Food Biotechnology Elective Subject B.Tech. (Biotechnology) 7th Semester Prepared by: Dr. A. K. Gupta (AEC, Agra)
B. Tech. Food Biotechnology Dr. A. K. Gupta Food spoilage 1 1-15 Microbial Rolein food spoilage
Unit 1 Course • Role of microbes in food spoilage • Food preservation (Principles, Operations and production) • New protein Foods-SCP • Mushroom • Food yeast • Algal proteins
Food Spoilage • Around a quarter of the world’s food supply is lost to spoilage by microbes and insects. • Over the years man has developed many ways of preserving foods and today’s food technologists have refined the techniques and come up with new ones. • spoilage is not necessarily a bad thing. It shows us that a food has not been made or kept in the best conditions, alerting us to the possible presence of pathogenic microbes. • Decomposition returns the chemicals in food back to the environment, to be used again in the life cycles of Earth.
Role of microbes in food spoilage • Like us, microbes need food to stay alive. The foodstuffs that keep us healthy also provide the ideal nutrients for the growth of microbes. • Microbes are all around us – in the air, the soil, water and our bodies. • Microbes can soon get into food and, if the conditions are right, multiply rapidly. • Unfortunately, when certain microbes grow on food, it soon begins to smell nasty, look slimy, change colour, taste awful or even acquire a furry coating. • The food ‘goes off’ – it is spoiled. Even though it may not harm us, it is inedible and must be thrown away. There is also a chance that pathogenic microbes are present along with the spoilers.
Microbes causing food spoilage Three main types of microbes cause spoilage Bacteria • Single-celled microbes that reproduce by splitting in two. • Each individual bacterium is capable of carrying out all of the activities needed to metabolise and reproduce. • There are more than 5,000 known species of bacteria, with new ones constantly being discovered. • Familiar species of bacteria include: E.coli, Salmonella, Bacillus
Growth conditions for bacteria • Bacteria prefer moist conditions and can live in a wide range of temperatures. Most cannot grow at low pH (i.e. in acid conditions). • In the right conditions of warmth, acidity and moisture they can multiply very fast, producing millions of cells in a few hours. Some bacteria form spores which are resistant to drying and heating. When conditions become favorable again, they germinate and an active cell is released.
The different shapes of bacteria. Salmonella bacteria have flagella which they use to move around.
Types of bacteria • Bacteria cells have four basic shapes: • spheres • rods • spirals • commas. • They can be found as single cells, in pairs, chains or clusters. • A bacterial cell has a wall which maintains its shape and protects it. Some bacteria can move. • Usually they use flagella, which are like little corkscrews. • These rotate from the base like a ship’s propeller. • The flagella may be distributed randomly over the whole cell surface, in groups or singly. • Some bacteria have numerous fringe-like projections called fimbriae which enable them to stick to each other. • Other bacteria produce a sticky substance around the cell wall. This provides protection and helps them to stick to substrates, as well as each other.
Fungi • Fungi are a large and diverse group of organisms. Their main characteristics are: • Their cells have membrane-bound nuclei (we call them eukaryotic) • They do not use photosynthesis • They form spores • They have rigid cell walls • Respiration takes place in bodies called mitochondria in the cytoplasm. • Fungal cells have an elaborate arrangement of internal membranes. Fungi can be divided into two broad groups: filamentous fungi (including moulds and mushrooms) and yeasts
Fungi reproduce by sexual and asexual means. • Most produce spores which in some types are borne on bodies called sporangia. • Both spores and sporangia vary widely in size and form, depending on how they are spread – by wind, water, mechanical means or vectors. • Macrofungi produce large fruiting bodies which are familiar to us as mushrooms and toadstools. • These produce spores in huge numbers and disperse them into the environment. In favourable conditions, these spores germinate and produce hyphae.
Moulds • Moulds are filamentous (thread-like) fungi. A single filament is called a hypha. The hyphae branch as they grow forming a network called a mycelium. • Each hypha grows from the tip and divides repeatedly along its length. The hyphae penetrate their food source (usually dead, but sometimes living, plant and animal matter). They excrete enzymes which break down the complex organic molecules into simpler substances. The soluble nutrients pass through the cell wall and membrane, enabling the fungus to grow. • In most moulds the hyphae are divided by cross walls called septa which help to make filaments rigid but also control nutrient flow. • Moulds can grow in dry and acid conditions and can tolerate a wide range of temperatures. These fungi produce airborne spores. • Examples of moulds are: Penicillium, Mucor, Aspergillus.
Yeasts • These are microscopic. • single celled fungi that are usually round or oval in shape. • Most reproduce by budding. • When yeasts respire anaerobically they convert sugars into ethanol and carbon dioxide by a process known as fermentation. • They are mainly used to make fermented foods such as beer, wine or bread,. • The biochemical activities of yeasts can have unwanted effects in some food products. Yeasts can tolerate dry and acid conditions. • Examples of yeasts include: Saccharomycescerevisiae, Candida
B. Tech. Food Biotechnology Dr. A. K. Gupta 2 15-28 Food preservation Principles
Pasteurization • Pasteurization is a process which slows microbial growth in foods. • The process was named after its creator, French chemist and microbiologist Louis Pasteur. • The first pasteurization test was completed by Louis Pasteur and Claude Bernard on April 20, 1862. • The process was originally conceived as a way of preventing wine and beer from souring.
Unlike sterilization, pasteurization is not intended to kill all pathogenic micro-organisms in the food or liquid. • Instead, pasteurization aims to reduce the number of viable pathogens so they are unlikely to cause disease (assuming the pasteurization product is refrigerated and consumed before its expiration date). • Commercial-scale sterilization of food is not common because it adversely affects the taste and quality of the product. • Certain food products are processed to achieve the state of Commercial sterility.
Pasteurization typically uses temperatures below boiling since at temperatures above the boiling point for milk, caseinmicelles will irreversibly aggregate (or "curdle"). • There are two main types of pasteurization used today: High Temperature/Short Time (HTST) and Extended Shelf Life (ESL) treatment. • Ultra-high temperature (UHT or ultra-heat treated) is also used for milk treatment. • In the HTST process, milk is forced between metal plates or through pipes heated on the outside by hot water, and is heated to 71.7 °C (161 °F) for 15-20 seconds. • UHT processing holds the milk at a temperature of 138 °C (280 °F) for a fraction of a second. ESL milk has a microbial filtration step and lower temperatures than HTST. • Milk simply labeled "pasteurization " is usually treated with the HTST method, whereas milk labeled "ultra-pasteurization " or simply "UHT" has been treated with the UHT method.
The HTST pasteurization standard was designed to achieve a 5-log reduction, killing 99.999% of the number of viable micro-organisms in milk. • This is considered adequate for destroying almost all yeasts, mold, and common spoilage bacteria and also to ensure adequate destruction of common pathogenic heat-resistant organisms (including Mycobacterium tuberculosis, which causes tuberculosis and Coxiella burnetii, which causes Q fever). • HTST pasteurization processes must be designed so that the milk is heated evenly, and no part of the milk is subject to a shorter time or a lower temperature.
Pasteurization is typically associated with milk, first suggested by Franz von Soxhlet in 1886. HTST pasteurized milk typically has a refrigeratedshelf life of two to three weeks, whereas ultra pasteurized milk can last much longer when refrigerated, sometimes two to three months. When UHT treatment is combined with sterile handling and container technology (such as aseptic packaging), it can even be stored unrefrigerated for 3-4 months.
In addition to the standard HTST and UHT standards, there are other lesser-known pasteurization techniques. • The first technique, called "batch pasteurization“. • Itinvolves heating large batches of milk to a lower temperature, typically 63 °C (145 °F) for 30 minutes, followed by quick cooling to about 4 °C (39 °F). • The other technique is called higher-heat/shorter time (HHST), and it lies somewhere between HTST and UHT in terms of time and temperature. • Pasteurization causes some irreversible and some temporary denaturation of the proteins in milk.
Milk pasteurization has been subject to increasing scrutiny in recent years, due to the discovery of pathogens that are both widespread and heat resistant (able to survive pasteurization in significant numbers). • Researchers have developed more sensitive diagnostics, such as real-time PCR and improved culture methods that have enabled them to identify pathogens in pasteurized milk. • Some of the diseases that pasteurization can prevent are tuberculosis, diphtheria, salmonella, strep throat, scarlet fever, listeriosis and typhoid fever.
B. Tech. Food Biotechnology Dr. A. K. Gupta Food Preservation 3 28- Food Preservation Operations
Flash Pasteurization • Flash pasteurization, also called "High Temperature Short Time" processing. • It is a method of heat pasteurization of perishable beverages like fruit and vegetable juices, beer, and dairy products. • Compared to other pasteurization processes, it maintains color and flavor better. • It is done prior to filling into containers in order to kill spoilage microorganisms, to make the products safer and extend their shelf life. • The liquid moves in a controlled, continuous flow while subjected to temperatures of 71.5 °C (160 °F) to 74 °C (165 °F), for about 15 to 30 seconds, a ratio expressed as pasteurization units. • Flash pasteurization is widely used for fruit juices. • Tropicana Products has used flash pasteurization since the 1950s.
Food irradiation • Food irradiatio is the process of exposing food to ionizing radiation to destroy microorganisms, bacteria, viruses, or insects that might be present in the food. • Further applications include sprout inhibition, delay of ripening, increase of juice yield, and improvement of re-hydration. • Irradiation is a more general term of deliberate exposure of materials to radiation to achieve a technical goal (in this context 'ionizing radiation' is implied). • As such it is also used on non-food items, such as medical hardware, plastics, tubes for gas-pipelines, hoses for floor-heating, shrink-foils for food packaging, automobile parts, wires and cables (isolation), tires, and even gemstones. • Compared to the amount of food irradiated, the volume of those every-day applications is huge but not noticed by the consumer.
The genuine effect of processing food by ionizing radiation relates to damages to the DNA, the basic genetic information for life. • Microorganisms can no longer proliferate and continue their malignant or pathogenic activities. • Spoilage-causing micro-organisms cannot continue their activities. Insects do not survive or become incapable of proliferation. Plants cannot continue the natural ripening or aging process. • The speciality of processing food by ionizing radiation is that the energy density per atomic transition is very high; it can cleave molecules and induce ionization (hence the name), which is not achieved by mere heating. • This is the reason for both new effects and new concerns. The treatment of solid food by ionizing radiation can provide an effect similar to heat pasteurization of liquids, such as milk. However, the use of the term "cold pasteurization" to describe irradiated foods is controversial, since pasteurization and irradiation are fundamentally different processes. • Food irradiation is currently permitted by over 40 countries and volumes are estimated to exceed 500,000 metric tons annually world wide.
Canning • In 1809, a French confectioner and brewer, Nicolas Appert, observed that food cooked inside a jar did not spoil unless the seals leaked, and developed a method of sealing food in glass jars. • The reason for lack of spoilage was unknown at the time, since it would be another 50 years before Louis Pasteur demonstrated the role of microbes in food spoilage. However, glass containers presented challenges for transportation. • Glass jars were largely replaced in commercial canneries with cylindrical tin or wrought-iron canisters (later shortened to "cans") following the work of Peter Durand (1810). • Cans are cheaper and quicker to make, and much less fragile than glass jars. Glass jars have remained popular for some high-value products and in home canning. • Tin-openers were not invented for another thirty years — at first, soldiers had to cut the cans open with bayonets or smash them open with rocks.
B. Tech. Food Biotechnology Dr. A. K. Gupta Food Preservation 4 28- Food Preservation Operations
Food Canning Process Canning is a method of preserving food in which the food is processed and sealed in an airtight container. • The packaging prevents microorganisms from entering and proliferating inside. • To prevent the food from being spoiled before and during containment, quite a number of methods are used: pasteurization, boiling (and other applications of high temperature over a period of time), refrigeration, freezing, drying, vacuum treatment, antimicrobial agents that are natural to the recipe of the foodstuff being preserved, a sufficient dose of ionizing radiation, submersion in a strongly saline, acid, base, osmotically extreme (for example very sugary) or other microbe-challenging environments.
From a public safety point of view, foods with low acidity (a pH more than 4.6) need sterilization under high temperature (116-130°C). Foods that must be pressure canned include most vegetables, meats, seafood, poultry, and dairy products. The only foods that may be safely canned in an ordinary boiling water bath are highly acidic ones with a pH below 4.6, such as fruits, pickled vegetables, or other foods to which acidic additives have been added.
Modern double seams provide an airtight seal to the tin can. This airtight nature is crucial to keeping bacteria out of the can and keeping its contents sealed inside. Thus, double seamed cans are also known as Sanitary Cans. Developed in 1900 in Europe, this sort of can was made of the traditional cylindrical body made with tin plate. The two ends (lids) were attached using what is now called a double seam. A can thus sealed is impervious to the contamination by creating two tight continuous folds between the can’s cylindrical body and the lids. This eliminated the need for solder and allowed improvements in manufacturing speed, reducing cost. Double seaming uses rollers to shape the can, lid and the final double seam. To make a sanitary can and lid suitable for double seaming, manufacture begins with a sheet of coated tin plate. To create the can body rectangles are cut and curled around a die and welded together creating a cylinder with a side seam.
Rollers are then used to flare out one or both ends of the cylinder to create a quarter circle flange around the circumference. Precision is required to ensure that the welded sides are perfectly aligned, as any misalignment will cause inconsistent flange shape, compromising its integrity. A circle is then cut from the sheet using a die cutter. The circle is shaped in a stamping press to create a downward countersink to fit snugly in to the can body. The result can be compared to an upside down and very flat top hat. The outer edge is then curled down and around approximately 140 degrees using rollers to create the end curl. The result is a steel tube with a flanged edge, and a countersunk steel disc with a curled edge. A rubber compound is put inside the curl.
Nutrition Value • Canning is a way of processing food to extend its shelf life. The idea is to make food available and edible long after the processing time. Although canned foods are often assumed to be of low-nutritional value (due to heating processes or the addition of preservatives), some canned foods are nutritionally superior -- in some ways -- to their natural form. For instance, canned tomatoes have a higher, available lycopene content.
B. Tech. Food Biotechnology Dr. A. K. Gupta Food spoilage 5 1-15 New Protein Foods
Single Cell Protein (SCP) • The dried cells of microorganisms (algae, bacteria, actinomycetes and fungi) used as food or feed are collectively called microbial protein. • Microorganisms which are allowed to grow on waste products from agro based industries produce a large amount of proteins and store them in their cell bodies. These organisms are called as single cell proteins. • Number of microorganisms are the part of diet since ancient time. • Fermented yeast (Sacchromyces sp.) recovered as aleavening agent for bread (2500 B.C.).
The worldwide food protein deficiency is becoming alarming day to day. During World War II, when there were stortages in proteins and vitamins in the diet, the Germans produced yeasts and a mould (Geotrichum candidum) in some quantity for food; this led to the idea to produce edible proteins on a large scale by means of microorganisms during 1970s. Several industrial giants investigated the possibility of converting cheap organic materials into protein using microorganism. Single-Cell Protein (SCP) is a term coined at Massachusetts Institute of Technology by Prof C.L. Wilson (1966) and represents microbial cells (primary) grown in mass culture and harvested for use as protein sources in foods or animal feeds. Many scientists believe that single-cell protein production are possible solution to meet out the shortage of protein.
Single cell protein has the potential to be developed into a very large source of supplemental protein that could be used in livestock feeding. In some regions single cell protein could become the principal protein source that is used for domestic livestock, depending upon the population growth and the availability of plant feed protein sources. This could develop because microbes can be used to ferment some of the vast amounts of waste materials, such as straws; wood and wood processing wastes; food, cannery and food processing wastes; and residues from alcohol production or from human and animal excreta. Producing and harvesting microbial proteins is not without costs, unfortunately. In nearly all instances where a high rate of production would be achieved, the single cell protein will be found in rather dilute solutions, usually less than 5 % solids. Methods available for concentrating include, filtration, precipitation, coagulation, centrifugation, and the use of semi-permeable membranes. These de-watering methods require equipment that is quite expensive and would not be suitable for most small-scale operations. Removal of the amount of water necessary to stabilize the material for storage, in most instances, is not currently economical. Single cell protein must be dried to about 10 % moisture, or condensed and acidified to prevent spoilage from occurring, or fed shortly after being produced. Caution: Microbial protein has a high nucleic acid content, so levels need to be limited in the diets of monogastric animals. Some organisms can also produce mycotoxins. Source: Single cell protein can be produced on a number of different substrates, often this is done to reduce the Biological Oxidation Demand of the effluent streams leaving various type of agricultural processing plants.
Microbial protein term is replaced by single cell protein during the first international conference on microbial protein at MIT. • Some actinomycetes and filamentous fungi were reported to produce protein from various substrates.
Advantages of producing SCP • Rapid succession of generations • High protein content • Easily modifiable genetically • Large no of raw materials can be used for the production of SCP • Production in continuous culture
B. Tech. Food Biotechnology Dr. A. K. Gupta Protein Food 6 28- Mushroom
Mushroom • A mushroom is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source. The standard for the name "mushroom" is the cultivated white button mushroom, Agaricus bisporus, hence the word mushroom is most often applied to those fungi (Basidiomycota, Agaricomycetes) that have a stem (stipe), a cap (pileus), and gills (lamellae, sing. lamella) on the underside of the cap, just as do store-bought white mushrooms. • The word "mushroom" can also be used for a wide variety of gilled fungi, with or without stems, and the term is used even more generally, to describe both the fleshy fruiting bodies of some Ascomycota and the woody or leathery fruiting bodies of some Basidiomycota, depending upon the context of the word.
Oyster mushroom (Pleurotus ostreatus) cultivated using artificial logs made from compacted sawdust in plastic containers, harvested early morning. • The button mushroom (Agaricus bisporus), one of the most widely cultivated mushrooms in the world.
Edible mushrooms are used extensively in cooking, in many cuisines (notably Chinese, European, and Japanese). Though mushrooms are commonly thought to have little nutritional value, many species are high in fiber and provide vitamins such as thiamine, riboflavin, niacin, biotin, cobalamins, ascorbic acid. Though not normally a significant source of vitamin D, some mushrooms can become significant sources after exposure to ultraviolet light, though this also darkens their skin. Mushrooms are also a source of some minerals, including iron, selenium, potassium and phosphorus. • Most mushrooms that are sold in super markets have been commercially grown on mushroom farms. The most popular of these, Agaricus bisporus, is generally considered safe for most people to eat because it is grown in controlled, sterilized environments, though some individuals do not tolerate it well. Several varieties of A. bisporus are grown commercially, including whites, crimini, and portobello. Other cultivated species now available at many grocers include shiitake, maitake or hen-of-the-woods, oyster, and enoki.
There are a number of species of mushroom that are poisonous, and although some resemble certain edible species, eating them could be fatal. Eating mushrooms gathered in the wild is risky and should not be undertaken by individuals not knowledgeable in mushroom identification, unless the individuals limit themselves to a relatively small number of good edible species that are visually distinctive. However even A. bisporus contains 'agaritine' which metabolises when eaten into hydrazine, which is carcinogenic, but this chemical is largely or completely removed by cooking. • More generally, and particularly with gilled mushrooms, separating edible from poisonous species requires meticulous attention to detail; there is no single trait by which all toxic mushrooms can be identified, nor one by which all edible mushrooms can be identified. • Additionally, even edible mushrooms may produce an allergic reaction, from a mild asthmatic response to severe anaphylaxis shock. • People who collect mushrooms for consumption are known as mycophagists, and the act of collecting them for such is known as mushroom hunting, or simply "Mushrooming".