Excellent answers all round. And in addition, we may consider hurdles those forms of Unit Operations with a focus on preservation, i.e. shelf-life and food safety promotion. From food technology, we see the order of unit operations adopted for any food production processes, depends on a range of factors - but mainly the type of product desired. So, I agree with Jagan above, the combination of hurdles adopted will depend on the food product. Another interesting concept is to consider parallel versus sequential/ consecutive hurdles. Examples of parallel hurdles? Storing acidified food @ low temperature produces parallel hurdles of low pH and low temperature. Products with modified atmosphere packaging are frequently stored at low temperature.

A "hurdle" is a barrier that a contaminant must overcome in order to continue to grow and survive. Common hurdles include low pH, low or high temperature, low water activity, antimicrobial agents, etc. When developing a food product, it is important to keep these hurdles in mind and to develop a food safety procedure that involves multiple hurdles. That way your food has multiple layers of protection and thus it is less likely that a contaminant will be able to overcome all the hurdles. 

Hurdles are usually specific to the food product as each food product intrinsic factors are different from one another.

These are a series of hurdles which prevent microbial growth in a food product. Each on its own may be lacking 100% effectiveness. However, the thinking is that in combination they make bacterial growth impossible. 

Hi Tinashe Gwasera

I agreed with the above answers

Excellent answers all round. And in addition, we may consider hurdles those forms of Unit Operations with a focus on preservation, i.e. shelf-life and food safety promotion. From food technology, we see the order of unit operations adopted for any food production processes, depends on a range of factors - but mainly the type of product desired. So, I agree with Jagan above, the combination of hurdles adopted will depend on the food product. Another interesting concept is to consider parallel versus sequential/ consecutive hurdles. Examples of parallel hurdles? Storing acidified food @ low temperature produces parallel hurdles of low pH and low temperature. Products with modified atmosphere packaging are frequently stored at low temperature.

i equally agree with the above answers.

Mr. Apenten is more specific to the question. As hurdle technology is the combination of techniques that focuses on food preservation and safety. You can call it combination of unit operation in food for preservation

Hurdle Technology is specific combination of food preservation subjected to food safety, the result is to guarante the safety of product. And it should be underlined that by combining the technique, each tech may kept comparatively low concentration to minimize the loss of quality, however still the impact is remain high.

Very Interesting suggestion, Dr Arum. The combination of hurdles could result in better preservation efficiency and some synergism - meaning that combinations of say two separate hurdles might lead to better preservation compared to each hurdle on their own.  I have not examined this issue for microbes-but we are interested in synergism between anticancer agents.