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Does Lowering Storage Temperature Increase the Reducing Sugar Content of Potatoes?

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Introduction

Does Lowering Storage Temperature Increase the Reducing Sugar Content of Potatoes? Hypothesis: Potatoes kept at below freezing for a week will have significantly more reducing sugar in their cells than those kept at 5 degrees Celsius which will contain more than those kept at room temperature, displaying evidence of conversion of starch polysaccharides to maltose at low temperatures. Background The main food store in potatoes is starch, a mixture of the two insoluble polysaccharides amylose and amylopectin. Starch is a good storage material because it is insoluble and so can be accumulated without increasing the water potential of the potato cells. This is essential to the normal function of the cell as it prevents the cells being damaged by absorption of too much water by osmosis. When water freezes and turns to ice, its volume increases. The formation of ice crystals inside cells can cause serious and permanent structural damage to the cells. To reduce the problem of ice damage, many fruits and vegetables respond to frost by converting their starch reserves into maltose. Maltose is a soluble reducing sugar. By dissolving in the cell cytoplasm, the maltose will increase the concentration inside the cell and resultantly decrease the freezing temperature of the cytoplasm. This enables the cells to avoid freezing even at temperatures a few degrees below zero, allowing them to escape structural damage in all but the most extreme conditions. If this response to cold occurs in potatoes it should be possible to detect the increase in reducing sugar content using a qualitative Benedict's test, a check which can be used to detect the presence of reducing sugars in a solution. Reducing carbohydrates, e.g. glucose, have a free carbonyl group (C = O), which reduces boiling Benedict's solution to produce a green, brown or brick red precipitate. Polysaccharides and non-reducing sugars do not have this free group and so do not reduce the Benedict's solution. ...read more.

Middle

to ensure each has the same length of time to acclimatise its starch/reducing maltose levels. The potato type will be the same for all samples, and samples will be taken from the same potato to ensure that initially their reducing sugar levels are as similar as possible. The constant conditions of tests, care in not contaminating equipment, precise timing and accurate measuring procedures listed in the method should produce a set of reliable and repeatable results. Results Storage Temperatures Room Temperature Sample = 21�C Fridge Sample = 7�C Freezer Sample = -9�C Analysis Table 3 -Processed mean Absorbencies for all the tested solutions Table 4 - Estimated Concentrations of Potato Samples derived from the graph of glucose concentrations, showing estimated values for the actual concentration of the samples and scaled up values for a 100% sample. Sample Name Estimated Reducing Sugar Concentration of diluted samples (7.5%) (mol/dm�) Estimated Reducing Sugar Concentration of 100% Potato sample (mol/dm�) Room Temperature 0.008 0.106 Fridge 0.005 0.067 Freezer 0.007 0.093 Graph 1 - Plotted mean absorbency values for the standard glucose solutions with error bars showing minimum/maximum values. Includes estimations for potato sample concentrations. Conclusions �The results used to draw conclusions are those which represent 7.5% potato samples. Due to the filtering and blending processes the composition of the samples was significantly changed and so the values for a 100% solution in the table are not appropriately accurate to draw firm conclusions. As such the 7.5% potato values for reducing sugar concentration do not represent the actual concentration within potato cells and are instead used to determine the relationship between reducing sugar levels in the different potato solutions. �The values for potato sugar concentration in the second column of table 4 will be those used to draw conclusions. �The graph clearly indicates the expected relationship between volume of precipitate produced during the Benedict's test and the sugar concentration of the glucose solutions. ...read more.

Conclusion

The value for absorbency prior to the test on the potatoes could be deducted from the final absorbency values after the test to try and eliminate the negative effect of suspended starch on the accuracy of the results. This would work best if the Benedict's test heating stage for the standard glucose solutions occurred at the same time as the heating of the potato samples, and these two sets of samples were tested for their absorbency separately. -An additional or repeated additional filtrations on the potato samples would also improve accuracy by further reducing the suspended starch in the samples. This could be implemented after the proposed heating phase for the various potato samples prior to the Benedict's Test but before the first absorbency test on the samples. This would work best were a greater volume of potato sample prepared as filtration of small samples using the method used in this experiment is difficult. -An increase in the volume of potato sample produced would benefit the accuracy of the samples and make filtering samples more efficient. It would also enable more repeats on the same sample. In addition were the blender to be swirled out as suggested above then using more water to do this would increase the effectiveness, increasing the volume of sample produced would allow a greater volume to be used. As such I would propose doubling the mass of potato to be blended and scaling up further stages of the procedure accordingly. -A change to more specific temperatures that would prevent the unknowns surrounding the sample being frozen. The proposed tested temperatures and storage locations would be: Freezer between -1�C and -3�C Fridge at no higher than 5�C Room Temperature as in initial method. Implementing the above improvements would greatly increase the accuracy of the procedure and potentially allow better supported conclusions to be drawn from the results. This would enable far more accurate judgements as to the accuracy of the hypothesis to be made. (Pilot testing would be necessary to ensure that implementation of these changes into the existing method is a possibility.) ?? ?? ?? ?? ...read more.

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