The purpose of this experiment is determining the best storage conditions for potatoes for a specific time period. Colorimeter was used to make comparison between surface colors of potatoes.
Solanine is a gylcoalkoloid molecule. Mostly found in nightshade family in nature. It provides protection to wounded organs of plants against microorganisms (Eie & Larsen, 2012). It’s an important molecule due to its undesirable significant effects on humans.
Plants of Solanaceae family are rarely eaten because their possible effects on human are negligible. However, its existence in potato is very important. Naturally, potato leaves, stems and shoots contain high amounts of glycoalkaloids. According to FDA data potatoes’ average content of Solanine is 8 mg per 100g and the toxic dose is 20- 25 mg so development of toxic glycoalkaloids is highly possible in the case of improper processing and storage.
Being exposure to light of potato leads undesirable greening of tubers due to increase in chlorophyll (which can be identified as an indicator of solanine) synthesis and also cause increase in formation of glycoalkaloids and these molecules disrupt membrane structure (Grunenfelder, 2005).
Solanine poisoning causes disorders in gastrointestinal and neurogenic systems. Diarrhea, nausea, abdominal pain, fever and vomiting occur. In severe cases it causes cardiac arrhythmia and respiratory failure and can lead to death.
There are several experiments for inhibiting solanine formation. Effects of level of light and temperature on formation of glycoalkaloids are being studying. And also there are studies on packaging that can lengthen shelf-life.
Five potatoes which are approximately same size and shape were stored and subjected to different light and temperature conditions for 14 days. While deciding length of time period, consumption habits and storage time of potatoes at homes are considered.
First sample has been exposed to high density daylight near the window and changing high temperature. (Temperature was changing with time from day to night)
Second sample has been stored on a shelf at room temperature and relatively darker condition. Temperature differences were small. (Place provided protection from air circulation and sudden temperature changes)
Third sample has been stored at room temperature and in completely dark container. Temperature differences were small.
Fourth sample’s temperature was lowered to +4oC and fixed for 14 days at that temperature. It has been stored in completely dark container.
Fifth sample was frozen at -18oC and fixed for 14 days at that temperature. It has been stored completely dark container.
By using colorimeter CR-10, colors of the potatoes were measured.
CR-10 colorimeter gives the L*, a* and b* values. These values are quantified by CIE L*A*B* color model. Color is defined in three dimensions by this model. L* values symbolize the color change in the range from 0 which is black to 100 which is white. Color change from red to green is represented by a* values. And b* value represents color change from yellow to blue (Grunenfelder L., 2005).
Rate of solanine production changes according to light and temperature conditions. As density of light and temperature increases, a significant increasing in amount of solanine production is observed. Solanine is a green pigment that causes shifting color of peel from fawn to green and decreasing brightness (Eie & Larsen, 2012). According to these facts it is expected that first sample has the lowest L* value and a* value while fifth sample has highest L* and a* values. On this range, rather than b* value, L* and a* values are more important, to make comparison (Grunenfelder L., 2005). Colorimeter results of samples are showed at the table below.
Sample No.
|
L*
|
a*
|
b*
|
1
|
48.1
|
2.3
|
20.2
|
2
|
51.7
|
2.7
|
27.4
|
3
|
54.6
|
7.6
|
33.4
|
4
|
52.7
|
9.6
|
25.0
|
5
|
53.2
|
11
|
29.7
|
According to colorimeter results, as it is expected, first sample has the lowest L* and a* value and fifth sample has the highest a* value. On the other hand, unexpectedly, small changes are observed on third, fourth and fifth samples’ L* values, and third sample has the highest L* value.
There may be several reasons to explain this situation. Firstly, solanine is a protective compound against microorganisms. Potato that had been damaged while harvesting or transporting, it may produce more solanine and unexpected L* values may reflect this situation (Eie & Larsen, 2012). Secondly, although before beginning of experiment, areas on the potatoes are selected by considering same surface properties (roughness, density of spots and color), potatoes were not peeled so small differences may occur. Roughness can cause small errors. On this basis, colorimeter is relatively but not completely consistent measure of skin color (Trujillo, Vanezis & Cermignani, 1996).
In conclusion, although L* values are confusing for samples stored at dark conditions, a* values show shifting from fawn to green on surface color. First sample has been exposed to day light and relatively high temperatures. As a result it has produced the highest amount of solanine, without doubt. Samples, stored at dark conditions are brighter and have significantly higher a* values than samples that have been exposed to day light.
Experiment shows that high density light and high temperature conditions promote production of solanine. Potatoes are best stored in dark and cool places.
REFERENCES
1. Colorimeter CR-10 [Web Photo]. Retrieved from http://www.usinenouvelle.com/industry/konica-minolta-sensing-div-plastiques-33436/colorimeter-cr-p200584.html
2. Eie, T., & Larsen, H. (2012). In 18th IAPRI World Packaging Conference (pp. 149-155). California: California Polytechnic State University.
3. Grunenfelder, L. (2005). Physiological studies of light-induced greening in fresh market potatoes. (Master's thesis, Washington State University)Retrieved from;
https://research.wsulibs.wsu.edu/xmlui/bitstream/handle/2376/321/L_Grunenfelder_050405.pdf?sequence=1
4. Trujillo, O., Vanezis, P., & Cermignani, M. (1996). Photometric assessment of skin colour and lightness using a tristimulus colorimeter: reliability of inter and intra-investigator observations in healthy adult volunteers. Forensic Sci Int., 31(81(1)), 1-10.
5. (n.d.). Retrieved from http://www.accessdata.fda.gov/scripts/plantox/detail.cfm?id=1364
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