How does Ethiopia use solar pasteurization to juice guava fruit?
In many tropical regions, guava is a widely cultivated fruit that contains a lot of nutrients such as vitamin C, dietary fiber, and many minerals.
However, due to its perishability, guava has a short shelf life, and rapid deterioration also limits its range of sales and transportation. Therefore, it is very necessary to seek effective preservation treatment methods.
In Ethiopia, locals have developed a solar thermal technology that, in addition to supplying heat energy to produce steam, is also used to disinfect, pasteurize, and evaporate fruits with excessive moisture.
To do this, they used a three-stage assembly pot for steam generation, by-product collection and perforated pasteurization sections. (as shown)
A solar collector is a thermal system in which the focus of solar radiation is concentrated to the bottom of the receiver and converted into usable heat.
The system has an average power of about 6kW, an average solar radiation intensity of 800W/m2, and a capacity of 5 liters of water can boil in 5 minutes.
The concentrator is a 3-meter diameter parabolic reflector with movable connecting rods that enable the user to load and unload products out of focus.
Once the fruit has passed the required moisture content for sterilization, boiling and evaporation, it moves on to the next processing stage – sealing
The softened fruit is evenly mixed, squeezed and filtered by using a clean filter, and sealed.
A total of 255 W of peak photovoltaic (PV) power was used to drive the mixer and sealer.
This technology solution offers a comprehensive solution for juice processing in rural areas, where there is no modern energy supply.
Photovoltaic power not only provides running power for mixers and sealers, but also provides farmers with lights and mobile charging ports so that they can communicate using mobile technology.
Ripe and uniformly sized guava fruits purchased from the market are sorted according to overall quality and washed with tap water to remove dirt, dust, pesticide residues and reduce microbial load.
After washing, use a fruit knife and cut into four pieces to reduce its size. 1 kg of cut guava is placed in a perforated pot and the steam generated by 1 liter of water in a solar steam cooker is used for sterilization and pasteurization. The boiling process takes half an hour to soften the fruit and evaporate the excess water.
Subsequently, 2 g of the chemical preservative citric acid is added, mixed and stirred well, and filtered through the white fabric.
The filtered juice is filtered through a sieve, boiled and filled into glass bottles and marked for the first extraction.
The remaining pulp is mixed with water in a ratio of 1:1 and boiled in a solar steam cooker for half an hour for filtration, while the filtered juice is filled into glass bottles.
The bottle is cooled at room temperature and then stored. Beverage samples are periodically checked for total soluble solids and total microbial load 30, 60 and 90 days after the first date.
Microbiological analysis of guava juice includes determination of total soluble solids, pH, and total microbial load. THE TOTAL SOLUBLE SOLIDS OF GUAVA JUICE WERE DETERMINED BY A HANDHELD REFRACTOMETER ACCORDING TO THE Ruck method, and their pH was measured using a ph meter described by aoac (1995).
Similarly, microbial load is determined by diluting samples using sterile normal saline and preparing them to a concentration of 10−6. Take 0.1 ml of each dilution evenly coated on nutrient agar medium and incubate at 37 °C for 24 h.
Petri dishes are screened for discrete colonies after an incubation period and the actual number of bacteria (log CFU/ml) is estimated. Perform colony counting on selective media to determine the loading of specific microorganisms.
Total E. coli count (TCC), fecal E. coli count (FCC), total staphylococcus count (TSC), and total fungal count (TFC) were performed by MacConkey agar medium, Enterococcus mensius (mFC) agar medium, Mansson's salt agar medium (MSA), and Sabroud glucose agar medium (SDA).
Eventually, in this case, the researchers perform three plates and count from Petri dishes with fewer than 300 colonies. Bacterial load estimation is based on the standard methodology of the International Committee for Food Microbiology Codes.
While the storage time and extraction times are interactive, the effect on the total soluble solids (TSS) of guava juice is shown in the figure and table. Total soluble solids can describe the sugar and soluble mineral salt content in the juice.
The initial TSS of fresh juice is 5°Brix. Data from TSS showed a significant decrease in TSS as storage days increased and juice extraction was repeated. There was no significant difference in TSS between sap extracted after zero-day storage and sap extracted after 1, 2, and 3 months storage, both at 5°Brix.
However, TSS continues to decline in duplication during extraction and storage. This decline may be due to the addition of water during the continuous extraction process. As water is added, the solute concentration decreases, resulting in a decrease in TSS.
The figure shows that the total soluble solids in guava fruit decrease in the extract as water is added during the extraction process. The pH of fresh juice is 3.8, 3.9 and 4, corresponding to E1M0, E2M0 and E3M0, respectively.
After 1 month, 2 months and 3 months of storage, the pH values were 3.9, 3.97 and 4.2, respectively. This indicates that the pH gradually increases as the number of extractions and storage time increases.
It can be said that the application of Ethiopia's solar pasteurization technology in modern agriculture has become the main trend of innovation and development.
In addition to guava, the technology can also be applied to other types of agricultural cultivation, such as vegetables, fruits, cereals and so on.
In return, this technology creates jobs at a sustainable scale, reduces youth unemployment, accelerates sustainable rural urbanization, and contributes to the achievement of the Sustainable Development Goals.
