Organic Foods Are No More Nutritious Than Conventionally Grown Foods

Abstract

This experiment compared the vitamin C in organic and conventional oranges.

It is commonly perceived that organic produce have more nutrients than their conventional counterparts, and this project did further investigation on this assumption. It was hypothesized that organic oranges contained more vitamin C than conventional oranges. The amount of vitamin C of each fruit was determined by using a reference sample and comparing the amount of iodine it took to oxidize a milligram of vitamin C, to the amount of drops of iodine it took to oxidize an ounce of both the juice of organic and conventional oranges.

The results of this experiment rejected the null hypothesis and the research hypothesis, and showed on average that conventional oranges contained approximately 4 milligrams per ounce of juice produced on average. This contradicted the view held by many that organic produce has higher nutrients than its conventional counterparts, but does not mean this is completely true. The data showed that conventional oranges had significantly more vitamin C than the organic ones, but a larger sample needs to be tested to come to this definite conclusion due to the many other studies that came to the conclusion that organic produce contained a significantly higher amount of vitamins, or that there was no significant difference between the two.

Introduction

It is highly perceived that organic food has a higher nutritional value when compared to its conventional counterparts, but this common assumption is not necessarily true. The difference between organic and conventional items is the method of farming used during the food production.

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In organic farming, many artificial and synthetic ingredients, such as artificial pesticides and preservatives, that are allowed in conventional farming are prohibited (Red Lion Organic Farms, 2016). Many make the assumption that because organic foods lack these chemicals and are more natural than conventional foods that must make them healthier.

This project did further study on this assumption and studied if by altering the method of farming, it was possible to change the nutritional content of a fruit or vegetable. Many studies have been conducted on organic vs. conventional produce as a whole, but they contradict one another. Researchers at Stanford University analyzed 245 studies comparing the nutrients in organic and conventional foods (fruits, vegetables, grains, poultry, meat, and eggs), and discovered that there was a slight difference in nutritional content (Watson, 2012). This led to a conclusion that organic food has little to no more nutrition than conventional food, but this was contradicted by an analysis made by Virginia Worthington, a nutritionist who earned a doctorate from John Hopkins.

In this analysis of 41 studies comparing organic and conventional produce, it was found that organic was higher in nutrition. It was found that there were insignificant differences in levels of protein and minerals, but organic foods had significantly more Vitamin C, iron, magnesium, and phosphorus (Worthington, 2001). This project tested Worthington’s claim that organic produce contains significantly higher amounts of vitamin C, and used conventional and organic oranges to do so. Vitamin C in organic vs. conventional produce has frequently been tested on brussel sprouts, cabbage, carrots, celeriac, corn salad, endives, kale, kohlrabi, leek, lettuce, mangel, peppers, potatoes, snap beans, spinach, tomatoes, turnips, and currants (Worthington, 2001).

Despite the fact that oranges have one of the highest Vitamin C contents, they have not been frequently tested on, which is why this study used oranges. This study compared the Vitamin C levels in organic and conventional navel oranges per ounce of obtained fruit juice and it was hypothesized that organic oranges contained significantly more vitamin C than their conventional counterparts. The hypothesis was based off the research done by Worthington which claimed that organic foods as a whole has more vitamin C than conventional foods. Also, in a German Comparative Literature Review conducted by the German Government, vitamin C was found significantly higher in organic produce half the time, but insignificant the other half (Woese et al., 1995). In this study, conventional produce never contained more vitamin C and organic produce had significantly higher amounts of vitamin C half the time, which in combination with the Worthington review, led to the hypothesized.

Methodology

To test Vitamin C levels, the experiment used titration, and the amount of iodine tincture (2%) it took to oxidize one milligram of vitamin C was compared with the amount of iodine tincture it took to oxidize one ounce of both organic and conventional orange juice. Titration is when a solution of a known concentration and volume, known as the titrant, is slowly added to another solution with a known volume, but unknown concentration until the reaction reaches neutralization, or in this case oxidation, which is indicated through color change (LibreTexts, 2016).

The reference Vitamin C sample consisted of five ounces of water, thirty-one milligrams of vitamin C and a teaspoon of a cornstarch solution. To get the reference Vitamin C sample, a five-hundred milligram Vitamin C tablet was crushed and dissolved into a sixteen ounce glass of water, and 1 ounce was removed from this solution using a syringe and placed into a separate clear glass. Four more ounces of water were added to this single ounce, and this solution contained 31 milligrams of vitamin C. Then a starch solution consisting of a teaspoon of cornstarch and 2 tablespoons of water was boiled into 4 ounces of water, and then a teaspoon of this solution was added to the Vitamin C solution. This was the Vitamin C reference sample, and it was tested by adding iodine to the solution. This project used cornstarch and iodine because when starch and iodine react, the oxidation is obviously shown through a persistent deep blue color.

This reaction occurs because the amylose in cornstarch forms into a spiral structure when mixed with hot water, and the iodine molecules slip into the coils of the amylose spiral, which causes an intense blue color (Libretexts, 2019). Iodine was added in drops using an eyedropper, and in between each drop, the solution was stirred for fifteen seconds. Drops were added and counted until the blue color persisted in the solution despite the stirring. If the color showed, but faded once stirred, another drop was added, but if the color was sustained even when stirred for fifteen seconds, no more iodine was added and the amount of drops of iodine added in total were recorded. The number of drops was the amount of iodine needed to oxidize thirty-one milligrams of vitamin C.

To find the number of drops it would take to oxidize one milligram, the recorded number of drops it took to oxidize thirty-one milligrams of vitamin C was divided by thirty-one. This number was recorded. To test the organic fruit juice, one certified organic navel orange was juiced using a juicer and the amount of juice it produced was recorded in ounces. Then, one ounce of the fruit juice was added to a clear glass of water containing four ounces of water. In this, a teaspoon of the starch solution which was used for the reference sample was added. This created the unknown vitamin C fruit juice sample. Then the iodine was dropped into the sample using the same eyedropper used in the reference sample, and the solution was stirred for fifteen seconds in between each added drop. The drops were added until the deep-blue color was sustained in the solution despite the stirring. The number of drops it took to oxidize the fruit juice was recorded.

The amount of vitamin C per ounce of fruit juice was calculated by dividing the total number of iodine drops it took to oxidize the fruit juice sample by the recorded number of drops it took to oxidize one milligram of vitamin C from the reference sample. The approximate vitamin C in the whole fruit was determined by multiplying the calculated vitamin C per ounce of fruit juice by the total number of ounces of fruit juice obtained from the orange. These steps were repeated three times with organic oranges, and then three more times using three different conventional oranges. Then the vitamin C levels from each trial were compared between the organic and conventional oranges.

Data Analysis

The independent variable in this experiment was the type of orange (organic or conventional) and the dependent variable was the amount of vitamin C in the orange per ounce of juice.

Table 1. Amount of Fruit Juice Obtained from Orange in Ounces

Number of Ounces

Trial 1

Number of Ounces

Trial 2

Number of Ounces

Trial 3

Conventional Oranges

3.9 ounces

4.3 ounces

4.5 ounces

Organic Oranges

3.2 ounces

3.6 ounces

3.9 ounces

Table 2. Number of Iodine Drops to Oxidize One Ounce Of Fruit Juice

Number of Iodine Drops Trial 1

Number of Iodine Drops Trial 2

Number of Iodine Drops Trial 3

Conventional Oranges

47 drops

50 drops

54 drops

Organic Oranges

38 drops

44 drops

38 drops

Table 3. Vitamin C in Organic v. Conventional Oranges Per Ounce

Amount of Vitamin C (per ounce) Trial 1

Amount of Vitamin C (per ounce) Trial 2

Amount of Vitamin C (per ounce) Trial 3

Conventional Oranges

20.00 mg

21.28 mg

22.98 mg

Organic Oranges

16.17 mg

18.72 mg

16.17 mg

Table 4. Vitamin C in Organic v. Conventional Oranges in Whole Fruit

Amount of Vitamin C (Whole Orange) Trial 1

Amount of Vitamin C (Whole Orange) Trial 2

Amount of Vitamin C (Whole Orange) Trial 3

Conventional Oranges

78.00 mg

91.50 mg

103.40 mg

Organic Oranges

51.74 mg

67.40 mg

63.06 mg

Table 1 summarizes the amount of fruit juice obtained from each orange, and it was seen that the conventional oranges contained a noticeably higher amount of juice than, and on average they contained .67 more ounces of juice than the organic oranges. Table 2 shows the amount of iodine drops it took to oxidize one ounce of the fruit juice. When looking at table 2 and table 3 side by side, it was seen that the more drops of iodine it took to oxidize the ounce of juice, the more vitamin C that ounce contained. In table 4, it was seen that the conventional oranges contained a much higher amount of vitamin C as a whole, and had 30.2 more milligrams of vitamin C in total on average, and this was because of the higher amounts of vitamin C per ounce of juice and higher concentration of vitamin C per ounce of juice.

The mean amount of vitamin C in conventional oranges per ounce is 21.42 milligrams, whereas the mean amount of vitamin C in organic oranges per ounce is 17.02 milligrams. The variance of the data of the conventional oranges is 2.2348, while the variance of the data of the organic oranges is 2.1675. Both sets of data have relatively small variances, though the conventional oranges’ Vitamin C levels are very slightly more variant than the organic oranges’. When using a one tailed t-test to calculate if the difference of the Vitamin C in the two types of oranges is significant, with a df of 4, the t-value was -3.63223. The p-value was .011058. The result was significant at p < .05.This means that difference in Vitamin C between the organic and conventional oranges was significant, and conventional oranges, on average, showed to have 4.4 more milligrams of Vitamin C per ounce compared to organic oranges.

Conclusion

The purpose of this experiment was to compare the Vitamin C in organic versus conventional oranges. It was hypothesized that organic oranges contained significantly more vitamin C than its conventional counterparts. The data and the t-test rejected both the null and the research hypothesis, and supported the conclusion that conventional oranges contain significantly more Vitamin C than its organic counterpart. On average, the conventional oranges contained 4.4 more milligrams per ounce of fruit juice the orange consisted of, and there was a small variance in both sets of data, making it consistent for each trial. The mean of the vitamin C in both the entire oranges was much higher in the conventional oranges due to the fact that they produced more juice, which is most probably due to the fact that much of non-organic produce is selectively bred, giving it different traits, such as being larger in size (“What is Selective Breedings?”, 2017). This meant that conventional oranges had more vitamin C in the whole fruit than its organic counterpart due to the fact that they were larger in size, and also they showed to have higher concentration of vitamin C.

The results of this experiment were contradicted by the Worthington analysis, which found organic foods contained significantly more than vitamin C than conventional foods (Worthington, 2019). Similarly, in 2010, a study by Washington State University scientists found organic strawberries have more vitamin C than conventional strawberries (Chang, 2012). Another contradiction is a 2009 meta-analysis of 162 studies finding that the differences in nutrition between organic and conventional products are insignificant, and their nutritional contents do not vary (Dangour, et al., 2009). These are three of many studies that have contradicted the findings of this experiment, claiming the conventional produce contained more vitamin C than the organic produce, but the results of these studies are a result of many different types of food and nutrients, and did not focus specifically on oranges and vitamin C. A study conducted at the University of Alberta’s Department of Science has similar results to this experiment where conventionally grown navel oranges had a higher vitamin C concentration than the organically grown navel oranges (Esch, Friend, & Kariuki, 2010).

A possible reason the conclusion that the conventional oranges contained significantly more vitamin C than the organic oranges resulted from this experiment is the selective breeding used on the conventional oranges that is prohibited by organic produce standards. The majority of citrus fruits are hybrids, and in conventional agriculture, these citrus fruits are often selectively bred (Stone, 2017). Selective breeding changes genetic features of the orange and could have possibly cause a difference in the amount of nutrients, including vitamin C.

A possible reason for the contradiction of multiple studies could have been that the mentioned contradicting studies used many different types of produce when testing organic and conventional, but when only focusing on oranges, conventional oranges contained more vitamin C. This is further supported by the research done at the University of Alberta, which focused on specifically conventional and organic navel oranges, and had results similar to this experiment. This could lead to the conclusion that the nutritional content in organic vs. conventional food varies based on the food being tested on and the nutrients being tested for, and the general statement that one is more nutritional than the other can not be made.

This study could have been majorly improved with more trials tested for each type of orange to give more data to analyze, which could have possibly led to a different conclusion due to the fact that there are so many studies against organic produce containing less nutrients than conventional produce. If more data points were added, the results could have supported a conclusion that there was an insignificant difference between vitamin C in organic and conventional oranges. Even if these results were obtained, there would still be a contradiction of the assumption that all organic food contains more nutrients than conventional food. The methodology also could have been made to be more precise because the iodine was measured with an eyedropper, and not every drop was guaranteed to be the same size, which could affect the calculated vitamin C content. This experiment also could have tested more nutrients than vitamin C, such as phosphorus and iron.

Bibliography

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