Phytate degradation in composite wheat/cassava/sorghum bread: Effects of phytase-secreting yeasts and addition of yeast extracts.

Iron deficiency anemia is highly prevalent in developing countries due to the consumption of cereal-based foods rich in phytate that chelates minerals such as iron and zinc making them unavailable for absorption by humans. The aim of the present study was to degrade phytic acid in composite flour (wheat/cassava/sorghum) bread by the addition of phytase-producing yeasts in the baking process to achieve a phytate-to-iron molar ratio <1 and a phytate-to-zinc molar ratio <15, ratios needed to achieve an enhanced absorption by humans. The high-phytase (HP)-producing yeasts were two Saccharomyces cerevisiae (YD80 and BY80) that have been genetically modified by a directed mutagenesis strategy, and Pichia kudriavzevii TY13 isolated from a Tanzanian lactic fermented maize gruel (togwa) and selected as naturally HP yeast. To further improve the phytase production by the yeasts, four different brands of phytase-promoting yeast extracts were added in the baking process. In addition, two yeast varieties were preincubated for 1 h at 30°C to initiate phytase biosynthesis. The phytate content was measured by high-performance ion chromatography (HPIC) and the mineral content by ion chromatography (HPIC). The results showed that all three HP yeasts improved the phytate degradation compared with the composite bread with no added HP yeast. The composite bread with preincubated S. cerevisiae BY80 or P. kudriavzevii TY13 plus Bacto yeast extract resulted in the lowest phytate content (0.08 µmol/g), which means a 99% reduction compared with the phytate content in the composite flour. With added yeast extracts from three of the four yeast extract brands in the baking process, all composite breads had a phytate reduction after 2-h fermentation corresponding to a phytate: iron molar ratio between 1.0 and 0.3 and a phytate: zinc molar ratio <3 suggesting a much-enhanced bioavailability of these minerals.

Effects of blanching, acidification, or addition of EDTA on vitamin C and ß-carotene stability during mango purée preparation.

The impact of acidification with citric acid, addition of EDTA or water blanching at high temperature, and short time (HTST) conducted at 90°C for 4 min, on the retention of vitamin C (L-AA and DHAA) and ß-carotene was studied in mango purée 30 min after crushing. HTST blanching prior to matrix disruption into purée resulted in complete inactivation of polyphenol oxidase (PPO) and minor residual activity (8%) of ascorbic acid oxidase (AAO). The retention of total vitamin C was 100% in blanched purées and in purée with EDTA and about 90% in purées at pH 3.9 and 5.0. Acidification, blanching, and addition of EDTA preserved vitamin C mainly as L-AA, while complete conversion into DHAA was observed in purée at pH 5.0. The retention of all-trans-ß-carotene was between 65 and 72%, with the highest value in purée with EDTA and the lowest value in purée of blanched mango. The ratio of 13-cis-ß-carotene in fresh mango was 8.2 ± 0.5% that increased significantly after blanching and in purée at pH 5.0.

Effect of hydrocolloids and emulsifiers on the shelf-life of composite cassava-maize-wheat bread after storage.

The objective of this study was to evaluate the effect of hydrocolloids and/or emulsifiers on the shelf-life of composite cassava-maize-wheat (ratio 40:10:50) reference bread during storage. Added hydrocolloids were carboxymethylcellulose (CMC) and high methoxyl pectin (HM pectin) at a 3% level (w/w) and/or the emulsifiers diacetyl tartaric acid esters of monoglycerides (DATEM), lecithin (LC), and monoglycerides (MG) at a 0.3% level (w/w). After 4 days of storage, composite breads with MG had comparatively lower crumb moisture while crumb density was similar in all breads. The reference bread crumb firmness was 33.4 N, which was reduced with an addition of DATEM (23.0 N), MG (29.8 N), CMC (24.6 N) or HM pectin (22.4 N). However, the CMC/DATEM, CMC/LC, and HM pectin/DATEM combinations further reduced crumb firmness to <20.0 N. The melting peak temperature was increased from 52 C to between 53.0 C and 57.0 C with added hydrocolloids and/or emulsifiers. The melting enthalpy of the retrograded amylopectin was lower in composite bread with hydrocolloids and emulsifiers, 6.7-11.0 J/g compared to 20.0 J/g for the reference bread. These results show that emulsifiers in combination with hydrocolloids can improve the quality and extend the shelf-life of composite cassava-maize-wheat breads.

Effect of Infrared Blanching on Enzyme Activity and Retention of ß-Carotene and Vitamin C in Dried Mango.

The objectives of this work were to evaluate infrared (IR) dry blanching in comparison with conventional water blanching prior to hot air drying of mango to inactivate polyphenol oxidase (PPO) and ascorbic acid oxidase (AAO) enzymes, and to study its effect on color change and retention of vitamin C and ß-carotene. Mango cylinders were blanched under similar temperature-time conditions either by IR heating or by immersion in a water bath during 2 min at 90 °C (high-temperature-short-time-HTST) or for 10 min at 65 °C (low-temperature-long-time-LTLT). After blanching mango was hot air dried at 70 °C. PPO was completely inactivated during the blanching treatments, but AAO had a moderate remaining activity after LTLT treatment (∼30%) and a low remaining activity after HTST treatment (9% to 15%). A higher retention of vitamin C was observed in mango subjected to IR dry blanching, 88.3 ± 1.0% (HTST) and 69.2 ± 2.9% (LTLT), compared with water blanching, 61.4 ± 5.3% (HTST) and 50.7 ± 9.6% (LTLT). All-trans-ß-carotene retention was significantly higher in water blanched dried mango, 93.2 ± 5.2% (LTLT) and 91.4 ± 5.1% (HTST), compared with IR dry blanched, 73.6 ± 3.6% (LTLT) and 76.9 ± 2.9% (HTST). Increased levels of 13-cis-ß-carotene isomer were detected only in IR dry blanched mango, and the corresponding dried mango also had a slightly darker color. IR blanching of mango prior to drying can improve the retention of vitamin C, but not the retention of carotenoids, which showed to be more dependent on the temperature than the blanching process. A reduction of drying time was observed in LTLT IR-blanching mango.

Effect of Hydrocolloids and Emulsifiers on Baking Quality of Composite Cassava-Maize-Wheat Breads.

Cassava is widely available worldwide but bread quality is impaired when cassava is used in the bread formulation. To overcome this problem, different improvers were tested in the preparation of composite cassava-maize-wheat (CMW) breads. Emulsifiers, diacetyl tartic acid ester of monoglycerides (DATEM), sodium stearoyl-2-lactylate (SSL), and lecithin (LC); and hydrocolloids, carboxymethylcellulose (CMC) and high-methylated pectin (HM pectin) were added during dough preparation of the composite flours (cassava-maize-wheat, 40 : 10 : 50). Each emulsifier was tested in combination with the hydrocolloids at levels of 0.1, 0.3, and 0.5% while hydrocolloids were used at a level of 3%. Bread quality attributes such as specific loaf volume, crust colour, crumb moisture, and firmness were measured. The specific volume of the fresh breads significantly improved with the addition of hydrocolloids (7.5 and 13%) and in combination with emulsifiers (from 7.9 to 27%) compared with bread produced without improvers. A significant improvement of brownness index and firmness of the composite flours breads was achieved with the addition of hydrocolloids and emulsifiers. The results show that emulsifiers and hydrocolloids can significantly improve the baking quality of CMW breads and thereby enhance the potential for using locally produced flours in bread baking.

Effect of Cassava Flour Characteristics on Properties of Cassava-Wheat-Maize Composite Bread Types.

Replacement of wheat flour by other kinds of flour in bread making is economically important in South East Africa as wheat is mainly an imported commodity. Cassava is widely available in the region, but bread quality is impaired when large amounts of cassava are used in the bread formulation. Effect of differently processed cassavas (sun-dried, roasted and fermented) on composite cassava-wheat-maize bread quality containing cassava levels from 20 to 40% (w/w) was evaluated in combination with high-methylated pectin (HM-pectin) added at levels of 1 to 3% (w/w) according to a full factorial design. Addition of pectin to cassava flour made it possible to bake bread with acceptable bread quality even at concentration as high as 40%. In addition to cassava concentration, the type of cassava flour had the biggest effect on bread quality. With high level of cassava, bread with roasted cassava had a higher volume compared with sun-dried and fermented. The pectin level had a significant effect on improving the volume in high level roasted cassava bread. Crumb firmness similar to wheat bread could be obtained with sun-dried and roasted cassava flours. Roasted cassava bread was the only bread with crust colour similar to wheat bread.

Degradation of phytate by Pichia kudriavzevii TY13 and Hanseniaspora guilliermondii TY14 in Tanzanian togwa.

The fermented cereal-based gruel togwa is used as weaning food for children in Tanzania. Togwa is rich in minerals but these are often not available for uptake in the human intestine due to natural inhibitors, such as phytate (IP(6)). The yeasts Pichia kudriavzevii TY13, Hanseniaspora guilliermondii TY14 and TY20, isolated from Tanzanian togwa, and selected for high phytase activity in complex yeast medium YPD, were now studied regarding their ability to degrade IP(6) in maize-based model togwa. A modified constitutively high-phytase producing Saccharomyces cerevisiae BY80 and commercial Aspergillus ficuum phytase were included for comparison. In addition, a strain of Lactobacillus plantarum was included in the model-togwa set-up. All yeasts in the study grew and reached final cell density 1.5-2 log units higher than the start value. S. cerevisiae BY80 degraded 85% of the IP(6) in 48 h; the same degradation level as with A. ficuum phytase (89%). Of the togwa-isolated yeasts, P. kudriavzevii TY13 and H. guilliermondii TY14 showed strong phytate degradation in the model-togwa; 95% or more of the initial IP(6) was degraded after 48 h. This corresponds to a remaining level of 0.4 and 0.3µmol IP(6)/g dw. Co-inoculation with L. plantarum did not increase IP(6) degradation. Moreover, fermentation with P. kudriavzevii TY13 yielded a successive increase in inorganic phosphate (P(i)), from 0.7 to 5.4 mM, suggesting a phytase production in TY13 which is fairly insensitive to P(i) repression. The study shows that phytate in a model togwa is available for yeast phytase enzymes, and addresses the importance of strain selection for effectively degrading the phytate. Certain yeasts originating from togwa seem to have developed a natural high phytase production, and P. kudriavzevii TY13 and H. guilliermondii TY14 seem particularly well adapted to phytate degradation in togwa, and is our choice for further studies and strain improvement.

Effects of thermal processing on the in vitro bioaccessibility and microstructure of ß-carotene in orange-fleshed sweet potato.

The effects of different preparation methods on the bioaccessibility of ß-carotene in orange-fleshed sweet potato (OFSP), an important food crop in sub-Saharan Africa, have been evaluated using an in vitro digestion procedure. The preparation methods included, on fresh roots, boiling followed by puréeing and oil addition (BOL) and homogenization followed by boiling and oil addition (HOM); on milled flour from freeze-dried fresh roots, cooking of porridge followed by oil addition (POA) and oil addition to flour followed by cooking of porridge (POB). The retention of all-trans-ß-carotene ranged from 58% (POB) to 72% (BOL). The presence of oil during heating resulted in a significantly higher formation of 13-cis-ß-carotene for the POB-treated samples than for the other samples. The efficiency of micellarization of all-trans-ß-carotene after in vitro digestion was 50% (HOM), 48% (POB), 31% (POA), and 16% (BOL). Brightfield microscopy of the cell structure after processing and in vitro digestion showed a high degree of cell-wall rupture for the HOM-treated samples, whereas cells appeared intact for the BOL samples. Also, coherent anti-Stokes Raman scattering (CARS) microscopy showed smaller ß-carotene bodies residing in the HOM samples than in the BOL samples after digestion. These results suggest that the in vitro bioaccessibility of ß-carotene in an OFSP meal can be improved by processing methods that promote cell-wall rupture.

Processing of tomato: impact on in vitro bioaccessibility of lycopene and textural properties.

BACKGROUND: Human studies have demonstrated that processing of tomato can greatly increase lycopene bioavailability. However, the difference between processing methods is not widely investigated. In the current study different thermal treatments of tomato were evaluated with regard to their impact on in vitro bioaccessibility and retention of lycopene and beta-carotene as well as textural properties. Thermal treatments used were low (60 degrees C) and high (90 degrees C) temperature blanching followed by boiling. RESULTS: Lycopene was relatively stable during thermal treatment, whereas beta-carotene was significantly (P < 0.05) reduced by all heat treatments except for low temperature blanching. In vitro bioaccessibility of lycopene was significantly increased from 5.1 +/- 0.2 to 9.2 +/- 1.8 and 9.7 +/- 0.6 mg kg(-1) for low and high temperature blanching, respectively. An additional boiling step after blanching did not further improve lycopene bioaccessibility for any treatment, but significantly reduced the consistency of low temperature treated samples. CONCLUSION: Choice and order of processing treatments can have a large impact on both lycopene bioavailability and texture of tomato products. Further investigations are needed, but this study provides one of the first steps towards tomato products tailored to optimise nutritional benefits.

Biodiversity and phytase capacity of yeasts isolated from Tanzanian togwa.

The focus of the present investigation was on the Tanzanian fermented food togwa as a source for dietary iron and zinc, and the potential for mineral availability improvements using selected yeasts. To establish the content of target minerals and main inhibitor for intestinal uptake, iron and zinc as well as the mineral chelating phytic acid, (IP(6) or phytate) were determined in naturally fermented togwa. Yeasts were isolated from sorghum, maize and cassava based togwa, and identified by sequencing the D1/D2 region of the LSU rRNA gene. The isolated yeasts were subsequently screened for phytase activity. The total iron content in sorghum, maize and cassava based togwa were 41.5 (+/-7.2), 85.4 (+/-31.9) and 28.6 (+/-3.8) microg/g dw (dry weight) respectively. The zinc content was 12.3 (+/-3.1), 11.0 (+/-1.1) and 6.4 (+/-4.5) microg/g dw in sorghum, maize and cassava based togwa, and the phytate content in the three varieties were 2.6+/-1.2, 4.7+/-0.8 and 0.4+/-0.4 micromol/g dw respectively. The phytate levels in the sorghum and maize based togwa are expected to substantially reduce the availability of iron. The molar ratio phytate to iron for these two varieties were estimated to be 3.5:1 and 3.1:1 respectively. In general, a phytate to iron molar ratio below 1 is needed to increase the availability of iron. Among 26 isolates, 9 different species could be distinguished: Issatchenkia orientalis, Pichia anomala, Pichia norvegensis, Pichia burtonii, Pichia guilliermondii, Kluyveromyces marxianus, Saccharomyces cerevisiae, Hanseniaspora guilliermondii and Candida glabrata. The strains were screened for phytase activity in YPD supplemented with 0.5 mM IP(6). Of 26 screened strains, the phytase activity was most prominent in strains of I. orientalis and H. guilliermondii. The strains and data constitute a basis for further improvements of iron and zinc bioavailability in togwa.

In vitro bioaccessibility of beta-carotene from heat-processed orange-fleshed sweet potato.

Orange-fleshed sweet potato (OFSP) is currently promoted in parts of sub-Saharan Africa as a biofortified staple food with large potential to provide considerable amounts of provitamin A carotenoids. However, the bioaccessibility of provitamin A carotenoids from OFSP has not been widely investigated, especially not as an effect of different preparation methods. In this study, we used an in vitro digestion model to assess the bioaccessibility of beta-carotene from differently heat-processed OFSP. The fraction of carotenoids transferred from the food matrix to a micellar phase obtained after microfiltration and to a supernatant obtained after low-speed centrifugation was investigated. The percentage of accessible all-trans-beta-carotene in the micellar phase varied between 0.5 and 1.1% in the heat-processed OFSP without fat and between 11 and 22% with the addition of 2.5% (w/w) cooking oil. In comparison with the micellar phase, the percentage of accessible all-trans-beta-carotene in the supernatant phase was significantly higher (P < 0.001), between 24 and 41% without fat and between 28 and 46% with fat. These results support the importance of fat for an improved micellarization of beta-carotene. Overall, the high in vitro bioaccessibility of beta-carotene from heat-processed OFSP indicates that sweet potato might be a promising dietary approach to combat vitamin A deficiency.

Physical and chemical characteristics of golden-yellow and purple-red varieties of tamarillo fruit (Solanum betaceum Cav.).

Golden-yellow and purple-red tamarillos (Solanum betaceum Cav.) cultivated in Ecuador were studied for their physical properties, proximate composition, pH, degrees Brix, acidity, sugars, organic acids, minerals, vitamin C and beta-carotene content in the edible part. Results were compared with those for Spanish fruits. The golden-yellow and purple-red Ecuadorian fruits were larger (107 and 188 g) than the respective Spanish fruits (43 and 63 g), softer but generally similar in chemical composition except for fat (0.72 and 0.6%) and malic acid (0.32 and 0.53%) contents in the golden-yellow and purple-red Ecuadorian fruits. Tamarillo fruits are a good source of potassium (approximately 400 mg/100 g fresh weight). Total phenolics in the golden-yellow and purple-red varieties were 125 and 187 mg gallic acid equivalents/100 g fresh weight, respectively. The golden-yellow variety had weaker anti-DPPH radical activity than the purple-red variety. Flavonols were only found in the peel of both varieties, while hydroxycinnamic acid derivatives were found in peel and pulp.

Impaired uptake of beta-carotene by Caco-2 human intestinal cells in the presence of iron.

At present, there are conflicting data regarding whether or not beta-carotene has a positive effect on iron absorption. This study was undertaken to evaluate possible interactions involved in the uptake of beta-carotene and iron in a human intestinal cell model (Caco-2). The Caco-2 cells were incubated with test solutions containing different amounts of ferrous chloride (10-50 microM) and beta-carotene (0.3-2.5 microM) incorporated in synthetic micelles. In the absence of iron, cellular accumulation of beta-carotene from synthetic micelles was proportional (r (2)=0.97, P <0.001) to the beta-carotene concentration in the test solution. However, with addition of ferrous chloride (30 microM), the beta-carotene uptake was significantly reduced (P <0.05), on average by 22%. There was also an inverse relationship between the beta-carotene uptake and iron concentration in the test solution (r (2)=0.93, P <0.05). Iron provided in physiological amounts inhibited the uptake of beta-carotene in the in vitro Caco-2 cell system.

Plasma levels of retinol, carotenoids, and tocopherols in relation to dietary pattern among pregnant Tanzanian women.

In Tanzania, as in other developing countries, dietary intake of nutrients in pregnant women is marginal or lower than the recommended intakes and therefore these women are at high risk for deficiencies. Our aim was to evaluate the relationship between diet and plasma levels of retinol, carotenoids, and alpha-tocopherol in the third trimester of pregnancy. Ninety pregnant women aged between 18 and 45 years were equally recruited from three villages. Seven-day food frequency data was collected by questionnaire. Plasma levels of retinol, carotenoids, and tocopherols were assessed by high-performance liquid chromatography (HPLC). Results indicated that cooked green leafy vegetables constituted the major source of provitamin A carotenoids, with low intake of yellow/orange fruits and preformed vitamin A. Lutein, lycopene, and beta-carotene were the predominant carotenoids in the plasma with mean values of 1.61, 0.84, and 0.63 mumol/L, respectively. There was no significant correlation between frequencies of vegetable consumption and either plasma retinol or carotenoids. However, increased consumption of green leafy vegetables with oil, which increases bioavailability, was correlated with high plasma retinol levels (p = 0.03). Low retinol levels (< or = 0.70 mumol/L) were present in 26% of women. The mean plasma retinol concentration was 0.89 mumol/L and 63% of the women had values below 1.05 mumol/L. The mean plasma alpha-tocopherol concentration was 15.4 mumol/L and women with plasma retinol concentration > 1.05 mumol/L had significantly higher mean alpha-tocopherol than women with plasma retinol concentration < or = 0.70 mumol/L (p < or = 0.01). Twenty-four percent of the women were anemic (hemoglobin: Hb < 110 g/L) and the mean Hb value was 116.3 g/L.

In vitro accessibility of carotenes from green leafy vegetables cooked with sunflower oil or red palm oil.

Although vegetables and fruits are readily available and consumed in most areas of Tanzania, vitamin A deficiency is still prevalent. The objective of the present study was to measure the in vitro accessibility (available for absorption) of alpha-carotene and beta-carotene in vegetable relishes prepared with or without oil. Derived results were used to calculate the contribution of vegetable relish to recommended daily intake of retinol. Five sundried green leafy vegetables from Tanzania were cooked without oil, with sunflower oil or with red palm oil. The total amount and in vitro accessibility of alpha-carotene and beta-carotene from a portion (100 g) of vegetable relish was determined. The in vitro method used simulated the digestion process in the gastrointestinal tract. Carotenoids released after digestion were quantified using high-performance liquid chromatography. The total amount of beta-carotene varied between 1211 and 3659 microg/100 g among the five vegetable sources studied. From green leaves cooked without oil, 8-29% of the beta-carotene content became accessible after in vitro digestion and 39-94% from leaves cooked with sunflower oil or red palm oil. Adding red palm oil instead of sunflower oil resulted in about twice as much accessible beta-carotene, due to the high accessibility of its beta-carotene content. The red palm oil contributed also a considerable amount of alpha-carotene. The results showed that by eating vegetable relishes with added oil daily, it should be possible to provide the recommended intake level of vitamin A.