The most probable number (MPN) technique is extensively used in food microbiology. However, because statistics involved often are cumbersome and it is difficult to obtain some of the widely scattered literature, many individuals are not able to delve into the subject to gain a thorough understanding of the method. To overcome these inherent difficulties, this review and discussion was prepared as an introduction and aid in presenting the MPN method to students and individuals working in food microbiology.
Phcnoloxidase(PO) from lobster cuticle existed as a large inert enzyme (IPOI) which became active (15fold increase) upon incubation at 4°C and 3 days storage. Electrophoresis of day 3 extracts showed that the large enzyme disappeared gradually while a new PO (EAPO) developed (Mw of 62.5 kDA).
In a comparative study to determine their effectiveness for early detection of prolific histamine-producing bacteria from tuna samples, Niven's medium proved to be superior to three modifications of the medium. Presumptive colonies could be detected in 24 h on Niven's agar surface-plated and incubated at 35°C. Following confirmatory histamine determination with high performance liquid chromatography of the tuna fish infusion broth inoculated with presumptive histamine-producers and non-producers, detection rates of 95.8 and 93.9% were obtained from temperature-abused and bacteria-spiked tuna samples, respectively, using Niven's agar. The other three modifications provided much lower detection rates and higher false-positive and false-negative results than did Niven's agar.
Plesiomonas shigelloides is an oxidase-positive, gram-negative rod that has been implicated as an agent of human gastroenteritis for almost 40 years. Reports of gastroenteritis associated with Plesiomonas have been increasing in recent years, although inadequacies in isolation techniques and recognition procedures have undoubtedly resulted in the underreporting of this organism in the past. Existing information indicates that P. shigelloides, while mainly an aquatic species, is widely distributed in the environment. Recent outbreaks of gastroenteritis associated with consumption of oysters contaminated with P. shigelloides have resulted in an increased awareness of this organism by public health officials.
AJ3STRACTFrozen orange juice concentrate (63.8" Brix) was reconstituted with water to single strength juice and supplemented with a commercial citrus pectinesterase (PE) to give an activity of 1.5 PE units/ml juice. Reconstituted juice and freshly squeezed single strength orange juice -_ were treated with a cation exchange resin. Resin treatment decreased the OH of the iuice from 3.75 to 2.0 and comuletelv inactivated PE. PE &as also &activated following acidification' of the juice to pH 2.0 with concentrated hydrochloric acid. Very little cloud loss occurred in refrigerated (4°C) juice at pH 2.0 for approximately 12 wk; however, a loss (> 95%) of ascorbic acid resulted. Only microorganisms died-off rapidly (> 99.9%) in juices adjusted to pH 2.0 using ion exchange resin, but not in juices lowered to pH 2.0 with HCl.
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