Page 175 - Natural Antioxidants, Applications in Foods of Animal Origin

154 Natural Antioxidants: Applications in Foods of Animal Origin
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4.4.2.3 MICROBIAL SOURCES

Microorganisms are one of the most abundant and diverse species found on
earth and their exploitation to produce food ingredients has been going on
for the past decade. However, the isolation of microbial antioxidants became
a focus of research in the early 1980s, Forbes et al. (1958) established a

relationship between antioxidants and microorganisms and since this early
work, a vast number of compounds and microorganisms have been charac-
terized. Several studies have demonstrated the antioxidant activity of micro-
organisms. Using the thiocyanate method, the antioxidant activity of ethyl
acetate extracts of several Penicillium and Aspergillus species was evaluated
(Yen & Lee, 1996). Extracts of these species protected linoleic acid better
than the control. In a study by Yen and Chang, it was reported that sucrose or
lactose and ammonium sulphate in culture media enhanced the Aspergillus
candidus production of antioxidants (Yen & Chang, 1999). Extracts with

similar activity were produced from ethyl acetate extraction of the broth and
mycelium.
In a study conducted by Aoyama et al. (1982), 750 filamentous fungi

isolated from soil were screened. Two antioxidants were identified as
citrinin and protocatechuic. A third compound, curvulic acid, isolated from
an unidentified Penicillium was also evaluated for antioxidant activity in
linoleic acid. All three compounds were reported to have good antioxidant
activity. The curvulic acid had the largest antioxidant activity followed by
the curvulic acid methyl ester, protocatechuic acid, and citrinin.
According to Esaki et al. (1997) Aspergillus species are effective

producers of antioxidant activity compounds. In their study, 30 strains
of Aspergillus were evaluated and it was found that methanol extracts of
fermented soybeans (MEFS) prevented oxidation of methyl linoleate. The
MEFS of 28 strains had better antioxidant activity than the non-fermented
soybean while all strains were better than the control. Separation of the
MEFS revealed 2,3-dihydroxybenzoic acid as a component of the most
active fraction. Hayashi et al. (1995) also identified this compound in Peni-

cillium roquefortii IFO 5956 cultures.
In another study, Esaki et al. (1997) evaluated the antioxidant activity of

methanol extracts (MEs) of miso, natto, and tempeh and found that tempeh
was the most effective followed by miso. They further stated that fermenta-
tion by mold cultures are more active than bacterial (Bacillus natto) ones
in producing antioxidants. This was evident as a result of the antioxidant
activity of the natto ME being less than that of other fermented products
but was equivalent to that of unfermented soybeans. Hoppe et al. (1997)