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One of the components of the General Agreement on Tariffs and Trade Sanitary and Phytosanitary agreement that will have far-reaching effects on International trade in foods and food products is the requirement for countries to provide risk assessments as part of the process of resolving disputes that involve food safety issues. Risk assessment is a means of evaluating the likelihood and impact of hazards. It provides a framework for systematically considering available data, providing rationales for assumptions, and identifying areas where additional information is needed. While the application of quantitative risk assessment techniques to microbial food safety has been limited, recent studies have increasingly demonstrated its feasibility. Quantitative risk assessment is particularly well suited for use with the hazard analysis critical control point and appears to have potential as an approach for comparing the equivalence of international food safety programs and inspection systems.

Feruloylated glucuronoarabinoxylans were extracted from wheat bran by means of cold water, steam and dilute alkali, yielding approximately 1, 20 and 3%, respectively, of the glucuronoarabinoxylans originally present in the bran. The extracts had ferulic acid contents ranging from 0.1 to 0.6% (w/w). Both the cold water and steam extract had a low total sugar content and a relatively low content of high molecular weight material. Moreover, the ferulic acid content of the water extract was low (0.1 %) and the amount of degradation products in the steam extract was relatively large. Both extracts appeared to give no increase in viscosity upon addition of oxidative reagents, such as hydrogen peroxide plus peroxidase or ammonium persulphate. The alkaline extracts obtained with saturated calcium hydroxide or 0.05 M barium hydroxide had high total sugar contents, the majority of which was accounted for by glucuronoarabinoxylan (>90%). These extracts had moderate ferulic acid contents of 0.3% and consisted predominantly of high molecular weight material. Addition of oxidative reagents resulted in an increase of viscosity. The extent of this increase in viscosity was shown to be influenced by the oxidative reagent used, the purity of the extract, its molecular weight distribution and the degree of substitution of the glucuronoarabinoxylan.

The ICMSF has recommended several steps for the management of microbiological hazards in foods in international trade, applying existing Codex documents in a logical sequence. The steps include: the conduct of a risk assessment and an assessment of risk mnanagement options, the establishment of a food safety objective (FSO), and confirmation that the FSO is achievable by application of GHP and HACCP. A FSO is a statement of the frequency or maximum concentration of a microbiological hazard in a food considered acceptable for consumer protection. FSOs can be used by risk managers to communicate to industries this acceptable level of a hazard, in order to establish effective control measures. The effectiveness of control measures is assured through adhering to performance criteria and process criteria set by the industry to meet the FSO. This system of food safety management will facilitate acceptance of seemingly different, but in reality equivalent, food production and food control practices.

Mixtures of sucrose and sodium cyclamate were studied to evaluate possible interactive effects between these sweeteners and orange aroma compounds. Equisweet mixtures (10% sucrose equivalent value) of the sweeteners were prepared by taking into account the observed synergistic effects between sucrose and sodium cyclamate. The release of volatile compounds from the solutions containing these mixtures and a water soluble orange aroma was studied. The volatile compounds were quantified and identified by gas chromatography combined with flame ionization detection (GC/FID) and mass spectrometry (GC/MS). The presence of sucrose significantly changes the release of 15 selected volatile compounds from a solution containing the aroma compared to the aqueous control. Increasing sucrose concentrations in the solutions (0−60 w/v %) caused an increased release of the volatile compounds with short GC/FID retention times and a decreased release of the compounds with longer retention times. Increasing sodium cyclamate co...

This paper presents the structural stability of patatin, the major potato (Solanum tuberosum cv. Bintje) tuber protein. Using far- and near-ultraviolet circular dichroism and fluorescence spectroscopy, the conformation of patatin was studied under various conditions as a function of temperature. Patatin is a protein that unfolds partly due to either heat or acid treatments. When the protein is highly structured at the start of a heat treatment (near-neutral pH), an apparent two-state thermal unfolding is observed. At low pH, when the starting conformation is already irreversibly unfolded to a certain extent, only minor changes occur upon heating. The residual structures could be part of one or more relatively stable domains. The acidic and the thermal unfolding appear to be similar, but are not identical. These results could contribute to an improved method of isolation, enabling novel food applications of potato proteins.

The exopolysaccharides produced by Lactobacillus delbrueckii subsp. bulgaricus NCFB 2772 grown in defined medium were investigated. At equal cell densities, the strain produced 95 mg l−1 exopolysaccharides with glucose and 30 mg l−1 with fructose as the carbohydrate source. High-performance size-exclusion chromatography of the exopolysaccharides produced on glucose showed the presence of two fractions with relative molecular masses (M r) of 1.7 × 106 and 4 × 104 in almost equal amounts. The exopolysaccharides produced on fructose contained mainly a fraction of low M r of 4 × 104. The high-M r fraction of the purified exopolysaccharides produced on glucose appeared to have a sugar composition of galactose, glucose and rhamnose in the molar ratio of 5:1:1, whereas the low-M r weight fraction contained galactose, glucose and rhamnose in the molar ratio of approximately 11:1:0.4. The purified exopolysaccharide fractions produced on fructose showed comparable ratios. The high-molecular-mass fractions contained terminally linked galactose, 1,2,3-linked galactose, 1,3,4-linked galactose, 1,3-linked glucose and terminally linked rhamnose. The low-molecular-mass fractions contained mainly 1,3-linked galactose and 1,6-linked galactose and lower amounts of other sugar linkages. The production of the high-M r fractions appeared to be dependent on the carbohydrate source, whereas the low-M r fractions were produced more continuously.

In the dairy industry microbiological contamination may arise from equipment used for handling or processing. In this study it was demonstrated that Bacillus cereus spores could adhere to stainless steel, germinate and/or multiply in a tube heat exchanger. The levels of B cereus detected in the tubes, after 24 h at 20°C, varied from less than 1 to 2600 cm -2 . Adhering cells and/or spores were more resistant to cleaning with K500 and sodium hydroxide, determined by laboratory suspension tests and surface tests on stainless steel. This was confirmed in afield trial with a tube heat exchanger; after cleaning B cereus could still be isolated from all tubes determined by swab samples of individual tubes. The identity of the isolates was checked by polymerase chain reaction/ randomly amplified polymorphic DNA typing to confirm that the organisms found on the surfaces were the same as the bacteria in the ingoing milk.

Efficient enzymic degradation of cellulose in isolated cell wall material of apples requires prior removal of its xyloglucan coating. In this study, raw and blanched apple fruit tissues were treated with pectin lyase and various (combinations of purified) cellulases. These experiments confirmed that xyloglucanase activity is important for cellulose degradation in apple fruit tissue. Apart from this, it was observed that raw apple material disintegrated faster than blanched. Typically, the release of xyloglucan oligosaccharide XXXG from raw apple material was slower (relative to XXFG) when compared to that from blanched material. The endogenous enzyme, xyloglucan endotransglycosylase (XET), is probably responsible for these phenomena. It is hypothesised that XET activity accelerates disintegration of apple tissue once its depolymerising mode is triggered by xyloglucan oligosaccharides released by exogenous endoglucanases. © 1997 SCI.

The incidence and some characteristics (carbohydrate metabolism, growth profiles, haemolysin production and enterotoxin production) of Bacillus cereus, in pasteurised, low-fat (1.5%) milk, in household refrigerators in the Netherlands was investigated. In 247 (74%) of the 334 milk samples analyzed, the mesophilic aerobic counts were between 50 and 5000 per millilitre. B. cereus could be isolated from 133 (40%) of the samples. In general the B. cereus counts were low; numbers of less than five per millilitre were observed in 258 (77%) of the samples. As expected, both the mesophilic aerobic counts and levels of B. cereus increased with increasing storage temperatures in the refrigerator and prolonged storage times. In total, 143 presumptive B. cereus colonies were isolated. According to the ISO confirmation tests and the carbohydrate patterns (API 50 CHB) 134 (94%) of these isolates were confirmed to be B. cereus. Of these 134 isolates 20% fermented lactose and 53% of the 106 strains tested were able to grow at 7 degrees C. These percentages are much higher than expected for strains isolated from non-dairy products, suggesting that strains can adapt to environmental conditions in milk. All 106 strains tested, produced haemolysin, 27% showed the discontinuous haemolytic pattern characteristic for haemolysin BL, possibly a virulence factor. Of the 37 B. cereus isolates tested for enterotoxin production 27 (73%), 28 (76%) and 26 (70%) were found to be enterotoxigenic (as determined by the Western immunoblot technique, polymerase chain reaction (PCR) and Vero cell assays, respectively). Isolates unable to ferment lactose, produced less enterotoxin in comparison with those able to utilize lactose. Although only a few outbreaks of food poisoning caused by B. cereus in milk (products) have been reported, most strains isolated from these products are able to produce enterotoxins and may represent a health hazard.

Pectin methylesterase (PE) is present in green beans and may have an influence on the texture of green beans after commercial sterilization. Two fractions of PE were partially purified from the pods and the seed hulls of green beans (cv. Odessa). PE-1 and PE-2 had molecular weights of 45 and 29 kD, respectively, under native conditions and of 42 and 33.5 kD under denaturating conditions. PE-1 and PE-2 both contained two isoforms of PE activity with isoelectric points of 8.4 and 9.8 and 10.5 and >11, respectively. The active fractions showed a difference in salt dependency, and PE-2 was less heat stable than PE-1. Keywords: Isoforms; pectin methylesterase; Phaseolus vulgaris; purification; texture

Campylobacteriosis is one of the most frequently occurring acute gastroenteritis diseases in humans. Studies have revealed that the main risk factors in contracting campylobacteriosis are eating undercooked poultry meat, drinking raw milk, or drinking untreated water, and to a lesser degree, living in a household with a cat or dog. During the past 5 years many transmission routes of Campylobacter have been elucidated. However, knowledge on the significance of surface waters in causing Campylobacter infections remains scarce. Various reports have shown that the aquatic environment is regularly contaminated with Campylobacter. Risk analysis indicates that the contribution of contaminated recreational water to human infections may be higher than previously assumed. The contribution of viable but nonculturable Campylobacter cells in the contamination cycle has been found to be negligible. Water Environ.

Cell wall material (CWM) was isolated from noncooked, 5 min cooked, and 15 min cooked potato tissue and accompanying cooking media from the cultivars Irene and Nicola. A mass balance of the materia...

The development of a new selective medium, LAMVAB, for the isolation of Lactobacillus species from faeces is described. The medium is highly selective due to a low pH and the presence of vancomycin (20 mg l−1). In addition, the medium contains cysteine–HCl to enhance anaerobic conditions, and bromocresol green as a pH indicator. Competing faecal flora is inhibited by the low pH (enterobacteria, bacteroides and other Gram-negative anaerobes, clostridia) and the vancomycin (enterococci, bifidobacteria, clostridia). Characterization of the strains isolated on LAMVAB from human faeces included all common faecal lactobacilli and no other lactic acid bacteria. In one sample, vancomycin-resistant cocci were present and in another sample, yeasts were isolated. It can be concluded that the new medium is highly selective and permits the growth of all common faecal lactobacilli. The new medium can also be applied as a selective medium for lactobacilli in probiotics, which contain mixed populations of lactobacilli, bifidobacteria and enterococci.

Germination of Rhizopus oligosporus sporangiospores is characterized by swelling of the spores and subsequent emergence of germ tubes. Changes in spore morphology and alterations in intracellular pH (pH(infin)) of the sporangiospores were assessed during the germination process by flow cytometry. Sporangiospores were stained with carboxyfluorescein by incubation with carboxyfluorescein diacetate. The nonfluorescent carboxyfluorescein diacetate is passively transported into intact cells and subsequently cleaved by esterases, which results in intracellular accumulation of the fluorescent carboxyfluorescein. Given that the fluorescence of carboxyfluorescein is pH dependent, the pH(infin) of the individual spores could be assessed simultaneously with spore size. For R. oligosporus, swelling of the sporangiospores was accompanied by an increase of pH(infin). In the presence of nonanoic acid, a self-inhibitor produced by various fungi, increase of the pH(infin) was prevented and swelling was inhibited at concentrations of less than 1 mM. Octanoic acid and decanoic acid were equally effective. Acetic acid also inhibited germination but at much higher concentrations (>8 mM). The mechanism of action of these fatty acids is most likely dissipation of the pH gradient. A model is proposed in which the pH(infin) plays a crucial role in the germination of R. oligosporus sporangiospores.

The relation between consistency of soya beans, polysaccharidase activities and the non-starch polysaccharides (NSP) content of soya beans was investigated during tempe fermentation. The fermentations were carried out in a rotating drum reactor (RDR) as well as in the traditional stationary tempe process. The firmness of the soya beans decreased rapidly during the first day of incubation. At increased incubation temperatures the hardness of the beans decreased more rapidly. In the RDR glycosidase activities became significantly higher beyond 48 h of incubation compared with the traditional process. This might have resulted from (a) the better control of temperature and gas composition in the RDR, and/or (b) the agitation in the RDR. The content of arabinose, galactose and uronic acids in the water-unextractable solids of NSP decreased more rapidly than that of glucose, mannose, xylose and fucose. These results indicate that during enzymatic maceration of soya beans in tempe fermentation, the arabinogalactan and pectin fractions are preferentially solubilised. © 1997 SCI.

The naturally occurring compatible solutes betaine and L-carnitine allow the food-borne pathogen Listeria monocytogenes to adjust to environments of high osmotic strength. Previously, it was demonstrated that L. monocytogenes possesses an ATP-dependent L-carnitine transporter (A. Verheul, F. M. Rombouts, R. R. Beumer, and T. Abee, J. Bacteriol. 177:3205-3212, 1995). The present study reveals that betaine and L-carnitine are taken up by separate highly specific transport systems and support a secondary transport mechanism for betaine uptake in L. monocytogenes. The initial uptake rates of betaine and L-carnitine are not influenced by an osmotic upshock, but the duration of transport of both osmolytes is directly related to the osmotic strength of the medium. Regulation of uptake of both betaine and L-carnitine is subject to inhibition by preaccumulated solute. Internal betaine inhibits not only transport of external betaine but also that of L-carnitine and, similarly, internal L-carnitine inhibits transport of both betaine and L-carnitine. The inhibition is alleviated upon osmotic upshock, which suggests that alterations in membrane structure are transmitted to the allosteric binding sites for betaine and L-carnitine of both transporters at the inner surface of the membrane. Upon osmotic downshock, betaine and L-carnitine are rapidly released by L. monocytogenes as a consequence of activation of a channel-like activity. The osmolyte-sensing mechanism described is new and is consistent with various unexplained observations of osmoregulation in other bacteria.

Cell wall material (CWM) isolated from non-cooked potato tissue of the cultivars Irene (mealy cooking) and Nicola (non-mealy cooking) was successively extracted with buffer, CDTA, Na2CO3 at 4 and 2...

Absorption aspects of flavours and chemicals are important quality criteria when plastic bottles are reused or recycled. In the present study absorption of methanol and toluene by polyester-based bottles (PET and PEN) was studied at different temperatures in the range 20-40°C for a period of 16 weeks with two different ways of exposure: one-sided and two-sided. Saturation levels were not reached in such a period of storage. However, absorption levels are affected by temperature. An increase in temperature causes an increase in absorption level. Also, the polarity and size of the chemicals, the composition of the plastic (PET and/or PEN) and the crystallinity of the specimens influences absorption. The results did not show whether two-sided exposure is representative of the one-sided situation. © 1997 John Wiley & Sons, Ltd.

An NADP-dependent branched-chain alcohol dehydrogenase was purified from Saccharomyces cerevisiae var. uvarum grown under anaerobic conditions. Its quaternary structure is monomeric, and it has a molecular mass of 37 kDa and a pI of 5.9. A possible role of the enzyme in flavor production during alcoholic fermentation is discussed.

Germination of Rhizopus oligosporus sporangiospores is characterized by swelling of the spores and subsequent emergence of germ tubes. Changes in spore morphology and alterations in intracellular pH (pH(infin)) of the sporangiospores were assessed during the germination process by flow cytometry. Sporangiospores were stained with carboxyfluorescein by incubation with carboxyfluorescein diacetate. The nonfluorescent carboxyfluorescein diacetate is passively transported into intact cells and subsequently cleaved by esterases, which results in intracellular accumulation of the fluorescent carboxyfluorescein. Given that the fluorescence of carboxyfluorescein is pH dependent, the pH(infin) of the individual spores could be assessed simultaneously with spore size. For R. oligosporus, swelling of the sporangiospores was accompanied by an increase of pH(infin). In the presence of nonanoic acid, a self-inhibitor produced by various fungi, increase of the pH(infin) was prevented and swelling was inhibited at concentrations of less than 1 mM. Octanoic acid and decanoic acid were equally effective. Acetic acid also inhibited germination but at much higher concentrations (>8 mM). The mechanism of action of these fatty acids is most likely dissipation of the pH gradient. A model is proposed in which the pH(infin) plays a crucial role in the germination of R. oligosporus sporangiospores.

The maceration of potato tuber (Solanum tuberosum cv Bintje) by technical enzyme preparations was examined with the aid of fluorescence microscopy using fluorescein diacetate as a dye. Treatment with Pectinex Ultra-SP-L from Aspergillus aculeatus resulted in a higher release of single viable cells and smaller clumps of cells than treatment with Rohament P from Aspergillus niger. Fractions with high pectin lyase and low polygalacturonase activity obtained by anion exchange chromatography of Pectinex Ultra SP-L showed the highest degree of maceration. When two different cloned polygalacturonases (PG1 and PG2) and a cloned pectin lyase (PL1) from A aculeatus were examined, the highest degree of maceration was observed with PL1. In conclusion, pectin lyase is probably the main enzyme in Pectinex Ultra-SP-L responsible for the maceration of potato tuber. © 1997 SCI.

The technique of gas chromatography/sniffing port analysis was evaluated for studying the release of aroma compounds from rehydrated diced French beans. The aroma compounds 2-—methylbutanal and hexanal were released at a constant rate over time. An identical selection of odour active compounds was obtained at different sampling times. Mutual proportions were remained among the sampling times, although the total number of perceptions of assessors were different.

Xlyoglucan, a cell wall polysaccharide and part of the dietary fiber fraction of the diet, can be degraded by the intestinal microflora. Degradation is not common among intestinal bacterial species. Of 138 strains (representing 75 species) only nine strains were able to degrade the xyloglucan polymer. These strains, seven clostridia, one bifidobacterium and one bacteroides, all produced apparent extracellular enzymes, which degraded the glucan backbone. Gas production was detected in the individual clostridia. The other two strains did not produce any gas. Selective elimination of bacterial groups from faecal slurries indicated that clostridia are the main group of intestinal bacteria responsible for degradation of xyloglucan polymer. In addition to the polymer-degrading strains, some other strains were able to degrade and ferment oligosaccharides produced from tamarind seed xyloglucan with a fungal endo-s-glucanase. HPAEC analysis showed that the fungal oligosaccharides were identical to the oligosaccharides produced by the polymer-degrading species suggesting the presence of an endo-s-glucanase in these bacteria. It is proposed that xyloglucan is degraded in vivo by endo-s-glucanases produced mainly by clostridia, followed by fermentation of the oligosaccharides by a larger group of bacteria.

All confirmation and identification methods used in this study can be used for the screening of suspected colonies on isolation media for Listeria spp. In traditional enrichment procedures the Microscreen Listeria latex test gives fast results. The DNA probes (Accuprobe and Gene-Trak) are very specific in detecting Listeria monocytogenes. For identification of Listeria spp. both tests (API and Micro-ID) performed equally well. Preference may be given to the API test, since differentiation of L. monocytogenes from L. innocua is based on the absence of arylamidase, through which tests for haemolytic activity and/or CAMP reactions can be omitted. However, the use of Enhanced Haemolysis Agar as isolation medium makes further testing essentially superfluous, since L. monocytogenes strains can be differentiated from L. innocua.

Two approaches were investigated in attempts to obtain a high extraction yield of (glucurono) arabinoxylans from water-unextractable cell wall material (WUS) of wheat bran using saturated barium hydroxide containing 0·26 M sodium borohydride. First, the effect of three pretreatments (autoclave treatment, alkaline peroxide and chlorite delignification) of the WUS prior to extraction appeared to have no effect on the extraction yield. Moreover, modifications to the composition and molecular weight distribution of the (glucurono)arabinoxylans occurred when such treatments were used. Second, the effect of an increasing extraction temperature and concentration of alkali was investigated. Increasing the extraction temperature improved the extraction yield of (glucurono)arabinoxylans from 29% at 20°C to 50% at 95°C. Increasing the barium hydroxide concentration with the temperature resulted in no further improvements in extraction yield up to 70°C. Above this temperature the extraction yield decreased. Substitution of barium hydroxide by calcium hydroxide resulted in lower yields and a lower selectivity; the lower solubility of calcium hydroxide may have been responsible for this. Supplementary experiments to investigate the mechanism of the selectivity of the bivalent hydroxide extraction with addition of sodium borohydride indicated a possible role for borate, derived from borohydride.

The albedo of Spanish lemons (16.0% w/w of lemon fresh weight) was extracted to obtain a chelating agent soluble pectin fraction, a diluted sodium hydroxide soluble pectin fraction and a residue (4.2, 1.8, and 5.0% w/w of fresh albedo, respectively). These fractions represented 61.3, 12.4, and 10.4% of the galacturonic acid present in the albedo, respectively. Fractions were studied and their characteristics were compared with those of lemon albedo modified hairy regions (MHR) (1.4% w/w of fresh albedo), solubilised from the albedo after treatment by a technical enzyme preparation. All extracted pectins were rich in galacturonic acid, next to varying amounts of arabinose, galactose, and glucose residues. Based on molecular size, albedo-MHR consisted of at least five populations. From the rhamnose:galacturonic acid ratio (0.21-0.28), the high acetyl content, and the degradability by rhamnogalacturonase, it was concluded that the four major fractions represent rhamnogalacturonans having only small differences within their fine structure. The fifth fraction contained more galacturonic acid and was only degraded by polygalacturonase.