microbial food spoilage Growth and multiplication of micro organisms

FOOD MICROBIOLOGY SPOILAGE

1. Microbial food spoilage

2. Group # 1 Presentation team ; Ayesha Batool (109) Nisha Kafeel (104) Maryam Zulifiqar (105) Tahreem Fatima (106) Saleha Ashfaq (107) Mahreen Gul (108) Bareera Ashraf (110) Alisha Faiz (111) Farah Irshad (112) Balqees Fatima (113)

3. Content Definition of microbial food spoilage Causes of microbial food spoilage Classification of food Microorganisms involved in food spoilage The process of microbial food spoilage Refrences

4. Microbial food spoilage The microbial food spoilage is defined as the contamination of food by the growth and enzymatic activity of  microorganisms . Food spoilage is the process, in which the quality of the food deteriorates to some extent that renders food unacceptable for human consumption. Food spoilage occurs due to the microbial attack, enzymatic digestion, chemical degradation, physical injury etc.

5. The microbial food spoilage can be determined physically by the following changes: Change in appearance: it is characterized by the cloudiness and liquid formation in the food. Change in texture: occurs due to an accumulation of microbial cells and tissue degradation resulting in slime formation and rotting.

6. Colour change: it mainly occurs due to the chlorophyll breakdown and mycelial growth. change in test and odour : the taste and odour of the food changes due to the oxidation of nitrogenous compounds, sulphides , organic acids etc. by the mocrobial enzymes.

7. Microorganisms like bacteria, yeasts and moulds primarily cause food spoilage. Food serves as a good growth medium and contains proteins, carbohydrates and lipids that are utilized by the microorganisms residing in the food. The degradation of food material typically involves hydrolysis of proteins (putrefaction) via proteolytic microorganisms, undesired fermentation through saccharolytic microorganisms and rancidity by the lipolytic microbes.

8. In this post, you will get to know the definition, causes and the mechanism of microbial food spoilage along with the microorganisms involved in the food.

9. Definition of Microbial Food Spoilage: Microbial food spoilage is the biological process that causes degradation or decomposition of the food item due to microbial growth and activity that brings undesirable changes and makes the food undesirable for consumption. It primarily depends upon the two factors, namely food matrix (physical and chemical properties of food), the type of microorganisms and the storage conditions.

10. Food spoilage merely refers to the physical state where it does not meet the quality characteristics. Microbial food spoilage can be controlled by subjecting the food under refrigeration, lyophilization and by adding preservatives .

11. Causes of Microbial Food Spoilage Two common factors favour the growth and multiplication of microorganisms:

12. Storage Conditions of the Food The storage conditions basically involve environmental factors like temperature, pH and oxygen that favours the microbial growth. Temperature: The psychrophilic temperature, i.e. -17, is considered to be safe, and it can prevent the growth of microorganisms. The temperature above this is called mesophilic temperature that is the most favourable for the microbial growth.

13. Oxygen: There are aerobic and anaerobic microorganisms that attack the food in storage conditions in the presence or absence of oxygen, respectively. Aerobic storage conditions favour the aerobic bacteria and moulds. If there are anaerobic storage conditions, it will favour anaerobic bacteria like Clostridium species.

14. Chemical Properties of the Food The food spoilage is caused due to the degradation of the food components by the microorganisms’ enzymatic activity. The chemical properties of the food that influence microbial growth includes:

15. Classification of Food The food is classified into three types based on the spoilage:

16. Non-perishable:   food has no water content, and it can be stored for a long time. These have a long shelf life. Semi-perishable:   food has less water content, and it can be stored for some time. These have a medium shelf life. Perishable:  food has high water content, and it cannot store for a longer period. These have a short shelf life.

17. The high water or moisture content is a factor that directly influences microbial growth, as water promotes the growth of all living beings. Therefore, the food which is susceptible to the spoilage process called perishable food.

18. Microorganisms Involved in Food Spoilage There are commonly three kinds of microorganisms, which causes food spoilage: Yeasts: Yeast, a eukaryotic organism, is a subgroup species of organism known as fungus. Yeasts are well recognized for their beneficial fermentations that produce bread and alcoholic beverages and can grow with or without oxygen.  

19. In addition, they are used to increase the surface of cheese and meat as well. They generally colonize foods with maximum sugar or salt content, such as sauerkraut, pickles, maple syrup, low pH fruits, and liquids, and deteriorate them. 

20. cause’s of yeast The four main yeast species that cause yeast spoilage are  Zygosaccharomyces, Debaryomyces hansenii,Brettanomyces,  and  Candida. Zygosaccharomyces  species spoil the foods such as honey, dry fruits, jams, and soya sauce by releasing the off odors or flavors and carbon dioxide that sometimes causes containers to swell and burst. 

21. Debaryomyces hansenii  can grow in high salt concentration (approx. 24%) so, are frequently isolated from salt brines used for cured meats, cheeses, and olives. Saccharomyces  spp.,  and  Candida,  spoils fruits, some vegetables, and dairy products.  Dekkera /Brettanomyces  only spoil fermented foods such as alcoholic beverages and dairy products by producing phenolic compounds which cause off-flavors on food.

22. Mould:   that are characterized by multicellular filaments known as hyphae . It is an organism that helps in decaying dead animals and plants. They also ruin the wide range of food products. Some molds that cause food spoilage are Zygomycetes , a primitive fungus that proliferates on fruits and vegetables rich in fruits like strawberries and potatoes. Some of them also grow in bread.

23. The Zygomycetes that are commonly observed in spoiled products are  Mucor   and  Rhizopus . Penicillium   and related genera ( Furcatum ) are found in soil and plant debris. Many of these species produce antibiotics used as medicine by humans. 

24. Still, some species cause harm by releasing mycotoxin ( spatulin , ochratoxin , citreoviridin , penitrem ) in different fruits and vegetables ( pear, citrus fruits, and apples).  Byssochlamys   are the genera that cause spoilage to pasteurized juices due to heat-resistant spores.  Aspergillus  typically develop more quickly, are much more resistant to high temperatures and low water activity, and predominate spoiling in warmer areas. 

25. This mold affects a wide range of food products (grains, dried beans, peanuts, tree nuts, and some spices) and non-food products (paper, leather) by releasing the mycotoxins such as aflatoxins , ochratoxin , territrems , and cyclopiazonic acid.  Fusarium spp.  does not spoil the food, but the mycotoxins released in harvested grains can cause a health threat.

26. Bacteria The bacteria-producing spore is present in heat-treated food due to their abilities to sustain life even in high temperatures. Spore-producing bacteria are Gram-positive, thermophiles anaerobes. Some of them can be facultative.  These bacteria produce hydrogen sulfide (e.g.,  Desulfotomaculum ), and others release hydrogen and carbon dioxide (e.g.,  Thermoanaerobacterium ) when kept at high temperatures (like soups sold in vending machines). 

27. Psychrotolerant spore-producer organisms such as  Clostridium spp   release gas and sickly odors in food products (meats and brine-cured hams), whereas  Bacillus   spp produces off-fragrances and gas in chilled and milk products. Lactic Acid Bacteria (LAB) such as  Lactobacillus ,  Pediococcus , Leuconostoc ,  and   Oenococcus  help to form fermented foods such as yogurt and pickles. malty, sour, buttery). 

28. Still, they damage the foods (meat, wine, or juices) in low oxygen, low temperature, and acidic conditions producing off flavors (mousy, cheesy, malty, sour, buttery). 

29. These organisms secrete gas and vast amounts of extra-polysaccharides resulting in slime on meat and ropy spoilage in some food products. Pseudomonas  generally need maximum water activity for growth and are inhibited by a pH below 5.4. Some species ( psychrophilic ) require refrigeration to grow, whereas others can thrive and grow at warmer ambient temperatures.  

30. The  Pseudomonas  groups of four are mainly responsible for causing food to spoil, i.e.,  P. fluorescens , P. fragi , P. lundensis ,  and  P. viridiflava . P. fluorescens , P. fragi , P. lundensis , and S. putrefaciens   ruin foods originating from animals (meat, fish, and milk) by secreting lipases and proteases that result in the release of sulfides and trimethylamine (off-odors), as well as by producing biofilms (slime) on surfaces. 

31. Some strains ruin the meals in the refrigerator since they can grow at low temperatures, whereas  X. campestris , P. fluorescens , and P. viridiflava   secrete enzymes such as pectic lyase enzymes that break down the pectin in the plant-derived food and produce musky or slime layer within it (3).

32. Other than these microorganisms, other factors can also cause food deterioration. The insects such as flies, mites, moths, beetles, and weevils are the leading cause of spoilage of stored-food products like flour, dried fruits, grains, nuts, cheese, corn, and dried vegetables. These insects carry disease-causing microorganisms or toxins produced in their body. 

33. The indigenous enzymes such as catalase , proteinase , and lipase amylase in plants and animals continue to function. In addition, they deteriorate the quality of food if not appropriately destroyed during storage. For example, the peroxidase enzyme causes off-flavors during storage in green vegetables. The temperature is an essential factor that may cause food spoilage as well.

34. For instance: the food kept at a low temperature makes it partially frozen, which leads to the breakage of cells and damages food quality.  The foods are exposed to irradiation to kill the deteriorating microorganism, increasing the shelf-life of food. However, prolonged exposure of food to rays cause a loss in micronutrients (mostly vitamin A, B, C, and E), affecting the nutritional value of food (5).

35. The Process of Microbial Food Spoilage Microbial food spoilage can be summarized into the following steps:

36. Microbes first attack the food : As the food contain all the nutrients required by the microorganisms, at a favourable temperature, pH, moisture, oxygen etc. Food degradation : Microorganisms degrades the food material by utilizing the nutrients available in the food and decompose the food material.

37. Decomposition : The enzymatic reaction occurs between the food components like protein, lipid, fat, carbohydrates etc., and the microbial enzymes carry out some chemical changes. Changes as a result of food decomposition : The changes appear in the form of appearance, texture, colour , taste, odour etc. as a result of spoilage.

38. Prevention of Food Spoilage by organisms Food preservation  is a technique to keep food safe and unharmed from the metabolic activities of microorganisms. The best way of preserving the food depends on the abilities of microorganism metabolism. The most common food preservative methods are: The use of weak organic acids such as acetic acid, lactic acid, benzoic acid, and sorbic acid reduces the chance of deteriorating the food products (pickles, sauce, jam, jelly)

39. by preventing the growth and development of various species of bacteria and fungi. The addition of sugar concentration in about 68% -70% helps to prevent food like jam and jelly by exerting osmosis and limiting the water activity for the multiplication of microbes.

40. 15%-20% of salt concentration in food products hinders growth by exerting osmotic pressure that creates plasmolysis of cells and restricts abilities dissolving the oxygen. The heating and freezing also increase the shelf life of food (4 ) Pickling is a method of preserving food in an edible anti-microbial liquid. Pickling can be broadly categorized into two categories: chemical pickling and fermentation pickling.

41. Drying is one of the most ancient food preservation techniques, which reduces water activity sufficiently to prevent bacterial growth. Vacuum-packing stores food in a vacuum environment, usually in an air-tight bag or bottle. The vacuum environment strips bacteria of oxygen needed for survival, thereby slowing spoiling. Vacuum-packing is commonly used for storing nuts to reduce the loss of flavor from oxidation.

42. smoking is used to lengthen the shelf life of perishable food items. This effect is achieved by exposing the food to smoke from burning plant materials such as wood. Most commonly subjected to this method of food preservation are meats and  fish that have undergone curing. Fruits and vegetables like paprika, cheeses, spices, and ingredients for making drinks such as malt and tea leaves are also smoked, but mainly for cooking or flavoring them. It is one of the oldest food preservation methods, which probably arose after the development of cooking with fire.

43. Canning involves cooking food, sealing it in sterile cans or jars, and boiling the containers to kill or weaken any remaining bacteria as a form of sterilization. Foods have varying degrees of natural protection against spoilage and may require that the final step occur in a pressure cooker. High-acid fruits like strawberries require no preservatives to can and only a short boiling cycle, whereas marginal fruits such as tomatoes require longer boiling and addition of other acidic elements.

44. Low acid foods, such as vegetables and meats require pressure canning. Food preserved by canning or bottling is at immediate risk of spoilage once the can or bottle has been opened.

45. References Hayes PR. Food Spoilage. Food Microbiol Hyg . 1995;106–83. El-Hay MMA. Processing and preparation of fish. Postharvest Postmortem Process Raw Food Mater Unit Oper Process Equip Food Ind. 2022 Jan 1;315–42. Rawat S. Food Spoilage: Microorganisms and their prevention. Pelagia Res Libr Asian J Plant Sci Res [Internet]. 2015;5(4):47–56. Available from:  www.pelagiaresearchlibrary.com Blackburn CDW. Food spoilage microorganisms. Food spoilage microorganisms. 2006. 1–712 p.