Thermosonication: A new approach in food processing and preservation

HarshithaS B* and Dr. Laxman Kukanoor*

Introduction

Thermalpasteurization is the most common heat treatment applied for food preservationto date. It assures good shelf-life and stability of fruit and vegetableproducts; however, this process may affect the quality in terms of nutritionaland physicochemical parameters such as: vitamins (C and E), carotenoids,polyphenols, organic acids, pH, color and to some extent in sensory parametersof the processed food.

Alternativemethods of pasteurization have gained relevance in the food industry. Nowadaysthere are new technologies that offer options for food processing to ensure thestability and quality of products. Particularly in processed fruit andvegetable products, consumers search for additive-free and minimally processedproducts. Novel food technologies are described as complete or partialalternatives to thermal processing, among which ultrasound applications standout, which have a proven potential for use in the food industry.

Thermosonication (TS)

Thethermosonication technology is a novel approach which combines the applicationof moderate heat of 37 to 75 °C with ultrasound treatment (>20 kHz) and is a potentialalternative processing technique to enhance inactivation of enzymes andmicrobes. The principle aim is toreduce the processing time, save energy and improve the shelf life and qualityof food products.

Microbialinactivation

Thermal treatment (i.e. pasteurization, ultrahigh temperature) is generally considered to be main method for theinactivation of bacteria but often result in some un- desirable results such asformation of unwanted flavors and loss of nutrients. Nowadays, ultrasound isused for inactivation of microorganisms to overcome the undesirable results ofthermal processing.

Mechanism involved in the microbial inactivationare-

•      Cavitation phenomena –extremely rapid creation and collapse of bubbles formed by ultrasonic waves ina medium creates the antimicrobial effect of ultrasound

•      Localizedchanges in pressure and temperature cause break- down of cell walls, disruptionand thinning of cell membranes, and DNA damage via free radical production

Figureone shows the schematic diagram of the automated sonicator (probe type), control systemlies outside the sonicator which will monitor the power, pulse and time ofexposure. Transducer convert electrical energy into sound waves; generatedwaves are fed into the reaction solutions through the probe tip provided at theend,  length and diameter of the probemay differ from manufacturer to manufacturer and also depth of immersion willalso vary according to food type and the purpose. The temperature controlsystem lies outside the system, will maintain the temperature of the solutionby supplying heated buffer solution to the double jacketed sonicator, once thecore temperature of the reaction solution reached to pre fixed range then thesonication will start and ultra sounds hit the solutions. As soon as sound waves enter the reaction solution,bubbles will start to emerge, grow to their maximum size to ultimatelycollapse, causing the cell disruption and particle dispersion leading toinactivation of microbial cell and enzymes (fig. 1).

Types of sonicator-

ü  Bathsonicator

ü  Probesonicator

Theseboth can be either batch type or continuous flow type based on the purpose,design and type of food.

Applicationsof thermosonication

ü  Microbialinactivation

ü   Enzyme inactivation - Glucose oxidase, Peroxidase,Pectin methyl esterase(PME), Protease, lipase and Poly phenoloxidase (PPO)

ü   As an alternative to blanching  and pasteurization

ü   Quality and structure maintenance

ü   Quality improvement

Advantagesof Thermosonication

ü  Greater homogenity and effective mixing

ü  Increased mass transfer

ü  Reduced energy consumption/ significant energysavings

ü  Reduced temperature and increased production rate

ü  Minimization of flavor loss

ü  Preservation of heat sensitive nutrients, vitaminsand other organic compounds

ü  Elimination of microorganisms and enzymes withoutdestroying nutrients of foods

ü  Potential to ensure stable product in compliancewith standards set by FDA-HACCP

ü  Effective treatment for inactivation of enzymes

ü  Conserve nutrients and bioactive compounds

ü  A rapid, efficient and reliable alternative toimprove the quality and extend the shelf life of fruits and vegetables

Conclusion-

Thermosonication(TS) is a novel and viable technique in food processing that is employed toreplace the conventional thermal processing. It can increase the microbial andenzymatic inactivation rates, extend product shelf life and reduce the impacton the nutritional content and overall quality of fruit and vegetable processedproducts.

Authorsare from *Department of Postharvest Technology, Kittur Rani Channamma College ofHorticulture, Arabhavi, UHS Bagalakote.