Soy and colours hit the science headlines in August

By Stephen Daniells

- Last updated on GMT

Related tags: Soybean, Isoflavones

Natural blue pigments from oyster-friendly bacteria and red pigments from prickly pear, and concerns for men over soy consumption have been the highlights of this month's science.

Natural colours from interesting sources

French researchers reported that a blue-green pigment from microalgae responsible for the greening of oyster gills may also provide a natural blue-green colouring for food.

The compound called marennine, produced by the microalgae Haslea ostrearia, not only has potential to act as a pigment, but it also “exhibit[s] significantly higher antioxidative and free radical scavenging activities than natural and synthetic antioxidants commonly used in food,”​ wrote researchers from five French universities and institutes in the Journal of Agricultural and Food Chemistry​.

The pigment shows excellent properties for use in foods, including high water solubility, high resistance to heat and light, and stability at the pH range 6 to 8.

Spanish researchers devised an optimal process for spray drying the juice of betalain-rich Opuntia stricta​, or prickly pear, so it can used as a natural red food colouring in yoghurts and soft drinks.

According to Jose Maria Oban and colleagues, whose study has been accepted for publication in the Journal of Food Engineering​, presented a method to obtain a powder colourant from fruit juices by spray drying, since this format is easier to handle for some applications and not so heavy to transport as liquids. It also has high storage stability.

“This colourant was successfully applied in two food model systems: a yoghurt and a soft drink. Food presented a vivid red tonality very attractive for consumers that was maintained after one month under refrigeration.”

“There is an increasing interest for large-scale cactus pear fruit processing for the production of colouring foodstuffs, opening up new markets on functional foods to dairy and beverage industries,”​ wrote the researchers from the Universidad Politecnica de Cartagena.

Concerns over soy

Harvard researchers grabbed the headlines around the world when they reported that men who consume an average of half a portion of soy products per day are more likely to have a lower concentration of sperm, particularly if they are overweight or obese.

The study, published in the journal Human Reproduction ​(doi:10.1093/humrep/den243), indicated that there may be a link, and if further randomised trials reach the same conclusions could lead to advice that men should avoid eating too much soy if they are planning a family.

Soy contains a number of isoflavones that exert an oestrogen-like affect, like daidzein, genistein and glycitein. They are marketed to menopausal women as a natural alternative to hormone replacement therapy (HRT), but some animal studies have indicated that high consumption of soy isoflavones could affect fertility.

The effect on sperm concentrations seemed to be more pronounced in men who already had higher sperm counts.

"The implication is that men who have normal or high sperm counts may be more susceptible to soy foods than men with low sperm counts, but this remains to be evaluated,"​ said Dr Jorge Chavarro of the Harvard School of Public Health, who believes that further randomised trials are needed.

He said it may be down to the oestrogenic activity of the isoflavones interfering with hormone signals, and therefore affecting sperm production.

In the overweight and obese men, this may be further accentuated by their higher levels of body fat, which produce more oestrogen than in slimmer men.

It is worth noting, however, that Asian populations have long consumed soy-rich diets without signs of reduced fertility or other health problems being traced back to the plant.

Related topics: Science, Proteins, Flavours and colours

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