Gram Negative Bacteria Infographic

Practical tip of the month

Nicole Martin

Gram-negatives provide more information about post-pasteurization contamination than coliforms

Do you want to improve your fluid milk quality? Start testing your finished product for total Gram-negative bacteria in addition to coliforms.

It’s not surprising that after a century of monitoring processed dairy products for coliforms, much of the industry has become adept at eliminating these contaminants. In our long-term monitoring program, the Voluntary Shelf-Life (VSL) program, we’ve seen coliform prevalence in pasteurized fluid milk steadily drop over the last 20 years. But that doesn’t mean that rates of post-pasteurization contamination (PPC) in fluid milk have declined, on the contrary, this is still a major issue for many fluid milk processors. So, you may be asking yourself if coliforms are not frequently detected in the finished product, how do we know there is PPC? The answer starts with the bacterial cell wall. There are two main types of bacterial cell walls, we call these Gram-positive and Gram-negative – named for Danish bacteriologist Hans Christian Gram who developed a method for classifying bacteria by their cell wall properties. The important difference between Gram-positive and Gram-negative bacteria as it pertains to PPC, is that Gram-negative bacteria are very heat sensitive, meaning they are easily killed by pasteurization. When Gram-negative bacteria are detected in pasteurized dairy products it’s very likely that they were introduced after the heat treatment – they are therefore indicators of PPC.

In current fluid milk supplies, the primary types of bacteria that are contaminating pasteurized fluid milk after pasteurization are non-coliform Gram-negative bacteria, especially Pseudomonas. In fact, a recent study from the Milk Quality Improvement Program determined that of 132 samples with PPC, Pseudomonas was the primary cause in 101 of those samples. Fluid milk processors who aren’t testing for Gram-negative bacteria are not likely to catch PPC when it happens – this leads to marketplace failures and unhappy customers.

If you’re convinced that monitoring your pasteurized fluid milk for Gram-negative bacteria is the right move, there are a couple of methods that you can use. The standard method for detection of Gram-negative bacteria uses Crystal Violet Tetrazolium Agar (CVTA), but this method may be challenging for processors without the capability of making traditional agar in-house. Fortunately, our team recently developed a method to detect Gram-negative bacteria in fluid milk by modifying the Coliform Petrifilm method. In short, simply incubating Coliform Petrifilm for an additional 24 hours (a total of 48 hours) then counting any growth, with or without gas production, provides a simple way to quickly determine if the product is contaminated with Gram-negative bacteria like Pseudomonas.

We’ve seen great results from fluid milk processors who implement Gram-negative testing in their overall quality program. If you have any questions on how to get started with this method, feel free to reach out for more information.

Practical Tip of the Month

Gas Production in Cheese

Cheesemakers are tasked with making a product that has a life of its own while also trying to be as consistent as possible. There are several types of issues that can arise that lead to unwanted gas production, ultimately causing cheese blowing, flavor and odor defects, and the creation of slits and cracks. These issues are costly to plants, and leave consumers with an unpleasant taste in their mouth (literally)!

The below table outlines several different types of these issues, their sources, the types of cheeses that are impacted, and hallmark characteristics of these gassy issues.

For further questions about cheese defects, please reach out to Dr. Sam Alcaine, alcaine@cornell.edu or Rob Ralyea, rdr10@cornell.edu.

Aljosa Trmcic

When I write articles and scientific papers, I find it difficult to do a proper critical review of my own work because I am so intimate with the sentences and ideas behind them that during review I often switch to just reciting the text by heart instead of truly reading it. What I need is a fresh pair of eyes to read the text for the first time and put every single detail to proper scrutiny. The same way I am intimate with my sentences and ideas, dairy industry workers are intimate with their environment, equipment and work. This intimacy means that any deviation from the usual state of their environment, equipment and work will either be immediately noticed, or it will never be noticed because it soon becomes part of the usual state. So, the same way I need fresh pair of eyes to review my text, the dairy industry workers need a fresh pair of eyes to review their environment, equipment and work.

First example is a problem with post-pasteurization contamination (PPC) that persisted in one of the fluid milk processing plants for months. Since the PPC problem did not seem sporadic and a relatively similar spoilage was observed across all fluid milk processed each day the multiple different fillers used by the processor were excluded as the main cause of the problem. Instead, the p-tanks, used to store pasteurized product before filling, were again and again identified as the most likely source, but what part of the p-tanks exactly was the source the workers were not able to determine. They determined each investigation that integrity of the p-tanks was not compromised in any way and the cleaning and sanitation procedures were appropriate. It took that fresh pair of eyes to determine that membrane pressure sensor, used to monitor product volume in the p-tank, was leaking and retained a lot of solid residues in the sensor port. While the sensor is designed to seal the port opening and have only the membrane of the sensor exposed to the product, it will only seal properly if the integrity of the rubber gasket surrounding the membrane is not compromised. Fresh pair of eyes identified that the sensor includes a gasket and needs to be checked and maintained regularly. Since then, the processor put the tank pressure/level sensors on their regular PM schedule and the rest is PPC history.

Second example is a food safety one; troubleshooting persistence of Listeria in a dairy processing environment. A processor with a five-star environmental monitoring program is dealing with persistent strain of Listeria in one the drains; 15 drains present in the processing environment only one continuously comes back positive for an entire year. It took again a fresh pair of eyes, or better yet fingers, to detect a small crack in the drain that leads to a large opening behind the drain wall. A niche that never gets scrubbed and provides Listeria with plenty of food to grow and persist in the environment. Since then, the processor replaced the drain to eliminate the crack as well as the open space behind it and rest is persistent pathogen contamination history.

So, when you look upon your perfect environment, equipment and work keep in mind the value of putting it all under additional scrutiny by taking another look with a fresh pair of eyes; and let us know if you want Cornell’s Dairy Foods Extension to be those eyes for you.

Aljosa Trmcic

On May 18 & 19, 2022 Milk Quality Improvement Program traveled to Austin, Texas to attend DairyTech;  a conference on dairy technology innovations organized by IDFA. What promises to be an annual event aligns perfectly with the mission of MQIP; as the leaders in Digital Dairy, we are working on assisting the dairy industry in adopting the technologies of tomorrow and help them enter the fourth industrial revolution popularly referred to as the Industry 4.0. IDFA featured at the conference some of the hot topics and success stories in dairy technology innovation and the common word connecting all of it was “data” and everything about how data can be captured, stored, analyzed, and used to provide added value to the company.

First hot topic of the conference was Data Analytics where one of the companies introduced a process of determining the optimal number, type, and quantity of products a food company should be manufacturing in any given situation. The data analyzed in this process covers all aspects of food processing including (i) the price and composition of all incoming ingredients, (ii) the ingredients and ingredient components needed to make each product, (iii) the costs of making each product, and (iv) the price of the product on the market. Using advanced statistics and computer modeling, for example machine learning and artificial intelligence, the company has been able to make recommendations on the optimal processing plan to minimize the cost and waste while maximizing the profit of the entre food company. MQIP has been taking similar statistics and computer modeling approaches to develop free tools that can be used to evaluate interventions that reduce spoilage and optimize the processing plan (click here for more details). Some of the open-access tools that are already available on our Digital Dairy page can be used to predict spoilage of both milk and cheese and there are others that are currently being developed.

One of the companies that participated in the conference introduced improvements to their Laboratory Information Management System (LIMS) and encouraged entire dairy industry to move away from paper-based records which are still very common in many aspects of the dairy production, processing, and distribution. While digitization, transformation of analog information to digital, can already be considered a beneficial step, the ultimate goal is for each operation and dairy industry as a whole to embrace digitalization. Digitalization goes a step further from digitization by transforming the process of collecting and using the data itself; for example, instead of writing the pH of your yogurt on your paper make-sheet, you would type it into the make-sheet on your tablet and eliminate the paper step, or better yet have pH meter display the measurement directly into your make-sheet on your tablet and eliminate the copying part altogether. LIMS and similar electronic systems represent the key to successful digitalization of the dairy industry and the base for using the true potential of predictive modeling. A vision MQIP has is that information captured in electronic systems like LIMS could immediately be used in the type of predictive models we are developing to more accurately predict characteristics of each product batch. For example, results of spore testing on raw milk, post-pasteurization testing on pasteurized milk, and electronic temperature recordings along the entire milk supply chain could be used to provide accurate information to the end consumer about expected shelf-life of that specific jug of milk they want to buy in the grocery store.

One downside of digital transformation and replacing paper records with electronic ones is that we are not just making all this information more accessible within our organization but also potentially to people outside of our organization that want to take and misuse this information. Cyber-attacks are real and dairy industry is not speared from this risk. Therefore Industry 4.0 and IDFA consider cybersecurity equally important aspect of digital transformation. The DairyTech conference featured several experts in cybersecurity who together provided some of the most important actions you can do when cybersecurity crisis hits, and they say the first step is to seek legal counsel and engage law enforcement as soon as possible. While knowing what to do during attack is important, as always, prevention and knowing what to do so the attack does not occur in the first place is even more important; the experts say that the cyber-attackers are not only motivated by the value of the data but also by the ease of getting access to this data. You can see it similar as motivation for stealing your bicycle; it is only a matter of time when it will get stolen if you don’t keep it locked.

New technologies including digital technologies offer number of benefits to the dairy industry and will be inevitable part of the overall transformation of the dairy industry, but these technologies will need to be safe, effective, and promising for the companies for them to invest and implement these new technologies. The Milk Quality Improvement Program is continuously searching for new technologies that might be of interest to the dairy industry and are also directly supporting the transformation by developing new digital solutions. Feel free to reach out to us with any questions or concerns by emailing Aljosa Trmcic at at543@cornell.edu or Rob Ralyea at rdr10@cornell.edu.

Efraim Shachter
Commercial Analyst

 We all enter a pre-formed world and want to both understand it and find a place in it that makes sense. For as long as I can remember, I have been interested in understanding how the everyday items with which I interact came to be. When I became old enough to surf the web, much of my free time became dedicated to researching the scientific processes and historical development of common foods, in particular. I became increasingly fascinated by cheese, due to the milestone in food preservation technology that its development represented, the many chemical processes involved in its production, and the iconic cultural significance that many types of cheese have throughout the world. In 8^th grade I taught a Food Science elective class to my peers during which we made mozzarella, butter, and ice cream, among other foods, and I would explain the scientific processes taking place. It was around that time that I visited a family friend’s dairy farm in Okeechobee, Florida and became intrigued by the dairy industry. I then began working at a summer camp; taking care of the barn animals, milking the goats, and making chevre cheese with the campers.

In undergrad at Cornell, I majored in Food Science, and then decided to minor in Business, after multiple advisory council members emphasized the need to integrate business objectives within product development. I had two internships: one was an R&D internship for Mondelez International and the other was R&D for a startup company in Israel called Amai Proteins. Amai is a designer protein company, and while I was there we were working on a sweet protein similar to Monellin for food industry applications. On campus, a few CALS friends and I decided to revive ChocTech, the chocolate and confections technology club, where we made chocolate from scratch, explored the historical relevance of chocolate, and learned to appreciate the unique flavor notes of chocolates made from cocoa sourced from different parts of the world. My ongoing interest in dairy manifested through working for a semester at the FPDL making cheese twice a week before my first class, volunteering in the teaching barn, muck raking and milking for the late, warmly remembered Dr. Michael Thonney, in exchange for 2 gallons of sheep milk to use to make cheese and yogurt in my apartment, and more formally by taking AEM 3040 Dairy Markets and Policy. At the time of my graduation, I was in the process of trying to facilitate the cheese club’s use of the FPDL to make a batch of a traditional sheep’s milk cheese, sourced from the teaching barn. Perhaps someone will continue this pleasantly unifying effort.

I am currently in a management training program at Dairy Farmers of America (DFA). My title is Rotational Commercial Analyst. I have completed a 7 month rotation in International Sales and now split my time between Springfield, Missouri and Kansas City, working as an R&D Scientist. My work consists of developing specialty dairy powders, dairy concentrates/pastes, and dairy flavors for companies throughout the world. I have also had the privilege to work with some innovative dairy beverages and snacks. These dairy products all add value to the milk provided by DFA’s farmers, which helps them to continue to produce their life-giving product.

Overall, at Cornell, I did not feel that my studies were particularly dairy focused. I felt that the Cornell food science program covered the gamut of food science topics fairly equally. As a sophomore transfer to Cornell, I was exempt from Professor Chris Loss’s FDSC 1101, a very popular class that fills up with seniors from throughout Cornell, after the reserved seats are given to Food Science freshman. Professor Loss kindly allowed me to audit the class and join a team for the ice cream development competition. During my team’s (“Currant Events”) pilot plant trial in the FPDL, I learned that some students get to actually work in the plant making Big Red Cheddar! I was determined to be one of those students and signed up for FDSC 4970 with Mr. Rob Ralyea. I learned a lot from working in the pilot plant and from my discussions about cheese and the dairy industry with Mr. Ralyea. Over the course of the rest of my time at Cornell, Mr. Ralyea encouraged me to apply for various Dairy awards and scholarships, three of which I was awarded, allowing me to begin to get to know the many faces of the dairy industry.