Pulsed Light Treatments for Food Preservation

Pulsed Light Treatments for Food Preservation

With the increase in consumer awareness, demand for minimally processed foods and Eco-friendliness, various technologies were developed for food processing and preservation. The conventional thermal food preservation and processing techniques appears to have the shortcoming of adversely affecting the food quality, organoleptic properties and nutrients. However, many non-thermal food preservation technologies were developed to serve the purpose.

Many of such technologies are -

• Active packaging
• Pulsed electric field processing
• High pressure processing
• Ultraviolet light processing and
• Pulsed light processing.

Pulsed light technology appears to be one of the best alternatives to conventional thermal and chemical decontamination process.It is a method of cold sterilization. Pulsed light processing technique has been commercialized and there have been many reports on the wide spectrum application of this technology. The technology not only decontaminates the food or packaging but also maintains its texture, nutrients etc. The germicidal effect was found to be due to photochemical and photo-thermal effect. It also has many other applications apart from decontamination, one such being reducing the allergen potent of some naturally occurring foods.

This processing technique was developed as a non-thermal food processing technique, involving discharge of high voltage electric pulses (up to 70 Kilovolt/cm²) into the food product placed between two electrodes for few seconds .Pulsed light treatment can be used for in-activation of microorganisms at the surface of the food & packaging materials & with transparent solids , liquids, gases.

MECHANISM OF MICROBIAL INACTIVATION

• Light pulse duration= 10⁻⁶-10 ^-1 ,energy density=0.01-50 J/cm ² is used.
• Application of intense light pulses transfers large amount of thermal energy to the surface of the material and rises temperature of the thin superficial layer resulting in inactivation of surface micro-organisms,viruses & enzymes.
• The lethality of Pulsed Light may be attributed to its rich broad spectrum ultraviolet content, its short duration, high peak power,the ability to regulate the pulse duration and frequency output of flash lamps.
• As a substantial portion of the Pulsed light spectrum covers ultraviolet light, it is considered that ultraviolet plays a vital role in the microbial cell inactivation.
• It was also found that that there is no killing effect if a filter is used to remove ultraviolet (UV) wavelength region lower than 320 nm.
• The ultraviolet spectrum comprises of three wave ranges: Long-wave ultraviolet -A (320-400 nm), Medium-wave ultraviolet -B (280-320 nm) and Short-wave ultraviolet -C (200-280 nm).
• Normally UV-A and UV-C are used for pulsed light treatment.
• Mechanisms include photochemical (visible spectrum) and photo-thermal effect of UV radiation.
• Ultraviolet light absorbed by the conjugated carbon-carbon double bonds(C=C) in proteins and nucleic acids induces the antimicrobial effect as it changes the DNA and RNA structures and disrupts cellular metabolism.
• Ultraviolet irradiation usually generates thymine dimers in large quantities.
• These di-mers inhibit the formation of new DNA chains in the process of cell replication resulting in the death of affected microorganisms by ultraviolet.

FACTORS   AFFECTING MICROBIAL INACTIVATION BY PULSED LIGHT 

Microbial inactivation by pulsed light mainly depends on the following factors-

• Type of micro-organism.
• Interaction between light and the substrate (i.e.microbial cells /micro-organism).
• The distance from the light source.
• Design of pulsed light system.

APPLICATION OF PLI TREATMENT –

Pulsed light treatment is used in-

• Waste water treatment.
• Sterilization of packages.
• Pasteurization of various liquid foods, fruit juices etc.
• Preservation of baked goods , sea foods , meats etc

ADVANTAGES -

• The intensity of light, which lasts for only a second, is 20,000 times brighter than sunlight, but there is no thermal effect, so quality and nutrient content are retained.
• The xenon-flash lamps used in pulsed light treatment are more eco-friendly than the mercury vapour lamps used in ultraviolet (UV) treatment.
• Pulsed white light is not strictly a non-thermal, but the thermal action, due to its very short duration; it doesn’t show much adverse effect on the nutrients.

DISADVANTAGES -

• A possible problem of this preservation method is that folds or fissures in the food may protect microbes from being exposed to the pulsed light.
• There might be some strains of micro-organisms which are resistant to the pulsed light treatment, for example Listeria monocytogenes.
• This technique for decontamination of micro-organisms is useful mostly in case of liquid foods and surface of solid foods and hence limiting its application.                  

 PACKAGING MATERIAL REQUIREMENTS-

• The packaging materials for irradiation should be chemically stable, for example, they should not undergo depolymerisation or significant changes in elastic modulus.
• The material should be transparent in order to allow the light to pass into the food.
• Due to the low-temperatures of operation or treatment, the packaging system does not require high melting temperature for heat seal, so cold sealing using adhesives can be performed.
• This leads to less volatile odour production generally associated with burning of plastic, additives and printing solvent.
• This low temperature sealing is also beneficial to high fat and frozen foods.
• The packaging material thus, is chosen on the basis of its stability to the treatment, consumer acceptance and regulations.

CONCLUSION -

• The pulsed light processing is a new concept and has many applications in the food industry as a non thermal technique of food preservation.
• While developing the applications of pulsed light processing, it is to be taken into consideration that the food to be processed, the microbial type and load affect the efficacy of the treatment.
• Though with some limitations, if complemented with other processing techniques this technology can help in better food preservation with minimal effects on the food quality.
• There are some microbial species resistant to the pulsed light processing technique and so such species should be studied and also the foods they contaminate be considered separately for processing.
• This technique has showed potent in reducing peanut allergy.
• It can be further studied to reduce other allergies associated with food.
• This technique being still new and hardly commercialized should be researched for economization.

SLICED APPLE UNDER PLI -

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