Exer 9.2

• Starting material


  Contains high amount of sugar that can be converted to ethanol and then acetic acid
• Preparation of Yeast Starter Culture

  Increase the number of yeast cells that will initiate the fermentation
• Shaking


  Aeration; dissimilation of one molecule of glucose under aerobic conditions results to more ATP molecules, and hence faster growth but only up to some extent
• Alcoholic fermentation


  Addition of sugar increases the concentration of fermentable hexoses in coconut water
• Starter Culture


  • Selected strains of yeasts, generally those of S. cerevisiae
  • Strains used are selected according to criteria that enhance the efficiency of the process and product quality
  • Inoculated into the juice at a relatively high cell concentration
• Conversion of sugars to ethanol

  1. Glycolysis - sugars are broken-down by the yeasts to form pyruvate molecules

  2. Fermentation - pyruvate is converted to acetaldehyde then into ethanol with the release of carbon dioxide under anaerobic conditions
• Bung Setup


  • Allows the carbon dioxide buildup to be released from the fermentation container
  • Limits the exposure of the fermenting liquid to oxygen
  • Fermentation is monitored through the formation of bubbles
• Acetic Acid Fermentation


  • Performed by obligate aerobes (from genus Acetobacter, Gluconobacter, Gluconoacetobacter, Acidomonas, and Komagataeibacter)
  • Fermentation is initiated by either pure culture or backslopping
  • Ethanol is oxidized back to acetaldehyde; acetaldehyde is further oxidized to acetic acid
  • Substrate (ethanol) and product (acetic acid) are both toxic to other competing microorganisms
• Tempeh


  • Mold-fermented soybean product first produced in Indonesia
  • Soybeans held together by the mycelium of Rhizopus microsporus var. oligosporus
• Acidification of soybeans


  1. Endogenous lactic acid bacteria grow and produce lactic acid causing the pH to decrease during soaking

  2. Steep water can be acidified directly with acetic acid

  3. Low pH restricts the growth of undesirable spoilage microorganisms, as well as pathogens
• Boiling


  1. Enhances the extraction of soluble nutrients

  2. Inactivates microorganisms that might interfere with subsequent fermentation

  3. Denatures trypsin inhibitor, an anti-nutritional factor soy protein
• Methods of inoculum preparation

  • R. oligosporus spore suspension is added directly to the beans
  • Using dried tempeh culture that serves as backslop material
  • Use of "usar" which is made by inoculating wild Rhizopus spores onto surface of Hibiscus plant
• Growth of R. oligosporus on soybeans


  • Production off the mass of mycelia that holds the soybeans together
  • Lipids and proteins serve as substrate; releases free fatty acids and amino acids
  • Other anti-nutritional factors are also degraded: trypsin inhibitors that interfere with digestion, tannins that reduce protein quality, phytic acid that reduces mineral adsorption, hemagglutenins that causes blood to clump, goitregens that causes metabolic disturbances