«——[·Preface·] ——»
Mango is a tropical fruit and is one of the most popular fruits worldwide. It is currently ranked fifth among the world's major fruits and is one of the second most grown fruits in Ethiopia. According to the Ethiopian Fresh Fruit Market Update Report, mango production increased by 45% from 2013 to 2018.
In Ethiopia, the main consumption of mangoes is restricted. As a result, fresh mangoes in Ethiopia suffer from quality loss and limited shelf life. The loss rate is estimated to be between 25 and 40 per cent.
This is mainly due to improper handling and preservation facilities. In order to effectively resolve the existing state. Different strategies must be used to consume this balanced fruit throughout the year.
One way to address postharvest mango loss is drying. The shelf life of dried products is almost infinite, and transportation, handling and storage costs are much lower than other preservation methods. While drying is already a common technique, it is not widely available in Ethiopia.
Consumers who buy fresh fruit are also not processed. Therefore, it is important to strengthen and promote improved postharvest management, value-added products and active research programs. Over the past few years, there has been a significant increase in demand for mango products, with the most popular mango product being dried mango slices.
Despite the improved shelf life, the drying method may alter the nutrition of the dried product. Pretreatment is usually performed before the fruit is dried to reduce undesirable changes during drying and subsequent storage.
However, because of the lack of different pretreatment methods and different drying methods, it is necessary to select the influence of pretreatment methods (lemon juice, brine soaking, hot water blanching and control) and drying methods (solar, tray, frozen and fluidized bed drying) on the quality parameters of dried mango slices.
«——[·Comparison of pretreatment methods.] ——»
The mango is washed and peeled, then cut into slices of about 5 mm in the direction of the fibers with a stainless steel knife. Divide these slices into 200 g per serving, soak in equal proportions of lemon juice and distilled water mixed solution 0.5 v/v, container ensures complete coverage of slices, and leave for 10 min.
The pretreated sections are then removed from the solution, evenly distributed on a perforated tray, and allowed to dry the excess solution for 20 min. Soak the slices in boiling water at 90 degrees Celsius for 1 minute for hot water blanching and make sure to cover the slices completely.
Alternatively, soak the sectioned samples in the prepared 0.011 g/mL concentration of saline, make sure to completely cover the sections, and leave for 10 min. The pretreated sections are then removed from the solution, evenly distributed on a porous tray, and the excess solution is allowed to drip dry for 20 minutes. Finally, a sample is set aside without any treatment as a control group.
«——[Drying method·] ——»
Place the mango flakes in a desiccant. Periodically flip different sides of the slice to increase drying efficiency. Measure the temperature and relative humidity of the collector inlet and dry chamber using a digital hygrometer.
Tray drying of mango flakes is carried out on tray drying equipment under computer control. The drying temperature is kept at 70 °C.
Laboratory-scale fluidized bed dryers are used to dry prepared mango flakes. The air temperature is set digitally to 50°C and the air flow rate is 1.5 m/s. All samples were dried to a wet base with less than 10% moisture content of the sample.
Use SAS software package for statistical analysis, using ANOVA. At a significance level of 5%, Fisher's Minimum Significant Difference Test is used to determine significant differences between samples.
«——[Effect of drying method on the composition of fresh mango·】——»
The total vitamin C content in fresh mango averaged 49.53 mg/100 g. This difference is due to the ripening stage, regional fruit varieties, different measurement and extrusion techniques. Ascorbic acid in fruits is also affected by other factors, such as climatic conditions, temperature, sunlight, and the amount of nitrogen in plants. Similarly, the type of storage can also affect the amount of vitamin C.
The mango flakes produced by the entire dryer contain less than 9.91% wet base, which is sufficient to inhibit the growth of bacteria, yeast and mold.
The average final moisture content of the samples was 5.63 to 9.91% in the drying method and 7.85 to 8.13% in the pretreatment method. In the study, fluidized bed drying led to a decrease in the moisture content of dried mango flakes, which reduces the spoilage of food and increases its value and shelf life. Fluidized bed drying has the lowest moisture content due to the homogeneous flow of particles in the gas stream resulting in high heat and mass transfer coefficients.
In terms of pretreatment, the order of moisture content of the flakes is:
Lemon juice 7.85%, < salt solution 8.01%, < hot water blanching 8.05% < control group 8.13%.
Saline-treated sections have a lower water content than lemon juice-treated samples. This is because osmotic compression in the osmotic solution causes moisture to flow out of the internal tissues, which occurs even before drying. Similarly, hot scalded flakes have a lower water content than untreated samples. This indicates that blanching reduces the water content of mangoes.
Previous studies have explained that blanching softens the texture, which in turn makes the moisture removal process easier to proceed. There were no significant differences between hot water scalding and saline solution-treated flakes, but these two differed significantly from lemon juice and control group samples. Drying methods and pretreatment resulted in significant differences in moisture content.
Fluidized bed and freeze-drying in combination with pretreatment reduce the water content of dried mangoes. The interaction of pretreatment and drying methods affects the water content of dried mangoes. Similar findings were found in the drying of tomato, banana, mango and papaya leaf powders.
The average fat content of samples by solar dryer, tray dryer, freeze dryer and fluidized bed drying method was 2.89%, 2.92%, 3.15% and 3.16%, respectively.
There is no significant difference between the first two values, as is the last two values. However, there were significant differences between the first and second groups. The fat content values were statistically the same for all four treatments.
There were no differences between all four treated samples dried by solar dryers and tray dryers, but they were statistically lower than values for freeze and fluidized bed drying methods, regardless of pretreatment. The former range of values from 2.83% to 2.94%, while the latter group shows values between 3.03% and 3.26%. A short drying time prevents the melting of the fat, which increases its value.
Fiber is very important for the gastrointestinal tract to reduce the risk of cardiovascular and coronary heart disease while maintaining a normal weight. Fiber content values ranged from 6.45% to 6.64%, with no significant differences except for a very small number of samples. The data shows that these products have a high fiber content and are acceptable from a healthy eating perspective.
The table shows the effect of different drying methods and pretreatments on the protein content of the sample. The protein content of solar and tray-dried samples was 2.50% and 2.49%, respectively, and there was no significant difference between the two.
The protein content of the samples after freezing and fluidized bed drying was 2.71% and 2.62%, respectively, and there was no significant difference. In addition, the protein content of the samples with different pretreatments ranged from 2.57% to 2.59%, again without significant differences.
As shown in the figure above, the carbohydrate content of mango slices dried by tray and fluidized bed was between 75.51% and 79.35% and 77.06% to 77.34%, respectively, while the control group and samples pretreated with lemon juice were between 77.06% and 77.34%. The difference may be due to their different moisture content, which leads to different dry matter content.
«——[Effect of pretreatment and drying methods on mangoes.] ——»
The L-values of solar, tray, freeze, and fluidized bed dried samples were 55.58, 55.28, 56.0, and 57.00, respectively, indicating that the brightness of dried fruit flakes decreased from 58.76 in Table 2 of fresh samples during the drying process.
L is an important drying parameter that is often the first quality attribute that consumers use to determine brand acceptance. Pretreatment prior to drying, no significant difference was shown, with a slight decrease in L value compared to fresh sample 58.76. It was also observed that lemon juice treatment had no significant effect on the brightness of dried mangoes.
Solar and tray-dried samples had A-color coordinate values of 12.62 and 12.84, which again did not differ significantly.
During the drying process, both enzymatic and non-enzymatic reactions cause yellowing of fruits and vegetables. Conversely, freezing and fluidized bed dryers cause the A value to drop and the red color of the final product is lost.
This may be due to the presence of salts, acids, and bleach, which cause enzymatic yellowing reactions. Most treatment combinations did not show significant differences in A-values. However, the highest A value of 14.07 for dried mango was obtained during tray drying and control sample handling. The value of parameter a* indicates the redness of the sample, which in its positive form is also an important indicator of fruit quality.
Compared to fresh samples, the yellow color of mango after drying was reduced by 52.65. But all samples have a positive B value. These positive values indicate that they still have a yellow degree.
Solar and tray-dried samples had the lowest B values, while frozen and fluidized bed dryers exhibited higher B values, and there were significant differences between the two.
The yellowness of the dehydrated material is greatly affected by temperature and humidity. Carotene-like isomerization contributes in particular to the degradation of β-carotene's yellow pigment, as well as oxidation stages.
After different pretreatments, the B values of the samples varied significantly. Compared to fresh samples, samples treated with trays and freeze dryers, as well as controls and lemon juice, had the highest B-values of 31.69 and 49.48, with significant differences. There were also significant differences between 42.49 and 47.52 B values for samples using fluidized bed dryers and 30.47 and 35.12 for solar drying.
This may be attributed to better retention of sample carotenoids, with high B parameters giving more yellow product, which is recommended for dry products. Color has an important factor in food choices, even if the difference depends on changes in fruit chemistry, pretreatment, and drying methods.
As shown in the table, different drying methods affect the mango slice color parameters. Compared to freeze and fluidized bed dryers, samples using solar and tray dryers, were a total chromatic difference of 19.91 and 20.02.
Of all the drying process comparisons, only two methods, the freeze and fluidized bed dryers, maintained the color loss, as they gave minimum values of 5.15 and 7.75. This is due to the removal of moisture to prevent enzymatic browning reactions, resulting in relative color stability to freeze-drying techniques. Again, it could also be because there is less oxygen in the drying chamber.
«——[Effect of drying technology on vitamin C and phenol content of dried mango·]
The loss of vitamin C depends on the drying method and the type of raw material, such as pretreatment. The highest recorded values for vitamin C were obtained from frozen and fluidized bed dried samples at 41.06 and 41.24 mg/100 g, and there were no significant differences.
This high retention rate is the result of reduced ascorbic acid loss due to rapid drying and the use of vacuum technology at low temperatures. In contrast, a freeze dryer is a costly-to-produce, time-consuming drying method that confirms the average retention of vitamin C between 73% and 81% and 96.95% freeze-drying methods by using hot steam drying methods and vacuum drying methods, respectively. Vitamin C retention can be used as a reference for nutrient retention in foods.
The solar dryer has a vitamin C value of 33.18 mg/100 g, which is lower than other dryers. This is due to ascorbic acid degradation due to oxygen and light exposure. In addition, the presence of oxygen in the drying medium can cause undesirable changes on the dehydrated cargo. The main enzyme responsible for the enzymatic degradation of ascorbate is ascorbate oxidase.
As shown in the table, lemon juice pretreated samples found higher vitamin C compared to hot water blanching pretreatment, exceeding the value of 38.07 mg/100 g hot water blanching pretreatment sample, and its high retention may be due to the addition of acid that contributes to vitamin stability.
Most treatment combinations showed significant differences in vitamin C content in dried mangoes. The treatment combination of lemon juice and freeze dryer yielded the highest value of 43.09 mg/100 g, and solar drying without pretreatment yielded the lowest value of 32.05 mg/100 g.
It was found that samples treated with lemon juice and dried by a freeze dryer had a higher vitamin C retention rate of 43.09 mg/100 g than other treated samples. In the freeze-drying process, due to the very low temperature, it does not lead to a significant loss of ascorbic acid, while lemon juice is due to its natural vitamin C content.
Maintaining vitamin C is very important because it is an essential nutrient for our body's specific metabolism and as a preparation reagent in many pharmaceutical and food industries. Vitamins prevent many diseases and play an important role in building tissues such as skin, tendons, cartilage, and blood vessels.
«——[Eating dried mango can provide the body with the vitamin C it needs.] ——»
Mango is a rich source of vitamin C, β-carotene, and various polyphenolic compounds. Vitamin C is the body's main food nutrient, and fruits and vegetables provide 90% of vitamin C.
Vitamin C promotes cell growth, proper calcium absorption, normal tissue growth and damage repair, and strengthens capillary walls. For infants and lactating women, the recommended daily intake ranges from 40 to 120 mg of vitamin C.
For some people, dried mango may be the only source of vitamin C, so a minimum of 120 grams, 211 grams, and 100 grams of dried mango must be consumed to reach the minimum amount of vitamin C in the daily intake range.
As can be seen from the table, the total phenolic content of samples for different drying methods ranges from 131.13 to 251.12 mg/100 g, and there are significant differences between them. The freeze dryer produced a lower phenol content of 131.13 mg/100 g. Similar results were also found and noted the low phenolic content of freeze-dried samples.
This can be caused by low temperatures, which create ice crystals in the tissue matrix, disrupt cell walls and release oxidized and hydrolases, damaging polyphenolic compounds.
The phenolic content of tray-dried samples was 178.05 mg/100 g, which was lower than samples dried at 220 mg/100 g in fluidized bed and 251.12 mg/100 g in solar. This is because of the thermal sensitivity of polyphenolic compounds, and prolonged heat leads to irreversible chemical changes, promoting the binding of polyphenolic compounds to other compounds or changes in chemical structure.
Regarding the pretreatment, the hot water blanching process obtained a maximum value of 203.90 mg/100 g, which exceeded the phenolic content of 195.62 mg/100 g in lemon juice.
Phenol is the active compound of antioxidants and has more free radical scavenging power than vitamins C and E. As can be seen from the figure below, there is a difference between the total phenolic content of the samples from the solar and fluidized bed dryers after four pretreatments.
Author's opinion:
Through pretreatment and drying methods, different treatments were carried out on the dried fruit slices, and the gaps and effects of color, vitamin C, total phenolic compounds, cellulose, carbohydrates and other indicators were obtained. Among the different pretreatment methods, samples treated with lemon juice and hot water had the effect of optimal color and stable retention of vitamin C. The sample quality after drying by freeze drying and fluidized bed drying is better.
For food processing enterprises and scientific research institutions, when processing dried fruit slices, appropriate pretreatment and drying methods should be selected according to the required product characteristics to achieve better economic benefits and market competitiveness.
It is hoped that the results of this study will provide some new ideas and directions for the utilization of fruit resources, and also make certain contributions to promoting the development of mainland fruit industry and improving the income of fruit farmers!
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