FOOD ENGINEERING

Lesson 46. IRRADIATION, PULSED ELECTRIC FIELD, ULTRASOUND PROCESSING, NANO TECHNOLOGY

Module 6. Recent trends in food processing

Lesson 46

IRRADIATION, PULSED ELECTRIC FIELD, ULTRASOUND PROCESSING, NANO TECHNOLOGY

46.1 Introduction

Food radiation has has many advantages in food processing like (i) it can extend shelf life of many fresh foods., by preventing sprouting, deactivating moulds and killing spoilage bacteria. (ii) It can improve world food supllies by reducing postharvest losses. (iii) it could replace fumigants and other pesticides, resulting in a reduction of chemical recidues in food (iv) It improves food safety by destroying the microorganisms that cause food borne illness and parasites that cause diseases.

46.2 Food Irradiation

Food irradiation is the process of exposing food to controlled levels of ionized radiation to kill harmful bacteria, pests, or parasites, or to preserve its freshness.
The process of food irradiation is often called cold pasteurization , because it kills harmful bacteria without heat. The process of radiation is carried out by Gamma Rays or Electron Beams or X-rays.

The amount of radiation used to expose food is controlled by the intensity of the radiation and the length of exposure. The dose permitted for use in food varies according to the type of food and the desired action. Treatment levels have been approved by FDA and adopted by Codex General Standards for irradiated foods are as follows:

“Low” doses, (< 1 kGy)

1. Control insects in grains and fruits.

2. Inhibit sprouting in tubers.

3. Delay the ripening of some fruits/vegetables.

4. Reduce the problems of parasites in products of animal origin, (e.g., trichinella spiralis in pork).

“Medium” doses, (1-10 kGy)

1. Control Salmonella, Shigella, Campylobacter, Yersinia, Listeria and E. coli in meat, poultry, and fish.

2. Delay mold growth on strawberries and other fruits.

“High” doses, (> than 10 kGy)

1. Kill microorganisms and insects in spices.

2. Commercially sterilize foods, destroying all microorganisms of public health concern (i.e., special diets for people with weakened immune systems) .

It is reported that all the fresh produce is not suitable for irradiation and some radiation treated foods may taste slightly different but nutritional value of food is virtually unchanged.

46.2.1 Infra red treatment

Infrared rays belong to one type of electromagnetic waves, and any object with its temperature above absolute zero degree (- 273°C. ) radiates infrared rays. The wavelength of infrared rays is about between 1 and 1,000 microns. Infrared rays can be classified into near infrared rays (between 1 and 1.5 microns), middle infrared rays (between 1.5 and 5.6 microns), and far infrared rays (between 5.6 and 1,000 microns) according to their energies carried.

Generally, infrared rays radiated from heaters, firebrands, or electric cookers almost belong to near infrared rays which produce a large quantity of thermal effects for short wavelength. Where as with near infrared rays, far infrared rays will not result thermal effect due to their long wavelengths and relative low energy. Far infrared rays also differ from electromagnetic waves of low frequency (60 Hz) as they have a strong penetrability and change the characteristics of product. Thus they are highly suspected as a serious factor to cancer. The case of far infrared rays is different. In fact, human bodies themselves radiate far infrared rays (9 microns). External far infrared rays only penetrate into skin to 0.1-0.1 centimeter.

In recent years, far infrared ray technologies have been used in military industries, household appliances, food processing and preservation and biochemistry industry, and have achieved quite good effects. Far infrared products not only have multiple functions, but also have small space occupied and low cost.

In future, technology will be advance that process food will not deteriorate its quality till it reaches to the hands of consumer. This is possible with the help of Nanotechnology and Encapsulation of Food.

Nutrient deficiency and malnutrition are basically as a result of mismatch of production and requirement. Therefore, there will be a need to find out alternate sources of the nutrients. These nutrient, must be having biological origin, may be plant or animal. Extraction of the nutrient in pure form, dilution / conversion in the digestible form and fortification or encapsulation will be the one in future food.

46.3 Pulsed Electric Field

It is a technique in which a food is placed between two electrodes and exposed to a pulsed high voltage field (typically 20–80 kV cm^–1). PEF uses strong electric field processing to deactivate microbial cells, effectively preserving foods with little or no actual heat. For food quality attributes, PEF technology is superior to traditional heat treatment of foods because it avoids or greatly reduces the detrimental changes to the sensory and physical properties of foods. One drawback is that only pumpable fluids can be treated. Flavour freshness, low energy utilization, and extended shelf life, are some of the virtues attributed to PEF treatment. A number of studies have demonstrated effectiveness of pulsed electric filed process.

46.4 Ultrasound Processing

When ultrasound passes through a liquid medium, Cavitation occurs, causing alternate rarefactions and compressions and is responsible for cellular disruption. The mechanisms involved in cellular disruption are multifactorial and may include shear forces generated during movement (subcellular turbulance) of the bubbles or sudden localised temperature and pressure changes caused by bubble collapse

46.5 Nano Technology

Nanotechnology exhibits great potential for the food in­dustry. New methods for processing nanostructures are being developed having novel properties that were not previously possible. Parallel to the development of na­nostructure fabrication techniques, nanoscale analysing methods are being developed, which can provide new knowledge and explanations to previously empirically gained knowledge.

46.5.1 Nano technology in food packaging and safety

Nanotechnology offers many possibilities here. Hollow nanofibres and silicate nanoparticles or metallic/ceramic nanoparticles (carbon nanofibres) combine light weight and strength. These new materials are currently routi­nely produced in laboratories and can be used for both equipment and structures.

Another promising application in food packaging is Gas-barrier structures with low permeability. Nanopar­ticles embedded in plastics may be used to retard the diffusion of gases such as oxygen or water vapour by creating tortuous paths. Such products are already in the market.

Encoding or decoding individual surfaces, coun ­terfeit protection using nanotaggants, nanocrystaline indicators to sense and signal modified atmosphere environments within packages, light-activated oxygen sensing links, food deterioration sensors and power for smart packagings, such as radiofrequency identifica­tion (RFID) are also possible application. Nanotubes may be filled with materials such as antimicrobials to disperse in the plastic matrix.

Materials that could improve bioactivity and thereby biodegradability of polyesters like PLA are boon to environmental control. Surfaces can be nanostructured in order to influence their adhesiveness to products or dirt and there by their susceptibility to fouling, which is important in food processing and food packaging.

46.5.2 Nano technology in food processing

Principal applications are on demand preservatives and interactive foods. Nanocapsules can be incorporated into food to deliver nutrients. Addition of nanoparticles to existing food can enable increased absorption of nu­trients. Applications that are already being tested in new products to enter the market. Another key application is additives which could easily be absorbed by the body and could increase product shelf life. Nanosized disper­sions, emulsions and filled micelles have the advantage that they are not subjected to sedimentation which gives better product life span and storage. As their size is much smaller than the wavelength of light, they can be incorporated in clear and transparent foods without causing muddiness. Substances difficult to dissolve can more easily be absorbed by the body if they are of nanoscale size due to their large surface area. If the active substance is to be protected during storage or passage through the intestines the existing nanotechnology can produce perfect protective layers. It is also possible to tailor protective layers to release active substances in an “intelligent” way, e.g. caused by a change of pH-value.