemongrass) were significantly (p < 0.05) lower than that of uncoated samples during 16 days of storage at 10 ◦ C (Fig. 1A). Edible coatings have potential to decrease the respiration rate of fresh-cut fruit (Olivas and Barbosa-Cánovas, 2005). This may be associated with creating an internal modified atmosphere and decreasing the interchange of carbon dioxide and oxygen between environment and coated fruit (Olivas and Barbosa-Cánovas, 2005; González-Aguilar et al., 2010). Results obtained in this study also show that the respiration rates of coated samples incorporated with all concentrations of lemongrass were significantly (p < 0.05) lower than with coated samples without lemongrass after 8 days of storage (Fig. 1A). According to Raybaudi-Massilia et al. (2008), the incorporation of lemongrass into an alginate-based coating caused minor carbon
Fig. 1. Effect of different concentrations of lemongrass essential oil incorporated into alginate-based edible coating on (A) respiration rate, (B) weight loss and (C) firmness of fresh-cut pineapple during 16 days of storage at 10 ± 1 ◦ C; 65 ± 10% RH. Means with the same letters (lowercase: amongst different treatments for the same time; uppercase: for the same treatment during different storage times) are not significantly different according to Tukey’s test (p > 0.05). EC = alginate-based edible coating; Lg = lemongrass.
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dioxide production and oxygen consumption because of the antimicrobial effects of lemongrass and the lipophilic nature of this essential oil, which possibly increased the resistance of the coating to gas diffusion. 3.2. Weight loss Fresh-cut fruit are highly susceptible to weight loss (Watada and Qi, 1999). Therefore, evaluating weight loss is very important for fresh-cut fruit during storage. Results obtained in this study indicated that weight loss significantly (p < 0.05) increased for all samples during 16 days of storage at 10 ◦ C (Fig. 1B). The weight loss of all coated samples (with and without lemongrass) was significantly (p < 0.05) lower than for the uncoated samples. Adding sunflower oil to the coating formulations as a lipid source could be responsible for lower weight loss in coated samples (Tapia et al., 2008). In addition, alginate-based coatings can act sacrificially, with moisture lost from the coating before it is lost from the food (Lacroix and Tien, 2005). In the present study, no significant (p > 0.05) differences were found between the weight loss of coated samples incorporated with or without lemongrass. In addition, no significant (p > 0.05) differences in weight loss were observed among coated samples with different concentrations of lemongrass (Fig. 1B). Rojas-Graü et al. (2007) observed that the incorporation of lemongrass into alginate-apple puree edible film did not significantly (p > 0.05) affect water vapor permeability. They noted that it could be related to the main components of this essential oil, which is not lipid and mostly contains terpene-like compounds. 3.3. Firmness Tissue softening is one of the major problems that limit the shelf-life of fresh-cut fruit (Toivonen and Brummell, 2008), and firmness is an important factor that influences the consumer acceptability of these products (Rojas-Graü et al., 2008). Results obtained in this study showed that the coated samples could significantly (p < 0.05) maintain the firmness as compared to uncoated samples during 16 days of
storage at 10 ◦ C (Fig. 1C). The firmness of uncoated samples was significantly (p < 0.05) lower than in all coated samples (day 8, 12 and 16) (Fig. 1C). It could be due to lower weight loss of coated samples and beneficial effects of calcium chloride on firmness retention of fresh-cut fruit. In this study, incorporation of (0.1 and 0.3%, w/v) lemongrass into alginate-based coating formulation did not have any significant (p > 0.05) effect on firmness. However, the coating formulations with a high concentration (0.5%, w/v) of lemongrass significantly (p < 0.05) decreased firmness (Fig. 1C). Results obtained in the present study were in agreement with Raybaudi-Massilia et al. (2008) who studied the effects of an alginate-based coating on firmness of fresh-cut melon. They reported that calcium chloride was effective in maintaining firmness of coated samples. However, the coating formulations with a high concentration (0.7%) of lemongrass significantly (p < 0.05) decreased the firmness of samples due to the action of lemongrass over the cell tissues which possibly undergo structural changes. They noted that lemongrass essential oil has active compounds such as citral, and secondary compounds such as geraniol, which have a synergistic effect with active compounds and could be related to firmness changes in fresh-cut melon. 3.4. Colour Colour change is one of the most important changes in fresh-cut fruit during storage which directly affects perception of quality by customers (Olivas and Barbosa-Cánovas, 2005). Colour parameters namely, L value, chroma and hue angle, of coated and uncoated fresh-cut pineapples during 16 days of storage at 10 ◦ C are shown in Fig. 2A–C. Results indicated that all coated samples (with and without lemongrass) were significantly (p < 0.05) effective in maintaining these values as compared to uncoated samples. It could be related to added ascorbic acid and citric acid in the coating formulations. These acids function as antibrowning agents. González-Aguilar et al. (2004) studied the colour changes of fresh-cut pineapple treated with antibrowning agents during 16 days storage at 10 ◦ C. They reported that the antibrowning agents (isoascorbic acid, ascorbic acid or acetyl cysteine)
Fig. 2. Effect of different concentrations of lemongrass essential oil incorporated into alginate-based edible coating on (A) L value, (B) chroma and (C) hue angle of fresh-cut pineapple during 16 days of storage at 10 ± 1 ◦ C; 65 ± 10% RH. Means with the same letters (lowercase: amongst different treatments for the same time; uppercase: for the same treatment during different storage times) are not significantly different according to Tukey’s test (p > 0.05). EC = alginate-based edible coating; Lg = lemongrass.
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Fig. 3. Effect of different concentrations of lemongrass essential oil incorporated into alginate-based edible coating on (A) total plate counts and (B) yeast and mould counts of fresh-cut pineapple during 16 days of storage at 10 ± 1 ◦ C; 65 ± 10% RH. Means with the same letters (lowercase: amongst different treatments for the same time; uppercase: for the same treatment during different storage times) are not significantly different according to Tukey’s test (p > 0.05). EC = alginate-based edible coating; Lg = lemongrass.
significantly (p < 0.05) reduced changes in L and b values as compared to the control. Moline et al. (1999) found that the combination of citric acid and ascorbic acid was effective in reducing the browning of fresh-cut banana. 3.5. Microbiological analysis Fresh-cut fruit have a large area of cut surface with high moisture conditions and a rich source of nutrients, which provides a good environment for growth of microorganisms (Olivas and Barbosa-Cánovas, 2005; Oms-Oliu et al., 2010). Results obtained in this study showed that total plate counts (TPC) and yeast and mould counts increased significantly (p < 0.05) during storage for all treatments (Fig. 3). There was no significant (p > 0.05) difference between the TPC for alginate-based coating without a natural antimicrobial agent (lemongrass) and uncoated samples at the same storage time (similar results were observed for yeast and mould counts). The incorporation of lemongrass in the alginate-based coating formulation significantly (p < 0.05) reduced the TPC and yeast and mould counts of coated samples during storage. Among different concentrations (0.1%, 0.3%, 0.5%, w/v) of lemongrass, 0.3 and 0.5% (w/v) were more effective than 0.1% (w/v) in reducing the TPC and yeast and mould counts (Fig. 3). Rojas-Graü et al. (2007) who studied the effects of lemongrass incorporated into alginate-based edible coating for fresh-cut apple reported that this coating significantly (p < 0.05) reduced the microbial growth of fresh-cut apple during storage. According to the Institute of Food Science and Technology (IFST), 106 CFU/g is considered the limit of acceptance of fruit-based products during the study of shelf-life (Bierhals et al., 2011). In this study, TPC and yeast and mould counts for uncoated and coated samples without lemongrass reached 106 CFU/g at day 8 of storage at 10 ◦ C. However, addition of lemongrass increased the shelf-life. TPC and yeast and mould counts for coated samples with 0.3% and 0.5% (w/v) lemongrass reached 106 CFU/g after 12 and 16 days, respectively (Fig. 3). Several studies have been done to extend the shelf-life of fresh-cut pineapple during cold storage. Mantilla et al. (2013) studied the effects of multilayered edible coating with a microencapsulated antimicrobial complex (betacyclodextrin and trans-cinnamaldehyde) on quality and shelf-life. They reported that trans-cinnamaldehyde affects the pineapple flavour. However, the application of this antimicrobial coating extended the shelf-life of samples to 15 days at 4 ◦ C by inhibiting microbial growth. Wu et al. (2012) studied the effects of high pressure argon treatment to maintain the quality of fresh-cut pineapple during cold storage. They reported that the application of high pressure argon treatment extended the shelf-life of samples to 18 days during storage in modified atmosphere packaging at 4 ◦ C as compared to the control (only 12 days). Bierhals et al. (2011) studied the effects of cassava starch coating on quality and shelf-life of fresh-cut pineapple. They found that this coating did not increase the shelf life due to the higher microbial growth in coated samples as compared to uncoated samples. They reported that the shelf life of coated and uncoated samples stored at 5 ◦ C were 7 and 8 days, respectively. Torri et al. (2010) evaluated the shelf-life of fresh-cut pineapple by using an electronic nose. They reported that the shelf-life was about 5 days at 4 ◦ C, 2 days at 7.6 ◦ C and 1 day at 16 ◦ C. Egidio et al. (2009) evaluated the shelf-life of
fresh-cut pineapple using infrared spectroscopy and microbiological analysis. They reported that the microbial shelf-life in their study was 8–10 days at 5.3 ◦ C, 4–5 days at 8.6 ◦ C and about 2 days at 15.8 ◦ C. In the present study, the incorporation of 0.3% and 0.5% (w/v) lemongrass in the coating formulation extended the microbial shelf life of fresh-cut pineapple to 12 and 16 days, respectively. 3.6. Sensory analysis Edible coatings are usually consumed with coated fresh-cut fruit (Rojas-Graü et al., 2009). Therefore, sensory analysis is very important, especially for coatings incorporated with active components such as antimicrobial agents. These components may impact on the sensory attributes such as taste and odour of coated fruit (Zhao and McDanie, 2005). In the present study, sensory evaluation based on colour, appearance, odour, taste, texture and overall acceptability scores of coated and uncoated samples was carried out after 8 days of storage at 10 ◦ C (Fig. 4), because at this time uncoated samples reached the limit of acceptance (106 CFU/g). The results obtained indicated that coated samples had significantly (p < 0.05) higher scores as compared to uncoated samples. The incorporation of (0.1 and 0.3%, w/v) lemongrass into alginate-based coating formulation did not have any significant (p > 0.05) effect on sensory attributes of coated samples and lemongrass odour and taste were not detected by assessors at these concentrations. However, incorporation of 0.5% (w/v) lemongrass affected the sensory attributes of coated samples. Taste evaluation showed that 0.5% (w/v) lemongrass had a negative (p < 0.05) effect on taste scores (below 5). In addition, samples containing 0.5% (w/v) lemongrass had a negative (p < 0.05) effect on texture score (below 6) (Fig. 4). The incorporation of 0.5% lemongrass negatively affected the overall acceptability of samples where its score decreased by two points (about 5) when compared to other coated samples (about 7). Results obtained in the present study were in agreement with those of RaybaudiMassilia et al. (2008), who studied the effects of alginate-based edible coating as a carrier of lemongrass on sensory characteristics of fresh-cut melon. They observed that the firmness score was significantly (p < 0.05) reduced by incorporation of 0.7% lemongrass in coating formulation. In addition, Rojas-Graü et al. (2007) studied the effects of lemongrass incorporated into apple puree-alginate edible coating on sensory characteristics of fresh-cut apple. They reported that lemongrass (1.0 and 1.5%, w/w) had a negative effect on texture of coated fresh-cut apples. 3.7. Morphological properties Images from scanning electron microscopy (SEM) of fresh-cut pineapple (day 0) and uncoated and coated samples incorporated with 0.3% (w/v) lemongrass after 8 days of storage at 10 ◦ C, are shown in Fig. 5. SEM images demonstrated that the cell walls of coated fresh-cut pineapple had an appearance almost similar to those of fresh pineapple, while more cell wall disruption and high microbial growth was observed in stored uncoated samples (Fig. 5). Results obtained in the present study were in agreement with those of Quiles et al. (2007) who studied the effect of calcium propionate on the microstructure of fresh-cut apples using SEM. After 1 week of
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N. Azarakhsh et al. / Postharvest Biology and Technology 88 (2014) 1–7
Fig. 4. Effect of different concentrations of lemongrass essential oil incorporated into alginate-based edible coating on sensory characteristics of fresh-cut pineapple after 8 days storage at 10 ± 1 ◦ C; 65 ± 10% RH. Means with the same letters are not significantly different according to Tukey’s test (p > 0.05). EC = alginate-based edible coating; Lg = lemongrass.
Fig. 5. Scanning electron microscopy images of (A) fresh-cut pineapple at Day 0, (B) coated fresh-cut pineapple with 0.3% (w/v) lemongrass, (C) and (D) uncoated fresh-cut pineapple after 8 days of storage at 10 ± 1 ◦ C; 65 ± 10% RH.
N. Azarakhsh et al. / Postharvest Biology and Technology 88 (2014) 1–7 storage, they observed that the cell walls of samples treated with calcium propionate maintained the integrity and uniformity as compared to untreated fresh-cut apples. They suggested that the ionic bounds formed between pectic polymers and calcium maintained the cell wall strength.
4. Conclusions Results obtained in this study showed that among all formulations, the alginate-based edible coating incorporated with 0.3% (w/v) lemongrass significantly (p < 0.05) reduced respiration rate, weight loss, TPC, yeast and mould counts while maintained the firmness, colour, sensory characteristics and morphological properties of fresh-cut pineapple during low temperature storage. Thus, it can be concluded that alginate-based edible coating formulation incorporated with 0.3% (w/v) lemongrass has potential to extend the shelf-life and maintain the quality of fresh-cut pineapple. References Antoniolli, L.R., Benedetti, B.C., Sigrist, J.M., Souza Filho, M.M., Alves, R.E., 2006. Metabolic activity of fresh-cut ‘Perola’ pineapple as affected by cut shape and temperature. Braz. J. Plant Physiol. 18, 413–417. Azarakhsh, N., Osman, A., Ghazali, H.M., Tan, C.P., Mohd Adzahan, N., 2012. Optimization of alginate and gellan-based edible coating formulations for fresh-cut pineapples. Int. Food Res. J. 19, 279–285. Bhande, S.D., Ravindra, M.R., Goswami, T.K., 2008. Respiration rate of banana fruit under aerobic conditions at different storage temperatures. J. Food Eng. 87, 116–123. Bico, S.L.S., Raposo, M.F.J., Morais, R.M.S.C., Morais, A.M.M.B., 2009. Combined effects of chemical dip and/or carrageenan coating and/or controlled atmosphere on quality of fresh-cut banana. Food Control 20, 508–514. Bierhals, V.S., Chiumarelli, M., Hubinger, M.D., 2011. Effect of cassava starch coating on quality and shelf life of fresh-cut pineapple (Ananas Comosus L Merril cv “P’erola”). J. Food Sci. 76, 62–72. Brasil, I.M., Gomes, C., Puerta-Gomez, A., Castell-Perez, M.E., Moreira, R.G., 2012. Polysaccharide-based multilayered antimicrobial edible coating enhances quality of fresh-cut papaya. Food Sci.Technol. 47, 39–45. Chien, P.J., Sheu, F., Yang, F.H., 2007. Effects of edible chitosan coating on quality and shelf life of sliced mango fruit. J. Food Eng. 78, 225–229. Egidio, V.D., Sinelli, N., Limbo, S., Torri, L., Franzetti, L., Casiraghi, E., 2009. Evaluation of shelf-life of fresh-cut pineapple using FT-NIR and FT-IR spectroscopy. Postharvest Biol. Technol. 54, 87–92. González-Aguilar, G.A., Ayala-Zavala, G.F., Olivas, G.I., de la Rosa, L.A., AlvarezParrilla, E., 2010. Preserving quality of fresh-cut products using safe technologies. J. Consum. Prot. Food Saf. 5, 65–72. González-Aguilar, G.A., Ruiz-Cruz, S., Cruz-Valenzuela, R., Rodríguez-Félix, A., Wang, C.Y., 2004. Physiological and quality changes of fresh-cut pineapple treated with antibrowning agents. Food Sci. Technol. 37, 369–376. James, J.B., Ngarmsak, T., 2010. In: Rolle, R.S. (Ed.), Processing of Fresh-cut Tropical Fruits and Vegetables: A Technical Guide. RAP Publication 2010/16 FAO, Bangkok, pp. 1–86. Lacroix, M., Tien, C.L., 2005. Edible films and coatings from non-starch polysaccharides. In: Han, J.H. (Ed.), Innovations in Food Packaging. Elsevier Academic Press, London, pp. 338–361. Mantilla, N., Castell-Perez, M.E., Gomes, C., Moreira, R.G., 2013. Multilayered antimicrobial edible coating and its effect on quality and shelf-life of fresh-cut pineapple (Ananas comosus). LWT-Food Sci. Technol. 51, 37–43.
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