Various botanical and structural characteristics of starchy foods are considered to modify the rate of starch digestion and the glycaemic responses in humans. The main objective of the study was to examine the impact of fermented barley and oat microstructure on the rate of in vitro starch hydrolysis. A dynamic gastrointestinal model was used to estimate the degree of starch hydrolysis during in vitro digestion of fermented whole grain cereal meals. Light microscopy and confocal laser scanning microscopy were used to study the microstructural changes. In parallel to the in vitro studies, the impact of fermented barley and oats on postprandial plasma glucose responses was evaluated in a human study. Micrographs were taken during in vitro digestion experiments with fermented whole grains and compared with micrographs of boiled barley (undigested). Images showed that most of the oat starch granules were degraded after 120 min of digestion, whereas barley starch granules were less degraded, even after 180 min of digestion. The findings were confirmed by faster starch hydrolysis from the fermented oat meal, measured as maltose generated during in vitro digestion. The area under the curve (AUC) was calculated from the plotted maltose curves of the meals. AUC for barley tempe (266 ± 33) was 40 % of the AUC for oat tempe (663 ± 8) and significantly different (p < 0.007) from AUC oat tempe. The in vitro data closely resembled the AUCs for plasma glucose from the parallel human study. In terms of glucose response, the mean AUC for barley tempe was 46 % of the AUC for oat tempe in the human study. The agreement between the in vitro and in vivo data indicates the potential of the in vitro method as a tool to predict the rate of starch degradation of cereal products.

Background: Several factors can affect glycemic and insulinemic responses from cereal foods. Some suggested factors lowering the responses are; intact botanical structure, high amylose/high β-glucan cereal varieties, organic acid produced during fermentation and food processes inducing retrogradation of starch. Aim of the study: To evaluate the impact of fermented whole grain cereal kernels with high content of amylose (40%) and/or β-glucan (4.6%) on postprandial glucose and insulin responses in healthy adults. Methods: Thirteen healthy volunteers (4 men and 9 women) were given 25 g available carbohydrate portions of: glucose solution; tempe fermented whole-grain barley and tempe fermented whole-grain oat. Blood samples were collected directly before the meal (fasting) and 15, 30, 45, 60, 90 and 120 min after the start of the meal. The GI (glycemic index) and II (insulin index) of meals were calculated for each subject according to FAO/WHO standards. Results: Peak glucose response was lowest after the tempe meal with high-amylose/ high-β-glucan barley tempe while insulin response was lowest after the meal with high β-glucan oat tempe. The mean blood glucose responses for both the barley and the oat tempe meals were significantly lower than from the reference glucose load (P < 0.0001) during the first 60 min. The calculated GI:s for barley and oat tempe were 30 and 63, respectively. Mean serum insulin responses from barley and oat tempe were significantly lower compared with the glucose load (P < 0.002) during the first 60 min, and the calculated II was lower for oat tempe (21) compared with barley tempe (55). Conclusions: The results suggest that cereal products with beneficial influence on postprandial plasma glucose and insulin responses can be tailored by fermentation and enclosure of high-amylose and/or high-β-glucan barley and oat kernels. © 2008 Spinger.

Barley tempeh was produced by fermenting barley kernels with Rhizopus oligosporus. The potential of the yeasts Saccharomyces cerevisiae (three strains), S. boulardii (one strain), Pichia anomala (one strain) and Kluyveromyces lactis (one strain) to grow together with R. oligosporus during barley tempeh fermentation was evaluated. All yeast strains grew during the fermentation and even during cold storage of tempeh (P &lt; 0.01). The growth of yeasts slightly increased the ergosterol contents, but did not influence amino acid contents and compositions, and did not reduce phytate contents. Slight increases of vitamins B6 and niacinamide, and slight decreases of B1 and biotin were observed. Quantification of fungal growth is difficult during mixed species fermentations because ergosterol is found in all fungal species, and colony-forming-unit (cfu) estimations are not reliable for R. oligosporus and other sporulating fungi. Therefore, we developed a quantitative real-time PCR method for individually quantifying S. cerevisiae and R. oligosporus growth in barley tempeh. The PCR results were highly correlated with the ergosterol content of R. oligosporus and with the number of cfu of S. cerevisiae. Thus, real-time PCR is a rapid and selective method to quantify yeasts and R. oligosporus during mixed species fermentation of inhomogenous substrate such as barley tempeh. © 2006 Elsevier Ltd. All rights reserved.

The effects of different pretreatments on phytate and mineral contents were investigated in whole grain barley and oat tempe fermented with Rhizopus oligosporus. Different varieties of barley and oats were exposed to pretreatments such as pearling, rolling, moistening, autoclaving and soaking before fermentation. Pearling was the most effective pretreatment for reduction of phytate content for both oats and barley. Nevertheless, mineral contents were reduced, and most likely cell wall rich fractions were also reduced by this process. In the first experiments the phytate content reduction in the oats and barley samples were reduced by 74% (3.3 μmol/g, d.m.) and 89% (1.4 μmol/g, d.m.), respectively. However, to improve iron absorption the phytate levels should not exceed 0.5 μmol/g, and further phytate degradation was necessary. Therefore, in the final experiments barley samples were exposed to an optimised process with prolonged soaking at a higher temperature and the pearling residues were returned before fermentation. When the outer layers of the barley kernels were returned before fermentation the phytate content was successfully reduced by 97% to 0.4 μmol/g (d.m.) and Fe and Zn levels were well preserved. © 2006.

The iron dialyzability and uptake in relation to transit time through the stomach and small intestine was investigated using a dynamic in vitro gastrointestinal model in combination with Caco-2 cells. Three test meals were evaluated, consisting of lactic fermented vegetables with white (I) or whole meal bread (II) and of sourdough-fermented rye bread (III). Three transit times were tested (fast, medium, and slow transport). Iron dialyzability and absorption differed significantly between medium and slow transit time for meal I and between fast and medium transit time for meal III. For meal II, high in phytate, the iron dialyzability and absorption were low irrespective of transit time. The meals could be ranked with respect to iron dialyzability and uptake in the order I > III > II. Although the in vitro models used have limitations compared to in vivo experiments, the results suggest that an increased transit time may improve iron availability.