Food Spoilage Lecture 6 PDF

FOOD SPOILAGE LECTURE 6  A microorganism can reproduce to reach 100 million in 9 hours under optimal conditions. There are groups of microorganisms that can reproduce in almost any conditions, except for extreme ones such as high temperatures, acidity, or salinity. ...

FOOD SPOILAGE LECTURE 6  A microorganism can reproduce to reach 100 million in 9 hours under optimal conditions. There are groups of microorganisms that can reproduce in almost any conditions, except for extreme ones such as high temperatures, acidity, or salinity.  FOOD SPOILAGE Food spoilage: Any alteration in a food’s appearance, texture, smell, or taste that makes it unsuitable for consumption. These changes are often caused by microbial growth, chemical reactions, or physical damage, which ultimately lead to food becoming unappetizing or unsafe to eat. *It is reported that ¼ of the world’s food resources are spoiled by microorganisms. CAUSES OF FOOD SPOILAGE Microbiological (MOST IMPORTANT CAUSE) Insects and rodents Enzymatic activity (enzymes naturally found in plant and animal tissues) Non-enzymatic chemical changes Physical changes (such as drying, freezing, damage, etc.) When evaluated in terms of resistance to microbiological spoilage, foods can be classified as perishable, semi-perishable and non-perishable. Although there is a certain degree of correlation between the perishability of foods and its safety in terms of foodborne illness, there is no one-to-one correlation. A food can be non-perishable but still risky in terms of pathogens, a perishable food can also be safe.  Types of food based on its perishability 1. Non-perishable foods: Foods that have a long shelf life (months to years) and do not spoil under normal storage conditions e.g. grains, flour, sugar etc. 2. Semi-perishable foods: Foods those remain unspoiled for relatively long (a few weeks to a few months) under normal storage conditions e.g. potatoes, onions, apples, nuts etc. 3. Perishable foods: Foods that spoil easily, decay, or become unsafe to eat in a very short time (one to a few days) unless special preservative methods are used. These foods should be stored properly and kept in the refrigerator or freezer. e.g. milk, meat, eggs, fish, poultry, most fruits and vegetables. Factors effecting the perishability of food The microorganisms present in the food Type Number Dominant microflora The structure of the food (intrinsic factors) Any processes applied to the food (if applicable) Environmental conditions (extrinsic factors) The groups of microorganisms present in food and that form the dominant microflora over time play the most important role in spoilage. Depending on the intrinsic and extrinsic factors, one or more groups become dominant. For example, bacteria, yeasts, or molds psychrophilic, thermophilic, mesophilic, thermoduric, etc. aerobic, anaerobic, etc. halophilic, osmotolerant, etc. neutrophilic, etc. EXAMPLES (Under conditions where unspecified factors are favorable for the microflora) pH 4.0 Yeast, mold, lactic acid bacteria pH 4.0 Yeast, mold aw 0.88 pH 4.0 Psychrophilic and aw 0.80 psychrotrophic molds 40C pH 6.5 All spoilage aw 0.98 microorganisms, except special groups (obligate 300C thermophiles or aerobic conditions anaerobes) No antimicrobials or salt In a food product where conditions favor the growth of various microbial groups (mold, yeast, or bacteria), the dominant group is typically determined by competitive interactions among these microorganisms. Microbial competition is influenced by the genetic characteristics of each microorganism, including growth rate, enzyme systems, and the capacity for adaptation or resistance to environmental conditions. These genetic traits enable certain microorganisms to outcompete the others, allowing them to dominate the microbial ecosystem within the food product. Microorganisms present in food decompose available nutrients based on the enzymatic systems they possess, leading to spoilage. For example: Proteins → degrade into polypeptides, peptides, and amino acids. In certain cases, amino acids are further broken down into smaller subunits. This degradation of amino acids can result in the formation of sulfur-containing compounds with unpleasant odors. For instance, Pseudomonas spp. is known to degrade alanine into ammonia, CO₂, acetic acid, and propionic acid, contributing to spoilage and undesirable sensory changes in food products. Carbohydrates Complex polysaccharides → simple sugars Glucose is broken down to water and CO2 under aerobic conditions. Under anaerobic conditions, by using glucose: Yeasts produce ethanol and CO2 through alcohol fermentation. Lactic acid and/or CO2, acetic acid, H2, propionic acid, and other substances are produced through lactic acid fermentation. Coliforms produce lactic acid, acetic acid, formic acid, ethanol, CO2, H2, acetoin, and butanediol. Propionic acid bacteria produce propionic acid, succinic acid, acetic acid, and CO2. Some Clostridium species can convert glucose into butyric acid, acetic acid, CO2, H2, and in some cases, acetone and butanol.  Organic acids → CO2 and water Lipids → glycerol and fatty acids Pectin → pectic acid and methanol Microorganisms use nutrients starting from the simplest structure.In this case, they first use carbohydrates, then non- protein nitrogenous compounds, and finally fats. What kind of application can be made to create a "protein- protecting effect" in meats? Microbiological spoilage in meat and meat products 1. Red meats Fresh meat is one of the most susceptible foods to microbiological spoilage. This is due to both the structure of the meat and the high likelihood of microbial contamination. Rich nutritional content, which supports the growth of microorganisms pH that is near neutral, providing an ideal environment for microbial proliferation High water activity, facilitating microbial growth and enzymatic reactions High redox potential on the surface, coupled with a lower redox potential in the interior, creating favorable conditions for the growth of different microbial species at varying depths of the meat. Sources of contamination to meat Animal (intestinal system, lymph nodes, outer surfaces - skin, fur, etc.) Equipment and surfaces Personnel Environment (dust, air, etc.) Factors influencing the spread of microorganisms to tissues following animal slaughter include: Microbial load in the intestines The physiological condition of the animal before slaughter (in exhausted animals, glycogen is depleted, leading to an undesirable change in meat pH after slaughter) Slaughter and bleeding method Cooling rate  Microbial contamination as a result of damage during the skinning process Increased surface contact with the meat leads to a higher likelihood of contamination. Chemical properties of the meat, such as pH can create favorable conditions for microbial growth. Presence of oxygen, which supports the growth of aerobic microorganisms. Temperature, which, if not properly controlled, can accelerate microbial growth. Sanitation practices and personnel hygiene, which play a crucial role in minimizing contamination during processing. Factors influencing microbial growth and spoilage in fresh meat The number and variety of contaminated microorganisms (e.g., the proportion of psychrotrophs) Physical properties of the meat (whole, cut, ground) Water activity of the meat and relative humidity of the surrounding environment pH of the meat Oxygen levels (aerobic, anaerobic packaging) Storage temperature  Spoilage of fresh red meats under aerobic conditions 1. BACTERIA (The most common spoilage factor in fresh meat) 1.1 Stickiness on the surface Pseudomonas, Alcaligenes, Flavobacterium, Acinetobacter, Moraxella, Enterobacter, Protues, Streptococcus, Bacillus, Lactobacillus, Micrococcus 1.2. Changes in meat color The natural red color of the meat changing to green, brown, or grayish due to bacterial activity 1.3 Other Bad odor Off-flavors Fat spoilage in meat etc. Spoilage of fresh red meats under aerobic conditions 2. YEASTS 2.1. Surface stickiness 2.2. Lipolysis 2.3. Off-flavors and off-odors 2.4. Change in color (white, cream, pink, brown, etc.) Spoilage of fresh red meats under aerobic conditions 3.MOLDS 3.1. Stickiness 3.2. Whiskers (e.g., Thamnidium elegans, some Mucor, Rhizopus spp.) 3.3. Black spots (Cladosporium herbarum) 3.4. White spots (Sporothricum carnis) 3.5. Green spots (Penicillium spp.) 3.6. Fat degradation 3.7. Off-flavors and off-odors  Mold spoilage is not common in fresh meat, as bacteria reproduce and cover the surface more quickly than molds. Therefore, mold spoilage in fresh meat occurs under conditions where bacteria cannot grow. For example, drying the meat surface (reaching water activity (aw) levels that inhibit bacterial growth) or application of an antimicrobial substance to the meat surface that will prevent bacterial growth. Spoilage of fresh red meats under anaerobic conditions 1. Sourness: Sour odor and taste, can be caused by various organic acids. Usually Clostridium species, coliforms, lactic acid bacteria 2. Putrid spoilage: off-odor (H2S, NH3, indole etc.) Clostridium Proteus Pseudomonas 2. Microbiological Spoilage in Meat Products The shelf life of meat products varies depending on the processing (such as curing, fermentation, drying, etc.). For example, while Gram-negative bacteria cause spoilage more in fresh meat, Gram-positive bacteria, molds and yeasts usually have the chance to grow in cured meats. In cured meats, lactic acid bacteria can cause spoilage, including: Sourness Stickiness Greening Gas production In casing sausages, when there is sufficient moisture on the surface, Micrococcus species and yeasts can grow, forming a slime layer. When the moisture content on the surface decreases, mold growth may be observed. In vacuum-packaged sausages, the growth of heterofermentative lactic acid bacteria can lead to Sourness CO2 production Stickiness Greening In salami; Micrococcus spp. and yeasts growth on the surface form a slime layer. Micrococcus, Lactobacillus and Leuconostoc species can grow between the casing and the salami surface during storage and cause sourness. The pink color on the surface fades as a result of the formation of organic acids and some reducing compounds by various bacteria. A ring-shaped greening may occur on the surface of the salami and just below the surface. 3. Fish and other seafood products Microorganisms naturally present in fish and seafood: The natural microflora of fish and seafood. Microorganisms found in seawater. Microorganisms contaminated from the environment and personnel during transportation, processing, etc. Fish and other Seafoods As with red meats, fish and seafood also undergo various spoilages due to autolytic and microbial activity. However, in fresh fish, autolytic activity and pH are higher compared to red meats. As a result, fish is more susceptible to spoilage than red meat. Fish and other Seafoods The rate of spoilage in fish depends on the following factors: Fish species: Shape (flat or round), meat pH, fat content, etc. Condition of the fish at the time of capture: The amount of glycogen in the muscles Level of microbial contamination Temperature 4. POULTRY The contamination sources and microbial spoilage factors mentioned for red meats are the same for poultry. Products such as meat, fish, and poultry are among the leading causes of foodborne illnesses. 5. Microbiological Spoilage in Milk and Dairy Products Raw milk is one of the most favorable foods for microbial growth. In dairy products, however, microbial spoilage varies depending on factors such as salt concentration, pH, and water activity (aw). The structure of raw milk in terms of microbial growth: pH: Neutral Water activity (aw): High Redox potential (O/R): High Nutritional content: Very rich (lactose, fat, protein, vitamins, minerals) Contamination Sources in Milk and Dairy Products Raw Milk Dairy Products The animal Microorganisms Personnel contaminating raw milk Environment (air, soil, etc.) Personnel Milking machines, Equipment milk containers, Additives and coolers, and other ingredients equipment Packaging materials etc. Water etc. Although raw milk is sterile while present in the body of the milking animal, it rapidly becomes contaminated once milked and spoils quickly due to its structure. Therefore, raw milk must be rapidly cooled immediately after milking and subjected to thermal processing as soon as possible. MICROBIAL SPOILAGE OF RAW MILK 1. ACID PRODUCTION This is the most common type of spoilage in raw milk. Acid fermentation occurs as lactic acid bacteria utilize fermentable sugars in the milk. As a result of lactic acid fermentation, the milk first develops a sour taste and then the milk protein coagulates. Different microorganisms cause acid production in milk at different temperatures, resulting in the synthesis of one or several substances such as lactic acid lactic acid + H₂ + CO₂ acetic acid, formic acid, alcohol, and butyric acid. MICROBIAL SPOILAGE OF RAW MILK (continue) 10 – 37oC : Streptococcus lactis Coliforms Micrococcus spp. Lactobacillus spp. 37–50oC: Streptococcus thermophilus, S. feacalis 50oC < : Bacillus coagulans After pasteurization thermoduric Enterococcus and Lactobacillus spp. S. termophilus In the refrigerator Heat-resistant spore-forming psychrophilic/ psychrotrophic bacteria 2. GAS FORMATION Different microorganisms can produce gas in milk depending on the processing and storage temperature applied. Except for special cases like the production of cheese with holes (or eyes), gas formation in cheese is undesirable. H2 and CO2 Coliforms Some Clostridium spp. Some Bacillus spp. CO2 Yeasts Propionic acid bacteria Heterofermentative lactic acid bacteria  3. PROTEOLYSIS Proteolysis is the process of breaking down proteins into smaller peptides or amino acids, typically through the action of enzymes. In dairy products, proteolysis can occur due to microbial activity or enzymatic reactions. This type of spoilage is more common in milk when: lactic acid bacteria have been killed by heat treatment, the acid formed in milk is broken down by yeasts and molds, or the milk acid is neutralized by other microorganisms. These spoilage events are typically observed in milk stored at low temperatures, and include processes like acid proteolysis, sweet curdling, and enzymatic proteolysis.  4. ROP FORMATION Rop formation is a type of spoilage caused by the production of a sticky substance by certain bacteria. This spoilage results in the milk's consistency becoming thick and sticky. There are two main types of rop formation in milk: On the surface: Caused by Alcaligenes viscolactis, which produces a sticky substance that forms a layer on the surface of the milk. Throughout the entire milk: Caused by bacteria such as Enterobacter aerogenes, some lactic acid bacteria, and other microorganisms that produce a sticky substance throughout the milk, altering its texture and consistency.  5. CHANGES IN MILK FAT Many different types of bacteria, molds, and yeasts can cause changes in milk fat. Some changes that occur in milk fat include: Lipolytic activity: This can lead to the release of glycerol and fatty acids, affecting the flavor and texture of the milk fat. Oxidation of unsaturated fatty acids: This results in the formation of aldehydes, ketones, and acid compounds, which can cause off-flavors and undesirable changes in the fat. Lipolytic and oxidative activity: These processes can lead to rancid spoilage, where the milk fat becomes unpleasantly odoriferous and off-flavored due to the breakdown of fats and the formation of rancid compounds. 6. FLAVOR DEFECTS Changes in milk flavor after microbial growth include: Sour (acidic), Bitter, Burnt (caramel-like), Soapy, Earthy, Fruity, etc. 7. COLOR DEFECTS Changes in milk color due to microbial growth include: Blue (e.g., Pseudomonas syncyanea) Yellow (e.g., Flavobacterium) Red (e.g., Serratia marcescens) Brown (e.g., Pseudomonas putrefaciens) etc. These microbial activities can alter both the sensory qualities (taste and appearance) of milk, which may lead to its rejection by consumers.  Milk Spoilage After Pasteurization (HTST) Causes of milk spoilage after pasteurization: Survival of microorganisms after pasteurization: Some microorganisms, such as thermoduric (heat-resistant) bacteria and spore-forming bacteria, can survive the pasteurization process and continue to grow if they find a suitable environment (e.g., in improperly stored or handled milk). Post-pasteurization contamination: Contamination can occur after pasteurization if the milk is exposed to unclean equipment, air, or surfaces. Heat-resistant microbial enzymes: Some enzymes produced by microorganisms can remain active even after pasteurization. These enzymes, such as proteases or lipases, can continue to break down milk proteins and fats, leading to changes in flavor, texture, and overall quality. Storage temperature mistakes: Improper storage conditions, such as storing milk at temperatures higher than recommended, can encourage the growth of microorganisms and lead to spoilage, even after pasteurization. Maintaining the correct refrigeration temperature is crucial to prevent bacterial growth and maintain milk quality. Microbial Spoilage in Cheese Microbial spoilage in cheese varies depending on factors such as the cheese's pH, water activity, redox potential, salt content, and the quality of the raw materials. In addition to the general types of spoilage seen in cheese, there are also cheese-specific spoilage types that depend on the characteristics and processing of the cheese. Types of spoilage seen in cheeses (all types of cheeses) MOLD GROWTH Alternaria, Aspergillus, Cladosporium, Monilia, Mucor, Penicillium, etc. can affect cheese. In soft cheeses: Geotrichum. GAS PRODUCTION Early blowing: This typically occurs in the early stages of cheese maturation, often due to coliform bacteria, leading to gas bubbles, swelling, or holes. Late blowing: Caused by Clostridium species, typically after the cheese has been produced, and may lead to undesirable bubbling or bloating. SPOILAGE OF THE RIND Softening of the rind, changes in color and odor, often caused by yeasts, molds, or proteolytic bacteria. COLOR DEFECTS For example: Aspergillus niger: Black color. Sporendema casei: Red color, etc. Types of spoilage seen in cheeses (depending of cheese type) In Cheddar and Other Hard Cheeses Internal discoloration: Caused by the growth of Lactobacillus plantarum subsp. rudensis. Rancidity: Due to heat-resistant lipase enzymes from bacteria like Pseudomonas spp. Cheeses with holes Excessive hole formation and cracks: Occurs due to secondary fermentation, where gas production by certain bacteria (such as Propionibacterium) leads to an abnormal or excessive hole structure, often accompanied by cracks in the cheese. Fermented Cheeses with Molds Excessive mold growth: Can lead to overgrowth on the surface of the cheese, affecting texture and flavor. Insufficient mold growth: Inadequate mold development, which can result in uneven ripening, improper texture, or off-flavors. Sengun et al., Mycotoxins and mould contamination in cheese: a review, World Mycotoxin Journal, August 2008; 1(3): 291-298  SPOILAGE OF YOGHURT Microbial spoilage in yoghurt is mostly caused by molds, yeasts, and lactic acid bacteria (LAB) that can grow at low pH and temperature. Yeasts: Flavor defects, gas production. Molds: Formation of surface films (white, blue, etc.), bitter taste (due to proteolytic activity), sour taste (due to lipolytic activity). LAB: Sourness due to increased acidity. Types of Spoilage in Yoghurt Changes in Taste and Odor LAB (Lactic Acid Bacteria): Low acetaldehyde production results in a chalky and sour taste High acetaldehyde production leads to flavor off-flavors. High diacetyl production causes a buttery taste and odor. Bitter taste: Caused by Lactobacillus bulgaricus. Long storage: As the lactic acid content increases, it leads to a sour/acidic aroma and surface mold growth. Gas formation/Fruity aroma: Caused by yeasts. Types of Spoilage in Butter Change in taste and odor - Sour/acid: Lactobacillus spp. - Bitterness: Pseudomonas fragi, P. fluoresence - Fruit: P. fragi Putrid spoilage on the surface : Pseudomonas putrefaciens Changes in color: - Coliform and Enterococcus spp. - Red: Fusarium spp. - Black: Pseudomonas nigrificans - Pink: yeast