الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Nowadays, awareness of consuming healthy food for a healthy life is becoming more and more prevalent. In this respect, fruits and vegetables serve as important sources of a wide variety of vitamins, minerals and dietary fibers essential for human nutrition. They are recommended as important sources of health-promoting phytochemical compounds that may provide desirable health benefits beyond basic nutrition to reduce the risk of chronic diseases.
Papaya fruits are delicious and healthy due to their high content of vitamins, minerals, proteolytic enzymes and many other biological active compounds. They are commonly known for their nutritional, medicinal and neutraceutical properties worldwide.
The lack of storage facility and perishable nature of papaya fruits can result in severe postharvest losses of this nutritious fruit. Processing of papaya fruits into functional foods not only extends their shelf life but also preserves the nutritive value of the fruit.
This investigation was designed to evaluate the physicochemical and antioxidant properties of papaya fruits, improve the storage stability and keeping quality of fresh papaya puree (stored at ambient and refrigeration temperatures) by using pasteurization and/or chemical preservatives, add value to papaya fruits by turning them into delicious and healthy nutritious juices, jams, fruit powder and leathers, and to improve the storage stability and keeping quality of papaya juices (stored under refrigeration conditions) by using pasteurization and/or chemical preservatives.
The study consisted of three chapters. The first one deals with the physicochemical and antioxidant properties of fresh papaya fruits, and improving the storage stability and keeping quality of papaya puree stored at ambient and refrigeration temperatures, the second deals with improving the storage stability and keeping quality of papaya juices stored under refrigeration conditions, and the third deals with adding value to papaya fruits by turning them into delicious and healthy nutritious jams, fruit powder and leathers.
The obtained data could be summarized as follows:
The weight of whole papaya fruit ranged from 648 to 1300g. The pulp accounts about 83.21% from the whole fruit weight. The peels account about 11.21% and the seeds account about 5.57% from the whole fruit weight.
Fresh papaya fruits contained 87.53% moisture, 12.47% total solids, 11.50% total soluble solids (TSS as °Brix), 0.59% protein, 0.57% ash, 0.25% crude fat, 1.54% fibers, 7.64% total soluble sugars, 3.41% total reducing sugars, 4.23% total non-reducing sugars and 9.52% nitrogen free extract (NFE) as such basis.
The energy value of fresh papaya fruits was found to be 42.69 Kcal/100g (as such basis).
Fresh papaya fruits provide significant amounts of ascorbic acid (78.63 mg/100g fresh weight), total carotenoids (2.72 mg/100g fresh weight), total phenols (48.19 mg GAE/100g fresh weight) and total flavonoids (30.40 mg QE/100g fresh weight). The antioxidant activity (DPPH radical scavenging activity) was found to be 67.55%.
The pH and titratable acidity values of fresh papaya fruits were 5.22 and 0.18% (as citric acid), respectively.
The color parameters of fresh papaya fruits were found to be 43.40 for lightness (L), 20.05 for redness (a), 45.69 for yellowness (b), 66.31 for hue angle and 49.90 for chroma.
During storage of papaya puree, the values of moisture, pH, ascorbic acid, total carotenoids and total phenolics significantly decreased as the storage time increased. While the total soluble solids and titratable acidity values significantly increased. Despite this decrease, all preserved papaya puree samples remained satisfactory sources of ascorbic acid, total carotenoids and phenolic compounds over the storage period.
The combined action of the thermal treatment (pasteurization at ” " ~ " ” 65ºC/20 min) and chemical preservatives (PS, KMS and citric acid) on the quality and shelf stability of fresh papaya puree stored at ambient (25ºC) and refrigeration (4ºC) temperatures was better than using either of them alone.
Potassium sorbate (PS) and potassium metabisulphite (KMS) should be used in combination as chemical preservatives for papaya puree. PS is antifungal and KMS is antibacterial and antioxidant. They can increase the stability and prolong the shelf life of fresh papaya puree at ambient and refrigeration conditions, when added according to the recommended level of food safety.
The total bacterial counts slowly increased throughout the storage period, but still lower than the critical microbial limit for fruit purees. They were less than 102 cfu/g for all preserved papaya puree samples. This indicated that the applied preservation treatments and storage conditions were efficient and post contamination did not occurred.
The preserved papaya puree (T2 – T5 – T7) stored under refrigeration conditions achieved a shelf life up to 9 months below the microbial load limit (106 cfu/ml). The rest of preserved papaya puree (T1 – T3 – T4 – T6) achieved a shelf life up to 6 – 8 months below the microbial load limit (106 cfu/ml).
Yeasts and moulds were absent (Nil) during refrigerated storage for all preserved papaya puree samples. Consequently, no potential microbial risk was associated with the storage conditions.
The preservation treatments and storage intervals did not affect the sensory quality significantly up to the 4th month of storage for all papaya puree samples. Then the sensory assessment values began to decrease. This decrease was significantly in some puree samples, but the values remained above the acceptable level.
All preserved papaya puree samples had excellent sensory assessment values (85 – 95%) in terms of color, flavor, texture and overall quality. These values remained above the acceptable level up to the end of storage (9 months) for most puree samples.
As a conclusion, the preserved papaya puree (T2 – T5 – T7) had acceptable quality attributes, desired nutritional value, improved shelf stability and microbiological safety for up to 9 months.
The combined action of the thermal treatment (pasteurization at ” " ~ " ” 65ºC/20 min) and chemical preservatives (0.05% potassium sorbate + 0.05% potassium metabisulphite) on the quality and shelf stability of papaya juices was better than using either of them alone.
All preservation treatments and storage intervals both had a significant effect on the moisture content values for most juice samples. The data indicated a gradual inecrease in moisture content up to the third month of storage for all juice samples (except the formula contined 75% papaya + 25% orange). Then there was a gradual decrease up to the end of storage (6 months) for all juice samples.
The storage intervals had a significant effect on the TSS values for all juice samples. While in most juice samples, the preservation treatments did not affect the TSS values significantly. The data indicated a gradual increase in TSS values during storage for all juice samples.
The pH values were significantly decreased during storage for all juice samples. The pH values of 100% papaya juice were significantly decreased from 4.71, 4.72 and 4.73 at zero time and reached 3.61, 3.96 and 4.30 for T1 (pasteurization at ” " ~ " ” 65ºC/20 min), T2 (0.05% PS + 0.05% KMS) and T3 (pasteurization at ” " ~ " ” 65ºC/20 min + 0.05% PS + 0.05% KMS), respectively at the end of the storage period. The highest decrease percent was observed in T1 (23.35%) followed by T2 (16.10%), while T3 recorded the lowest decrease percent (9.09%).
The storage intervals had a significant effect on the titratable acidity values for all juice samples. While in most samples, the preservation treatments did not affect the titratable acidity significantly.
All preservation treatments and storage intervals both had a significant effect on ascorbic acid values for all juice samples. The data indicated a gradual decrease in ascorbic acid values during storage for all juice samples. The highest decrease percent was observed in T1 (30.45%) followed by T2 (15.32%), while T3 recorded the lowest decrease percent (15.21%). Despite this decrease, all juice samples remained satisfactory sources of ascorbic acid over the storage period of six months.
All preservation treatments and storage intervals both had a significant effect on the total phenols values for all juice samples. The data indicated a gradual decrease in total phenols values during storage for all juice samples. The highest decrease percent was observed in T1 (14.23%) followed by T2 (11.08%), while T3 recorded the lowest decrease percent (9.79%). Despite this decrease, all juice samples remained satisfactory sources of phenolic compounds over the storage period of six months.
The total bacterial counts slowly increased throughout the storage period, but still lower than the critical microbial limit for fruit juices. They were less than 102 cfu/g for all preserved juice samples. This indicated that the applied preservation treatments and storage conditions were efficient and post contamination did not occurred. The preserved papaya juice samples achieved a shelf life up to 6 months below the microbial load limit (106 cfu/ml).
Yeasts and moulds were absent during refrigerated storage for all preserved juice samples. Consequently, no potential microbial risk was associated with the storage conditions.
The preservation treatments and storage intervals did not affect the sensory quality significantly up to the third month of storage for all juice samples. Then the sensory assessment values began to decrease. This decrease was significantly in some juice samples, but the values remained above the acceptable level.
All papaya juice blends (100% papaya, 75% papaya + 25% orange, 75% papaya + 25% strawberry, 75% papaya + 25% mango and 75% papaya + 25% guava) had excellent sensory assessment values in terms of color, flavor, texture and overall quality. These values remained above the acceptable level up to the end of storage (6 months under refrigerated storage) for all juice samples.
As a conclusion, the papaya fruits could be successfully used singly or in combination with orange, strawberry, mango and guava to obtain delicious and healthy nutritious juices. The modified papaya juices (100% papaya, 75% papaya + 25% orange, 75% papaya + 25% strawberry, 75% papaya + 25% mango and 75% papaya + 25% guava) had acceptable quality attributes, improved nutritional value, improved shelf stability and microbiological safety for up to 6 months under refrigeration conditions.
All papaya fruit jams (100% papaya, 75% papaya + 25% orange, 75% papaya + 25% strawberry, 75% papaya + 25% mango and 75% papaya + 25% guava) recorded nearly the same sensory quality in terms of color (94 – 95%), flavor (91 – 93%), texture (94 – 95%) and overall quality (91 – 93%). They had excellent sensory assessment values in terms of color, flavor, texture and overall quality.
The drying process caused a sharp decrease in moisture content of papaya fruits (from 87.53 to 6.82%) and consequently led to an increase in the dry matter content (from 12.47 to 93.18%).
The nutritional properties of papaya fruit powder are greater than the fresh fruits because all the nutrients are concentrated due to the drying process.
The papaya fruit powder contained 6.82% moisture, 93.18% total solids, 4.30% protein, 4.24% ash, 1.84% crude fat, 11.46% fibers, 55.13% total soluble sugars, 24.42% total reducing sugars, 30.71% total non-reducing sugars and 71.34% nitrogen free extract (NFE) as such basis.
The energy value of papaya fruit powder was found to be 319.12 Kcal/100g (as such basis).
Papaya fruit powder provides significant amounts of ascorbic acid (494.25 mg/100g), total carotenoids (19.87 mg/100g), total phenols (337.46 mg GAE/100g) and total flavonoids (220.40 mg QE/100g). The antioxidant activity (DPPH radical scavenging activity) was found to be 65.70%.
The dried papaya fruits are considered as an excellent source of phytochemicals, especially vitamin C, carotenoids and polyphenols. They are exerting strong antioxidant properties.
The pH and titratable acidity values of papaya fruit powder were 5.24 and 0.19% (as citric acid), respectively.
The color parameters of papaya fruit powder were found to be 59.64 for lightness (L), 19.87 for redness (a), 45.75 for yellowness (b), 16.24 for ΔE, 66.52 for hue angle and 49.88 for chroma. These data indicated that papaya fruit powder revealed optimum color values. The drying process did not affect the color characteristics of papaya fruits.
All papaya fruit leathers (100% papaya, 75% papaya + 25% orange, 75% papaya + 25% strawberry, 75% papaya + 25% mango and 75% papaya + 25% guava) revealed optimum quality attributes in terms of color (93 – 95%), flavor (90 – 92%), texture (90 – 91%) and overall quality (90 – 91%).
In the light of the obtained results, it could be concluded that the papaya fruits (fresh or dried) are considered as an excellent source of phytochemicals (beneficial to human health), especially vitamin C, carotenoids and polyphenols. They are exerting strong antioxidant properties. Papaya fruits could be successfully used singly or in combination with orange, strawberry, mango and guava to obtain delicious and healthy nutritious juices, jams and fruit leathers. The combined action of the thermal treatment (pasteurization at ” " ~ " ” 65ºC/20 min) and chemical preservatives (PS, KMS and citric acid) on the quality and storage stability of fresh papaya puree or papaya juices stored under refrigeration conditions was better than using either of them alone. Potassium sorbate (PS) and potassium metabisulphite (KMS) should be used in combination as chemical preservatives for papaya puree or papaya juices.