Fish Microbiology - Module 5 - University of the Philippines Visayas PDF

FISH 154 - Fish Microbiology Microbiology of Food and Water Module 5 Outline: ❑ Introduction to Food Microbiology ❑ Factors Influencing Growth of Microorganisms in Food ❑ Fish processing technologies: ✔ Low temperature preservation ✔ High temperature...

FISH 154 - Fish Microbiology Microbiology of Food and Water Module 5 Outline: ❑ Introduction to Food Microbiology ❑ Factors Influencing Growth of Microorganisms in Food ❑ Fish processing technologies: ✔ Low temperature preservation ✔ High temperature preservation ✔ Salting ✔ Smoking ✔ Fermentation Why study Food Microbiology? Microorganisms as causative agents of disease in humans. Microorganisms and food spoilage. Microorganisms as food sources. Microorganisms exploited for the production of food. Agents of Disease (Foodborne Pathogens) Bacteria: E coli O157:H7, Salmonella spp., Vibrio cholera, Clostridium botulinum, Listeria monocytogenes, Campylobacter, Staphylococcus aureus, etc Viruses: Enteroviruses, Norwalk virus, Hepatitis virus Prions: Mad Cow Disease (BSE) and Creutzfeldt-Jakob Disease Protozoa: Giardia lamblia, Cryptosporidium parvum, Entamoeba histolyticum, Cyclospora cayetanesis Helminths: Tapeworms (Beef, Fish and Pork), Flukes (Fish and Shellfish), Roundworms and Hookworms Foodborne Illness Commonly referred to as food poisoning. Occurs when a pathogen or its toxin is consumed Food intoxication - illness resulting from consumption of an exotoxin produced by organisms growing in food product Foodborne infection requires consumption of living organisms Common food borne bacteria Acetobacter Corynebacterium Proteus Acinetobacter Enterobacter Pseudomonas Aeromonas Erwinia Salmonella Alcaligenes Escherichia Serratia Alteromonas Flavobacterium Shigella Bacillus Lactobacillus Staphylococcus Brochothrix Leuconostoc Streptococcus Campylobacter Micrococcus Vibrio Citrobacter Moraxella Yersinia Clostridium Pediococcus  Common genera of molds in food Alternaria Colletotrichum Mucor Aspergillus Fusarium Penicillium Botrytis Geotricum Rhizophus Byssochlamys Gloeosporium Sporotrichum Cephalosporium Helminthosporium Thamnidium Cladosporium Monila Trichothecium  Common genera of yeasts in food Brettanomyces Kloeckera Saccharomycopsis Candida Kluyveromyces Schizosaccharomyces Debaryomyces Mycoderma Torulopsis Endomycopsis Rhodotorula Trichosporon Hansenula Saccharomyces Agents of Food Spoilage Spoiled food is generally not harmful but considered unsafe. Food spoilage encompasses any undesirable change in food. Food spoilage results from growth of microbes in food which alters food visibly and in other ways. Involves predictable succession of microbes, different foods undergo different types of spoilage processes toxins are sometimes produced. Common Spoilage Microbes Wide range of bacteria important in food spoilage Pseudomonas can metabolize a wide variety of compounds Psychrophilic organisms can multiply in refrigerator Most common genera include: Erwinia, Acetobacter, Alcaligenes Some of the most common spoilage fungi include : Rhizopus, Alternaria, Penicillium, Aspergillus, Botrytis Fungi grow readily in acidic low-moisture environments Conditions for Spoilage Water pH Physical structure Oxygen temperature Dine in or take out: Microbes we can eat Fungi: Mushrooms, cheese Yeasts: Vegemite (Yeast Paste) Bacteria: Spirulina platensis (a cyanobacterium) Algae: Chlorella (fresh water), Dunaliella (salt water) Microbes that we can exploit Bacteria—cheese, yogurt, vinegar, bread and sauerkraut Yeasts—bread, beer, liqueurs, wine Molds—cheeses Acid produced in yogurt, cheese and pickled vegetables inhibit growth of many spoilage organisms and foodborne pathogens Tastes of yogurt, pickles, sharp cheeses and some sausages due to production of lactic acid by lactic acid bacteria Production of fermented milk products do not rely on naturally occurring lactic acid bacteria, starter cultures are added Microorganism Growth in Foods Intrinsic Factors composition pH presence and availability of water oxidation-reduction potential physical structure presence of antimicrobial substances Composition and pH Carbohydrates–do not result in major odor Proteins and/or fats result in a variety of foul odors (e.g., putrefactions Putrefaction, proteolysis and anaerobic breakdown of proteins, yielding foul- smelling amine compounds pH impacts the make up of microbial community and therefore types of chemical reactions that occur when microbes grow in food Low pH allows yeasts and molds to become dominant; higher pH allows bacteria to become dominant; higher pH favors putrefaction (the anaerobic breakdown of proteins that releases foul-smelling amine compounds) Water Activity (Aw) In general, lower water activity inhibits microbial growth. Water activity can be lowered by: drying addition of salt or sugar Even under these conditions spoilage can occur by certain kinds of microorganisms osmophilic microorganisms -prefer high osmotic pressure xerophilic microorganisms - prefer low water activity Physical structure Grinding and mixing (e.g., sausage and meat burger) increases surface area, alters cellular structure, and distributes microorganisms throughout the food Vegetables and fruits have outer skins that protect against spoilage; spoilage microorganisms have enzymes that weaken and penetrate such protective coverings Antimicrobial Substances Many foods contain natural antimicrobial substances coumarins – fruits and vegetables lysozyme – cow’s milk and eggs aldehydic and phenolic compounds – herbs and spices allicin – garlic polyphenols – green and black teas Extrinsic Factors Temperature -lower temperatures retard microbial growth Relative humidity -higher levels promote microbial growth Atmosphere -oxygen promotes growth -modified atmosphere packaging (MAP) -use of shrink wrap and vacuum technologies to package food in controlled atmospheres Primary sources of microorganisms found in food Soil and water Plants and plant products Food utensils Intestinal tract of man and animals Food handlers Animal feeds Animal hides Air and dust Fish Processing Technologies Microflora of Dried and Salted Fish Preservative effect of drying and addition of salt is due to the withdrawal of water from the microorganisms microorganisms and enzymes (inherent or microbial origin) need water in order to be active reduces Aw : increase the concentration of solutes in the aqueous phase of the food Most bacteria and molds can be checked by addition of 5% salt but halophiles can still grow. Types of microorganisms of concern halophiles -- 15% salt concentration (saturation) halotolerant- can resist a wide range of salt concentration -Bacillus -Clostridia -Micrococcus halophobic - salt sensitive group: fail to grow at high concentration though they remain viable for sometime - Pseudomonas - Achromobacter - Human pathogens Microflora of dried and salted fish Two most important conditions in dried salted fish: 1.Pinking: - caused by a group of halophilic bacteria: Halobacterium and Sarcina - pinking bacteria are killed by preservatives like sulphur dioxide. Microflora of dried and salted fish 2. Dun - brown discoloration of the fish caused by the growth of molds, Sporendonema spp. - Dun molds have a temperature range of 10-370C and an optimum of 250C. - Sporodonema is not so biochemically-active against fish flesh compared with the pinking bacteria which break down the flesh. Low temperature : icing, chilling, freezing Principle : - retard and/or stop the growth of microorganisms in foods - different temperature requirement for growth of each group of microorganisms - prevent growth but metabolic activity continues slowly Effects: - retard chemical reactions - retard actions of food enzymes - slows down or stops growth and activity of microorganisms in food Icing/Chilling temperature just above freezing temporary preservative measures Principle: cooling of the environment to prevent microbial/enzyme activities, hence, prevents spoilage but not indefinitely. slowing down the enzymatic processes and microbial growth Freezing Definition: temperature just below chilling Mechanisms: 1. Prevents the growth of microorganisms. 2. Kill bacteria due to osmotic damage and intracellular growth of ice crystals. 3. Increase the concentration of dissolved substances in the unfrozen state, hence, decreasing Aw 4. Paradoxically, freezing is a well-recognized method of preservation. Effects of freezing on microorganisms sudden mortality immediately on freezing vary with species Example: cocci are more resistant than rods Salmonella < S. aureus < vegetative cells of clostridia endospores and food poisoning toxins not affected The cells that are still viable immediately after freezing die gradually when stored in the frozen state. Factors affecting Lethality of Freezing the kind of microorganisms and its state - log phase - spore and vegetative cells e.g. gram + cocci – resistant gram – rods - sensitive the temperature during freezing and storage - method: rapid or slow - 1 to -5 oC - most bacteria die Factors affecting Lethality of Freezing time of storage in the frozen condition -those that are still viable, gradually die on storage the kind of food: nature and composition -glycerol, egg white, meat extracts (increase viability) - high Aw and low pH – decrease viability High Temperature Blanching - denature enzymes Pasteurization – destroys pathogens Commercial sterilization - pathogenic and toxin- forming organisms are destroyed canning, bottling, and aseptic processing Sterilization - complete destruction of all microorganisms including both vegetative cells and spores High Temperature Thermophilic Bacteria flat sour spoilage: the ends of the can remain flat and spoilage cannot be detected unless the can is opened. - B. coagulans and B. sterothermophilus thermophilic acid (TA) spoilage: production of CO2 and H2 - Clostridium thermosaccharolyticum sulphide spoilage: sulphur stinker, H2S produced from putrefying proteins. - Clostridium nigrificans High Temperature Mesophilic Bacteria - under processing -Clostridium butyricum and C. pasteurianum -B. subtilis and B. mesentroides -B. polymyxa, B. macerans Molds and yeast and their spores Bacteria – high Aw > 0.90 Yeasts -- low Molds -- lower Smoking Smoke component : bactericidal non-sporeforming rods: survived the process introduced during handling e.g. Penicillium sp. ; Aspergillus sp. (can grow at refrigeration temperature) Fermentation Principle : the presence of organic acids has antimicrobial effect decrease of pH below the growth range metabolic inhibition by the undissociated acid molecules antimicrobial products: H+. CO2, organic acids, peroxides, antibiotics  Activity: Innovation Time! From what you have learned in this module, create a concept map describing the different post-harvest technologies and the mechanism of how they inhibit microbial/bacterial growth.