Intrinsic and extrinsic parameter factors

Intrinsic and extrinsic parameter factors of food

1. INTRINSIC AND EXTRINSIC FACTORS DM-323- Food and Industrial Microbiology (2+1) Contact hours 2+2

2. INTRODUCTION Foods characteristics or composition affect the growth of microorganisms. Foods evolved mechanisms of defense against the invasion and proliferation of microorganisms These phenomena can be used to devise strategy for preventing or retarding the microbial spoilage of the products. The parameters of food (plant and animal tissues) that are an inherent part of the tissues are referred to as intrinsic parameters. Intrinsic parameters are very important as far as microbes are concerned

3. INTRINSIC PARAMETERS pH Moisture content Oxidation-reduction potential (Eh) Nutrient content Antimicrobial constituents Biological structures

4. PH Most microorganisms grow best at pH values around 7.0 (6.6-7.5) while few grow below 4.0 Microorganisms have minimum, optimum and maximum pH values for their growth. Below minimum and above maximum cells start dying due to intracellular changes. In relation to pH bacteria tend to be more fastidious than molds and yeasts. LAB are fastidious Pathogenic bacteria are also fastidious as compared to fungi.

5. Table 1. Approximate pH values permitting the growth of selected pathogens in food Microorganism Minimum Optimum Maximum Clostridium perfringens 5.5 - 5.8 7.2 8.0 - 9.0 Bacillus cereus 4.9 6.0 -7.0 8.8 Campylobacter  spp. 4.9 6.5 - 7.5 9.0 Shigella  spp. 4.9  - 9.3 Vibrio parahaemolyticus 4.8 7.8 - 8.6 11.0 Clostridium botulinum    toxin 4.6  - 8.5 Clostridium botulinum    growth 4.6   8.5 Staphylococcus aureus    growth 4.0 6.0 - 7.0 10.0 Staphylococcus aureus    toxin 4.5 7.0 - 8.0 9.6 Enterohemorrhagic  Escherichia coli 4.4 6.0 - 7.0 9.0 Listeria monocytogenes 4.39 7.0 9.4 Salmonella  spp. 4.2 7.0 - 7.5 9.5 Yersinia enterocolitica 4.2 7.2 9.6 Minimum pH range: 4.2 to 5.8; Maximum pH range 8.5 to 11; Optimum pH range: 6-8.6 S. Aureus and Salmonella spp , Vibrio parahaemolyticus , Y. enterocolitica wide pH range

6. Table 2. pH ranges of some common foods . Food pH Range Dairy Products Butter 6.1 - 6.4 Buttermilk 4.5 Milk 6.3 - 6.5 Cream 6.5 Cheese 4.9; 5.9 Yogurt 3.8 - 4.2 Meat and Poultry Beef (ground) 5.1 - 6.2 Ham 5.9 - 6.1 Veal 6.0 Chicken 6.2 - 6.4 Fish and Shellfish Fish (most species) 6.6 - 6.8 Crabs 7.0 Shrimp 6.8 - 7.0 White Fish 5.5 Dairy products pH range: 3.8-6.4 Meat and poultry products: 5.1-6.4 Fish and shellfish: 5.5-7.0

7. Cont.. Fruits and Vegetables Apples 2.9 - 3.3 Bananas 4.5 - 4.7 Grapefruit (juice) 3.0 Limes 1.8 - 2.0 Watermelons 5.2 - 5.6 Grapes 3.4 - 4.5 Beets (sugar) 4.2 - 4.4 Cabbage (green) 5.4 - 6.0 Carrots 4.9 - 5.2; 6.0 Cauliflower 5.6 Corn (sweet) 7.3 Cucumbers 3.8 Eggplant 4.5 Eggs yolks (white) 6.0 - 6.3 (7.6- 9.5) Potatoes (tubers and sweet) 5.3 - 5.6 Pumpkin 4.8 - 5.2 Spinach 5.5 - 6.0 Range :1.8 to 6.3 Fruits pH range: 1.8-4.5 Vegetable pH range: 3.8-7.3

8. Fruits, soft drinks, vinegar, and wines- No bacterial growth The excellent keeping quality of these products is due in great part to pH. Fruits generally undergo mold and yeast spoilage. Fungi grow at pH values <3.5 Meats and seafoods - final ultimate pH of about 5.6 bacteria and fungi spoilage. Vegetables have higher pH values than fruits- prone to bacterial than fungal spoilage. Cont..

9. Some foods are characterized by inherent acidity Others as result of biological acidity and is displayed by products such as fermented milks, sauerkraut, and pickles. Some foods are better able to resist changes in pH than others and called buffered foods. In general, meats are more highly buffered than vegetables. Various proteins contributing to the buffering capacity of meats. Vegetables are generally low in proteins Consequently, lack the buffering capacity to resist changes in their pH during the growth of microorganisms Cont..

10. Adverse pH affects at least two aspects of a respiring microbial cell: Functioning of its enzymes Transport of nutrients into the cell. The cytoplasmic membrane of microorganisms is relatively impermeable to H+ and OH- ions. Their concentration in the cytoplasm therefore probably remains reasonably constant despite wide variations that may occur in the pH of the surrounding medium. Internal pH of almost all cells is near neutrality. Bacteria such as Sulfolobus and Methanococcus may be exceptions pH Effects

11. Often organisms brings environmental pH optimum when grown in under or above pH Cellular compounds such as DNA and ATP require neutrality. When placed in acid environments, the cells must either keep H+ from entering or expel H+ ions as rapidly as they enter (acidic) . When most microorganisms grow in acid media, their metabolic activity results in the medium or substrate's becoming less acidic, whereas those that grow in high pH environments tend to effect a lowering of pH. The amino acid decarboxylases that have optimum activity at around pH 4.0 and almost no activity at pH 5.5 cause a spontaneous adjustment of pH when cells are grown in the basic range. Cont..

12. Clostridium acetobutylicum raise the substrate pH by reducing butyric acid to butanol . Enterobacter aerogenes produces acetoin from pyruvic acid to raise the pH. When amino acids are decarboxylated , the increase in pH occurs from the resulting amines. The morphology of some microorganisms can be affected by pH. Other environmental factors interact with pH. With respect to temperature, the pH of the substrate becomes more acid as the temperature increases. Cont..

13. Cont… Concentration of salt has a definite effect on pH growth rate curves An increased lag phase results. Increased lag phase duration if the substrate is a highly buffered as compared to one that has poor buffering capacity. Increased lag phase is due to organisms require more time to bring external environment in to their optimum pH growth range.

14. MOISTURE CONTENT Water requirements of microorganisms described in terms of the water activity (aw) in the environment. Water activity is defined by the ratio of the water vapor pressure of food substrate to the vapor pressure of pure water at the same temperature— aw = p/ po , Where p is the vapor pressure of the solution and po is the vapor pressure of the solvent (usually water). The a w  of a food describes the degree to which water is "bound" in the food, its availability to participate in chemical/biochemical reactions, and its availability to facilitate growth of microorganisms.

15. Cont… Microorganisms need water in an available form to grow in food products. The a w  of a food on this scale from 0.00 - 1.00 Most fresh foods, such as fresh meat, vegetables, and fruits, have a w values (0.97 - 0.99). The control of the moisture content in foods is one of the oldest exploited preservation strategies. The a w  can be manipulated in foods by adding salt or sugar, drying or baking, or binding of water to various macromolecular components Weight for weight, these food components will decrease a w

16. Microorganisms generally have optimum and minimum levels of a w  for growth. Microorganisms respond differently to a w . Microbial growth, and, the production of microbial metabolites is sensitive to alterations in a w . Gram (-) bacteria are generally more sensitive to low a w  than Gram (+) bacteria. S. aureus  can grow and produce toxin below a w  0.90. Many bacterial pathogens are controlled at water activities well above 0.86 Cont…

17. Table 3 Approximate a w  values of selected food categories . Animal Products a w fresh meat, poultry, fish 0.99 - 1.00 natural cheeses 0.95 - 1.00 Pudding 0.97 - 0.99 Eggs 0.97 cured meat 0.87 - 0.95 sweetened condensed milk 0.83 Parmesan cheese 0.68 - 0.76 Honey 0.75 dried whole egg 0.40 dried whole milk 0.20 Meat, some cheeses have water activity of 0.87-1.00 Honey, dried whole milk, dried whole egg have water activity of 0.20-0.75

18. Plant Products a w fresh fruits, vegetables 0.97 - 1.00 Bread ~0.96 bread, white 0.94 - 0.97 bread, crust 0.30 baked cake 0.90 - 0.94 Jam 0.75 - 0.80 Jellies 0.82 - 0.94 uncooked rice 0.80 - 0.87 fruit juice concentrates 0.79 - 0.84 cake icing 0.76 - 0.84 Flour 0.67 - 0.87 dried fruit 0.55 - 0.80 Cereal 0.10 - 0.20 Sugar 0.19

19. Table 4 Approximate a w   for growth of selected pathogens in food Organism Minimum Optimum Maximum Campylobacter spp. 0.98 0.99   Clostridium botulinum   type E* 0.97     Shigella spp. 0.97     Yersinia enterocolitica 0.97     Enterohemorrhagic  Escherichia coli 0.95 0.99   Salmonella  spp. 0.94 0.99 >0.99 Vibrio parahaemolyticus 0.94 0.98 0.99 Bacillus cereus 0.93     Clostridium botulinum types A & B** 0.93     Clostridium perfringens 0.943 0.95-0.96 0.97 Listeria monocytogenes 0.92     Staphylococcus aureus    growth 0.83 0.98 0.99 Staphylococcus aureus    toxin 0.88 0.98 0.99

20. Effects of Low aw Increase the length of the lag phase of growth Decrease the growth rate and size of final population. Cell membrane, which must be kept in a fluid state. Drying of internal parts of cells when placed in a medium of lowered aw. The effect is due to adverse metabolic activities because all chemical reactions of cells require an aqueous environment . aw is influenced by other environmental parameters such as pH, temperature of growth, and Eh. The interaction between aw and temperature was the most significant.

21. Microorganisms as protection against osmotic stress is the intracellular accumulation of compatible solutes. Bacteria accumulate proline by mechanism of enhanced transport ( S. aureus ) Halo-tolerant and xero -tolerant fungi tend to produce polyhydric alcohols such as glycerol, erythritol , and arabitol . L. monocytogenes growing on culture media accumulated K+, betaine , and glutamate. E. coli, synthesizes trehalose . In general bacteria accumulate K+ ions, glutamate, glutamine, proline , 7-aminobutyrate, alanine , glycine betaine , sucrose, trehalose , and glucosylglycerol . Cont…

22. OXIDATION-REDUCTION POTENTIAL The O/R potential of a substrate may be defined generally as the ease with which the substrate loses or gains electrons. When an element or compound loses electrons, the substrate is said to be oxidized, whereas a substrate that gains electrons becomes reduced: Substance that readily gives up electrons is a good reducing agent, and one that readily takes up electrons is a good oxidizing agent. When electrons are transferred from one compound to another, a potential difference is created between the two compounds.

23. Cont…. This difference may be measured by use of an appropriate instrument, and expressed as millivolts (mV) . Highly oxidized substance- more positive will be its electrical potential Highly reduced a substance- more negative will be its electrical potential. When the concentration of oxidant and reductant is equal, a zero electrical potential exists. The O/R potential of a system is expressed by the symbol Eh. Microorganisms display varying degrees of sensitivity to the oxidation-reduction potential (O/R, Eh) of their growth medium.

24. Eh requirements of microorganisms, some bacteria require reduced conditions for growth initiation (Eh of about -200 mV), whereas others require a positive Eh for growth. In the former category are the anaerobic bacteria such as the genus Clostridium; in the latter belong aerobic bacteria such as some members of the genus Bacillus. Some aerobic bacteria actually grow better under slightly reduced conditions, and these organisms are often referred to as microaerophiles ( lactobacilli and campylobacters ). Some bacteria have the capacity to grow under either aerobic or anaerobic conditions ( facultative anaerobes) Coliforms . Most molds and yeasts encountered in and on foods are aerobic, although a few tend to be facultative anaerobes. Cont….

25. Among the substances in foods that help to maintain reducing conditions are —SH groups in meats and ascorbic acid and reducing sugars in fruits and vegetables. With regard to the Eh of foods, plant foods, especially plant juices, tend to have Eh values of from 300 to 400 . Aerobic bacteria and molds are the common cause of spoilage of products of this type. Solid meats have Eh values of around -200 mV; in minced meats, the Eh is generally around 200 mV. Cheeses of various types have been reported to have Eh values on the negative side, from -20 to around -200 mV Cont….

26. Table 5 Redox potentials on some foods. FOOD Presence of air Eh (mV) Milk + +300 to +340 Cheese Cheddar + +300 to -100 Dutch + -20 to -310 Emmenthal + -50 to -200 Butter serum - +290 to +350 Egg + +500

27. Meats Liver, raw minced - -200 Muscle Raw, post-rigor - -60 to -150 Raw, minced + +225 Minced, cooked + +300 Cooked sausages and canned meat - -20 to -150 Cereals Wheat (whole grain) - -320 to -360 Wheat (germ) - -470 Barley (ground) + +225 Potato tuber - ~ -150 Plant juices Grape - +409 Lemon - +383 Pear - +436 Spinach - +74 Canned foods "Neutral" - -130 to -550 "Acid" - -410 to -550 Cont….

28. Eh Effects Microorganisms affect Eh of their environments during growth. Aerobes lower the Eh of their environment; anaerobes cannot. As aerobes grow, O 2 in the medium is depleted, resulting in the lowering of Eh. The Eh of a medium can be reduced by microorganisms by their production of certain metabolic byproducts H 2 S, which has the capacity to lower Eh to -300 mV Because H2S reacts readily with O 2 , it will accumulate only in anaerobic environments. Growth of anaerobes is normally believed to occur at reduced values of Eh, the exclusion of O 2 may be necessary for some anaerobes.

29. NUTRIENT CONTENT Microorganisms require certain basic nutrients for growth and maintenance of metabolic functions. The amount and type depends on the microorganism. These nutrients include water, a source of energy, nitrogen, vitamins, and minerals . Varying amounts of these nutrients are present in foods. Meats have abundant protein, lipids, minerals, and vitamins. Plant foods have high concentrations of different types of carbohydrates and varying levels of proteins, minerals, and vitamins. Foods such as milk and milk products and eggs are rich in all nutrients.

30. Food borne microorganisms can derive energy from carbohydrates, alcohols, and amino acids. Most microorganisms-simple sugars (glucose). Complex carbohydrates, (starch or cellulose found in plant foods), Some microorganisms can use fats as an energy source. Amino acids serve as a source of nitrogen and energy and are utilized by most microorganisms. Some microorganisms are able to metabolize peptides and more complex proteins. Other sources of nitrogen include, for example, urea, ammonia, creatinine , and methylamines. Examples of minerals required for microbial growth include phosphorus, iron, magnesium, sulfur, manganese, calcium, and potassium. Cont….

31. In general, the Gram (+) bacteria are more fastidious in their nutritional requirements and thus are not able to synthesize certain nutrients required for growth. Gram (+) foodborne pathogen S. aureus  requires amino acids, thiamine, and nicotinic acid for growth. Fruits and vegetables that are deficient in B vitamins do not effectively support the growth of these microorganisms. The Gram (-) bacteria are generally able to derive their basic nutritional requirements from the existing carbohydrates, proteins, lipids, minerals, and vitamins that are found in a wide range of food. An example of a pathogen with specific nutrient requirements is  Salmonella   enteritidis . Growth of  Salmonella enteritidis may be limited by the availability of iron . Cont….

32. Microorganisms may require B vitamins in low quantities, and almost all natural foods tend to have an abundant quantity Gram-positive bacteria are the least synthetic and must therefore be supplied before they will grow. The gram-negative bacteria and molds are able to synthesize most or all of their requirements. These two groups of organisms may be found growing on foods low in B vitamins. Fruits tend to be lower in B vitamins than meats , along with the usual low pH and positive Eh of fruits, helps to explain the usual spoilage of these products by molds rather than bacteria. Cont….

33. NATURALLY OCCURRING AND ADDED ANTIMICROBIALS Some foods intrinsically contain naturally-occurring antimicrobial compounds- microbiological stability to them. Plant-based antimicrobial constituents- essential oils , tannins, glycosides, and resins , that can be found in certain foods. Eugenol in cloves , allicin in garlic , cinnamic aldehyde and eugenol in cinnamon, allyl isothiocyanate in mustard , eugenol and thymol in sage Other plant based antimicrobials- phytoalexins and the lectins . Lectins are proteins that can specifically bind to glycoproteins of cell surfaces

34. Animal-based foods contains antimicrobial constituents- lactoferrin , conglutinin and the lactoperoxidase system in cow's milk, lysozyme in eggs and milk, and other factors in fresh meat, poultry and seafood. Lysozyme -hydrolyze the cell wall of bacteria. LP- system in bovine milk- lactoperoxidase , thiocyanate , and hydrogen peroxide. Gram (-) psychotrophs ( pseudomonads )- sensitive to the lactoperoxidase system. LP system- keeping quality of raw milk in developing countries where adequate refrigeration is scarce. Cont….

35. Processing of food result in the formation of antimicrobial compounds in the food. The smoking of fish and meat- deposition of antimicrobial substances onto the product surface. Maillard compounds (sugars and amino acids or peptides) upon heating of certain foods can impart some antimicrobial activity. Smoke condensate includes phenol , which is not only an antimicrobial, but also lowers the surface pH. Fermentations- natural production of antimicrobial substances, including bacteriocins , antibiotics etc. Cont….

36. Nisin is a polypeptide that is effective against most Gram (+) bacteria but is ineffective against Gram (-) organisms and fungi. Nisin can be produced in the food by starter cultures or, more commonly, it can be used as an additive in the form of a standardized preparation. Nisin has been used to effectively control spore-forming organisms in processed cheese formulations, and has been shown to have an interactive effect with heat. Cont….

37. Chemical preservatives and additives can also extend the shelf life of food and/or inhibit pathogens, either singly or in combination. The selection and use of these preservatives is typically governed by food law regulation of a country or region of the world. Ideally, the preservative should have a wide spectrum of activity against the target spoilage organisms and pathogens expected to be encountered in the food. The preservative must be active for the desired shelf life of the food and under the expected formulation conditions in the food. It should cause minimal organoleptic impact on the food and should not interfere with desirable microbiological processes expected to occur in the food, such as the ripening of cheese or leavening of baked goods. Cont….

38. Added antimicrobial compounds can have an interactive or synergistic effect with other parameters of the formulation. One example is the interaction with pH. Many preservatives have an optimum pH range for effectiveness. Other factors include a w , presence of other preservatives, types of food constituents, presence of certain enzymes, processing temperature, storage atmosphere, and partition coefficients. The effective use of combinations of preservatives with other physico -chemical parameters of a food formulation can stabilize that food against spoilage organisms or pathogens. Cont….

39. Table 6. Preservatives frequently used in conjunction with main groups of foods in the U.S. Foodstuff Nitrate, Nitrite Sulfur Dioxide Acetic Acid Propionic Acid Sorbic Acid Benzoic Acid BHA and BHT Smoke Nisin Parabens Fat Emulsions - - + - ++ + + - - + Cheese - - - + ++ (+) - - + - Meat products ++ - - - + - - ++ - - Seafood products + + ++ - + + - ++ - (+) Vegetable products - + ++ - ++ ++ + - - - Fruit products - ++ + - ++ ++ (+) - - + Beverages - (+) - - ++ ++ + - - + Wine - ++ - - ++ - - - - - Baked goods - - + ++ ++ - - - - (+) Confectionery - - - - ++ (+) (+) - - -

40. BIOLOGICAL STRUCTURES Plant and animal derived foods-biological structures that may prevent the entry and growth of microorganisms. Physical barriers include skin of fruits and vegetables , shell of nuts , animal hide, egg cuticle, shell, and membranes . Although these foods may have microorganisms attached to the surface or trapped within surface folds or crevices. Intact biological structures thus can be important in preventing entry and subsequent growth of microorganisms. Several factors may influence penetration of these barriers. The maturity of plant foods will influence the effectiveness of the protective barriers.

41. Cont… Physical damage during harvest, transport, or storage, invasion of insects can allow the penetration of MO. Foods processing (slicing, chopping, grinding, and shucking )- destroy the physical barriers. Thus, the interior of the food can become contaminated and growth can occur depending on the intrinsic properties of the food. Salmonella  spp. have been shown to grow on the interior of portions of cut watermelon, honeydew melons and tomatoes, given sufficient time and temperature.

42. Fruits are an example of the potential of pathogenic microorganisms to penetrate intact barriers. After harvest, pathogens will survive but usually not grow on the outer surface of fresh fruits and vegetables. Growth on intact surfaces is not common because foodborne pathogens do not produce the enzymes necessary to break down the protective outer barriers on most produce. This outer barrier restricts the availability of nutrients and moisture. Cont…

43. EXTRINSIC PARAMETERS The extrinsic parameters of foods are those properties of the storage environment that affect both the foods and their microorganisms. Those of greatest importance to the welfare of foodborne organisms are as follows: Temperature of storage Relative humidity of environment Presence and concentration of gases Presence and activities of other microorganisms

44. TEMPERATURE OF STORAGE Microorganisms, individually and as a group, grow over a very wide range of temperatures. Proper temperature for the storage of different types of foods. The lowest temperature -34°C and highest is excess of 10O C has been reported. Three groups based temperature requirements for growth. Grow well at or below 7°C and have their optimum between 20 C and 30 C are referred as psychrotrophs . Those that grow well between 20 C and 45°C with optima between 30 C and 40 C are referred as mesophiles , That grow well at and above 45 C with optima between 55°C and 65°C are referred to as thermophiles .

45. Table 7. Temperature ranges for prokaryotic microorganisms . Group Temperature °C Minimum Optimum Maximum Thermophiles 40 – 45 55 – 75 60 - 90 Mesophiles 5 – 15 30 – 45 35 – 47 Psychrophiles -5 - +5 12 – 15 15 – 20 Psychrotrophs -5 - +5 25 - 30 30 – 35

46. Cont.. Psychrotrophic species are found among the following genera Alcaligenes , Shewanella , Brochothrix , Corynebacterium , Flavobacterium , Lactobacillus, Micrococcus, Pseudomonas, Psychrobacter , Enterococcusetc . Cause spoilage of meats, fish, poultry, eggs, and other foods normally held at low temperature. SPC on such foods are generally higher when the plates are incubated at about 7°C for at least 7 days than when incubated at 30⁰C and above. Mesophilic species and strains do not grow at this temperature but do grow at temperatures within the mesophilic range if other conditions are suitable. However, some organisms can grow over a range from 0⁰C and 30⁰C or above ( Enterococcus faecalis ) .

47. Most thermophilic bacteria of importance in foods belong to the genera Bacillus and Clostridium. Great interest- canning industry. Molds are able to grow wide ranges of temperature. Molds grow at refrigerator temperatures ( Aspergillus , Cladosporium , and Thamnidium ) on eggs, sides of beef, and fruits. Yeasts grow over the psychrotrophic and mesophilic temperature ranges but generally not within the thermophilic range. Cont..

48. The quality of the food product must also be taken into account in selecting a storage temperature. For example, bananas keep better if stored at 13-17°C than at 5-7°C. A large number of vegetables are favored by temperatures of about 10 C, including potatoes, celery, cabbage, and many others. In every case, the success of storage temperature depends to a great extent upon the RH of the storage environment and the presence or absence of gases such as CO 2 and O 3 . Cont..

49. RELATIVE HUMIDITY OF ENVIRONMENT The RH of the storage environment is important both from the standpoint of aw within foods and the growth of microorganisms at the surfaces. When foods with low aw values are placed in environments of high RH, the foods pick up moisture until equilibrium has been established. Likewise, foods with a high aw lose moisture when placed in an environment of low RH. In general, the higher the temperature, the lower the RH, and vice versa.

50. Foods that undergo surface spoilage from molds, yeasts, and certain bacteria should be stored under conditions of low RH. Improperly wrapped meats such as whole chickens and beef cuts tend to suffer much surface spoilage in the refrigerator before deep spoilage occurs, due to the generally high RH of the refrigerator and the fact that the meat-spoilage biota is essentially aerobic in nature. However, food itself will lose moisture to the atmosphere under such conditions and thereby become undesirable. By altering the gaseous atmosphere, it is possible to retard surface spoilage without lowering the RH. Cont..

51. PRESENCE AND CONCENTRATION OF GASES IN THE ENVIRONMENT Carbon dioxide (CO2) is the single most important atmospheric gas that is used to control microorganisms in foods Ozone (O 3 ) is the other atmospheric gas that has antimicrobial properties, and it has been tried over a number of decades as an agent to extend the shelf life of certain foods. However, it is a strong oxidizing agent, It should not be used on high-lipid-content foods since it would cause an increase in rancidity. Ozone was tested against Escherichia coli 0157:H7 in culture media, and at 3 to 18 ppm , the bacterium was destroyed in 20 to 50 minutes.

52. PRESENCE AND ACTIVITIES OF OTHER MICROORGANISMS Some foodborne organisms produce substances that are either inhibitory or lethal to others Antibiotics: Fungi Bacteriocins : LAB Hydrogen peroxide- Lactobacilli organic acids- LAB and other organisms

53. General Microbial Interference This phenomenon refers to the general nonspecific inhibition or destruction of one microorganism by other members of the same habitat or environment. Whereas lactic antagonism is a specific example of microbial interference More recent studies have demonstrated the general antagonist activities of the normal food biota against L. monocytogenes and against pathogenic strains of E. coli. The suppressive effects of a sufficiently large aerobic bacterial biota against the growth of C. botulinum in fresh meats is well established as is the suppression of yeasts and molds by the bacterial biota of comminuted fresh meats

54. The microorganisms that can be added to a food product to effect preservation have been designated protective cultures. Among the desirable properties that protective cultures should possess are the following: Present no health risks, Provide beneficial effects in the product, Have no negative impact on sensory properties, and serve as "indicators" under abuse conditions. The lactic acid bacteria constitute the largest and most important group that falls under this category. Cont….

55. Protective cultures could be an advantage such as, Improving the safety and quality of the product Extending the product shelf-life Bioprotective Cultures have a major potential for use in biopreservations as they are safe for consumption Their association with food fermentations, their long tradition as food-grade bacteria and Generally Recognized as Safe (GRAS) Bioprotective culture

56. S.No . Isolate   Species 1 1 Lactobacillus rhamnosus 2 3 Lactobacillus plantarum 3  19 Lactobacillus plantarum 4 30 Lactobacillus paracasei 5 9M3 Lactobacillus plantarum 6 17K Lactobacillus plantarum List of Bio-protective Lactobacillus Cultures ( Taufiqq and R. K. Malik ,2014)

57. 10 15 20 25 30 Control - - + + + + Sample A - - - - + + Sample B - - - - - + Sample C - - - - - + Storage study 15°C Days Control Sample A Sample B Sample C L. rhamnosus , L. plantarum , L. paracasei Control: Dahi Culture NCDC 261

58. COMBINED INTRINSIC AND EXTRINSIC PARAMETERS: THE HURDLE CONCEPT Under intrinsic and extrinsic parameters, the effect of single factors on the welfare of microorganisms is presented. In the hurdle concept, multiple factors or techniques are employed to effect the control of microorganisms in foods. Barrier technology, combination preservation, and combined methods are among some of the other descriptions of this concept. Referred to as "hurdle technology" since the mid-1980s by L. Leistner in Germany, the practice has been applied to some foods for over a century.

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