Titration and Food Chemistry Techniques

Titration is a familiar laboratory technique for general chemistry students. There are many different types of titration, including acid/base titration, reduction/oxidation titration, precipitation titration, and complexometric titration. As an analytical technique, titration is frequently used in the food industry to ensure that food products have the correct amount of vitamins and other essential components.

Titration’s Role in Nutrition

One of the most important parts of good health is adequate nutrition. In order to accurately assess someone’s nutrient intake, nutritionists need reliable data on the composition of the foods we eat. From analytical lab tests such a titration, food chemists can help in the construction of food composition tables. Knowledge about food composition is necessary for accurate diet quality assessment and is therefore essential to public health.

Analysis of food products using titration ensures that the foods we purchase have a balanced composition. For instance, food chemists can measure the salt content in canned vegetables using manual titration. It involves the use of silver nitrate (AgNO3) as the titrant and sodium chloride (NaCl) as the analyte. The AgNO3 and NaCl react in a 1:1 mol ratio. Therefore if we know the concentration of AgNO3 solution used as a titrant and the volume of the solution necessary to reach the endpoint of the titration, we can use stoichiometry to determine the concentration of NaCl in the food product. This way, food chemists are able to ensure that canned products are not too salty. Foods high in sodium can be hazardous to our health, making titration important for food analysis. Diets higher in sodium are associated with an increased risk of high blood pressure, a major cause of stroke and heart disease (FDA).

Food Texture and the Karl Fischer Titration

Titration can also be used to control the texture or crunchiness of food. Karl Fischer was a German chemist that invented a method for determining trace water content in food, which is important for ensuring foods have the correct texture. Crunchy foods can not have too much moisture or they will lose their crunchiness. Hence Fischer’s discovery is crucial for maintaining the correct texture of many of the foods we eat such as chips, crackers, pretzels, etc. The Karl Fischer titration uses the reaction involving the oxidation of sulfur dioxide to sulfuric acid by iodine in the presence of water. From this reaction, Fischer proposed a titration method using a standard solution of iodine, sulfur dioxide, and pyridine in methanol during the year 1937. A suitable base like pyridine or aniline added as a titrant would drive the equilibrium to the right, according to Le Chatelier’s Principle (since the products are more acidic). In this type of titration, the endpoint is reached when the presence of the brown iodine persists since the reaction can no longer proceed towards products. The method was extremely sensitive (able to detect ppm levels of water), automatic, robust, and fast. Later, the coulometric Karl Fischer method for water was altered slightly and marketed as a titration kit for use by chemists. 

The Karl Fischer titration method was further altered in the year 1959. A. S. Meyer and C. M. Boyd, two electrochemists at the Oak Ridge National Lab (ACS Publications),  discovered an alternative set up that used oxidation reduction titration. They reasoned that if the iodide could be converted to iodine at a platinum electrode in methanol, then the charge transferred would be proportional to the amount of water content in the sample. In Meyer and Boyd’s set up, two compartment cells were constructed with two platinum electrodes. The end point of this titration was detected by a current surge between the two electrodes. The total electric charge transferred from the surge was proportional to the amount of water in the unknown sample (Chemistry World).

Isothermal Titration Calorimetry

A notable advanced titration technique used in the food industry is isothermal titration calorimetry (ITC). ITC is used to derive the thermodynamic properties of biological reactions that are relevant to food quality, nutrition, and safety (International Institution of Food Science and Technology). Thermal characterization of food systems and their components gives us information that helps us optimize food processing and preservation techniques. Many temperature dependent food preservation and processing methods such as heating, cooling, or freezing can be optimized using data obtained from ITC (Modern Chemistry and Applications). According to Dr. Richard Frazier, a professor at the University of Reading, ITC provides us with “‘complete thermodynamic data including enthalpy (ΔH), entropy (ΔS), free energy (ΔG), association constant (Ka), and stoichiometry’” National Library of Medicine (for details on how these thermodynamic calculations are performed, please refer to: Thermodynamics Equations).

ITC is usually used to test macromolecule-ligand binding reactions. These are reactions in which a smaller ligand molecule binds to a larger macromolecule such as DNA or protein. In ITC, a sample of the macromolecule is titrated using a titrant containing the ligand that binds to the macromolecule. The calorimeter consists of two thermal conducting cells wrapped in an adiabatic jacket that allows changes in temperature but no heat flow (BCCampus). One cell contains water or a buffer solution (a solution of weak acid and conjugate base that resists changes in pH) while the other contains the macromolecule being tested. The temperature differences between the two cells is determined by thermocouple circuits (a circuit in which two different metals are joined for the purpose of measuring temperature). A constant power source provides heat to the cell with the sample, allowing the biological reaction being tested to occur. An appropriate ligand, which acts as the titrant, is titrated into the sample cell. The ligand and the macromolecule in the sample then react, causing heat to be released or absorbed, depending on the reaction. The temperature measurements are recorded and subsequent calculations can be performed (New Food Magazine).

Titration is a chemistry technique that is essential to food quality. Since the food we eat is connected to our health, this common laboratory technique is highly important to our everyday lives. Knowing the content and nutrients in foods stocked on grocery store shelves, analyzing the water content in foods to preserve proper texture, and understanding thermodynamic data to ensure safe food preservation and processing are a few of the applications of titration in the food industry. Overall, our food supply would not be as safe or high quality without the use of this essential laboratory technique.