Postharvest quality of cocona ( Solanum sessiliflorum Dunal ) stored under ambient condition

Recebido para publicação em 05/05/2010 e apr ovado em 05/07/201 1 Agronomist Engineer , Doctor Science. Postdoctoral position at the Plant Science Department, Universidade Federal de Viçosa, Av. PH Rolfs s/n, 36570-000, Viçosa, Minas Gerais, Brasil. PNPDCAPES Grant holder . danieele@ufv .br 2 Agronomist Engineer , Doctor Science. Unidade Acadêmica de Agronomia e Tecnologia de Alimentos, Universidade Federal de Campina Grande, 58840-000, Pombal, Paraíba, Brasil. 3 Agronomist Engineer , Doctor Science. Departamento de Fitotecnia, Universidade Federal de Viçosa, Av. PH Rolfs s/n, 36570-000, Viçosa, Minas Gerais, Brasil. salomao@ufv .br Danielle Fabíola Pereira da Silva , Railene Hérica Carlos Rocha , Luiz Carlos Chamhum Salomão 3 Postharvest quality of cocona ( Solanum sessiliflorum Dunal) stored under ambient condition


INTRODUCTION
Solanum sessiliflorum Dunal or Cocona is a tropical shrub belonging to the Solanaceae family.In Brazil, cocona is known as maná-cubiu, maná, topiro and "tomate de índio" (Yuyama et al., 2007).Cocona is native to the western Amazon and was domesticated by pre-Columbian Amerindians (Lopes & Pereira, 2005).It is a semihardwood, fast-growing plant and can reach up to two meters high.The flowers are complete, 4-5 cm wide, arranged in inflorescences of short racemes (Rascio et al., 2002).The trees produce up to 100 ton/ha of fruits, which are used in juices, ice creams, sweets and sauces for meats (Silva Filho et al., 2003).
Fruits are mostly globose, 31-92 mm long, 33-77 mm in longitudinal diameter, 1.5-19.5 mm of pulp thickness and 18.5-30.1 grams of mass.Cocona is a low-calorie food with carbohydrates and lipids ranging from 1.3 to 27.2% and 58.5 to 87.3% per 100 g of pulp, respectively.Potassium (54.6 mg to 463.5 mg per 100 g of pulp) and iron (97.3 to 352.0 µg per 100 g of pulp) are among the macro and micro elements occurring in higher concentrations (Silva Filho et al., 2003).
Because cocona contains high levels of niacin (vitamin B3), higher than in eggplant, cashew, star fruit, sugar beet and persimmon, it can be considered a medicinal fruit, fighting cholesterol and high triglyceride levels, anemia, diabetes, high blood pressure, migraine and depression (Salick, 1989).
The fruits grow rapidly in the early development, up to 80 days after anthesis.At this stage, they are yellow, changing to orange, around 90 days, to deep orange, around 100 days, and orange-brown, around 110 days after anthesis.The whole cycle of fruit development and ripening, on the plant, is around 90 days (Souza et al., 2008).
Studies on this species have been especially related to the floral biology and genetic improvement (Paiva, 1999;Rascio et al., 2002, Bezerra & Machado, 2003;Silva Filho, 2003).However, there is a lack of studies on fruit quality and postharvest life.
Considering the scarce information on quality and shelf life of cocona, we highlight the need for studies on postharvest biology.In this study, we evaluated quality and postharvest shelf life cocona fruits during storage under the ambient conditions.

MATERIALS AND METHODS
Physiologically matured (uniform yellow skin) fruits of cocona var.'Mosquet' were harvested from an experimental orchard located in the Mesoregion of Zona da Mata of Minas Gerais (20°45'14" S latitude, 42°52'55" E longitude, 648 m altitude), in September 2006.The climate of the region is classified as tropical of altitude, with average annual temperatures around 19°C, varying between 14°C (minimum average) and 26°C (maximum average).
After harvesting, the fruits were washed with tap water and soaked in a solution of the fungicide Prochloraz (49.5 g/100 L of water) for 5 minutes.After drying, the fruits were packed in plastic containers, previously disinfected with sodium hypochlorite and lined with paper towels, and stored at 24 ± 2 °C and relative humidity 60 ± 5%, for 15 days.The evaluations were carried out at regular intervals, every three days.
The CO 2 production was determined by gas chromatography.Fruits were placed in sealed glass jars of 1680 mL volume.Sixty minutes after closing the jars, 1.0 mL aliquots were taken with a hypodermic syringe and injected into a Gow Mac Series 550P gas chromatograph equipped with a thermal conductivity detector and aluminium column filled with Porapak Q.The working conditions were: helium as a carrier gas at a flow rate of 40 mL/min; electric current of 150 mA; column temperature of 50 ºC; detector temperature of 70 ºC; injector temperature of 80 °C, and room temperature of 20-23 ºC.CO 2 was measured by comparing the peak areas of the sample, in the chromatogram, with those produced by the injection of a standard aliquot consisting of 5.96% mol CO 2 per mol of the mixture CO 2 + N 2 .The results were expressed as mg CO 2 kg -1 h -1 .
The weight loss was evaluated gravimetrically, by subtracting the initial weight of the fruit from the weight obtained in each sampling period; the fruit volume was measured by the volume of water displaced after immersing the fruit in a 1000 mL measuring cylinder.
Skin and pulp resistance was determined by a digital penetrometer Shimpo model DFS 100 (Digital Force Gauge) with 12 mm circular flat head.Firmness of fruit with skin was measured by pressing the epicarp, and pulp firmness was measured by pressing the fruit mesocarp without skin, with two readings per fruit.The results were expressed in kPa.Determination of soluble solids was carried out with a digital refractometer and expressed in ° Brix.Titratable acidity was determined by titration of an aliquot of 5 mL of juice with NaOH (0.1 N) previously standardized, and the results expressed as a percentage of citric acid per 100g of pulp.
The experiment was arranged in a completely randomized design with six treatments: storage periods (0, 3, 6, 9, 12, and 15 days) and four replications.Each experimental unit consisted of two fruits.Data were examined using analysis of variance and regression analysis using the SAEG software (2007).The models fit by regression were chosen based on the significance of coefficients at 5% probability level by the t test, the coefficient of determination and the potential to explain the biological phenomenon.

RESULTS AND DISCUSSION
There was an increase in the production of CO 2 with storage (Figure 1A).The lowest value was observed on day 3 (30.13mg CO 2 .kg -1 h -1 ) and the highest on day 9 (194.52 mg CO 2 kg -1 h -1 ).From the day 9 after harvest, there was a decrease in CO 2 production, reaching 88.66 mg CO 2 kg -1 h -1 on day 15 of storage.This respiratory pattern of cocona is typical of climacteric fruits.
Mass loss of fresh weight increased with storage (Figure 1 B).Mass loss of accumulated fresh weight reached 17.10% on day 15.According to Silva et al. (2009), the mass loss of fresh weight has marked effects on the physiology of plant tissues, anticipating, in some cases, ripening and senescence of fruits.
The storage temperature can affect cell turgor, mass loss and mechanical properties of the fruit (Silva et al., 2010).Fruit volume decreased during storage possibly due to tissue dehydration (Figure 1 C).
Skin and pulp resistance decreased with increasing storage time and reached reductions corresponding to 62.98 and 85.9%, from harvest to the end of day 15 (Figures 2 A, B).On day 6, when the fruits were apparently firm, firmness corresponded to 532.30 kPa for skin and 117.42 kPa for pulp.Fruit softening, characterized by the decrease in resistance, is generally associated with lower adherence between cells.This results from the dissolution of pectic polysaccharides and hemicellulose in the middle lamella, leading to disruption of the cell wall, thus providing separation of cells, changes in turgor and dehydration of the membrane (Waldron et al., 2003).
Soluble solids (SS) responded quadratically to time intervals (Figure 2 C).There was increase in SS up to day 9 of storage, from 4.05 ° Brix, at the beginning of storage, to 6.53 ° Brix, on day 9. Values found for SS in this study confirm those reported by Souza et al. (2008) in cocona var.'Santa Lucia'.From day 9 after harvest, SS decreased and reached a minimum of 4.56 ° Brix on day 15 of storage.This reduction in SS has probably occurred because of the use of substrates in the tissue fruit, due to the climacteric pattern of respiration.
The soluble solids content is related to sugar content and therefore, is often used to assess the quality (Silva et al., 2009).SS content has been used as an indicator of the fruit quality in melon (Mendonça et al., 2004), guava (Natale et al., 1995) and apple (Ventura et al., 1998).
Titratable acidity (TA) responded quadratically to day of evaluation (Figure 2 D).Similar to SS content, acidity also decreased after day 6, from 1.04% at time zero to the minimum value of 0.28% on day 15.The level of TA observed in this study is in agreement with that reported by Souza et al. (2008), with variations ranging from 1.1 to 2.0% of citric acid.The authors found a negative correlation between the SS content and TA level during fruit development: while there is an increase in the SS content, there is a decrease in TA, a phenomenon possibly related to the climacteric respiration.

Figure 1 .
Figure 1.CO 2 Production (A), mass loss of fresh weight (B) and volume (C) of cocona fruits of var.Mosquet, stored at 24 ± 2 °C and 60 ± 5 relative humidity, as a function of storage period.

Figure 2 .
Figure 2. Skin resistance (A), pulp resistance (B), soluble solids (C) and titrable acidity (D) in of cocona fruits of var.Mosquet, stored at 24 ± 2 °C and 60 ± 5 relative humidity, as a function of storage period.Days after harvest (D) Days after harvest (D)