Greener burgers

C&I Issue 12, 2015

Meat is a key constituent of global diets. In the US alone, around 45bn kg of meat and poultry were produced in 2013 – some 8.6bn chickens and 33.2m cattle.1 Such demand will only rise with the growth in the world’s population, which is expected to reach 9bn by 2050. A report by the UN Food and Agriculture Organisation estimates that to feed this number of people, current global food production will need to almost double.2

Many people believe that producing and eating so much meat is environmentally unsustainable and damaging to our planet – raising livestock requires large amounts of water, food, land and energy, and cattle are notorious for producing huge amounts of the greenhouse gases methane and carbon dioxide. What we eat and how we produce it may therefore need to change.

One idea is to use plant-based products to mimic meat. While many products made from soya, wheat, pea proteins, tofu and mycoproteins – the fungal protein common to all Quorn products – are already on the market and have proved successful with vegetarians and vegans, for plant-based products to replace meat they must also appeal to the carnivores among us.

Creating a product that tastes like meat is difficult. Flavour is a combination of two senses – aroma and taste. Our sense of smell is stimulated by volatile, low molecular weight compounds, while that of taste is stimulated by certain water-soluble compounds. Most volatile compounds in meat – over 1000 have been identified – are generated during heating. The main reactions involved are the oxidation of lipids and the Maillard reaction between amino acids, notably cysteine, and sugars, notably ribose. The products of the Maillard reaction are furans substituted with a thiol or a disulfide group that are the key to meat flavour. Significantly, without trace amounts of 2-methyl-3-furanthiol and bis(2-methyl-3-furyl) disulfide, the characteristic aroma of meat cannot be achieved. Other compounds formed in the Maillard reaction that contribute to meat aroma include pyrazines, thiazoles and thiopenes.

Food scientist Jane Parker, at the University of Reading, UK, comments: ‘The aroma profile of cooked meat is one of the most complex. Much of it is generated from the reaction between sugars and amino acids naturally present in meat during cooking. Significantly, the mixture of aroma precursors, including ribose and cysteine, as well as various taste components, are not abundant in plants.’

In addition, she says, fat has an important part to play and often provides the flavour specific to different species. ‘To get a really beefy flavoured beef burger requires some beef fat to be present,’ she says.

Other chemicals responsible for the savoury taste of meat are 5’- ribonucleotides, for example inosine monophosphate, which is a post-slaughter breakdown product of adenosine triphosphate (ATP), a component of muscle cells. ‘These compounds work in synergy with the amino acid glutamic acid to provide a unique taste and boost the overall flavour of meat,’ explains Parker. Yeast extracts provide a rich source of ribonucleotides and are therefore widely used as components of meat flavourings.

It’s not just flavour that’s tricky to copy. ‘If you are trying to generate a meat analogue, it is very difficult to reproduce the texture of meat’, says Don Mottram, professor of food chemistry at Reading University. ‘The important features of meat texture are the myofibrillar proteins, which give live muscles their ability to expand and contract. These proteins are contained in muscle cells that are long and thin and held together in fibre bundles. This gives meat its characteristic texture and chewing breaks these fibre bundles.’

Fake meats

In the US, Patrick O’Brown, a Stanford University professor turned entrepreneur, however, believes that it is possible to replicate red meat using plants. His start-up company, Impossible Foods, is working to make meat mimics that look, smell and taste like real meat, and even sizzle on the grill. Its mission, according to a company spokesman, is to ‘give people the enjoyment of food that comes from animals without the health and environmental drawbacks’. The company’s first product – a raw, ground meat that can be used to make any of the dishes that you would from conventional ground beef, including hamburgers – is expected in the US in 2016.

From his lab in California, O’Brown has already demonstrated a plant version of a hamburger, which looks, tastes and cooks ‘almost’ like the real thing. At a press conference in 2014, journalists witnessed a dark red patty similar in looks to raw mince being cooked on a grill. The patty caramelised, gradually browned, sizzled and even produced the smells of cooked meat. The taste was less realistic though, with his audience rating the product as several rungs below a gourmet burger, and more similar in taste to turkey.

The patty was made from a plant species yet to be disclosed, which was reportedly harvested in large quantities and fed into giant blenders, where the plant material was broken down into its constituent proteins. In the lab, amino acids, fats, and nutrients were selected from the plants for their texture, colour and flavour. Currently each patty costs about $20 to produce, but the cost of manufacturing is expected to fall when larger batches are made. 

To replicate the flavour of meat, O’Brown’s team spent hours categorising the hundreds of molecules responsible for cooked meat. The metallic taste of blood, for example, is down to haem, the Fe2+ in the centre of haemoglobin, which carries oxygen in all blood cells. Haem is also found in myoglobin, a protein found in muscles.

O’Brown’s team managed to identify a plant protein that contains haem, which looks the same, and has the same distinct metallic taste as the meat protein. ‘We use a haem protein naturally found in the root nodules of legumes, functionally and structurally analogous to the muscle protein myoglobin, to give our meat its unmistakable meaty flavour,’ said a representative from Impossible Foods.

To recreate the chewy texture of a meat burger required a different approach. O’Brown had to find the right mix of plant proteins that could mimic animal tissue. So far, he claims he has found suitable plant molecules that can copy the textures of fat, connective tissue and muscle fibres.

O’Brown is not the only scientist looking to produce meat alternatives from plants. Beyond Meat, based in California, US, markets plant ‘chicken strips’, ‘beef crumbles’ and the Beast Burger. The latter is made by mixing soya with powdered pea protein, water, sunflower oil, and various nutrients and natural flavours. The mixture is placed into a machine, ‘the steer’, where the plant material gets pulled apart, before being reassembled into fibrous bundles of protein that resemble the muscle fibres of meat. The product is then cooked, pressurised and shaped into patties ready to be put on the grill. Technicians test the resulting patties to see how moist and ‘tearable’ they are, at the same time adding liquid coloured with turmeric to recreate the look of myoglobin. According to Ethan Brown, food scientist and ceo of Beyond Meat, the patties contain more iron and protein than the same amount of ground beef, and more omega-3s than the same amount of salmon.

‘Designing the right texture required matching the architecture of meat,’ says Tim Geistlinger, vp of r&d. ‘[The product] had to have muscle-like protein fibres that were similar to the myofibrils found in muscle tissue; it had to have moisture levels that were equal to meat. The lipid profile had to be similar to meat, and we knew that it all had to be combined in a way that created distinct compartments, very much like the cellular substructure of meat.’ These compartments are critical to trapping the moisture and oils that are released when meat is chewed, explains Geistlinger. Moreover, he adds that the product must not be dry, powdery, bouncy or soggy, characteristics of high gluten and carbohydrate products.

To get the architecture of the product right, Brown and his team worked with Fu-Hung Hsieh, professor of bioengineering at the University of Missouri, US, who has over 15 years’ experience creating meat texture from soya protein. ‘By using water, high pressure and relatively low temperatures, we have been able to gently align the plant proteins in a laminar flow process to form the muscle-like fibres,’ explains Geistlinger. ‘These fibres functionally surround and physically trap the water, lipids, and carbohydrates, into different compartments. Together they create the proper architecture, which can then be fine-tuned to the texture of meat.’

However, not everyone is convinced by the latest meat mimics. ‘Meat analogues are not new’, explains Mottram. ‘Texturised vegetable protein based on soya has been around for many years and has been developed by a number of companies. But texture and off-flavours have been problems.’

Quorn, adds Mottram, is probably the best meat mimic to date. In Quorn, a meat-like texture is achieved by using a single cell ‘mycoprotein’ derived from Fusarium venenatum, a mushroom based fungus. This is grown in a glucose-based media before the cells are harvested. The cells are long and thin, like muscle cells, giving them a structure similar to meat.

‘RHM (Rank Hovis McDougall) and ICI (as Marlow Foods) put many millions of pounds and a number of years during the 1980s and 1990s into Quorn’s development,’ says Mottram. ‘But, even Quorn, with all the scientific resources it had available, found it difficult to emulate meat flavour fully in their product and to attain the optimum flavour release characteristics.’

Lab grown products

Another way of creating a meat mimic is by growing it in a lab. In 2013, Mark Post, a vascular biologist and surgeon at Maastricht University in The Netherlands, presented the world’s first burger grown using stem cells.

The stem cells, specifically myoblasts, were extracted from pieces of muscle tissue taken from a cow. The cells were soaked in nutrient-rich serum, and left to multiply for several days. They were then suspended in a scaffold consisting of a gel around a central column, which forced them to align together and form muscle fibres. After a few weeks, around 3000 cells, enough to create a small hamburger, were harvested.

At the product launch, testers reported that the burger tasted almost like a real one, but not as juicy and ‘surprisingly crunchy’. However, the technology is still very much in the basic research phase, and Post believes it will be some 20–30 years before we see lab-grown meat in the supermarkets.

In theory, cultured meat offers something closer to meat than plant-based products; it should be possible, says Post, to recreate the complex flavours of meat in the lab exactly. The main challenges that scientists face is that as well as muscle fibres, they still need to figure out how to build intramuscular fat, sinew, cartilage and even bone from scratch, as well as copy the structure of veins and blood vessels that supply the muscle cells with blood.

The lab-grown meat has its own opponents. Joseph D. Puglisi, professor of structural biology at Stanford University, US, and chair of the scientific advisory board of Beyond Meat, believes that lab-grown meat is a non-starter. ‘Lab-based meat culture is a losing proposition. Animals long ago evolved to perform the “synthesis” of meat protein fibres efficiently and cost-effectively. Reproducing this in the laboratory at a cost effective scale would be nearly impossible.’

Parker, however, has a more positive view of the prospects of lab-grown meat. She believes that cultured meat could be made to taste the same as meat as long as all the precursor chemicals and reaction products involved in its flavour and aroma profile were provided. The success of plant burgers on the other hand, she says, will depend on how fussy and discerning the consumer is. ‘I think it will be very hard to make plant-based burgers that are indistinguishable from a true beef burger. There will always be consumers who can tell the difference, but there will be others for whom the ketchup, gherkins, mayo and cheese sufficiently disguise the differences in such a way that the alternatives are perfectly acceptable,’ she continues.

Meanwhile, ‘another contribution to flavour perception occurs in the brain, so marketing and the individual’s willingness to accept them as suitable alternatives will also come into play.’


1 The United States meat industry at a glance, North American Meat Institute, https://www.meatinstituteorg/index.php?ht=d/sp/i/47465/pid/47465

2 Edible insects, future prospects for food and feed security. Food and Agriculture Organization of the United Nations, Forestry Paper, 2013 http:/

Jasmin Fox-Skelly is a freelance science writer based in Cardiff, UK

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