Microorganisms in Food Industry

Beneficial Microorganisms in Food Industry

• Microorganisms are used in the food industry in several ways, including:
  • Actively growing cells for fermentation
  • Metabolic by-products, such as bacteriocins, vitamins, amino acids, and Single-Cell Protein (SCP)
  • Cellular components, such as enzymes

Fermentation

• Fermentation is a process where raw materials are converted into fermented foods by the growth and metabolic activities of edible microorganisms
• Microorganisms' enzymes, such as amylases, proteases, and lipases, hydrolyze polysaccharides, proteins, and lipids to produce nontoxic products with pleasant flavors, aromas, and textures

Benefits of Fermented Foods

• Enrichment of the human diet through development of diverse flavors, aromas, and textures
• Preservation of substantial amounts of food through lactic acid, alcoholic, acetic acid, alkaline, and high salt fermentations
• Enrichment of food substrates biologically with vitamins, protein, essential amino acids, and essential fatty acids
• Detoxification during food fermentation processing

Microorganisms Used in Fermentation

• Lactic Acid Bacteria (LAB): Lactococcus lactis, Streptococcus thermophilus, Leuconostoc spp., Lactobacillus spp., Pediococcus spp.
• Related bacteria: Aerococcus, Microbacterium, Propionibacterium, Carnobacterium, Non LAB Bifdobacterium
• Yeasts: Saccharomyces cerevisiae, Saccharomyces spp., Zygosaccharomyces
• Molds: Aspergillus, Rhizopus, Penicillium, Botrytis

Types of Fermentation

• Homofermentation: produces only lactic acid, such as Lactococcus, Pediococcus, and Streptococcus
• Heterofermentation: produces equimolar amounts of lactic acid, acetic acid, CO2, and ethanol, such as Leuconostoc

Types of Fermentation by LAB

• Natural fermentation: carried out by natural microflora, such as Lactobacillus sp and Leuconostoc mesenteroides
• Controlled fermentation: uses high numbers of pure culture of single or mixed strains or species of microorganisms, with controlled acidification

Starter Cultures

• Concentrated frozen cultures: prepared by growing cells in a suitable medium, concentrating by centrifugation, and resuspending in a liquid with cryoprotectant agents
• Freeze-dried concentrates: prepared by drying concentrated frozen cells under vacuum

Problems with Starter Cultures

• Strain antagonisms: production of compatible strains to avoid strain antagonism
• Loss of a desired trait: physical and chemical stresses can result in loss of a trait
• Cell death and injury: ensuring a large number of viable cells and a short lag phase
• Inhibitors in raw material: antibiotics, sanitizers, nitrite, or phosphate in cured meat

Factors Affecting the Effectiveness of Fermentation

• Initial product pH
• Buffering capacity and food composition
• Nature and concentration of fermentable Carbohydrates (CHO)
• Rate of growth of LAB and targeted pathogens

Biopreservation

• Refers to the extension of the shelf-life and improvement of the safety of food using microorganisms and/or their metabolites
• Organic acids, such as lactic, acetic, and propionic acids, provide an acidic environment unfavorable for the growth of many pathogenic and spoilage microorganisms
• Production of a range of other antimicrobial metabolites, such as H2O2, diacetyl, reuterin, and reuterocyclin
• Bacteriocins: proteinaceous inhibitors produced by LAB, acting through depolarization of the target cell membrane or inhibition of cell wall synthesis

Benefits of Bacteriocins

• Generally recognized as safe (GRAS) substances
• Not active and non-toxic on eukaryotic cells
• Become inactivated by digestive proteases, having little influence on the gut microbiota
• Show a bactericidal mode of action, usually acting on the bacterial cytoplasmic membrane
• Permit the marketing of novel foods (less acidic, lower salt content) without compromising food safety

Probiotics

• Beneficial effects on human health:
  • Lactose hydrolysis (lactose intolerance)
  • Reduce serum cholesterol level
  • Reduce colon cancer
  • Reduce intestinal disorders
• Benefits thought to occur via:
  • Biochemical effects (altering associated metabolic and enzymatic activities of resident harmful or developing pathogens)
  • Competition for nutrients
  • Competition for binding sites

What it Takes to be a Probiotic

• Known microorganism origin from the intestinal tract of healthy persons
• Stability during production, growth, or fermentation, concentration, freezing, drying, distribution, etc.
• No adverse sensory properties
• Genetic stability
• Stability during incorporation into food/feed; pH, heat, drying, encapsulation, etc.
• Competitiveness: stability at target site, resistant to bile acid and digestive enzymes, able to compete with normal microflora, resistant to antimicrobials produced by bacteria

Minimum Inhibition Concentration (MIC) and Minimum Bactericidal Concentration (MBC)

• MIC: the minimum concentration of an antimicrobial necessary to inhibit the growth of a particular strain of microorganism
• MBC: the lowest concentration of an antimicrobial able to produce complete killing of a defined number of bacteria, in defined media and within a defined time

Targets of Food Antimicrobials

• Cell membrane or cell wall: increasing permeability and loss of cellular constituents
• Inactivation of essential metabolic enzymes, protein synthesis, and genetic material
• Transport mechanism for nutrients

Factors Affecting Antimicrobial Activity in Food

• Level and type of microorganism
• Storage conditions of food product, such as time, temperature, and humidity