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OCR for page 151
VI. HUMAN
HEALTH, SAFETY,
AND NUTRITION
OCR for page 152
OCR for page 153
22
Nutrition and Safety Considerations
O. Paredes Lopez
Fermentation was one of the first methods used by Man to produce
and preserve foods. Microbial fermentations have played an important
role in food processing for thousands of years. Fermentations provide
a way to preserve food products, to enhance nutritive value, to destroy
undesirable factors, to make a safer product, to improve the appearance
and taste of some foods, to salvage material otherwise not usable for
human consumption, and to reduce the energy required for cooking
(1~. Preservation of foods by salting is an age-old practice; while
preventing the growth of pathogenic microbes, it allows the develop-
ment of harmless, halotolerant ones that produce desirable censorial
changes in the substrate (2~.
Traditional fermented foods may be divided into two broad cate-
gories: (a) submerged culture-fermentations (SCFs) and (b) solid-
substrate fermentations (SSFs). In SCFs microbial activity occurs at
a relatively low biomass concentration in the liquid phase, while in
SCFs microbial growth and product formation occur on the surfaces
of solid substrates (3,4~. Some examples of traditional fermented foods
for SCFs are pulque and tesguino, soy sauce, fish sauce, kaffir beer,
and palm and rice wines. Examples of SSFs are tempe, miso, pozol,
oncom, and natto. One of the major characteristics that distinguishes
SSFs from SCFs is that SSF processes usually occur at low-moisture
contents (e.g., 10 to 20 percent), conditions under which water activity
favors the development of filamentous fungi. However, for many
indigenous fermentations the microbial interactions are complex and
mixed fungal-bacterial, fungal-yeast, and yeast-bacterial combinations
occur (51. These interactions play an important role in the nutritional,
safety, and sensory characteristics of the end product (61.
153
OCR for page 154
154
FERMENTED FOODS
EFFECT OF FERMENTATION ON NUTRITIONAL COMPOSITION
Changes in Proximate Composition and Soluble Components
During fermentation the microorganisms secrete hydrolytic enzymes
into the substrate and assimilate some of the fatty acids, amino acids,
and simple sugars thus liberated. These are converted into microbial
structural components and secondary metabolites. Lactic acid fermen-
tation is an ancient process whereby a varied group of bacteria ferment
carbohydrates, producing lactic acid as the major end product. This
type of fermentation is used for the production of dairy products,
sauerkraut, bread, meat, and silage. In particular, traditional SSFs of
legumes, cereals, and starchy substrates have been associated in many
regions of the world with the activity of lactic acid bacteria (7~; during
fermentation lactic acid accumulates, with a concomitant increase in
acidity and a decrease of dry matter yields. The higher pH values
of fermented legumes, compared to other materials under similar
conditions, have been attributed to their higher protein content (8,91.
It seems that the only fermented food showing significant changes
In its crude composition is pozol. The fermentation mixture contains
Agrobacterium azotophilum, which is capable of fixing nitrogen (10~.
Due to the crude methods of analysis, the proximate composition of
foods does not change much during fermentation. However, there is
almost always a high increase in the soluble fraction of a food
during fermentation. The proteolytic activity of bacteria in traditional
fermentations degrades complex proteins into simpler proteins, pep-
tides, and amino acids. The bacteria used in natto fermentation cause
substantial increases in the level of free amino acids and soluble
carbohydrates. On the other hand, Rhizopus spp., used in the fermenta-
tion of various types of tempe, are highly hydrolytic, and outstanding
increases in soluble fat, protein, and carbohydrate are observed. Free
fatty acids, including the essential fatty acids, linoleic and linolenic
acids, may increase in these indigenous fermented foods (11,121; this
increase is thought to be of nutritional significance.
The increase in soluble solids is a nutritionally desirable event, as
the food is effectively digested prior to consumption. In some cases
the microorganisms are capable of producing pectinases and cellulases,
softening the texture of the food and liberating sugars that would
otherwise be unavailable to the human digestive system. Consequently,
fermented foods are expected to be more digestible than their unfer-
mented counterparts.
Changes in Composition of Amino Acids and Vitamins
Methionine, the limiting amino acid in legumes, has been reported
to increase during tempe kedele production, and lysine, the limiting
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NUTRITION AND SAFETY CONSIDERATIONS
155
amino acid in cereals, increases during fermentation with Rhizopus
spp. (11. During kocho production, an acidic fermentation, the essential
amino acid content is considerably enhanced. On the other hand,
during tape' ketan and enjera production, the levels of some essential
amino acids fall, whereas others remain unchanged (111. In general,
most traditional fermented foods exhibit slight changes in essential
. · .
amino aclos.
Interestingly, isolation of improved strains of Aspergillus niger for
an SSF process allowed 200 to 300 percent lysine overproduction
compared to the parent strain (51. However, it should be emphasized
that bioavailability and balance of amino acids are more important than
their total content. Hence, biological experiments to assess their
nutritional value are warranted.
Traditional fermentations dramatically improve the vitamin content
of a wide variety of substrates. Of all the foods investigated, only
enjera showed a decline in vitamin content (1,131.
Changes in Unwanted Components
Unwanted components, such as physic acid, trypsin inhibitor, flatus
factors, and lectins, may be present in high concentrations in several
desirable foods. Phytic acid and trypsin inhibitor interfere with
digestion by binding enzymes. Phytic acid may also bind minerals,
reducing their bioavailability. Lectins are capable of binding to the
intestinal wall and thus interfering with nutrient absorption. Presoaking
and cooking of foods can reduce the levels of some, but not all,
of these antinutritional factors. However, microorganisms have the
capacity to hydrolyze them, reducing their levels even further (14~.
Hence, bacteria, yeasts, and fungi that degrade antinutrients at a fast
rate and at early stages of fermentation need to be identified or
developed (11.
Changes in Biological Value
Since fermentation increases the quantity of soluble proteins in
foods, it may improve the amino acid profile, and because it reduces
the levels of certain antinutritional factors that interfere with digestion,
it would not be unreasonable to suggest that fermented foods will be
more efficiently utilized by the human digestive system. Single- as well
as mixed-culture fermentations of pearl millet by yeasts improve starch
and protein digestibility (15~. Enjera is one of the few traditional
fermented foods that shows a decline in protein efficiency ratio (PER),
probably due to a decline in the essential amino acid content (161.
Also, increases in PER values of some indigenous fermented foods can
be obtained by incorporating soybeans into cereal-based substrates.
OCR for page 156
156
FERMENTED FOODS
SAFETY ASPECTS OF TRADITIONAL FERMENTED FOODS
Because many fermented foods are produced using fungi, the risk
of mycotoxin contamination is high. During natural fermentations,
food-poisoning flora and coliforms may also grow with the tactics.
These microorganisms need to be eliminated to make fermented foods
safe for consumption (161. Several factors contribute to the safety of
fermented foods: (a) Soaking and cooking. Washing, soaking, and
cooking treatments reduce the in situ microbial contaminants.
(b) Salting. Various fermented foods are made with the addition of
salt, which acts as a preservative. (c) Acid formation. Many indigenous
fermentations are carried out by acid-producing microorganisms, where
these organic acids (e.g., lactic, acetic, fumaric acids) act as preserva-
tives or as bacteriostatic agents. An inhibitory pH for bacterial growth
is considered to be 3.6 to 4.1. (d) Antibiotic production. Molds used
in some traditional fermentations produce antimicrobial glycopeptides.
(e) Low moisture content. In the case of SSF processes, the low water
activity may be an important preservative factor. and (f) Reduction of
aflatoxin by some microorganisms. Rhizopus and Neurospora species,
among others, are reported to decrease aflatoxin content of contami-
nated substrates.
Despite these factors, it has been reported that the sanitary quality
of some Oriental fermented foods is poor (17,181. Safe products are
usually obtained when the following recommendations are observed:
(a) appropriate soaking of the beans in acid at a low pH; (by adequate
cooking time; (c) using hygienic conditions during production, handling,
and storage; and (d) good refrigeration of products (5°C) between
production and consumption.
In summary, production of foods with high nutritional and sensory
values, and free of microbiological health risks, is a key component of
any policy aimed at upgrading the social role of traditional fermented
foods in less developed countries.
REFERENCES
1. Paredes-Lopez, O., and G. I. Harry. 1988. Food biotechnology
review: Traditional solid-state fermentations of plant raw materials.
Application, nutritional significance, and future prospects. Critical
Reviews in Food Science and Nutrition 27:159-187.
2. Beuchat, L. R. 1978. Traditional fermented food products. Pp.
22~253 in: Food and Beverage Microbiology, L. R. Beuchat (Ed.),
Westport, Conn.: The AVI Publishing Co.
3. Tengerdy, R. P. 1985. Solid substrate fermentation. Trends in
Biotechnology 3:9~99.
OCR for page 157
NUTRITION AND SAFETY CONSIDERATIONS
157
4. Paredes-Lopez, O., and A. Alpuche-Solis. 1991. Solid substrate
fermentation. A biotechnological approach to bioconversion of wastes.
Pp. 117-145 in: Bioconversion of Waste Materials to Industrial Prod-
ucts, Vol. 1, A. M. Martin (Ed.), London: Elsevier, Applied Science
Publication.
5. Rogers, P. L. 1989. Principles and applications of bioprocess
technology in the food industry. Pp. 223-239 in: Biotechnology and
the Food Industry, P. L. Rogers and G. H. Fleet (Eds.~. New York:
Gordon and Breach, Science Publishers.
6. Hall, R. J. 1989. Application of biotechnology to traditional
fermentations. Pp. 241-277 in: Biotechnology and the Food Industry.
P. L. Rogers and G. H. Fleet (Eds.~. New York: Gordon and Breach
Science Publishers.
7. Fukushima, D. 1985. Fermented vegetable protein and related
foods of Japan and China. Food Reviews International 1: 149-209.
8. Zamora, A., and M. L. Fields. 1979. Nutritive quality of
fermented cowpeas and chickpeas. Journal of Food Science 44:23=
237.
9. Paredes-Lopez, O., J. Gonzalez-Castaneda, and A. Carabez-
Trejo. 1991. Influence of solid substrate fermentation on the chemical
composition of chickpea. Journal of Fermentation and Bioengineering
71:58-62.
10. Cravioto, O. R., Y. O. Cravioto, G. Massiew, and J. Guzman.
1955. El pozol, forma indigene de consumir el maiz en el sureste de
Mexico y su aporte de nutrientes a la dicta. Ciencia (Mexico) 15:27-
30.
11. Steinkraus, K. H. 1983. Indonesian tempe and related fermenta-
tions. Pp. 217-251 in: Handbook of Indigenous Fermented Foods,
Microbiology Series, Vol. 9, K. H. Steinkraus (Ed.~. New York:
Marcel Dekker.
12. Paredes-Lopez, O., G. I. Harry, and R. Montes-Rivera. 1987.
Development of a fermentation procedure to produce a tempe-related
food using common beans as substrate. Biotechnology Letters 9:333-
333.
13. Soni, S. K., and D. K. Sandhu. 1989. Fermentation of idli:
Effects of changes in raw materials and physical-chemical conditions.
Journal of Cereal Science 10:227-238.
14. Mital, B. K., and S. K. Garga. 1990. Tempe Technology and
food value. Food Reviews International 6:213-224.
15. Khetarpual, N., and B. M. Chauhan. 1990. Fermentation of
pearl millet flour with yeasts and lactobacilli: In vitro digestibility and
utilization of fermented flour for weaning mixtures. Plant Foods and
Human Nutrition 40:167-173.
16. Wang, H. L., and C. W. Hesseltine. 1981. Use of microbial
cultures: Legume and cereal products. Food Technology 33~11:79-83.
OCR for page 158
158
FERMENTED FOODS
17. Tanaka, N., S. K. Kovats, J. A. Guggisberg, L. M. Meske, and
M. P. Doyle. Evaluation of the microbiological safety of tempe made
from unacidified soybeans. Journal of Food Protection 48:438~41.
18. Samson, R. A., J. A. van Kooij, and E. de Boer. 1987.
Microbiological quality of commercial tempe in the Netherlands.
Journal of Food Protection 50:92-94.
OCR for page 159
23
Mycotoxic Flora of Some
Indigenous Fermented Foods
Felixtina E. ,Ionsyn
Fermented foods have a wide usage in Sierra Leone as baby/weaning
foods. Ogi (fermented maize/sorghum) and foofoo pap (fermented
cassava) are examples. Foofoo is also one of the two staples of the
Creoles that is now widely used by other tribes especially when rice
is scarce. Ogiri (fermented sesame seeds) is a favorite condiment used
mostly by the poor as a low-cost protein substitute. Several studies
( 1-4) have shown that toxigenic fungi do not participate in the
fermentation processes but contaminate the product during or after the
fermentation.
It has been demonstrated ( 1~) that at times the substrate for
fermentation (maize, sesame seeds) has had prior exposure to myco-
toxin. In the case of maize, an aflatoxin B. level of 200 ~g/kg was
reduced to 58 ~g/kg in the resulting fermented mashogi (51. The long
cooking period (6 hours) of sesame seeds before fermentation accounts
for the loss of mycotoxins. Studies carried out by Ogunsanwo et al.
(6) have shown that losses of 64 percent aflatoxin B. and 83 percent
aflatoxin Go could be observed in ogiri product prepared from Aspergil-
luspavus-contaminated melon seeds.
In Sierra Leone, ogiri is produced by moist solid fermentation of
sesame seeds, a process similar to Nigerian ogiri, which is made from
fermented melon seeds (Citrullus vulgaris) (7) and Dawa-dawa from
fermented locust beans (Parkiafilicoidea) (81. Traditionally, the boiled
seeds are wrapped in jute bags and allowed to ferment for 4 to 5 days
before smoke treatment is applied. In such processes whitish threads
are observed after day 2 and molds become obvious after 3 to 6 days
This study was funded by the International Foundation for Science, Stockholm,
Sweden.
159
OCR for page 160
160
FERMENTED FOODS
(31. Microscopic examination of these whitish threads revealed the
presence of toxigenic and nontoxigenic Aspergilli and Penicillia species.
Detection of the corresponding mycotoxins of these toxigenic fungi in
the fermented, marketed, and stored ogiri (4) led to the present study
to design appropriate fermentation and storage techniques to reduce
the risk of mycotoxin contamination.
MATERIALS AND METHODS
Fermentation Process
Sesame seeds were soaked overnight and pounded in a mortar to
dehull. The seeds were then washed and boiled for 6 hours. The boiled
seeds were divided into three portions. One portion was transferred
to a clean dry nylon fiber bag; the other was placed in a clean dry jute
bag. Both were tightly wrapped. The third was placed in a plastic bowl
with a tight-sealed lid. Three replicates of each of the nylon fiber and
jute bag arrays were made. These were divided into three groups.
Group one was left to ferment for 5 days without smoke treatment.
Group two received early smoke treatment, from day 2 until day 5.
Group three was smoked consistently from day 3 to day 8, and
thereafter on alternate days for 2 weeks.
Marketing and Storage
The three common methods for wrapping ogiri are (a) the use of
dried banana leaves Musa sapientum, (b) the use of fresh or smoked
leaves of the plant Newbouldia laevis, and (c) the use of small plastic
wraps.
Leaf and plastic-wrapped ogiri samples bought from the local markets
were examined immediately under a stereo microscope. Samples with
no obvious fungal presence were selected. Three experimental designs
were set up as follows: (a) a set of six samples (three from each type
of leaf wrap) was smoked consistently for a week, (b) another set of
six (two from each type of leaf and plastic wrap) remained unsmoked
and stored at room temperature, and (c) the three types of wraps
(minus ogiri) were placed in sterile plastic petri dishes and stored at
room temperature.
Determination of Mycotoxins
Twenty gram samples from each experimental design (jute and nylon
fiber bags) were analyzed for aflatoxin using the method of Kellert and
OCR for page 161
MYCOTOXIC FLORA
161
Spott (91. The modified method of Nowotny et al. (10) was used to
screen 10-g samples for the other mycotoxins.
RESULTS
The use of clean dry nylon fiber bags proved very effective.
Fermentation was observed to last 3 or 4 days. No fungal growth was
noticed on the outside of the bag or on the fermented product even on
day 3 before smoke treatment.
Using jute bags, fermentation lasted 5 to 6 days, and evidence of
fungal contamination was obvious between days 2 and 3 of the
fermentation. But when the jute bags received smoke treatment from
day 2 to the final day of fermentation, no fungal contamination was
observed. Whitish threads observed on jute bags on day 3 disappeared
when smoke treatment was applied. The use of plastic bowls for
fermentation was highly unsuitable because the process took longer
2 weeks.
When ogiri was smoked for 2 weeks, it had a very appealing aroma
and texture. In contrast, the end product from the plastic bowl
experiment lacked the characteristic ogiri aroma. When ogiri samples
from both the jute and nylon fiber bags were assayed for mycotoxins,
there was no evidence of contamination.
Effect of the Types of Wraps
Samples wrapped in dry leaves of the banana plant were less
susceptible to fungal attack than ogiri wrapped in leaves of Newbouldia
laevis. However, regular smoke treatment reduced the incidence of
fungal contamination of ogiri in both types of leaf wraps. Plastic-
wrapped samples had no observable fungi even up to 2 weeks of
incubation but were devoid of the pleasant aroma characteristic of the
smoked product.
DISCUSSION
It has been clearly demonstrated in this study that the use of clean
dry nylon fiber bags instead of jute bags for the fermentation and early
smoke treatment of the fermenting mash contributed significantly to
the exclusion of fungi and thereby reduced the risk of mycotoxin
contamination during ogiri production. Further related studies on
methods of improving fermentation techniques on other products are
now being considered.
OCR for page 162
162
REFERENCES
FERMENTED FOODS
1. Jonsyn, F. E. 1988. Mycopathologia 104:123-127.
2. Jonsyn, F. E. 1989. Mircen Journal 5:547-562.
3. Jonsyn, F. E. 1990. Mycopathologia 110:113-117.
4. Jonsyn, F. E. 1991. In press.
5. H. G. Muller, personal communication.
6. Ogunsanwo, B. M., O. O. Faboya, O. R. Idowo, T. Ikotun, and
D. A. Akano. 1989. Die Nahrung 33 :983-988.
7. Odunfa, S. A. 1981. Journal of Plant Foods 3:245-250.
8. Antai, S. P., and M. H. Ibarahim. 1986. Journal of Applied
Bacteriology 61: 145-148.
9. Kellert, M., and H. J. Spott. 1980. Bundesgesundheitsblatt
23(1/2): 13-21.
10. Nowotny, P., W. Baltes, W. Kroenert, and R. Weber. 1983.
Chemie Mikrobiologie Technologie Der Lebersmitteln 8:2~28.
Representative terms from entire chapter:
smoke treatment
