Identifying Nucleotidic Materials Released by Fermenting Brewer's Yeast

SUMMARY— During fermentation a brewer's yeast released into the medium substantial amounts of materials absorbing ultra-violet light at 260 mμ These materials were separated by chromatography and identified by further chromatography and spectrophotometry. Nine nucleotides, five free bases (purines and pyrimidines) and four nucleosides were identified in the fermented medium and in the intracellular pool of the yeast. Some of these released materials may be of consequence in the fermented beverage industry since they were not reabsorbed by yeast and can be expected to persist to the finished product.     

Chemical Induction of Mutation or Variation In Aflatoxin-Producing Cultures of Aspergillus Flavus

SUMMARY– The mutation or variation of a strain of Aspergillus flavus was induced chemically after six successive "generations" of exposures to barium ions. Colony isolates of A. flavus , developing from spores harvested from cultures grown in barium medium, were examined for mutation on the basis of morphology, loss of aflatoxin-producing capacity, and loss of ability to grow in basal medium. The new characteristics exhibited by the mutant of A. flavus are the inability to produce aflatoxins and yellow pigment, accompanied by the loss of fluorescence in the culture under ultraviolet light. These changes did not revert after more than eight successive transfers in a barium-free medium. Mutagenic action of barium ions on the fungus A. flavus was shown by the mutatation of colonies arising from single spores, The characteristics of the mutant are permanent and irreversible.     

Effect of Chlorophenoxyacetic Acid Growth-Regulator Sprays on Residues in Canned Apricots and Grapes

SUMMARY— A, gas-liquid chromatographic method coupled with an electron capture detector has been developed for analyzing chlorinated phenoxyacetic acid residues in canned fruits. The technique involves converting the acid to its methyl ester with diazomethane, chromatography on a 5% silicone grease SE-30 column at 210°C, and subsequent detection of the compound by an electron capture detector. As low as 0.02 ppm of the residue could be detected. The method is superior to the calorimetric method because parachlorophenoxyacetic acid (PCPA), 2,4-D, and 2,4,5-T can be separated and quantitatively determined simultaneously. However, separate standard curves are needed for each, because they differ in chlorine content and in sensitivity toward the electron capture detector. Levels of 2,4-D and 2,4,5-T residues in canned apricots, and of PCPA in canned grapes are reported.     

Characterization of Polyphenoloxidase from Ravat 51 and Niagara Grapes

Polyphenoloxidase (PPO) was isolated from two varieties of grapes grown in the northeastern United States and its characteristics were studied. The temperature and pH optima for both enzymes were 25°C and 5.5, respectively. The thermal inactivation of PPO followed first-order kinetics; with the Niagara enzyme being more heat stable than Ravat PPO. The substrate specificity of the grape PPO clearly showed high affinity toward the o-diphenolic compounds, with a high affinity toward caffeic acid. Inhibition studies indicated that L-cysteine and sodium diethyldithiocarbamate were the most potent.     

Microflora, Sensory and Exudate Changes of Vacuum- or Nitrogen-Packed Veal Chucks Under Different Storage Conditions

Apart from increases in microflora number at —4°C under vacuum and at 0°C under nitrogen, there was in general no significant (P gt; 0.05) differences in numbers of lactobacilli, psychrotrophs, aerobes and anaerobes between vacuum- and nitrogen-packed veals during 49 days of storage at 3 and 7°C, regardless of dark and lighted displays. The initial psychrotrophs consisted primarily of Pseudomonas putida (> 72%) but by day 49 Lactobacillus spp. comprised at least 64% of the total in both atmospheres. Sensory and exudate data showed a highly significant (P < 0.05) difference due to the effect of storage time and temperature above 0°C. Nitrogen-packed veals exhibited a lower incidence of greening and exudate loss at 0, 3 and 7°C. Light generally had important effects on off-odor and exudate loss, irrespective of package types.     

A Comparison of Methods for Polyuronide Methoxyl Determination

A comparison was made between three basic methods for determining methoxyl (OMe) groups in a polyuronide, viz., step-wise oxidation-reduction initiated by hydriodic acid, neutralization of de-esterified carboxyl groups with potassium hydroxide, and direct combustion of methanol by gas chromatography. Accuracy and precision of the methods were ascertained by analyzing methyl fuorate. All the methods were accurate. The neutralization and gas chromatographic methods had major advantages of simplicity and shortness of time of completion over the hydriodic acid/bromine method. Dimethylsulfoxide in the the saponification medium had no special effect.     

Cr-Si粉末冶金工艺及其物理-力学性能

粉末冶金制作法主要有热压(HP)、热等静压(HIP)及常压烧结(Sinter)三种.采用热压及热等静压法可以很容易地得到高致密化的高温金属硅化物,但若要进行大尺寸的产品烧结,必须提升生产设备的规格和能力,例如加大热压机力吨位、扩大热压炉腔体等,致使设备投资及生产成本相对昂贵.所以大部分厂商宁可采用常压烧结法,虽然该法的高致密化工艺条件不易控制,却因可以制作大尺寸金属硅化物,加上设备投资及生产成本相对降低,使许多大厂已投入相当大的人力和物力在开发此工艺.该文作者试用不同真空烧结温度,造成Cr-Si合金粉末烧结性质的差异,探讨稳定而可大量生产的可行性;并通过对温度的控制,来改善Cr-Si的物理性质与力学性质.结果表明,提高烧结温度会使Cr-Si合金产生部分液相烧结的现象,从而使孔隙率显著下降;但显微结构也随之有偏析与晶粒粗化的现象.