Spoilage of Dairy, Meat and Fish Products Of all foods, dairy, meat and fish products are more vulnerable for microbial growth High nutrient content High level of simple nutrients Favorable pH High water activity Absence of antimicrobial factors
FT 5105 Food Microbiology 2 The quality and safety of milk, dairy, meat and fish products are of primary concern in the industry 30 million cases of foodborne diseases are reported each year in the U.S. at a cost of $5-8 billion annually and 900 fatalities. The incidence rate in Canada is estimated at 2.2 million cases per year at a cost of $ 1-3 billion annually.
FT 5105 Food Microbiology 3 Common foodborne pathogens in dairy
Salomnella typhimarium Salmonella typhi Camphylobactor E coli (verotoxigenic) Listeria monocytogenes
FT 5105 Food Microbiology 4 Dairy Products
Milk is very nutritious Fresh milk contains MOs of a large variation The type and number depend on the hygienic conditions of the dairy farm, cleanliness of utensils etc. Milk contains lactoperoxidase and agglutinins but not effective
5 Point of sampling Range (SPC/mL)
Aseptically drawn milk 500-1000
Milk pail/machine 1000-10,000
Bulk tank 5000-20,000
6 Diseases potentially arises from contaminated milk
Tuberculosis Diphtheria Scarlet fever Brucellosis
Mycobacterium paratuberculosis post-pasteurization contamination This may be as a result of cross- contamination of finished product with raw product, inadequate sanitation procedures in the plant environment, or inadequately sanitized equipment.
FT 5105 Food Microbiology 8 Commonly found spoilage bacteria in milk Enterococcus Lactococcus Streptococcus Leuconostoc Lactobacillus Microbacterium Propionibacterium Proteus Pseudomonas Upon pasteurization all Mos are destroyed except thermodurics (Micrococci, Enterococci, Lactobacilli and Sterptococci), spore formers of Bacillus group and spores 72C for 15 sec. may go up to 79 for 25 sec. Pasteurized milk is spoilt by heat resistant Streptococci that utilize lactose
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They produce lactic acid which brings pH down to 4.5 thus, leading to curdling Molds can grow on the surface bringing pH up to neutrality Thus, proteolytic type bacteria can start growing Proteolytic Pseuodomonas can quickly grow and liquefy curdle
10 Raw Milk
Milk spoilage Sourness Flavor changes Curdling Color changes Gas formation Fermentaiton
11 Sourness is developed and thus pH decreases Curdling happens and then whey is released Lactic acid formation is the major cause Raw milk held at 10-37 is more likely to be fermented by Streptococcus lactis In addition Colifirms, Enterococci, 12 Lactobacilli and Micrococci also contribute • 37-50C • Sterptococcus thermophillus and S. faecalis • Little acid is formed at elevated temperatures
• Gas production (hydrogen and carbon dioxide) is carried out by Clostridia • Gas production is evidenced by frothing on top • Proteolysis is favored at low temperatures
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Proteolysis 1. Acid proteolysis 2. Proteolysis with little acidity 3. Sweet curdling
14 Ropiness (Sliminess) in Milk
Bacterial and non-bacterial Bacterial sliminess is due to the slimy capsular materials from cells (gums and mucins) Developed mostly at low temperature Caused by Alcaligenes viscolactis This is favored by low holding temperatures 15 1. Surface ropiness Alcaligenes viscolactis Grows best at 10C and Micrococcus spp.
2. Ropiness throughout and Klebsiella oxytoca, Enterobacter cloacae
Alkaline producers Pseudomonas fluorescens and A. viscolactis 16 Hydrolysis Color changes Blue milk Yellow milk Red milk Brown milk
17 Flavor changes
• Cheesiness • Rancid • Beany • Musty • Flat flavor • Unclean • Malty • yeasty
18 Foods can be categorized into 3 groups on the basis of spoilage Stable – nonperishables – sugar, flour, dry seeds, cereals Semiperishable foods – potatoes, nuts Perishable foods – meats, fish, poultry, eggs, dairy etc.
FT 5105 Food Microbiology 19 Spoilage can happen due to
Growth and activity of MO Damages due to insects Physical damages Enzymic action Non-enzymatic chemical reactions Physical changes due to freezing, burning drying, high temperature etc.
FT 5105 Food Microbiology 20 Number and type of MO in a food depend on Source – where the food is originated Microbial quality of raw materials Sanitary conditions under which food is handled/processed Subsequent packaging/handling/storage Inner parts of plant or animal tissues are sterile Contaminations are most likely to happen
FT 5105 Food Microbiology 21 Thus, the microbial number in a fresh product reflects the quality of it Therefore SPC is an important criterion in determining the quality of a fresh product
FT 5105 Food Microbiology 22 Spoilage of Meat and Meat Products
FT 5105 Food Microbiology 23 Composition of Meat
Constituent Percentage water 75 Protein 19 Lipids 2.5 CHO 1.2 Soluble NPN 1.65 Minerals 0.65
FT 5105 Food Microbiology 24 Tissues of healthy animal are relatively free of MOs Microbial count of freshly slaughtered animal tissues is less than 10 cfu/Kg Most contaminated areas of animal body are hide and GIT Number and type of MOs depend on the envt. The animal lived
FT 5105 Food Microbiology 25 Animal hide contains Micrococci Staphylococci Pseudomonas Yeasts and molds Viscera contains large no. of MOs including pathogens Surface microbial count goes up to 102- 104/Cm2 Generally lamb and pork contains more MOs than beef
FT 5105 Food Microbiology 26 Skinning is not usually done with poultry Thus, skin MOs are not removed GIT of poultry too contain very high no. of MOs and pathogens such as Salmonella and Campylobacter
FT 5105 Food Microbiology 27 Common Genera of Bacteria Found in Meats Genus Fresh Vacu. Poultry Sea food Acenetobacter Aeromonas Alcaligenes Bacillus Brocathrix Carnobacterium Corynebacterium Enterobacter Enterococcus
FT 5105 Food Microbiology 28 Genus Fresh Vacu. Poultry Sea food Escherichia Flavobacterium Lactobacillus Listeria Micrococcus Moraxella Pseudomonas Psychrobacter Shewanella Salmonella
FT 5105 Food Microbiology 29 Genus Fresh Vacu. Poultry Sea food Staphylococcus Vibrio
FT 5105 Food Microbiology 30 Common Molds in Meats Genus Fresh Poultry Proces Fish & sed Seafood Alternaria Aspergillus Botrytis Cladosporium Fusarium Geotrichum Mucor Penicillium Rhizopus Thamnidium FT 5105 Food Microbiology 31 Comminuted meats contain more MOs Ground meat contains trimmings Higher surface area – most spoilage MOS are aerobic Handled many times – contaminated blades, saws, utensils One heavily contaminated piece can inoculate the whole lot Organ meats such as kidney, liver, tongue, heart contain less MO
FT 5105 Food Microbiology 32 MOs in Vacuum packaged meat – mainly Pseudomonas Oxygen permeability determines the refrigerated storage life The higher the permeability the lesser the storage life When permeability is very low CO2 concentration goes up and this favors LABs an Brochothrix
FT 5105 Food Microbiology 33 Common bacteria in vacuum packaged meats Streptococci Bacillus Micrococci Moraxella Acinetobactor Pseudomonas
FT 5105 Food Microbiology 34 Spoilage Most common indications of spoilage are Off odor and slimy surface due to the action of aerobic bacteria on the cut surfaces Fungal growth favored at water activity low for bacterial growth Bone taint = deep spoilage due to anaerobic or facultative MOs Discolorations due to change of myoglobin color
FT 5105 Food Microbiology 35 A. Under aerobic conditions Bacteria Surface slime Changes in meat color Changes in fat Off odors and off tastes Yeasts Sliminess Lipolysis, off odors and tastes White, cream-pink, brown colors due to yeast pigments
FT 5105 Food Microbiology 36 Molds Stickiness Whiskers – Thamnidium, Mucor and Rhizopus Black spots - Cladosporium White spots – Chrysoporium Green patches – Penicillium Decomposition of fats, off odors and tastes
FT 5105 Food Microbiology 37 Under anaerobic conditions Souring Putrefaction – production of foul smell under anaerobic conditions – hydrogen sulfide, mercaptans, indole, skatole, ammonia, amines. When meat is stored in refrigerated conditions psychropilic and psychrotropic MOs attack Sliminess Discolorations & souring
FT 5105 Food Microbiology 38 Alcaligenes Lactobacillus Leuconostoc Mainly responsible MOs Streptococcus Flavobaterium
FT 5105 Food Microbiology 39 Molds do not grow on meats at temperatures less than -5C Candida and Rhodotorula are partly responsible for spoilage of refrigerated meat Ground meat is exclusively spoilt by bacteria Pseudomonas Acinetobacter
FT 5105 Food Microbiology 40 Growth of MO on meat
1. Type and quantity of MO E.g. If psychrotroph population is high very high chance of spoilage under chilling conditions 2. Physical properties of meat The quantity of meat exposed to air has a great influence
FT 5105 Food Microbiology 41 Mincing of meat greatly increases spoilage Mincing increases aeration, distribute Mos throughout the mixture and releases moisture from tissues 3. Chemical properties of meat pH Moisture content – surface may go dry - this will promote mold growth
FT 5105 Food Microbiology 42 Low in CHO thus non fermenting Mos grow well 4. Availability of oxygen Aerobic conditions favor mold and yeast growth on the surface True putrefaction is favored by anaerobic conditions
FT 5105 Food Microbiology 43 5. Temperature Putrefaction is very low at low temperatures At room temperature mesophiles grow and produce moderate amounts of acids using limited quantities of CHO.
FT 5105 Food Microbiology 44 Types of Spoilage
1. Surface Sliming Caused by Pseudomonas, Acinetobacter, Moraxella, Alcaligenes, Streptococcus, Leuconostoc, Bacillus and Micrococus In addition, some Lactobacilli too can produce Temperature and moisture mainly determine the type of MO
FT 5105 Food Microbiology 45 At chilling temperatures with high moisture – Pseudomonas and Alcaligenes Less moisture favors Micrococus 2. Color changes Red color may change to green/brown or gray Color change is mainly due to production of oxidizing compounds
FT 5105 Food Microbiology 46 Different colored spots are developed Red spot – Serratia marcenscens growing on surface Blue spots – Pseudomonas synscyaneae growing on surface Yellow coloration – Micrococcus
FT 5105 Food Microbiology 47 Greenish-blue or brownish black spots – Chromobacterium lividum Purple (stamping ink color) – discoloration by yellow pigmented cocci and rods due to discoloration of surface fat Off odors and taste Called taints Sour odor is formed by acids
FT 5105 Food Microbiology 48 Leuconostoc, Heterofermentative Lactobacilli are mainly responsible 3. Changes in fat Unsaturated fatty acids undergo oxidation Hydrolysis Adds off flavors to meat
FT 5105 Food Microbiology 49
B – Under Anaerobic conditions
1. Souring – due to Acetic, succinic, butyric, propionic and higher FAs 2. Putrefaction True putrefaction is due to decomposition of proteins under anaerobic conditions – produce foul smell – hydrogen sulfide, mercaptans, skatole. Ammonia and amines
FT 5105 Food Microbiology 50 Psuedomonas and Alcaligenes species are mainly responsible Species ending with putrefaciens, putida, putrificum Clostridium produces gases such as H and CO2
FT 5105 Food Microbiology 51 3. Taint development – Pseudomonas Acinetobacter Moraxella Alcaligenes Lactobacillus Leuconostoc, Streptococcus, Flavobacterium
FT 5105 Food Microbiology 52 Number of Mos at the time of appearance of odor and slime
Type When Odor is Slime is identifiable identifiable (X106/cm) (X106/cm)
Poultry 2.5-100 10-60 Beef 1.2-100 3-300 Frankfurters 100-130 130 Bacon 1.5 -100 Fish 1-130
FT 5105 Food Microbiology 53 Spoilage of fresh beef
1. changes in hemoglobin and myoglobin 2. white, green, yellow and greenish blue or brown spots and purple discoloration 3. Phosphorescence – 4. Spots due to bacteria, yeasts and molds
FT 5105 Food Microbiology 54 Cured meat
Curing selectively favor the growth of Lactic acid bacteria Pathogens are destroyed
FT 5105 Food Microbiology 55 Sausages
Bacterial growth in encased sausages is possible On the casing Between the casing and meat Interior meat Greening is common in sausages
FT 5105 Food Microbiology 56 Greening is favored by slightly acidic pH and little oxygen This happens 12-36 after production even under refrigerated conditions Production of peroxides, mainly H2O2 is attributable
FT 5105 Food Microbiology 57 Lactobacillus and Leuconostoc and other catalase negative bacteria are responsible for peroxide production
FT 5105 Food Microbiology 58 Bacon
Molds are common Aspergillus, Fusarium, Mucor, Rhizopus, Monilia, Oidium, Botrytis and Penicillium Streptococcus faecalis – salt tolerant and can grow at low temperatures Micrococcus can be present on surface
FT 5105 Food Microbiology 59 Sausage, Frankfurters, Bologna etc.
Three major types Souring – caused by Lactobacilli, Enterococci. Sliminess – also known as slimy spoilage occurs on the outside of the casing Greening – two types of greening can
occur by H2O2 and H2S
FT 5105 Food Microbiology 60 Greening due to H2O2 occurs mainly in frankfurters and other vacuum packaged meats Generally appears after exposing anaerobically stored meat into air
Upon exposure to air H2O2 is produced and it reacts with nitrosohemochrome This produces green color oxidized porphyrin
FT 5105 Food Microbiology 61 Greening also occurs due to the
accumulation of H2O2 in the core where Redox potential is low. Lactobacillus viridescens is the major causative agent
H2S type greening occurs in fresh red meats held at 1-5C packed in vacuum packages
H2S reacts with myoglobin to produce sulphmyoglobin
FT 5105 Food Microbiology 62
Microorganisms in cured meat
MO type Meat Salami Lactobacilli Bologna Leuconostoc mesenteroides , hetero Lactobacilli Pork (fresh) Leuconostoc, Lactobacillus, Pseudomonas Bacon Lactobacilli, Micrococcus Ham Lactobacilli, Micrococcus, Microbacterium
FT 5105 Food Microbiology 63 POULTRY Poultry is mainly spoilt by Pseudomonas Acinetobacter Flavobacterium Corynebacterium Fungi is less importance in poultry spoilage Main symptom of poultry spoilage is sliminess on the surfaces and cut surfaces
FT 5105 Food Microbiology 64 Unlike meats in poultry spoilage is mainly restricted to the surface The inner tissues do not contain high no. of Mos Pseudomonas is the major spoilage organism which forms colonies on the surface which finally coalesce to form sliminess
FT 5105 Food Microbiology 65 Methods to Determine Meat Spoilage
Measurement of
Mercaptans, H2S, TMA, tyrosine complexes Catalase, creatinine, hypoxanthine Lactic acid Change in color pH changes RI of meat juices Impedance
FT 5105 Food Microbiology 66 Bacteriological Methods
Total aerobes Total anaerobes Ratio of aerobes to anaerobes
Extract Release Volume (ERV) This method is used to measure spoilage and potential shelf life
FT 5105 Food Microbiology 67 ERV is the volume of aq. Extract released by a homogenate of meat when allowed to pass through a filter paper
Detection of foul odor due to H2S etc. happens only when amino acids are started to be utilized
FT 5105 Food Microbiology 68 Dark firm and dry meats (DFD) have high pH values (>6) are spoilt quicker than other meats In vacuum packed meats – nitrites control Bacillus thermoscapta Lactobacillus is insensitive to nitrites and thus they predominate
FT 5105 Food Microbiology 69 Spoilage of Fish and Shellfish
FT 5105 Food Microbiology 70 Fat is interspersed between muscle fibers Little connective tissues In non-fatty fish fat content is 0.5% Fatty fish may contain from 3-25% Contains 1% CHO
71 Like meat, fish and other sea foods are spoilt by Autolysis Oxidation and Microbial activity Fish muscles are more quickly spoilt than meats due to higher enzyme activity Presence of highly unsaturated fats and Higher pH
72 Factors affecting fish spoilage
Type of fish Flat fish spoil more rapidly than the round fish as flat fish undergo rigor mortis rapidly Fish with high content of PUFA undergo deterioration rapidly Condition when caught Struggled, exhausted fish spoil faster Fish underwent lack of oxygen conditions
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Fish with the full gut contents are more perishable The extent of contamination Microbes come from water, mud, slime on the surface and gut contents Gills are rich in MOs The greater the microbial load the quicker the spoilage is
74 Spoilage might start in the net during transporting etc.
75 Microflora associated with fish
Depends upon the environment they live in They can be contaminated during catching, handling and storage The slime is rich in Pseudomonas Alcaligenes Micrococcus Flavobacterium
76 Corynebacterim Serratia Vibrio Bacillus Fish intestine is rich in Alcaligenes Pseudomonas Vibrio Bacillus Clostridium E coli
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Skin contains 102-107 cfu/cm2 Gills and guts 103 – 109 cfu/g Most crucial factor in fish spoilage is temperature Fish stored at 0C starts spoiling with a lag of 1-2 days In fish spoilage the following microbes become dominant Pseudomonas Acinetobacter and Flavobacterium
78 As spoilage progresses the Pseudomonas population increases rapidly The type of species changes with spoilage When temperature is increased Pseudomonas population goes down and mesophilics start dominating Trimethylamine oxide (TMAO) naturally present in fish is reduced to TMA This is a volatile compound and
79 responsible for the fishy odor
As spoilage progresses volatile bases, amines and organic acids are formed due to decarboxylaiton or deamination of amino acids Hydrogen sulfide, mercaptans and disulfides are the main compounds producing the odor other than TMA Spoilage organisms use TMAO, creatine, taurine, anserine and amino acids
80 Total volatile compounds include Total volatile bases (TVB) Total volatile acids (TVA) Total volatile nitrogen (TVN) Total volatile substances (TVS) Fish odor is explained as a complex of Fishy stale
81 ◦ Musty ◦ Rancid ◦ Sour ◦ Ammonical ◦ Fruity and ◦ Acids
Discoloration of fish leads to development of green and yellow colors Pseudomonas fluorescens is mainly responsible
82 Histidine present in fish is converted to histamine by bacteria Only bacteria that have decarboxylase enzymes can do the converion Histamine is associated with scombroid poisoning
83 Indicators of Fish Spoilage
Histamine Cadaverine – a diamine Putrescine – a diamine Total volatile substances
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