Food industry professionals are increasingly searching for intelligent food packaging that can signal when consumables are unsafe to use. Solutions encompass time-temperature indicators that give real-time shelf-life indicators and labels that change color to show potential contamination. Recent work in this area focuses on pH-reliant options.

Foods have various pH levels, and lower pH products typically have longer shelf lives, as they are less hospitable to the growth of microorganisms. Following are some of the latest efforts to harness the power of pH to enhance food safety.

Films Made from Bio-Based Ingredients

Researchers are looking at plant-based pigments to create pH-responsive packaging and reduce the use of chemical-based triggers. Efforts in this area include pH-responsive films made from hydrogels, including films made of anthocyanins (water-soluble pigments) from red cabbage, which contains 24 types of anthocyanins. The films, which are biodegradable, change color as the pH of the food changes. In another case, scientists wanted to see how pH-sensitive packaging would perform in high-ammonia environments. They put film on a package of fish for 72 hours and noticed a resultant color change that indicated spoilage.

Work elsewhere has involved making color-changing films from chitosan, a sugar derived from external shellfish skeletons. The main benefit of these films is that they provide visible and easy-to-understand indicators of possible spoilage. A secondary perk is that chitosan has antimicrobial properties, which could extend shelf life and help manufacturers maintain quality.

One low-tech option involves packaging a consumable with a sachet filled with a substance that can alter the food’s pH level.

Moving pH Sensors from Processing Plants to Packaging

Food processors have long used pH sensors to provide valuable data during specific food development and manufacturing processes, ranging from fermentation to pasteurization. The main goal is to verify that the pH level is within the desired range after a process’s completion. In a 2022 study, researchers tested a salicylic acid-based carbon electrode paired with a pH sensing element based on electropolymerized flavanone and found that the sensor had a 0.03-pH-unit maximum error rate.

A 2020 study, which involved treating lychee fruit with a specially engineered chitosan-based coating, showed the coating reduced pH levels during an 18-day storage period, making the fruit stay fresher for longer.

Elsewhere, researchers used 3D printing to make fruit labels that preserve freshness. Each label contained cellulose nanofibers that held growth regulators and chitosan. The team pre-programmed the nanofibers to inject the contents into the fruits at desired intervals. Tests showed this innovation caused a six-day extension of fruit shelf life. The labels included a color-changing component to monitor freshness.

In addition to a developing biodegradable options, researchers are also finding ways to make pH sensors smaller. A graduate student at Southern Methodist University recently developed a disposable pH sensor that’s only 10 millimeters wide and 2 millimeters long. That small size makes it suitable for virtually all food packages. Additionally, this device is inexpensive to develop with minimal labor, making it an economical option.

It has become increasingly clear that use and sell-by dates are not the most accurate means to inform consumers if food is still safe. However, intelligent food packaging developments that track pH levels can facilitate improvements that reduce food waste and the risk of illness due to foodborne pathogens.

Some of these technologies are still under development, and it will take time to determine if they’re sufficiently scalable for industrial use. But, as intelligent food packaging becomes more commonplace, decision-makers will have new tools to gain a competitive edge, and protect both their bottom lines and consumers’ health.