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Flavor improvement in pork from barrows and gilts via inhibition of intestinal skatole formation with resistant potato starch.

Skatole originates from microbial processing of tryptophan in the large intestine of pigs and accumulates in adipose tissue. Formation may be inhibited by the anti-apoptotic function of butyrate formed out of raw potato starch. Two groups of pigs (each consisting of gilts and barrows) were fed from 30 to 110 kg life weight either a conventional diet (controls; n = 35) or an isocaloric diet containing 300 g of raw potato starch/kg of body weight (RS; n = 34). Skatole concentrations were measured in colon content, blood, and adipose tissue. Odor of cooked meat samples was evaluated by a test panel. RS reduced concentrations in colon content and blood plasma (P < 0.001). Back fat concentrations were decreased significantly from 25 to 1.40 ng/g (barrows; P < 0.001) and from 40 to 9 ng/g (gilts; P < 0.001). Odor rating (scale of 1-5 from very unpleasant to very pleasant) was 3.07 for low skatole concentrations and 2.66 for both medium and high skatole concentrations (P < 0.05).

Animal Feed↗

Cloning and mapping of the porcine cytochrome-p450 2E1 gene and its association with skatole levels in the domestic pig.

The porcine cytochrome-p450 2E1 (CYP2E1) gene was isolated by screening a pig BAC library and partially sequenced. This sequence information was used to identify six single nucleotide polymorphisms (SNPs) within the CYP2E1 gene and its promoter. In addition, a microsatellite marker tightly linked to the CYP2E1 gene was subcloned from the BAC. One of these markers was used to map the CYP2E1 gene distal of SWC27 on SSC14, well outside reported quantitative trait loci on SSC14 for skatole, indole and taste test measures of boar taint. However, in a population of commercial pigs scored for backfat skatole levels, there was evidence of association between a SNP in the CYP2E1 promoter and skatole deposition, although there was no significant association between this SNP and skatole levels in the experimental cross.

Adipose Tissue↗

Isolation and characteristics of a skatole-producing Lactobacillus sp. from the bovine rumen.

A bacterium that is capable of decarboxylating indoleacetic acid to skatole (3-methylindole) has been isolated from an L-tryptophan enrichment of bovine rumen fluid. The bacterium is a gram-positive, nonmotile, nonsporeforming rod. It is an obligate anaerobe, and strains predominatly produce D-(-)-lactic acid, with smaller amounts of L-(+)-lactic acid and acetic acid, from sugar. All four strains isolated gave a negative reaction to the indole test because they cannot form skatole directly from tryptophan. This is the first report of indoleacetic acid decarboxylation to skatole in pure culture and the demonstration of skatole production by a Lactobacillus species.

Acetates↗

Production of Skatole and para-Cresol by a Rumen Lactobacillus sp.

The objective of this study was to examine the substrate specificity of several ruminal strains of a Lactobacillus sp. which previously was shown to produce skatole (3-methylindole) by the decarboxylation of indoleacetic acid. A total of 13 compounds were tested for decarboxylase activity. The Lactobacillus strains produced p-cresol (4-methylphenol) by the decarboxylation of p-hydroxyphenylacetic acid, but did not produce either o-cresol or m-cresol from the corresponding hydroxyphenylacetic acid isomers. These strains also decarboxylated 5-hydroxyindoleacetic acid to 5-hydroxyskatole and 3,4-dihydroxyphenylacetic acid to methylcatechol. Skatole and p-cresol were produced in a 0.5:1 ratio, when indoleacetic acid and p-hydroxyphenylacetic acid were combined in equimolar concentrations. Competition studies with indoleacetic acid and p-hydroxyphenylacetic acid suggested that two different decarboxylating enzymes are involved in the production of skatole and p-cresol by these strains. This is the first demonstration of both skatole production and p-cresol production by a single bacterium.

Journal Article↗

Rapid determination of skatole and indole in pig back fat by normal-phase liquid chromatography.

A rapid normal-phase high-performance liquid chromatographic method for the quantitative determination of indole and skatole in pig back fat samples has been developed. The compounds were extracted by shaking the samples at ambient temperature in hexane-2-propanol (92:8, v/v). The sample preparation procedure was simple because it was not necessary to remove the fat from the samples. The compounds were separated on a 250 x 4.6 mm I.D., 5 micron Hypersil aminopropylsilica column. Fluorescence (excitation at 280 nm and emission at 360 nm) was used for selective detection. Recoveries for skatole and indole, relative to the internal standard, were 10.3 +/- 0.9% and 99.6 +/- 4.4%, respectively. Linearity determined in fat samples was in the range of 0.05-1 microgram/g and the correlations observed were R2 = 0.9914 for the indole and R2 = 0.9916 for skatole.

Adipose Tissue↗

Laboratory and field responses of the mosquito, Culex quinquefasciatus, to plant-derived Culex spp. oviposition pheromone and the oviposition cue skatole.

Laboratory and field studies were conducted on the oviposition behavior of the pathogen-vectoring mosquito, Culex quinquefasciatus, in response to the oviposition pheromone 6-acetoxy-5-hexadecanolide, produced from a renewable plant resource, Kochia scoparia (Chenopodiaceae) (plant-derived pheromone, PDP), and via an established synthetic route (synthetic oviposition pheromone, SOP). Responses to the oviposition cue skatole (3-methylindole), presented individually and in combination with the plant-derived and synthetic oviposition pheromone, were also studied. Both laboratory and field assays showed that PDP and SOP were equally attractive. Synergistic effects were observed with one combination of PDP and skatole combinations in laboratory assays. Synergy was also observed under field conditions. SOP and skatole combinations showed additive effects in laboratory assays, but were not tested in field bioassays. Although synergism has been previously demonstrated with combinations of SOP and polluted waters, the work presented here is the first example of synergy between a specific oviposition attractant and the oviposition pheromone. Furthermore, the efficacy of mosquito pheromone produced from a cheap, renewable botanical source has been demonstrated.

Animals↗

Detection of quantitative trait loci for androstenone, skatole and boar taint in a cross between Large White and Meishan pigs.

'Boar taint' is a strong perspiration-like, urine-like unpleasant odour given off upon heating or cooking of meat from some intact (uncastrated) male pigs. Data from the F(2) generation of a Large White (LW) x Meishan (MS) crossbred population were analysed to detect quantitative trait loci (QTL) for traits associated with boar taint. Fat samples from 178 intact male pigs slaughtered at 85 +/- 5 kg were analysed for the major contributors to boar taint (androstenone, indole and skatole). Fat and lean samples from cooked meat were scored for boar, abnormal and pork flavour and odour by a trained sensory panel (SP). A scan with 117 markers covering the whole genome was performed in the F(2) individuals, together with their F(1) parents and purebred grandparents. At the 5% chromosomal significance threshold (approximately equal to the genome-wide suggestive significance threshold), QTL were detected for the laboratory estimate of androstenone on chromosomes 2, 4, 6, 7 and 9. However, only on chromosome 6 were there QTL for boar flavour (BF) traits in the same or adjacent marker intervals as a QTL for the laboratory estimate of androstenone. On chromosome 14, QTL were detected for the laboratory estimates of indole and skatole, the SP score for skatole and the scores for BF in lean and BF in fat. In all five cases, the MS allele generally increased the estimate or score, compared with the LW allele, but it appeared that desirable and undesirable alleles were present in both breeds. This locus on chromosome 14 has considerable potential for use to reduce the incidence of boar taint, especially if further research can identify the causative polymorphism or strongly associated markers.

Androsterone↗

Dose-dependent effects of resistant potato starch in the diet on intestinal skatole formation and adipose tissue accumulation in the pig.

Resistant starch (RS) intake leads to a reduction of apoptosis in the pig colon and thus to a reduction of skatole in the carcass. To determine the minimal amount of RS which is required for the effect, diets with varying amounts (20, 30 and 40%) of RS were fed to barrows and gilts. Controls were fed instead with 55% pre-gelatinized starch. Skatole was determined after slaughter in distal colon content and in adipose tissue (flare fat and belly fat). Resistant starch led to a dose-dependent reduction of skatole in the gut content from 134 microg/g dry matter (controls) to 4.8 microg/g in the 40% group. Flare fat concentrations were decreased from 159 to 20 ng/g fat and belly fat concentrations from 64 to 16 ng/g fat. Strategies to improve sensorial quality by feeding RS continuously or for only 1 week prior to slaughter are discussed.

Adipose Tissue↗

Time profile of putrescine, cadaverine, indole and skatole in human saliva.

The concentrations of putrescine, cadaverine, indole and skatole were determined in the saliva of healthy human volunteers upon waking and at time points during the day. Putrescine was found to be the most abundant of the amines studied, followed by cadaverine then indole. Skatole could not be detected in the saliva samples at any time point. The amines were found in the highest concentrations immediately upon waking (mean concentrations (microg/ml): putrescine 33.0+/-19.0, cadaverine 17.6+/-16.7 and indole 0.4+/-0.4) with a rapid decrease following consumption of breakfast and brushing their teeth (mean concentrations (microg/ml): putrescine 7.0+/-6.4, cadaverine 3.1+/-4.7 and indole 0.04+/-0.09). Putrescine and cadaverine then increased in concentration during the day apart from a decrease post-lunch caused by increased salivary flow and mechanical cleaning due to mastication. An analytical method based on high performance liquid chromatography and fluorescence detection has been developed to quantify amines in human saliva. Sodium fluoride has been shown to be an effective inhibitor of amine formation in saliva at room temperature allowing samples to be collected and kept without requiring cold storage.

Adolescent↗

Chemical cleavage of bovine beta-lactoglobulin by BNPS-skatole for preparative purposes: comparative study of hydrolytic procedures and peptide characterization.

A comparative study of various procedures for tryptophanyl peptide bond cleavage by BNPS-skatole [2-(2-nitrophenyl)-3-methyl-3-bromoindolenine] was carried out on native and on reduced and alkylated bovine beta-lactoglobulin (BLG). The reaction yield and the composition of the derived products were studied in acetic acid, trifluoroacetic acid (TFA), and ethanol/TFA. For BNPS-skatole removal, extraction by water or ethyl ether was compared with dialysis and gel filtration. The three expected peptides (1-19, 20-61, 62-162) and incomplete cleaved fragments (1-61, 20-162) were separated and characterized by electrophoresis, reverse-phase high-performance liquid chromatography, and mass spectrometry. The highest hydrolysis yield (67.4%) occurred with native BLG cleaved in 88% acetic acid at 47 degrees C for 60 min. Subsequent water extraction and gel filtration led to total recovery of the material, but reagent elimination was only quantitative after gel filtration. Cleavage specificity was ensured by mass spectrometry and the amino acid composition of peptides 1-19 and 62-162. The chemical side reactions identified are discussed.

Amino Acids↗

Improved preparation and structural elucidation of the tryptophan cleavage reagent 2-(2'-nitro-phenylsulfenyl)-3-methyl-3-bromoindolenine (BNPS-skatole).

Methods are described for a high yield preparation (overall yield greater than 90%) of analytically pure 2-(2'-nitrophenylsulfenyl)-3-methyl-3-bromoindolenine (BNPS-skatole). The chromatographic and spectroscopic data are given. The yield of tryptophan cleavage is considerably dependent on the degree of purity of the BNPS-skatole.

Chemical Phenomena↗

[Determination of indole and skatole in seafood using high performance liquid chromatography (HPLC)].

A rapid and specific high-performance liquid chromatographic (HPLC) method for the determination of indole and 3-methylindole (skatole) is described. The detection limit of the two compounds is approx. 0.02 mg/kg. Gas chromatographic-mass spectrometric (GC-MS) confirmation of the identity has been carried out in shrimps. About 95% of added indole was recovered. The indole formation in shrimps, herring, and turbot, held under different storage conditions, is compared with other common quality indices such as TBA-value and alpha-tocopherol content.

Animals↗

Gas chromatographic determination of indole and 3-methylindole (skatole) in bacterial culture media, intestinal contents and faeces.

A simple, rapid and inexpensive gas chromatographic method was developed for the determination of indole and 3-methylindole (skatole) in faeces, intestinal contents and bacterial cultures. It involves a simple homogenization and extraction with chloroform. The extract is injected onto a gas chromatograph equipped with a 12.5-m fused-silica capillary column coated with BP20 and a film thickness of 0.5 micron. To simplify the chromatograms and to get a higher sensitivity a nitrogen-phosphorus-sensitive detector is applied. The detection limit for indole and 3-methylindole under the conditions employed is 20 micrograms/kg, which is well below the values typically found in intestinal contents (up to 100 mg/kg). Recovery for both compounds was close to 100%, and the mean coefficients of variation were 3.5% for indole and 3.0% for 3-methylindole. The method has demonstrated its practical value in the analysis of more than 50,000 samples in our laboratory. More than 100 samples can be analyzed per day.

Animals↗

Peptide fragmentation suitable for solid-phase microsequencing. Use of N-bromosuccinimide and BNPS-skatole (3-bromo-3-methyl-2-[(2-nitrophenyl)thio]-3H-indole).

BNPS-skatole (3-bromo-3-methyl-2-(2-nitrophenyl)thiol-3H-indole) and N-bromosuccinimide have been used to specifically cleave at peptide bonds after amino acids with available C-gamma=C-delta double bonds, i.e. tryptophan, tyrosine and histidine. The resulting C-terminal lactones conveniently attach to amino-glass supports for sequencing with DABITC (4-NN-dimethylaminoazobenzene 4'-isothiocyanate). Also, peptides having such C-termini, i.e. from a chymotryptic digest, can be readily made to react with these reagents and thus be easily attached and sequenced by solid-phase methods.

Amino Acid Sequence↗

3-Methylindole (skatole) and indole production by mixed populations of pig fecal bacteria.

Pig fecal slurries converted added L-tryptophan either to indole without detectable intermediates or to 3-methylindole (skatole) via indole-3-acetate. The initial rate of production of 3-methylindole was greatest at pH 6.5 and less at pH 5.0 and 8.0; the initial rates of indole production were similar at pH 6.5 and 8.0. More than 80% of the tryptophan added was converted to 3-methylindole at pH 5.0; at pH 8.0 85% was converted to indole. Both pathways had similar Km values for tryptophan and similar maximum rates. Indole-3-carbinol and indole-3-acetonitrile completely inhibited the production of 3-methylindole from indole-3-acetate but had no effect on the reactions involving L-tryptophan.

Animals↗