Food Biochemistry and Food Processing (2 edition)

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780 Part 7: Food Processing

processes have gained wide applications for products such as

those derived from refined vegetable oils, e.g., deodorizer dis-

tillate of vegetable oils, palm oil for obtaining tocotrienols and

tocopherols, rice oil for oryzanol recovery, monoglyceride con-

centration, carotenoid recovery from palm oil, heavy petroleum

characterization, and herbicides (Barnicki et al. 1996, Sakiyama

et al. 2001, Batistella et al. 2002a,b, Fregolente et al. 2005, Ito

et al. 2006, Shi et al. 2007c). Recently, a new process of molec-

ular distillation was developed for recovery of tocotrienols and

tocopherols from rapeseed by a combination of acid-catalyzed

methyl esterification and crystallization followed by fractional

distillation of derived products and for the recovery of orange

peel oil and essence products rich in aldehydes, esters, and other

special volatile compounds (Lutisan et al. 2002, Jiang et al.

2006). An industrial production of a typical industrial fractional

vacuum distillation plant is shown in Figure 40.10. In order to

increase the yield and quality of the final products, the distiller

is operated continuously.

Figure 40.10.The vacuum fractional molecular distillation column.

SUMMARY

One of the most important trends in the food industry today is

the demand for “natural” foods and ingredients that are free from

toxic chemical additives. The growing interest in natural foods

has raised the demand for natural health-promoting products of

nonsynthetic origin. High-value functional substances can be

obtained from biological materials by various purification and

separation methods from plant materials or by-products. Among

the separation processes being used or developed are physical

and chemical processes such as centrifugation, filtration, mem-

brane separation, precipitation, chromatography, solvent extrac-

tion, supercritical fluid extraction, crystallization, evaporation,

and distillation.

The separation problems presented by the production of sol-

uble material have a number of aspects that influence the nature

of the extraction technique chosen. An important factor is the

stability of the extracted product. In the case of unstable prod-

ucts, a rapid separation process is necessary in order to avoid

significant loss of products. Extraction with organic solvents

by traditional methods is a well-established method for the se-

lective separation of specific constituents from raw materials.

The conventional procedures for preparing concentrated extracts

are steam distillation or solvent extraction with an organic sol-

vent. Extractants with a low boiling point, such as ethyl acetate,

methanol, dichloromethane, etc., are traditionally used for iso-

lating valuable constituents from such products as hops, spices,

and oil seeds and also for removing or reducing the level of less-

desirable accompanying substances (such as nicotine, caffeine).

But a very important step in the process is the complete re-

moval of the solvents from extracts and its residue as they are

in part toxicologically objectionable. In addition, organic sol-

vents have a low selectivity. Extraction must be followed by

removal of the solvent from the extract, for example by distil-

lation. The challenges in the separation processes are to both

meet food regulations and to conduct the separation effectively

and economically. Many compounds in the concentrated ex-

tract will be thermally labile and prone to degradation if heated

too vigorously. The removal of the solvent can pose serious

problems since the residual level of the solvent must be min-

imized, but not at the expense of the degradation of the final

extract. Public health, environment, and safety issues are the

major concerns in the use of organic solvents in food processing.

The possibility of solvent residues remaining in the final prod-

uct has been a growing concern to consumers, thus warranting

stringent environmental regulations. The extent of residual sol-

vent levels and also the composition of the extraction solvents

used in the food industry are well regulated within the existing

laws and regulations. The solvents used for this purpose must

meet the requirements of foodstuffs legislation, which can vary

from country to country. In recent years, national and interna-

tional bodies (such as the Food and Drug Administration, USA;

the EC Codex Committee; and the FAO/WHO, Geneva) have

increasingly emphasized the importance of complying with such

criteria.

The demand for ultra-pure and high value-added products is

redirecting the focus of the food and pharmaceutical industries