Papaya (Carica papaya L.) fruits of Tainung n˚ 1 variety were purchased in local market and processed at maturity stage 4 (bark surface 50% to 75% yellow). The fruits were washed in water and immersed in solution with 100 mg/L of chlorine for 15 minutes. Fruits were peeled, the seeds removed and cut crosswise into 1.2 cm thick slices.

The slices were subdivided into pieces of 3.0 × 3.0 cm and submitted to the following treatments: T1―control treatment (without antioxidant treatment); T2―papaya immersion in solution containing 25 mg/L citric acid + 75 mg/L of ascorbic acid for 10 minutes, according to Reis et al. [12] .

The papaya slices (T1 and T2) were dehydrated at 60˚C in a dryer with fixed air velocity of 1.5 m/s until reaching final humidity between 15% and 25% (w.b). The dried papayas were packed in polyethylene terephthalate/aluminum/polyethylene (PET/Al/PE) and stored for 120 days at room temperature (28˚C ± 2˚C).

The fresh and dried papayas were evaluated for color, moisture, pH, titratable acidity (TA), water activity (a_w) and soluble solids (SS).

The color was determined using the colorimeter (Konica Minolta, model CR400, CIELAB system, illuminant D65). A sample of ten pieces of each treatment was analyzed. The coordinates L* (lightness), a* (green/red intensity) and b* (blue/yellow intensity) and the color attributes C* (color intensity/chroma) and h* (hue/color angle). The color variation (ΔE*) was also calculated by the Equation (1) [13] .

Δ E * = [ ( L 0 * − L * ) 2 + ( a 0 * − a * ) 2 + ( b 0 * − b * ) 2 ] 1 / 2 (1)

The analysis of moisture, pH, soluble solids and titratable acidity were performed according to the Adolfo Lutz Institute [14] . The water activity was determined at 25˚C by direct reading in water activity determinant (Aqualab Series 3/3TE).

The total carotenoid contents were determined according to Rodriguez-Amaya and Kimura [15] . The extraction was carried out with acetone, followed by the petroleum ether partition and the UV-visible spectrophotometer reading at 450 nm. The results were expressed in μg of carotenoids per g of pulp.

The content of vitamin C was determined by the reaction of ascorbic acid with 2.6-dichlorophenol indophenol (DCFI), according to the procedure described by Oliveira [16] , expressed in mg of ascorbic acid per 100 g of pulp.

For the determination of TEP and antioxidant activity, papaya extracts were prepared as described by Larrauri et al. [17] , with modifications. The extraction was done with 50% methanol for a period of 20 minutes in an ultrasonic bath, followed by centrifugation at 11,000 rpm for 15 minutes. The residue was subjected to the second extraction in 70% acetone, following the same procedure. The extracts were mixed and transferred to the 50 mL volumetric flask, the volume was filled with distilled water. The TEP contents were determined using the Folin-Ciocalteau reagent (1:3) and the standard curve of gallic acid, according to the method described by Singleton et al. [18] and following the modifications proposed by Rufino et al. [19] .

The total antioxidant activity was determined by capture of the radical ABTS⁺ according the methodology proposed by RE et al. [20] , with modifications. The decrease in absorbance was measured after 6 minutes of reaction and the reading at 734 nm. The results were expressed as µM trolox/g of fruit, from trolox standard curve.

The color, moisture, pH, titratable acidity, water activity, total carotenoids and vitamin C were determinated at zero time and every 30 days of storage for a period of 120 days for the stability of the dried papaya. Degradation of the total carotenoids and vitamin C during storage followed the first-order reaction, and the data were evaluated using the following model:

C = C 0 e − k t

where C 0 in C that represent component concentrations at zero and t time, respectively, and k is the reaction rate constant (time⁻¹).

The study was approved by the Research Ethics Committee of Maria Milza College, located in Governador Mangabeira, Bahia, Brazil (authorization n˚ 246/11). The sensory test was performed in individual cabins under white light by fifty not trained judges, with age between 18 and 60 years. The tests were carried out at 30-day storage. The acceptance test was made using a structured 9-points hedonic scale, in which 1 represents “dislike extremely” and 9 represents “like extremely”. The attributes intensity of color, aroma, flavor and texture were evaluated using a nine-point intensity scale as described in Meilgaard et al. [21] .

All drying processes and all analysis were repeated three times. The one-way analysis of variance (ANOVA) was used to compare the two treatments of dried papaya (T1 and T2) at 5% significance level, by F test. Results were expressed as mean ± standard deviation.

The study of stability was performed in the completely randomized design in a split plot system. Two treatments (T1 and T2) constituted the plots and five storage times (0, 30, 60, 90, 120 days) constituted the subplots. The data were analyzed by ANOVA at 5% significance level and regression analysis using Sisvar and R programs.

The results of characterization of fresh and dried papaya (zero storage time) were shown in Table 1. The antioxidant treatment with citric acid and ascorbic acid (T2) used in papaya slices had no significant effect (p > 0.05) in physicochemical characteristics and in content of bioactive compounds when compared to the control treatment (Table 1). The dried papaya presented, on average, 23.42% moisture and water activity 0.57. In general, these low values of moisture and water activity are sufficient to guarantee the microbiological stability of dehydrated products. According Sagar and Kumar [10] , the pathogenic bacteria do not grow in products with a_w below 0.85, while fungi and yeasts are more tolerant and, to inhibit them, the product must have a_w lower than 0.62. Therefore, the dried papaya obtained in this study can be considered as a microbiologically stable product.

Means followed by the same letter in the same row are not significantly different (p > 0.05) by F test. ⁽¹⁾Control Treatment; ^(2)Immersion in aqueous solution containing 25 mg/L citric acid + 75 mg/L ascorbic acid for 10 minutes. ⁽³⁾Average values of treatments T1 and T2; a_w: water activity; TEP: total extractable polyphenols; ABTS = antioxidant activity by the ABTS method; ΔE * = total variation of color dried papaya compared to fresh papaya.

After drying process, the solids and organic acids of papaya were concentrated. The SS/TA increased 48.52%, which may positively influence in the acceptance of the dried papaya by consumers, since products with higher SS/TA have more pronounced sweetness. There were also increased levels of bioactive compounds in dried papaya, where values were approximately six times higher than those presented in fresh one. The increase in concentration of these compounds, promoted the increase of its antioxidant activity, which passed from 4.35 for fresh to 7.86 μM trolox/g for dried papaya (T1 and T2 average) (Table 1).

The use of the citric acid and ascorbic acid combination did not have a significant effect (p > 0.05) on coloration of dried papaya (Table 1). By comparing the chromatic attributes of fresh and the dried papaya (T1 and T2 average), it was found that the lightness of papaya (L*) did not change during the drying process, indicating that there was no browning of the product. However, the dried papaya showed a more intense and more reddish color than the fresh papaya, which can be seen by the higher values for a* and C* and lower values for h*. These results may be associated with the concentration of papaya carotenoids after drying, especially lycopene, which is the main carotenoid on fresh papaya and responsible for the red color of the fruit [22] . Mishra et al. [5] also observed an increase in the values of a* coordinate in dehydrated papaya by using a combination of osmotic dehydration and infrared drying. However, different from that observed in this study, L* decreased and the product presented a reddish brown coloration. Different results from this study was also observed by Canizares and Mauro [23] , in which papayas dehydrated by convective drying at 60˚C and 70˚C showed more yellowish color and less intense than the fresh papaya.

The total color variation, ΔE*, was 12.10 (Table 1), a value close to that reported by Chong et al. [9] , which was 10.36, in papaya dried by hot-cold air technology. Despite close values, in the study conducted by Chong et al. [9] , papaya color changed from deep red to yellow-brown, an opposite result to the present study. According to these authors, the use of high drying temperatures, above 70˚C, in spite of promoting the inactivation of the PPO enzyme, favor the oxidation of papain enzyme, releasing free amino acids that react with the reducing sugars of the papaya, triggering the Maillard reaction. Therefore, the drying temperature used in this study (60˚C) was satisfactory, allowing color preservation and obtaining a dried product with high concentration of bioactive compounds.

When comparing the contents of the bioactive compounds on dry basis (Table 2), some of these compounds were lost after drying. There was loss of 17.69% for TEP and dried papaya showed an average of 347.36 mg GAE/100g. Chong et al. [9] , evaluate the effect of different papaya dehydration methods and found losses

Means followed by the same letter in the same row are not significantly different (p > 0.05) by F test. ⁽¹⁾Control Treatment; ⁽²⁾Immersion in aqueous solution containing 25 mg/L citric acid + 75 mg/L ascorbic acid for 10 minutes; ⁽³⁾Average values of treatments T1 and T2; ⁽⁴⁾Calculated for average value of treatment T1 and T2 in relation of fresh papaya; ⁽⁵⁾Calculated by difference between 100 and the % of degradation.

from 7% to 69% for phenolic content, and the dried product had contents from 84.78 to 250 mg GAE/100g, lower values than the results of this study.

Degradation of vitamin C during the drying process was only 13.02% (Table 2), representing 86.98% of retention of vitamin C in the dried product (T1 and T2 average). These values were similar to those reported by Garcia et al. [24] , which found a retention of 83.03% and 87.30%, in dehydrated papaya at 60˚C and 70˚C, respectively. Hawlader et al. [25] investigated the dehydration of guava and papaya using the same drying conditions of the present study and verified that 75% of vitamin C was retained in papaya and only 25% in guava. This result suggests that vitamin C degradation is dependent on the food matrix and that papaya may present a natural barrier to oxidation during drying [24] . Another factor that interferes on the degradation of bioactive compounds is the drying parameters used. Kurozawa et al. [26] observed that increasing air velocity promotes a greater retention of vitamin C in dried papaya at 60˚C, a fact that is associated with the shorter time papaya is exposed to high temperatures. This may explain the high vitamin C retention of dried papaya in this study.

For carotenoids, the drying process employed promoted the 13.51% degradation. Factors such as high temperature, presence of light, oxygen, acids and metals can promote the degradation of these pigments during the drying process. However, Udomkun et al. [27] , tested several drying temperature combinations (50˚C, 60˚C, 70˚C and 80˚C), air velocity (0.2, 0.5 and 0.7 m/s) and air specific humidity (10 and 25 g water/kg of dry air), in papaya dehydration process, and found losses of 5.7% to 75% of β-carotene content, and from 34.66% to 76.41% of lycopene content, but did not find a direct relationship between these variables and the degradation of the evaluated carotenoids. The low degradation of carotenoids during the papaya drying may be related to the moisture reduction of the product. According to Goula et al. [28] , the kinetics of lycopene degradation depends on product moisture, and when the moisture content is high (55% - 95%), chemical reactions occur faster than in low moisture content (below 55%). This is due to the greater solubilization and mobility of the catalytic substances in the reaction. Di Scala and Crapiste [29] verified the same behavior during the drying of red peppers.

There was no significant difference (p > 0.05) between the two treatments (T1 and T2) regarding sensorial acceptance (Table 3). Sensory acceptance was

Means followed by the same letter in the same row are not significantly different (p > 0.05) by F test. ^(1)mean hedonic score (n = 50) according nine-point scale, with the terms “dislike extremely” (1) and “like extremely” (9). ⁽²⁾Attribute intensity according to nine-point scale: very light color (1) to very dark (9); weak aroma (1) to strong aroma (9); weak flavor (1) to strong flavor (9); very soft texture (1) very hard texture (9). ⁽³⁾Control Treatment; ^(4)Immersion in aqueous solution containing 25 mg/L citric acid + 75 mg/L of ascorbic acid for 10 minutes. ⁽⁵⁾Average of treatments T1 and T2.

intermediate and the dried papaya was classified as “neither like nor dislike” and “liked slightly”. A similar result was obtained Canizares and Mauro [23] for papayas coated with pectin and dehydrated at 60˚C, which received a mean score of 5.30, and papayas coated with pectin added vitamin C that received a mean score of 5.36, for the overall acceptance attribute.

Regarding intensity scale, dried papaya was considered dark (6.42), a fact confirmed by the values of C*, h*, a* and ΔE (Table 1). The aroma and taste were considered intermediate (neither strong nor weak), probably due to the loss of part of the volatile compounds during the drying process. The note for the texture was 6.51, indicating that the dried papaya presented a hard texture. Such results may explain the intermediate acceptability of dried papaya.