Rofandi Hartanto1
Ketut Indrayana2
1Department of Agricultural Engineering, University of Lampung, Bandar Lampung, Indonesia, 35145
email: rofandi_hartanto@yahoo.com
2Alumnus of Department of Agricultural Engineering, University of Lampung
email: indra.yanaindra.yana9@gmail.com
Abstract
Modified atmospheres composed by 1-3% CO2, 2-8% O2 and N2 as the rest were used to store citrus (Citrus reticula B.) fruits with various temperatures, those were 12 oC, 18 oC and 27 oC. These conditions were refreshed by the same gas compositions every two days. Respiration rate, total of soluble solid, and total of acid of citrus fruit were measured during storage.
The respiration rate of the fruit was decreased by temperature treatment of 12 and 18 oC with composition of CO2 of 1, 2, and 3% by volume, and composition of O2 of 2, 4, and 8% by volume. These atmosphere compositions could prolong their shelflife up to 20 days of storage. The change of total of soluble solid at 1% CO2 treatment tends stable compared to other treatments, whereas the change of the total of acid tends increased during storage. The respiration rate of the fruit was suitable with Michaelis-Menten enzyme kinetic model where CO2 as an uncompetitive inhibitor. (158 words)
I. INTRODUCTION
‘Siam’ citrus (Citrus reticulate Blanco) fruit is one of popular fruit in Indonesian communities. In horticultural map, citrus is placed in the third important fruit after banana and mango. Especially, ‘Siam’ citrus is characterized by its sweet taste, soft texture and strongly citrus aroma. Citrus fruit riches of vitamin C, as well known, which the sugar content is about 12.5 oBrix and the total acid content is about 1.4% by volume. Citrus fruit is picked up after ripening at its stem, therefore categorized as a non-climacteric fruit. The ripe citrus can be stored just only for 3-5 days at room (25-28 oC), whereas at 0 oC it can be stored until 12-14 days. The convenience relative humidity of storage room of citrus is about 85 to 90 percent.
The citrus is perishable commodity, which need to be handled safely after harvesting. Deterioration of the fruit may be caused by many factors such as physiology, chemical and microbiology. This deterioration can decrease the quality of the fruit and then lowering its economic price. This deterioration may also be caused by temperature treatment during handling and storing, and storage method. One of method to decrease the level of deterioration that caused by the physiological disorder is by storing the fruit at low temperature combined by modified atmosphere treatments. The modified atmosphere treatment is how to take advantage by decreasing of oxygene content and increasing of carbon dioxide content of surrouding storage atmosphere of the fruit that simultaneously decreases its respiration rate as well as its overall metabolism.
Objective of the research
The research aims to analyse influence of temperature and O2 and CO2 treatment toward the respiration rate, total of soluble solid, total of acid and shelf life of citrus fruit during storage at modified atmosphere condition.
II. MATERIALS AND METHODS
The materials used in this research consisted of ripe citrus fruits from wholeseller of Bandar Lampung traditional market which were shipped from West Kalimantan Province. The other materials were oxygene (O2), carbon dioxide (CO2) and nitrogen (N2) to compose modified atmosphere condition, benlet solution, bromthymol blue indicator, sodium bicarbonate, sodium hydroxide, phenolphthalein indicator, wax and demineralised water.
The equipments used in this research consisted of storage bottle (cuvette) of 3300 ml in volume, mixing gas bottle, tube with on/off water flow, hole maker of cuvette coverer, vacuum pump, stainless steel knife, refrigerator, venojack, syringe, spectrophotometer, refractometer ‘Atago’ PR 201 α, flask tube, reaction tube, digital balance, thermometer, measurement glass, buret, static, straw, erlenmeyer, measurement straw, and intake rubber.
Method of Storage at Modified Atmosphere Condition
1. The citrus which was chosen as a sample has a criteria such as optimally ripe, uniformity in size, and without physical as well as physiological disorder. The sample was washed by water, immersed in benlet solution (2 gs benlet within 1 l water), then dried off. The sample was weighed, measured of its volume, and the freespace of the cuvette was calculated. Ten pieces of citrus fruits as a sample were then stored at the modified atmosphere condition. The cuvette coverer, which made by plastic material with holes to insert the O2, CO2 and N2, then was tightened, and the hole was closed with rubber and wax to avoid gas losses from the cuvette.
2. The cuvette that was inserted with 10 pieces of samples then was vacummed, and it was replaced by modified atmosphere gas compositions (Table 1).
3. How to make the gas composition of modified atmosphere was, first, mixing bottle was filled with water fully. Seconly, the N2 was filled to the mixing bottle by pushing the water within the mixing bottle, replaced by this gas, followed by O2 and CO2 similarly.
Tabel 1. Modified atmosphere gas composition and temperature treatments.
No. CO2:O2:N2 (%) Temperature (˚C)
1. 1 : 2 : 97 12
2. 1 : 4 : 95 12
3. 1 : 8 : 91 12
4. 1 : 8 : 91 18
5. 2 : 2 : 96 12
6. 2 : 4 : 94 12
7. 2 : 8 : 90 18
8. 3 : 2 : 95 27
9. 3 : 4 : 93 27
10. 3 : 8 : 89 18
11. 3 : 8 : 89 27
12. 0 : 21 :79 27
CO2 production
To analyse the carbon dioxide produced by respiration, it was used spectrophotometer analyser. Carbon dioxide of a gas sample was diluted into a bromthymol blue solution, and its colour was read by the spectrophotometer in 650 nm wavelength. Spectral readings were then consulted to the standard curve, which consists of CO2 concentrations vs. known spectral readings, to know the carbon dioxide concentration from the gas sample. CO2 production as a respiration rate was calculated by total CO2 minus previous CO2 concentration within cuvette per sample weigh per time, how long the sample was stored.
In the first day of storage, the gas sampling was performed every 4 hours, and in the second day and so on the gas sampling was performed every 24 hours of storage.
Total soluble solid
Every two days the total soluble solid of the sample was measured using refraktometer ‘Atago’ PR 201 α. The citrus fruit flesh from the sample was pulped and diluted. The total of soluble solid was read in oBrix.
Acidity
Organic acid is one of interesting matter of the fruit. During storage, sometime this can be decreased. Knowing the influence of the modified atmosphere condition and temperature treatmen therefore is fruitfull. Total acid was analysed by titration (Sudarmadji at al., 1989), every two days.
Shelf life
Shelf life of citrus fruit was determined based on the level of deterioration which could be consumed or after senescence condition which off flavour and other disorder come. Shelf life of the fruit also defined as physiological disorder which bacteria and fungi infected.
III. RESULTS AND DISCUSSIONS
Respiration rate
Respiration rate is a good parameter to determine the shelf life of the fruits and vegetables after harvesting. Storage of citrus fruit at the modified atmosphere condition combined with low temperature degree influenced the respiration rate pattern. The respiration rate of the fruit was defined as rate of CO2 production which influenced by storage condition such as gas composition of micro atmosphere surrounding the product, that is level of CO2 and O2 concentration, as well as the temperature treatment. The modified atmosphere composition of 2-8% O2, 1-3% CO2 and temperature treatment of 12, 18 and 27 oC could control the respiration rate at various levels. Figure 1 shows respiration rate pattern of citrus fruit at various micro atmosphere conditions, those are 12 and 18 oC of temperature treatments, 2% CO2 and 2, 4, and 8% O2, consecutively. The other treatments were also showing similar pattern, which increasing CO2 concentration would decrease respiration rate and decreasing O2 concentration would also decrease respiration rate.
Figure 1. Respiration rate of citrus fruit under some modified atmosphere treatments, i.e. 2% CO2, 2,4 and 8% O2 and 12 and 18 oC.
Respiration Model
The respiration rate of the citrus fruit, using data of elevation of carbon dioxide within cuvvette and diminishing of oxygen concentration within cuvette was suitable with Michaelis-Menten kinetic model (Hartanto, 2000) where the constants were shown in Table 1. The model is assumed that CO2 is as an uncompetitive inhibitor.
Table 1. The constant values of Vmax, Km, and KCO2 of citrus fruit respiration rate model, during storage at 12, 18 and 27 oC at 1-3% CO2, 2-8% O2.
No. Constant Temperature, oC
12 18 27
1 Vmax 1.233 1.630 1.810
2 Km 3.269 149.066 3.481
3 KCO2 333.3 500 1000
The increasing of Vmax value by increasing of temperature treatment shows that the respiration rate model reflects reality that increasing of temperature treatment will increase rate of metabolism as well as rate of respiration of the fruit.
Total soluble solids
Sugar was main component of total soluble solid then therefore the total soluble solid was defined as sugar content. The research showed that total soluble solid tends stable during storage. The data showed that the total soluble solid tend increase, although it is not significantly visible.
Theoretically, starch can be hydrolysed to be glucose, then the sugar level within flesh fruit increased. Actually, this hydrolysis was not always produce sugar at certain level, even to be not produce and the sugar level did not changed. By citrus fruit, the sugar content was not increased during storage at modified atmosphere; the sugars were at their optimum content when the fruit was picked out. The micro atmospheric compositions surround the fruits may influence the total soluble solid change rate. Although the sugar content was used by the fruit for respiration or was used by the fruit to become another compounds. Figure 2 showed the change of total soluble solid of citrus fruit during storage at modified atmosphere condition at 12 oC.
Figure 2. Total soluble solid of citrus fruit that stored at 12 oC, 1% CO2 and 2, 4 and 8% O2 for 20 days of storage.
Total Acids
Organic acids within citrus fruit mainly were citric acid and malic acid. It may unusual the research showed that the total acid was increased during storage. The beginning level of total acid was about 0.035%. The highest level of total acid was achieved at the end of 20 days of storage that was 0.09%. The increase of total acid during storage was caused by composing together with composing of many substances at ripening period, such as composing of some pigments. The respiration processes of the post harvest of fruit may transform of pyruvic acid to become other organic acids, aerobically, by producing CO2, O2 and energy. Figure 3 showed the increase of total acid during storage at modified atmosphere conditions at 12 oC, 1% CO2 and 2, 4, and 8% O2.
Figure 3. The increase of total acids of citrus fruit during storage at modified atmosphere at 12 oC, 1% CO2, and 2,4, and 8% O2.
Shelf life
Citrus fruit which was stored within impermeable cuvette by modified atmosphere at the room temperature could only prolong the shelf life of 6-11 days, whereas which was stored at 12 to 18 oC could prolong the shelf life until 20 days. The modified atmosphere composition would not influence when was applied singularly. Only when it was compounded by low temperature this treatment would work effectively to prolong its shelf life.
Other advantage of storage the fruit at low temperature is that the peel appears fresh for its long storage, the flesh is relatively fresh and it was not off-flavor occurred. Apandi (1986) mentioned that controlling temperature and humidity was important thing to prolong the shelf life of fresh fruit. Smith (1965) cit. Pantastico (1986) mentioned that humid atmosphere around the fruit was also to control shrinking of the peel of fresh fruit.
IV. CONCLUSIONS
Based on the research it was concluded that:
1. The respiration rate of the citrus fruit tended decrease during storage at modified atmosphere conditions at various temperatures treatments. The Michaelis-Menten kinetic model was suitable to model the respiration of citrus fruit stored at modified atmosphere by carbon dioxide as uncompetitive inhibitor.
2. The total soluble solid as represented by its sugar content tended increase during storage at modified atmosphere conditions at various temperature treatments.
3. The total acid tended increase in various ways during storage at modified atmosphere at various temperature treatments.
4. Generally, modified atmosphere conditions could prolong the shelf life of citrus fruit. The better treatment was 1% of CO2, 2% of O2 and 97% of N2 at 12 oC where the fruit could be stored until 20 days.
V. LITERATURE CITED
Apandi, M. 1986. Teknologi Buah dan sayur (In bahasa Indonesia). Alumni. Bandung.
Hartanto, R. 2000. The model of sugar change rate of salacca (Salacca edulis REINW cv. Pondoh) fruit during modified atmosphere storage (In Bahasa Indonesia) Agritech. Vol. 20. No.1.
Pantastico, Er. B. 1986. Fisiologi Pasca Panen, Penanganan dan Pemanfaatan Buah-buahan dan Sayur-sayuran Tropika dan Sub-Tropika. (Terjemahan). Gadjah Mada University Press. Yogyakarta.
Sudarmadji, S., Bambang K., Suhardi. 1989. Analisis Bahan Makanan dan Pertanian. Liberty. Yogyakarta.
Tranggono, Suhardi dan Umar Santoso. 1992. Prolong shelf life of salacca fruit by controlled atmosphere storage. (In Bahasa Indonesia). PAU Pangan dan Gizi, UGM, Yogyakarta.
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