Framework ranks pathogen risks in dried ingredients

ILSI Europe has published a qualitative decision framework intended to help food manufacturers assess microbiological hazards in dried fruits, vegetables, herbs, and spices, where low water activity can prevent bacterial growth without necessarily eliminating viable pathogens.

The framework is set out in a peer-reviewed review published in Comprehensive Reviews in Food Science and Food Safety. It follows dried ingredients from production and harvest through processing, packaging, incorporation into finished food, and subsequent handling, combining the available evidence into a structured basis for deciding which risks require additional control.

The central problem is that “dry” and “safe” are not interchangeable terms. Low water activity limits the ability of most bacterial pathogens to multiply, but organisms already present can remain viable for prolonged periods and may later enter a food in which the conditions, subsequent process, or final use changes the risk.

The same ingredient can therefore require different controls depending on where it enters production. A dried herb added before a validated heat treatment is not equivalent to the same material added after cooking to a chilled ready-to-eat product, even if both batches were sourced from the same supplier.

The framework brings together evidence on pathogen virulence and contamination levels, how an ingredient is incorporated into food, how the finished product is subsequently handled, outbreak history, prevalence data, and product-specific information. It is intended as a qualitative decision tool rather than a numerical ranking system.

That distinction prevents an apparently precise score from hiding weak evidence. Microbiological datasets for dried ingredients remain uneven across products, pathogens, origins, and production systems, making a universal league table difficult to justify.

For manufacturers, one of the most practical uses is supplier specification. A dried ingredient associated with previous outbreaks, carrying limited microbiological evidence, and intended for post-process addition to a ready-to-eat product can warrant tighter requirements than material entering a process with a validated lethality stage.

Those requirements can extend beyond a certificate of analysis. Supplier approval may need to address raw-material origin, process controls, treatment validation, sampling plans, microbiological specifications, traceability, transport, storage, and notification when a supplier changes a critical stage of production.

The framework also helps technical teams decide whether an additional decontamination step is justified. The review examines both conventional and emerging treatments, but selecting an intervention is not simply a matter of applying the harshest possible process.

Dried fruits, vegetables, herbs, and spices are purchased partly for attributes that can be damaged by treatment. Colour, aroma, flavour, volatile compounds, particle characteristics, and texture may all be affected by heat, steam, irradiation, or other interventions, creating a balance between microbial reduction and product quality.

Validation consequently has to be specific to the ingredient and process. A treatment demonstrated on one spice, particle size, moisture condition, or pathogen cannot automatically be assumed to deliver the same reduction on another material.

The physical behaviour of low-moisture contamination makes that validation more difficult. Desiccated microorganisms can show greater resistance to stresses than cells grown under wetter conditions, while contamination can be distributed unevenly through a large ingredient lot.

Finished-product testing is therefore only one layer of control. A negative sample cannot prove that every part of a large lot is free of low-level contamination, particularly where the organism is present sporadically and the analytical sample represents a very small proportion of the material received.

The more reliable approach combines supplier assurance, preventive processing, traceability, application knowledge, and appropriate verification. The new framework formalises those factors so the decision is tied to the actual use of the ingredient rather than a general assumption based on moisture content.

This is particularly relevant to ready-to-eat production. Dried powders, seasoning mixes, fruit pieces, vegetable flakes, and herbs are often added late in a process specifically to preserve flavour, colour, or texture, which can place them after the principal pathogen-reduction stage.

A recipe change can consequently alter microbiological risk even when the ingredient specification remains unchanged. Moving a seasoning from pre-cook addition to post-cook application, for example, can remove the kill step that previously controlled an incoming hazard.

The same applies to procurement changes. Two suppliers may offer apparently equivalent ingredients on price, particle size, moisture, and sensory performance but use different agricultural sources or microbial-reduction treatments. Technical equivalence on the purchasing specification does not necessarily mean equivalent hazard control.

The framework is also intended to improve communication between manufacturers, regulators, suppliers, and auditors. A structured record of why an ingredient was ranked as a particular risk and why a mitigation step was selected gives businesses a more defensible basis for decisions than simply citing industry custom.

ILSI Europe’s Dried Ingredients Expert Group developed the work through its Microbiological Food Safety Task Force. The full paper was published open access and includes practical examples showing how the framework can be applied to different ingredient and finished-food combinations.

The tool does not establish a new legal limit, microbiological specification, or mandatory treatment. Its value lies in making manufacturers ask the questions that are easily missed when a stable, dry ingredient is treated as inherently low risk.

For processors, the uncomfortable part is that the answer may vary from one product to another. A single incoming ingredient can be acceptable without further treatment in one application and require substantially stronger controls in another.

That is a more demanding approach than assigning every dried ingredient to a convenient fixed risk category, but it reflects the way contamination behaves in real factories. Water activity determines whether organisms can grow; it does not, by itself, demonstrate that they were never there.