Food Biochemistry and Food Processing (2 edition)

BLBS102-c39 BLBS102-Simpson March 21, 2012 14:20 Trim: 276mm X 219mm Printer Name: Yet to Come

748 Part 7: Food Processing

with the Food and Drug Administration in 1997 by Tetra Pak, fol-

lowing two workshops conducted in 1995 and 1996 by Center for

Advanced Processing and Packaging Studies (multi-University

partnership of The Ohio State University, North Carolina State

University, and University of California-Davis) and the National

Center for Food Safety and Technology.

Aseptically processed products have shelf life of 1–2 years and

they have superior sensory and nutritional characteristics com-

pared to conventional thermally processed products. Some of the

difficulties associated with the techniques include variation of

residence time of particulates in different parts of the processing

equipment, control of heat transfer rate between heated liquid

and solid particulates, fouling in heat exchangers, potential sur-

vival of enzymes, and potential damage to solids by pumping.

Sous-Vide Processing

Sous vide is a French word, which essentially means under

vacuum. Chef Georges Pralus is credited with using sous-vide

cooking for the first time to reduce shrinkage on a foie gras

terrine by cooking in a laminated plastic film sachets in France

in 1967. In this technique, ingredients or the raw food materials

are put in a plastic pouch, vacuum sealed and pasteurized at

varying time–temperature combinations (usually below 100◦C

and time longer than traditional cooking). The products can be

regarded as minimally processed since they are typically cooked

at lower temperatures. After being cooked, the food is cooled

to temperatures in the range of 1–8◦C. Sous vide is increas-

ingly being used to process convenience foods (ready-to-eat

meals) as it is reputed to produce superior quality product be-

cause of the mild heat processing and the absence of oxygen

in the pack (Creed 2001). Pasteurized sous-vide pouches when

held below 3.3◦C remain safe and palatable up to 3–4 weeks

(Armstrong and McIlveen 2000, Nyati 2000, Rybka-Rodgers

2001, Gonz ́alez-Fandos et al. 2005, Peck and Stringer 2005).

Sous-vide processed products retain fresh-like textures and su-

perior flavors. They also tend to show higher mineral, vitamin,

and color retention. However, inappropriate heating, refrigera-

tion, and storage temperatures can be the breeding ground for

Clostridium botulinumand more specifically the type A, B, and

E spores, which can produce toxins dangerous for human health.

AfterClostridium botulinum,Listeriais the most heat-resistant

non-spore forming pathogen that has the ability to grow at re-

frigerator temperatures. Therefore, there is greater risk for food

poisoning, and it is important to achieve 6D reduction (Rybka-

Rodgers 2001). It is vital to use the sous-vide techniques within

systems that minimizes contamination. At industrial level, there

is need to implement HACCP practices to get high-quality and

microbiologically safe minimally processed food.

Electrical Heating of Foods

In electrical heating, electromagnetic energy is applied to in-

crease the temperature of a product in such a way that the entire

volume and not just a part of the product is heated rapidly in

order to minimize quality losses. The technique was developed

to address the limitation of conventional surface conduction-

based methods. As a result of the rapid heating, quality changes

in electrical processed foods are generally better and are more

controlled compared to HTST processing. Electric heating of

different foods can be achieved by using different methods, in-

cluding ohmic heating, microwave, radio frequency (RF), and

infrared heating.

Ohmic Heating

Ohmic heating involves passing electric currents (primarily al-

ternating currents) through a food product for the purpose of

heating it. The process is also sometimes called Joule heating,

electrical resistance heating, direct electroheating, and electro-

conductive heating. Heat is generated internally in the product

as a result of its electrical resistivity. The electrical resistance

of the food determines the extent of current or voltage and the

relative amount of heat generated. It is a promising method of

food processing as the food heats volumetrically and provides

the potential to reduce overprocessing problems associated with

typical inside–outside heating pattern of conventional heat trans-

fer (Lima 2007, Wang et al. 2007b). The process is efficient for

foods with large particulates, which are not easy to process by

conventional thermal processing techniques. Rapid heat rates

greater than 1◦C/s can be obtained along with considerable en-

ergy saving with better control of process parameters (tempera-

ture and time).

Ohmic heating systems typically use electrodes contacting

the food. Applications of the technology include evaporation,

blanching, dehydration, and extraction. Zhong and Lima (2003)

studied the effect of ohmic heating on drying rate of sweet pota-

toes. The authors reported that ohmic heating of potato increased

the vacuum drying rate and 24% drying time was saved, which is

crucial in controlling economics of the process. The technique

is being used in the United States and Japan for processing

strawberries and different fruits to be used in yogurt prepara-

tion (Sastry and Barach 2000, Castro et al. 2003). Red apple,

golden apple, peach, pear, pineapple, and strawberry have been

heated ohmically in the temperature range of up to 25–140◦C

(Sarang et al. 2008). It has been reported that the application

of electric current has no impact on the rheological, color, and

chemical content of ohmically treated liquid juice (Yildiz et al.

2009). Quality of carrot pieces that had received varied ther-

mal treatments, such as blanching at low and high temperatures,

were tested for qualitative changes when three different heating

methods, namely conventional, microwave, and ohmic heating,

were applied. It was observed that time/temperature of thermal

pretreatment rather than method of heating influenced quality of

products (Lemmens et al. 2009).

Dielectric Heating

RF heating and microwave (MW) heating are based on the use

of electromagnetic energy to quickly heat foods. When poor

conducting dielectric food products are brought into a rapidly

altering electrical field, the H+and OH−components of water

molecule separate to form an electric dipole and orient them-

selves in the direction of the applied varying electric field. Thus,