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Microbiology Of Cereals And Cereal Products

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Microbiology Of Cereals And Cereal Products

  1. 1. MICROBIOLOGY OF CEREALS AND CEREAL PRODUCTS PRESENTED BY :- MD KAMIL DEPT. OF FOOD SCIENCE AND TECHNOLOGY MAKAUT, WEST BENGAL
  2. 2. CONTENTS ✓ INTRODUCTION ✓ SOURCES OF CONTAMINATION ✓ SPOILAGE OF CEREALS ✓ SPOILAGE OF CEREAL PRODUCTS ✓ ROPINESS OF BREAD ✓ PRESERVATION OF CEREALS
  3. 3. INTRODUCTION • Cereal grains, such as wheat, corn, rye, oat, rice, etc., are important nutrients and energy sources for humans. • Cereal grains are the most commonly consumed food group worldwide and they are grown on about 60% of the cultivated land in the world. • Cereals are consumed in variousforms in the food industry. • Cooked cereals are eaten directly after cooking (rice, maize). • Flours are made by grinding cereals (such as wheat, maize, rice, and rye) and productsprocessed from them, e.g. biscuits, cookies, etc. • Bread is usuallymade from flours of wheat and rye by yeast fermentation. • Manufactureddried cereal productsproduced from wheat, maize, oats, and rice. • However, cereals are also used to produce dough, batter, pasta, noodles, pastries, cake, etc. • These productsare subject to physical,chemical, and microbiologicalspoilagethat affects the taste, aroma, leavening, appearance,and overallquality of the end consumer product.
  4. 4. SOURCES OF CONTAMINATION • The exteriors of harvested grains retains some of the natural flora they had while growing plus contaminationfrom soil, insects & other sources. • There then is possibility of contaminationduring other procedures such as blending & conditioning. • Freshly harvested grains contain loads of a few thousand to million of bacteria /gm and mold spores. • Bacteria are mostlyin the families Pseudomonas, Micrococci, Lactobacilli and Bacilli. • Scouring & washing the grains remove some of the microorganisms, but mostof the microorganisms are removed with the outer portions of the grains during milling. The milling processes especially bleaching reduce no. of organisms.
  5. 5. SOURCES OF CONTAMINATION • Corn meal and flour containseveral hundredto several thousandbacteria and mold per gram. Species of Fusarium and Penicilliumare dominantmolds. • The surface of freshly baked bread is free of viablemicroorganisms but is subject to contaminationby molds spores from the air during cooling& before wrapping. • Cakes are similarlysubject to contamination.Spores of bacteria able to cause ropiness in bread will survive the baking process. • The contaminationof cereals grains productswith molds such as Fusaria & Penicilliumhas become a significant concern because of the presence of mycotoxin. •Bacteria in wheat flour includespores of Bacillus, coliform bacteria ,and few representativesof the genera Achromobacter, Flavobacterium,Sarcina, Micrococcus and Serratia. Moldspores are of Aspergillus, penicillium,Alternaria & Cladosporium.patent flours usuallygive lower countsthan straight or clear & no. Decreases with storage of flour.
  6. 6. SPOILAGE OF CEREALS • Spoilage is the term used to describe the deterioration of food texture, color, odour or flavor to the point where it is unappetizing or unsuitablefor human consumption. • Cereals usually contain 70–75% carbohydrates, 8–15% protein, fat, fiber, vitamins,and minerals with near-neutral pH and hence are susceptible to microbial growth leading to spoilage. • Microbial growth is normally prevented due to sufficiently low water activity (i.e. Below 0.70). • Mold is considered the primary organism for causing spoilage in cereal. • Bacteria can also cause spoilage of cereals, but yeasts cause few spoilage problems.
  7. 7. SPOILAGE OF CEREALS • The most commonly associated bacterial familieswith cereals are Bacillaceae, Micrococcaceae, Lactobacillaceae, and Pseudomonadaceae. • Yeast that is found in cereal includes Candida, Cryptococcus, Pichia, Sporobolomyces, Rhodotorula, Trichosporon. • Mold spores in cereals and flour are chiefly Aspergillus, Penicillium,Alternaria, Mucor, Cladosporium, Fusarium, Helminthosporium,Cladosporium, and Rhizopus. • Mycotoxins are the toxic secondary metabolites produced by mold that is found in cereal crops under favorable growth conditions. The genera of molds producing mycotoxins are Aspergillus, Penicillium, and Fusarium.
  8. 8. SPOILAGE OF CEREALS MOLDS MYCOTOXINS Aspergillus Parasiticus Aflatoxins B1,B2, G1, G2 Aspergillus Flavus Aflatoxins B1, B2 Penicillium Islandicum Islanditoxin,Luteoskyrin Fusarium Sporotrichioides Trichothecenes : T-2 toxin • Some examples of mycotoxins and the mold that produce them are :
  9. 9. SPOILAGE OF CEREALS MICROORGANISMS DEFECTS IN CEREALS Alternaria, Fusarium, Drechslera, Cladosporium and Botrytis Blights and Blemishes Aspergillus fumigatus,A. Penicillioides, A. ochraceus Discolored germs A. candidus Powdery white patches A. flavus Greenish discoloration Eurotium Discolored germs, green eye Fusarium Red streaking, particularly on maize Penicillium Blue coloration Alternaria Darkening Fusarium or Alternaria Pink or black tips on wheat • Some of the microorganisms and the defects caused by them in cereals are :
  10. 10. SPOILAGE OF CEREAL PRODUCTS (FLOUR SPOILAGE) • The moisture content of flour is less than 13% that prevents the growth of microorganisms. • However, the addition of water to flour tends to make it susceptible to microbial growth in flour. • The molds found in flours are mostly Eurotium species and Aspergillus candidus. The molds produce typical mycelium in flour. • The spoilage flour contains many psychrotrophs, flat sour bacteria, and thermophilic spore-forming bacteria such as Acetobacter spp, Bacillus spp, Lactic acid bacteria. • If acid-forming bacteria are present in flour, acid fermentation occurs followed by alcoholic fermentation by yeasts and then acetic acid by Acetobacter spp. • Bacillus spp is known for producing lactic acid, gas, and acetoin in flour.
  11. 11. SPOILAGE OF CEREAL PRODUCTS (SPOILAGE OF BAKERY PRODUCTS) • There are a wide variety of bakery products including leavened and unleavened bread, rolls, buns, croissants, muffins, cakes, doughnuts, pastries, pancakes, waffles, biscuits, cupcakes, and sweet rolls. • The nutrient content of bakery products includes carbohydrates, proteins, lipids, vitamins, and minerals. • Therefore, bakery products are susceptible to microbial growth due to their high nutrient content and also because the most commonfactor of these products is water. • The most famous bakery product that is consumed worldwide for a very long period is bread. • The ambient temperatures, product pH levels between 5.4 and 7.5, and water activity in the range of 0.75–0.98 promote spoilage of baked cereal foods with mold, yeast, and rope bacteria.
  12. 12. SPOILAGE OF CEREAL PRODUCTS (SPOILAGE OF BAKERY PRODUCTS) • The most common source of microbial spoilage of bread is mold growth. The bacterial spoilage condition is known as ‘rope’ caused by the growth of the Bacillus species. The least common of all types of microbial spoilage in bread is that caused by certain types of yeast. • Typical genera of mold involved in spoilage are Penicillium, Aspergillus, Cladosporium, Fusarium, Monilia, Endomyces, Rhizopus, and Mucor. • Yeasts that can cause surface spoilage of bakery products include Saccharomyces, Debaryomyces, Kluyveromyces, Pichia, Candida, and Zygosaccharomyces. • Pastry spoilage is similar to bread, but the pastry filling or topping is more susceptible to microbialgrowth. • However, due to high sugar concentration, pastries are rarely spoiled by bacteria. • The most common spoilage is caused by mold. They cause sugar fermentation and make them sour in taste with an alcoholic odor.
  13. 13. SPOILAGE OF CEREAL PRODUCTS (ROPINESS OF BREAD) • Ropiness of bread is fairly common in home baked bread, especially during hot weather ,but it is in commercially baked bread because of preventive measures now employed. • Ropiness is caused by a mucoid variant of Bacillus subtilis. • The spores of these species can withstand the temperature of the bread during baking , which does not exceed 100 ̊C , can germinate and can grow in the loaf if conditions are favorable. • The area of ropiness is yellow to brown in color & is soft, sticky to touch. In one stage the slimy material can be drawn out into long threads when the bread is broken and pulled apart first the odour is evident ,then discoloration and finally softening of the crumb , with stickness and stringiness.
  14. 14. SPOILAGE OF CEREAL PRODUCTS MICROORGANISMS DEFECTS IN BREAD Rhizopus stolonifer (bread mold) White cottony mycelium & black rot Penicillium expansum Green colour Aspergillus niger Greenish or purplish- brown to black color Moniliasitophila Pink or reddish colour on bread Aspergillus glaucus Green and gray- green colour Aspergillus flavus Olivegreen colour MICROORGANISMS DEFECTS IN BREAD Mucor Gray colour Endomycopsis fibuliger Trichosporon variable Chalky defect Bacillus subtilis, Bacillus mesentericus, Bacillus licheniformis, Clostridium spp, Lactobacillus spp, Leuconostoc spp. Ropiness Serratia marsescens Red or bloody bread Saccharomyces cerevisiae Alcoholicoff-flavour • Some defects observedon bread due to microbial spoilage are :
  15. 15. SPOILAGE OF CEREAL PRODUCTS (PASTA AND NOODLE SPOILAGE) • Both pasta and noodle manufacture includes no cooking step, microbial contamination may occur during the mixing and drying process. • They are stored and distributed in dry form so spoilage is rare. • During the manufacturing process, it may spoil from bacterial or fungal growth. • For example, Enterobacter (Aerobacter) cloacae have been found in pasta and noodle that causes gas production. • Cooked and fresh homemade pasta shouldbe stored in the refrigerator to slow moldgrowth and preserve its freshness as long as possible.Most pastas last in the fridge for 3–5 days.
  16. 16. PRESERVATION OF CEREALS • There are several methods of preservation of cereals : ASEPSIS : Improperly sanitized equipmentsmay be source of rope bacteria and the acid –forming bacteria that cause sourness of dough. Bread, cakes and other baked products may be subject to spoilage by molds should be protected against contamination by mold spores. USE OF HEAT : Bakery products may be sold unbaked, partially baked or fully baked .the completebaking process destroys all the bacterial cells, yeasts ,mold spores but not spores of rope –forming bacteria.they can surviveduring heat so unbaked products are kept for short period or kept cool during longer storage of time.
  17. 17. PRESERVATION OF CEREALS USE OF LOW TEMPERATURE : Baked products should be kept under cool conditions or refrigerated in home for the prevention of food spoilage. These can be stored for months in the frozen conditions. USE OF CHEMICAL PRODUCTS : A large number of preservatives have been employed particularly as mold inhibitors, in breads, rolls, cakes. Sodium and calcium propionate, sodiumdiacetate and sorbates are used extensively.acidification of dough with acetic acidhas been used to combat rope. USE OF IRRADIATION : In bakeries, ultraviolet rays have been used to destroy or reduce the numbers of mold, bacteriain dough and proof rooms, on the knives of slicing machine , on the surface of breads ,cakes. ionizing radiations, gamma and cathode rays have been applied experimentally for the preservation of baking goods.
  18. 18. THANKYOU

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