The uniform, healthy, full-bearing mango trees (25 years old) growing under similar conditions from two commercial orchards, one in district Multan (30.15°N; 71.36°E) and other in district Lodhran (29.32°N, 71.38°E), Punjab province were selected for the experiments. Uniform sized, well-developed and healthy fruit were harvested at mature green stage from each tree. The fruit were treated with fungicide (Sportak), completely air dried (30 ± 2°C; 75-80% RH),packed in the corrugated fiber board boxes, and were shifted to Postharvest lab, Institute of Horticultural Sciences, University of Agriculture, Faisalabad (Punjab) by reefer van at 18°C. The study was comprised of two experiments.
Experiment 1: Comparative fruit quality of Mango cv. Samar Bahisht Chaunsa from two commercial orchards at ambient conditions (30±2°C; 50-60% RH) in relation to nutritional management.
The experiment was laid out according to the Completely Randomized Design (CRD), replicated thrice. Nine fruit were taken as replication unit. The fruit from two commercial orchards were kept under ambient conditions (30±2°C; 50-60% RH) for 6 days until fruits were ripened. The data were recorded regarding leaf mineral contents (at flowering, fruit set and harvest), soil mineral contents (at flowering, fruit set and harvest), fruit peel and pulp mineral contents (at harvest and ripening at each removal), physical characteristics of fruits (daily at shelf), organoleptic characteristics of fruits (on ripening) and biochemical characteristics of fruits (on ripening).
Experiment 2: Comparative fruit quality of Mango cv. Samar Bahisht Chaunsa from two commercial orchards in relation to nutritional management following cold storage (11°C; 80-85% RH).
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The experiment was laid out according to the Completely Randomized Design (CRD) with factorial arrangements, replicated thrice (9 fruit per replication). Fruit were stored at (11±1°C; 80-85% RH) for 4 and 6 weeks. Following cold storage, fruit were ripened at ambient temperature (30±2°C; 50-60% RH). The data were recorded regarding leaf mineral contents (at flowering, fruit set and harvest), soil mineral contents (at flowering, fruit set and harvest), fruit peel and pulp mineral contents (at harvest and ripening at each removal), physical characteristics of fruits (every 4th day during storage and daily at shelf), organoleptic characteristics of fruits (on ripening) and biochemical characteristics of fruits (on ripening).
The experimental parameters were determined by using three types of samples:
Leaf sampling was done at thee stages (at flowering, fruit set and harvest) to determine the status of different nutrients (Ca, Mg, N, P, K). The leaf samples comprised of 15-20 mature and healthy leaves were collected from the experimental trees at flowering, fruit setting and harvesting stage.
Soil samples were taken from the soil of the selected trees between the trunk and the outer edge of the tree canopy. One sample per tree was taken from the surface to a depth of 15-20 cm with a soil auger. Soil sampling was done at flowering, fruit setting and harvesting stage.
The mineral contents were determined in leaves of experimental trees and in the peel and pulp of the fruits to find out their relationship with fruit quality in mango cv. Samar Bahisht Chaunsa. For the mineral analysis of leaves, the leaf samples comprised of 15-20 mature and healthy leaves were collected from the experimental trees. First leaves were washed with tape water then water having 5% detergent in it and finally washed them with tape water again and rinsed with distilled water. Then the samples were air-dried. The dried leaves were ground to powder form. For peel and pulp mineral analysis, fruit were washed with detergent, rinsed with distilled water for 3-4 times and air dried at room temperature. Then peel and pulp samples were taken after peeling the fruit. These peel and pulp sample were already dried at 65°C, subjected to air drying under ambient conditions (25±1°C, 75-80% RH) for the period that no moisture could be found in the samples. Then these samples were subjected to oven drying at 65°C for 24-48 hours, grinded and the powder (about 100 g) was saved in plastic bottles for the determination of N, P K, Ca and Mg.
Digestion of the samples for determination of Ca, Mg, P and K
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One gram of oven dried leaf material was transferred to a 100 ml beaker and 10 ml of concentrate HNO3 was added to it. It was allowed to stand till initial reaction was completed. It was covered with watch glass and low heat was provided until the solid material disappeared. After cooling, to each sample 5 ml of HClO4 was added and then again the sample was heated gently at first and then vigorously until a clear colorless solution resulted. When the volume reduced to 1 ml, it was cooled and transferred through filter paper to a 50 ml volumetric flask and the volume was made up to mark. This filtrate was stored in plastic bottles for further analysis to estimate Ca, Mg, P and K (Chapman and Parker, 1961).
The Ca contents in leaves, peel and pulp were determined by using flame photometer (Flame photometer 410, Sherwood, Nottingham, England) as outlined by Sobkowska and Basinska (1975). The standard curve (Fig. 3.1) was obtained by using standard solutions of different concentrations. For the determination of Ca, the already prepared filtrate was fed into flame photometer at optimum sensitivity level and reading was recorded. The quantity of the element was found in ppm by comparing the emission (at 624 nm wavelength) of flame photometer with that of standard curve which was then converted to percentage by using the formula:
Mg was determined by atomic absorption spectrometry (Analyst-100, Parkin Elmer, Waltham, U.S.A.) at 318.4 nm wave length (di-nitrogen oxide-acetylene flame) as described by Vargas et al. (1994). The filtrate was fed to the apparatus and magnesium contents were recorded in mg/litre (ppm).
The P was determined according to the method described by Chapman and Parker (1961). The standard solutions ranging from 0.5 to 5.0 ppm were made at a continuous difference of 0.5 ppm. For making standard solution, colour was developed by adding each of 5% 1:6 H2SO4, 5% ammonium molybdate and 0.25% ammonium vanadate. The standard curve (Fig. 3.2) was obtained by using potassium hydrogen phosphate instead of samples. Then the samples were fed to spectrophotometer (Evolution 300, Thermo Electron Corporation, Waltham, USA) at a wavelength of 420 nm and transmittance was noted which was compared with that of standard curve to find out the quantity of the element in ppm.
The percentage of phosphorus in the samples was calculated by using following formula:
Potassium was also determined according to the method described earlier by Chapman and Parker (1961). Potassium concentration was determined by the flame photometer taking 5 ml of wet digestion material. Standard curve (Fig 3.3) was obtained by using potassium chloride.
The quantity of the element was found in ppm by comparing the emission of flame photometer with that of standard curve which was then converted to percentage by using the formula as under:
For the determination of N, the procedure described by Chapman and Parker (1961) was used which included digesting the plant material (1 g) with 30 ml concentrated H2SO4 and 5 g digestion mixture (FeSO4: K2SO4: CuSO4 = 1:10:0.5). On cooling, the contents were then transferred to 250 ml volumetric flask and volume was made up to the mark. Then 5 ml of aliquot from this prepared material was distilled in micro-kjeldhal apparatus using 40% sodium hydroxide, 4% boric acid and mixed indicator of methyl red and bromo creso green (BCG). This distillate was titrated against N/10 H2SO4 till the original colour of methyl red was restored. From the quantity of acid used in titration, the percentage of N was calculated by using the following formula:
A = Quantity of acid used
B = Blank reading
0.0014 = Constant (which is equal to grams of nitrogen present in 1
ml of N/10 sulfuric acid)
Blank reading was taken for estimating the actual percentage of N in sample. All the procedure of digestion, distillation and titration was same for blank but it was done without leaf sample.
Following parameters were included in Physical analysis.
One fruit from each replication was randomly selected and placed into a sealed plastic jars for 1 h. Respiration rate was determined by measuring CO2 production using a CO2 analyzer (Vaisala MI 70, Vaisala Inc., Helsinki, Finland) and expressed as mg CO2 kg‾¹ h‾¹.
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Skin colour development was scored manually according to the following scale used by Malik and Singh (2005), where 1 = 100% Green, 0% Yellow; 2 = 75% Green, 25% Yellow; 3 = 50% Green, 50% Yellow; 4 = 25% Green, 75% Yellow; 5 = 0% Green, 100% Yellow.
Textural softness was also scored manually using the scale used by Malik and Singh (2005) where 1 = Hard, 2 = Sprung, 3 = Slightly soft, 4 = Eating soft, 5 = Over ripe
Fruit weight Loss
Fruit weight loss was calculated on the basis of initial weight (before storage) and final weight (at the end of storage period).
Skin shriveling of fruit were scored manually using the following scale described by Malik and Singh (2005), Where 1 = Nill, 2 = <10%, 3 = 10-25%, 4 = 25-50%, 5 = 50%
Injuries were assessed manually by scale used by Akhtar and Alam (2002) where 1= Nill, 2 = <5%, 3 = 5-10%, 4 = 10-25%, 5 = >25%.
Extent of internal breakdown
Extent of internal breakdown was assessed by scale already described by Raymond et al. (1998). The symptoms were visually rated as early, intermediate, or advanced. For Stem end cavity (SEC) rating of the symptoms was based on the presence and/or the size of the cavity at the proximal end of the fruit. Early symptoms of SEC were those in which no visible cavity was formed at the peduncular extension of the fruit. Symptoms of SEC were considered as intermediate when a 0.1-0.5 cm diameter cavity was visible at the proximal end of the fruit, accompanied by a necrotic area around that cavity. Symptoms were ranked as advanced when the cavity was larger than 0.5 cm diameter and was accompanied by deterioration of the fruit mesocarp around the stone.
For jelly seed and soft nose, early symptoms were characterized by a pronounced yellow colouration of the mesocarp around the stone (jelly seed) or at the distal end or at the sinus of the fruit (soft nose), indicating that the senescence process had been initiated. Intermediate symptoms were those in which the disordered mesocarp had an orange colour, whereas the surrounding tissue (exterior of the mesocarp) was still white or pale yellow, indicating that the exterior of the mesocarp was not ripe. Symptoms of jelly seed and soft nose were considered as advanced if the mesocarp showed advanced deterioration and/or discoloration.
Biochemical analysis of fruit pulp was done to study the different components of fruit quality i.e. solubel solids content (SSC), titratable acidity (TA), ascorbic acid and sugars (total sugars, reducing and non reducing sugars). For the determination of biochemical components, all the fruits of each replication were peeled off with a stainless steel knife. The juice was extracted from each sample and homogenized to study the biochemical parameters.
A)Solubel solids content (SSC)
Digital Refractometer (RX 5000, Atago, Japan) was used for the determination of SSC. A drop of juice was placed on the prism of refractometer, the lid was closed and SSC (°Brix) was noted directly from the digital scale of refractometer at room temperature.
C) Titratable Acidity (TA)
For the determination of TA, method given by Hortwitz (1960) was used. Ten ml fruit juice was taken from each sample in a beaker, diluted (1:4) with distilled water and titrated against N/10 NaOH solution by adding 2-3 drops of phenolphthalein (C20H14O4) as an indicator. The results were expressed as % citric acid. Following formula was used for the determination of total TA.
SSC: TA ratio
It is calculated by given formula
B) Ascorbic acid
For the estimation of ascorbic acid in the pulp, the method described by Ruck (1969) was used. For this purpose extracted juice from each sample was filtered through Whatman® filter paper. Ten ml of filtered aliquot was taken in 100 ml round bottom flask, then volume was made up to the mark by adding 0.4% oxalic acid. Out of 100 ml aliquot, 5 ml was taken in a beaker and titrated against freshly prepared dye (2, 6-dichlorophenol indophenol) till light pink end point appeared which persisted for 10-15 seconds. For the preparation of dye, 42 mg baking soda (NaHCO3) and 52 mg 2, 6-dichlorophenol indophenol were taken in a 200 ml volumetric flask and volume was made up to the mark by adding distilled water. Ascorbic acid was calculated by using following formula:
D1 = ml dye used in titration of aliquot
D = ml of dye used in titration of 1ml standard ascorbic acid solution prepared
by adding 1ml of 0.1% ascorbic acid + 1.5 ml of 0.4% oxalic acid
A = ml of juice used
V = volume of aliquot made by addition of 0.4% oxalic acid
B = ml of aliquot used for titration
Method described by Hortwitz (1960) was used to estimate the pulp sugars. Following solutions were prepared for determination of reducing and non reducing sugars:
i) Juice filtrate
ii) Invert sugar solution
iii) Fehling's solution
i) Preparation of juice filtrate
Ten ml of juice was taken in 250 ml flask in which 100 ml distilled water, 25 ml lead sub acetate solution (430 g of lead acetate/L) and 10 ml of 20% potassium oxalate solution were added. The volume was made up to the mark using distilled water. The solution was filtered and then the filtrate was used for the estimation of reducing and non reducing sugars.
ii) Preparation of standard invert sugar solution
As neutral or alkaline solutions of sugar should not be kept for longer time and should be prepared when required (Ronald and Sawyer, 1981); therefore standard sugar solution was freshly prepared. For the preparation of standard invert sugar solution, 23.75 g pure sucrose (analytical grade) was dissolved in about 120 ml water in a 250 ml volumetric flask, 9 ml concentrated HCl was added and the solution was kept for 8 days at room temperature for inversion of the sugar contents. On completion of inversion, volume was made up to the mark with distilled water (When inversion is complete, rotation in a 200 mm tube is 11.80°± 0.05 °S). Two hundred ml of the solution was transferred into a 2 L volumetric flask, 200 ml water was added and 71.4 ml of sodium hydroxide solution (40 g/L) containing 4 g benzoic acid was added along with continuous shaking. Then 1 L of distilled water was added, mixed, pH was adjusted at 3 and volume was made up to the mark. In this way, a stable 1% m/v stock solution of invert sugars was obtained which was diluted to make 0.25% standard solution and neutralized by using 1N NaOH.
iii) Preparation of fehling's solution
Fehling's solution deteriorates slowly so fresh fehling's solution was made sufficient to meet immediate requirements only. For the preparation of fehling's solution, equal quantities of solution A and B were transferred to a dry flask and mixed thoroughly. Fehling's solution A and B were prepared using following procedure.
Solution A: Copper sulphate pentahydrate (69.3 g) was dissolved in water and Volume was made up to 1 L.
Solution B: Sodium hydroxide (100 g) and 345 g sodium potassium tartrate (345 g; KNaC4O6.4H2O) were dissolved in water and volume was made up to 1 L.
The filtrate was taken in burette and titrated against 10 ml fehling's solution using 2-3 drops of methylene blue trihydrate (C16H18ClN3S. 3H2O) as an indicator with continuous boiling till brick red end point appeared. Reducing sugars were calculated by using following formula:
Reducing sugars (%) = 6.25 x (A/B)
A = ml of standard sugar solution used against 10 ml Fehling's solution
B = ml of sample aliquot used against 10 ml Fehling's solution
For estimation of total sugars, 25 ml of aliquot already prepared for reducing sugars was taken in a 100 ml volumetric flask in which 20 ml distilled water and 5 ml concentrated HCl was added and solution was kept for 24-48 hours for converting the non-reducing sugars into reducing sugars. Then it was neutralized with 50% concentrated NaOH solution and volume was made up to the mark (100 ml) with distilled water. The prepared solution was taken in burette and titrated against continuous boiling Fehling's solution (10 ml) to brick red end point using 2-3 drops of methylene blue trihydrate (C16H18ClN3S. 3H2O) as an indicator. Total sugars were calculated by using formula:
Total sugars (%) = 25 x (A/C)
A = ml of standard sugar solution used against 10 ml Fehling's solution
C = ml of sample aliquot used against 10 ml Fehling's solution
For the estimation of non-reducing sugars, following formula was used:
Non reducing sugars (%) = 0.95 x (% Total sugars - % Reducing sugars)
Total carotenoids were estimated by the method given by Lalel et al. (2003). One gram of homogenized ripe fruit pulp was grounded with 0.05 g of magnesium carbonate in silica sand using glass mortar and pestle and centrifuged at 5000 rpm. Two extractions were made using 20 mL of acetone: n-hexane (75:60, v/v) mixture per sample. The extract was collected in separating funnel and washed with a 40 mL of 10% NaCl and 2 x 40 mL of distilled water to avoid acetone. The hexane extract was determined for its absorbance at 436 nm using spectrophotometer (Evolution 300, Thermo Electron Corporation, Waltham, USA) and was expressed as μg.g-1 of β-carotene equivalent from a standard curve of β-carotene.
The fruits were evaluated at fully ripe stage for organoleptic acceptability on the basis of taste, flavour, pulp colour, texture and aroma using the 9 point hedonic scale described by Peryam and Pilgrim (1957). Nine judges were called in the panel for organoleptic evaluation of treatments.
Hedonic scale (Peryam and Pilgrim, 1957)
Product: ______________ Variety: _________________ Date: ______________
Name of Judge: _________________________ Signature: __________________
Instructions: (Please read the instructions carefully before filling the blanks)
This is an organoleptic evaluation form for different mango treatments.
Please follow the numerical system for scoring the samples.
Dislike extremely……………..1 Like slightly……………6
Dislike very much…………….2 Like moderately………7
Dislike moderately……………3 Like very much………..8
Dislike slightly…………………4 Like extremely…………9
Neither like nor dislike………5
Please do not disturb the sequence of the samples provided.
Please wash the tongue before testing next sample, with the water provided.
The collected data was statistically analyzed using the computer software MSTAT- C (Russel and Eisensmith, 1983). Analysis of variance techniques was employed to test the overall significance of the data, while the Least Significant Difference (LSD) test (P ≤ 0.05) was used to compare the differences among treatment means (Steel et al., 1997).