mikrobiologi-umum-pertumbuhan

Food Microbiology

Elok Zubaidah

Food MicroorganismsFood Microorganisms

BacteriaBacteria Yeast Yeast MoldMold VirusesViruses

How Long do Bacteria Need to Grow?

Under ideal conditions, some bacteria can double in number every 15-30 minutes

Example: bacteria with a 20 min doubling time:

Start

20 Min

40 Min

1 Hour

TIME

Bacterial Multiplication

Time Numbers

0 1

20 2

40 4

80 16

160 256

420 2,097,152

TimeLag Phase

Gro

wth

Pha

se

Stationary Phase

Death Phase

Bacterial Growth Curve

Number of

Bacteria (log10)

Time

Changing the Bacterial Growth Curve

*Sub-optimal means lowered: pH, AW,Temp., etc.

SUB-OPTIMAL*

IDEA

L C

ON

DIT

ION

S

Much longer Lag Phase

Number of

Bacteria (log10)

Conditions for Spoilage

•Water•pH •Physical structure•Oxygen•temperature

Microorganism transferMicroorganism transfer

Soil and WaterSoil and Water Plants and animalsPlants and animals Raw to processed food / cross Raw to processed food / cross

contaminationcontamination Person to FoodPerson to Food Person to PersonPerson to Person

Microorganism Growth in Foods

Intrinsic FactorsIntrinsic Factors

compositioncomposition pHpH presence and availability of waterpresence and availability of water oxidation-reduction potentialoxidation-reduction potential

– altered by cookingaltered by cooking

physical structurephysical structure presence of antimicrobial substancespresence of antimicrobial substances

Factors Affecting Microbial Factors Affecting Microbial Growth in FoodsGrowth in Foods

What are the factors affecting What are the factors affecting microbial growth in foods?microbial growth in foods?

F-F-

A-A-

T-T-

T-T-

O-O-

M-M-

(P)- (P)-

F (“Food” for the microbes to eat)

Nutrients in food affect microbial growth:

• Sources of energy (e.g., sugars, proteins)

• Sources of nitrogen (e.g., proteins)

• Vitamins

• Minerals

In order for bacteria to grow, the food has to have the right nutrients for the bacteria andthe bacteria have to be able to “get to” the food...

• So the “biological structure” of the food is important:– Plants have outer

“skins” which protect them from microbial growth

– What happens when the skin is damaged (or cut into like this watermelon)?

Acid (pH)

• Microorganisms grow best at pH near 7– As the pH goes lower, if microorganisms grow, they

grow slower

• Most pathogens do not grow or at least don’t grow well at pH < 4.6– However, they may survive at least for a short time at

low pH

• Many yeast, molds, and spoilage bacteria can grow at pH < 4.6– Why is this important?

Clarification of Acidity (pH)Clarification of Acidity (pH)

pH scale:pH scale:

• no matter what extracellular pH a microorganism prefers, intracellular pH is relatively

near neutrality

Temperature and Time

• Classifying bacteria by growth temperatures:– Thermophiles(very hot)

– Mesophiles (cool to very warm or hot)

– Psychrotrophs (cold or warm)

– Psychrophiles (only cold)

• In food microbiology, we are most concerned with mesophiles and psychrotrophs

Classification of Bacteria by Classification of Bacteria by Temperature RequirementsTemperature Requirements

variations in temperature optimavariations in temperature optima::

• Refrigeration (< 41°F)– Slows or stops pathogen growth

– Most pathogens don’t grow in refrigerated foods

– However, a few pathogens can grow slowlyunder refrigeration (they are psychrotrophs)• Listeria monocytogenes

• Yersinia enterocolytica

• Aeromonas hydrophila

• Clostridium botulinum type E

– Many spoilage microbes are psychrotrophs

• Freezing does not kill bacteria• Some may die when frozen, but this can’t be counted on

• Heat– Cooking to > 165°F kills most pathogens

• Remember which ones aren’t killed/destroyed?– Spores, toxins

– If food is held on a hot serving line at >140°F, pathogens can NOT grow or produce toxins

Oxygen (Oxidation- Reduction Potential)

• O-R potential generally refers to the amount of oxygen present

• Pathogens:– Most bacterial pathogens can grow with

or without Oxygen (Facultative anaerobes)

– Some food pathogens can only grow when no Oxygen is present (anaerobes)• Example?

oxygen relationships of microorganismsoxygen relationships of microorganisms::

• Spoilage microorganisms:– Obligate aerobes:

• Pseudomonas spp.

• Molds

• How do you think food processors use this information about obligate aerobe spoilage microbes?

– Microaerophiles:• Lactic Acid Bacteria

– Anaerobes • Desulfotomaculum spp. (food processing concern--can

spoilage)

• Others

Relation to Oxygen

Aerobes: use oxygen in metabolism; obligate.Microaerophiles: require oxygen (also obligate), but in small amounts.Anaerobes: grow without oxygen; SEE NEXT

•Capnophiles: require larger amounts of carbon dioxide than are found normally in air.

A: aerobeB: microaerophile

Anaerobes grow without O2

Classifications vary, but our definitions:

Obligate (strict) anaerobes: killed or inhibited by oxygen.

Aerotolerant anaerobes: do not use oxygen, but not killed by it.

Facultative anaerobes: can grow with or without oxygen

C: could be facultative or aerotolerant.D: strict anaerobe

Protections of bacteria against oxygen

Bacteria possess protective enzymes, catalase and superoxide dismutase.

Catalase breaks down hydrogen peroxide into water and oxygen gas.

Superoxide dismutase breaks superoxide down into peroxide and oxygen gas.

Anaerobes missing one or both; slow or no growth in the presence of oxygen.

Fe3+ -SOD + O2- → Fe2+ -SOD + O2

Fe2+ -SOD + O2- + 2H+ → Fe 3+ -SOD + H2O2

enzymes that destroy toxic oxygen species:

toxic forms of oxygentoxic forms of oxygen::

enzymes that destroy toxic oxygen species:

catalasecatalaseH2O2 + H2O2 2 H2O + O2

negativenegative positivepositive

testing microbial culture for presence of catalase:

Moisture (water)

• Why is water important to bacteria?

– To survive?

– To grow?

• Is it the total amount of water present in the food that’s important?

• Water in food is present in two forms:– BOUND

– FREE

• Bound water is unavailable for bacteria to grow

Water Activity (AW)

• A measure of the FREE WATER- - water that is available for microbial growth

– AW is simply the Relative Humidity of the food (at equilibrium with the air around the food)

• AW can range from:– 0.00 (no free water) to 1.00 (all free water)

• We don’t usually measure AW values in the Air Force, but you can look them up in food microbiology books

Aw Foods (some examples)0.98 to 1.00 Fresh meats, fruit, vegetables, canned fruit in

light syrup, canned vegetables, beverages0.93 to 0.98 Processed cheese, bread dough, lightly salted

meats (e.g., hot dogs), canned fruit in heavysyrup

0.85 to 0.93 Ham, aged cheddar cheese, most bread, drysausage, sweetened condensed milk

0.60 to 0.85 Flour, cereals, jams/jellies, nuts, some cheese,heavily salted foods, dried fruit

< 0.60 Chocolate, honey, noodles, crackers, potatochips, dried milk, dried vegetables

*Pathogens do not grow or produce toxins at AW < 0.85Adapted from APHA, Compendium of Methods for the Microbial Examination of Foods, 1992.

*

Water activity and microbial growth

–Most bacteria can’t grow below aw = 0.85

–Most yeasts & molds can’t grow below aw = 0.65

Rel

ativ

e gr

owth

or

reac

tion

rat

e

Water activity1.00.80.70.60.50.40.30.20.10.0 0.9

Low water activity:halophiles, osmophiles, and xerotolerant

Water is critical for life; remove some, and things can’t grow. (food preservation: jerky, etc.)

Halophiles/halotolerant: relationship to high salt.

Marine bacteria; archaea and really high salt.

Osmophiles: can stand hypertonic environments whether salt, sugar, or other dissolved solutes

Fungi very good at this; grandma’s wax over jelly.

Xerotolerant: dry. Subject to desiccation. Fungi best

Bread, dry rot of wood

Survival of bacterial endospores.

salt tolerancesalt tolerance::

Typical water activity of some foods

0.95 – fruits, vegetables, meat, fish, milk

0.91 – some cheeses, ham

0.87 – salami, pepperoni, dry cheeses, margarine,

0.80 – fruit juice concentrates, sweetened condensed milk, syrups, flour, rice, high sugar cakes

0.75 – jam, marmalade

0.65 – oatmeal, fudge, marshmallows, jelly, molasses, sugar, nuts

0.60 – dried fruits, honey

0.50 – dried pasta, dried spices

0.30 – cookies, crackers

0.03 – dry milk, dehydrated soups, corn flakes

Aw – examples

Most bacterial pathogens can not grow or produce toxins at AW < 0.91

Exception: Staph. aureus can grow and produce toxin down to 0.85

How do you think AW can be decreased?

1.

2.

3.

How do these methods work?

• Growth of microbes in food follows a typical microbial growth pattern

• Growth rate depends on the nutritional value andtemperature of the food

• Number of microbes depends on both inoculum size and growth rate• Food spoilage occurs at high populations density (at stationary phase) - retarding microbial growth delays spoilage

Food Spoilage

Food is considered spoiled when an undesirable change in the color, flavor, odor or texture has occurred. Foreign substances in food products make foods undesirable.

Spoilage is a natural phenomenon; it occurs at varying rates depending on the storage temperature, kind of food involved, kind of microorganisms present, packaging materials used, food additives used and method of preservation.

It is a gradual process occurring because of poor sanitation, enzymatic or chemical reactions, improper temperature controls, microbial growth or physical abuse.

II. Microbial Growth and Food Spoilage

Meats and dairy products are ideal environments for spoilage by microorganisms because of their high nutritional value and the presence of easily utilizable carbohydrates, fats, and proteins; proteolysis (aerobic) and putrefaction (anaerobic) decompose proteins;

Fruits and vegetables have much lower protein and fat content than meats and dairy products and undergo different kind of spoilage;

the presence of readily degradable carbohydrates in vegetables favors spoilage by bacteria; high oxidation-reduction potential favors aerobic and facultative bacteria; molds usually initiate spoilage in whole fruits

1. Frozen citrus products are minimally processed and can be spoiled by lactobacilli and yeasts

2. Grains, corn, and nuts can spoil when held under moist conditions; this can lead to production of toxic substances, including aflatoxins and fumonisins

3. Shellfish and finfish can be contaminated by algal toxins, which cause of variety of illnesses in humans

The microbial agent causing spoilage The microbial agent causing spoilage depends on the source of the food depends on the source of the food and its nutritional value:and its nutritional value:Meats may be contaminated by intestinal Meats may be contaminated by intestinal

pathogens released during slaughterpathogens released during slaughterDairy products - lactic acid bacteriaDairy products - lactic acid bacteriaFruit and vegetables - soil and water Fruit and vegetables - soil and water

microbesmicrobesSome microbes that cause spoilage Some microbes that cause spoilage

may be human pathogens but the may be human pathogens but the majority are not!majority are not!

Growth of microbes in food Growth of microbes in food follows a typical microbial follows a typical microbial growth patterngrowth pattern

Growth rate depends on Growth rate depends on the the nutritional valuenutritional value and andtemperaturetemperature of the food of the food

• Number of microbes depends on both inoculum size and growth rate• Food spoilage occurs at high populations density (at stationary phase) - retarding microbial growth delays spoilage

Food preservation:Food preservation:The principles discussed in Ch. 20 (microbial growth The principles discussed in Ch. 20 (microbial growth

controls) are used herecontrols) are used here

TemperatureTemperature Lower: decreased growth Lower: decreased growth

rate - but, psychrophilic rate - but, psychrophilic microbes microbes

Perishable food will only Perishable food will only last for a few days at 4 last for a few days at 4 ooCC

Freezing ( - 20 Freezing ( - 20 ooC) C) destroys the texture of destroys the texture of many products and does many products and does not completely stop not completely stop growthgrowth

Deep freezing (- 80 Deep freezing (- 80 ooC) is C) is costlycostly

AcidityAcidity Most foods at neutral or Most foods at neutral or

acidic pHacidic pH At pH < 5 microbial growth is At pH < 5 microbial growth is

inhibitedinhibited PicklingPickling: Decreased food pH : Decreased food pH

by the addition of vinegar by the addition of vinegar (acetic acid bacteria); (acetic acid bacteria); veggies, meats, fishveggies, meats, fish

Fermented foodsFermented foods: acid is : acid is produced during food produced during food production (e.g., sauerkraut, production (e.g., sauerkraut, yogurt, etc); lactic acid, yogurt, etc); lactic acid, acetic acid, and propionic acetic acid, and propionic acid bacteria; limited to pH acid bacteria; limited to pH > 4> 4

Controlling Food Spoilage

1. Removal of microorganisms-filtration of water, wine, beer juices, soft drinks and other liquids

2. Low temperature-refrigeration and/or freezing retards microbial growth but does not prevent spoilage

3. High temperature Canning

Canned food is heated in special containers called retorts to 115°C for 25-100 minutes to kill spoilage microorganisms

Pasteurization-kills disease-causing organisms; substantially reduces the number of spoilage organisms

•Low-temperature holding (LTH)-68°C for 30 min

•High-temperature short-time (HTST)-71°C for 15 seconds •Ultra-high temperature (UHT)-141°C for 2 seconds

•Shorter times result in improved flavor and extended shelf life

•Water availability-dehydration procedures (e.g., freeze-drying) remove water and increase solute concentration

•Chemical-based preservation

•Radiation-nonionizing (ultraviolet or UV)

•Microbial product-based inhibition Bacteriocins-bacteriocidal proteins produced by bacteria; active against only closely related bacteria (e.g., nisin)

What are Food-Borne Diseases?

People get sick with a food-borne disease when they consume foods or beverages contaminated with disease-causing microbes, chemicals, insects or other harmful substances.

Bacteria, viruses and parasites cause most of these diseases. Toxins, poisons and chemicals can also contaminate food and cause illness.

Food-Borne DiseasesFood-Borne Diseases

two primary typestwo primary types food-borne infectionsfood-borne infections food intoxicationsfood intoxications

•There are a reported 76 million cases of food-borne disease occurring every year in the United States alone.

•Most of these cases are mild and cause symptoms for a day or two. More serious cases require 323,000 hospitalizations annually, and even cause 5,000 deaths a year.

•People most at risk tend to be those who are very old, very young, women who are pregnant.

• Even robustly healthy people are vulnerable if they are exposed to a very high dose of an unhealthy organism.

One symptom these diseases produce in common is that because they enter the body through food, the first sign of illness is usually nausea, vomiting, abdominal pain and cramps and diarrhea.

the spectrum of food-borne diseases constantly changes and evolves even as the science of food safety continues to make significant advances and discoveries.

Some diseases, such as cholera, tuberculosis and typhoid fever have been eradicated thanks to food safety improvements.

Other diseases are just now being discovered or are adapting and evolving into new strains. E.Coli 0157:H7, for example, didn't exist 25 years ago.

Foodborne diseases and microbial Foodborne diseases and microbial sampling:sampling:

Food poisoning - Caused by preformed Food poisoning - Caused by preformed toxin in the food; organism may or may toxin in the food; organism may or may not be alive and growing; not be alive and growing; Clostridium Clostridium botulinum botulinum and and Staphylococcus aureusStaphylococcus aureus

Food infection - Live cells delivered by Food infection - Live cells delivered by contaminated food; organism multiply contaminated food; organism multiply once food is ingested; once food is ingested; SalmonellaSalmonella

Sampling: Process food to release Sampling: Process food to release microbes; culturing and use of molecular microbes; culturing and use of molecular probes (antibodies, gene probes, PCR) to probes (antibodies, gene probes, PCR) to detect detect specificspecific microbes microbes

Examples of foodborne diseases Examples of foodborne diseases most are infections and associated with animal most are infections and associated with animal

products:products:

OrganismOrganism Number of Number of cased per year cased per year

(U.S.)(U.S.)

Foods to watchFoods to watch

Campylobacter Campylobacter jejunijejuni

1,963,0001,963,000 Poultry and diary Poultry and diary productsproducts

SalmonellaSalmonella spp. spp. 1,340,0001,340,000 Poultry, meat, Poultry, meat, diary and eggsdiary and eggs

Clostridium Clostridium

perfringensperfringens248,000248,000 Cooked and Cooked and

reheated meat reheated meat productsproducts

Giardia lamblia Giardia lamblia 200,000200,000 Contaminated Contaminated meatmeat

Norwalk-like Norwalk-like virusesviruses

9,200,0009,200,000 Shellfish, other Shellfish, other foodfood

StaphylococcusStaphylococcus aureus:aureus:

Common skin, respiratory, and GI tract floraCommon skin, respiratory, and GI tract flora Grows readily in unrefrigirated meats and creamy Grows readily in unrefrigirated meats and creamy

foods; toxins are heat resistancefoods; toxins are heat resistance Produces 7 entrotoxins; the most potent is A Produces 7 entrotoxins; the most potent is A

((entAentA); a superantigen (T cell stimulation ); a superantigen (T cell stimulation cytokines cytokines intestinal inflammation intestinal inflammation gastroenteritis)gastroenteritis)

Severe but short response (1-6 hrs following Severe but short response (1-6 hrs following ingestion; done by 48 hrs) ingestion; done by 48 hrs)

Detection of toxins or the organism in foodDetection of toxins or the organism in food Antibiotics are uselessAntibiotics are useless

Clostridial diseases:Clostridial diseases:

Gram positive, spore-forming, anaerobes common Gram positive, spore-forming, anaerobes common in soil; in soil; C. perfringens C. perfringens and and C. botulinumC. botulinum

C. perfringensC. perfringens - food poisoning: ingestion of > 10 - food poisoning: ingestion of > 1088 cells (inappropriate cooking followed by cells (inappropriate cooking followed by unrefrigirated storage in closed containers) unrefrigirated storage in closed containers) spore spore germination in the intestine leads to neurotoxin germination in the intestine leads to neurotoxin production production

Alteration of water permeability of intestinal lining Alteration of water permeability of intestinal lining diarrhea and intestinal cramps (no vomiting or diarrhea and intestinal cramps (no vomiting or fever); onset within 7 - 16 hrs of ingestion but gone fever); onset within 7 - 16 hrs of ingestion but gone in 24 hrsin 24 hrs

Diagnosed by isolation of microbe or detection of Diagnosed by isolation of microbe or detection of toxin in feces toxin in feces

Botulism (Botulism (C. botulinumC. botulinum):): The most potent toxin known; few The most potent toxin known; few

cases but high mortality (25%); cases but high mortality (25%); destroyed by 10 min in 80 destroyed by 10 min in 80 ooCC

Flaccid paralysis of musclesFlaccid paralysis of muscles Common in soil and waterCommon in soil and water How? Improper canning How? Improper canning spore spore

germination germination toxin production toxin production canned food used without canned food used without cooking cooking disease disease

Infant botulismInfant botulism: consumption of : consumption of honey that is contaminated by honey that is contaminated by spores (0 - 2 months)spores (0 - 2 months)

Treatment: antitoxin and Treatment: antitoxin and ventilationventilation

Salmonellosis:Salmonellosis: Gram negative enteric Gram negative enteric

bacterium; all strains are bacterium; all strains are pathogenic; transmission is pathogenic; transmission is from sources (eggs, meats) from sources (eggs, meats) and by food handlersand by food handlers

Colonization of of intestinal Colonization of of intestinal epitheliumepithelium

• Two diseases:

– Enterocolitis (most commonly by S. typhimurium): 105 - 108 viable cells; disease onset within 8 - 48 hrs; headaches, chills, vomiting, diarrhea and fever (2-3 days); continuous shading of organism for months/years (Typhoid Mary); treatment - none

– Typhoid fever (S. typhi): Septicemia leading to high fever that can last for several weeks; mortality is 15% if untreated; antibiotics

• Prevention: Cooked food (70 oC for 10 min); monitor for carrier state among food handlers

Pathogenic Pathogenic E. coliE. coli:: Some strains of Some strains of E. coliE. coli; diarrhea and urinary tract infection; ; diarrhea and urinary tract infection;

classification of pathogens is based on toxin and diseasesclassification of pathogens is based on toxin and diseases EnterohemorrhagicEnterohemorrhagic (O157:H7) - colonization of the small (O157:H7) - colonization of the small

intestine and intestine and verotxinverotxin production production diarrhea and kidney diarrhea and kidney infection; uncooked and undercooked ground meat; infection; uncooked and undercooked ground meat; occasional epidemicsoccasional epidemics

EnterotoxigenicEnterotoxigenic (Travelers diarrhea) - heat labile toxin; (Travelers diarrhea) - heat labile toxin; water and produce in developing countries; immunity water and produce in developing countries; immunity

EnteropathogenicEnteropathogenic - diarrhea that afflicts young children - diarrhea that afflicts young children EnteroinvasiveEnteroinvasive - invasive colon infection; bloody diarrhea; - invasive colon infection; bloody diarrhea;

survival in phagosomes; in developing countriessurvival in phagosomes; in developing countries Treatment and prevention: diseases are self-contained but Treatment and prevention: diseases are self-contained but

antibiotics help; antibiotics help; irradiation of ground beefirradiation of ground beef!!

Campylobacter: Campylobacter:

Gram negative microaerophile common in Gram negative microaerophile common in poultry and sometimes in beefpoultry and sometimes in beef

C. jejuniC. jejuni and and C. coliC. coli bacterial diarrhea; bacterial diarrhea; C. C. fetusfetus spontaneous abortion in livestock spontaneous abortion in livestock

Ingestion of 10Ingestion of 1044 cells cells colonization of small colonization of small intestine intestine inflammation inflammation high fever (104 high fever (104 ooC), headache, malaise, nausea, cramps, C), headache, malaise, nausea, cramps, diarrhea diarrhea subsides in 1 week; erythromycin subsides in 1 week; erythromycin to shorten infectious stage to shorten infectious stage

Prevention by proper cooking and hygiene Prevention by proper cooking and hygiene (including utensils)(including utensils)

Listeriosis:Listeriosis: Listeria monocytogenesListeria monocytogenes: a gram (+) bacillus; Cold and salt : a gram (+) bacillus; Cold and salt

tolerant; wide distribution; found in soil water and raw milk; tolerant; wide distribution; found in soil water and raw milk; contaminates all food products either at source or during contaminates all food products either at source or during processing; mostly in processed foodprocessing; mostly in processed food

Pathology (2500 per year): Pathology (2500 per year): Uptake by phagocytes Uptake by phagocytes growth growth lysis of phagocyte lysis of phagocyte

infection of nearby cellsinfection of nearby cells Immunity due to cell-mediated TImmunity due to cell-mediated THH1 cells 1 cells macrophage macrophage

activationactivation In normal individuals - gastrointestinal food infection; in In normal individuals - gastrointestinal food infection; in

immuno-compromised individuals - acute bacterimia and immuno-compromised individuals - acute bacterimia and meningitis (20% death rate)meningitis (20% death rate)

Prevention: cleanliness during food processing; avoiding outdated Prevention: cleanliness during food processing; avoiding outdated foodsfoods

Diagnosis by culturing from blood and spinal fluid; treated with Diagnosis by culturing from blood and spinal fluid; treated with trimethoprim drugstrimethoprim drugs

Other foodborne infectious Other foodborne infectious diseases :diseases :

Bacterial diseasesBacterial diseases Yersinia enterocoliticaYersinia enterocolitica

- enteric fever- enteric fever Bacillus cereusBacillus cereus - food - food

poisoning by heat poisoning by heat stable toxinstable toxin

ShigellaShigella spp. - spp. - shigolosis (100,000 shigolosis (100,000 per year)per year)

VibrioVibrio spp. - spp. - contaminated contaminated seafoodseafood

Viral diseasesViral diseases - the - the most common cause most common cause of gastrointestinal of gastrointestinal diseases; “24-hour diseases; “24-hour flu” - fast and self-flu” - fast and self-containing; fecal containing; fecal contaminationcontamination Norwalk viruses, Norwalk viruses,

rotaviruses, rotaviruses, astroviruses, hepatitis astroviruses, hepatitis AA

Preventing Foodborne DiseasePreventing Foodborne Disease

•Food infections (microbes are transferred to consumer)•Food poisoning (results from the toxin consumption)

Food-Borne IntoxicationsFood-Borne Intoxications

ingestion of toxins in foods in which ingestion of toxins in foods in which microbes have grownmicrobes have grown

include staphylococcal food include staphylococcal food poisoning, botulism, poisoning, botulism, Clostridium Clostridium perfringensperfringens food poisoning, and food poisoning, and Bacillus cereusBacillus cereus food poisoning food poisoning

ToxinsToxins

ergotismergotism toxic condition caused by growth of a toxic condition caused by growth of a

fungus in grainsfungus in grains aflatoxinsaflatoxins

carcinogens produced in fungus-carcinogens produced in fungus-infected grains and nut productsinfected grains and nut products

fumonisinsfumonisins carcinogens produced in fungus-carcinogens produced in fungus-

infected corninfected corn