Applied Microbiology for Food Safety Program Lecture Notes PDF

Applied Microbiology for Food Safety Program Food Microbiology Dr. Hamed Abou-Aly Professor of Agricultural Microbiology Benha University FOOD MICROBIOLOGY Food microbiology is the study of the microorganisms that inhabit, create, or contamin...

Applied Microbiology for Food Safety Program Food Microbiology Dr. Hamed Abou-Aly Professor of Agricultural Microbiology Benha University FOOD MICROBIOLOGY Food microbiology is the study of the microorganisms that inhabit, create, or contaminate food. It includes: Microorganisms that cause food spoilage Pathogenic microbes that are transmitted via food Microorganisms that are used to manufacture a wide variety of food and food products Microorganisms that have other beneficial roles, such as probiotics Food Safety Food Safety refers to handling, preparing and storing food in a way to best reduce the risk of individuals becoming sick from foodborne illnesses or diseases. Food spoilage The process that leads to a product becoming either undesirable or unacceptable for human consumption (changes in taste, smell, appearance or texture, flavor, and stability of the food) These changes are made of the food also sometimes becoming toxic. The changed food is called spoiled food. Food poisoning Food poisoning (also referred to as Foodborne diseases) is an illness caused by eating contaminated food with any foodborne pathogens (bacteria, molds, or virus) or their toxins. Food poisoning includes foodborne intoxications and foodborne infections foodborne intoxications vs foodborne infections  Benefits of Microorganisms in food People often think of bacteria and other microorganisms as harmful, but the fact is the opposite. Most of bacteria are helpful. Beneficial effects: Fermentation Digest food ▪ Production of metabolites Destroy pathogens ▪ Organic acids Produce vitamins ▪ Antibiotics Single cell protein ▪ Fermented food ▪ Cheese Probiotics ▪ Yogurt ▪ Fermented sausage Single cell protein Single cell protein (SCP) refers to dead, dry cells of microorganisms, such as yeast, fungi, bacteria, and algae. SCP have nutritional quality in protein content, vitamins, fats, and minerals etc. Advantages of SCP Need for SCP ❑ High protein and essential amino acids content. ▪ An idea to solve global food scarcity. ❑ Some microorganisms are rich in vitamins. ▪ Give relief to the agriculture sector ❑ High growth rate. which uses large area for production of protein crops. ❑ Flexibility in the use of substrate. ▪ SCP technology is not affected by ❑ Independence of cultivable land and climate. climate. ❑ Eco-friendly and low cost. The selection criteria of microorganisms Several microorganisms, such as algae, fungi, protozoa and bacteria can used for production of SCP when have the following criteria: High protein and nutritive value of cell mass. Non-toxic. Non-pathogenic. Able to utilize different carbon and nitrogen sources. Moderate growth conditions. Tolerate to pH, temperature, and mineral concentrations. Resistant against viral infection.  Microorganisms used in SCP production Algae and Cyanobacteria: Spirulina (is used most extensively), as well as biomass from Chlorella and Scenedesmus used on large scale. But the main problems for SCP from algae are their foul odor and tastelessness. Algae are rich in proteins (40-60 %), fats, vitamins, minerals and nucleic acid. Yeasts: Saccharomyces and Candida are good candidates for SCP production, due to their ability to withstand abiotic conditions. Dry yeast contains about 50% proteins. Yeasts contains lysine, thiamine, biotin, riboflavin, niacin, folic acid, but deficient in methionine. Molds: Aspergillus, Chaetomium, Trichoderma, Penicillium etc. are good candidates for SCP production, due to their wide range of substrate utilization. Fungi contains the B-complex group of vitamins, and the amino acid content is reasonably high. Bacteria: Bacillus and Lactobacillus are used for SCP but the success is not so encouraging. the crude protein content is around 80% of the dry weight. SCP Production Processes The production of single cell protein takes place in fermentation Screening of the potent strains of microorganisms which are multiplied on suitable raw materials The technical conditions of cultivation for the optimized strains are done Large technical scale of SCP was done using : Submerged fermentation (SmF) Solid state fermentation (SSF) Semisolid fermentation  Submerged fermentation SmF Cultivation of the microorganisms is carried out in liquid medium containing more than 95% water. The fermentation process was conducted in bioreactor (fermenter) Aeration is an important operation in cultivation. Microbial biomass can be harvested by centrifugation (for single cell organisms like yeast and bacteria) or filtration by filamentous fungi. There are three types for SmF: Batch – Fed batch - Continuous Solid state fermentation (SSF) SSF is distinguished by the absence of a liquid medium but used a solid culture substrate, such as rice or wheat bran, on flatbeds after seeding it with microorganisms Moisture content in the substrate about 12-15% The substrate is then left in a temperature-controlled room for several days Most of SSF processes are batch fermentation Aeration is generally done via mixing or agitation of the media Semi solid fermentation Production involves basic steps of preparation of suitable medium with water content about 30-60%. Stirring and mixing of a multiphase system, transport of oxygen from the gas bubbles through the liquid phase to the microorganisms. Problems associated with SCP technology About 70 to 80% of the total nitrogen is represented by amino acids while the rest occur in nucleic acids The concentration of nucleic acid is higher than other conventional protein sources High nucleic acid containing protein (18-25 g/100g protein dry weight) is the production of high concentration of uric acid level in the blood causing health disorders such as kidney stone The microbial cell wall may be indigestible There may be intolerable colors and flavors (especially in algae) and in yeast The filamentous fungi show slower growth rate than yeasts and bacteria there is high contamination risk, and some strains produce mycotoxins Probiotics Probiotics (for-life) defined as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host” (Probiotic + Prebiotic = Synebiotic) Saccharomyces boulardii Prebiotic Prebiotic was described as “a non-digestible food A few compounds of fibers ingredient that beneficially affects the host by and carbohydrate, such as selectively stimulating the growth and/or activity Fructo-oligosaccharides and of one or a limited number of bacteria in the galacto-oligosaccharides can colon, and thus improves host health” be classified as prebiotics The following criteria are used to classify a compound as a prebiotic: (i) It should be resistant to pH of stomach, cannot be hydrolyzed by host enzymes, and should not be absorbed in the gastrointestinal tract (ii) It can be fermented by intestinal microbiota (iii) The growth and activity of the intestinal bacteria can be selectively stimulated by this compound and this process improves host’s health Types of microorganisms used as probiotics Probiotics may contain a variety of microorganisms Lactic acid bacteria, mainly the Lactobacillus and Bifidobacterium genera. Other genera are also used such as the Enterococcus, Streptococcus, Leuconostoc genera Other bacterial genera not included in lactic acid bacteria, such as Escherichia coli or Propionibacterium The yeast Saccharomyces boulardii has also been used for several decades Bifidobacterium Bifidobacterium are gram positive, strictly anaerobic, non-spore- forming, and usually branch-shaped, rod bacteria. The oxygen-poor environment in the large intestine makes the perfect home for them. Bifidobacterium are known as LAB (Lactic Acid Bacteria) as they ferment carbohydrates and produce lactic acid. Bifidobacteria are known to have the ability to break down oligosaccharides, complex carbohydrates (prebiotics). Lactic acid produced by Bifidobacterium helps to inhibit the growth of pathogenic bacteria Bifidobacteria also produce a large amount of acetic acid, a short chain fatty acid (SCFA), which is more effective than lactic acid on yeasts and moulds in the gut environment Bifidobacterium animalis - B. breve - B. lactis Lactobacillus Lactobacillus are rod-shaped, gram-positive, non-spore- former, nonmotile and can survive in both aerobic and anaerobic environments. Lactobacillus are characterized by their ability to produce Lactic acid from lactose fermentation. Amount of lactic acid produced by different Lactobacillus species varies. L. acidophilus, L. casei, and L. plantarum, described as homofermentative (lactic acid representing at least 85 % of end metabolic products). However, L. brevis and L. fermentum, is heterofermentative, with lactic acid making up about 50 % and ethanol, acetic acid, and carbon dioxide making the other 50 %. Lactobacillus are commensal inhabitants of the gastrointestinal tracts, as well as the human mouth and the vagina. Commercial preparations of lactobacilli are used as probiotics to restore normal flora after the imbalance created by antibiotic therapy. Saccharomyces boulardii Saccharomyces boulardii is a tropical strain of yeast, oval cells with thick-walled cells, can grow under aerobic or anaerobic conditions S. boulardii is used as a probiotic with beneficial microbes into the large and small intestines and conferring protection against pathogens, produce proteins that inhibit pathogenic bacteria and their toxins Tolerates human body temperature, gastric acid, and digestive enzymes S. boulardii is currently classified as Saccharomyces cerevisiae var. boulardii  Mode of actions of probiotics Competitive exclusion (colonization capacity Produce lactic acid and short-chain fatty which preventing or limiting pathogenic acids (SCFAs) such as acetic acid and bacteria colonization) benzoic acid that induces a decrease of the pH (little favorable for pathogens Competition for binding sites and inhibition of Produce antibacterial compounds, adhesion with pathogenic bacteria not by including bacteriocins and small interacting with the epithelial cells themselves antimicrobial peptides (AMPs) but by forming aggregates with the pathogens, thereby preventing them from associating Modulate the immune system by closely with the cell surface induction of anti-inflammatory cytokines Improve the gut mucosa by preventing any direct contact with bacteria of the intestinal Probiotics possess functions such as lumen by producing antimicrobial peptides antiallergic activity and stimulation of calcium uptake