Hurdle Technology

Food processing, food preservation and food security, these sums up the modern era requirement of safe food. Rate of food spoilage is quite high, which can be estimated by recent report of FAO stating one third of the total harvested food is wasted and is not available for consumption. In majority of cases, microorganisms were the lead cause for the spoilage or poisoning of food products.

Despite the availability of wide range of preservation techniques like freezing, blanching, pasteurization, canning etc. spoilage of food materials by microorganisms is still a major challenge, thus for achieving microbial safety & stability in food products, a new technology was discovered by Leister, termed as hurdle technology which combines non-thermal food processing with traditional or other emerging technologies. This technology preserves the food product by using more than one preservation techniques for arresting the growth of microbes in food product, without disturbing food products in built chemical composition and organoleptic characteristic.

 

What Is Hurdle Technology

Hurdle technology, a gentle and effective preservation technique, using intelligent combination of “hurdles” for production of safe, stable, nutritious, tasty, and economic foods. These hurdles can be defined as physical or chemical parameters that can be adjusted to ensure the microbial stability and safety of foods. There are more than 60 potential hurdles for processed food products, where as the principal hurdles preservative factors in food safety are temperature (higher or lower), water activity (aW), acidity (pH), redox potential (Eh), chemical preservatives (nitrite, sorbate, sulfite), vacuum packaging, modified atmosphere, HHP/HPP, UV, and competitive microorganisms.

Concept behind Hurdle Technology

Hurdle technology makes use of “hurdles” which the pathogen has to overcome if it has to remain active in the food. The right combination of hurdles can ensure elimination of all pathogens to safer limit. In this a preservation parameter can be used at an optimum level in order to get a maximum lethality against microorganisms by a combination of two or more such parameters.

The whole concept of hurdle technology mechanism is based on various responses given by any microorganism. The whole phenomenon can be understood by following:

1. Homeostasis: It is a tendency of any organism to maintain its internal status. Homeostasis of microorganism plays a major role in food preservation. Food preservation can be achieved by disturbing the homeostasis of microorganism, temporarily or permanently, as any hurdle disturbing the homeostasis of these microorganisms impacts on its ability to reproduce and thus they remain constant in number or will die before the re-establishment of homeostasis.
2. Metabolic Exhaustion: Another important phenomenon for food preservation is metabolic exhaustion of microorganisms. As a response to the hurdles applied to foods, microorganisms try to stable their homeostasis, for this they utilize all their energy and become metabolically exhausted. This leads to an auto-sterilization of such foods. The foods which are preserved with the concept of hurdle technology are microbiologically stable, become safer during storage at ambient temperature. The microbes can respond better to the hurdles at ambient temperature than at refrigeration and become metabolically exhausted.
3. Stress Reactions: As a response of various hurdles e.g. heat, pH, water activity, ethanol, oxidative compounds, as well as starvation, a stress shock protein is produced by some bacteria. These stress proteins may hamper food preservation and could turn out to be problematic for the application of hurdle technology if only one hurdle has been applied. If different stresses are received by the microorganism at the same time, the activation of genes for the synthesis of stress shock proteins, would be difficult. Synthesis of many stress shock proteins due to simultaneous exposure to different stresses will be very energy-consuming and would lead to metabolic exhaustion of the microorganism.

4. Multi-Target Preservation: A combined effect could be achieved by hitting various targets within the microbial cell (e.g., cell membrane, DNA, enzyme systems, pH, aW, Eh) by using different hurdles simultaneously. This disturbs the homeostasis of the microorganisms present in several respects. In this case, the replenishment of homeostasis and activation of stress shock proteins becomes more difficult. Therefore, simultaneous application of different hurdles in a particular food would lead to optimal microbial stability.

Classification of Hurdles

We can classify various hurdles on the basis of their function, nature and their type which is discussed in brief. Generally classified into physical, chemical & biological parameters.

[1] Hurdles grouped according to Primary Function

1. Microcidal hurdles reduces microbiological load: These contains a group of mild techniques, which reduces the microbial flora to safer limit without changing the original chemical composition. Technologies used for achieving this function are: Bactofugation, Competitive Micro flora, Microfiltration, Theorization, High Pressure Treatment, Ultrasonification etc.
2. Micro biostatic Hurdle limit or/and prevent growth by biochemical means: These include hurdles such as pH, carbon dioxide, use of preservatives, redox potential, lacto peroxidase system etc.
3. Micro biostatic hurdles limit or prevent growth by physical means: It includes the techniques, which arrests the growth of microbes by means of refrigeration, pasteurization and freezing.
4. Hurdle preventing Contamination: These include various types of packaging and coatings, which helps in protecting the contents from damage, dust, dirt, leakage, pilferage, evaporation, watering, contamination and so on.

[B] Primary types of Hurdles

1. High Temperature: Most common and oldest forms of microbial control. It is applied in food preservation techniques like canning, pasteurization, UHT, Retort Processing etc. Heat kills microbes by altering their membranes and denaturing proteins. The thermal death time (TDT), is the length of time needed to kill all microorganisms in a sample at a given temperature, which is used as an important parameter to describe sterilization procedures that use high heat. Different microorganisms will respond differently to high temperatures, with some (e.g., endospore-formers such as  botulinum) being more heat tolerant.
2. Low temperature: exposing microbes to low temperatures can also be an easy and effective method of microbial control, with the exception of psychrophilic, which prefer cold temperatures. Refrigerators maintain low temperatures which inhibits microbial metabolism, slowing the growth of microorganisms significantly and helping to preserve food products such as foods or medical supplies.
3. Water activity: The concept of a_w has been very useful in food preservation and on that basis many processes could be successfully adapted and new products designed. Water has been called the universal solvent as it is a requirement for growth, metabolism, and support of many chemical reactions occurring in food products. Free water in fruit or vegetables is the water available for chemical reactions, to support microbial growth, and to act as a transporting medium for compounds. In bound state, water is not available to participate in these reactions as it is bound by water soluble compounds such as sugar, salt, gums, etc. (osmotic binding), and by the surface effect of the substrate (matrix binding). Water activity can be reduced by using techniques such as Curing, Drying etc.

4. Chemical Preservatives: These are substances which, under certain conditions, either delay the growth of microorganisms without necessarily destroying them or prevent deterioration of quality during manufacture and distribution. Example include Sugar, salt, SO₂

5. Acidity: Microorganisms, including yeasts, molds, and bacteria are sensitive to food’s pH. Very low or very high pH values will prevent microbial growth. 
6. Bio preservatives:These are compounds derived from natural sources or formed in food, able to prevent or retard spoilage related with chemical or biological deterioration that prolong product shelf life.

Hurdle technology not only improves product quality and microbial safety but also saves money, energy and several other resources. Food remain stable and safe, high in sensory and nutritive value due to gentle process applied. It does not affect the integrity of food pieces and can be applicable in both large and small-scale industries. This technology is used for making new products and for reducing energy-consuming hurdles or chemical preservatives. It is gratifying to know that this technology has a bright future in food industry as it can be used in manufacturing of minimally processed food and RTE foods which can be stored without refrigeration.