Yeast Extract Sucrose Broth Research Articles

Rubratoxin Formation in Soybean Substrates

Sterile soybeans, low and full fat soy meal, soy residue, soy curd, and soy whey fortified with different nutritional supplements were inoculated with spore suspensions of Penicillium rubrum P-3290. Yeast extract-sucrose (YES); glucose-malt extract; maltose-soytone; soy whey containing 1.75, 3.5, and 5.5% dissolved solids; and a maltose-salts medium were also inoculated. Cultures were incubated quiescently at 28 C for 7, 10, or 14 days. Rubratoxins were extracted with ethyl acetate and diethyl ether and resolved by thin-layer chromatography. Greatest yields of toxin were obtained from natural rather than chemically defined media. Semisynthetic media supported formation of moderate amounts of rubratoxins. Malt extract and glucose supported greatest production of both rubratoxins A and B. Unsupplemented soy whey or soy milk did not support rubratoxin production. Although soy meal supported production of both rubratoxins A and B (0.12–0.24 mg/g and 0.55–0.71 mg/g), low fat soy meal was more suitable for toxin formation than was full fat meal. Both rubratoxins A and B were produced by P. rubrum grown in soy whey fortified with soytone, malt extract, or glucose; only rubratoxin B was produced when yeast extract or sucrose served as supplements. YES broth supported formation of only rubratoxin B. Production of toxin in soybeans was influenced by time of incubation and temperature. Maximum yields of toxin on soybeans were obtained after 14 days of incubation at 25 C, after 28 days at 28 C, after 7 days at 32 C, and after 3 days at 37 C. Rubratoxin was not produced at 40 C. Yields of rubratoxin A in soy whey media ranged from 35–40 and from 15–28 mg/100 ml when malt extract or glucose were added; values for rubratoxin B ranged from 55–100 mg/100 ml and 65–125 mg/100 ml.

EXAMINATION OF SWISS CHEESE FOR INCIDENCE OF MYCOTOXIN PRODUCING MOLDS

ABSTRACTSamples of 11 brands of Swiss cheese were analyzed by plate count for molds capable of growing at 5 and 21°C. Portions of each sample were stored at 5°C and observed for visible mold development throughout a 6‐wk storage period. Representative molds were isolated from counted plates and moldy samples, and identified to genus. Isolates were grown in yeast extract sucrose broth and rice powder corn steep agar cultures at 12°C for 2 wk, and then extracted with chloroform. The extracts were tested for toxicity to 7‐day‐old chicken embryos, and analyzed for the presence of known mycotoxins using TLC. Cheese samples that developed visible mold growth during storage were extracted with acetonitrile. The extracts were examined for the presence of known mycotoxins using TLC. Mold counts ranged < 10 to 1580 colonies/g of surface cheese at 5°C and from < 10 to 5700 colonies/g of surface cheese at 21°C. AlI cheese samules stored at 5°C develoued visible mold growth within 6 wk. Of the 183 molds isolated, 87% were Penicillium species; 93% of the isolates that grew at 5°C were penicillia. Toxicological screening of the mold isolates showed extracts of 34% of all isorates, and 35% of Penicillium isolates were toxic to chicken embryos. Chemical analyses of the culture extracts detected known mycotoxins in 5.5%. Toxins detected were penicillic acid, patulin and aflatoxins. Analyses of moldy cheese stored at 5°C for 6 wk for known mycotoxins showed peniciliic acid in 4 of 33 samples. The isolated penicillic acid was comparable to standard penicillic acid by TLC in three different solvent systems using three different derivatization procedures. UV and IR absorption spectral data supported the TLC data.

EFFECT OF LOW DOSE GAMMA IRRADIATION ON GROWTH AND AFLATOXIN PRODUCTION BY ASPERGILLUS PARASITICUS

Spores and growing vegetative mycelia of Aspergillus parasiticus strains NRRL 2999 and NRRL 3000 were irradiated at 100 and 200 Krad, and the effects on growth and aflatoxin production in yeast-extract sucrose (YES) broth were measured. Irradiation of growing mycelia reduced subsequent growth in YES broth by a greater amount than irradiation of spores. Irradiation of spores at 100 Krad resulted in more B1 and G1 production by strain NRRL 2999 than the non-irradiated control, however, strain NRRL 3000 produced less aflatoxins B1 and G1 after irradiation at 100 Krad than its non-irradiated control. Spores of both strains irradiated at 200 Krad produced less aflatoxins B1 and G1 than non-irradiated controls. Irradiation of growing vegetative mycelia of both strains at 100 and 200 Krad resulted in a definite decline in both aflatoxins B1 and G1 in subsequent cultures at each irradiation level. Apparent stimulation of production of both B1 and G1 occurred after irradiation of spores of strain NRRL 2999 at 100 Krad. However, the variation of the values as determined by the standard deviation was such that one would conclude that no differences existed among means. The apparent stimulation was slight and of much less magnitude than that which has been reported by other investigators using A. flavus. No stimulation of toxin production was observed with the other strain when grown from irradiated spores or with either strain when vegetative mycelia were irradiated.