Food Microbiology II- NFSC 278Industrial MicrobiologyVinegar

Vinegar A dilute solution of acetic acid produced by a two-stage fermentation process In the first stage, fermentable sugars are converted into ethanol by the action of yeasts In the second stage, bacteria of the genus Acetobacter oxidize the ethanol to acetic acid

Vinegar Production FruitGrain, Root Crops (Starch)Starch Glucose + MaltoseEnzymesFermentable Mono- & Disaccharides Alcoholic FermentationGlucose or Fructose ethyl alcohol + carbon dioxideYeastAnaerobic conditionsEthyl Alcohol

Vinegar Production Ethyl Alcohol Acetic AcidEthyl Alcohol Acetic acidAcetic acid bacteriaairACETIFICATIONTheoretical conversion1g glucose 0.51 g ethyl alcohol 0.67g acetic acid

Vinegar Production of vinegar can occur as a spontaneous fermentation Both types of microorganisms necessary for vinegar production are commonly associated with plant products as part of their natural microflora pH of vinegar is 3 or below

Uses of VinegarFood Uses: Individual vinegars have their own particular flavor reflecting the process by which it was made and the raw material used It is a good solvent for the essential oils of herbs and spices and has been a sauce ingredient throughout history

Uses of Vinegar Vinegars flavored with tarragon, chili, garlic, rosemary and the like are produced commercially for use in home-produced marinades and salad dressings The range of food products prepared using vinegar include: mayonnaise, ketchups, sauces, chopped pickles, brined vegetables

Uses of Vinegar Pickling foods in vinegar is one of the traditional technologies of food preservation The preservative action of vinegar is due to its acetic acid content 0.1% of the undissociated acid will inhibit the growth of most food poisoning and spore-forming bacteria

Raw Materials Vinegar can be made from any non-toxic raw material that furnishes a juice or solution containing fermentable sugars A vinegar takes its name from the raw material used E.g. malt vinegar, wine vinegar, rice vinegar

Raw Materials Vinegar is an inexpensive commodity, its economic production requires a relatively low cost raw material

In most cases the raw material used contains sufficient nutrients to support the growth and metabolism of acetic acid bacteria

Alcoholic Fermentations Normally the yeast used in alcoholic fermentation is a strain of the species Saccharomyces cerevisiae The transformation of a hexose by S. cerevisiae can be represented chemically by the Gay-Lussac equation:C6H12O6 2C2H5OH + 2CO2Fermentable hexose (180g)Ethanol (92g)Carbon dioxide (88g)

Alcoholic Fermentations The catabolism of sugar provides the yeast cell with a source of biosynthesis intermediates as well as energy Not all the sugar is converted to ethanol Some of the sugar is diverted to the production of yeast cell biomass, glycerol and succinic acid

Alcoholic Fermentations This leads to a decrease in ethanol yield: a realistic theoretical yield would be 95%, and a good practical yield is 90% The fermentation in vinegar production are less susceptible to microbial contamination than many other industrial fermentations It is possible to carry it out in simple vessels such as open vats of wood or concrete

Processing of Vinegar After acetification, vinegar is usually matured in full closed vats for up to a year During this time it develops its characteristic flavor and aroma and some settlement on unstable colloids takes place Raw vinegar is normally cloudy with suspended bacteria and other particles

Processing of Vinegar A haze or precipitate may form in vinegars that have been in contact with non-acid resistant materials This is usually due to the formation of iron and copper (metal-containing precipitates), which spoil the appearance of vinegar and make it unsuitable for use in pickling

Processing of Vinegar Bacterial growth and turbidity in bottled vinegar can be prevented by a heat treatment Gram negative acetic acid bacteria is not heat resistant, so use 600C for few minutes is enough to eliminate the numbers encountered Product is either hot-filled into bottles after treatment or pasteurized in the bottle

Processing of Vinegar There is considerable advantage in producing a vinegar containing high levels of acetic acid, it is more effective in the pickling of high moisture content foods The maximum concentration of acetic acid that can be produced by fermentation is usually around 10-15%

Vinegar Standards, Composition and Analysis Normally a standard identifies particular qualities associated with a foodstuff, describes the method of analysis to be used and makes some recommendations as to acceptable limits The principal competitor of vinegar is edible-grade synthetic acetic acid, diluted with water and usually colored with caramel

Vinegar Standards, Composition and AnalysisAcc to Codex:

Vinegar is a liquid fit for human consumption, produced from a suitable raw material of agricultural origin, containing starch, sugars or starch and sugars, by the process of double fermentation, alcoholic and acetous and contains a specified amount of acetic acid

Vinegar Standards, Composition and Analysis The principal quality criterion of vinegar is the acetic acid content, the minimum level is usually set at 4% (w/v) Many bottled vinegars normally contain 5% The determination of acidity cannot distinguish between a true vinegar and diluted acetic acid!