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Hurdle technology:1. This is also method of dairy product preservation.2. Leistner in 1976 introduced term hurdle effect.3. Factors used for food preservation is known as hurdles                   4.  The products whose storage life and microbiological safety are extended by use of preservation factor, non of which individually would be lethal towards spoilage or pathogenic microbes are known as HT product.                   5. In this technology three or more hurdles (preservatives) are employed in a suitable combination and every hurdle is used at an optimum level so that damage to the overall quality of food is kept to the minimum.                   6. There is a great scope of using bacteriocin in combination with other preservatives factors to get hurdle effect.  Hurdle technology has great potential for preservation of indigenous dairy product because,? No change in sensory /nutritional characteristic of the product.? Can be used at room temperature.? Reduced energy consumption. Less susceptible to non enzymatic browning or lipid oxidation.  Need for hurdle technology           Consumer demanding for fresh, natural, minimally processed food products.           Ongoing trends has been eat out and to consume ready to eat foods.               New ecology routes for microbial growth evolved.                      A crucial phenomenon in hurdle technology is known as the homeostasis of microorganisms .                       This multi-targeted approach is the essence of hurdle technology.                      It is more effective than single targeting and allows hurdles of lower intensity, improving product quality.                           There is the further possibility that different hurdles in a food not only have an added effect on stability, but can act synergistically.Principles for hurdle technology             1. Preservative factors or hurdle disturb the homeostasis of microorganisms           2. Microorganisms should not be able to jump over all hurdles present in food product           3. Preservative factors prevent microorganisms from multiplying or causing them to remain inactive or even die            4. Hurdle concept illustrates that complex interactions of temperature, water activity, pH etc are significant to microbial stability                PRINCIPLES HURDLE USED FOR PRESERVATION Parameter symbol application High temperature  F  Heating Low temperature  T  Chilling, freezing Reduced water activity aw Drying, curing, conserving Increased acidity  pH  Acid addition or formation Reduced redox potential Eh Removal of oxygen or addition of ascorbate Biopreservatives  Competitive ?ora such as microbial fermentation Other preservatives Sorbets, sul?tes, nitritesTypes of hurdles There are mainly three types of hurdles used i.e1. Physical2. Physico chemical 3. Microbial1. Physical hurdles: there are many physical hurdles routinely used some of them are • Aseptic packaging• electromagnetic energy (microwave, radio frequency, pulsed magnetic ?elds, high electric ?elds)• high temperatures, (blanching, pasteurization, sterilization, evaporation, extrusion, baking, frying) • ionizing radiation• low temperature (chilling, freezing)• modi?ed atmospheres, packaging ?lms (including active packaging, edible coatings)• photodynamic inactivation, ultra high pressures, ultrasonication, ultraviolet radiation 2.physic chemical hurdles • Carbon dioxide, ethanol, lactic acid, lactoperoxidase, low pH, low redox potential, low water activity, • Maillard reaction products, organic acids, oxygen, ozone, phenols, phosphates, salt, smoking, sodium nitrite/nitrate, sodium or potassium sulphite, spices and herbs, surface treatment agents 3. Microbial hurdles                   The microbial hurdles compete with the bacteria for survival                  Antibiotics,                      Bacteriocin,                      Competitive ?ora,                      Protective cultures. MICROBIOCIDAL HURDLES THAT REDUCE MICROBIOLOGICAL LOAD | Hurdle Technology For Milk ProductsThe principles of the most common Hurdles within this category are:1. Bactofugation: The removal of microbial cells of high density from milk using high centrifugal forces.2. Competitive micro flora: The reduction of the number of undesirable microorganisms by lowering the pH, consumption of nutrients, and production of bacterial antimicrobial substances (such as nisin, other bacteriocins and hydrogen peroxide). Usually, this Hurdle is applied by choice of starter cultures.3. Microfiltration: Removal of microbial cells, clumps and somatic cells by recirculation over a micro filter.4. Ripening (ageing): The holding for such time, at such temperature, and under such conditions as will result in the necessary biochemical and physical changes characterizing the cheese in question. When applied as a Hurdle, the multifactorial, complex system developing in cheese (pH, antagonistic flora, decreased water activity, metabolism of bacteriocin and organic acids) is utilized to influence the microenvironment in and on the food and consequently the composition of the micro flora present.5. Thermization: The application to milk of a heat treatment of a lower intensity than pasteurization that aims at reducing the number of microorganisms. Thermized milk is alkaline phosphatase positive.6. High-pressure treatment: Application of high hydrostatic pressures (> 3000 Bar) to irreversibly damage the membranes of vegetative cells.7. Ultrasonication: The application of high intensity ultrasound (18-500 MHz) that cause cycles of compression and expansion as well as cavitations in microbial cells. Implosion of microscopic bubbles generates spots with very high pressures and temperatures able to destroy cells.8. Electromagnetic energy treatment: Electromagnetic energy results from high voltage electrical fields, which alternate their frequency millions of times per second (< 108 MHz). Examples are microwave energy (thermal effect), radio-frequency energy (non-thermal effects) or high electric field pulses (10 – 50 kV/cm, non-thermal effects). The treatment destroys cells by establishing pores in the cell walls due to the buildup of electrical charges at the cell membrane.9. Low-intensity irradiation: The submission of beams of photons/electrons to destroy viable microorganisms.Three basic approaches in dairy for application of hurdles• Use of microbiocidal step without use of other hurdles           eg; in container sterilized milk• use of microbiocidal step as combination with other hurdles, this is wide spread used for all dairy products 1. Drinking milk- heat treatment and cold chain2. Cheese – fermentation, salting, heat treatment, ageing3. Butter- heat  treatment, fermentation, salting, water dispersion 4. Milk powder- heat treatment, water activity • Use of hurdle technology without combination with microbiocidal step with or without preventive step at primary production level                Eg:  production of cheese from micro filtrated and thermized milk                  The first ever hurdle technology in India was made in author's laboratory for preservatives of ready to eat paneer curry.

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