CHALLENGE STUDIES WITH CLOSTRIDIUM BOTULINUM TYPE E IN A VALUE-ADDED SURIMI PRODUCT STORED UNDER A MODIFIED ATMOSPHERE

Challenge studies were carried out on raw, cooked, and sterilized surimi nuggets, inoculated with 10⁴ spores/g of C. botulinum type E spores. All products were packaged in air and air with an Ageless SS oxygen absorbent and stored at 4, 12 and 25C. Toxin was not detected in any raw product throughout storage (28 days). The absence of toxigenesis was attributed to the low pH (4.1–4.3) due mainly to the growth of lactic acid bacteria (10⁷CFU/g). Toxin was also not detected in any cooked product after 28 days. Product pH did not decrease as previously (due to the absence of LAB), but counts of C. botulinum still decreased throughout storage.
In sterile nuggets , C. botulinum counts increased to 10⁶ cfu/g at both 12 and 25C, respectively, by 28 days. Lactic acid bacteria and Bacillus spp. were not detected throughout the 28 days storage period. Toxin was detected by days 28 and 14 at 12 and 25C, respectively, and toxigenesis preceded spoilage. The absence of toxin in cooked nuggets was attributed to the anti-botulinal role by Bacillus species, the predominant spoilage bacteria in cooked nuggets.     

Evaluation of a CPU Scheduling Mechanism for Multimedia Systems

Multimedia applications handling audio and video data have to obey time characteristics of these media types. Besides a basic functionality to express time relations, correctness with respect to time constraints requires mechanisms which lead to favoured processing of multimedia operations. CPU scheduling techniques based on the experience from real-time operating systems offer a solution and provide multimedia applications with the ability to meet time-related quality of service requirements. This paper discusses mechanisms to express time in multimedia systems and describes an implementation of a CPU scheduler designed to run under IBM's UNIX derivate AIX. The evaluation of the implementation based on measurements shows that the scheduler is able to support the time requirements of multimedia applications and that such mechanisms are indeed necessary since otherwise deadline violations occur.     

HEXOSAMINE PRODUCTION BY PSYCHROTROPHIC FOOD-SPOILAGE BACTERIA UNDER VARYING GROWTH CONDITIONS

Four psychrotrophic, gram negative meat isolates were grown at 6 and 22°C with and without aeration, in AOAC synthetic broth with 0.1% glucose and in a basal medium containing 0.1% glucose and 0.5% glycine (BMGG-1). In AOAC broth, three strains produced more hexosamine at 6°C, while the fourth produced more at 22°C. Three of the four strains also produced more slime at 6°C. All four strains grew faster with aeration at both temperatures, but produced less hexosamine. Under all conditions, the growth rate of each strain was inversely proportional to its hexosamine production. During the growth cycle in BMGG-1, medium pH dropped until the log phase was under way and then rose again through the stationary phase. This rise coincided with the depletion of glucose. Hexosamine production first became detectable at the end of the log phase, rose during the stationary phase, and then leveled off. Adjusting pH to prevent the initial drop increased both growth and hexosamine production. Raising the concentration of glucose to 0.5% accelerated growth but decreased hexosamine production. Approximately 95.1% of the hexosamine produced was cell-associated. It consisted primarily of glucosamine polymers with a lesser amount of galactosamine. Only 3.0% of the nitrogen from the BMGG-1 was utilized by the cells. Of this 3.0%, 58% was used for ammonia, 27.2% for hexosamine, and 14.8% for other substances. Of the 40.7% used for total cell production, 63.8% went into hexosamine.     

BIOFILM FORMATION BY SALMONELLA SPP. ON CANTALOUPE MELONS**

The ability of two strains of Salmonella to form biofilms on whole cantaloupe melons was investigated. Ten microliters of bacterial suspensions was spot‐inoculated onto cantaloupe melon rinds in pre‐marked areas, and the cantaloupe melons were held at either 10 or 20C. Biofilm formation was monitored using scanning electron microscopy on excised portions of the cantaloupe melon rind at 2, 24, 48, 72 and 144 h postinoculation. Micrographs indicated that biofilm formation occurred rapidly following introduction of cells (2 h at 20C) onto the cantaloupe melon rind. A fibrillar material was visible after just 2 h at 20C, and cells were embedded in extracellular polymeric material after 24 h at either temperature. These results indicate that a human pathogen is capable of forming a biofilm on plant tissue and that biofilm formation may be responsible for the increased recalcitrance of bacteria to aqueous sanitizers.     

EFFECT OF FILMS OF DIFFERENT OXYGEN TRANSMISSION RATE ON TOXIN PRODUCTION BY CLOSTRIDIUM BOTULINUM TYPE E IN VACUUM PACKAGED COLD AND HOT SMOKED TROUT FILLETS

Studies were done to determine the effect of film oxygen transmission rate (OTR) on the time to toxicity in vacuum packaged cold and hot smoked rainbow trout fillets challenged with C. botulinum type E (10² spores/g) and stored at refrigerated conditions (4C), and under mild (8C) and moderate (12C) temperature abuse conditions. While no samples were toxic at 4C, toxin was detected within 28 days at 8C for cold smoked trout fillets vacuum packaged in films with high OTR. Toxin was also detected for most vacuum packaged hot smoked trout fillets within 14–28 days at 8C, with the exception of trout fillets packaged in films with an OTR > 10,000 cc/m²/day. In most cases at 8C, spoilage, based on odor/color scores, preceded or occurred simultaneously with toxigenesis. At 12C all cold and hot smoked trout were toxic after 14–21 days and samples packaged in films with an OTR <5000 cc/m²/day became toxic before, or at the same time as, samples became spoiled. This study has shown that vacuum packaging of trout fillets in low gas barrier films, ranging in OTR from approximately 3,000 to approximately 10,000 cc/m²/day at 24C and 0% relative humidity (RH), did not prevent the growth and toxin production by C. botulinum in vacuum packaged cold and hot smoked trout fillets at 12C. Additional barriers, other than the OTR of the packaging film, need to be considered to ensure the safety of vacuum packaged trout fillets, particularly at mild to moderate temperature abuse storage conditions.     

A practical overview of neural networks

This paper overviews the myths and misconceptions that have surrounded neural networks in recent years. Focusing on backpropagation and the Hopfield network, we discuss the problems that have plagued practical application of these techniques, and review some of the recent progress made. Both real and perceived inadequacies of backpropagation are discussed, as well as the need for an understanding of statistics and of the problem domain in order to apply and assess the neural network properly. We consider alternatives or variants to backpropagation, which overcome some of its real limitations. The Hopfield network's poor performance on the traveling salesman problem in combinatorial optimization has colored its reception by engineers; we describe both new research in this area and promising results in other practical optimization applications. Overall, it is hoped, this paper will aid in a more balanced understanding of neural networks. They seem worthy of consideration in many applications, but they do not deserve the status of a panacea – nor are they as fraught with problems as would now seem to be implied.     

ACTIVE DAMPING OF MAGLEV VEHICLES USING SUPERCONDUCTING LINEAR SYNCHRONOUS MOTORS

ABSTRACT

This paper explores the use of linear synchronous motor control to provide active damping for magnetically-levitated vehicles. Using a single LSM, only heave and surge damping can be provided, but, with a dual LSM, roll and yaw damping can also be achieved. The paper gives design data applicable to the reference design of theCanadian 500 km/h Maglev system.     

EFFECT OF ETHANOL VAPOR ON GROWTH AND TOXIN PRODUCTION BY CLOSTRIDIUM BOTULINUM IN A HIGH MOISTURE BAKERY PRODUCT

To determine the effect of ethanol vapor on toxin production by Clostridium botulinum, studies were done in English style crumpets (a_w 0.990, pH 6.5) challenged with 500 spores/g C. botulinum types A and proteolytic B and packaged in high gas barrier bags [ethanol transmission rate (ETR) 0.21 g/m²/day @ 25 C]. Crumpets were packaged in air with either commercially available ethanol vapor generators (Ethicap® 2, 4 or 6G) or cotton wool pads saturated with 2, 4 or 6 g of 95% food grade ethanol and stored at 25C. Toxin was detected in all inoculated control crumpets (0% ethanol) after 5 days at ambient temperature (25C). Ethicap® 2G delayed toxicity for 10 days while complete inhibition (>21 days) was observed in all crumpets packaged with 4 or 6G Ethicap® or with 2, 4 or 6 g of ethanol per pad. However, all crumpets were overtly spoiled by this time. Both headspace ethanol and absorption of ethanol by crumpets increased as a function of Ethicap® size/weight of ethanol. Based on these preliminary studies, ethanol vapor would appear to be an effective additional barrier to control the growth and toxin production by C. botulinum in high moisture bakery products and ensure the safety of these products at ambient temperature.     

EFFECT OF HEADSPACE OXYGEN AND FILMS OF DIFFERENT OXYGEN TRANSMISSION RATE ON TOXIN PRODUCTION BY CLOSTRIDIUM BOTULINUM TYPE E IN RAINBOW TROUT FILLETS STORED UNDER MODIFIED ATMOSPHERES

Studies were conducted to determine the effect of various levels of headspace oxygen (0–100%, balance CO₂) or film oxygen transmission rate (OTR) on the time to toxicity in modified atmosphere packaged (MAP) fresh trout fillets challenged with C. botulinum type E (10² spore/g) and stored under moderate temperature abuse conditions (12C). In all cases, trout were toxic within 5 days, irrespective of the initial levels of oxygen in the package headspace. However, spoilage preceded toxigenesis. Packaging of trout fillets in low gas barrier films, with OTRs ranging from 4,000 to 10,000 cc/m²/day at 24C and 0% relative humidity, also had no effect on time to toxicity in all MAP trout fillets. All fillets were toxic within 4–5 days and spoilage again preceded toxigenesis. This study has shown that the addition of headspace O₂, either directly to a package or indirectly by using a low gas barrier film, had no influence on the time to toxigenesis or spoilage. Additional barriers, other than headspace O₂ or film transmission rate, need to be considered to ensure the safety of MAP trout fillets, particularty at moderate temperature abuse conditions.