UNIT 3

FOOD MICROBIOLOGY

BY PROF. PRIYANKA S. OULKAR

 CONTENT

• INTRODUCTION TO MICROBIOLOGY AND ITS SIGNIFICANCE IN FOODS –

PATHOGENIC AND SPOILAGE ORGANISMS AND BENEFICIAL ORGANISMS

• MAJOR GROUPS OF MICROORGANISMS- BACTERIA, YEAST, MOLDS AND

VIRUSES AND ITS RELATIONSHIP WITH FOODS

• PROKARYOTES AND EUKARYOTES MORPHOLOGY

• STRUCTURE AND FUNCTION OF MICROBIAL CELL

• THE TERM MICROBIOLOGY WAS INTRODUCED BY A FRENCH CHEMIST LOUIS
PASTEUR, WHO DEMONSTRATED THAT FERMENTATION WAS CAUSED BY THE
GROWTH OF BACTERIA AND YEAST.

• HE IS KNOWN AS FATHER OF MICROBIOLOGY.

• THESE MICROORGANISM CANNOT BE SEEN BY NAKED EYES, THEY ARE ONLY SEEN
UNDER THE MICROSCOPE.

• MICROORGANISMS ARE PRESENT EVERYWHERE ON EARTH, INCLUDING HUMAN

BEINGS, ANIMALS, PLANTS, SOIL, WATER, FOOD AND ATMOSPHERE.

• MICROORGANISMS MAY BE BENEFICIAL OR HARMFUL TO HUMAN BEINGS.

• MICROBIOLOGY IS THE STUDY OF LIVING ORGANISMS OF MICROSCOPIC SIZE
WHICH INCLUDES:
• 1. BACTERIA
• 2. FUNGI
• 3. ALGAE
• 4. PROTOZOA
• 5. VIRUSES
• MICROBIOLOGY IS THE STUDY OF MICROORGANISMS, WHICH CAN BE
BENEFICIAL OR HARMFUL TO FOOD.

• MICROORGANISMS ARE SINGLE-CELLED ORGANISMS.

• THEY CAN BE SEEN WITH A MICROSCOPE THAT MAGNIFIES ABOUT 1,000

TIMES
• FOOD MICROBIOLOGY
• FOOD MICROBIOLOGY IS A BRANCH OF MICROBIOLOGY THAT STUDIES A
VARIETY OF MICROORGANISMS INVOLVED IN THE SPOILAGE OF FOOD,
MANUFACTURE OF FOOD, AND TRANSMISSION OF DISEASES VIA FOOD.
• FOOD SAFETY IS AN IMPORTANT PART OF FOOD MICROBIOLOGY AS FOOD CONTINUES
TO ACT AS A MODE OF TRANSMISSION OF VARIOUS INFECTIOUS AGENTS.
• SPOILAGE OF FOOD BY MICROORGANISMS HAS BECOME A PROBLEM FOR MANY
PEOPLE AROUND THE WORLD AS FOODS ACT AS A NUTRIENT SOURCE FOR
MICROORGANISMS.
• FOOD MICROBIOLOGY FOCUSES NOT ONLY ON THE DETECTION OF FOOD SPOILAGE
BUT ALSO ON THE PRESERVATION OF FOOD AGAINST SUCH MICROORGANISMS.
• PRESERVATION TECHNIQUES LIKE RADIATION, DRY AND MOIST HEAT STERILIZATION,
FILTRATION USES PHYSICAL AND CHEMICAL METHODS IN FOOD MICROBIOLOGY.
• THE USE OF LACTOBACILLUS IN THE PRODUCTION OF CURD, CHEESE, AND BUTTER IS
AN IMPORTANT EXAMPLE OF THIS.
• INDUSTRIAL MICROBIOLOGY

• IT IS THE STUDY OF INDUSTRIALLY USEFUL MICROORGANISMS IN THE PRODUCTION

OF ALCOHOLIC BEVERAGES, VITAMINS, AMINO ACIDS, ENZYMES, ANTIBIOTICS AND
OTHER DRUGS. •
• IT ALSO INCLUDES FERMENTATION TECHNIQUES FOR THE PRODUCTION OF
DIFFERENT COMPOUNDS.

• FOOD MICROBIOLOGY
• • IT DEALS WITH THE INTERACTION OF MICROORGANISMS AND FOOD IN THE
RELATION TO FOOD PROCESSING, FOOD SPOILAGE, FOOD BORNE DISEASES, THEIR
PREVENTION AND INCLUDES PREPARATION AND PRESERVATION OF FOOD PRODUCTS.
• PROKARYOTIC CELLS •
• GENETIC MATERIAL IS NOT ENCLOSED BY THE NUCLEAR MEMBRANE.
• • ABSENCE OF NUCLEAR MEMBRANE

• EUKARYOTIC CELLS
• • GENETIC MATERIAL IS ENCLOSED BY THE NUCLEAR MEMBRANE.
• • PRESENCE OF NUCLEAR MEMBRANE.
• SIGNIFICANCE

• • MICROBIOLOGY IS THE STUDY OF MICRO-ORGANISMS, TOO SMALL TO BE

CLEARLY UNSEEN BY THE EYE (< 1 MM)

• • MICRO-ORGANISMS FACILITATE MANY IMPORTANT CHEMICAL

REACTIONS IN NATURE: - MAKING OF CHEESE, YOGHURT, BREAD –
• PRODUCTION OF ALCOHOL

• RETTING OF FLAX (COCONUT HUSKS)

• - BREAKING DOWN ORGANIC MATTER (E.G. BOD)

• MICROORGANISMS ARE IMPORTANT IN FOOD BECAUSE THEY CAN:
• CAUSE FOOD SPOILAGE: MICROORGANISMS CAN CAUSE FOOD TO SPOIL,
WHICH CAN LEAD TO ECONOMIC LOSSES FOR THE FOOD INDUSTRY AND
INCREASED HOSPITALIZATION COSTS FOR CONSUMERS.
• CAUSE FOODBORNE DISEASES: SOME MICROORGANISMS, CALLED
PATHOGENS, CAN CAUSE FOODBORNE DISEASES THAT CAN LEAD TO ILLNESS
AND DEATH. COMMON FOODBORNE PATHOGENS INCLUDE SALMONELLA,
CAMPYLOBACTER, AND ESCHERICHIA COLI.
• BE USED TO PRODUCE FOOD: MICROORGANISMS ARE USED TO PRODUCE
MANY FOOD PRODUCTS, INCLUDING WINE, BEER, BREAD, YOGURT, AND CHEESE.
• BE USED AS NATURAL PESTICIDES: SOME MICROORGANISMS CAN BE USED
TO CONTROL PESTS THAT DAMAGE CROPS.
• PRODUCE PROBIOTICS: SOME MICROORGANISMS CAN BE USED TO PRODUCE
PROBIOTICS.
• HERE ARE SOME EXAMPLES OF MICROORGANISMS AND THEIR ROLES IN
FOOD:
• SACCHAROMYCES SPP. THESE MICROORGANISMS ARE USED TO PRODUCE
BREAD AND WINE, BUT SOME STRAINS CAN ALSO SPOIL ALCOHOLIC
BEVERAGES.

• CANDIDA AND RELATED GENERA: THESE YEASTS CAN SPOIL FRUITS,

VEGETABLES, AND DAIRY PRODUCTS.

• DEKKERA/BRETTANOMYCES: THESE MICROORGANISMS ARE INVOLVED IN

SPOILAGE OF FERMENTED FOODS, INCLUDING ALCOHOLIC BEVERAGES AND
SOME DAIRY PRODUCTS.
 IMPORTANCE OF MICRO-ORGANISMS IN
FOODS
• MANY PATHOGENIC MICRO-ORGANISMS (BACTERIA, MOLDS AND VIRUSES) CAN
CONTAMINATE FOODS DURING VARIOUS STAGES OF THEIR HANDLING, BETWEEN
PRODUCTION AND CONSUMPTION.

• CONSUMPTION OF THESE FOODS CAN CAUSE FOOD BORNE DISEASES.

• FOOD BORNE DISEASES CAN BE FATAL AND MAY ALSO CAUSE LARGE ECONOMIC
LOSSES.
• FOOD SPOILAGE STEMS FROM THE GROWTH OF THESE MICRO-ORGANISMS IN
FOOD OR IS DUE TO THE ACTION OF MICROBIAL ENZYMES.

• COMMON SYMPTOMS OF FOODBORNE ILLNESS ARE DIARRHEA AND/OR

VOMITING, TYPICALLY LASTING 1 TO 7 DAYS. OTHER SYMPTOMS MIGHT
INCLUDE ABDOMINAL CRAMPS, NAUSEA, FEVER, JOINT/BACK ACHES, AND
FATIGUE

• PROBIOTICS CONSUMPTION OF FOODS CONTAINING LIVE CELLS OF BACTERIA

AND THAT HAVE APPARENT HEALTH BENEFITS HAS GENERATED INTEREST
AMONG CONSUMERS.
• FOOD SPOILAGE IS A METABOLIC PROCESS THAT CAUSES FOODS TO BE
UNDESIRABLE OR UNACCEPTABLE FOR HUMAN CONSUMPTION DUE TO
CHANGES IN SENSORY CHARACTERISTICS.
• SPOILAGE OF FOOD IS IDENTIFIED BY OFF-COLORS, OFF-ODORS, SOFTENING OF
VEGETABLES, FRUITS, AND SLIME PRODUCTION.

• SPOILAGE MAY ARISE FROM INSECT DAMAGE, PHYSICAL DAMAGE, AND

INDIGENOUS ENZYME ACTIVITY IN FOOD OR BY MICROORGANISMS
(BACTERIA, VIRUSES, FUNGI).

CROSS CONTAMINATION OCCURS WHEN MICROORGANISMS PRESENT IN RAW

FOOD, UTENSILS AND CONTAMINATED SURFACES ARE TRANSFERRED TO
COOKED OR WASHED FOODS OR EVEN TO CLEAN SURFACES.
• FOOD SPOILAGE BY MICROORGANISMS DEPENDS UPON INTRINSIC (PH, WATER
ACTIVITY, NUTRIENT CONTENT, OXIDATION-REDUCTION POTENTIAL,
ANTIMICROBIAL PROPERTY) AND EXTRINSIC FACTORS (TEMPERATURE,
RELATIVE HUMIDITY, PRESSURE).

• DIFFERENT SPOILAGE-CAUSING MICROORGANISMS HAVE DIFFERENT NUTRIENTS

REQUIREMENTS.

• MICROORGANISMS ARE THE BIOLOGICAL AGENTS THAT CAUSE FOODBORNE

DISEASES WHEN CONSUMED HOWEVER THE MICROORGANISMS NOT ONLY
CAUSE SPOILAGE, SOME OF THEM ARE BENEFICIAL FOR FOOD FERMENTATION
• BACTERIA IN FOOD
• FOOD IS MOST COMMONLY SPOILED BY BACTERIA AS IT CAN GROW IN A
WIDE VARIETY OF CONDITIONS HOWEVER BACTERIA ARE USED FOR
BENEFICIAL FERMENTATIONS OF PICKLES, MILK PRODUCTS, AND SOME
FERMENTED VEGETABLE PRODUCTS.

• BACTERIA DO NOT GROW AT A WATER ACTIVITY LEVEL BELOW 0.91 AND

REQUIRE NEUTRAL PH (6.5-7) TO CAUSE FOOD SPOILAGE (E.G. MILK,
MEAT, GREEN VEGETABLES, FRUITS, ETC.)

• SOME BACTERIA ARE CAPABLE OF SPORE FORMATION SO THEY ARE

HIGHLY HEAT RESISTANT AND SOME ARE CAPABLE OF PRODUCING HEAT-
RESISTANT TOXINS
• BACTERIA ARE UNICELLULAR ORGANISMS.

• THE CELLS ARE DESCRIBED AS PROKARYOTIC BECAUSE THEY LACK A NUCLEUS.

• THEY EXIST IN THREE MAJOR SHAPES: BACILLUS (ROD SHAPE), COCCUS

(SPHERICAL SHAPE), SPIRILLA (SPIRAL SHAPE)
• THE CONSUMPTION OF SUCH SPOILED FOOD LEADS TO FOODBORNE ILLNESS.

• THE MOST COMMON BACTERIA THAT CAUSE FOOD SPOILAGE ARE-

• GRAM-POSITIVE BACTERIA SUCH AS STAPHYLOCOCCUS AUREUS, BACILLUS SPP,
CLOSTRIDIUM SPP, LACTIC ACID BACTERIA
(LAB), LEUCONOSTOC SPP, STREPTOCOCCUS SPP, BROCHOTHRIX SPP, WEISSELLA SPP, MY
COBACTERIUM BOVIS, ETC.
• GRAM-NEGATIVE BACTERIA SUCH AS SALMONELLA SPP,
SHIGELLA, VIBRIO SPP, ESCHERICHIA COLI, CAMPYLOBACTER JEJUNI, YERSINIA
ENTEROCOLITIS, BRUCELLA SPP, COXIELLA BURNETII, AEROMONAS SPP, PLESIOMONAS
SHIGELLOIDES, ETC.

• THESE BACTERIA CAUSE OFF-ODORS AND OFF-FLAVORS, DISCOLORATIONS, GAS

PRODUCTION, SLIME PRODUCTION, AND DECREASES IN PH.
• ACCORDING TO THE WAY THEIR CELL WALL STRUCTURE STAINS, BACTERIA CAN
BE CLASSIFIED
• 1. GRAM-POSITIVE
• 2. GRAM-NEGATIVE

• BACTERIA CAN BE FURTHER DIVIDED BASED ON THEIR RESPONSE TO GASEOUS

OXYGEN INTO THE FOLLOWING GROUPS:
• 1.AEROBIC (LIVING IN THE PRESENCE OF OXYGEN)
• 2.ANAEROBIC (LIVING WITHOUT OXYGEN)- THOSE BACTERIA LIVE UNDER
WATER
• 3.FACULTATIVE ANAEROBES (CAN LIVE IN BOTH ENVIRONMENTS).
• FUNGI IN FOOD
• FUNGI IS THE MOST ABUNDANT GROUP OF MICROORGANISMS THAT PLAYS
IMPORTANT ROLE IN FOOD SPOILAGE.

• FUNGI ARE OSMOTROPHIC THEY OBTAIN THEIR NUTRIENTS BY ABSORPTION.

• FUNGI CAN BE DIVIDED INTO MOLD AND YEAST.

• FUNGI (MUSHROOM, MOLDS, AND YEASTS) ARE EUKARYOTIC CELLS (WITH A
TRUE NUCLEUS)
• MOLDS
• MOLDS ARE THE MOST COMMON FOOD SPOILAGE-CAUSING MICROORGANISMS.

• MOLDS GROW ON THE SURFACE OF FOOD (THEY REQUIRE FREE OXYGEN FOR GROWTH)
AND IN A WIDE RANGE OF PH VALUES (FROM 2 TO 8.5), BUT THE MAJORITY OF THEM
PREFER ACIDIC PH.

• MOLDS CAN GROW AT VERY LOW WATER ACTIVITY LEVELS (0.7–0.8) ON DRIED FOODS
(E.G. GRAINS, BEANS, PEANUTS, AND SOME SPICES)

• THE MOST COMMON FOOD SPOILAGE CAUSING MOLDS ARE MUCOR, ASPERGILLUS SPP,
RHIZOPUS SPP, PENICILLIUM SPP, ALTERNARIA SPP, BOTHRYTIS, BYSSOCHLAMYS,
FUSARIUM SPP.

• THIS MOLD CAUSES OFF-FLAVORS, MYCOTOXINS CONTAMINATION, DISCOLORATION,

ROTTING, AND IS EXTERNALLY VISIBLE IN THE FOOD.
• YEASTS

• COMPARED TO BACTERIA AND MOLDS, YEASTS PLAY A MINOR ROLE IN FOOD SPOILAGE

• YEASTS CAN GROW WITH OR WITHOUT OXYGEN AND ARE USED FOR BENEFICIAL FERMENTATION IN
BREAD AND ALCOHOLIC DRINKS FERMENTATION.

• THEY OFTEN SPOIL FOOD THAT HAS HIGH SUGAR OR SALT CONTENT (E.G. MAPLE SYRUP, PICKLES,
JAMS, SOY SAUCE, AND SAUERKRAUT.)

• YEASTS REQUIRE A WATER ACTIVITY LEVEL OF 0.90–0.95 FOR GROWTH AND THEY CAN GROW IN A
WIDE RANGE OF PH (3 – 8) BUT IN GENERAL, THEY PREFER ACIDIC PH (4.5-5.5).
• MOST COMMONLY FOOD SPOILAGE CAUSING YEAST
ARE ZYGOSACCHAROMYCES SPP,
SACCHAROMYCES SPP., CANDIDA SPP, DEKKERA SPP

• THESE YEASTS CAUSE A CHANGE IN COLOR, A CHANGE IN TEXTURE, AN

UNPLEASANT ODOR, OR AN UNDESIRABLE TASTE IN FOOD.
• YEAST CELLS MAY BE ROUNDED, EGG SHAPED

• PLAY INITIAL ROLE IN VINEGAR PRODUCTION

• VIRUSES IN FOOD
• VIRUSES ARE OBLIGATE INTRACELLULAR PARASITES THAT CAUSE A WIDE RANGE
OF DISEASES IN PLANTS, ANIMALS, AND HUMANS.

• VIRUSES NEED SPECIFIC LIVING CELLS TO REPLICATE AND THEREFORE THEY

CANNOT REPLICATE IN FOOD OR WATER. THE WATER AND FOOD ACT AS A
CARRIER FOR TRANSMISSION OF VIRUSES FROM ONE HOST TO ANOTHER.

• FOODBORNE VIRUSES ARE QUITE STABLE OUTSIDE THE HOST AND ARE ACID-
RESISTANT.

• SOME OF THE FOODBORNE VIRUSES ARE NOROVIRUS, HEPATITIS A

VIRUS (HAV), HEPATITIS E
VIRUS (HEV), ASTROVIRUS (ASTV), ROTAVIRUS (RV), CORONAVIRUS, SAPOVIRUS (SAV).
• VIRUSES ARE NONCELLULAR ENTITIES THAT CONSIST OF A NUCLEIC ACID
CORE (DNA OR RNA) SURROUNDED BY A PROTEIN COAT.

• ALTHOUGH VIRUSES ARE CLASSIFIED AS MICROORGANISMS, THEY ARE

NOT CONSIDERED LIVING ORGANISMS.

• VIRUSES CANNOT REPRODUCE OUTSIDE A HOST CELL AND CANNOT

METABOLIZE ON THEIR OWN.

• VIRUSES OFTEN INFEST PROKARYOTIC AND EUKARYOTIC CELLS CAUSING

DISEASES.