The stability of natural red/pink food colours in ultrahigh-temperature (UHT) products.

BACKGROUND: The aim of this experiment was to select a pool of potential red/pink natural colour candidates and evaluate their stability during ultrahigh-temperature (UHT) processing and subsequent storage and to compare their behaviour against the artificial colour erythrosine. It was hypothesised that heat processing and post-treatment storage conditions would have a negative effect on the stability of the natural colourants. RESULTS: All colourants except fermented red rice showed significant colour loss post-UHT processing (α=0.05). Analysis of the colour parameters L*, a* and b* determined that lycopene was the least stable of the colourants and red radish the most stable under all conditions. Fermented red rice was observed to be heat-stable after exposure to UHT processing and also remained relatively stable during storage, as was black carrot. The variation across trials and the spoilage of some samples were attributed to the fluctuations in temperature (±5 °C) observed during processing. CONCLUSION: Heat processing and post-treatment storage conditions had a negative effect on the stability of the natural colourants.

S-equol, a potent ligand for estrogen receptor beta, is the exclusive enantiomeric form of the soy isoflavone metabolite produced by human intestinal bacterial flora.

BACKGROUND: The discovery of equol in human urine more than 2 decades ago and the finding that it is bacterially derived from daidzin, an isoflavone abundant in soy foods, led to the current nutritional interest in soy foods. Equol, unlike the soy isoflavones daidzein or genistein, has a chiral center and therefore can occur as 2 distinct diastereoisomers. OBJECTIVE: Because it was unclear which enantiomer was present in humans, our objectives were to characterize the exact structure of equol, to examine whether the S- and R-equol enantiomers are bioavailable, and to ascertain whether the differences in their conformational structure translate to significant differences in affinity for estrogen receptors. DESIGN: With the use of chiral-phase HPLC and mass spectrometry, equol was isolated from human urine and plasma, and its enantiomeric structure was defined. Human fecal flora were cultured in vitro and incubated with daidzein to ascertain the stereospecificity of the bacterial production of equol. The pharmacokinetics of S- and R- equol were determined in 3 healthy adults after single-bolus oral administration of both enantiomers, and the affinity of each equol enantiomer for estrogen receptors was measured. RESULTS: Our studies definitively establish S-equol as the exclusive product of human intestinal bacterial synthesis from soy isoflavones and also show that both enantiomers are bioavailable. S-equol has a high affinity for estrogen receptor beta (K(i) = 0.73 nmol/L), whereas R-equol is relatively inactive. CONCLUSIONS: Humans have acquired an ability to exclusively synthesize S-equol from the precursor soy isoflavone daidzein, and it is significant that, unlike R-equol, this enantiomer has a relatively high affinity for estrogen receptor beta.