Impact of Maturity Stages, Shrink-Wrap Packaging and Storage Temperature on Shelf Life and Quality of Pineapple (Ananas comosus (L.) Merr.) Fruit ‘Mauritius’

Pineapple ‘Mauritius’ fruits were harvested at three maturity stages, i.e., 25, 50, and 75% of tubercles turned yellow. Fruits with around 75% tubercles turning yellow are normally sold in retail markets, and those with 25 to 50 yellow tubercles are transported to wholesale markets from where fruits are further transported to retail markets or consumer outlets depending upon the extent of coloration of tubercles. These fruits were harvested from farmers’ fields in the Ernakulam district of Kerala, a prominent pineapple-growing belt in the state. Harvested fruits were quickly transported to the Department of Post Harvest Technology, College of Agriculture, in plastic crates. The fruits were sorted to remove the deformed and damaged ones, followed by a dry brushing of the thick rind to remove adhering dirt and dust. The stalk of the fruits was clipped to retain a 1-cm stalk length. These fruits were subsequently pre-cooled at 12–13 °C, for 8 hours. This was followed by overwrapping each fruit loosely with polyolefin film of 25 μ thickness with an impulse sealer and then passing it through the tunnel of a shrink-wrapping machine maintained at 120 °C for 10 seconds, resulting in individual pineapple fruits being tightly wrapped with the polyolefin film. The shrink-wrapped fruits, along with the unwrapped samples in the three maturity stages, were subsequently held under two storage conditions, viz., ambient temperature of 30–32 °C (maximum) and 18–20 °C (minimum) with 80–90% relative humidity (RH) and also, in a cool chamber (12–13 °C and 85–90% RH). The experiment consisted of twelve treatments, viz., T₁ – unwrapped fruits with 75% of eyes having yellow color, stored at ambient temperature (control – ambient temperature); T₂ – unwrapped fruits with 75% of eyes having yellow color, stored in cool chamber (control – cool chamber); T₃ – shrink-wrapped fruits with 75% of eyes having yellow color, stored at ambient temperature; T₄ – shrink-wrapped fruits with 75% of eyes having yellow color, stored in a cool chamber; T₅ – unwrapped fruits with 50% of eyes having yellow color, stored at ambient temperature (control – ambient temperature); T₆ – unwrapped fruits with 50% of eyes having yellow color, stored in a cool chamber (control – cool chamber); T₇ – shrink-wrapped fruits with 50% of eyes having yellow color, stored at ambient temperature; T₈ – shrink-wrapped fruits with 50% of eyes having yellow color, stored in a cool chamber; T₉ – unwrapped fruits with 25% of eyes having yellow color, stored at ambient temperature (control – ambient temperature); T₁₀ – unwrapped fruits with 25% of eyes having yellow color, stored in a cool chamber (control – cool chamber); T₁₁ – shrink-wrapped fruits with 25% of eyes having yellow color, stored at ambient temperature; T₁₂ – shrink-wrapped fruits with 25% of eyes having yellow color, stored in a cool chamber. Observations on titratable acidity, ascorbic acid, loss in weight, shelf life, rate of respiration, firmness, and total soluble solids (TSS) were recorded at weekly intervals. The various treatments, stages of maturity at harvest, and storage conditions are presented in Table 1.

Cell wall degradation during ripening is a result of the action of enzymes like polygalacturonase, pectin methyl esterase, and cellulose. Measurements of fruit firmness indicated hardness or softness and is also an indirect indicator of the shelf life of fruits. Initial firmness of fruits with 25, 50, and 75% yellow tubercles were 0.84, 0.78, and 0.57 kg·cm⁻², respectively (Fig. 1). Othman (2008) and Mandal et al. (2015) described that the firmness of fruits declined as they matured. Fruit firmness in our experiment showed a declining trend in all the treatments during storage. The most stable firmness values up to 7 weeks of storage were recorded in fruits of the lowest maturing stage during harvest and cold stored, especially in those fruits that were also foil wrapped. After one week, the firmness decreased most rapidly in fruits harvested at the stage of 75% and 50% yellow tubercles and ambient-stored. Fruits harvested at the stage of 75% yellow tubercles lost their firmness the slowest when they were stored in cold. Among all the treatments, shrink-wrapped fruits with 25% yellow tubercles held in a cool chamber had the highest firmness till the end of storage (more than 6 kg·cm⁻²). The less ripeness of fruits intended for storage means that they have to go through more transformations to change their firmness, so it takes longer. Storage of fruits at lower temperatures might have slowed down the rate of biochemical reactions leading to higher firmness in fruits held in a cool chamber. Shrink-wrap packaging might have resulted in the modification of atmospheric gases surrounding the fruits leading to reduced respiratory activity. Atmospheric modification of the shrink-wrapped fruits occurs as a result of the inherent respiratory activity of the fruits coupled with the selective permeability of the polyolefin film to atmospheric gases, particularly O₂ and CO₂. Similar results on better retention of firmness of the ‘Neelum’ mango as a result of shrink-wrap packaging were reported by Gomez et al. (2021).

Figure 1

Loss in the weight of fruits during storage is an indication of the metabolic activity of fruits during their postharvest handling period, which has a direct bearing on their shelf life. Loss in weight occurs as a result of respiration and the transpiration of moisture through the skin of fruits. A gradual weight loss was recorded in all the treatments during storage (Fig. 2). Fruits harvested with 25% yellow tubercles held in a cool chamber recorded significantly lower weight loss throughout storage. Further, fruits with 25% yellow tubercles subjected to shrink-wrapping and subsequently held in the cool chamber, recorded the lowest weight loss among all the treatments during the entire storage period. Significantly lower weight loss in fruits stored in the cool chamber at all maturity stages compared to those held under ambient conditions may be due to a reduction in metabolic activities as a result of the temperature of 12 to 13 °C and 85 to 90% RH. The lowest weight loss in shrink-wrapped fruits held in cool chambers may be due to the modification of atmospheric gases surrounding the fruit, leading to reduced respiratory activity in these fruits. Paull and Chen (2014) reported a storage temperature of 7 to 12 °C and an RH of 85 to 95% as ideal for the storage of pineapple fruit at the color break stage. Kamol et al. (2014) reported that the maximum weight loss of 19.135% was recorded in the control fruits of pineapple ‘Giant Kew’ and the minimum (3.42%) in nonperforated polyethylene bags on the eighteenth day of storage.

Figure 2

Respiration is a catabolic process in which reserve photosynthates are used up. Unhindered respiration will detrimentally affect the quality and shelf life of fruits. CO₂ could not be detected in the headspace of fruits with 25% yellow tubercles at the beginning of storage, whereas fruits with 50% and 75% yellow tubercles had 1.0 and 2.0 ml·kg⁻¹·h⁻¹ CO₂ in the head-space, respectively. The respiratory activity of pineapple recorded a gradual rise in all the treatments (Fig. 3). Unlike climacteric fruits, pineapple being a nonclimacteric fruit, no respiratory peak was observed in any of the treatments, irrespective of maturity stage and storage temperature. However, fruits stored in a cool chamber recorded significantly lower respiration rates compared to the ones stored under ambient conditions. Unwrapped fruits with 75% and 50% yellow tubercles held under ambient conditions (T1 and T5) became unmarketable after 1 week of storage due to senescence. Both unwrapped and wrapped fruits with 50% yellow tubercles (T6 and T8) and unwrapped samples with 75% yellow tubercles (T2) kept in a cool chamber remained marketable for up to 6 weeks. Even though shrink-wrapping reduced respiratory activity at low temperature, the storage of wrapped fruits with 75% and 50% yellow tubercles (T3 and T7) under ambient conditions became unmarketable after 1 week due to fungal decay as a result of condensation of moisture inside the package. Similarly, unwrapped and wrapped fruits with 25% yellow tubercles (T9 and T11) stored under ambient conditions became unmarketable after 2 weeks due to spoilage. Stage of maturity and shrink-wrap packaging along with low-temperature storage significantly reduced the respiratory activity of fruits. Fruits with 25% yellow tubercles, subjected to shrink-wrap packaging and subsequently stored in a cool chamber, recorded the lowest respiratory activity throughout storage. After 7 weeks of storage, the unwrapped (T10) and shrink-wrapped fruits (T12) with 25% yellow tubercles held in a cool chamber showed respiratory rates of 18.0 and 7.0 ml·kg⁻¹·h⁻¹ CO₂, respectively. Lower rates of respiration in the wrapped fruits held in a cool chamber may be due to the combined effects of atmosphere modification and reduced metabolic activity at low temperatures. Shrink-wrap packaging may have retarded the respiratory activity of fruits due to a reduction in O₂ concentration and an increase in CO₂ levels surrounding the fruits as a result of atmosphere modification. Similar results were obtained in the mango ‘Neelum’ when subjected to shrink-wrap packaging, followed by storage in a cool chamber (Gomez et al. 2021). Polyethylene bagging on individual pineapple fruit resulted in an atmospheric composition of 8–10% O₂ and 7% CO₂ (Abdullah et al. 1985; Rohrbach & Paull 1982). Yahia (1998) recommended 2–5% O₂ and 5–10% CO₂ as the ideal atmospheric gas composition for pineapple fruits. Paull and Chen (2014) reported that the rate of respiration of pineapple rose exponentially with a rise in storage temperature. They found that the respiratory rate of pineapple was 2, 4–7, 10–16, and 19–29 mg CO₂·kg⁻¹·h⁻¹ at 5, 10, 15, and 20 °C, respectively.

Figure 3

Postharvest handling techniques have a considerable impact on the shelf life of fruits. Packaging with polymeric films and subsequent storage at ideal temperatures and humidity have a direct bearing on the shelf life of fruits. Sudhakar Rao and Shivashankara (2015) reported that shrink-wrapping of mango ‘Alphonso’ and ‘Banganapalli’ with Cryovac film (D-955, 15 μ thickness), followed by storage at 8 °C could extend the shelf life of the fruits by 5 weeks. In the present study, the most important in the length of shelf life was storage temperature (Fig. 4). Fruits stored at ambient temperature were marketable for about 7 days when harvested at the stage of 75% and 50% of yellow tubercles and about 14 days when had 25% of yellow tubercles, whereas shelf life of fruits stored in cold was 3, 4, and 6–7 weeks, respectively. The wrapping was significantly beneficial only for fruits harvested at the stage of 25% of yellow tubercles. The shelf life was longer for fruits harvested at the stage of 50 and 25% of yellow tubercles. Maximum shelf life of 7 weeks was recorded in fruits harvested with 25% yellow tubercles, followed by shrink-wrapping and subsequently held in the cool chamber at 12–13 °C and 85–90% RH (T12). The extension of the shelf life of fruits as indicated by the maturity stage and low-temperature storage may be due to the retardation of respiratory activity of fruits induced by the reduction in CO₂ levels and increase in O₂ concentration surrounding the fruit. Low-temperature storage may have further slowed down the biochemical reactions, which resulted in extended shelf life. Further, fruits with 25% yellow tubercles might have had slower rates of ripening and senescence. Dhar et al. (2008) reported the shelf life of the pineapple ‘Giant Kew’ could be extended to 21 days when harvested 14 days before optimum maturity. In another study, pineapple when held at temperatures of 7 to 12 °C had a storage life of 14 to 20 days, when harvested with 25% yellow tubercles. Besides, the treatments were considered unmarketable when the fruit firmness showed values less than 0.1 kg·cm⁻². Similar values were also taken into consideration for determining the shelf life of the pineapple fruit ‘Giant Kew’ (Mandal et al. 2015).

Figure 4

The flavor of fruits is considerably influenced by TSS, which along with aroma are the most important factors responsible for consumer acceptability. In the present study, TSS significantly varied with maturity stages. Fruits with 25, 50, and 75% of yellow tubercles had initial TSS contents of 4.0, 7.0, and 9.0 °Brix, respectively (Fig. 5). Higher TSS in pineapple fruits with 75% yellow tubercles may be due to higher levels of simple sugars like glucose and fructose and also, due to lower levels of organic acids. Higher levels of TSS in a pineapple with the advancement of maturity were reported by Dhar et al. (2008). In the present study, the TSS content of pineapple fruits increased throughout storage, irrespective of the treatments adopted. The rise in TSS during storage may be due to the initial hydrolysis of starch into disaccharide sucrose and further into simple sugars by the enzyme amylase and invertase, respectively. Here, the TSS content of pineapple fruits was independent of the maturity stage, which was significantly influenced by the storage temperature, and less by the shrink-wrap packaging. In the first week, fruits stored under ambient conditions had higher TSS than those held at low temperatures. This might be due to faster rates of biochemical reactions at higher temperatures. Shrink-wrap packaging of pineapple fruits followed by storage at low temperatures resulted in lower levels of TSS in these fruits. The same trend continued until the end of the storage period. Kumara and Hettige (2020) reported that the highest TSS content of 17.75 ± 0.67 was seen in the 100% yellow tubercles stage in the pineapple ‘Mauritius’.

Figure 5

Organic acids, along with sugars have a prominent role in contributing to the flavor of fruits. Fruits with lower organic acids are preferred by consumers. The titratable acidity of pineapple differed significantly with maturity stages. Fruits with 25, 50, and 75% yellow tubercles had titratable acidity levels of 0.89, 0.76, and 0.64%, respectively (Fig. 6). The organic acids content in fruits generally shows a declining trend as maturity progresses. In the present experiment, the acidity of fruits fell during storage, irrespective of maturity stage and storage temperature, and this situation was observed in our experiment. Kamol et al. (2014) reported that premature and optimum mature pineapple fruits of the ‘Giant Kew’ contained titratable acidity of 0.77% and 0.68%, respectively. The fall in the acidity of pineapple fruits during storage may be due to their utilization in the respiratory process. A similar pattern of decline in acidity was reported by Siti Rashima et al. (2019) in three different cultivars of pineapple grown in Malaysia, which confirms the findings of the present study. However, this report contradicts the findings of Dhar et al. (2008) who reported an increase in the acidity of pineapple as fruits developed. Next to the maturity stage at harvest, storage temperature had significant effects on the titratable acidity of pineapple fruits after 1 week of storage. Fruits held in cool chambers retained higher levels of acidity than those stored under ambient conditions. After 7 weeks of storage, shrink-wrapped fruits with 25% yellow tubercles held in a cool chamber recorded titratable acidity of 0.36%. Low-temperature storage may have retarded the rate of respiratory activity of fruits held in a cool chamber. Retention of higher acidity (0.97%) in polyethylene-packed mango ‘Chaunsa’ was reported by Rathore et al. (2010) as compared to the unwrapped fruits (0.44%).

Figure 6

Vitamin C is known for its antioxidant properties as well as for its immunity-boosting activity. Fruits with high levels of ascorbic acid are often valued for their nutritive quality and also, form essential ingredients in formulating healthy and balanced diets. The ascorbic acid content of pineapple varied significantly with maturity stages and its content decreased with maturity (Fig. 7). The initial ascorbic acid content of pineapple fruits with 25, 50, and 75% yellow tubercles was 46.8, 36.4, and 31.2 mg·100 g⁻¹. Mandal et al. (2015) reported an ascorbic acid content in the range of 18.86 to 23.14 mg·100 g⁻¹ in the ‘Giant Kew’. Ascorbic acid content declined with progress in ripening. After 1 week of storage, fruits with 25% yellow tubercles held in a cool chamber, irrespective of the packaging had the maximum ascorbic acid content of 48.8 mg while the lowest (26.0 mg·100 g⁻¹) was seen in the fruits with 75% yellow tubercles stored under ambient conditions. Ascorbic acid is prone to oxidative degradation, and holding the fruits at high temperatures has also been found to result in substantial losses of this vital nutrient. The fall in the ascorbic acid content of pineapple during storage might be due to its conversion to dehydroascorbic acid by the action of the enzyme ascorbic acid dehydrogenase. The maturity stage, storage temperature, and packaging significantly affected the ascorbic acid content in pineapple. Towards the end of storage (after 6 weeks), fruits with 25% yellow tubercles subjected to shrink-wrapping and subsequently held in a cool chamber retained the highest ascorbic acid content (23.7 mg), followed by the unwrapped fruits in the same storage condition (12.0 mg·100 g⁻¹). Similar observations were also reported by Kamol et al. (2014) wherein pineapple fruits of the cultivar ‘Giant Kew’ at the premature stage had higher levels of ascorbic acid than the fruits of optimum maturity, and the ascorbic acid content of fruits declined throughout storage, irrespective of maturity stage and duration of storage. Hossain et al. (2018) also reported that the vitamin C content of the ‘Kew’ pineapple declined from 21.33 ± 0.88 to 8.66 ± 0.66 mg·100 g⁻¹, and that of the ‘MD-2’ from 95.33 ± 2.40 to 34.66 ± 3.53 mg·100 g⁻¹ during 9 days of storage under ambient conditions.

Figure 7

The research has some limitations, which we encountered during the course of the study. As the response of the fruits to harvest maturity, shrink-wrapping, and storage temperature was highly variable; uniformity with regard to the duration of the experiment, the shelf life, and quality parameters could not be attained. This resulted in considerable complexity in the interpretation of data as well as the statistical analysis. However, a completely randomized design was found to be the most appropriate for this experiment. As some treatments resulted in unmarketable fruits during the course of the experiment, data for these treatments are lacking and this makes the interpretation of the results more complex.