J.H.J. Huis in 't Veld

Occurrence and formation of biologically active amines in foods

Attention is given to the toxicology of biogenic amines and their occurrence and formation in foods, with special emphasis on fermented foods. The role of the associated flora, the starter cultures used and their interaction is discussed.

Bringing a probiotic-containing functional food to the market: microbiological, product, regulatory and labeling issues.

Properly formulated probiotic-containing foods offer consumers a low risk, low cost dietary component that has the potential to promote health in a variety of ways. Several such products are available commercially, although markets in Japan and Europe are more developed than in the USA. Once healthful attributes of a probiotic product have been identified, there remain microbiological, product, regulatory and labeling issues to be addressed prior to marketing. Microbiological and product issues include safety, effective scale-up for manufacturing, definition of probiotic activity, probiotic stability in the product over the course of product manufacture, shelf-life and consumption, definition of effective dose and target population(s), and development of quality assurance approaches. Examples of probiotic-containing foods are given. Regulatory and labeling issues are complicated because they differ for each country, but are likewise critical because they provide the means for c ommunication of the product benefits to the consumer. The regulatory climate worldwide appears to be one of caution about overstating the benefits of such products but at the same time not preventing corporate commitment to marketing.

A selective medium for the two major subgroups of the bacterium Streptococcus mutans isolated from human dental plaque and saliva

A selective medium was developed on which both major subgroups of Strep. mutans (c/e/f and d/g) can be cultured and recognized on the basis of colonial morphology, Trypticase, yeast, cystine (TYC) agar was modified by adding separately autoclaved sucrose to a final concentration of 20 per cent and 0.1 unit/ml bacitracin (TYCSB). This medium yielded significantly higher counts of Strep. mutans than the widely used mitis-salivarius bacitracin (MSB) medium.

Purification and characterization of thermophilin T, a novel bacteriocin produced by Streptococcus thermophilus ACA-DC 0040

ACA‐DC 0040 produced an antimicrobial agent, which was named thermophilin T, active against several lactic acid bacteria strains of different species and food spoilage bacteria, such as Clostridium sporogenes C22/10 and Cl. tyrobutyricum NCDO‐1754. The crude antimicrobial compound is sensitive to proteolytic enzymes and α‐amylase, heat‐stable (100 °C for 30 min), resistant to pH exposure at pH 1–12 and demonstrates a bactericidal mode of action against the sensitive strain Lactococcus cremoris CNRZ‐117. The production of bacteriocin was optimized approximately 10‐fold in an aerobic fermenter held at constant pH 5·8 and 6·2. Ultrafiltration experiments with culture supernatant fluids containing the bacteriocin, and further estimation of molecular weight with gel filtration chromatography, revealed that bacteriocin in the native form has a molecular weight in excess of 300 kDa. SDS‐gel electrophoresis of partially purified thermophilin T showed that bacteriocin activity was associated with a protein band of approximately 2·5 kDa molecular mass.

The transmission of campylobacter in piggeries; an epidemiological study

The campylobacter infection of 10 sows and their piglets was monitored. These pigs werekept on two multiplier farms. Rectal faeces samples were taken from the sows shortly beforelittering and at different intervals after littering. Swab samples of rectal content were taken fromsix piglets per sow at different intervals after birth. Nine sows were shown to be infected withcampylobacter before litter and all sows after litter, with an average colony count of 4·1in log N g–1 of faeces. Half of the piglets became infected withcampylobacter during the first week of life and 85%, after four weeks. Two genetic subtypingmethods (ERIC‐PCR and RFLP) were used to study the relationships between campylobacterisolates from sows and piglets. A large diversity of campylobacter subtypes was found.Nevertheless, piglets and their mothers often harboured campylobacter isolates with identicalgenetic subtyping profiles, suggesting that piglets become infected via their mothers. However,observed similarities in genetic subtyping profiles between campylobacters isolated on differentfarms made this difficult to prove.

RAPD analysis: a rapid technique for differentiation of spoilage yeasts

Techniques for the identification of the spoilage yeasts Saccharomyces cerevisiae and members of the Zygosaccharomyces genus from food and beverages sources were evaluated. The use of identification systems based on physiological characteristics resulted often in incomplete identification or misidentification. Also the cellular fatty acid analysis failed on differentiating species within the Zygosaccharomyces genus. However, the Random Amplified Polymorphic DNA (RAPD) assay, using selected 10-mer oligonucleotides, allowed discrimination between all species tested. For this RAPD assay, a simple and reproducible method of DNA isolation from spoilage yeast cells is described.

A decision support system for the prediction of microbial food safety and food quality

The development of a method to predict microbial food safety and quality is described. The manufacture of a food from its ingredients is simulated, using a recipe. Food engineering heuristics are combined with models developed in predictive microbiology. Parameter values of ingredients of foods, such as water activity and pH, and models for microbial growth and decay are used for the prediction of the kinetics of microorganisms generally found in ingredients. The values of these parameters are collected in databases. If required information is lacking, methods are described for making reliable guesses of the parameters. Food quality can be calculated as a function of fluctuating temperature in time. Several food distribution chains can be simulated in order to assess the influence of distribution chains on food quality. The described methods were implemented into a computerised decision support system that can be used in food production, product development and training. In the future it may be possible to apply specific expert knowledge in production and development of foods to improve the quality of prediction.

Streptococcus mutans and dental caries in humans: a bacteriological and immunological study.

Plaque samples from caries-active subjects showed a higher incidence of S. mutans than plaque samples from caries-free subjects. This was especially evident in approximal incisor plaque. S. mutans serotype d was almost exclusively present in approximal plaque obtained from caries-active subjects. Tooth surfaces infected with S. mutans still harbored this micro-organism 10 months later, while uninfected tooth surfaces remained free of S. mutans. Caries development predominantly occurs on those tooth surfaces which harbor relatively high percentages of S. mutans (> 5%). It is unlikely that serum or saliva antibodies against S. mutans play a major role in the protection against dental caries in these caries-free subjects since subjects with the greatest number of decayed surfaces showed the highest antibody titre as measured by haemagglutination or by the enzyme-linked immuno sorbent assay (ELISA).Plaque samples from caries-active subjects showed a higher incidence of S. mutans than plaque samples from caries-free subjects. This was especially evident in approximal incisor plaque. S. mutans serotype d was almost exclusively present in approximal plaque obtained from caries-active subjects. Tooth surfaces infected with S. mutans still harbored this micro-organism 10 months later, while uninfected tooth surfaces remained free of S. mutans.Caries development predominantly occurs on those tooth surfaces which harbor relatively high percentages of S. mutans (> 5%). It is unlikely that serum or saliva antibodies against S. mutans play a major role in the protection against dental caries in these caries-free subjects since subjects with the greatest number of decayed surfaces showed the highest antibody titre as measured by haemagglutination or by the enzyme-linked immuno sorbent assay (ELISA).

Enhanced Antigen-Specific Delayed-Type Hypersensitivity and Immunoglobulin G2b Responses after Oral Administration of Viable Lactobacillus casei YIT9029 in Wistar and Brown Norway Rats

ABSTRACT In this study, the effects of orally administered viableLactobacillus casei Shirota strain YIT9029 on the immunity parameters of Wistar and Brown Norway rats were examined. For this purpose, we used the Trichinella spiralis host resistance model. Two weeks before and during T. spiralisinfection, rats were fed 109 viable L. casei bacteria 5 days per week. The T. spiralis-specific delayed-type hypersensitivity (DTH) response was significantly enhanced in both Wistar and Brown Norway rats given L. casei. In both rat strains fedL. casei, serum T. spiralis-specific immunoglobulin G2b (IgG2b) concentrations were also significantly increased. In the model, no significant effects ofL. casei on larval counts or inflammatory reactions in the tongue musculature, body weights, or lymphoid organ weights were observed. Serum specific antibody responses, other than IgG2b, were not changed by feeding of L. casei. In contrast toL. casei, it was shown that orally administeredBifidobacterium breve or Bifidobacterium bifidum had no influence on the measured infection and immunity indices in the rat infection model. Since the rat DTH response is considered to be a manifestation of Th1 cell-mediated immunity and the IgG2b isotype has been associated with Th1 activity, it was concluded that Th1 cells could play an active role in the immunomodulatory effects of orally administered L. casei. Furthermore, our data do not indicate that the effect of oral supplementation withL. casei is dependent on the genetic background of the host.

Anti-Cariogenic and Remineralizing Properties of Xylitol in Combination with Sucrose in Rats Inoculated with Streptococcus mutans

The anticariogenic and remineralizing properties of xylitol were studied in Osborne-Mendel rats inoculated with Streptocococcus mutans, with special emphasis on the general health of the rats. A purified diet containing 20% sucrose and 5% glucose and supplemented with 5% xylitol (diet SX) induced significantly fewer fissure lesions than the unsupplemented control diet (diet S). Initial lesions induced by diet S were significantly reduced by subsequent exposure to the SX diet, while the very advanced lesions increased markedly. Changing from the SX diet to the S diet resulted in substantial caries progression. The percentage of S. mutans in plaque samples, the body weight gains and the health of the rats were not influenced by xylitol, although the cecum showed a reversible enlargement. This study confirms the suggested therapeutic effect of xylitol even when mixed with sucrose, while nonspecific effects were eliminated.