Introduction

A key safety and quality element in beverage manufacturing is microbial control. Good manufacturing practices, including proper and controlled pasteurization techniques—and of course impeccable clean-manufacturing methodologies—go a long way toward ensuring the safety and quality of processed beverages. Still, one of the biggest challenges in beverage processing is mitigating contamination from yeasts and heat-resistant molds (HRMs).

To tackle this challenge, Beverage Industry’s editor-in-chief Jessica Jacobsen hosted an expert-led webinar featuring Emilia Rico, PhD, CEO of BCN Research Laboratories, and Christopher McNamara, PhD, Senior Manager of Food Safety and Quality at Ocean Spray Cranberries. The session explored key issues and solutions around HRMs. Watch the full webinar on-demand here.

In the sections below we summarize some of the key insights from the webinar. You’ll learn more about the sources and risks of HRMs, practical steps to take in combatting HRMs, and how solutions from bioMérieux can help address this significant challenge.

General Overview of Heat-Resistant Molds

HRMs are exactly what their name states: Molds, which are filamentous fungi, whose dormant ascospores can be activated by the heating during pasteurization or hot-filling and can survive temperatures that exceed the typical pasteurization temperatures that range from 63°C/145°F (for 30 minutes) to 72°C/161°F (for 15 seconds). This pasteurization-induced germination is a potential risk factor for spoilage.

For mycotoxins to be produced, HRMs must not only germinate but also grow sufficient mycelium. While some of these molds have been shown to produce mycotoxins in laboratory media—and such compounds can withstand high temperatures, including flash-heating at or above 135°C (275°F)—it remains unclear whether significant mycotoxin production would occur in a spoiled beverage. The low pH and limited oxygen typical of these products may restrict toxin formation, making the associated health risk uncertain rather than definitive. Moreover, higher-temperature pasteurization is not always an option for certain formulations as it can have a negative impact on flavors, textures, colors, and shelf life.

Nature and Life Cycle

Some HRMs survive heat treatment through the formation of heat-resistant spores, known as ascospores. This protects them from heat and other environmental stressors. One of the main offenders in beverage and food processing are the ascospores, that are formed inside of a saclike structure or shell. They are abundant in the cultivated soil of most crops. Due to their presence in cultivated soil, they tend to contaminate fruits, vegetables, tea, and anything that is grown commercially. Organic, preservative-free, and shelf-stable products are especially susceptible to these spores. Ironically, lower pasteurization temperatures activate the spores and allow them to germinate and produce mycelium. 

Detecting HRMs

Traditional detection methods can fail to detect ascospores. Dr. Emilia Rico, founder, owner and CEO of BCN Research Laboratories Inc., is the developer of several methods for accurate detection of the presence of ascospores of HRMs such as Paecilomyces variotii (syn. Byssochlamys spectabilis), which she described as “one of the most notorious” HRMs found in sweeteners. This HRM is also considered one of the most challenging spoilers in canned fruit processing.

The identification of these heat-resistant ascospores in juice concentrates, sweeteners (including liquid sugars, high-fructose corn syrup, and maltodextrin, which are known carriers of HRMs), pectin, tea leaves, root powders, and other powdered ingredients relies on exploiting their defining characteristic: heat tolerance.

Experts like Dr. Rico also point out that even packaging materials and the processing environment itself can be tainted with ascospores, with packaging being “particularly risky.”

Some important side notes are that since they thrive in warm environments, contamination is higher in products cultivated in early fall following warm summer months. Also, with so many manufacturers switching to natural colorants, this is another possible point of contamination. In fact, high amounts of HRMs have been found in deep purple carrot juice colorant indicating it as a source of HRMs. “Anything that is grown in soil will be contaminated by that soil and the chances are that they do have HRMs,” Dr. Rico asserts.

Typically, in an activation step that breaks the outer membrane (which heats samples for 30 minutes at 75°C/167°F) the necessary “shock” step is provided to kick off their life cycle. Another such shock step would be High Pressure Processing. Since it only takes a few spores to initiate rampant growth and spoilage, Dr. Rico recommends samples used for detection be a minimum of 100g of product. Even 5 spores per 100g is undesirable; it only takes a few spores to cause spoilage.

Strategies for Mitigation

Traditional culture tests, such as the CMMEF Ch22 Reference Method, can be accurate but are labor and time intensive, requiring more hands-on time and creating bottlenecks due to a more than 15-day turnaround time to results. Previously developed yeast and mold rapid test kits do not target the ascospores, which are the heat-resistant structures of HRM. Those delays translate into costly storage fees while waiting for results.

Mitigating the risks of HRM contamination begins with the suppliers of raw materials, stresses Christopher McNamara, PhD, Senior Manager of Food Safety and Quality with Ocean Spray Cranberries Incorporated. “You’ve got to do a risk assessment and then think carefully about how you’re going to design your program to control this risk,” he says. “You start with suppliers of raw materials and ingredients. You have to know your suppliers, know their process.”

Supplier Considerations to Look For:

• if the supplier has controls in place to eliminate ascospores
• if the ingredient can be filtered
• if it can be heated at a high enough temperature to eliminate ascospores

In developing a sampling and testing program, McNamara underscores the critical importance of first establishing:

• how frequently testing will be done
• who verifies the controls are working

Aspects that should factor into risk assessment include:

• the specifics of where your supplier is located
• whether or not the supplier will be doing the testing
• knowing if there is a local lab able to perform the testing or if samples will be sent out
• assurance that the chosen lab has the systems, capacities, and certifications to properly perform such tests

McNamara further cautions that the same kind of concerns about when, how, and where to test apply to packaging materials. All these steps and procedures should also include environmental monitoring of the processing facility, controlling risk in the environment, identifying high-risk areas and having plans in place for quick and thorough reactions in the event of contamination.