Traditional Methods for Mineral Analysis

This chapter focuses on the principles and procedures involved in measuring pH and titratable acidity, two interrelated concepts both affected by the presence of compounds that can accept or donate protons. Each of these quantities is determined in separate ways and each provides its own particular insights on food quality. For example, while pH is important to assess the ability of a microorganism to grow in a specific food, titratable acidity is a better predictor than pH of how organic acids impact a food’s flavor. Most acids in foods are weak and therefore only partially dissociated. Some properties of foods are affected only by this ionized fraction of acid molecules while other properties are affected by the total acid content. The pH is defined as the negative logarithm (base 10) of the hydronium ion concentration and measured via pH meters, which quantify electrode potentials and convert these to pH using the Nernst equation. Titratable acidity, which denotes the total acid concentration in a food, is obtained by titration of intrinsic acids with a standard base. This parameter is often determined in fruits and fruit juices and changes with ripening stage. Since the perception of a tart flavor caused by organic acids is strongly influenced by the presence of sugars, the concept of Brix/acid ratio is also covered in this chapter.