What is pH?

pH stands for “potential of hydrogen” and represents the measurement of acidity or alkalinity of a solution. It is a logarithmic scale ranging from 0 to 14, with 7 being neutral. pH values below 7 indicate acidity, while values above 7 indicate alkalinity. In food science, pH is a crucial parameter as it influences various aspects such as taste, texture, microbial growth, and shelf life of food products. Understanding and controlling pH is essential in food processing to ensure product quality, safety, and stability.

How Is pH Measured?

pH Meter

Using a pH meter is the most accurate method for measuring pH. A pH meter consists of a probe connected to a meter that displays the pH value. The probe contains a glass electrode that senses the hydrogen ions in the solution. When the probe comes into contact with the solution, it generates a voltage that is proportional to the pH of the solution. The meter then converts this voltage into a pH value, which is displayed on the screen. pH meters are commonly used in laboratories and industrial settings where precise pH measurements are required.

pH Paper 

A pH paper is a simple and inexpensive tool for estimating pH. The paper is impregnated with pH-sensitive dyes that change color in response to the pH of the solution. To use pH indicator paper, a small amount of the solution being tested is applied to the paper or the paper is dipped into the solution. The paper then changes color, and the pH value is estimated by comparing the color of the paper to a color chart provided by the manufacturer.

pH and Microbial Stability

Microbial Growth

The growth of microorganisms, such as bacteria, yeast, and molds, is greatly influenced by pH. Most microorganisms have an optimal pH range for growth, and deviations from this range can either inhibit or promote their growth. For example, many pathogenic bacteria thrive in neutral to slightly acidic pH conditions, while some spoilage organisms prefer slightly acidic to acidic environments. By controlling the pH of foods, food processors can create conditions that are less favorable for the growth of undesirable microorganisms, thus improving microbial stability.

Enzyme Activity

Changes in pH can alter the structure and activity of enzymes, impacting their ability to catalyze biochemical reactions. In food processing, pH can be adjusted to inhibit the activity of enzymes responsible for food spoilage or to activate enzymes involved in food preservation techniques such as fermentation. For example, lowering the pH of a food product can inhibit the activity of enzymes that cause browning or deterioration, thus extending its shelf life.

pH and Food Texture

Protein Denaturation and Gelation

Proteins serve as fundamental structural elements in a wide array of foods, spanning from meat and dairy products to plant-based alternatives. pH levels exert a substantial influence on the charge distribution and structural conformation of proteins, thereby modulating their solubility, hydration, and interactions with other molecules. At specific pH thresholds, proteins undergo denaturation, where their native structure unfolds or aggregates to form a gel, process that contributes to textural changes. For instance, in cheese production, formation of protein gel occurs when the pH of the milk is lowered. This causes casein proteins to aggregate. As the protein gel forms, it entraps water and fat molecules, contributing to the characteristic texture and structure of cheese.

Starch Gelatinization

When starch is subjected to an acidic environment, such as in the presence of lemon juice or vinegar, it undergoes a process called hydrolysis. This process breaks down the long chains of amylose and amylopectin molecules into shorter chains or even individual glucose units. Consequently, the starch loses its structural integrity, leading to a softer and smoother texture in foods like sauces, soups, and custards. This transformation is particularly noticeable in dishes like lemon curd or hollandaise sauce, where the acidic component not only adds flavor but also plays a vital role in modifying the texture.

Emulsion Stability

Emulsion stability is intricately linked to pH through the behavior of emulsifiers, which are molecules that lower the interfacial tension between immiscible liquids, allowing them to form and maintain stable emulsions. pH influences emulsion stability primarily through its effects on the charge and conformation of these emulsifying agents. For instance, in an acidic environment, emulsifiers with functional groups such as carboxyl or amino groups may become protonated or deprotonated, altering their electrostatic interactions with water and oil molecules. This change in charge can impact the adsorption of emulsifiers at the oil-water interface, thereby affecting the stability of the emulsion. Consequently, emulsions prepared under different pH conditions may exhibit varying degrees of stability, leading to differences in the texture, mouthfeel, and overall sensory experience of emulsion-based products like salad dressings, mayonnaise, and sauces.

pH and Flavor

Taste Perception

The sensation of taste is primarily mediated by taste receptors on the tongue, which detect specific molecules and signal the brain to perceive various taste qualities such as sweetness, sourness, bitterness, saltiness, and umami. pH can modulate the perception of these taste qualities by altering the ionization state of taste-active compounds. For example, acidic pH levels enhance the perception of sourness by increasing the concentration of hydrogen ions (H⁺), which can interact with receptors responsible for detecting sour taste.

Aroma Release

pH can also influence the release of volatile aroma compounds, which contribute to the overall flavor perception of foods and beverages. Changes in pH can impact the solubility and volatility of aroma compounds, affecting their release from the food matrix into the air above the food. In some cases, acidic conditions can enhance the release of certain aroma compounds, leading to a more pronounced aroma perception.

Maillard Reaction

The pH of the food environment significantly impacts Maillard reaction, a crucial process responsible for generating flavor compounds and brown pigments in cooked foods. In acidic conditions, the Maillard reaction proceeds at a slower pace due to the protonation of amino groups in amino acids, hindering their reactivity with reducing sugars and promoting the degradation of Amadori products, leading to decreased flavor intensity. Conversely, alkaline environments accelerate the Maillard reaction by deprotonating amino groups, enhancing their reactivity with sugars and promoting the formation of reactive intermediates. Optimal Maillard reaction conditions typically lie within a neutral to slightly alkaline pH range, facilitating the generation of desirable aroma compounds and browning reactions while minimizing off-flavors and color degradation.

Masking and Synergistic Effects

In addition to directly influencing chemical reactions like the Maillard reaction, pH plays a pivotal role in modulating the overall flavor perception through masking and synergistic effects. When considering the interplay between pH and other flavor compounds within the food matrix, complex interactions arise that can either enhance or obscure specific taste qualities. For example, acidic pH levels not only intensify the perception of sourness but can also mask other taste qualities such as sweetness. This phenomenon occurs because the acidic environment accentuates the protonation of taste receptors responsible for detecting sourness, thereby amplifying the perception of acidity while potentially dampening the sensitivity to sweetness. Conversely, in alkaline environments, the perception of bitterness may be heightened, while sourness and sweetness might be subdued.

Wrapping Up

Food processors need to closely monitor pH levels during food processing for several crucial reasons. pH profoundly impacts food safety by influencing microbial growth; acidic environments inhibit pathogens, reducing the risk of foodborne illness. Additionally, pH affects the shelf life of products by influencing enzymatic and chemical reactions, thus controlling spoilage and maintaining quality over time. Moreover, pH plays a critical role in flavor development, texture, and mouthfeel, ensuring consistent and desirable sensory experiences for consumers. Therefore, meticulous control of pH throughout food processing is essential for ensuring food safety, quality, and consumer satisfaction.

Author

  • Courtney Simons

    Dr. Courtney Simons has served as a food science researcher and educator for over a decade. He holds a Bachelor of Science in Food Science and a Ph.D. in Cereal Science from North Dakota State University.