March 8, 2013 7:34 pm

In pursuit of the perfect tomato

A fightback for flavour is underway as scientists use genetics to satisfy consumers’ demand for flavour and growers’ need for shelf life
Different varieties of tomatoes©Dreamstime

For supermarket shoppers, the tomato symbolises what we have lost in terms of taste and texture, in exchange for being able to buy cheap vegetables and fruit year round. But a fightback for flavour is under way – and its scientific champion is Harry Klee, horticulture professor at the University of Florida, Gainesville.

“The big problem with the modern commercial tomato is that growers are not paid for flavour, they’re paid for yield and shelf life,” says Klee. “There is a complete disconnect between breeders and consumers.”

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The answer, according to Klee, is to “put together an integrated system that starts with consumers and what they want. We have come up with a recipe to breed a really great tomato but a lot of work will be needed to get it into the commercial system, which is loaded against the consumer.”

The Florida research started with what Americans call heirloom tomatoes – often called heritage varieties in Britain – which date back to the period before mass commercialisation. “In general the loss of flavour coincides with the intensive breeding that began after world war two. Since flavour started going down, yields of tomatoes have gone up by 300 per cent,” says Klee.

Biochemical analysis of the best-flavoured varieties – with input from many tasting panels – identified 68 flavour-associated compounds. Most important are “volatiles”, many of which also contribute strongly to the enticing scent of freshly picked tomatoes. Some chemicals (such as cis-3-hexanal) which scientists had previously thought important for taste were not. Others (such as geranial) which had been regarded as marginal contributors were actually key to good flavour.

At the same time, scientists are discovering the genetics of tomato flavour, appearance and durability. One particular mutation, favoured because it gives ripe tomatoes a beautifully even scarlet surface, turns out to reduce the biosynthesis of flavouring compounds.

Now the Florida researchers have bred “hybrids between great-tasting heirlooms and modern commercial lines, which consumers love and which are easier to grow,” Klee says. “I’d say we have 100 per cent of the flavour [of old varieties] and 80 per cent of the performance [of modern ones] – but we need 100 per cent of the performance before commercial growers will take them up.”

Although Klee worked for Monsanto until 1995, developing genetically modified crops, he does not see a role for GM technology in breeding better tomatoes, because of consumer resistance and because it would be too costly and time-consuming to obtain regulatory approval for a transgenic tomato. “We can do it through conventional breeding, using modern genetics and flavour chemistry,” he says.

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Getting under our skin

Human skin and body hair pose fascinating puzzles for evolutionary biologists. When and why did our ancestors shed most of their fur to become naked apes? Why does our skin colour vary so much? Nina Jablonski, anthropology professor at Penn State University, has led the search for answers.

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The genes activated for human speech are similar to those that songbirds use for singing, according to a study by Erich Jarvis, a neurobiologist at Duke University, North Carolina.

In Africa about two million years ago, as a drier climate changed woodlands into savannah and previously plentiful fruit and vegetables became more scarce, hominids began to hunt more. Natural selection reshaped the apelike proportions of our australopithecine ancestors into a longer-legged body capable of long-distance running after prey. To deal with the heat generated by sustained activity in the African sun, natural selection also removed most of their thick fur and added plentiful sweat glands, to cool the now bare body by evaporation.

Like chimpanzees, the australopithecines had pale pink skin beneath their fur. Later hominids, as they lost their hair, were exposed to sunburn and related skin damage, so their skin turned dark as its concentration of protective melanin pigment increased. By 1.2 million years ago, species such as Homo ergaster had naked, deeply pigmented skin.

But when humans moved out of Africa to more northerly latitudes in Asia and Europe, the paramount evolutionary pressure was no longer protection against excessive ultraviolet radiation. What mattered more was the need to let enough sunlight into the skin to synthesise vitamin D, a vital nutrient obtained mainly in this way rather than through diet. So skin became pale again.

“We know there must have been at least three separate instances of evolutionary lightening in human history,” says Jablonski. It happened to Neanderthals: DNA analysis of their fossils shows they had genes associated with pale skin (and reddish hair). Then our modern human ancestors developed pale skin separately in Europe and Asia.

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Salmon might thrive on a diet based on wood and gas©Corbis

Salmon might thrive on a diet based on wood and gas

Plenty more fish in the forest

Trees and North Sea gas are being made into salmon feed – via yeast and bacteria – in the latest efforts to wean aquaculture off expensive and environmentally harmful fishmeal to more sustainable feeds.

A project funded by the EU and Norway (which is the world’s largest salmon producer) starts with wood chip from the forest industry. This is broken down into lignin and cellulose and then by enzyme treatment into sugars, which are used to grow yeast in a fermentation vat. A pilot plant is in operation, though it will take another four years of development to scale it up for commercial production, says Margareth Øverland, director of the Aquaculture Protein Centre at the Norwegian University of Life Sciences.

The bacterial feed is made by growing Methylococcus capsulatus microbes, which metabolise methane, on North Sea gas. Sterilised by heat treatment and dried, they produce a meal that contains 70 per cent protein. Its composition makes it highly beneficial for fish health, Øverland says: “Dietary inclusion of bacterial meal for Atlantic salmon has been shown to support excellent growth performance and prevents intestinal inflammation induced by soyabean meal, thus allowing safe use of such plant ingredients in aquafeeds”.

People fear that salmon, which hunt smaller fish, will taste bland if they subsist in captivity on a fish-free diet. But Øverland insists: “The taste does not change if the salmon are fed microbial meal.”

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Cosmic rays are born in the death of a star

Astronomers have solved the mystery of cosmic rays, the high-energy, electrically charged particles that bombard Earth constantly from all directions.

Analysis of four years of data from Nasa’s Fermi Gamma-ray Space Telescope shows that the particles, mainly protons, are generated in the aftermath of supernovae, stellar explosions that are the most violent events in our universe. As the shockwave from a supernova travels out through interstellar space and encounters hydrogen atoms, it strips off their electrons. The resulting protons – hydrogen nuclei – are accelerated almost to the speed of light and zip off across the universe.

“The energies of these protons are far beyond what the most powerful particle accelerators on Earth can produce,” says Stefan Funk of Stanford University who led the analysis, published in the journal Science.

Because of their electric charge, protons are deflected by magnetic fields, making it impossible to trace them back to their source. The new study overcame that problem by focusing on gamma rays, intense electromagnetic radiation generated when the supernova protons collide with other particles. Gamma rays travel in a straight line, unaffected by magnetic fields, and come in a distinctive range of energies characteristic of the process in which they were created.

The analysis traced gamma rays to the remnants of two supernovae that exploded about 10,000 years ago. Confirmation of their origin comes 100 years after the discovery of cosmic rays.

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