Written by: Katie Rodger, Ph.D. | Issue # 91 | 2019
- Milk protein-based edible films can protect food from spoilage and provide an environmentally friendlier alternative to plastic.
- Cow milk immunoglobulins (Igs) have been added to milk protein-based edible films to increase antimicrobial properties.
- Igs increase the solubility, tensile strength, adhesiveness, and appearance of milk protein-based edible films.
We all know that plastics are bad for the environment, and there is ongoing research indicating they are harmful to humans as well. When microplastics—less than 5 mm in length—get into oceans and tributaries, they end up in the fish and plants that we may consume. But plastic is an integral part of our lives. Computers, cars, and many household appliances are, or include components made of, plastic. Medical equipment like syringes, gloves, and the little plastic filters that go over thermometers for each new patient are one-time use items that help ensure good hygiene. And, of course, much of the food we buy is wrapped in plastic for both convenience as well as protection from contamination. In fact, it’s hard to imagine giving up the assurances that plastic can provide us when it comes to keeping our food safe. But advances in the development of milk protein-based edible films may soon make those wrappers not only less wasteful but even beneficial to our health, thus letting us have our cake and safely eating it, too.
Edible films are not new, as researchers have been experimenting with different ways of making them for more than two decades . In a previous article in SPLASH!, we reported on a study conducted by Jean-Luc Audic and his colleagues from the Université de Rennes 1 in Rennes, France of a then-new film derived from milk casein . Audic et al. demonstrated certain functional properties of milk proteins and whey in the production of protein-based films and biomaterials . Among the benefits of that particular film were protective properties from light, oxygen, and humidity, making it a viable option for packaging foods like string cheese. It was also easily dissolvable, which could make it well-suited for packaged noodles that could be dropped into boiling water without needing to unwrap. Recently, researchers have looked at new ways to improve milk-based films’ antimicrobial properties that could both protect foods from spoilage and also possibly boost our health. These types of films are often dubbed “active films.”
Previously, milk-based edible films were sometimes given antimicrobial properties via non-milk additives. Mixing in organic sorbic, propionic, and benzoic acids, fatty acid esters (glyceryl monolaurate), polypeptides (lysozyme, peroxidase, and nisin), and even plant essential oils (cinnamon, oregano, and lemongrass) have all produced some level of antimicrobial benefit, primarily measured by keeping food from going bad . But in a recent study, researchers looked for a more targeted way to not only prevent contamination but to improve the antimicrobial potential of edible films with the addition of another milk component, immunoglobulin.
In March 2019, research scientists from the Natural Resources Institute Finland improved the quality of active films by successfully incorporating active immunoglobins (Igs) and further doping them with antibacterial proteins that enhance the films’ antimicrobial properties . The amount of Igs incorporated also affected the mechanical properties of the films such as adhesion and tensile strength. Pirjo Rantamäki and her colleagues believed that their team was the first to produce data of the novel Ig-incorporated biofilms.
In their study, Rantamäki and colleagues targeted particular microbes, believing that “If milk Igs which are specific against spoilage microbes or pathogens could be incorporated and released from film materials in biologically active form, then such materials could be used in products for passive immunization against harmful microbes” . In particular, the team looked at how edible films with added Igs harvested from bovine colostrum could minimize and even prevent dental cavities caused by Streptococcus mutans, a common cause of tooth decay.
Rantamäki and her team collected four milkings from 84 pregnant Friesian cows that were immunized against Streptococcus mutans and Streptococcus sobrinus, both of which are responsible for tooth decay. Milkings from nonimmunized cows were also collected for control purposes. Three types of protein sources were used for the study: β-lactoglobulin-enriched whey protein and two commercial milk proteins. The commercial milk protein used in the study consisted of WPC-75 and DSE1908, and sodium caseinate was also used as a film-forming material.
The films made from each protein source were tested for a number of mechanical properties. Solubility is an important test factor because researchers hope films that dissolve easily in water or saliva could be an effective means of pharmaceutical delivery. When testing solubility, the Rantamäki’s team used water, simulated saliva, and real human saliva and found that the Ig-blended edible films were, in fact, more easily dissolved. “It seems that in films containing high concentration of Igs, the dominant bonds were more easily loosened and more rapidly dissolved,” the researchers observed. “This result can be important regarding the release of various biologically active compounds from edible films.” In particular, Rantamäki’s team was interested in how Igs might be broken down by saliva and help prevent cavities. They found that “When the IP [immune preparation] used in the present edible film study was applied as a mouth rinse by adult volunteers for 3 days, it resulted in a higher resting pH in dental plaque and decreased the relative number of mutans streptococci significantly in the test group when compared with the control group” . It would seem that the Igs could, in fact, bring an added benefit to milk protein-based edible films.
Increasing Ig fractions not only increased the film’s solubility, but also its tensile strength, adhesiveness, stickiness, and appearance. The team found that with increasing Ig concentrations, the film would require more force before tearing. Similarly, the adhesiveness of films increased when increased Ig concentrations were used. WPC-75 films made with increased Ig fractions were also smoother and more transparent than films made without Ig. All of these mechanical properties, of course, increase the appeal of using such films in the food and pharmaceutical industries.
The benefits of using Igs in edible films are plentiful. As Rantamäki’s team notes, “The emergence of antibiotic-resistant pathogen strains will in near future put emphasis on the need to develop alternative ways to prevent and treat oral and gastrointestinal infections” . In the near future, we may see edible films that can prevent Escherichia coli or Salmonella, and perhaps the wrappers or coatings for candies, lozenges, and even chewing gum could help keep us healthy while minimizing plastic waste. Milk protein-based edible films are biodegradable and reduce the waste that ends up in landfills and our oceans. With the ongoing development of these active films, one thing is undeniably clear. The future is no longer plastic.
1. Rantamäki, P., Loimaranta, V., Vasara, E., Latva-Koivisto, J., Korhonen, H., Tenovuo, J., Marnila, P. 2019. Edible films based on milk proteins release effectively active immunoglobulins. Food Quality and Safety. 3(1): 23–24.
2. Audic, J., Chaufer, B., Daugin, G. 2003. Non-food applications of milk components and dairy co-products: A review. Lait. 83(6): 417–438.
3. Franssen, L. R. and Krochta, J. M. (2003) Edible coatings containing natural antimicrobials for processed foods. In: S. Roller, S. (ed.) Natural antimicrobials for minimal processing of foods. CRC Press, Boca Raton, pp. 250–262.