Cultures for Fermentation of Vegetables Fruits and Grains

Plant fermentations involve either lactic acid, acetic acid, or alcoholic fermentation or a combination of these fermentation types. In alcoholic fermentation, it is mainly yeast (Saccharomyces cerevisiae) and fungi (Aspergillus oryzae) that participate; however, lactobacilli and Pediococcus can also be involved. This fermentation is described in more detail in Sec. IV. Acetic acid fermentation, used for production of vinegar, is a two-stage fermentation process in which the first stage includes an alcoholic fermentation followed by the oxidization of ethanol via acetaldehyde to acetic acid (29). The typical raw materials are grapes, potatoes, or rice. Different subspecies of Acetobacter (A. acati, A. pasteurianus, and A. hansenii) and Gluconobacter oxydans are used for vinegar production. Pure cultures are not widely employed in the acetic acid fermentation industry (29,30). Interestingly, Nanda et al. (31) found that the Acetobacter strain responsible for the rice vinegar ''Ko-mesu'' and ''Kurosu'' spontaneously established an almost pure culture during its long production time.

Traditional fermentations of vegetables, fruits, and grains most often include a lactic acid fermentation involving many different species of LAB that are active at different stages of the fermentation process; this is followed by fermentation by yeast and mold (30,32-34). Lactobacillus plantarum and Leuconostoc mesenteroides are the major microorganisms; however, many other LAB (e.g., Lactobacillus species and Pediococcus) may be involved.

Fermentation of vegetables is difficult to control (35) because it depends on the quality of the raw material, the harvesting condition, and the temperature, which are vital in providing the optimal conditions for growth of the desirable microorganisms. The addition of salt, either as dry salt (2-3% w/v) or in solution (4-10% w/v) (called brining) and the creation of an anaerobic condition is commonly the initial step in fermentation of vegetables. One obstacle is that raw vegetables cannot normally be pasteurized without adverse effects on the product texture (11). Another issue is that vegetable fermentation often relies on a very complex process in which many different bacteria succeed each other in very specific ways.

Many different plant fermentations are commercially produced (35) and most often on a small scale. Currently only olives, pickled cucumbers, sauerkraut, and kimchi are industrially produced in economically important large amounts (36). Commonly, the fermentations are performed by spontaneous fermentation or back-slopping. In a few cases, utilization of LAB as single-strain cultures has been tried successfully. For production of sauerkraut, Lactobacillus plantarum (37,38), Lactobacillus curvatus (37), and Leuconostoc mesenteries alone (30) or combined with Lactococcus lactis (39) have been tried. Lactobacillus plantarum and Lactobacillus pentosus have been used in olive fermentation (4044); Lactobacillus plantarum (45-48), Lactobacillus pentosus (48), and Pediococcus pento-saceus (48) successfully for pickled cucumbers. Examples of plant fermentations in which starter cultures have been used are shown Table 7.

Different grains [e.g., maize, rice, sorghum (49-64)] and legumes [e.g., soybeans, lupins, peas, lentils (65)] can be fermented, and most do not involve addition of starter cultures but are fermented by spontaneous fermentation or back-slopping. However, starter cultures are used for production of sourdough from wheat or rye (30). They are used as either single- or multiple-strains starters, with or without the addition of yeast. The LAB used in starter cultures are shown in Table 7. However, back-slopping using a batch of dough derived from a previous fermentation to inoculate the next batch of dough is still a common practice in industrial production in Denmark, Finland, and Germany. Another

Table 7 Examples of Lactic Acid Bacteria Used as Starter

Cultures or Occurring

Spontaneously in

High Number in Fermented Plant Material

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