No abstract

The effects of black pepper, cinnamon, peppermint, cumin, ginger and clove on growth and aflatoxin formation of Aspergillus flavus were studied in rice powdercorn steep (RC) medium. The effects of the first five spices were judged to be inhibition of aflatoxin formation rather than of mycelial growth. Clove completely inhibited both mycelial growth and aflatoxin formation at a concentration above 0.1%. No aflatoxin was produced when cumin and mint levels of 5% and 10% were used. Black pepper and ginger levels of 10% decreased aflatoxin formation by 100%. Higher concentrations of cinnamon, mint, cumin and ginger stimulated mycelial growth.

The activities of three natural coumarins, xanthotoxin and bergapten (fromAmmi majus, Umbelliferae) and psoralene (fromFicus cycomorus, Moraceae), were tested against mycelial growth and aflatoxin production of a toxigenic strain ofAspergillus flavus grown in a rice/corn steep liquor medium. Two other natural chromones, khellin and visnagin (fromAmmi visnaga) were also compared. Complete inhibition of aflatoxin release occurred with either xanthotoxin or khellin at 5 mM. The other three compounds also at 5 mM reduced aflatoxin to 12 to 16% of its original concentration. The mould growth was only slightly inhibited by all the compounds used.

SUMMARYAmong 20 locally isolated fungi, Aspergillus niger isolate no. 58 proved to be suitable for the production of active extracellular milk-clotting enzyme. The addition of acetate buffer to the reaction mixture enhanced the clotting of milk by the enzyme whereas citrate +phosphate buffer hindered the process. The general properties of the crude enzyme were studied. Precipitation with ammonium sulphate, ethanol, acetone and tannin showed that ammonium sulphate was unsuitable for precipitation while the other precipitantgproduced sufficiently active fractions. I N T R O D U C T I O NStudies on the production of milk-clotting enzymes from microbial sources have gained interest during the last decade; the production of milk-clotting enzymes by different types of micro-organisms has been reported (Arima & Iwasaki, I 964; Veselov, Tipograf & Petina, I 965 ; Knight, I 966). The increasing demands on rennin for cheese making in Egypt and the prohibition of the slaughter of calves justified a study aiming to search for rennin substitutes from sources other than animals and in particular from micro-organisms. Cultivation. Transfers were made from the stock slants to Dox agar plates which were then incubated at 30' for 7 days. Two discs (0.5 cm. diam.) were cut from the 7-day culture and inoculated into 50 ml. sterile medium in 250 ml. flat bottomed flasks. Unless otherwise specified, the flasks were incubated for 3 to 4 days at 3 0 ' . At the end of the incubation period the culture medium was filtered off and its volume adjusted to 50 ml.

SUMMARYThe production of a rennin-like milk-clotting enzyme by Penicillium citrinum 805 was investigated. Corn-steep water was the best medium for the production of the enzyme. Dephytinization of corn-steep water lowered production of the enzyme. The extent of mycelial sporulation was correlated with the milk-clotting activity. Precipitation with ammonium sulphate and ethanol was unsuitable, but acetone produced active fractions. The enzyme action was optimal at 60" and at pH 6.0 while the stability of the enzyme was maximal at pH 5-37. The enzyme exhibited feeble proteolytic activity.