Other nutritional changes Antinutrients

Extrusion cooking also improves the nutritional quality of foods by destroying many natural toxins and antinutrients (Table 14.4). A dilemma exists as to whether it is desirable to remove these compounds. Enzyme inhibitors, hormonelike compounds, saponins and other compounds could impair growth and development in children, but these same compounds may offer protection against chronic diseases in adults. Allergens and mycotoxins are very resistant to thermal

Table 14.4 Antinutrients and toxins affected by extrusion cooking



Factors favoring reduction


Peanut, soy

Increased shear; added starch



Added ammonia



Added thiamine



Higher feed moisture



Increased mixing, lower temperatures; added

amine sources

Protease inhibitors

Legumes, potato

Higher extrusion temperatures

processing, but extrusion in combination with chemical treatment via reactive extrusion may effectively reduce these compounds to safe levels.

Glucosinolates found in many commercially important Brassica species might protect against certain forms of cancer (Van Poppel et al, 1999). Extrusion alone does not affect glucosinolates (Fenwick et al, 1986), but extrusion plus ammonia decreased glucosinolates in canola (Darroch, et al, 1990). Although extrusion with ammonium carbonate did not result in glucosinolate-free rapeseed meal, the process did improve nutritional parameters in a rat-feeding study (Barrett et al, 1997).

14.7.2 Phenolic compounds

The health benefits of phenolic acids and flavonoids are being actively studied today. Potato peels free phenolics, primarily chlorogenic acid, were reduced by extrusion (unpublished data, Camire and Dougherty), with improved retention at higher barrel temperature and feed moisture. Blueberry and grape anthocyanins were significantly reduced by extrusion and by ascorbic acid in sweetened corn breakfast cereals (Chaovanalikit, 1999).

14.7.3 Phytohormones

Phytoestrogens in soy and other foods may protect post-menopausal women from osteoporosis and heart disease and protect men against prostate and other testosterone-dependent cancers. Extrusion can transform soy into food products with broad appeal for consumers, but processing effects on soy isoflavones and other phytoestrogens should be evaluated for any products for which health effects are intended. Blends of soy protein concentrate and cornmeal (20:80) were processed under different extrusion conditions (Mahungu et al, 1999). Increasing barrel temperature caused decarboxylation of isoflavones, with increased proportions of acetyl derivatives, but total isoflavones also decreased.

Extrusion decreased the aglycone (genistein) of okara, a tofu by-product, mixed with wheat flour (Rinaldi et al, 2000). Glucosides of daidzin and genistin increased, but acetyl and malonyl forms decreased in the mixtures. Total isoflavone values were reduced in 40% okara samples extruded at high-temperature. Aglycones did not change in extruded corn-soy blends, but they were less effective in preventing proliferation of breast cancer cells in vitro (Singletary et al, 2000).

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