| 1. |
- Matuschek, Erika, 1974
(författare)
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In Vitro Availability of Iron in High-Tannin Sorghum. Effect of Enzymatic Oxidation of Phenolic Compounds
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Iron deficiency anemia is the most common nutritional disorder in the world. In low income countries, it is to a large extent caused by low bioavailability of iron in the vegetable diet. Vegetable diets contain large amounts of compounds that inhibit iron absorption, e.g. phytate and polyphenols (tannins). Polyphenols inhibit iron absorption by forming insoluble complexes with iron in the gastrointestinal tract. The aim of the present thesis was to investigate how enzymatic oxidation affects phenolic compounds and subsequently the bioavailability of iron in high-tannin cereals. The bioavailability of iron was estimated with an in vitro digestion method that has been validated against absorption data and found to be a suitable method. Oxidation of model phenolic compounds, i.e. tannic acid and green tea extract, with commercial polyphenol oxidase (PPO) significantly increased in vitro iron availability in a model food system. These results imply that the oxidation products have a lower iron binding capacity than the original phenolic compounds. Incubation of phytate-reduced flour of sorghum or millet also resulted in lower amounts of phenolic compounds and a higher availability of iron. The phenolic content in sorghum decreased by more than 50% with PPO incubation, and in vitro available iron increased by almost 100%. Furthermore, combining the enzymatic treatment with traditional processing methods, such as cooking, soaking, germination and lactic acid fermentation, resulted in a further improvement in iron availability. Polyphenol oxidase can be found in several common fruits and vegetables, and incubation of dephytinized high-tannin sorghum with dialyzed extract of pear, banana or avocado effectively increased the in vitro iron availability. The effect was more pronounced than with commercial PPO, and incubation with avocado extract improved the availability more than 1.7-fold. It is probable that peroxidase activity and organic acids in the fruit extracts contributed to the improved iron availability. Investigations of the effect of oxidation on phenolic structures, both simple phenolic compounds and complex structures such as sorghum tannins, showed a decrease after incubation with PPO. The decrease in tannins was probably due to coupled oxidation reactions involving simple phenols. Catechol (ortho-dihydroxyl) and galloyl (trihydroxyl) groups are identified as iron binding phenolic groups in plant foods. Model phenols containing catechol groups were more easily oxidized than those containing galloyl groups, while the percentage decrease in catechol and galloyl groups in sorghum phenols were similar. In combination with methods that reduce phytate, enzymatic oxidation of phenolic compounds may be a promising way to increase the bioavailability of iron in high-tannin cereals at the household level.
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| 2. |
- Matuschek, Erika, 1974, et al.
(författare)
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Oxidation of polyphenols and the effect on in vitro iron accessibility in a model food system
- 2002
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Ingår i: Journal of Food Science. ; 67:1, s. 420-424
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Tidskriftsartikel (refereegranskat)abstract
- Tannic acid and green tea extract were added to a model food system of wheat bread, before and after incubation with polyphenol oxidase (mushroom tyrosinase), and the effect on in vitro iron accessibility was studied. Tannic acid and green tea extract had a marked inhibitory effect on the in vitro accessibility of iron when added to the model food system. Incubation of the polyphenols with tyrosinase before addition to the model food system significantly increased the accessibility of iron. The results from the study therefore suggest that oxidation of polyphenols may be a promising way to increase the bioavailability of iron in polyphenol containing foods.
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| 3. |
- Matuschek, Erika, 1974, et al.
(författare)
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Oxidation of polyphenols in phytate-reduced high-tannin cereals: Effect on different phenolic groups and on in vitro accessible iron
- 2001
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Ingår i: Journal of Agricultural and Food Chemistry. ; 49:11, s. 5630-5638
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Tidskriftsartikel (refereegranskat)abstract
- After reduction of phytate with phytase, water-slurries of two high-tannin cereal flours were incubated with polyphenol oxidase (mushroom tyrosinase) and the effects on different phenolic groups and on in vitro accessible iron were studied. Enzyme incubation was also performed after cooking, soaking and germination of the cereals. Phytase incubation significantly decreased the phytate content and incubation with polyphenol oxidase had a reducing effect on the total phenol content, as well as on the amount of catechol and resorcinol groups. The in vitro accessible iron increased when the cereals were incubated with phytase and polyphenol oxidase, and the highest accessibility of iron was obtained when the germinated samples were incubated. The results from this study imply that oxidation of polyphenols in high-tannin cereals, after reduction of phytate, may be used to increase the bioavailability of iron in foods prepared from these cereals.
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| 4. |
- Matuschek, Erika, 1974, et al.
(författare)
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The effect of fruit extracts with polyphenol oxidase (PPO) activity on the in vitro accessibility of iron in high-tannin sorghum
- 2005
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Ingår i: Food Chemistry. - : Elsevier BV. - 0308-8146 .- 1873-7072. ; 90:4, s. 765-771
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Tidskriftsartikel (refereegranskat)abstract
- Dephytinized high-tannin sorghum flour was incubated with crude extracts from pear, banana or avocado, respectively, followed by investigation of the effects on the phenolic content and on in vitro accessible iron. All fruits contained polyphenol oxidase (PPO) activity and incubation resulted in significant reduction of phenolic compounds. Incubation with avocado extract resulted in the lowest levels of phenolic compounds, as well as the highest amount of in vitro accessible iron. Peroxidase activity and some organic acids in the fruit extracts might also have contributed to the positive effect on iron accessibility. Nevertheless, incubation of the sorghum flour with the fruit extracts under conditions enabling the PPO to oxidize phenolic compounds, resulted in the highest accessibility of iron. The results from this study suggest that the PPO activity in simple fruit extracts can be utilized to increase the accessibility of iron in dephytinized polyphenol-containing cereal foods.
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| 5. |
- Towo, Elifatio, 1962, et al.
(författare)
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Fermentation and enzyme treatment of tannin sorghum gruels: Effects on phenolic compounds, phytate and Fermentation and enzyme treatment of tannin sorghum gruels: Effects on phenolic compounds, phytate and in vitro accessible iron
- 2006
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Ingår i: Food Chemistry. - : Elsevier BV. - 0308-8146 .- 1873-7072. ; 94:3, s. 369-376
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Tidskriftsartikel (refereegranskat)abstract
- The presence of polyphenols and phytate in cereal products has been. shown to interfere with the bioavailability of minerals such as iron. In the present study, we added enzymes (wheat phytase and mushroom polyphenol oxidase) during fermentation of tannin sorghum gruels prepared from flour with or without addition of 5% flour of germinated tannin-free sorghum grains (power flour), and investigated the effects on phenolic compounds, phytate and in vitro accessible iron. Assayable phenolic compounds were significantly reduced by fermentation, with high reductions observed in gruels with added enzymes. Fermentation of the gruels with addition of enzymes reduced (on average) total phenols by 57%, catechols by 59%, galloyls by 70% and resorcinols by 73%. The phytate content was significantly reduced by fermentation (39%), with an even greater effect after addition of power, flour, (72%). The largest reduction of phytate (88%) was, however, obtained after addition of phytase. The in vitro accessible iron was 1.0% in the sorghum flour and it increased after fermentation with power flour and/or with enzymes. The highest in vitro accessibility of iron (3.1%) was obtained when sorghum was fermented with addition of power flour and incubated with phytase and polyphenol oxidase after the fermentation process.
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| 6. |
- Åkerlund, Anna, et al.
(författare)
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EUCAST rapid antimicrobial susceptibility testing (RAST) in blood cultures : validation in 55 European laboratories
- 2020
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Ingår i: Journal of Antimicrobial Chemotherapy. - : Oxford University Press. - 0305-7453 .- 1460-2091. ; 75:11, s. 3230-3238
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: When bloodstream infections are caused by resistant bacteria, rapid antimicrobial susceptibility testing (RAST) is important for adjustment of therapy. The EUCAST RAST method, directly from positive blood cultures, was validated in a multi-laboratory study in Europe.METHODS: RAST was performed in 40 laboratories in northern Europe (NE) and 15 in southern Europe (SE) from clinical blood cultures positive for Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus or Streptococcus pneumoniae. Categorical results at 4, 6 and 8 h of incubation were compared with results for EUCAST standard 16-20 h disc diffusion. The method, preliminary breakpoints and the performance of the laboratories were evaluated.RESULTS: The total number of isolates was 833/318 in NE/SE. The number of zone diameters that could be read (88%, 96% and 99%) and interpreted (70%, 81% and 85%) increased with incubation time (4, 6 and 8 h). The categorical agreement was acceptable, with total error rates in NE/SE of 2.4%/4.9% at 4 h, 1.1%/3.5% at 6 h and 1.1%/3.3% at 8 h. False susceptibility at 4, 6 and 8 h of incubation was below 0.3% and 1.1% in NE and SE, respectively, and the corresponding percentages for false resistance were below 1.9% and 2.8%. After fine-tuning breakpoints, more zones could be interpreted (73%, 89% and 93%), with only marginally affected error rates.CONCLUSIONS: The EUCAST RAST method can be implemented in routine laboratories without major investments. It provides reliable antimicrobial susceptibility testing results for relevant bloodstream infection pathogens after 4-6 h of incubation.
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