Produce Degradation Pathways and Prevention

Nutrient Loss 253

Walker, 2002). They produce lactic acid as the major end product of the fermentation
of carbohydrates. They are the most important bacteria in desirable food fermentation
and are responsible for the fermentation of pickled (fermented) vegetables such as
sauerkraut. Historically, bacteria from the genera Lactobacillus, Leuconostoc, Pedi-
ococcus, and Streptococcus have been the main species involved in food fermentation
(Hartley et al., 2001; Teitelbaum and Walker, 2002). Several more strains of bacteria
have been identified but play a minor role in lactic acid fermentation. Lactic acid
bacteria carry out the conversion of carbohydrate to lactic acid plus carbon dioxide
and other organic acids using only a small amount of oxygen (i.e., they are
microaerophilic). Thus, changes that they effect do not cause drastic changes in the
composition of the food. Some of the Lactobacillus family produce only lactic acid
(homofermentative), while others produce lactic acid and other volatile compounds
and small amounts of alcohol (heterofermentative) (Battcock and Azam-Ali, 1998;
Hartley et al., 2001). Homofermenters produce lactic acid through the glycolytic
(Embden-Meyerhof) pathway, while heterofermenters produce lactic acid and appre-
ciable amounts of ethanol, acetate, and carbon dioxide via the 6-phosphoglucon-
ate/phosphoketolase pathway. Table 8.4 shows the major lactic acid bacteria in
fermented plant products. Although all species of lactic acid bacteria are capable of
producing lactic acid, L. plantarum, a homofermenter, produces the highest acidity
in all vegetable fermentations and plays the major role (Battcock and Azam-Ali,
1998).

8.10.4.2 Acetic Acid Fermentation

Acetic acid fermentation involves Acetobacter bacterial species. Acetobacter con-
verts alcohol formed in food by action of yeast on sugars to acetic acid. This process
occurs in excess oxygen. The most desirable product of acetic acid fermentation is

TABLE 8.4
Major Lactic Acid Bacteria in Fermented Plant Products

Homofermenter Facultative Homofermenter Obligate Homofermenter

Enterococcus faecum
Enterococcus faecalis
Lactobacillus acidophilus
Lactobacillus lactis
Lactobacillus delbrueckii
Lactobacillus leichmannii
Lactobacillus salivarius
Streptococcus bovis
Streptococcus thermophilus
Pediococcus acidilactici
Pediococcus damnosus
Pediococcus pentocacus

Lactobacillus bavaricus

Lactobacillus casei

Lactobacillus coryniformis

Lactobacillus curvatus

Lactobacillus plantarum

Lactobacillus sake

Lactobacillus brevis

Lactobacillus buchneri

Lactobacillus cellobiosus

Lactobacillus confusus

Lactobacillus coprophilus

Lactobacillus fermentatum

Lactobacillus sanfrancisco

Lactobacillus dextranicum

Lactobacillus mesenteroides

Lactobacillus paramesenteroides

Source:Battcock, M. and Azam-Ali (1998), Food and Agriculture Organization, Rome.