Thermal and Alternative Processing Technologies

Pickling Cucumber Improvement Committee Meeting Abstract

K. P. Sandeep

Department of Food Science, North Carolina State University

In recent years, the demand for higher quality products from consumers is on the rise. In an effort to meet this need, researchers have been investigating alternative processing techniques. Some of the alternative thermal techniques that have been investigated are discussed here. Infrared heating (3 x 1011 – 4 x 1014 Hz) serves as a quick means for surface heating and disinfection (seeds, peas, ground beef patties, baked potatoes). Ohmic heating involves passing electric current through a product (liquid whole eggs, tomato sauces) to heat or sterilize it. The liquid and particulates in a food can be heated at the same (rapid) rate using this technique. However, products might have to be reformulated (to include more salts) to facilitate heating.

The effectiveness of microwave (3 x 108 – 3 x 1011 Hz) and radio frequency (3 x 103 – 3 x 108 Hz) heating depends on the dielectric properties of the food. In radio frequency heating, the food is placed between two plates, the polarity of which is reversed at radio frequency. Microwave radiations heat up most polar molecules, each having different dielectric properties, while radio frequency waves predominantly heat up only the highly polar water molecules.

High pressure (100-800 MPa) is effective in inactivating many microorganisms during processing of meats, fruit juices, jams, and jellies. Ultrasonic waves cause an irreversible lethal effect to some microorganisms due to cavitation (5550°C, 50 MPa). Membrane processing has been used for concentration of liquid foods, reduction of microbial counts, demineralization, production of whey protein concentrate, and for aroma recovery.

The pulsed light technology uses light flashes (200 nm-1 mm) at 1-10 Hz for a few microseconds to inactivate fungi and bacterial spores on surfaces of fruits, vegetables, poultry, fish, and meat. It is non-ionizing and cannot penetrate opaque materials. The pulsed electric field technology involves the use of high intensity electric field (1-40 kV/cm) at 1-5 Hz for a few microseconds to inactivate microorganisms (by electroporation) such as E. Coli, Staphylococus, and Pseudomonas in products such as liquid whole eggs, apple juice, milk, and soups.

Irradiation involves the use of gamma rays (produced from Co-60 or Cs-137), accelerated electrons or X-rays to destroy microorganisms (E. Coli, Trichinella, Salmonella) in spices, poultry, and pork. Ultraviolet light has been used to sterilize air, milk, food packaging surfaces, and packaging equipment and also to minimize souring of vegetables. Ozone is primarily used to purify water. Ozonated water has been used to wash fresh fish, meat, and vegetables. It is also used as a sanitizing agent and performs better than chlorine in this respect. Factors such as cost, scale-up issues, range of applicability, establishment of health effects of these technologies, and development of a database for approval by regulatory agencies are some of the reasons for these technologies not being adopted on a large scale.

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