Microorganisms Important to Foods PDF

MICROORGANISMS IMPORTANT TO FOODS MIC 322 Songsirin Ruengvisesh, PhD 1  2 Microorganisms of interest in foods Non-beneficial Pathogens *Pathogens do not...

MICROORGANISMS IMPORTANT TO FOODS MIC 322 Songsirin Ruengvisesh, PhD 1  2 Microorganisms of interest in foods Non-beneficial Pathogens *Pathogens do not spoil foods. cause foodborne diseases Spoilers do not cause disease. Spoilers Undesirable changes in foods visible growth large molecules (e.g. slime) gas/acid undesirable odor color changes  3 Microorganisms of interest in foods Beneficial Starters and probiotics used for food production (e.g. Acetobacter aceti for vinegar) Indicators used for indicating safety and quality of foods e.g. coliforms bacteria can be used to indicate adherence to GMP in processed foods  4 Primary Sources of Microorganisms Found in Foods Soil Water Plants and plant products Food Utensils Animal feeds Animal hides Animal feces Air and dust Food handlers Food ingredients  5 Microbial taxonomy Kingdom Division Class Order Species Genus Family *In food microbiology, ranks above family are not widely used  6 Microbial taxonomy Some major characteristics used in microbial taxonomy Base composition (mol% G+C content of DNA) If 2 strains differ by 10% or more, they are most likely not related. Nucleotide base sequence The sequences in 16S rRNA among strains are compared A sequence of about 1500 nucleotide bases over a stretch of 16S rRNA is most conserved, so related strains should have high homology Nucleic acid (DNA and RNA) hybridization Two strains are considered the same if their DNAs have 90% or more homology.  7 https://classificationsystemsccc.weebly.com/dna-dna-hybridisation.html  8 Nomenclature The species name for bacteria, yeasts, and molds has two parts (Binomial name). The first part is the genus name. The second part is the specific epithet. Both parts are Latinized; when written, they are italicized (or underlined), with the first letter of the genus written in a capital letter. Saccharomyces cerevisiae Saccharomyces cerevisiae  9 Nomenclature A bacterial species can be divided into several subspecies (subsp. or ssp.). A trinomial epithet (subspecific epithet) is used. Lactobacillus lactis ssp. lactis Ranks below subspecies are used to differentiate strains recognized by specific characters serovar = antigenic reaction biovar = producing a specific metabolite phagovar = sensitive to a specific phage. Lactococcus lactis ssp. lactis biovar diacetilactis  10 Nomenclature “spp.” can be used to represent the species and stains in a genus. Lactobacillus spp. Plural forms of the genus can be used lactobacilli for Lactobacillus lactococci for Lactococcus leuconostocs for Leuconostoc salmonellae for Salmonella  11 Nomenclature Viruses have not been given specific taxonomic names like bacteria or fungi often identified with the disease they produce Hepatitis A virus (causing liver inflammation) often identified with alphabet, number, or both T4 bacteriophage λ bacteriophage  12 Bacterial Structure  13 Bacterial Cell Wall 14  15 Fungal cell wall  16 Molds are multicellular Hyphae (filamentous, tube-like Mycelium = aggregate of hyphae strand)  17 Yeasts are unicellular  18 Virus  19 Important microorganisms in foods  20 Important bacterial groups in foods 1. Lactic acid bacteria (LAB) Homofermentative LAB: ferment sugar and produce lactic acid (main product) Pediococcus, Streptococcus, Lactococcus Lactobacillus (some species) Heterofermentative LAB: ferment sugar and produce lactic acid and other products (e.g. ethanol, acetic acid, CO2) Leuconostoc, Lactobacillus (some species)  21 Important bacterial groups in foods LAB can have positive effect or negative effect in foods Positive effect: used as starter cultures for fermented foods (e.g. yogurt, cheese, pickle) Negative effect: cause food spoilage (e.g. slime production, sour flavor, turbidity)  22 Important bacterial groups in foods 2. Butyric acid bacteria ferment carbohydrates into butyric acid and gases (1. CO2 and 2. H2) C6H12O6 → C4H8O2 + 2 CO2 + 2 H2 cause food spoilage Clostridium butyricum 3. Propionic acid bacteria Most are in genus Propionibacterium. ferment carbohydrates into propionic acid used in Swiss cheese production can be isolated from raw milk, cheese, and dairy product  23 Important bacterial groups in foods 4. Acetic acid bacteria oxidize ethanol and produce acetic acid Acetobacter aceti (used for vinegar production) 5. Proteolytic bacteria can hydrolyze proteins using extracellular proteinases cause food spoilage Undesirable odor (from amine, H2S, indole compound, mercaptans, fatty acids) Putrefactive bacteria : Clostridium, Bacillus, Pseudomonas  24 Important bacterial groups in foods 6. Saccharolytic bacteria able to hydrolyze disaccharide and polysaccharide into monosaccharide Bacillus, Clostridium, Aeromonas, Pseudomonas, Enterobacter 7. Lipolytic bacteria able to hydrolyze complex triglycerides to fatty acid and glycerol cause rancid smell Clostridium, Pseudomonas, Staphylococcus, Micrococcus  25 Important bacterial groups in foods 8. Pectolytic bacteria able to hydrolyze pectin (heteropolysaccharide found in plant) using pectinase Erwinia carotovora 9. Coliforms Gram-negative, non-spore forming bacteria that ferments lactose to acid and gas within 48 hr at 35-37°C not all of them are of fecal origin do NOT survive pasturization used to indicate adherence to GMP in processed foods (cooked, pasteurized)  26 Important bacterial groups in foods 10. Thermophilic bacteria grow well at temp > 41°C Campylobacter jejuni, Streptococcus, Lactobacillus, Bacillus stearothermophilus 11. Psychrotrophic bacteria able to GROW at refrigeration temperature Listeria monocytogenes, Pseudomonas, Yersinia enterocolitica, Aeromonas  27 Important bacterial groups in foods 12. Halotolerant Able to survive at high salt concentration (≥10%) Vibrio parahaemolyticus, Staphylococcus, Bacillus 13. Aciduric bacteria able to survive at low pH (< 4.0) Lactobacillus, Pediococcus, Lactococcus, Streptococcus  28 Important bacterial groups in foods 14. Gas-producing bacteria produce gas (CO2 , H2 , H2S) during metabolism of nutrients Propionibacterium, Escherichia, Enterobacter, Clostridium 15. Slime-producing bacteria produce slime due to polysaccharide synthesis Xanthomonas, Leuconostoc, Klebsiella  29 Important bacterial groups in foods 16. Aerobes requires oxygen for growth and multiplication Pseudomonas, Bacillus, Flavobacterium 15. Anaerobe cannot grow in the presence of oxygen Clostridium 16. Facultative anaerobes able to grow in both the presence and absence of oxygen Escherichia coli, Serratia, Salmonella, Klebsiella  30 Important molds in foods Mold can grow even in conditions in which many bacteria cannot grow low pH, low water activity (aw ) high osmotic pressure Important spoilage microorganisms Mycotoxins cause foodborne intoxication Many are used in food bioprocessing  31 Important molds in foods Alternaria causes brown to black rots in citrus fruits Some species produce mycotoxins  32 Important molds in foods Aspergillus appears yellow to green on foods causes brown to black rots in citrus fruits peaches, figs Some species produce aflatoxin (e.g. A. flavus, A. parasiticus) used in fermentation (e.g. A. oryzae, A. soyae ) Aspergillus produces protease and amylase break down protein and carbohydrate into amino acids and sugars Produces many useful enzymes used in food industry A. niger produces glucoamylase (used for HFCS production)  33 Important molds in foods Fusarium Field mold cottony mycelium (pink, red, brown, or purple) brown rot in citrus fruits and apple Grow on barley and wheat grain Several species produce toxins (e.g. zearalenone)  34 Important molds in foods Geotrichum Yeast-like fungi G. candidum “Dairy mold” widely used in dairy products imparts flavors and aroma to many types of cheese Machinery mold Builds up on food-contact equipment in food-processing plants Indicates plant sanitation and contaminated equipment  35 Important molds in foods Rhizopus R. stolonifer (also called bread mold) causes “soft rot” due to starch and pectin degradation cause black spot of beef R. oligosporus is important in the production of tempeh  36 Important molds in foods Penicillium Typical color on foods are blue to blue-green Blue and green mold rots of apples, grapes, pears, citrus fruits Some species produce toxins (e.g.citrinin) P. roqueforti used in blue cheese production https://www.youtube.com/watch?v=unVdU4MgRAA  37 Important yeasts in foods Saccharomyces Round, oval or elongated cells S. cerevisiae are used in baking for leavening bread alcoholic fermentation (e.g.wine, beer) also causes spoilage of food producing alcohol and CO2  38 Important yeasts in foods Pichia oval to cylindrical cells unable to ferment or assimilate lactose forms pellicles in beer, wine, and brine to cause spoilage also used in oriental food fermentation  39 Important yeasts in foods Rhodotorula Pigment-forming yeasts pink to red pigments R. glutinis, R. mucilaginosa are the most prevalent species in foods cause discolorant of foods (e.g. meat, fish, saeurkraut) can be found in nature (e.g. air, soil, dust, sea)  40 Important yeasts in foods Torulopsis spherical to oval cell causes spoilage fruit juice concentrates and acid foods causes spoilage of milk able to ferment lactose (e.g.Torulopsis versatilis)  41 Important yeasts in foods Candida spoils foods with high acid, salt, and sugar forms pellicles on the surface of liquids can cause rancidity in butter and dairy products (e.g. Candida lypolitica) also used in fermentation of cacao beans, beers, ales, and fruit juice https://www.semanticscholar.org/paper/Pellicle-associated-adherence-film-above-incubation-Fleischmann- Sripuntanagoon/970d1a1c153799c83000aeeac628db1e86fac026/figure/0  42 Important yeasts in foods Zygosaccharomyces Causes spoilage of high-acid foods (low pH) fruit juices pickles mustards fruit juice concentrates jams salad dressings strong fermenter of sugars also used in fermentation processes of some oriental foods Z. rouxii is the most prevalent species High tolerance to osmotic stress Can grow in environments with high concentrations of salts and sugars that other yeasts cannot grow  43 References Jay, M., Loessner J. M., and Golden A. D. 2005. Modern Food Microbiology. Springer Science Ray B., 2003. Fundamental Food Microbiology.Taylor & Francis