Effects of lactic acid bacteria on tempeh fermentation

There are no reports of food poisoning caused by consuming traditional soybean tempeh (Ko Swan & Hesseltine, 1979). Nout & Rombouts (1990) suggested that this safety is due to: 1) inherent properties of Rhizopus spp., 2) presence of lactic acid bacteria (LAB), 3) incubation under micro-aerobic conditions, and 4) the customary heating prior to consumption.

Table 2. Growth of potential pathogenic bacteria and their inhibition by lactic acid bacteria (LAB) during tempeh fermentation

Tempeh substrates

Initial substrate pH

Pathogenic bacteria

Growth of pathogenic bacteria (log cfu/g) without LAB

Growth of pathogenic bacteria in the presence of LAB (at inoculation level log cfu/g)

Reference

Soybean Soybean

Horsebean, pea, chickpea, soybean

Horsebean, pea, chickpea, soybean

Soybean

Pea, chickpea

unacidified acidified

Horsebean, Around 5.0 pea, chickpea, soybean

B. cereus B. cereus

B. cereus

B. cereus

7.1(tempeh)

5 to 8 Can not be inhibited, but tempeh is acceptable after the inoculation of L. plantarum, L. casei spp. alactosus and L. fermentum

2 to 8 in Can not be inhibited in (Ashenafi horsebean, horsebean, but & Busse,

6 to 7 in markedly decreased in 1991b) others, other substrates after the inoculation of L.

S. infantis, E. aerogenes, E. coli

Microccus sp., Bacillus sp.

monocytogenes

2 to >7 (horsebean, pea), 5 to 6 (chickpea, soybean)

plantarum (6.5)

Decrease after the inoculation of L. plantarum (3.5)

(Ashenafi & Busse, 1991b)

Completely inhibited (Ashenafi after the inoculation of & Busse, L. plantarum (6.2) 1989)

4 (natural Inhibited after the (Ashenafi occurred) to inoculation of L. & Busse,

>8 in storage plantarum (>6) during 1991a)

tempeh at 4 °C cold storage

L. plantarum (6.3) slightly reduces it in horse bean, completely inhibits it in other substrates

(Ashenafi, 1991)

Table 2. Continued

Tempeh

Initial

Pathogenic

Growth of

Growth of

Reference

substrates

substrate

bacteria

pathogenic

pathogenic bacterial

pH

bacterial (log

with the presence of

cfu/g) without

LAB (at inoculation

LAB

level log cfu/g)

Horsebean,

unacidified

S. infantis,

2.3 - >6.5

Inhibited to some

(Ashenafi

pea,

E. coli

(S. infantis);

extent after the

& Busse,

chickpea

2.3 - >6.5

inoculation of L.

1991c)

(E. coli)

plantarum (6.3)

Horsebean,

acidified

S. infantis,

2.3 - >6.0

Strongly inhibited

(Ashenafi

peas,

E. coli

( S. infantis);

after the inoculation of

& Busse,

chickpea

2.3 - >6.0

L. plantarum (3.3)

1991c)

(E. coli)

Horsebean,

unacidified

S. aureus

2-3 - 8

Markedly decreased in

(Ashenafi

pea,

(others),

horsebean (4.3), pea

& Busse,

chickpea,

4.7 ( chickpea)

(5.8) and in chickpea

1992)

soybean,

(3.2), completely

inhibited in soybean

after the inoculation of

L. plantarum (>6)

Horsebean,

acidified

S. aureus

<7

Completely inhibited

(Ashenafi

pea,

(horsebean,

in soybean, reduce to 4

& Busse,

chickpea,

pea and

in others after the

1992)

soybean,

soybean),

inoculation of L.

<5 (chickpea)

plantarum (2-3)

Notice: B. cereus=Bacillus cereus, L. plantaru=Lactobacillus plantarum, S. infantis=Salmonella infantis, E. aerogenes=Enterobacter aerogenes, E. coli=Escherichia coli, S. aureus=Staphylococcus aureus, L. monocytogenes=Listeria monocytogenes

Notice: B. cereus=Bacillus cereus, L. plantaru=Lactobacillus plantarum, S. infantis=Salmonella infantis, E. aerogenes=Enterobacter aerogenes, E. coli=Escherichia coli, S. aureus=Staphylococcus aureus, L. monocytogenes=Listeria monocytogenes

The LAB are important during two process stages in legume tempeh fermentation: 1) soaking, where they acidify soaking water during natural soaking of beans to reduce the growth of potential pathogenic bacteria (Nout et al., 1987c); 2) fermentation, where the growth of LAB limits the natural increase in pH during tempeh fermentation, which in turn inhibits the growth of a number of pathogenic bacteria (Table 2). The inhibitory effects of LAB on potential pathogens were found to depend on the substrates used and the initial substrates' pH values (Ashenafi & Busse, 1991c) (Table 2). Generally, higher initial substrates' pH values require larger inoculations of LAB to inhibit the growth of pathogenic bacteria.

The soaking time is shorter (3-6 h) in the barley tempeh process than for soybean tempeh production (6-24 h). This would not allow substantial growth of LAB and therefore, lactic acid was used instead of LAB strains during barley soaking to reduce the pH and inhibit the growth of potential pathogens. The growth of LAB

during barley tempeh fermentation has not been reported before. We investigated the growth of several LAB strains during barley tempeh fermentation. Five investigated strains of Lactococcus lactis and one strain of Pedicoccus pentosaceus did not grow during barley tempeh fermentation (Table 3), while L. reuteri grew very slowly (I). In contrast, L. plantarum and L. fermentum grew faster (I). L. plantarum showed especially strong growth, even at inoculations of less than 2 log cfu/ g moist barley (Fig. 9). This indicates the importance of selecting competitive species or strains for co-fermentation of tempeh.

The growth of LAB in barley tempeh did not reduce the pH (I) as it did in legume tempeh (Ashenafi & Busse, 1991d) (Fig. 4). This may be due to the fact that acid-soaked barley originally had a low pH value and a substantial buffering capacity. Many pathogenic bacteria are found to be difficult to grow under the the conditions prevailing during barley tempeh fermentation (Swanberg et al, unpublished 2000) (Fig. 10). This might be due to the low pH and to competition from R. oligosporus.

Table 3. Growth of Lactococcus lactis and Pedicoccus pentosaceus during barley tempeh fermentation (Feng, unpublished, n=1)

Species

Strain No.

Characteristics

Growth (log cfu/g)

0 h

23 h

P. pentosaceusa

fBB61

5.5

4.1

L. lactisb

SR3.52

Nisin producer from silage

4.3

3.1

L. lactis

SR3.53

Nisin producer from silage

6.3

5.7

L. lactis

SR 3.54

Nisin producer from silage

4.0

2.8

L. lactis

ATCC 11454

Nisin producer from cheese starter

4.6

<2

L. lactis

CNRZ 481

Lacticin producer from cheese

3.7

4.0

starter a: P. pentosaceus=Pedicoccuspentosaceus; b: L. lactis=Lactococcus lactis starter a: P. pentosaceus=Pedicoccuspentosaceus; b: L. lactis=Lactococcus lactis

LAB inoculated at 4 log cfu/g moist barley did not affect the growth of R. oligosporus (I and II), whereas larger inoculations did (Feng, unpublished). It is important to determine the degree of inoculation required when introducing LAB to tempeh. This will depend on the specific LAB strain, the substrate used and the germination ability of R. oligosporus spores.

The effects of LAB co-inoculation with R. oligosporus on the nutritional value of soybean or barley tempeh have not been investigated. However, some studies have been reported on the effects of LAB fermentation alone on the composition of barley fibres. p-glucan, total and soluble dietary fibre, but not starch, were reduced after 16 h fermentation of barley whole-grain flours with Lactobacillus spp. (Skrede et al., 2003). Chicken fed with this fermented barley whole-grain flour attained higher body weights compared with those fed on unfermented one. The contents of p-glucans and insoluble fibres, but not soluble fibre, were also reduced in barley fibre concentrates fermented with LAB (Lambo et al., 2005).

Fermentation Tempeh Process

Fig. 9. Growth of Lactobacillus plantarum at different inoculation levels (log cfu/g moist tempeh) during barley tempeh fermentation (■: initial level below detection limit of 102 cfu/g) (Feng, unpublished, n=1).

Fig. 9. Growth of Lactobacillus plantarum at different inoculation levels (log cfu/g moist tempeh) during barley tempeh fermentation (■: initial level below detection limit of 102 cfu/g) (Feng, unpublished, n=1).

Plantarum Growth

15 20

Time (hour)

Fig. 10. Growth of Bacillus subtilis alone (■) or co-inoculated with R. oligosporus in barley (▲ and ♦ from two individual experiments) (Feng, unpublished, n=1).

15 20

Time (hour)

Fig. 10. Growth of Bacillus subtilis alone (■) or co-inoculated with R. oligosporus in barley (▲ and ♦ from two individual experiments) (Feng, unpublished, n=1).

LAB can produce organoleptic compounds in yoghurt (Stien et al., 1999) and sourdough bread (Damiani et al., 1996), folate (Sanna et al., 2005; Kariluoto et al., 2006), low-calorie polyols such as mannitol that are used to reduce the sugar content (Wisselink et al., 2002) and other products such as sugar polymers, sweeteners and aromatic compounds (Leroy & de Vuyst, 2004). Furthermore, LAB can remove raffinose, stachyose, and verbascose from soybean (Scalabrini et al., 1998; Leroy & de Vuyst, 2004), and proteinase inhibitors from legumes and cereals to prevent maldigestion (Holzapfel, 2002). LAB can also degrade phytic acid and tannins from cereals and legumes to increase mineral bioavailability (Sharma & Kapoor, 1996; Holzapfel, 2002), and degrade natural toxins such as cyanogenic glucosides from cassava (Kimaryo et al., 2000; Holzapfel, 2002). Some LAB are considered as probiotics (Merk et al., 2005; Shimosato et al., 2006), and both viable and non-viable forms showed efficacy in shortening the duration of diarrhea (Ouwehand & Salminen, 1998). They can also inhibit the growth of fungi (Schnürer & Magnusson, 2005) and thereby reduce the production of mycotoxins, or reduce damage of mycotoxins to humans by binding them to their cell walls (Pierides et al., 2000; Mokoena et al., 2005; Shetty & Jespersen, 2006). Therefore, the growth of LAB in tempeh may improve both the nutritional value and safety of barley tempeh.

+1 0

Post a comment