Citrus Juice Lab Report

The freshly squeezed citrus juices of Lemon,lime and orange were analysed through titration over the period of 2 weeks. Initially the lime juice was found to be slightly more acidic than the other juices followed by lemon juice and then orange juice since it is known that usually lime is more acidic than lemon and orange. It was hypothesised that the acidity of each juice will increase or decrease after the period of two weeks depending upon the sugar content of that citrus fruit that the juice is extracted from. The acidity of the juice with the highest sugar level will gradually increase over the period of time since sugar contribute to the the fermentation of the citrus juice to lactic acid. The hypothesis was shown to be correct;however

the results did no show a significant increase in the acidity of the juice for the hypothesis to be shown precisely.
The highest sugar level was found o be present in orange juice with 15.4 g/L of sugar followed by lemon with 12.9 g/L and then lime with 10.3g/L . As orange juice had the highest amount of sugar, the acidity of orange juice was shown to have increased over the period of 2 weeks. The pH of orange decreased from 2.84 to 2. 75 . As the lactic acid bacterium of the Lactobacillus delbruckii type, normally present on the fruit aid in fermenting the citrus juice to lactic acid. The results agreed with the hypothesis but it did not flow with the expected range for results as there was not a very significant increase in acidity over the period of two 2 weeks mainly due to the time frame of the investigation that did not allow the juices to be fermented for an extended period of time. With the short time frame, other factors could have also affected the rate of fermentation of the juice in addition to the sugar content.

Lactic acid have more growth requirements than then normal bacteria since it was evolved in nutrient-rich environments. Lactic acid bacteria have diverse mechanisms for creating the energy needed to support and sustain biological activities. The availability of organic acid in the fruit can be important in allowing growth and metabolism. As lactic acid bacteria have the ability to produce large amount of acids, they often inhibit the development of other bacteria in juices and are able to cause their own autolysis. Excessive clarification and pre treatment of the fruit during the process of sending the fruit to the market which removes many of the natural yeasts and flora. The chemical compsition of juice also affect the rate of fermentation. Fruits generally tend to contain sufficient substrate (soluble sugars)that allow for the yeast and bacteria to fermented , so it can be said that because the fruits used did not show a very high increase in acidity it did not provide a sufficient substrate for the lactic acid bacteria that is present on the fruit to be used for fermentation.Temperature has an impact on the growth and activity of different strains of yeast. At temperatures of

10 to 15° C, the non-Saccharomyces species have an increased tolerance to alcohol and therefore have the potential to contribute to the fermentation. Different bacteria can tolerate different temperatures, which provides enormous scope for a range of fermentations. While most bacteria have a temperature optimum of between 20 to 30ºC, there are some (the thermophiles) which prefer higher temperatures (50 to 55ºC) and those with colder temperature optima (15 to 20ºC). Most lactic acid bacteria work best at temperatures of 18 to 22ºC. The Leuconostoc species which initiate fermentation have an optimum of 18 to 22ºC. Temperatures above 22ºC, favour the lactobacillus species. so it can said that because the temperature as recorded was slightly above the favoured it did not provide a very favourable condition for the lactic acid bacteria to ferment the citrus juice. Oxygen availability could also have affected the rate of fermentation as some of the fermentative bacteria are anaerobes, and does not require oxygen for their metabolic activities. Lactobacilli that are frequently present on the fruits and juices in particular, are microaerophilic that grow in the presence of reduced amounts of atmospheric oxygen. In aerobic fermentations, the amount of oxygen present is one of the limiting factors. It determines the type and amount of biological product obtained, the amount of substrate consumed and the energy released from the reaction.

Errors/Recommendations

i. There would have been very small amounts of acids other than lactic acid in the lemon,orange and lime juices, meaning that the percentage of lactic acid is actually slightly lower. For example, acetic acid would have been present in small quantities. From the the total acidity of citrus juice, the result being expressed as only lactic acid . This value includes all the substances of an acidic nature in the juice that react with NaOH; however even if the predominating organic acid in citrus juice is citric acid; other organic acids, namely, tartaric, malic, beizoic, and succinic are present this citrus juices, the acidity of the citrus juice has to be calculated of the dominant acids.

ii. Some of these other acids may have been strong acids, which would have affected the endpoint (the accuracy of the endpoint relied upon the assumption that all of the acids in the lemon juice were weak, like citric acid).
iii. Because lemon, orange juice is coloured, it is more difficult to observe the change in colour of phenolphthalein indicator at the endpoint.
iv. In between titrations, extremely small amounts of water would have evaporated from the sodium hydroxide solution, as well as the lemons, which may have affected results very slightly.
v.

Despite straining the lemon juice before titration, small amounts of pulp would have affected the titrations, because pulps was in some cases blocking the pipette when the juice is transformed from volumetric to conical flask. For future investigation, instead of straining the lemon juice, it could have been filtered to remove all pulp and thus increase the accuracy of the result

vi. One possible improvement could have been to add an extra part to the investigation, involving the formation of a calcium citrate precipitate from the citric acid in the lemon juice (using limewater of a known molarity), which could be extracted and weighed:

vii. This would allow the determination of the percentage of citric acid in the lemon juice specifically, rather than the total acidity. The results of this could have been compared to those of the titration, and the contribution of citric acid to the overall initial acidity could have been determined.

viii. The experiment could have been performed over one a longer period of time day (rather than 14 days), which would have greatly reduced any loss of water from the sodium hydroxide solution, which may have improved results slightly.

ix. citric acid increases the acidity of foods and makes it harder for bacteria to

grow.

Conclusion:
The purpose of the investigation was to find which citrus juice had the highest increase in acidity over a period of 2 weeks and thus find how the amount of the sugar that is already present in the juice affected the acidity. It was predicted that as the content of sugar in the citrus increases the acidity of the fruit will increase. From the experiment it was found that orange juice had the highest increase in acidity due to its highest sugar level among other citrus juices. It was also found that due to some errors in the experimental procedure that even though lemon and lime had the same pH value they contained different sugar levels. The main source of error is time in this investigation so it is recommended for future investigation to increase the time frame so a significant increase or decrease can be detect. It was found that other factors affects the rate of fermentation besides the availability of soluble sugars in the fruit juices such temperature, the pH medium that the bacteria grows in, etc. The investigation is described of medium validity due to some errors during the experimental procedure. For future investigation it is recommended to increase the accuracy is adding extra part to the investigation that will allow to calculate the specific percentage of citric acid rather than the total acidity. If these recommendations were taken into account in future studies a much more valid investigation will be achieved.