The blob
Before departing on holiday we emptied, defrosted and thoroughly cleaned the fridge section of our fridge-freezer, using an antibacterial kitchen spray and lots of hot water. The fridge was dried thoroughly and then left closed for three weeks, switched on. When we opened the fridge again there was 2-centimetre-high blob of colourless, transparent gel sitting on one of the shelves. The blob was irregular in outline, slightly taller than it was wide, and had a distinct base rather than spreading out on the shelf. There was no evidence of dripping or leakage within the fridge. What was this blob? If it was some kind of living organism, thriving in a cold, dark, dry fridge, then the implications for life on Mars are surely far-reaching.
鈥� It is not easy to identify what 鈥渢he blob鈥� in the fridge might have been from this brief description, without obtaining a sample and analysing it under a microscope.
If conditions in the fridge were such that there was a continuous drip of water onto one spot, however, it is possible that some sort of biofilm developed. Simply put, biofilms are a collection of microorganisms surrounded by the slime they secrete, attached to either an inert or living surface. Readers are probably already familiar with some biofilms such as the plaque that forms on your teeth and the slippery slime found on river stones.
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For such a biofilm to develop in your fridge, there must have been some water present, possibly in the form of condensation from the atmosphere that entered the fridge when the door was shut as you left for your holiday. Biofilms form when bacteria adhere to surfaces where water is present and begin to excrete a slimy, glue-like substance that can anchor them to all kinds of material, and also to each other. They can consist of a single bacterial species but more often consist of many species of bacteria, fungi, algae, protozoans, debris and corrosion products.
Essentially, a biofilm may form on any surface exposed to bacteria and some amount of water. Development can take anything from several hours to several weeks.
With thanks to Dave Malloch, professor of botany at the University of Toronto
Changing tastes
Monosodium glutamate is a common flavour enhancer that is used particularly in Chinese and Japanese cooking. Why is it so popular in these cuisines and, more pertinently, how does it enhance the flavour of food?
Monosodium glutamate or MSG is presumably most commonly used in oriental cooking for traditional reasons. For thousands of years the Japanese have incorporated a type of seaweed known as kombu in their cooking to make food taste better. It was not until 1908, however, that the actual ingredient in kombu responsible for improvement in flavour was identified as glutamate.
From then until 1956, glutamate was produced commercially in Japan by a very slow and expensive means of extraction. Then large-scale industrial production began and has continued, mainly involving the fermentation of natural substances such as molasses from sugar beet or sugar cane. Today, hundreds of thousands of tonnes of MSG are produced all over the world.
Monosodium glutamate contains 78.2 per cent glutamate, 12.2 per cent sodium and 9.6 per cent water. Glutamate, or free glutamic acid, is an amino acid that can be found naturally in protein-containing foods such as meat, vegetable, poultry and milk. Roquefort and Parmesan cheese contain a lot of it. The glutamate in commercially produced MSG, however, is different from that found in plants and animals. Natural glutamate consists solely of L-glutamic acid, whereas the artificial variety contains L-glutamic acid plus D-glutamic acid, pyroglutamic acid and other chemicals.
It is widely known that Chinese and Japanese food contains MSG, but people don鈥檛 seem to be aware that it is also used in foods in other parts of the world. In Italy, for example, it is used in pizzas and lasagne; in the US it is used in chowders and stews, and in Britain it can be found in snack foods such as potato crisps and cereals.
It is thought that MSG intensifies the naturally occurring 鈥渇ifth taste鈥� in some food 鈥� the other, better known, four tastes being sweet, sour, bitter and salt. This fifth taste is known as umami in Japanese, and is often described as a savoury, broth-like or meaty taste.
Umami was first identified as a taste in 1908 by Kikunae Ikeda of the Tokyo Imperial University, at the same time that glutamate was discovered in kombu. It makes good evolutionary sense that we should have the ability to taste glutamate, because it is the most abundant amino acid found in natural foods.
John Prescott, associate professor at the Sensory Research Science Center at the University of Chicago, suggests that umami signals the presence of protein in food, just as sweetness indicates energy-giving carbohydrates, bitterness alerts us to toxins, saltiness to a need for minerals and sourness to spoilage. A team of scientists has even identified a receptor for umami, which is a modified form of a molecule known as mGluR4.
Mark Bollie
Amersham, Buckinghamshire
This week鈥檚 questions
Cool shapes
Why are power station cooling towers shaped the way they are, with a wide circular top and an even wider circular base connected by an inward-curving middle?
Tom Fulton
Castleford, West Yorkshire
Shorthaul flight
I鈥檝e just been watching the athletics World Cup in Madrid on TV. Why do long jumpers adopt different styles when travelling through the air after take-off?
Some just hang with their arms and legs pointing forward, some cycle madly though the air, while others seem to keep running while they are airborne. Intriguingly, triple jumpers adopt nothing other than a simple floating technique during their final phase. Do any of these styles affect the distance gained or is the length of jump determined simply by take-off speed and trajectory?
Molly Howard
Wolverhampton, West Midlands