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KMID : 0380619860180050376
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Korean Journal of Food Science and Technology
1986 Volume.18 No. 5 p.376 ~ p.381
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Pigment - forming bacteria in the presence of L - typrosine and their possible role in the browning of fermented soybean products
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Abstract
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A hypothesis that Korean home-made fermented soybean products are brown-pigmented in large part by contaminated bacteria is proposed. Twenty six strains of bacteria forming brown pigments in the presence of L-tyrosine were isolated from home-made soybean paste. They were characterized and all were identified as strains of Bacillus subtilis. The isolates produced dark brown to brownish black pigmentation on yeast extract-peptone-glucose agar (YPGA) supplemented with 0.1% L-tyrosine in 72 hours but not on YPGA. They also caused different depress of lighter pigmentation on potato dextrose agar and nutrient agar. When an arbitrarily chosen pigmenting isolate was cultivated in a liquid medium supplemented with L-tyrosine, it began to produce pigments only after cell growth stopped. The tyrosinase enzyme was extracted and the enzyme activity was measured by using L-tyrosine and 3-hydroxytyrosine (L-dopa) as substrates. The crude enzyme preparation porduced pigments at rates of 2.1 × 10^(-3) and 5.0 × 10^(-3) optical density unitslmin measured at 490㎚ for tyrosine and dopa, respectively. Possible content of L-tyrosine in a soybean paste formula was calculated.
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