RESEARCH SPOTLIGHT: Topical application of lactose oxidase to inhibit spoilage microbes that cause blue discoloration of mozzarella cheese
This week, we are highlighting the work of MPS student, Pablo Torres. He is investigating enzymatic-preservation techniques to stop mozzarella cheese from turning blue! In 2010, over 70,000 mozzarella balls in Italy turned blue as a result of bacterial contamination that created a blue discoloration on the fresh cheese [1]. It was quite a spectacle!
Microbial contamination is one of the largest factors adversely affecting the profitability of the dairy industry, as it shortens the shelf life and increases waste. Mozzarella is produced via the pasta-filata, or stretched curd, technique that is done in high temperature water. The curd is mechanically stretched to obtain its unique textural and melting characteristics. Once the mozzarella is formed, it is susceptible to bacteria that can grow at refrigeration temperatures, or psychrotrophic bacteria. One of the main psychrotrophic organisms of concern in the dairy industry is Pseudomonas spp. which can cause spoilage defects. Among these defects are the blue discoloration produced by Pseudomonas fluorescens in dairy products like fresh mozzarella or queso fresco. This blue discoloration has also been observed in non-dairy products like salmon or rabbit meat!
So, what are some ways that we can stop the cheese from getting this blue defect? Enzyme-based preservation technologies have been a novel method for preservation in the dairy industry. Enzymatic preservation can be a clean label approach to reduce spoilage and extend shelf life. An enzyme of interest is lactose oxidase, a naturally derived enzyme that hydrolyzes milk sugar into lactobionic acid and reduces oxygen to hydrogen peroxide. This can potentially work as an antimicrobial against Pseudomonas fluorescens and stop the formation of the blue pigment.
To analyze if lactose oxidase can reduce the blue discoloration, Pablo topically applies lactose oxidase to cheese that has been contaminated with Pseudomonas fluorescens. Throughout the duration of the experiment, he takes photos of the mozzarella and compares the treatments to a control sample.
A software is used to quantify color using the CIE, or L*a*b* color space. Colors are measured on a scale for values of L*, a*, and b* which are determined by the color wheel of human vision. L* represents the lightness of a sample, 0 representing black and 100 pure white, a* quantifies the green-red scale, and the b* axis representing blue-yellow values. With the data provided by the software, a comparison between the treatment samples and the control can be made to determine if the lactose oxidase is effective at reducing the bacteria that cause the blue discoloration.
So far, lactose oxidase has been an effective enzymatic-preservation technique, resulting in reduced blue color in treated samples!
[1] Greenhalgh, M. (2010). Bacterial Contamination Caused Blue Mozzarella. Retrieved from: https://www.foodsafetynews.com/2010/06/bacterial-contamination-caused-blue-mozzarella/