How to better control undesirable microbes in the food industry

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How to better control undesirable microbes in the food industry

by Marjon Wells-Bennik

How to tackle undesirable microbes in foods, in particular bacterial spores?

High rates of spoilage before the end of shelf life of foods? Consumer complaints? Or worse, cases of foodborne illness due to consumption of your products? This must be avoided and safeguarded in production. As all foods placed on the market must be safe and of high quality, clearly, control of microbes that may cause food spoilage or that lead to foodborne illness has high-level priority in the food industry.

To control contaminants in fresh ready-to-eat foods, the food industry uses different conditions to prevent outgrowth of undesirable microbes. For example, low storage temperatures and short distribution chains. In processed foods, undesirable microbes are often eliminated by applying heat or alternative treatments that kill them. However, bacterial spores, which are the hardiest forms of life on earth, may survive such treatments. Their ubiquitous presence in the environment means that their presence in food ingredients and in food processing facilities is inevitable. As a result, sporeformers may lead to a reduced shelf life of products due to spoilage and in the case of foodborne pathogenic sporeformers, consumption of products in which growth has occurred may even lead to illness or death. Clearly, contaminants originating from ingredients or the processing environment must be controlled during and following production to achieve the required shelf life and assure food safety. But how to do that?

Please let us know if you have any questions!


1. Analyse the number of pathogenic spores which are present in ingredients and finished product

To prevent potential problems with spores in finished food products that undergo heat treatments, the ingredients generally have specifications for spores. Many different methods exist to detect spores of different types of sporeformers, as not all spores behave the same. Different growth media may be used and incubation may take place at specific temperatures (e.g. psychrotrophic, mesophilic or thermophilic species) or in the presence or absence of oxygen. In addition, a distinction can be made in the heat resistance of spores by applying different heat treatments (e.g. 10 min 80°C, 30 min 100°C, 30 min 106°C). When setting specifications for spore concentrations in ingredients, it is critical to apply meaningful methods with relevant detection limits. Ideally, the methods allow for a link between the sporeformers present in ingredients and the potential defect rates in finished products after production. Knowledge about spore detection, problem species, impact of processing on different spore types and growth potential in finished products is crucial for such assessments.

2. Identify the source of contamination

Sporeformers may enter the production chain via ingredients. Another contamination route is via processing equipment containing biofilms that shed spores into the product. This may happen in holding tanks, on transport belts, around seals and even in heating equipment, such as the regenerative section of pasteurizers or in evaporators (by thermophilic species). When spores cause problems in finished product, a ‘track-and-trace’ approach of the problem microbes can identify the source of the contamination. By assessing the genetic make-up of the problem organism and of isolates in ingredients and along the production lines, a source can be found.

3. Define acceptable levels of pathogenic spores in finished products

Even low levels of spores in finished product may lead to spoilage or foodborne illness if they survive and if outgrowth can occur: one per packaging unit may be enough! When spores are present in ingredients, reduction to acceptable levels can be achieved by inactivation (e.g. by heat treatments) or by removal (in liquid products e.g. by bactofugation or ultrafiltration). The efficacy of such treatments can be assessed experimentally. To do so, it is critical to use spores with representative properties. The efficacy can also be calculated using modelling approaches when relevant data are available. If adjustment of processing conditions does not suffice, reduction at source may be necessary.

4. Select conditions that prevent outgrowth

Spores can ‘wake up’ via the process of germination in nutritious environments. This may happen during food production or in finished products. When conditions in the product (e.g. water activity, pH) and during storage (e.g. temperature) are favourable for outgrowth, the sporeformers can multiply. Traditional preservatives that are effective in preventing germination and outgrowth of spores (for instance sorbate and benzoate) are used less nowadays. New formulations and novel processing methods are being developed, for instance based on clean label preservatives and combinatory treatments. The efficacy of such formulations must be evaluated in products using relevant strains of sporeformers and spores thereof. This requires knowledge of species to inoculate and often high-throughput testing of conditions, to ensure efficacy of treatments.

Find out more about food safety!

Protein, from source to digestibility: important for healthy ageing

Global demographic shifts and a world population projected to reach 9.7 billion by 2050 lead to an increasing demand for high-quality nutritional products, especially for elderly people. This will put pressure on food production and protein supply. To meet this growing demand, producers are combining vegetable and animal proteins and finding innovative ways to use available proteins more efficiently. The biggest challenge is developing high-protein applications with the right properties (structure, texture, flavour, digestibility) without increasing the food product’s carbon footprint.

Everyone needs protein

Elderly people need to maintain their muscle mass, so their diet must contain enough highly digestible protein. Other consumers need foods that help control weight and reduce the risk of obesity. For them, too, high-protein products can play an important role because they create a relatively high sense of satiety.

While proteins have obvious benefits, products with a high protein content can be undesirable from a sensory perspective: too viscous and hard to swallow in liquids, or too chewy in a solid state. Texture problems can also occur in low-fat products where fat has been replaced with extra protein. These products are perceived as drier and less juicy. To improve consumer acceptance of high-protein products, it is crucial to control their viscosity and texture. This means decreasing liquid products’ viscosity and improving the overall mouthfeel of both liquid and solid products.

Optimal digestibility

To meet the growing demand for protein, food manufacturers are turning to high-quality proteins from alternative sources, such as plants, algae and insects. The industry is also increasingly interested in pea protein, which has a good amino acid composition. However, digestibility is also of importance. Using Nizo’s SIMPHYD platform for in vitro modeling of food’s behaviour in the stomach, the digestibility of pea protein was compared with that of whey and casein proteins. Whey protein hardly increases in viscosity in the stomach, is easily degraded and hence readily available for absorption, making it ideal for rapid muscle recovery (as a ‘fast’ dietary protein). Casein, on the other hand, becomes significantly more viscous and is broken down slowly and absorbed later, making it more suitable for long-term recovery (a ‘slow’ dietary protein). Compared to whey and casein, pea protein turned out to be exactly in the middle. It creates some viscosity and breaks down more quickly than casein, but slower than whey. In other words, it is a moderately fast protein. This knowledge is essential for developing products than promote rapid recovery after a workout or products that can help maintain long-term muscle function.

In vivo measurement

Laboratory animals are sometimes used to test digestibility in an in vivo situation. As digestion takes place in the small intestine, this is also the spot where we would prefer to measure digestibility of proteins in humans.

The small intestine is essential for our health as this is where about 90% of nutrients are absorbed and key signals are generated to control our metabolism and immune system. There is increasing scientific evidence that an imbalance in our intestinal microbiome can lead to a number of diseases, including metabolic and immunological disorders such as obesity, diabetes, and inflammatory diseases. However, most studies focus on the fecal microbiome in the large intestine and pay scant attention to the possible role of the small intestinal microbiome. However, taking samples from the small intestine is a highly invasive procedure, requiring insertion of a tube through the esophagus and stomach.

At Nizo we recently made significant progress in solving this problem by developing the IntelliCap, a minimally invasive technology for taking samples from the small intestine. This measurement device, which had already been CE-marked for drug delivery and real-time measurement of temperature and pH in the gastrointestinal tract, was also approved for the aspiration of fluids. Therefore, the IntelliCap CR system can now also sample the small intestinal microbiota. Philips spin-off Medimetrics Personalized Drug Delivery BV developed the sampling device, which measures only 11mm by 26mm. This capsule has proven its worth as a means of measuring the microbiome in the small intestine, and could possibly also measure in vivo digestion of protein in the small intestine. This enables a more accurately assessment of digestibility, and hence the quality of different types of protein.


Just as the source of protein affects its digestibility, the way of processing could also have an impact on digestibility and hence the quality of proteins. Go4Dairy, a recently launched research programme, focuses on the impact of glycation on protein’s nutritional value. In the literature, Maillard products are associated with negative health effects, including hypersensitivity of the immune system, reduced digestibility, reduced bioavailability of lysine in particular, changes in gut bacteria and even carcinogenic effects. Much remains unknown, however. Go4Dairy’s aim is to reduce and control the glycation of proteins so as to optimise their nutritional value.

Proteins for the future

High-quality proteins are essential in our diet and are crucial for healthy ageing. In view of the impending protein shortage, current technological developments in plant protein structure, texture, taste and digestibility are all important steps toward creating a sustainable protein supply for a growing world population.

Find out more!

Developing flavours and products using fermentation

3 Factors which decrease processing efficiency


By Kevin van Koerten, expert from our Processing Department

Food and beverage manufacturers are presented with several challenges. Organisations strive to minimise production and supply-chain costs, realise a perfect delivery efficiency and meet a multitude of regulatory needs merely to stay reasonably competitive. Processing efficiency in both waste and energy management is a key component in reducing production costs and creating more value from ingredients. However, increasing efficiency is almost never a single straightforward solution, but a delicate trade-off between cost, energy and product quality. As such, to make the most appropriate decisions, a deeper understanding is needed of the effects of processing parameters on both product quality and capacity.


The processing temperature is one of the most important factors in multiple processing steps. Higher processing temperatures will result in larger heat flows, thus increasing capacity. Additionally, in pasteurisation processes, higher temperatures will more effectively destroy harmful microorganisms, ensuring product safety. On the other hand, lower processing temperatures generally decrease energy consumption and decrease the heat load on the product. The latter is especially important in protein-rich formulations, since proteins can denature at temperatures as low as 40°C. Not only will proteins lose their functionality when denatured, potentially negating their use in specific products, they also tend to aggregate with each other and equipment surfaces. The consequent fouling has a large effect on runtime and the amount of cleaning required. It is therefore important to take all these consequences into account when determining appropriate processing temperatures.

Water content

Another important factor in processing efficiency is the water content of the product, . Removing water from product streams is one of the main sources of energy consumption in the food processing industry. Some production processes revolve around the addition of water followed by removal of that same water (e.g. starch production). Less water usage in processes is therefore a direct improvement in energy efficiency. On the other hand there is a difference in energy usage for different water removal units:

  • Membrane concentration generally requires 20-40 MJ/tonns of water removed
  • Falling film evaporators, depending on number of stages and steam supply, require around 55-500 MJ /tonnes of water removed
  • Spray drying requires 3500-4500 MJ/tonnes of water removed.

It is clear from these numbers that if water removal can be moved from more energy intensive drying processes to less intensive drying, up to 99% energy savings can be achieved. Naturally there are limits to the amount of dry matter in a processing stream that certain equipment can handle, but even minimal changes will have a significant effect with the large throughputs generally used in food processing plants.


A final factor that stronlgy affects processing efficiency is the humidity or moisture content of the process air used for drying. The maximum moisture content of air at atmospheric pressure differs with temperature, from close to zero moisture per amount of dry air at temperatures below 0 °C up to an infinite amount at 100 °C (pure steam). As such, the capacity of spray dryers is highly dependent on the outlet temperature of the air. However, this outlet temperature is usually bound by the moisture content of the outgoing powder. Therefore, the only ways to improve capacity is to build a bigger spray dryer with more air or to decrease the humidity of the ingoing air. Naturally, the latter is the only option for optimization of an existing spray dryer. Dehumidification treatments with silica or zeolites are options for decreasing and/or standardizing the humidity of the drying air. Another option, which requires much less investment, is to match the dryer capacity to the outside air humidity, i.e. increase ingoing product flow when the outside humidity becomes lower. This can have a large impact on capacity as the daily variation in humidity can be quite significant.

The effect of product-process interactions on efficiency

Besides processing conditions, product-process interactions can also determine the process efficiency, as already mentioned in the form of protein denaturation. Another important interaction is the relation between product powder stickiness and drying air humidity in a spray dryer. The equilibrium between the moisture content of dry matter and air is described by a sorption isotherm. This captures the behaviour of moisture becoming harder to evaporate at higher dry matter content due to binding and adsorption energies. The stickiness of powders depends on moisture content and temperature, becoming more sticky at higher moisture contents and at higher temperatures. Since spray dryers approach ideal mixing, the outgoing powder is in near-equilibrium with the outgoing process air. Therefore, the stickiness of the powder depends on outgoing air humidity and temperature. If the powder becomes too sticky during spray drying, fouling will occur, leading to shorter runtimes and longer cleaning times. By modelling the drying process, the sorption isotherm and the dependence of powder stickiness on moisture and temperature, the optimal conditions for the spray dryer can be set to meet the requirements for non-sticky conditions, optimal capacity and final product moisture content.