2023 Volume 92 Issue 4 Pages 402-411
Passion fruit (Passiflora edulis) is a tropical fruit that can be consumed fresh or processed. It is a typical respiratory climacteric fruit which is highly perishable because of the loss of water that causes dehydration and thus shrinkage, affecting the fruit appearance; in addition, some quality traits such as fruit weight, firmness and vitamin C content can also be influenced. Therefore, this fruit has a short shelf life. Storage in low temperatures has been assessed to extent the passion fruit shelf life remaining its fruit quality traits; however, information about the application of the hypobaric method in this fruit is null. The objective of this research was to evaluate the physical and chemical characteristics of the yellow and purple passion fruit under hypobaric storage conditions in low temperature. Results showed the hypobaric method had a positive effect in decreasing fruit weight loss, declining the loss of firmness, and reducing the degradation of vitamin C during the storage period. It decreased the evolution of ethylene which is positive to delay fruit senescence, and the production of CO2. Finally, it was the only method which avoids the shrinkage completely in the purple passion fruits (‘Gulupa’, ‘Summer Queen’, and ‘Ruby Star’) and showed minor shrinkage in ‘POR1’ (yellow passion fruit). This method is considered as a promising technique to improve fruit storage.
Passion fruit (Passiflora edulis) is a tropical fruit that can be consumed fresh or processed. This fruit is consumed worldwide and it appreciated because its pulp contains vitamin C, antioxidants compounds and minerals (Viera et al., 2022a, b). Passion fruit consumption supports human health because of its nutritional composition that contributes to complement the amount of minerals and vitamins that body needs in addition to other fruits that are demanded by consumers. This fruit is highly consumed in South American countries such as Brazil, Colombia and Ecuador, and it is also demanded in less proportion in European and Asian countries.
Under environmental conditions, passion fruit can be stored up to seven days and after that it suffers fruit quality damages (Hernández and Fisher, 2009). In terms of fresh fruit, its shelf life (commercialization period) is limited because of rapid modifications in its appearance, mainly due to shrinkage (Ferreira et al., 2003). This loss in quality and thus in commercial value, is influenced by the intense respiratory activity and significant water loss which depend on differences in temperature, relative humidity, and water vapor pressure differential between the atmosphere and the fruit (Scheer, 1994).
Dehydration is one of the most important factors during storage because it causes weight loss and shell softening, which lead to a loss of appearance and thus fruit quality (De la Cruz et al., 2010). In fact, the commercializing period of passion fruit for fresh consumption is reduced mainly due to weight losses and external peel changes as result of the shrinkage (Ferreira et al., 2003), and thus it is mainly used in the industry. In contrast, purple passion fruit is more appreciated for fresh consumption due to its organoleptic traits (De Jesus et al., 2016), but it begins to lose moisture after harvesting, causing shrinkage and reduction in juice quality. Consequently, both cultivars suffer modification during the storage time which affects their quality for fresh consumption.
Different methods have been used for fruit storage to improve shelf life by the influence of the respiration rate and reducing the metabolic activities. Temperature reduction is increasingly being employed to conserve fruits because it decreases the respiratory rate and thus lowers the deterioration of quality traits such as color, flavor, texture and aroma (Prasad and Mali, 2000). Da Silva Araujo et al. (2017) have mentioned that cold storage helps to conserve pulp chemical traits such as pH, soluble solids (SS), and titratable acidity in passion fruit. Storage under low temperature is aiming to increase the shelf life by controlling the action of enzymes and microbial activity (Kishore et al., 2011).
Another novel method is hypobaric storage, also called vacuum storage or low pressure storage. It is a new postharvest technique based on cold storage, in which air is ventilated at less than atmospheric pressure and decrease CO2 partial pressure, consequently fruit respiration rate is reduced (Wang and Dilley, 2000; Wen-xiang and Min, 2005). Hypobaric pressure or sub-atmospheric pressure refers to pressure below 101 kPa (Vithu and Moses, 2017). Usually, an air pressure reduction of 10 kPa allows 2% reduction in oxygen concentration at normal atmospheric pressure, therefore storage under low pressure can reduce oxygen availability (Vithu and Moses, 2017), and the respiration and ethylene production rates become inferior when the level of oxygen is lower (Ballesteros et al., 2021). This method rapidly removes the heat, reduces the oxygen level, and expels the harmful gas (Wen-xiang and Min, 2005); therefore, it can inhibit postharvest ripening, fruit senescence and extend fruit shelf life (Gao et al., 2006). It also conserves the tissue better than other methods for horticultural storage such as packing technologies or controlled atmospheres (Vithu and Moses, 2017). Hypobaric storage maintains more uniform temperature, humidity and gas composition in the fruit, therefore fruits can be stored for longer in fresh condition (Vithu and Moses, 2017).
The hypobaric method has been used in other fruits such as bananas, peach, sweet cherries, loquat fruit and apples to avoid losses in fruit quality traits, physiological damages and improving shelf life (Dilley, 1982; Gao et al., 2006; Li et al., 2017; Romanazzi et al., 2003; Wen-xiang and Min, 2005). Therefore, lowering atmosphere pressure in a closed chamber is used to keep fruits fresh (Liu, 2003b).
Some studies have shown the benefits of low temperature for postharvest conservation of passion fruit; however, there is no research about the use of the hypobaric method in passion fruit, although it has been used in other fruit such as pear and loquat fruit to reduce respiration rates, ethylene production, loss of firmness and vitamin C (Gao et al., 2006; Li et al., 2017). Passion fruit, as a typical respiratory climacteric fruit, is highly perishable and easy to decay after harvest due to dehydration, oxidation and peel shrinkage (Jung et al., 2020). These factors cause that passion fruit has a short shelf life, affecting its quality after harvest and storage (Villacis-Chiriboga et al., 2020). Therefore, it is of great importance to develop appropriate postharvest preservation technologies to maintain the postharvest quality of passion fruit (Zhou et al., 2022).
In this context, due to the importance of preserve the physical and chemical properties of the fresh fruit to meet the quality, the objective of this study was to evaluate the physical and chemical characteristics of a yellow passion fruit (‘POR1’) and purple passion fruits (‘Gulupa’, ‘Summer Queen’, and ‘Ruby Star’) under hypobaric storage conditions in low temperature.
This research was carried out in the laboratory of Tropical Horticultural Science of the Department of International Agricultural Development belonging to Tokyo University of Agriculture.
Two Ecuadorian (‘POR1’ and ‘Gulupa’) and two Japanese cultivars (‘Summer Queen’ and ‘Ruby Star’) were used for this study. ‘POR1’ corresponds to yellow passion fruit (P. edulis f. flavicarpa Derg.), while ‘Gulupa’ (P. edulis f. edulis Sims), ‘Summer Queen’ and ‘Ruby Star’ (P. edulis Sims × P. edulis f. flavicarpa Derg.) are purple passion fruits.
Fruits were obtained from plants coming from seeds (‘POR1’ and ‘Gulupa’) and by cuttings (‘Summer Queen’ and ‘Ruby Star’), and transplanted to pots of 60 L of capacity on April 2022 and grown until flowering from May to June and harvesting in July-August 2022. The substrate used for plant growing was granular clay soil (Akadama, Japanese volcanic soil) and manure compost in a proportion of 70 and 30%, respectively. Irrigation was applied twice per day for 15 min per plant (4 L·h−1), and liquid fertilization (fertirrigation) contained 260 ppm of N, 120 ppm of P2O5, 405 ppm of K2O, 60 ppm of MgO, 1.5 ppm of Mn, 1.5 ppm of B2O3, 230 ppm of CaO, 2.7 ppm of Fe, 0.03 ppm of Cu, 0.09 ppm of Zn, and 0.03 ppm of Mo) was applied twice per week. Training system was placed when plants reached 1.8 m of height and then trained rounded, then pruning was carried out to get downward branches for fruit production. Manual pollination using the pollen from a flower of different plant was done to obtain fruit set.
Storage treatmentsIn terms of the hypobaric storage, fruit were placed in vacuum seal containers (Wide Systems Inc., Yamaguchi, Japan) of 1.4 L. A vacuum pump (Linicon LV-140A; Nitto Kohki Co., Ltd., Tokyo, Japan) and a vacuum regulator (IRV10-C06G; SMC Co., Tokyo, Japan) was used to reach the pressure of 40 kPa into the containers, and they were placed at 6°C and 45% of relative humidity for 20 days. For the cold storage method, fruits were placed in open containers and placed in the cold room (6°C and 45% of relativity humidity) during the storage time. In addition, fruit were also placed in open containers at environment temperature (25°C) and 75% of relative humidity in an incubator (CN-25C; Mitsubishi Electric Engineering, Tokyo, Japan). All methods were in dark conditions during the storage time.
VariablesFully colored fruits of the cultivars ‘Summer Queen’ and ‘Ruby Star’ and progeny of ‘POR1’ and ‘Gulupa’ were evaluated at 10 and 20 days after storage for each treatment. The following variables were recorded. Weight loss was estimated using the following formula (Brito and Vásquez, 2013):
Where X is the weight loss, Iw is the initial fruit weight, and Fw is the fruit weight after the storage time.
Firmness (N) was calculates using a penetrometer (model 2519-104; Illinois Tool Works Inc., MA, USA). Shrinkage was assessed using the following arbitrary scale: 0) No shrinkage, 1) up to 20% of shrinkage, 2) up to 80% of shrinkage, and 3) 100% of shrinkage (Fig. 1).
Scale for shrinkage evaluation. From left to right: 0) No shrinkage, 1) up to 20% of shrinkage, 2) up to 80% of shrinkage, and 3) 100% of shrinkage. ‘Ruby Star’ cultivar.
The chemical traits (pulp) were the following: SS content (°Brix) and acidity (%) were recorded using a Brix-Acidity meter (Hybrid PAL-BX I ACID F5; Atago Co., Ltd., Saitama, Japan). The pH was measured by a pH meter (LAQUAtwin-pH-11; Horiba Ltd., Kyoto, Japan). To measure the SS content and pH, one pulp drop (juice) was placed directly in the equipment; while 1 g of pulp was diluted in 99 g of distillated water (manufacturer’s protocol) and one drop of the mixture was placed in the acidity meter. The sugar acidity ratio (SAR) was determined using the relation between the SS and the acidity, according to the equation the following formula (Brito and Vásquez, 2013):
Where SS is the SS content, and A is the acidity.
Vitamin C (ascorbic acid mg/100 g) was measured using a reflectometer (RQflex plus; Merck, Darmstadt, Germany) and ascorbic acid strips (Reflectoquant®; Merck). First, 1 g of pulp was mixed with 2 mL of metaphosphoric acid at 5% in a 1.5 mL Eppendorf tube; then 1 mL of the mixture was centrifuged at 25°C and 5,000 rpm for five minutes using a centrifuge (MX-307; Tomy Seiko Co., Ltd., Tokyo, Japan); finally, the test strip was immersed in the solution and placed in the reflectometer.
In addition, each fruit was weighed and enclosed in an airtight plastic container of 1.65 L of capacity fitted with a rubber septum, and incubated at 25°C in the darkness. The gas produced by the fruit was extracted by a syringe, using 1 mL headspace of contained gas in the container. The quantification of the amount of ethylene (nL·g−1·h−1) and carbon dioxide (CO2) (μL·g−1·h−1) was carried out by gas chromatography (GC-14B; Shimadzu Co., Kyoto, Japan), with the following conditions for ethylene measurement: 180°C for the injection, 200°C for the flame ionization detector and 80°C for the column SunPak A; for CO2 was 150°C for injection, 150°C for the flame ionization detector, 150°C for the thermal conductivity detector and 40°C for the column SunPak A; using nitrogen and helium at 0.6 kg·cm−2 as carrier gases.
Statistical analysisA randomized completed design with a factorial arrangement of three storage methods × two periods of storage was used for the experiment. Three fruits (each fruit = one replication) per treatment were assessed. Data analysis was carried out in the R statistical software version 4.2.2. Skewness and Kurtosis test were carried out to check data normality and also a heteroscedasticity test was done with the data of each variable, using the gvlma function of R. Square root and log10 were used to transform data when was needed.
Two-way ANOVA for homoscedasticity of errors was carried out to determine statistical differences among treatments in the factorial arrangement (methods × storage periods). Tukey test at 5% was carried out to determine differences between means; this test was applied for the non-transformed and transformed data but results showed in the tables refer to the original data for better understanding.
The behavior pattern of passion fruit during postharvest storage depends on the storage conditions and ripening stage at harvest (Díaz et al., 2012). The use of low temperatures has been a beneficial method for storage fruits such as passion fruit (Maniwara et al., 2015); however, there are changes in the fruit due to the ripening process which accelerates the metabolic activities and cause changes in the respiration rates and ethylene production due to the storage temperature (De la Cruz et al., 2010).
The effect of the storage method in the time showed statistical differences mainly for physical fruit traits such as weight loss and firmness (Table 1). Weight loss of the fruit is produced basically by the dehydration of the fruit (De la Cruz et al., 2010). For this variable, the results of the cold and hypobaric storage were statistically similar for ‘POR1’ and ‘Gulupa’ but numerically the percentages were lower with the hypobaric method; while the weight loss was less for ‘Summer Queen’ (up to 1.43%) and ‘Ruby Star’ (up to 1.89%) with the hypobaric method. The weight loss values (around 1.00%) after 10 days of storage were not statistically different to the initial value (0.00%) in the hypobaric method for all purple passion fruits.
Effect of the storage treatment on physical fruit quality traits and respiration rates in the four passion fruit germplasm.
Firmness represents the combination of mechanical characteristics and physical structures; it is related to fruit texture and has an essential role in the supply chain of fruits (Wang et al., 2021). ‘POR1’ showed more fruit firmness (around 9.00 N) in the environment and hypobaric storage than the cold storage (4.18 N) after 10 days of storage. For ‘Ruby Star’ also the best results with this method (6.58 N) was after 10 days of storage. On the other hand, the hypobaric method showed better results for ‘Gulupa’ (9.99 N) after 20 days of storage. In terms of ‘Summer Queen’, it showed better firmness with the hypobaric method than the cold storage in both storage periods.
Díaz et al. (2012) reported that chilling damage such as shrinkage is developed at cold condition (4°C), whereas fruit decay is quickly developed at environmental conditions (20°C). The hypobaric method (storage at 6°C) could avoid the shrinkage after 10 days of storage for ‘POR1’; the other methods reach a value around 1 during the storage time (10 and 20 days of storage), but the fruit still remain marketable. However, there were a brown stained in the skin fruit after the 20 days of storage when they were removed from the containers, similar to those observed in the fruit storage at environment temperature after 10 and 20 days of storage. Using this method, ‘Gulupa’, ‘Summer Queen’ and ‘Ruby Star’ showed no damage for shrinkage at 10 and 20 days after storage. However, ‘Summer Queen’ and ‘Ruby Star’ obtained a few hole depressions in the peel (Fig. 2) when the pressure was brought out from the containers; this effect was not observed after 10 days of storage. ‘Gulupa’ did not show mechanical damage in the fruits due to the release of pressure after they were removed from the vacuum seal containers at 20 days of storage.
Mechanical damages produced in the peel fruit after removing fruits from the vacuum seal containers (Hypobaric method) after 20 days of storage. From left to right: ‘POR1’ (brown stained), ‘Gulupa’ (no damage), ‘Summer Queen’ and ‘Ruby Star’ (both hole depressions).
Peel thickness is a trait that vary depending of the passion fruit germplasm (Viera et al., 2020). There were not statistical differences for none of the storage methods for ‘POR1’ for this trait (around 7 mm) during the storage time. For ‘Gulupa’, there was a difference for the hypobaric method (5.30 mm) with the environment (3.54 mm) and cold (4.27 mm) storage after 20 days. Same trend was observed for ‘Summer Queen’ (5.01, 3.12, and 3.38 mm, respectively) and ‘Ruby Star’ (5.05, 3.62, and 4.24 mm) after 20 days of storage.
It was observed more stability in terms of the chemical fruit traits (Table 2). The SS content is a trait that has been used as a quality indicator of passion fruit (De Jesus et al., 2022). It was no significantly different for all passion fruit germplasm, therefore this parameter was not affected during the storage time.
Effect of the storage treatment on chemical fruit quality traits, ethylene production and respiration rates in the four passion fruit germplasm.
Acidity is an important trait for fresh fruit consumption (Kondo et al., 2021) and it is essential for industry because higher acidity allows longer shelf life without the need to add chemical preservatives (Dell’Orto et al., 2010). Only ‘Ruby Star’ showed differences for this trait, obtaining higher acidity (3.07%) in the cold storage compared to the hypobaric (2.27%) and environment (2.21%) storage. In terms of the SAR, there was no differences for the four evaluated passion fruit. The pH is also important for fruit conservation, it did not show statistical differences for all passion fruits, except to ‘POR1’ where the values reached for all storage methods were slightly higher than the initial value (2.80).
Passiflora edulis has been associated with high content of vitamin C (Barbosa et al., 2021). In all passion fruit germplasm, the vitamin C trended to decrease during storage and showed statistical differences for ‘POR1’ and ‘Summer Queen’ but not for ‘Gulupa’. In terms of ‘POR1’, the highest value (37.12 mg/100 gFW) was observed after 10 days of storage with the hypobaric method. For ‘Summer Queen’, the hypobaric method (40.00 and 35.62 mg/100 gFW) showed higher values than the cold storage (38.50 and 31.67 mg/100 gFW) after 10 and 20 days of the storage; both methods showed higher results than the environment storage (35.00 and 25.33 mg/100 gFW). In the case of ‘Ruby Star’, the initial measurement (fruit before storage) was 31.25 mg/100 gFW; however, it was recorded as “low” in all treatments at 10 and 20 days after storage, which means that the content was less than 25 mg/100 gFW, which is the minimum measurement detected by the reflectometer.
It has been reported that passion fruit can be stored around 20 days at low temperatures (Manrique et al., 2020) because this method reduces respiration rates (i.e. CO2 production) and ethylene production (Makule et al., 2022; Prasad and Mali, 2000), nevertheless the method promotes dehydration (Nunes et al., 2022). Both, ethylene and CO2 production increased in all germplasm (Table 1), these variables did not show statistical differences between the hypobaric and cold storage; however, the amount of these gases produced in the low temperature storage methods (hypobaric and cold storage) was lower than that produced by preserving the fruit in the environment temperature for all the evaluated passion fruits. ‘POR1’ showed the lowest amount of ethylene and CO2 in the cold conditions (159.26 nL·g−1·h−1 and 144.92 μL·g−1·h−1, respectively) after 10 days of storage. The same was also observed in ‘Gulupa’ (127.06 nL·g−1·h−1 of ethylene and 308.42 μL·g−1·h−1 of CO2). Turning to ‘Summer Queen’ and ‘Ruby Star’ the lowest amount of ethylene was obtained with the cold storage (163.65 and 169.34 nL·g−1·h−1, respectively) but the lowest CO2 amount was observed with the hypobaric method (302.47 and 261.25 μL·g−1·h−1, respectively) after 10 days of storage. After 20 days of storage, the cold storage showed the lowest amount of these gases for all the evaluated passion fruits.
Overall, the hypobaric method stood out among the storage methods in all passion fruit germplasm, especially in variables such as weight loss, firmness, shrinkage and vitamin C.
Hypobaric storage is recognized as a safe approach that preserves the freshness of food (Liu, 2003a). Under this storage, fruit suffers a series of changes, that can be favorable and undesirable according to the storage conditions because physiological and biochemical factors depend on storage pressure, relative humidity, temperature and time of storage (Vithu and Moses, 2017). Overall in this study, the cold storage showed similar effects to the hypobaric storage, mainly in pH, acidity, SS content. However, in other traits, such as weight loss, firmness, shrinkage and vitamin C content, the hypobaric method showed better results than cold storage. On the other hand, the cold storage affected the fruit appearance negatively, because it caused shrinkage in all the passion fruit germplasm (both 10 and 20 days after storage), which would be related to the dehydration (Nunes et al., 2022).
Weight loss is mainly associated with the loss of water through the peel (Manrique et al., 2020). In this context, peel thickness would play a role to decrease weight loss, especially at environment conditions; in fact, ‘POR1’ which showed the lowest percentage of weight loss during environmental and cold storage, also had thicker peel than the other evaluated passion fruits. Nevertheless, in the hypobaric storage, ‘Summer Queen’ and ‘Ruby Star’ showed less weight loss than the other passion fruit.
It has been reported that some germplasm of yellow passion fruit (i.e. INIAP 2009) can reach up to twice the peel thickness of purple passion fruit (Viera et al., 2022a); however, these authors did not find statistical differences for this trait between ‘POR1’ and ‘Gulupa’ grown in open field. In this study, ‘POR1’ showed higher peel thickness than the value (5.87 mm) reported by the latter authors but it has been reported that this trait might be varied due to a genotype × environment effect (Viera et al., 2020).
It has been reported that the weight loss of passion fruit increase with the time in cold storage, affecting the fruit external appearance (Arjona et al., 1992). The fruit weight loss reached with the hypobaric method at 10 and 20 days of storage was considerably less than that obtained by the cold storage, thus, the former is more efficient the reduce the dehydration of the fruit.
In terms of storage, fruit firmness is a key factor for the regulation of temperature, humidity and time (Osinenko et al., 2021). The softening of fruits is generally accompanied by the loss of water, the reduction of cell turgor and the degradation of cellulose, hemicellulose and pectin (Zepeda et al., 2018). Vithu and Moses (2017) have reported that the firmness loss is lower when fruits are stored under the hypobaric method. This trend was also observed in this study, especially for the purple passion fruit germplasm. In addition, decreasing in firmness has also observed when passion fruit is transported at environment temperature (Brito et al., 2023). Consequently, to avoid further mechanical damages in the fruit due to the loss of firmness, and adequate packaging that have resistance to compression, stackability, stability during fruit transportation is required (Ciro Velásquez, 2007). In most of cases, refrigerated trucks (temperature around 8°C) are used for extending fruit shelf life but in some cases (especially in South American countries) fruit is transported at environment temperature thus obtaining more loss in firmness, same as it was observed in this study in this kind of storage. Usually, passion fruit is packaged adequately in cardboard boxes; however, in South American producer countries there is a lack of knowledge of the resistance and mechanical behavior of tropical fruits which has caused in some cases an unappropriated management of harvest and postharvest of this fruit which is packaged in sacks that allow mechanical damage risks associated also to the decrease of fruit firmness, making the fruit less marketable for fresh consumption.
Visual quality is an important characteristic for consumer acceptance (Maryam et al., 2022), thus any damage occurred in the fruit peel cause losses for the fruit commercialization. Shrinkage is caused by the loss of water of the fruit which dehydrates the fruit peel. It damages fruit appearance and it occurs because of the ripening during storage in passion fruit, thus fruits loss their marketability (Shinohara et al., 2019). The hypobaric method was the only one which could completely avoid the shrinkage in the purple passion fruits up to 20 days of storage, and the effect was minor in ‘POR1’at the same time but at 10 days was null. Consequently, the hypobaric may be considered as a promising technique for extend passion fruit life remaining the fruit appearance; nevertheless, mechanical damage such as hole depressions were observed in ‘Summer Queen’ and ‘Ruby Star’ when the air pressure was released from the containers. The pulp of these fruits would remain acceptable for fresh consumption due to the hypobaric method did not influence variations in SS content and acidity during the storage time but the marketable value of the fruit is affected by the mechanical damage. The occurrence of hole depressions could be associated to the fact that passion fruit has a relatively large internal chamber in its fruit structure which is filled with the liquid pulp; and the release of pressure after the hypobaric storage period might directly affect the peel causing the depressions because the interior of the fruit is not completely solid.
SS content did not show statistical differences among methods, which meant that it could be considered stable during storage (Arjona et al., 1992; De la Cruz et al., 2010). In addition, these results are consistent to Li et al. (2017) who found in apples that the hypobaric method and control did not show differences for this parameter. The SS content is a trait which can be influenced by external growing factors (Mohammadi et al., 2014), as a result the environment and agronomical management (fertilization) are directly related to this parameter; however, the market preference is for fruits with levels above 13 °Brix (Maniwara et al., 2014). The values obtained with the cold and hypobaric method are appropriate with those mentioned by the latter author, which means that these storage methods do not affect negatively this characteristic, and no statistical differences were observed in the different values obtained during the storage time, which is a positive effect.
The pH did not show considerable variations among the storage methods for all passion fruit germplasm, thus this trait remained relatively stable during the storage. It had showed a trend to decrease in other fruit species such as blueberry stored at 20°C and pressures between 25 and 75 kPa (Li et al., 2019), but it increased in strawberries treated with a pre-storage hypobaric treatment of 40 kPa at 2°C (Maryam et al., 2022). Consequently, this response would vary depending of the fruit species and the storage conditions.
The response of acidity level is genotype depending (Viera et al., 2020), being observed that the purple passion fruits obtained lower values than ‘POR1’; nonetheless, there was not a clear influence of the storage methods in this parameter.
The SAR is considered to be one of the criteria to assess the palatability of fruits, and acidity is decisive in this parameter (Kolayli et al., 2010). In this study, this parameter was not influenced by the low temperature storage methods; no major variations were observed during the storage time for the different passion fruit germplasm.
There is a degradation of the vitamin C content during the fruit storage time (Aular et al., 2001). The hypobaric method could reduce in more proportion the degradation of the vitamin C than the cold storage. This effect would be related to the fact that the ascorbic acid content is associated to the metabolic activity (Mapson, 1970), and the low temperature storage methods reduce this activity. Jadhav et al. (2022) and Viera et al. (2022b) found that germplasm of purple passion fruit showed higher vitamin C content than germplasm of yellow passion fruit; the results of this study agree with the aforementioned because ‘Gulupa’ and ‘Summer Queen’ had higher vitamin C than ‘POR1’ during the storage time. However, it is still unknown whether yellow passion fruit cultivars tend to show lower vitamin C than the purple ones.
Kader (2002) has reported that passion fruit shows high ethylene production at environmental conditions (20°C). The ripening process of the passion fruit produce that the amount of ethylene and CO2 increase during the storage time (De la Cruz et al., 2010; Shinohara et al., 2019). Passion fruit can be considered as a climacteric fruit because it shows peaks in the CO2 production (De la Cruz et al., 2010); this trend was observed specially in ‘Gulupa’ after the 20 days of storage at environmental conditions.
Some studies have reported that hypobaric storage increases respiration rate and this can be attributed to the fruit stress response (Plaxton and Podesta, 2006; Tovar et al., 2011). In this research, both cold (6°C) and hypobaric method (40 kPa and 6°C) reduced the production of these two gases in comparison to the environmental conditions, but the latter showed lower values which would indicate that the respiration rates and metabolic processes for reaching full ripening were decreased.
The changes of fruit traits applying the hypobaric method have been reported in other fruit crops. In loquat fruit, the application of 40 or 50 kPa pressure significantly reduced rates of respiration and ethylene production and declined the vitamin C contents of loquat fruit during storage at 2 to 4°C (Gao et al., 2006). The latter results agree with those of the present research, where the hypobaric method (40 kPa and 6°C) reduced the weight loss, firmness loss, occurrence of shrinkage and degradation of vitamin C. On the contrary, Gao et al. (2006) mentioned that the hypobaric method declined fruit firmness and acidity, but in this study, passion fruit treated with this method showed minor loss in firmness and the acidity showed minor variations. Wen-xiang and Min (2005) carried out a study on hypobaric storage (10 and 20 kPa) in combination with cold storage (2°C), they found that the storage life of honey peach fruits was better in terms of freshness, taste and flavor, color, and texture; and they could be stored for lesser days when kept in cold storage; this trend can be also observed in this study where hypobaric method kept the fruit in better conditions without affecting SS and acidity, traits associated with fruit flavor. Nevertheless, the theoretical basis for this combined effect must be further explored.
In conclusion, the hypobaric method had a positive effect in decreasing fruit weight loss, declining the loss of firmness, avoiding shrinkage, reducing the degradation of vitamin C and not affecting the soluble solid content and acidity during the storage period. In addition, it also decreased the production of ethylene and CO2 in comparison to environment storage, which is positive to delay fruit senescence. Therefore, hypobaric storage in combination with low temperature is a viable method for extending the shelf-life of passion fruit; however, further research is required for defining management protocols for the application of this method, testing storage temperatures and pressure dose, and better understanding of the processes involved in the extension of storage time of perishables fruits under low pressure conditions. The results of this study, constitutes an initial information about the application of the hypobaric method using low temperature for passion fruit storage.
