الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
SUMMARY AND CONCLUSION
Fruits and vegetables have health benefits for consumers, due to their content of fiber, vitamins and antioxidant compounds. Meanwhile, the antioxidants can be occurring for many changes during harvesting, preparation and storage. So, the drying is the most appropriate processing method for producing of shelf life stable food products. Also, dried fruits can be stored and transported at a relatively low cost. Where, the hydration is the removal of water to optimum level to greatly minimize the microbial spoilage and deterioration of the reactions.
The objectives of this study were following main points
1- Studying the effect of different drying methods of cactus pear, papaya, grapes and figs on proximate chemical composition and determination the activity of peroxidase, polyphenol oxidase, pectin methyl esterase and protease initially after processing and during storage up to 6 months at 4±1℃.
2- Studying the effect of pasteurization of guava and papaya juices in the presence of 0.5%citric acid and 0.5% ascorbic acid on TSS, pH, total phenolics, ascorbic acid, and total carotenoids contents. The activity of peroxidase, polyphenol oxidase, pectin methyl esterase and protease were also studied during storage for 6 months at 4±1℃ in guava and papaya juices.
3- Investigation of the quality parameters of prepared dried samples and tested juices.
Part 1: Quality properties of selected fruits dried by different methods in relation to the enzyme activity
1-The proximate chemical composition of fresh and dried cactus pear, papaya, grapes and figs
The percentages of moisture were 86.50 and 84.20% for fresh papaya and cactus pear. However, the percentage of moisture were ranged from 9.00 to 11.00 and 15.00 to 16.60 % for oven dried and osmo- freeze drying of papaya and cactus pear, respectively
The crude protein was 0.95 and 1.03 % for fresh papaya and cactus pear and it was increased by using different drying methods. The protein content was higher in papaya dried by oven than other methods of drying. On the other hand, the crud fiber was 2.70% in fresh cactus pear and 1.60%in fresh papaya. The oven dried of both papaya and cactus pear recorded the highest percentage of crud fiber followed by osmo-freeze drying and osmotic dehydration respectively. The total carbohydrates of fresh papaya were 9.30% and increased as a result of using different drying methods which was recorded 68.55 and 60.15% for papaya and cactus pear dried by osmo- freeze drying. The percentages of moisture were 78.30 and 81.05% for freshly figs and grapes. The osmo- freeze drying grapes and figs had the highest percentage of total carbohydrates which was 76.45 and 73.93%. It could be noticed that, the ash was increased by drying where it was 1.80%and 0.62% for fresh figs and grapes and it was 4.5 3.41,3.21 % for oven, osmotic dehydration and osmo- freeze drying figs respectively.
2-Browning index for dried fruits
Results indicated that, the highest browning index as (O.D/ 420nm) for fresh fruits were 0.279, 0.230, 0.135 and 0.115 for fresh figs, cactus pear, grapes and papaya, respectively. The browning index was increased in all investigated samples by drying where the highest browning index was noticed for oven dried of all tested fruits followed by osmotic dehydration and osmo- freeze drying respectively. Therefore, the selected drying method for dehydration of tested fruits was correlated well with the increasing of browning index and it was considered as a good parameter and indication for the type of drying methods which used for dried fruits.
3-Activity of peroxidase, polyphenol oxidase, pectin methylesterase and protease for dried fruits samples
The activity of peroxidase in fresh cactus pear was 11.00*10-3 O.D/ min while, it was 0.71, 0.65 and 0.60 *10-3 O.D/ min immediately after processing for oven drying, osmotic dehydration and osmo-freeze drying respectively. Also results indicated that peroxidase activity was decreased gradually for cactus pear dried by different methods and also by extending the shelf life up to 6 months of storage at 4±1℃.
Peroxidase activity was 97.43*10-3 O.D/ min in fresh papaya and decreased by different values as a results of using drying methods recording 6.50, 2.35 and 1.29*10-3 O.D/ min for papaya dried by oven, osmotic and osmo- freeze drying respectively.
There was a gradually decrement in the residual activity of peroxidase for different drying methods of dried cactus pear and papaya by increasing the storage time up to 6 months at 4±1℃. Where, oven dried papaya recorded the highest residual activity of peroxidase (0.99%) followed by osmotic dehydration (0.46%) and osmo-freeze drying (0.40%).
The peroxidase activity in fresh grapes was 125.49 *10-3 O.D/ min. Fresh grapes lost its activity according to the used drying methods. Where, the activity of peroxidase in grapes was 9.31, 5.08 and 4.26*10-3 O.D/ min initially after drying by oven, osmotic and osmo- freeze drying respectively.
Results also indicate that, the peroxidase activity of grapes for osmo- freeze drying had the lowest activity immediately after drying and through storage period followed by osmotic dehydration and oven dried grapes, respectively. Forinstance, the treatments before the selected drying methods used for dried grapes and storage period are correlated well with the changes of peroxidase activity
Osmo-freeze drying was most effective for reducing the peroxidase activity for grapes and figs followed by osmotic and oven drying respectively. A gradually decreasing was noticed in the residual activity of peroxidase for figs and grapes dried with different methods by extending the storage time up to 6 months at 4±1℃. Where, oven dried figs recorded the highest residual activity of peroxidase (7.83%) followed by osmotic dehydration (4.97%) and osmo-freeze drying (3.85%)
The activity of polyphenol oxidase in fresh cactus pear was 5.73*10-3 O.D/ min while it was 0.266, 0.154 and 0.133 *10-3 O.D/ min immediately after drying of cactus pear by oven, osmotic and osmo-freeze drying, respectively.
Polyphenol oxidase activity was 68.00*10-3 O.D/ min in fresh papaya and decreased with various values as a results of tested drying methods which was recorded 2.3,1.17 and 0.70*10-3 O.D/ min for papaya dried by oven ,osmotic and osmo- freeze drying respectively. Since, the highest reduction was noticed for osmo-freeze drying of cactus pear and papaya followed by osmotic dehydration and oven drying respectively
The residual activity of polyphenol oxidase in papaya and cactus pear was decreased gradually by increasing the storage period up to 6 months at 4±1℃. The residual activity was 3.38, 1.72 and 1.02% for papaya dried by oven, osmotic and osmo-freeze drying initially after dehydration respectively. On the other hand, the longer of the storage period up to 6 months at 4±1℃, the higher the residual activity of PPO was in dried papaya by oven, osmotic and osmo-freeze drying.
The decremental of polyphenol oxidase activity in grapes was noticed by increasing the storage period for all dried samples up to 6 months of storage at 4±1℃. Meanwhile, the polyphenol oxidase recorded the lowest activity after 6 months of storage for dried grapes by oven, osmotic and osmo- freezing which were 0.51, 0.23 and 0.15 *10-3 O.D/ min at the end of storage (6 months) at 4±1℃.
Polyphenol oxidase activity in figs dried by osmo- freeze drying recorded the lowest activity (0.50 *10-3 O.D/ min) followed by osmotic dehydration (0.55*10-3 O.D/ min) and oven drying (0.77*10-3 O.D/ min) after 6 months of storage at 4±1℃ respectively.
Results showed that, the oven dried papaya recorded the highest residual activity of pectin methylesterase than those dried by osmotic and osmo¬-freeze drying. The osmo-freeze dried papaya had recorded the lowest residual PME (0.44%) followed by osmotic dehydration (0.51%) and oven drying (0.93%) after 4 months of storage at 4±1℃, respectively.
Oven dried of grapes and figs were recorded a higher pectin methylesterase activity than those dried by osmotic and osmo¬-freeze drying. While, the residual activity of pectin methylesterase for osmo-freeze drying grapes and figs were 1.37 and 1.02% followed by osmotic dehydration 1.61 and 1.14% and oven drying 1.76% and 1.41% respectively. But, The pectin methylesterase activity of fresh figs was 59.00 *10-3 O.D/ min and 0.83, 0.67 and 0.60 *10-3 O.D/ min directly after drying by oven, osmotic and osmo-freeze drying of figs. Also, it could be noticed that, the pectin methylesterase for figs dried by osmo- freeze drying recorded the lowest activity of pectin methylesterase (0.15 *10-3 O.D/ min) followed by osmotic dehydration (0.19*10-3 O.D/ min )and oven drying(0.25*10-3 O.D/ min) after 6 months of storage at 4±1℃ respectively. Meanwhile, the highest residual activity of protease was shown in oven dried papaya (8.73%) followed by osmotic (7.46%) and osmo–freeze drying of papaya (7.15%) immediately after dehydration.
4-Quality parameters of sensory evaluation for dried fruit samples
The osmotic dehydration cactus pear recorded 6.5, 7.0, 6.7, 6.8 and 7.0 for color, taste, aroma, texture and overall acceptability. While the correspondence values were 7.2, 7.0, 6.8,6.7 and 7.5 for osmo-freeze dried cactus pear.
It is clear that, the osmo-freeze dried papaya had the highest scores for overall acceptability, taste and color followed by osmotic and oven drying. Also, the less value of quality attributes for color and overall acceptability were noticed for papaya dried by oven. Our results indicated that, osmo-freeze dried grapes had the best score of color, taste, aroma, texture and overall acceptability after processing directly which were 8.6, 8.4, 8.5, 8.5 and 8.3 since, the osmotic dehydration grapes recorded 8.1,8.0, 8.2, 7.3, and 8.2, while oven dried grapes 6.6, 7.2, 7.7, 7.2 and 7.3. Forinstance, the obtained results indicated that both osmotic dehydration and osmo-freeze drying methods were improved the sensory attributes of dried figs compared with traditional oven drying figs.
The various sensory quality attributes including color, taste, aroma, texture and overall acceptability of oven drying, osmotic dehydration and osmo-freeze dried grapes were evaluated. The osmotic dehydration figs were (7.6, 7.6, 7.7, 8.2 and 7.7) and oven dried figs recorded (6.6, 6.8, 7.3, 6.6 and 6.8) for all tested sensory attributes (color, taste, aroma, texture and overall acceptability) both of osmotic dehydration and osmo-freeze drying methods enhanced sensory attributes of dried fig compared to traditional oven drying
osmo-freeze drying of both papaya and cactus pear had the highest score of all tested sensory characteristics after 3 months and / or 6 months of storage at 4±1℃ . On the other side, osmo-freeze drying of both fig and grapes had the highest scores of color, taste, aroma and overall acceptability followed by osmotic and oven drying. Analysis of variance indicated that an averaged significant difference in color, texture, taste, aroma and overall acceptability between dehydrated tested samples and correlated well with the used method of drying.
Part 2: Quality properties for the juices of guava and papaya in relation to the enzyme activity
1-Physicochemical properties of fruit juices
The pasteurized guava juice and pasteurized guava juice contained 0.5% ascorbic and /or 0.5% citric acid were recorded slightly decreased of pH. Where, the corresponding value of pH were 3.65, 3.39 and 3.11, respectively.
The pH of guava juices was slightly decreased as a result of the pasteurization process and/ or pasteurization with using additives. Where, the pasteurized juice of papaya contained 0.5%citric acid had the lowest pH (4.00) followed by pasteurized juice papaya contained 0.5%ascorbic acid (4.40), Pasteurized papaya juice (4.80) and fresh papaya juice (5.10).
The TSS was significantly (p≤ 0.05) increased as result of pasteurization and /or adding both 0.5% ascorbic and /or 0.5% citric acid which were recorded 15.10 0Brix in pasteurized guava juice and/or pasteurized guava juice contained 0.5% either ascorbic acid or 0.5% citric acid . While pasteurized papaya juice contained 0.5% either ascorbic acid or 0.5% citric acid recorded 12.50 0Brix.
Results indicated that, the total phenolics contents were increased by pasteurization processing for the juices of guava and papaya compared with control. where the phenolics contents were (50.10 and 82.20 mg/100 g) in fresh and (62.40 and 87.20 mg/100g) in pasteurized guava juice and pasteurized papaya juice. On the other hand, fresh papaya juice had the highest content of carotenoids (1.86 mg/ 100gm). Meanwhile, vitamin C in pasteurized guava juices were decreased by increasing the time of storage.
2-Browning index for fruits juices under investigated
Pasteurized guava juice had the highest browning index rate (0.078) followed by pasteurized guava juice contained 0.5% ascorbic acid (0.075) and pasteurized guava juice contained 0.5% citric acid (0.073) respectively. Meanwhile, the pasteurized papaya juice recorded the highest level of browning index rate (0.068) followed by pasteurized papaya juices contained 0.5% ascorbic acid (0.059) and pasteurized papaya juice contained 0.5% citric acid (0.057) respectively, initially after treatment.
3- Activity of peroxidase, polyphenol oxidase, pectin methylesterase and protease for fresh fruits juices.
The peroxidase activity of guava juice contained 0.5% of both citric acid and /or ascorbic acid was 3.40 and 3.57 *10-3 O.D/min immediately after preparing of the juice and it was 6.23 *10-3 O.D/min for pasteurized guava juice without any additives.
The pasteurized papaya juice prepared without the additives recorded the highest values of peroxidase activity either after processing and/or during 6 months of storage at 4±1℃ followed by papaya juice contained 0.5% ascorbic and 0.5% citric acid respectively.
The residual activity of peroxidase reached to 1.05, 0.57 and 0.70% for only pasteurized guava, pasteurized guava contained 0.5% citric acid and contained 0.5% ascorbic acid respectively. Pasteurized papaya juice contained 0.5% citric acid had the highest inactive polyphenol oxidase followed by juices contained 0.5%ascorbic acid and only pasteurized. Where, the polyphenol oxidase activity of guava juice was decreased gradually owning to the extension of the storage and reached to the minimum polyphenol oxidase activity after 6 months of storage time at 4±1℃ recording (0.70, 0.35 and 0.37 *10-3 O.D/min) for only pasteurized guava juice, pasteurized guava juice contained 0.5% citric and pasteurized guava juice contained 0.5% ascorbic acid, respectively.
The residual activity of PPO for papaya juice was clearly lower recording 3.32, 1.53and 1.96 % for pasteurized papaya, pasteurized papaya juice contained 0.5% citric and contained 0.5% ascorbic acid respectively. The residual activity of PPO was less than 1% for all tested juices at the end of storage at 4±1℃.
The PME for fresh papaya juice was 54.50*10-3 O.D/ min. However, the pasteurization only and /or pasteurization of papaya juices contained citric and ascorbic acid with ratios 0.5% were more effective for reduction of the PME enzyme. On the other hand, the reactivation was noticed for pasteurized guava juice contained either 0.5% of citric or ascorbic acid after one month of storage at 4±1℃ and after that, the residual activity of PME for all tested pasteurized guava juices either contained additives or not were increased gradually till the end of storage for 6 months at 4±1℃. Meanwhile, the reactivation of PME was observed and increased gradually by extending the shelf life up to 6 months at 4±1℃. The activity of PME was (0.17 and 0.19 *10-3 O.D /min ) pasteurized guava juice contained 0.5% citric acid and ascorbic acid after 1 month of storage at 4±1℃ and increased till to reach to (0.69 and 0.73*10-3 O.D /min) respectively after six months of storage at the same condition. The residual activity for papaya juice was lowering by the long time of storage up to 6 months at 4±1℃. Where, the residual activity was 0.33, 0.17 and 0.22% for pasteurized papaya juice, pasteurized with 0.5% citric and pasteurized papaya with 0.5% ascorbic acid after 6 months of storage, respectively compared with 1.47,1.28 and 1.32% initially after processing respectively
from the results it could be observed that, the initial activity of protease for fresh papaya juice was 6.00*10-3 O.D /min and there was no activity was noticed as results of pasteurization only or pasteurized juice in the presence of 0.5% citric or 0.5%ascorbic acid . Also, the results showed that the reactivity of protease was appeared after one month of storage at 4±1℃ for all tested juices pasteurized only or pasteurized papaya juices contained 0.5% citric or 0.5% ascorbic acid.
4- Sensory evaluation for tested juices of guava and papaya
The results show that, adding of ascorbic acid or citric acid to juice enhanced all sensory characteristics comparing with control (pasteurized juice). It could be noticed that, overall acceptability was high in juice contained ascorbic acid or citric acid the color of pasteurized juice contained 0.5% ascorbic acid appeared to be better color compared with pasteurized juice.
The pasteurized guava juice contained 0.5 % ascorbic acid had the best overall acceptability followed by treated with 0.5 % citric acid and pasteurized guava juice without adding additives, respectively.
Quality parameters for sensory evaluation of tested papaya juices including color, taste aroma, texture and overall acceptability, it could be noticed that, the pasteurized papaya juice contain 0.5% ascorbic acid recorded the highest value for color, taste and texture followed by papaya juice contained 0.5% citric acid and pasteurized juice ,respectively. Therefore, adding of ascorbic acid for papaya juice before pasteurization caused to improve the color, taste, texture and overall compared with other tested pasteurized papaya juices.