single cell protein 4.1 Introduction 4.2 Conventional protein sources 4.4 Substrates for SCP production 4.5 Micro-organisms for SCP production 4.6 sCP from carbon dioxide 4.7 SCP from carbohydrates 4.8 SCP from hydrocarbons and derivatives 4.9 The Pruteen process-a case study Summary and objectives Resource material
58 Single cell protein 4.1 Introduction 60 4.2 Conventional protein sources 60 4.3 Single cell protein 62 66 67 69 4.4 Substrates for SCP production 4.5 Micro-organisms for SCP production 4.6 SCP from carbon dioxide 4.7 SCP from carbohydrates 74 4.8 SCP from hydrocarbons and derivatives 85 4.9 The Pruteen process - a case study 88 Summary and objectives 106 Resource Material 107
ter 4 Single cell protein 4. 1 Introduction In this chapter we examine the processes that have been developed to produce micro-organisms as a source of food protein. We will examine the reasons why micro-organisms have been considered as alternative protein sources, the substrates on which they have been grown, the various process technologies developed and the comparative economics of these processes. One process will be mined in depth, to illustrate how a team composed of such diverse people as microbiologists, process engineers, patent lawyers and cost analysts work together to develop a marketable product The driving forces behind the development of many single cell protein projects emerged from global e conditions and social concerns of the 1960s. In the 1970s and early 1980s, there were considerable technological advancements associated with single cell rotein process developments and many types of prc ocesses were operated commercially. In this chapter we present technological and economic data derived from and animal feed source. You will see that many important principles underpinning modern process technology are based on the experiences gained in the development of single cell protein processes 4.2 Conventional protein sources essential Animals, including humans, cannot synthesise all the different amino acids they need amino aads and thus require them in their diet. These amino acids are called the essential amino acids. Proteins in food are hydrolysed in the digestive tract and the resulting amino acids are reassembled into proteins within the animals cells. All animals are ultimately dependent on plants for protein, as it is plants that create protein by combining inorganic nitrogen from the soil(as nitrate)with organic molecules derived from carbon from the atmosphere(as CO2) organoleptic For us to remain perfectly healthy the protein in our diet must supply suffidient ropertes quantities of amino acids. We prefer to eat our protein in particular forms, that is in foods having particular textures, tastes and smells(these are called organoleptic properties). Conventional sources of protein are plants, mainly as cereals and pulses, and animals, mainly as meat, eggs and milk. The proportions of such proteins eaten in various parts of the world differ widely(Figure 4.1)
60 Chapter 4 Single cell protein 4.1 Introduction In this chapter we examine the processes that have been developed to produce micro-organisms as a source of food protein. We will examine the reasons why micmrganisms have been considered as alternative protein sources, the substrates on which they have been grown, the various process technologies developed and the comparative economics of these processes. One process will be examined in depth, to illustrate how a team composed of such diverse people as microbiologists, process engineers, patent lawyers and cost analysts work together to develop a marketable product. The driving forces behind the development of many single cell protein projects emerged from global economic conditions and social concerns of the 1960s. In the 1970s and early 198Os, there were considerable technological advancements associated with single cell protein process developments and many types of processes were operated commercially. In this chapter we present technological and economic data derived from these early developments to provide a historical context for single cell protein as a food and animal feed source. You will see that many important principles underpinning modem process technology are based on the experiences gained in the development of single cell protein processes. 4.2 Conventional protein sources essential aminoacids Animals, including humans, cannot synthesise all the different amino acids they need and thus require them in their diet. These amino acids are called the essential amino acids. Proteins in food are hydrolysed in the digestive tract and the resulting amino acids are reassembled into proteins within the animal's cells. All animals are ultimately dependent on plants for protein, as it is plants that create protein by combining inorganic nitmen from the soil (as nitrate) with organic molecules derived from carbon from the atmosphere (as COJ. For us to remain perfectly healthy, the protein in our diet must supply suffiaent quantities of amino acids. We prefer to eat our protein in particular forms, that is in foods having particular textures, tastes and smells (these are called organoleptic properties). Conventional sources of protein are plants, mainly as cereals and pulses, and animals, mainly as meat, eggs and milk. The proportions of such proteins eaten in various parts of the world differ widely (Figure 4.1). organoleqtic PmeS
Single cell protein Eggs& Milk Meat VEGETABLE PROTEIN Figure 4. 1 World protein consumption ∏ List three factors you think account for such variations in the sources of proteins between various parts of the world? essentially the answer is history, climate, culture and money! Historically, people to eat the food available locally, and this would be controlled by the local nat
Single cell protein 61 Figure 4.1 World protein consumption List three factors you think account for such variations in the sources of proteins n between various parts of the world? Essentially the answer is history, climate, culture and money! Historically, people had to eat the food available locally, and this would be mntrolled by the local natural
62 Chapter 4 environment. Cultural influences have also led to preferences for certain food types. In more affluent countries foods such as meat, or high-protein feedstuffs on which to rear animals, can be produced or be imported. In less affluent countries such luxuries cannot be afforded, Increasing populations in some countries have overstretched food d so limited the availability of foods. changing There are problems, however, with these conventional sources of protein. Crop demands for oduction is dependent upon a suitable climate and in most countries available arable land is already fully farmed. Fish stocks in the oceans are in danger of becoming depleted. In countries where animal meat forms a high proportion of dietary protein, there are controversies such as whether or not the fats eaten with the protein are healthy,whether or not we are justified in keeping killing animals for food at all.Such animals in the unnatural conditions controversies are leading an increasin g eople to become vege likely that the worlds population will double in the next few decades, yet the United Nations estimate that about one thousand million people are already suffering protein deficiency. It is estimated that between 1980 and 2000 the annual demand for protein as food for humans will increase from 50x 10 tonnes to 79 x 10 tonnes, and the demand for protein as feed for animals will increase from 44 x 10 tonnes to 108 x 10 tonnes Biotechnology is being applied to the rapid improvement of conventional food sources, both plant and animal, in an effort to meet the increased demand in food. Interest has also been shown in growing micro-organisms source of protein and it developments in this area that we are going to examine here in detail 4. 3 Single cell protein Single cell protein, normally called simply sCP, is the term used to describe microbial cells, or proteins from them, which are used as food ( food for humans)or feed (food for farm animals or fish). Although the term micro-organisms covers viruses, bacteria fungi, algae and protozoa, viruses and protozoa are not considered suitable for sCP production. ∏ Why do you think viruses and protozoa are not suitable for sCP production? Both viruses and protozoa are difficult to grow in culture. Viruses need living cells to grow in and their small size makes them difficult to deal with. Protozoa need complex diets of organic materials. Bacteria, fungi and algae are relatively easy to grow in The term SCP is not exactly appropriate, as some filamentous organisms are used as SCP and these organisms are multicellular not unicellular You may be wondering why anyone should ever have considered using micro-organisms as a protein source. Let us consider why this should have been 4.3.1 The advantage of micro-organisms as a protein source Eating micro-organisms is nothing new. You might not have been aware that some foods traditionally eaten by man are in fact micro-organisms. Filamentous blue-green bacteria(often called blue-green algae, or cyanobacteria) were collected from lakes and rivers and eaten by the Aztecs in Mexico, and people inhabiting the shores of lake Chad in Africa still do so. Edible fungi have been collected from the wild for centuries and yeasts farmed throughout the last two. During the two World Wars this century, yeasts (unicellular fungi)were grown on a large scale in Germany and used as food and feed
62 Chapter 4 changing demands for dietary protein single cell and fwd proteinlfood filamentous blue-green bederia environment. Cultural influences have also led to preferences for certain food types. In more affluent countries foods such as meat, or high-protein feedstuffs on which to rear animals, can be produced or be imported. In less affluent countries such luxuries cannot be afforded, Increasing populations in some countries have overstretched food supplies, and so limited the availability of foods. There are problems, however, with these conventional sources of protein. Crop production is dependent upon a suitable climate and in most countries available arable land is already fully farmed. Fish stocks in the oceans are in danger of becoming depleted. In countries where animal meat forms a high proportion of dietary protein, there are controversies such as whether or not the fats eaten with the protein are healthy, whether or not we are justified in keeping animals in the unnatural conditions of some farms, or whether or not we are justified in killing animals for food at all. Such controversies are leading an increasing number of people to become vegetarian. It is likely that the world’s population will double in the next few decades, yet the United Nations estimate that about one thousand million people are already suffering protein deficiency. It is estimated that between 1980 and 2000 the annual demand for protein as food for humans will increase from 50 x lo6 tonnes to 79 x lo6 tonnes, and the demand for protein as feed for animals will increase from 44 x lo6 tonnes to 108 x lo6 tonnes. Biotechnology is being applied to the rapid improvement of conventional food sources, both plant and animal, in an effort to meet the increased demand in food. Interest has also been shown in growing micro-organisms as a source of protein and it is developments in this area that we are going to examine here in detail. 4.3 Single cell protein Single cell protein, normally called simply s8, is the term used to describe microbial cells, or proteins from them, which are used as food (food for humans) or feed (food for farm animals or fish). Although the term micro-organisms covers viruses, bacteria, fungi, algae and protozoa, viruses and protozoa are not considered suitable for SCP production. n Why do you think viruses and protozoa are not suitable for SCP production? Both viruses and protozoa are difficult to grow in culture. Viruses need living cells to grow in and their small size makes them difficult to deal with. Protozoa need complex diets of organic materials. Bacteria, fungi and algae are relatively easy to grow in culture. The term SCP is not exactly appropriate, as some filamentous organisms are used as SCP and these organisms are multicellular not unicellular. You may be wondering why anyone should ever have considered using micmaganisms as a protein source. Let us consider why this should have been. 4.3.1 The advantage of micro-organisms as a protein source Eating micro-organisms is nothing new. You might not have been aware that some foods traditionally eaten by man are in fact micro-organisms. Filamentous blue-p;reen bacteria (often called blue-green algae, or cyanobacteria) were collected from lakes and rivers and eaten by the Aztecs in Mexico, and people inhabiting the shores of Lake Chad in Africa still do so. Edible fungi have been collected from the wild for centuries and farmed throughout the last two. During the two World Wars this century, yeasts (unicellular fungi) were grown on a large scale in Germany and used as food and feed
Single ce‖ protein Micro-organisms are rich in protein. Microbial cells can contain as much protein as conventional foods. Bacteria can contain 60-65%(as a of dry weight) protein whereas fungi and algae contain about 40%. In addition, microbial cells can be a rich source of fibre, unsaturated fats, minerals and vitamins. They are low in saturated fats and sodium protein from Micro-organisms create protein Like plants, many micro-organisms can use inorganic nitrogen and can thus be used as an alternative to plants to create protei processes inorganic nitrogen is usually supplied as ammonia(or as ammonin which is readily available and is renewable, as it can be manufactured from atmospheric d can be recycled through the nitr compete with plant s for co, but there is no0gmp如mn is renewable by recycling through the carbon cycle. Other micro-organisms are heterotrophs(organisms which use organic sources of carbon) and can use a wide range of organic carbon sources. These can be materials unsuitable as food sources for animals (for example methanol). Others are waste products from industries or agriculture and have limited uses and can be a problem to dispose of by other means saves SCP processes are efficient on space. sCP production plants can be built on land bN of protein. Also they are much more efficient in terms of amount of protein produced unsuitable for agriculture and so need not compete for space with conventional sources per unit area(figures are quoted later for some processes) rapid growth Micro-organisms grow rapidly. Micro-organisms grow much more rapidly than plants or animals. Bacteria can grow with mean generation times(doubling times )as short as 20-30 minutes. The mean generation times of unicellular algae and fungi are about 1-3 hours, whereas those of multicellular algae and fungi may be longer. This means that micro-organisms have the potential to produce protein far more rapidly than is possible by rearing plants or animals By completing the following calculation you will be able to demonstrate the amazing potential for micro-organism to rapidly produce protein for food In batch culture, when growth is exponential, the number or organisms produced from one organism is given by 2, where n is the number of generations. So after one 2/eration there are 2(ie 2), after two generations 2 (ie 4)and after three generations Starting from a single bacterial cell with a mean generation time(doubling time)of 1 hour, and assuming exponential growth throughout, how many organisms would you have after 48 hours? As the dry weight of a bacterial cell is about 10 g what would the dry weight of these cells be? Assuming these cells to be 50% protein, how much protein would there be? Assuming you are an average person, you require about 70 g of protein in your diet per day. How long would this protein last you? (Do not cheat, try the calculation before reading on). Now repeat the calculation to find out how much protein would have after 72 After 48 hours there would be 248 or 2. x 10 4 cells This represents 2. x 10x10=2 8x10‘ g dry weight cells
Single cell protein 63 Micrmrganisms are rich in protein. Microbial cells can contain as much protein as conventional foods. Bacteria can contain 60-696 (as a 96 of dry weight) protein whereas fungi and algae contain about 40%. In addition, microbial cells can be a rich source of fibre, unsaturated fats, minerals and vitamins. They are low in saturated fats and sodium. protein from inorganic nitrogen autotrophs/ heterotrophs 8aV88 agricultural sparapid gmwth Micrmrganisms create protein. Like plants, many micmrganisms can use inorganic nitrogen and can thus be used as an alternative to plants to create protein. In SB processes inorganic nitrogen is usually supplied as ammonia (or as ammonium salts), which is readily available and is renewable, as it can be manufactured from atmospheric nitrogen and can be recycled through the nitrogen cycle. Microorganisms can use alternative carbon sources. Algae are autotrophs using atmospheric COZ (think of them as plants growing in water instead of soil). They compete with plank for COZ but there is not a shortage of COz in the atmosphere and it is renewable by recycling through the carbon cycle. Other micm-organisms are heterotrophs (organisms which use organic sources of carbon) and can use a wide range of organic carbon sources. These can be materials unsuitable as food sources for animals (for example methanol). Others are waste products from industries or agriculture and have limited uses and can be a problem to dispose of by other means. SCP processes are efficient on space. SCP production plants can be built on land unsuitable for agriculture and so need not compete for space with conventional sources of protein. Also they are much more efficient in terms of amount of protein produced per unit area (figures are quoted later for some processes). Micro-organisms grow rapidly. Micrmrganisms grow much more rapidly than plants or animals. Bacteria can grow with mean generation times (doubling times) as short as 20-30 minutes. The mean generation times of unicellular algae and fungi are about 1-3 hours, whereas those of multicellular algae and fungi may be longer. This means that micmrganisms have the potential to produce protein far more rapidly than is possible by rearing plants or animals. By completing the following calculation you will be able to demonstrate the n amazing potential for micmrganism to rapidly produce protein for food. In batch culture, when growth is exponential, the number or organisms produced from one organism is given by 2”, where n is the number of generations. So after one qneration there are 2’ (ie 21, after two generations 2* (ie 4) and after three generations 2 (ie 8) and so on. Starting from a single bacterial cell with a mean generation time (doubling time) of 1 hour, and assuming exponential growth throughout, how many %anisms would you have after 48 hours? As the dry weight of a bacterial cell is about 10- g, what would the dry weight of these cells be? Assuming these cells to be 50% protein, how much protein would there be? Assuming you are an average person, you require about 70 g of protein in your diet per day. How long would this protein last you? (Do not cheat, try the calculation before reading on). Now repeat the calculation to find out how much protein you would have after 721. After 48 hours there would be 2& or 2.8 x 1014 cells. This represents 2.8 x 1014 x lo-’’ = 2.8 x 104g dry weight cells