1. B. NOVEL METHODS OF FOOD PROCESSING AND PRESERVATION

2. 1. HURDLE TECHNOLOGY. The concept of Hurdle technology
1. HURDLE TECHNOLOGY The concept of Hurdle technology Applications of hurdle technology The future of hurdle technology

3. 2. HIGH-PRESSURE TREATMENT OF FOODS. Principles of High- Pressure
2. HIGH-PRESSURE TREATMENT OF FOODS Principles of High- Pressure Processing Effect of Pressure on Biomoleculs Industrial applications of h.- p. technology

4. 3. OHMIC HEATING. (a) Ohmic heating principle
3. OHMIC HEATING (a) Ohmic heating principle (b) Processing applications

5. 1. HURDLE TECHNOLOGY The concept of Hurdle technology The problem of achieving preservation procedures that have less of an impact on product quality while assuring food safety has led to the rediscovery of an old concept: hurdle technology.

6. Hurdle technology (also called combined processes, combination processing, combination preservation, combination techniques, or barrier technology) advocates the use of different preservation techniques in combination. Individually, the strength or intensity of the individual hurdles would not be sufficient to preserve the food, but in concert they have the desired level of effect. Individual hurdles used are, for instance, temperature, water activity (aw), pH, redox potential (Eh), and preservatives. It requires a certain amount of effort from a micro-organism to overcome each hurdle. The higher a hurdle, the greater this effort is. Some hurdles, such as pasteurization, can be high for a large number of different types of microorganisms, whereas others, such as salt content, have a less strong effect or the effect is limited in the range of types of microorganisms it affects.

7. This Figure gives an example of the hurdle technology effect
This Figure gives an example of the hurdle technology effect. t, chilling during storage; aw, low water activity; pH, acidity; Eh, low redox potential; pres., preservatives

8. Applications of hurdle technology Hurdle techniques of food preservation were developed empirically many centuries ago, and consequently many different types of food preserved in this way are commonly produced and marketed. For instance, fermented food products (sausages, cheeses, vegetables) are actually made safe and shelf-stable for long periods through a sequence of hurdles that arise at different stages of the ripening/fermentation process. With salami-type fermented sausages, salt and nitrite inhibit many microorganisms in the batter and are thus important hurdles in the early stage of the ripening process.

9. Other bacteria multiply and use up oxygen
Other bacteria multiply and use up oxygen. This reduces the redox potential of the product and enhances the Eh hurdle. This reduces growth of aerobic microorganisms and favors the selection of lactic acid bacteria. They are a competitive flora and cause acidification of the product, thus increasing the pH hurdle. Also with non-fermented foods, such as ready-to-eat products that are composed of different types of raw or minimally processed (washed, trimmed, sliced) vegetables, hurdle technology has been used to assure proper safety. Refrigeration and modified-atmosphere packaging are the main hurdles used to stabilize these perishable foods.

10. The future of hurdle technology With the increasing popularity of minimally processed foods, which are highly convenient for the consumer but preserved only by relatively mild techniques, the environmental conditions in foods as a habitat for microorganisms have changed dramatically, giving many new options for their survival and growth compared with traditionally preserved foods. In order to control food poisoning and spoilage microorganisms in these new food habitats, while keeping loss of product quality to a minimum, a hurdle technology approach is advocated which involves the educated selection and use of a set of preservative factors that can adequately ensure product stability and safety.

11. Minimal processing, however, should not lead to minimum food safety
Minimal processing, however, should not lead to minimum food safety. It is appreciated that combined processes used today do not eliminate micro-organisms but rather inactivate them. The proper use of hurdle technology needs to include sound information on factors affecting the survival and growth of target micro-organisms at both the macroscopic and the microscopic level. Perfecting hurdle technology will enable food manufacturers to improve food quality further without compromising on food safety, at some stage achieving processing and preservation treatments that are undetectable by the consumer.

12. 2. HIGH-PRESSURE TREATMENT OF FOODS

13. Principles of High- Pressure processing The idea of using high hydrostatic pressure (HHP) as a method of food processing is not new. Bert Hite, from West Virginia University, reported in 1899 that high-pressure treatment at ambient temperature could be used to preserve milk. In later studies he also reported that some micro-organisms, such as lactic acid bacteria and yeasts, associated with sweet, ripe fruit were more susceptible to pressure than spore-formers associated with vegetables. Research did not progress as the equipment was not available to routinely subject foods to the necessary pressures. However, in recent years there has been renewed scientific and commercial interest in the process.

14. High-pressure is generally a semi continuous bulk process for liquid foods and a batch process for solid foods. A typical high-pressure system consists of a pressure vessel and a pressure generator. Food packages are loaded into the vessel and the top closed. The pressure transmission fluid, usually water, is pumped into the vessel from the bottom. Once the desired pressure is reached, the pumping is stopped, valves are closed and the pressure is held without the need for further energy input.

15. Effect of Pressure on Biomolecules There are two main principles involved in high-pressure processing: the isostatic principle and the Le Chatelier principle. The former states that pressure is transmitted uniformly and instantaneously throughout the sample. This process is independent of the volume or geometry of the sample. This property gives HHP an important advantage over conventional thermal processing. The Le Chatelier principle states that the application of pressure to a system in equilibrium will favour a reduction in volume to minimize the effect of pressure. Thus, reactions that result in a volume decrease are stimulated, while those causing a volume increase are disrupted.

16. Hydrogen bonding tends to be favoured while ionic bonds are broken
Hydrogen bonding tends to be favoured while ionic bonds are broken. Hydrophobic interactions are disrupted below 100 MPa but can be stabilized at higher pressures. Covalent bonds appear to be unaffected by high pressure, so low-molecular-weight molecules – such as those responsible for the sensory and nutritional qualities of food – are left intact. However, the structure of high-molecular-weight molecules can be significantly affected and this can result in altered functionality of proteins and carbohydrates. These changes result in micro-organisms being killed, as well as the possibility of producing foods of improved sensory and nutritional quality.

17. Industrial applications of h. - p
Industrial applications of h.- p. technology The first commercial high-pressure processed product was a high-acid jam, launched in 1990 by the Meida-ya Food Factory Co., Japan. Since then several other pressure-treated products have been launched in the Japanese market, including fruit sauces, juices and jellies. A high-pressure processed orange juice is also available in France and a pressure-treated avocado dip is available in the USA. Pressurized fruit products are normally given a treatment of around 400 MPa at 20°C.

18. It is claimed that the color and flavor of the fresh fruit is maintained and there is only a slight decrease in vitamin C content. Yeasts and moulds, which are the main cause of spoilage in fruit products, are relatively sensitive to pressure, so the microbiological quality of the products can be improved. However, enzymes such as polyphenoloxidase, which causes browning, are resistant to pressure and therefore can limit the shelf life.

19. For these reasons the current commercial applications of HHP as a preservation method have been limited to high-acid, chilled foods where spore-forming bacteria are unlikely to be a problem and enzymatic activity is retarded by refrigerated storage. However, extensive research and development programmes are in progress in Japan, Europe and the USA and it is likely that other foods, including fruit, dairy, meat and fish products, will be launched into the international market

20. 3. OHMIC HEATING (a) Ohmic heating principle Ohmic heating is the term used to describe direct electrical resistance heating of food product by the passage of mains frequency (50-60Hz) electric current through the continuous flow of product (Fig. 3).

21. Fig. 3. Principle of ohmic heating

22. Depth of penetration is virtually unlimited and the extent of heating is determined by the spatial uniformity of electrical conductivity throughout the product and its residence time in the heater. The applicability of Ohmic heating is dependent on product electrical conductivity. Most food preparations contain a moderate percentage of free water with dissolved ionic salts and hence conduct sufficiently well for the Ohmic effect to be applied.

23. (b) Processing applications The Ohmic heater was originally developed by the UK Electricity Research and Development Center and in 1984, APV Baker, secured a license for the heater system and since then has undertaken substantial further development with respect to the following specific applications within the food processing industry: - Aseptic processing of high added value ready prepared meals for storage and distribution at ambient temperatures. - Pasteurization of particulate fruit products for hot-filling. - Pre-heating of food product prior to in-can sterilization. - The hygienic production of high added value prepared meals for storage and distribution at chilled temperatures.

24. A number of commercial systems are now operating in the production of a range of high added value food products. The benefits of Ohmic heating are summarized in Table 1.

25. Table 1. Benefits of Ohmic Heating-
Fresh tasting, high quality products with increased nutrient retention due to minimal thermal and mechanical damage.
High levels of product safety due to minimum residence time differences between liquids and particulates.
Low flow velocities and virtual absence of moving parts make Ohmic heating the ideal process for delicate, shear sensitive products.
Low maintenance costs.
Continuous flow without hot heat transfer surfaces, thereby eliminating plant fouling.
Rapid and even heating of both liquid and particles, minimizing heat damage and giving vastly superior organoleptic properties.
Quietness of operation giving a better working environment.
Easy to control with fast start-up and shut down minimizing product losses. A turndown facility is also available.
When combined with an aseptic filling system, product can be stored and distributed at ambient temperatures, avoiding the need for costly refrigeration.

26. (b) Pulsed Electric Fields
Brief description of:
OTHER NEW PROCESSING TECHNOLOGIES
(a) Dielectric Heating (Microwave or RF
Heating)
(b) Pulsed Electric Fields

27. DIELECTRIC HEATING
Dielectric heating: the techniques of Microwave and radio frequency (RF) heating.
Both are forms of electromagnetic energy
Selection of RF (3 kHz-300 GHz) or Microwave (300 MHz-300 GHz) heating: depends on product physical properties and process conditions
Basic principle: If a material is placed in an electric field alternating at radio or microwave frequencies, heat is generating throughout the mass of the material by the rapid reversal of polarization of individual molecules.

28. Microwave or RF Heating?
Polarization types:
Orientation (dipole) polarization (re-alignment of molecules already permanently polarized due to their chemical bonds)
Space -charge (interfacial) polarization (accumulation of charge at discontinuities within the material due to the migration of charge carriers under the influence of the applied electromagnetic field.
Microwave or RF Heating?
Product’s physical properties, product’s shape, products homogeneity, variation in loss factor within the product and with temperature rise

29. Applications of Microwave heating
Ready meal products
Blanching
Cooking
Bulk product pasteurization
Applications of RF heating
Typical application: Continuous pasteurization of various products (especially cooked meat products)
Advantages: reduced man powder, reduced energy consumption, continuous production, even heating, homogeneous product, equipment savings

30. PULSED ELECTRIC FIELD PROCESSING
Electroporation: Pore formation (reversible or irreversible in cell membranes exposed to high-intensity pulsed electric field.
Irreversible electroporation: the basis of the pasteurization of food by means of PEF.
PEF: Emerging technology (non thermal inactivation of m/o) with a promising future (color, flavor, texture & nutrients not affected).
Can be used either as single technology or as a hurdle in combination of various preservation methods.
Fundamental aspects of PEF
PEF: Application of high-intensity electric field to food product.
Main application: pasteurization of a variety of foods

31. The PEF processing system consists of
A High Voltage power supply
A Capacitor for Energy Storage
A treatment Chamber
The major technical drawback of PEF:
The dielectric breakdown of foods (when strength of applied el. Field is equal to the dielectric strength of the food)
Possible consequences: luminous spark, bubbles generation, pressure increase, formation of pits on the electrodes.
To avoid it: degassing and cooling of the food is recommended.