Chemical modification of isoflavones in soyfoods during cooking and processing

Abstract

The principal chemical forms of isoflavones in soybean are their 6''-O-malonyl-beta-glucoside (6OMalGlc) conjugates. Experiments were carried out to determine the best conditions for extraction of isoflavones from soyfoods and the effects of commercial processing procedures and of cooking on isoflavone concentrations and composition. Hot alcohol extraction of ground soybeans deesterified 6OMalGlc conjugates. Although room temperature extraction slowed the conversion, extraction at 4 degrees C for 2-4 h led to the highest yield of 6OMalGlc conjugates and the lowest proportion of beta-glucoside conjugates. Analysis of soyfood products by reversed-phase HPLC-mass spectrometry revealed that defatted soy flour that had not been heat treated consisted mostly of 6OMalGlc conjugates; in contrast, toasted soy flour contained large amounts of 6''-O-acetyl-beta-glucoside conjugates, formed by heat-induced decarboxylation of the malonate group to acetate. Soymilk and tofu consisted almost entirely of beta-glucoside conjugates; low-fat versions of these products were markedly depleted in isoflavones. Alcohol-washed soy-protein concentrates contained few isoflavones. Isolated soy protein and textured vegetable protein consisted of a mixture of all 3 types of isoflavone conjugates. Baking or frying of textured vegetable protein at 190 degrees C and baking of soy flour in cookies did not alter total isoflavone content, but there was a steady increase in beta-glucoside conjugates at the expense of 6OMalGlc conjugates. The chemical form of isoflavones in foods should be taken into consideration when evaluating their availability for absorption from the diet.

Chemical composition of tempeh from soybean cultivars specially developed for human consumption

“…During tempeh fermentation, the glycoside forms are reduced, while the aglycon forms increases (COWARD et al, 1998). Fermentation or moisture activates the β-glycosidase enzyme causing hydrolyze of isoflavone glycosides forming the aglycon isoflavones (MATSUURA; OBATA, 1993).…”

“…Isoflavones are affected by different processing techniques (COWARD et al 1998;CARRÃO-PANIZZI;GOÉS-FAVONI;KIKUCHI, 2004), and changes in chemical composition modifying the isoflavones forms (glycosides, malonyl and aglycones) are common (AGUIAR, 2002). Isoflavones are also highly influenced by genetic variability and environmental conditions (CARRÃO-PANIZZI et al, 2009b).…”

Conversão de malonil-beta-glicosil isoflavonas em isoflavonas glicosadas presentes em alguns cultivares de soja brasileira

“…Neste trabalho, o solvente utilizado na extração dos isoflavonóides, foi uma solução 80% de metanol e à temperatura ambiente. COWARD et al [6], mencionam que a temperatura de extração de 4ºC proporcionou eficiente extração de isoflavonas tanto quanto a temperaturas mais elevadas, contudo sem transformação do conteúdo de malonil isoflavonas original. No entanto, para os cultivares analisados neste trabalho, pode-se notar que não houve transformação das formas malonil a glicosiladas a temperatura de 25ºC e que somente a temperaturas em torno ou acima de 100ºC, foi observado a esta transformação térmica (Figuras 3 e 4).…”

“…Em resultados obtidos por nossa equipe, foi observado que há mudança na composição de isoflavonas extraídas em temperaturas ao redor ou acima de 100ºC, principalmente nos teores de malonil em relação aos isoflavonóides glicosilados, visto que as formas malonil são descritas por diversos autores como sendo termolábeis. Pesquisadores como COWARD et al [6], observaram que o conteúdo de malonil isoflavonas se manteve quando efetuada a extração de isoflavonas a 4ºC. COWARD et al [7] e KUDOU et al [17] reportaram que malonil-β-glicosil isoflavonas são as formas em maior quantidade em grãos de soja e que estes são termolábeis, sendo convertidos a suas isoflavonas glicosiladas sob aquecimento.…”

Urinary phytoestrogen concentrations in the U.S. population (1999–2000)

“…The bulk of the dietary dosage of phytoestrogens is attributed to two major phytoestrogen classes: isoflavones and lignans. The most significant sources of isoflavones are soybean and soy products (Table 1), especially fermented soy products (Reinli and Block, 1996;Coward et al, 1998;Murphy et al, 1999). Lignans are primarily found in oilseeds such as flaxseed (Table 1), and in lesser amounts in whole legumes, whole grain cereals, vegetables, and fruits .…”