Food spoilage

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Food spoilage

  1. 1. MICROBIAL GROWTH &FOOD SPOILAGE
  2. 2. Contents• Miracle of Bolsena• BACTERIAL FOOD SPOILAGE• Spoilage in Meat and Dairy Products• Steps in Milk Spoilage• Spoilage in fruits and vegetables• Favourable conditions for Spoilage• Spoilage in citrus fruits and juices• Increase in Water activity aw
  3. 3. • FUNGAL FOOD SPOILAGE• Fungal growth on tomatoes• Fungal growth grains and corn• Ergotism• Fungal toxins• Aflatoxins• Mode of action• Types of Aflatoxins• Ingestion of Aflatoxins• Fumonisins• Type of fumonisins• ALGAL TOXINS
  4. 4. Miracle of BolsenaOne of the most famous is the report of “blood”on communion wafers and other bread, calledthe “Miracle of Bolsena,” which occurred in1263.The mystery was eventually solved byBartolomeo Bizio in 1879, when he describedthe red-pigmented bacterium responsible forthis phenomenon named Serratia marcescens.
  5. 5. BACTERIAL FOODSPOILAGESpoilage in Meat and Dairy Products1. Proteolysis2. PutrefactionSteps in Milk Spoilage1. Acid production by Lactococcus lactis subsp. lactis2. Additional acid production associated with the growthof more acid tolerant organisms such as Lactobacillus.3. Yeasts and molds become dominant and degrade theaccumulated lactic acid4. Protein-digesting bacteria become active, resulting in aputrid odor and bitter flavour.
  6. 6. Spoilage In Fruits AndVegetablesExampleErwinia carotovora, bacteria that causes soft rotsby producing hydrolytic enzymes.Favourable conditions for Spoilage• high oxidation-reduction potential• lack of reduced conditions permitsaerobes and facultative anaerobes to contribute tothe decomposition processesSpoilage initiated by molds.
  7. 7. Spoilage In Citrus FruitsAnd JuicesFood spoilage problems occur with minimallyprocessed, concentrated frozen citrus products.Major spoilage can be caused byLactobacillusLeuconostoc spp.which produce diacetyl-butter flavours.Saccharomyces and Candida can also spoil juices.
  8. 8. Increase In Water Activity awConcentrated juice has a decreased water activity (aw-0.8 to 0.83), and when kept frozen at about -10°C, juices can be stored for long periods.Also, microorganisms in the frozen concentratedjuices can begin the spoilage process after additionof water.Ready-to-serve (RTS) juices present other problemsas aw values are sufficiently high to allowmicrobial growth.
  9. 9. FUNGAL FOOD SPOILAGE• Fungal growth on tomatoes– Alternaria– Cladosporium– Fusarium– Stemphylium• Fungal growth grains andcornMolds mostly– Penicillium (Green)– Rhizopus stolonifer (Black)(a) bread and (b) corn(a)(b)
  10. 10. ErgotismAscomycete Claviceps purpura causes ergotism,a toxic condition.• Hallucinogenic alkaloids produced by thisfungus can lead to1. Altered behavior2. Abortion3. Death
  11. 11. Fungal ToxinsCarcinogens include the aflatoxins and fumonisins.Aflatoxins• Discovered in 1960, Aspergillus flavusMode of action• These flat-ringed planar compounds intercalatewith the cells’ nucleic acids and act as frame shiftmutagens and carcinogens.• Mostly Hepato-carcinogens
  12. 12. Types of AflatoxinsA total of 18 aflatoxins are known. Aflatoxin B1(most potent carcinogen)Aflatoxins B1 and B2, after ingestion by lactatinganimals, are modified in the animal body to yieldthe aflatoxins M1 and M2.Effects1. Potent liver or hepato-carcinogens2. Effects on immune competence3. Growth and disease resistance in livestock andlaboratory animals.
  13. 13. Ingestion of AflatoxinsThe average aflatoxin intake in the typical– European-style diet 19 ng/day– Asian diets 103 ng/dayRisk factorIndividuals who have had hepatitis B have a 30-fold higher risk of liver cancer upon exposure toaflatoxins than individuals who have not hadthis disease.
  14. 14. FumonisinsThe fumonisins are fungal contaminants of corn thatwere first isolated in 1988. These are produced byFusarium moniliforme and cause1. Leukoencephalomalacia in horses (also called“blind staggers”—it is fatal within 2 to 3 days)2. Pulmonary edema in pigs3. Oesophageal cancer in humansThe fumonisins function by disrupting the synthesisand metabolism of sphingolipids
  15. 15. Type of fumonisins• There are at least ten different fumonisins; thebasic structures of fumonisins FB1 and FB2 shown.• The fumonisins inhibit ceramide synthase, a keyenzyme for the proper use of fatty subtances in thecell.• Eucaryotic microorganisms can synthesize potenttoxins other than aflatoxins and fumonisins.
  16. 16. Fumonisin Structure; The basic structure of fumonisins FB1 and FB2 produced byFusarium moniliforme, a fungal contaminant that can grow in improperly stored corn. FB1,R≐OH; FB2, R≐H.
  17. 17. ALGAL TOXINSContaminate shellfish and fin fish,Causative agentsDinoflagellates and DiatomsEffects– Amnesic– Diarrheic– Paralytic shellfish poisoningThese complex toxins, most of which are temperaturestable, are known to cause peripheral neurologicalsystem effects
  18. 18. Any Q?

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