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their contribution is likely to be negligible, particularly when compared
to the ability of LAB to produce lactic acid in quantities up to around
100 millimolar and a pH in the range 3.5 to 4.5.

9.4.2 Health-promoting Effects of Lactic Acid Bacteria-Probiotics

Fermented foods have long had a reputation for being positively beneficial
to human health in a way that ordinary foods are not. Ilya Metchnikoff,
the Russian founder of the theory of phagocytic immunity, was an early
advocate of this idea based on his theories on disharmonies in nature. He
held that the human colon was one such disharmony since intestinal
putrefaction by colonic bacteria produced toxins which shorten life. One
solution to this which he advocated in his book ‘The Prolongation of Life’,
published in 1908, was the consumption of substantial amounts of acidic
foods, particularly yoghurt. He thought that the antimicrobial activity of
the lactic acid bacteria in these products would inhibit intestinal bacteria in
the same way they inhibit putrefaction in foods and attributed the
apparent longevity of Bulgarian peasants to their consumption of yoghurt.
Since then a number of claims have been made for lactic acid bacteria,
particularly in association with fermented milks (Table 9.6). So much so,
that live cultures of lactic acid bacteria (and some others such as
Bifidobacteriumspp.) consumed in foods are frequently termed ‘probio-
tics’ (Greek: for life). Much of the evidence available on these putative
benefits is however inadequate or contradictory at present, and many
remain rather ill defined.
Several studies have shown improved nutritional value in grains as a
result of lactic fermentation, principally through increasing the content
of essential amino acids. Such improvements however may be of only
marginal importance to populations with a varied and well balanced diet.
It has also been reported that fermentation of plant products reduces
levels of antinutritional factors which they may contain such as cyano-
genic glycosides and phytic acid, although this effect is often the result of
other aspects of the process such as soaking or crushing rather than
microbial action. Some have claimed that fermentation of milks increases
the bioavailability of minerals, although this is disputed.

Table 9.6 Beneficial effects claimed for lactic

acid bacteria

Nutritional improvement of foods

Inhibition of enteric pathogens

Alleviation of diarrhoea/Constipation

Hypocholesterolaemic action

Anticancer activity

Simulation of the immune system

320 Fermented and Microbial Foods