BS2002 Lecture 9: Food Microbiology PDF

BS2002: Introductory Microbiology Lecture 9: Food Microbiology Assoc. Prof. Rebecca Case SCELSE/SBS [email protected]  Pasteurization Choice of pasteurization method depends on product and goal because pasteurisation can alter food nutrients or taste...

BS2002: Introductory Microbiology Lecture 9: Food Microbiology Assoc. Prof. Rebecca Case SCELSE/SBS [email protected]  Pasteurization Choice of pasteurization method depends on product and goal because pasteurisation can alter food nutrients or taste Traditional Pasteurization: High-Temperature-Short-Time Treatment (HTST) e.g. 72°C for 15 seconds. Low-Temperature-Long-Time Treatment (LTLT) e.g. 63°C for 30 minutes. For milk, HTST causes less damage to the nutrient composition and sensory characteristics compared to LTLT cells heat to kill vegetative cells that were previously spores killsi vegetative & requential heating I next also As i conformational folding in p & can cause its degradati/ taste reshaping & this changes its  Learning objectives To learn how microbes contribute to food spoilage and the food-factors that influence this process To understand how foods can be vectors of transmission for pathogenic microorganisms To understand how microorganisms cause illnesses due to food consumption To learn that microbes play an important role in the production of foods, food preservation and can be consumed directly That the role of microbes in foods is a continuum, food spoilages is just another aspect of food production and infection is linked to these processes, but differ in the specific microbes involved Impact of microbes on food safety and quality Microbes have a significant impact on foods Food spoilage ~ microbes thatusefoa set Food borne illnesses Food production As foods Note that “spoilage” and “poisoning” are separate phenomena Consumption of “off” food will not necessarily make one ill; conversely, food poisoning cannot be predicted by visual examination of the food. discolouraty  Microbial growth and food spoilage results from growth of microbes in food – alters food visibly and in other ways, rendering it unsuitable for consumption involves predictable succession of microbes different foods undergo different types of spoilage processes Toxins are sometimes produced temp of food carbohydrate/P/ lipid itself how much , ~ Microbial growth is controlled by intrinsic factors microbes that want to eat O-rich food/meats (factors related to the food) are distinct than those who eat carbohydrates And extrinsic factors (environment where food is & temp of fridge water availability stored) ,  Intrinsic factors food composition - carbohydrates – mold predominates degrades food by hydrolysis, tomatoes particularly - broken susceptible down into sugars & untritional value changes alters food compositi little odor ergotism – hallucinogenic alkaloids released by Claviceps purpurea – may cause death – earliest reference from 857 AD “a Great plague of swollen blisters consumed the people by a loathsome rot, so that their limbs were loosened and fell off before death." – Associated with the Salem Witch trials  Intrinsic factors precipitated milk, curdling (putrefact) food composition – proteins or fats – bacterial growth predominates putrefaction – proteolysis and anaerobic breakdown of proteins hydclusebyenzysa ~ into – yielding foul-smelling amine a a. - compounds La groups give. d. break down to amine Unpasteurized milk spoilage – acid production followed by putrification butter – short chain fatty acid production results in rancid butter chains putrefact/hydrolysis of lipids into fatty acid  Intrinsic factors pH – impacts make up of microbial community and therefore types of chemical reactions that occur when microbes grow in food ~ and pdcA bacteria introduced exclude unhealthy to bacteria excluded by are PH low bacteria – e.g., low pH favors yeast and mold that cause can disease presence and availability of water – in general, lower water activity inhibits microbial growth oxidation-reduction potential if there potential for e-flow is then will microbes looked food Spoils system in e – Altered by cooking faster than food raw use generate energy it to – Lower redox – more bacteria and anaerobes physical structure – Grinding andmixing distribute microbes; promotes microbial growth – Outer skin of vegetables and fruits slows microbial growth  found in food Antimicrobial substances ~ (natural) coumarins – fruits and vegetables lysea lysozyme – cow’s milk and eggs aldehydic and phenolic compounds – herbs and spices & allicin – garlic struct similar to antibiotics - potent antibiotic polyphenols – green and black teas  Microbial product-based inhibition small o/ peptides that are - secreted that actively acts as antimicrobials bacteriocins – bactericidal proteins active against related species – some dissipate proton motive force of susceptible bacteria – some form pores in cell membranes – some inhibit protein or RNA synthesis e.g., nisin from Lactococcus lactis – used in low-acid foods to inactivate Clostridium botulinum during canning process bacteriophages that kill bacterial pathogens – e.g. bacteriophages that target Listeria monocytogenes sprayed onto ready-to-eat meats prior to packaging  Extrinsic factors fast temperature allows high temp growth microbial & fact spoilage of foods – 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 & don't promote food spoilage  Controlling food spoilage modern era of food microbiology established by Louis Pasteur in 1857 methods of preservation – goal is to eliminate or reduce the populations of spoilage and disease causing microbes while maintaining food quality kills pathogens and substantially reduces number of spoilage organisms different pasteurisation procedures heat for different lengths of time – shorter heating times result in improved flavour  Removal and reduction of microorganisms water, wine, beer, juices, soft drinks, and other liquids Usually by filtration may better preserve flavor and aroma Refrigeration at 5 °C retards but does not stop microbial growth – microorganisms can still cause spoilage with extended storage – growth at temperatures below -10°C has been observed – Listeria monocytogenes  ~ involves pressures & high High temperature: canning food temp a usesdeam & preserve for longer Food heated in special containers (retorts) to 115 °C for 25-100 minutes kills spoilage microbes, but not necessarily all microbes in food Spoilage of canned foods – Spoilage prior to canning – Under processing – Leakage of contaminated water into cans during cooling process - any damage to I can change : pressure , allowing extrinsic factor that oxygen to be introduced it is are can cause microbial growth  Contamination in food handling 21 Would you think this is safe to eat? microbes inside pdcq gases ~ not all microbes poke gas  Water availability dehydration – e.g., lyophilization to produce freeze-dried foods is commonly used to eliminate bacterial growth – Food preservation occurs as a result of free-water loss and an increase in solute concentration  bacteria usually require more water while yeast, moulds , fungi can require less water Xerophilic fungi are yeasts and moulds that are capable of growth at or below a water activity (aw) of 0.85 Osmophilic yeast are capable of growth in an environment of high osmotic pressures don't need to Water activity and foods remorse 0.95 Pseudomonas, 0.87 0.75 0.60 Escherichia, 0.91 Salmonella, Many yeasts, 0.80 Most Osmophilic Proteus, Vibrio Shigella, parabaemolyticus, Candida, Most molds, most halophilic yeasts, few Saccharomyces spp., 0.03 Klebsiella, C. botulinum, Lactobacillus, some Torulopsis, Debaryomyces, Staphylococcus bacteria, molds Bacillus, Clostridium molds Hansenula aureus Mycotoxigeni 0.50 completely perfringens, micrococcus c aspergilli 0.40 dehydrated some yeasts => no microbes Highly Most fruit Dried fruits perishable Some cheese with 15-20% juice foods (fresh (Cheddar, Fermented moisture, concentrates, and canned Swiss, sausage, Jam, caramel, Whole milk condensed Provolone), sponge cakes, marmalade, toffee, honey powder with fruits, milk, syrup, vegetables, cured meat, dry cheese, glace fruits, Noodles with 2-3% flour, high- meat, fish), fruit juice margarine, marzipan, 12% moisture, sugar cakes, milk, cooked concentrates foods with marshmallow moisture, dehydrated pulses sausages, with 55% 65% sucrose s spices with soups containing breads, foods sucrose or or 15% NaCl 10% moisture 15-17% with up to 4 12% NaCl Whole egg moisture Source:Water Activity of Some Foods and Susceptibility to Spoilage by Microorganisms Adapted from Beuchat (1981)  Chemical-based preservation GRAS – chemical agents “generally recognized as safe” – agents include organic acids, sulfite, ethylene oxide gas, ethyl formate Legcitic used in as wis - – sodium nitrite – inhibits spore formation in often used in - meats, forms nitrosamines meats pH of food impacts effectiveness of chemical preservative Salt Ingredients: Pork with Ham Salt, Water, Sugar, Sodium nitrate often a mix of a whole lot of GRAS agents don't need to memorish  good for sterilisati but not alteringI properties ~ Radiation radappertization – use of ionizing radiation (gamma radiation) to extend shelf life or sterilize meat, seafoods, fruits, and vegetables – excellent penetrating power – food not radioactive – kills microbes in moist foods by producing peroxides from water death ~ cause cell peroxides oxidize cellular constituents to kill disease bacteria electron beams carsing - – electrons are electrically generated, so can be turned on only when needed – does not generate radioactive waste, but also does not penetrate foods as deeply as gamma radiation & to be for surface Sterilisati more tend  Packaging k out atmospheric air ~ she add in alternative air radicals that modified atmosphere packaging (MAP) e. present %. inent N2 , superoxide make it non-oxygen – gases in stored food affect microbial growth – shrink wrap materials and vacuum technology control atmosphere impermeable to oxygen superoxide radicals inhibit growth – polylactic acid green alternative to plastic made from wood and corn embedded with nisin which is slowly released & anti-microbial peptides  Types of food-borne disease… two primary types – food-borne infections common pathogens include: viruses such as Noroviruses, and bacteria such as E. coli, Campylobacter jejuni, Salmonella and Listeria monocytogenes – food intoxications there food intoxicat is also where make molecules microbes will make sick in that you food e 9 toxins etc. transmission ,.. – breakdown in hygiene washed wi not – fecal-oral route key - hands well..... soap – fomites also important Fomites are objects or materials which are likely to carry infection, such as clothes, utensils, and furniture  be recurrent associated don't need ~ can ~ usually & to removise i chicken can symptoms last for longer a period (2-5 days) make you ps ~ can  associated i raw meats, ~ diary , processed meats prequent n may can lose their babies acts almost instantly , makes food intoxicati , normally - you dehydrated ~ associated o fungi  ~ can pass who antibiotic Food-Borne Infection ingestion of pathogen, followed by growth, tissue invasion, and/or release of toxins antibiotic ~ can help for fod intoxicat raw foods (e.g., sprouts, raspberries, and seafood) haven'tsources are important gove though processing that kills microbes Listeriosis – pregnant women, the young and old, and immunocompromised individuals most vulnerable – responsible for the largest meat recall in U.S. – at-risk people should not eat soft cheeses, refrigerated smoked meats, deli meats,and undercooked hot dogs don't need to removise 35  Typhoid Mary In 1907, Mary Mallon was the first healthy person found to be a “healthy carrier” of typhoid fever in the United States She worked as a cook, and the most common ways to spread typhoid is via food or water sources She infected 47 people, 3 died She was identified as the source of the infection, captured and forced to live in isolation She appealed and was set free as long as she did not work as a cook 5 years after her release there was an outbreak of typhoid fever in a maternity hospital, 2 people died.  Clostridial food poisoning Both Clostridium perfringens and Clostridium botulinum cause serious food poisoning types of food-borne that cause botulism illness They are anaerobic spore forming bacteria grow sealed - can in cans that are Canning and cooking can kill the vegetative cells but not the spores quite high ~ a close >108 C. perfringens cells are required for food poisoning to occur (= 0.1 mg) Ingested C. perfringens sporulates in the gut and begins Ho disequilibrium of causes producing enterotoxin (toxin- watery diarrhoea pdcq balance in intestine targeting the small intestine) Poisoning starts 7 – 15 hours & microbe needs target to settle intoi after ingestion multiply pace organ , foxin & I Recovery after 24 hours Rarely fatal  Food-borne Intoxications Ingestion of toxins in foods in which microbes have grown Produce symptoms shortly after the food is consumed because growth of the disease-causing microorganism is not required Include staphylococcal food poisoning, botulism, Clostridium perfringens food poisoning, and Bacillus cereus food poisoning & mainly infects rice fungus-derived toxins – aflatoxins Carcinogens produced in fungus-infected grains and nut products – fumonisins Carcinogens produced in fungus-infected corn algal toxins Contaminate fish and shellfish  Microorganisms and food production Most food production processes involve fermentation Chemical changes in food brought about microbial action major fermentations used are lactic, propionic and ethanolic fermentations  Fermented milks majority of fermented milk products rely on lactic acid bacteria (LAB) belonging to the genera Lactobacillus, Lactococcus, Leuconostoc and Streptococcus – gram-positives that tolerate acidic conditions, non-spore forming, aerotolerant with a strictly fermentative metabolism broken down inside loug fermentati build pots have o term can be use to tolerance & reduce long allergy don't need to memorise  Probiotics and Standardization probiotics – live microorganisms, which when administered in adequate amounts, confer a health benefit to the host – specific requirements should be met microorganisms – Lactobacillus, Bifidobacterium & treated on fecal transplants Development of probiotics  Benefits of Probiotics ~ modulate immune system Immunomodulation Control of diarrhea Anticancer effects – colon cancer Possible modulation of Crohn’s Disease Treatment of enteric disease – competition with pathogens – antibiotic resistance is continually rising & taking probiotics can lower I fregt of antibiotics taking  have probiotics - Cheese Production The Romans made and exported a variety of cheeses Evidence for cheese production from 3100 BC approximately 2,000 distinct varieties representing 20 general types classified based on – texture, hardness (soft, semi-soft, hard, very hard) all from lactic acid fermentation – molds may further enhance pregnant people can only eat cheese made wo pasteurised milk Cheese Production but not raw milk helps wi for quality control preservat ~ ↑ animal derived causes ~ gurdlingt can be Short/ separate of & solid liquid ~ long Liquid releases liquid months to years https://sensorex.com/blog/2016/05/02/cheese-making-ph-measurements/ don't need to removise understand there is diff aging , communities, processes , microbes , metabolites 65  Cheese as an ecosystem for study there is also a A in intrinsic & extrinsic factors taste difference  Fermented meat and fish sausages hams bologna salami izushi – fish, rice, and vegetables Katsuobushi (bonito) – tuna fermented tuna Effects of culture on meat and meat products ham is a solid piece of ment cannot eat pregnant women while is sausage a mix of meats Salami has more basteria as ment solid piece of is hard for microbes inside e to grow tissue as muscle have to they penetrate whereas a mix wents of have microbes mixed all through them don't need to know all I details Wines and Champagnes enology (wine production) – crushed grapes separation and storage of liquid (must) before fermentation – fresh must treated with sulfur dioxide fumigant Saccharomyces cerevisiae or S. liposideus added for consistent results fermented for 3–5 days at 20–28 oC dry or sweet wines – controlled by regulating initial must sugar content racking – removes sediment produced during fermentation  need to know all - details don't Beers and Ales cereal grains used for fermentation – malt germinated barley grains having activated enzymes – mash the malt after being mixed with water in order to hydrolyze starch to usable carbohydrates – mash heated with hops – hops provide flavor and assist in clarification of wort – Heating inactivates hydrolytic enzymes wort inoculated (pitched) with desired yeast – bottom yeasts used in production of beers – top yeasts used in production of ales freshly fermented beers are aged or lagered – CO2 usually added at bottling beer can be pasteurized or sterilized by filtration  Production of Breads drain used in wine a been making ~ same Involves growth of Saccharomyces cerevisiae (baker’s yeast) under aerobic conditions – maximizes CO2 production, which leavens bread Other microbes used to make special breads (e.g., sourdough bread) Can be spoiled by Bacillus species that produce ropiness & contaminat ! don't need to memorise 78 Microorganisms as foods and food amendments micubes fundi pdefruiting bodsa such as ~ rooms mushrooms (e.g., Agaricus bisporus) cyanobacterium Spirulina dried cakes seaweeds probiotics – Lactobacillus acidophilus in beef cattle decrease E. coli O157:H7 – Bacillus subtilis (PREEMPT) in poultry limit colonization of gut by the process of competitive exclusion reduces Salmonella and Campylobacter Food in Singapore Majority of food in Singapore is imported – over 90% (SFA, 2021) In 2018, Singapore’s local farms produced: 9% of the country’s fish 13% of the country’s vegetables 24% of the country’s eggs Ensuring a constant supply of food in Singapore is a challenge Need for local food production to reduce reliance on food imports Sustainability 30 by 30 Launched in 2019, a plan to build up Singapore’s agri-food industry’s capacity to meet 30% of our nutritional needs locally and sustainably by 2030, helmed by the Singapore Food Agency (SFA) Co-funding schemes introduced by the SFA: $60M Agri-Food Cluster Transformation (ACT) Fund >$23M for R&D in sustainable urban food production Images from SFA Facebook page  Microbes and food production Alternate protein sources Single cell protein (SCP), lipids, vitamins, nutrients Aquaculture can use microbial feed Aquaculture fish killed by Vibrio infection One of 44 farms affected lost 60 ton of fish http://www.channelnewsasia.com/news/singapore/marine-bacteria-detected/ 1416826.html  Summary Microorganisms are important in food production processes and can be food Foods are susceptible to damage and decay by microorganisms because food is food Microorganisms present or growing in food can cause illness in organisms, e.g. humans, consuming those foods