Effect of Time on the Acid Value of Cooking Oils

Introduction

This study investigates the impact of reuse duration on the acid value of cooking oils within African households, where reusing oil is common practice. The acid value, indicating the presence of free fatty acids, becomes a health concern as it can degrade oil quality, making it potentially harmful and affecting heart health. This investigation seeks to understand how prolonged use affects the acid value and, consequently, the health implications of reusing cooking oil.

Variables

• Independent Variable: Duration oil is used (in minutes)
• Dependent Variable: Acid value of the oil
• Controlled Variables: Amount of oil used, type of oil, frying temperature, and type of food fried

Background Information

The acid value is used with fats and oils it is defined as the weight of KOH in mg needed to neutralize the organic acids present in 1g of fat and it is a measure of the free fatty acids present in the fat or oil.

FFA are a source of flavor and aroma but when the acid value of the oil or fat is increased it goes rancid and starts to produce a foul smell which causes defects in oils.

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The acid value is determined by directly titrating the oil in an alcoholic medium against standard potassium hydroxide/sodium hydroxide solution. the value is the measure of the amount of fatty acids that have been free due to the action of moisture and/ or temperature. This will allow the quality of the oil to be figured out. It is also an indicatoe of inadequate storage conditions (high temperature, relative humidity), besdies of free fatty acids, hydrolosis of triglycerides produce glycerol.

Hypothesis

Different fat samples may contin varying amount of fatty acids. In addition, the fats often become rancind during storage and this rancidity is as a result of a chemical and enzymatic hydroloside of fats into free acids and glycerol. The amount of free acids present or the acid value of fat is a useful parameter because its shows the increase in free acids/acid value. The increase in the acid value shows the rancidity of the oil , so it can be said that , the oil which was used for longer will have a highet value than the oil was was used for a shorter period of time.

Materials and Procedure

Materials include standard laboratory titration equipment, plantain for frying, and a balance for measurement. The procedure involves frying plantain slices in oil for varying durations (5, 10, 15, 20, 25 minutes), followed by titration to determine the oil's acid value.

Data and Analysis

The data collected includes the initial and final weights of oil samples, volume of potassium hydroxide solution used in titrations, and calculations of acid values for different time intervals. Here's a summarized representation of the raw data and calculated acid values:

Table 1: Titration Data and Calculated Acid Values

Conclusion

With regards to the research question “How does the duration an oil is used for affect its acid value?”, it appears that when the oil was used to fry plantain for a long period of time it had a higher acid value than oil that was used for only a minimum time. A close look at the uncertainties also shows the error from the devices were not significant. The results also indicated that the oil that wasn’t used to fry had a lower acid value than the ones that were used to fry the plantain, this helps prove the hypothesis that if an oil is used over again the rancidity and the acid value of the oil increases but when the oil hasn’t been used repeatedly the acid value is still relatively lower. The results show a significant increase in acid value as the time increased.

For example, when the oil was used for 5 minutes, the acid value was 3.39mg but at the end of the experiment the acid value had increased to 9.34mg. I was astonished by the results, but some experimental errors will be discussed in the evaluation section and this questions the validity of the results. The results therefore show that the free fatty acids are released when the oil is re used and is kept for a long time, it also shows the rancidity of the oil is bound to increase as the acid value increases. The rancidity of the oil is observed because over time, the oil changed color from yellow to dark brown almost black, this clearly shows that there are impurities in the sample.

From my analysis, I will inspire households in Ghana to not use oil for prolonged periods of time because oils looses its edibility when it passes 4.0mg KOH g-1 oil, this is dangerous for the human body to be consuming rancid oils. This experiment was successful in proving the hypothesis for the acid value of oils, however, the reason behind the change is still unclear. From this analysis, it is important to store oil in the right conditions because the temperature can also change the rancidity of the oil.

Evaluation

While the study's repeated measurements enhance reliability, potential errors, such as inconsistencies in frying conditions and measurement inaccuracies, could impact validity. Future studies could explore the effect of different food types and frying temperatures on oil degradation to provide a more comprehensive understanding of factors influencing oil quality and health implications.