Development of intermediate-moisture slices of papaya (Carica papaya L.) by hurdle technology Akanksha Shrivastava and I.N. Doreappa Gowda* Division of Post-harvest Technology ICAR-Indian Institute of Horticultural Research Hessaraghatta Lake Post, Bengaluru - 560 089, Karnataka, India *E-mail: dore@iihr.res.in ABSTRACT Papaya fruits are highly perishable, with over 25% post-harvest losses which further rise during storage. To prevent these losses, we attempted to convert papaya slices into intermediate moisture (IM) slices using a novel combination-technology which included a combination of osmotic removal of water by sugar syrup (60oB) containing various preservatives/additives, and, added use of chemicals such as CaCl2, citric acid, sodium metabisulphite or potassium metabisulphite (KMS), to reduce water activity. The osmosed slices were surface- dried and analyzed for physico-chemical characters and sensory attributes. Further, the product was stored upto six months at LT (Low Temperature) (4±1oC) and assessed for composition, stability and sensory attributes. Steam blanching of papaya slices, followed by osmosis in sugar solution of 60oB syrup containing a combination of preservatives, viz., citric acid 0.5%, CaCl2 0.5%, sodium metabisulphite 75ppm and KMS 350ppm, was superior as a treatment in terms of quality and stability of the product. These findings can help reduce post- harvest losses in papaya by providing a technology for preparing a ready-to-eat (RTE), nutrient rich intermediate-moisture product with good taste and flavour. Key words: Papaya, preservation, Intermediate Moisture Food (IMF), quality, RTE INTRODUCTION Papaya ranks among the top five nutritionally beneficial fruits (alongside guava, watermelon, grapefruit and kiwifruit) among the common fruits, based on nutritional score and percentage Recommended Daily Allowance (RDA). The fruits have appreciable amounts of protein (0.42g), folate (102.12 µg), fibre (4.69g), copper (0.12mg), potassium (502.32mg), magnesium (57.96mg), pantothenic acid (0.53mg); are high in antioxidants (85.57), total carotene (2,740mg), beta carotene (888mg) and vitamin C (168.08mg) per 100g fruit (Krishna et al, 2008). During storage, in addition to physical loss in fruit weight, considerable losses also occur in essential nutrients notably, vitamins, minerals and compromised fruit quality. Papaya is highly perishable and is difficult to preserve in the fresh form for long periods at ambient temperature and humidity. To prevent these losses, and to better utilize the fruit, processing and value-addition is very essential. Hurdle technology is a simple technology where a combination of preservation parameters are used at optimum levels to ensure maximum lethality of harmful microorganisms, so that damage to organoleptic properties of food is kept at a minimum. This technique was first introduced by Leistner (1992). The method is attractive, since, hurdles are used at low concentrations that do not adversely affect sensory quality of a product while maintaining stability and safety of the food item (Leistner and Gorris, 1995). The hurdle concept emphasizes complex interactions between temperature, water activity, pH, redox potential, etc. that are significant for microbial stability and safety of food (Leistner and Rodel, 1979). The present studies were made with an objective of preserving of ripe papaya slices using hurdle technology. MATERIAL AND METHODS Slice preparation and various hurdle treatments in papaya Papaya fruits were procured from the orchards of ICAR-Indian Institute of Horticultural Research (IIHR), and from the neighbouring farm, Hesaraghatta, Bengaluru. Semi-ripe fruits collected of uniform-size, shape and J. Hortl. Sci. Vol. 11(1):67-71, 2016 68 ripeness were weighed, washed, peeled and cut into uniform sized slices, followed by steam blanching for 2 min at 60°C. The slices were then dipped in 60°Brix sugar syrup containing different preservatives or additives in the ratio of 1:2 (slices:sugar) in various treatments and placed for osmosis for 12 hours at ambient temperature (25-30°C). At the end of the osmotic process, papaya slices were separated from the osmotic solution and weighed to assess the extent of water removed by osmosis. Surface-moisture removal of the product was done with the help of a cabinet tray drier at 55-60°C for 4 hours for achieving the desired level of moisture. Moisture content in all the samples was maintained in the range of IMF (Intermediate Moisture Food) by controlled drying in the cabinet tray drier. Various hurdle treatments imposed were: T1 (Control - Steeping in 60°B sugar syrup + Citric acid 0.5%); T2 (Steeping in 60°B + KMS 700ppm + Citric acid 0.5%); T3 (Steeping in 60°B + KMS 700ppm + CaCl2 0.5% + Citric acid 0.5%); T4 (Steeping in 60°B + CaCl2 0.5% + NaMS 150ppm + Citric acid 0.5%); T5 (Steam blanching + Steeping in 60°B + CaCl2 0.5% + NaMS 75ppm + KMS 350ppm + Citric acid 0.5%); T6 (Steam blanching + Steeping in 60°B + CaCl2 0.5% + Sodium benzoate 150ppm + Citric Acid 0.5%) and T7 (Steam blanching + Steeping in 60°B + CaCl2 0.5% + Sodium benzoate 150ppm + NaMS 150ppm + Citric acid 0.5%). Physical and biochemical analysis Papaya pulp (10g) was placed in a hot air oven overnight and subsequently weighed at hourly intervals until no further decrease in weight occurred. For calculating the moisture content, the formula mentioned below was applied: Moisture content (%) = (W1– W2/ W1) × 100 Where, W1= Initial weight, W2= Final weight Water activity was measured using a water activity meter (Model: Hygrolab, Rotronic). Total ascorbic acid content in papaya samples was estimated by the volumetric method (Ranganna, 1991), carotenoid content by spectrophotometer (Model: SP-3000 Plus) at 452nm, using β-carotene as the standard (Ranganna, 1991). Total antioxidant activity was measured by the FRAP method (Benzie and Strain, 1996) . Organoleptic evaluation Organoleptic evaluation was done initially (after drying the sample) and, subsequently, at three and six months of storage, by a panel of eight semi-skilled judges using a hedonic rating system of 100 points (with a maximum score of 30 each for colour and texture, and 40 for flavour) (Stone and Sidel, 1985). Statistical analysis was performed for Factorial Completely Randomized Design (FCRD). Analysis of variance (ANOVA) was conducted to arrive at significant differences between various factors. RESULTS AND DISCUSSION Chemical composition of the fresh papaya fruits used in the study is presented in Table 1. Ripe fruits had TSS 11.25°B, acidity 0.36% and ascorbic acid 40.2mg/100g, with total antioxidant content at 45.27mg/100g. These are in conformity with values obtained by Zaman et al (2006). Variation in physico-chemical and processing parameters can be attributed to varietal characteristic, seasonal conditions and level of fruit maturity. Similar observations were made by Goukh et al (2010), Othman (2009) and Campostrini & Glenn (2007) in papaya fruit. Moisture content in fresh papaya samples was fairly high (86.49%) and this can support microbial growth. Therefore, various combinations of different preservatives, osmotic removal of water and blanching treatment were used for reducing moisture content. Similar conclusion was drawn by Mishra et al (2015). Hurdle-processed papaya slices were analyzed for physico-chemical properties and sensory attributes at the initial stage prior to storage, and at six months of storage at (i) ambient and (ii) low temperature conditions. The best hurdle treatments were identified on the basis of retention of nutritional quality along with high organoleptic scores, apart from the product storage stability. At the initial stage (Table 2a), moisture content Table 1. Composition of fresh papaya fruits used in product preparation Composition Value Moisture (%) 86.49 Total Solids (TS) (%) 13.51 Total Soluble Solids (TSS ) (°B) 11.25 Total Titratable Acidity (%) 0.36 Ascorbic acid (mg/100g) 40.2 Reducing sugars (%) 2.21 Non-reducing sugars (%) 1.26 Total sugars (%) 3.47 Total carotenoids (mg/100g) 0.842 Total antioxidants (mg equivalent of ascorbic acid /100g) 45.27 Akanksha Shrivastava and Doreappa Gowda J. Hortl. Sci. Vol. 11(1):67-71, 2016 69 among different treatments was in the range of 35.19 to 45.96%, with a maximum in T6 (Steam blanching + Steeping in 60°B + CaCl2 0.5% + Sodium benzoate 150ppm + Citric acid 0.5%) and the minimum was recorded in T1 (Control - Steeping in 60°B sugar syrup + Citric acid 0.5%) (Table 2b). In treatment T1 (Control), 17.2% decrease was observed in moisture content, while the other treatments showed a range from 34.6 to 42.8% during the entire storage period. Decrease in titrable acidity during storage is attributable to acid hydrolysis of polysaccharides, and non- reducing sugars to similar components, where the acid is utilized for converting these sugars to hexose sugars or complexes in presence of metal ions (Sagar and Kumar, 2006). Reduced in acidity in the segments during storage was observed in osmo-dehydrated ripe pineapple slices preserved using hurdle process (Michael, 2012). At three months of storage, T6 (Steam blanching + Steeping in 60°B + CaCl2 0.5% + Sodium benzoate 150ppm + Citric acid 0.5%) showed maximum moisture content (47.94%) and lowest acidity (0.206%), which could be the reason of spoilage, as, effectiveness of the preservative (i.e., sodium benzoate) used in this treatment depends on the level of acidity. At the initial stage (i.e., at the onset of storage), ascorbic acid content among the different treatments imposed was in the range of 33.63 - 36.49mg/100g; But, at six months of storage, T1 showed a 21.27% decrease in ascorbic acid content compared to that at the initial stage. The reason for this could be thermal degradation of ascorbic acid during processing, and subsequent oxidation and light reaction (Brockmann et al, 1998). In comparison to other blanching treatments, T1 (Control) with no blanching treatment showed a drastic change (from 2.88mg/100g in the initial period, to 1.48 mg/ 100g at six months after storage) in carotenoid content. Storage for six months resulted in a gradual decline in total antioxidant content. However, decrease was higher in Control compared to that in the hurdle-processed papaya samples. Treatments involving preservatives (KMS, NaMS, etc.), registered more stability in total carotenoids and antioxidant content in comparison to Control, as, these preservatives prevent oxidation reaction that leads to deterioration of the respective constituents. Organoleptic evaluation Results of organoleptic evaluation are presented in Tables 3(a) & (b). Table 3. Sensory evaluation of hurdle-processed papaya slice product Treatment Colour Texture Flavour Overall (30 marks) (30 marks) (40 marks) acceptability (100 marks) (a) At the initial stage (on set of storage) T1 23.35 22.54 31.36 76.47 T2 23.18 22.56 30.25 75.96 T3 23.13 23.04 30.79 77.35 T4 23.16 23.31 28.60 75.08 T5 24.61 25.39 32.30 82.29 T6 23.69 24.27 28.57 76.56 T7 24.54 25.08 32.32 82.08 (b) At six months of storage T1 9.52 7.84 11.43 28.79 T2 19.38 17.02 22.47 58.86 T3 20.29 18.05 23.06 61.39 T4 20.68 20.02 23.56 64.62 T5 21.65 21.41 25.06 68.14 T6 - - - - T7 21.40 21.31 24.82 67.70 Table 2. Chemical composition of hurdle-processed papaya samples Treatment Titratable Moisture Ascorbic Total Total acidity content acid carotenoids antioxidants (%) (%) (mg/100g) (mg/100g) (mg equivalent of ascorbic acid /100g) (a) At the onset of storage T1 0.321 35.19 36.49 2.88 41.21 T2 0.315 36.46 35.7 2.19 38.63 T3 0.311 37.85 34.97 2.12 32.63 T4 0.315 36.82 35.07 2.13 37.18 T5 0.270 41.48 34.97 2.60 40.22 T6 0.315 45.96 33.63 2.12 33.86 T7 0.308 44.19 33.66 2.30 34.39 F-test * * * * * S.E±m 0.015 0.386 0.282 0.029 0.061 CD 0.0403 1.094 0.810 0.078 0.175 (P=0.05) *Significant at 5% Treatment Titratable Moisture Ascorbic Total Total acidity content acid carotenoids antioxidants (%) (%) (mg/100g) (mg/100g) (mg /100g) (b) At six months of storage T1 0.121 17.2 15.22 1.48 12.26 T2 0.262 34.6 34.51 3.06 26.96 T3 0.257 36.6 32.24 1.83 26.61 T4 0.259 34.9 30.44 1.90 27.05 T5 0.254 41.3 32.66 2.41 34.71 T6 - - - - - T7 0.260 42.8 31.13 2.23 27.87 F-test * * * * * S.E±m 0.008 0.421 0.264 0.032 0.052 CD 0.022 1.194 0.749 0.091 0.146 (P=0.05) *Significant at 5%; - : Product get spoiled before the end of 6 months Processing of papaya slices using hurdle technology J. Hortl. Sci. Vol. 11(1):67-71, 2016 70 Higher score for overall acceptability was recorded in low-temperature storage in treatment T5 (82.65) upto six months of storage (68.14). These results are in conformity with findings in osmo-dehydrated ripe pineapple slices using hurdle processes (Michel, 2012), in mango powder (Hymavathi and Vijaya 2005), in mango slices (Jose et al, 2008), in osmo-air dehydrated pineapple fruits (Rashmi et al, 2005), in sun-dried sapota (Vaghani and Chundawat, 1997), in minimally processed papaya by a combination of methods (Lopez et al, 1994), in high hydrostatic pressure-processed mango puree (Guerrero, 2006), in minimally processed Chinese cabbage (Ahn et al, 2005), and, in minimally processed fruits by combined methods (Alzamora et al, 1995). In conclusion, it is stated that for preparation of good quality hurdle-processed papaya slices with stability and higher organoleptic scores, a treatment combination consisting of steam blanching + steeping in 60°B sugar syrup + CaCl2 0.5% + NaMS 75ppm + KMS 350ppm + citric acid 0.5%), followed by a combination of steam blanching + steeping in 60°B sugar syrup + CaCl2 0.5% + sodium benzoate 150ppm + NaMs 150ppm + citric acid 0.5%) produced good results. In these hurdle combinations, even though a lower concentration of preservatives was used, inclusion of blanching in the methodology retained good colour, quality and stability in the product. Apart from preservation of slices, these combinations helped obtain fresh fruit like quality in the product as, moisture could be maintained in the range prescribed for IMF (Intermediate Moisture Foods). 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