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Functional foods are receiving much attention recently because of their potential role in improving consumers health, and future trends are moving towards this type of foods because of their health effects on the consumer. Consumers have increased their demand for functional foods, which have a role in improving health and may prevent some diseases. Functional foods include a number of foods that contain functional ingredients for health benefits besides their nutritional value.
Therefore, this study was carried out to develop and evaluate some of functional fermented cereals products (i.e. cereal-based fermented beverages and tarhana) by combining the health benefits of starter cultures of probiotic bacteria and the nutritional value of whole cereal grains meal (i.e. wheat, oat and barley).
The chemical composition and total phenolic compounds of different whole grains meal were determined to provide us with data that may employ as guidelines for the production of some functional fermented foods. The suitability of different whole grains meal for the production of cereal-based fermented beverages and tarhana were studied under different fermentation conditions. The microbiological, physical, sensory properties and shelf-life of fermented products were determined.
The obtained results can be summarized as follows:
Chemical composition of raw materials:
Oat flakes meal had the highest amount of lipids (8.25%), ash (4.10%) and crude fibers (3.70%), in comparison to the other samples. While, whole barley meal had the highest amount of crude protein (13.75%) compared to 12.88% for whole wheat meal. Total phenolic compounds were significantly (P≤0.05) different depending on the raw material. Whole barley meal had significantly higher total phenolic contents (2.72 mg/g) than that of oat flakes meal (1.55 mg/g).
Manufacture and development of cereal-based fermented beverage:
In the present study, whole meal of oat flakes and barley grains were fermented with L. plantarum and L. acidophilus and B. lactis to produce cereal-based fermented beverages. The effect of different fermentation parameters (i.e. pure and mixed bacterial cultures, cereal grains meal concentrations, mixed cereal substrate and beverage supplementation) on the cell population, pH values and titratable acidity were monitored during fermentation for 24 h at 37℃.
Application of pure bacterial cultures:
After 24 h of fermentation at 37℃, the highest cell count was observed in 2% oat beverage (Ob) with L. plantarum and L. acidophilus (1×108 and 8×107 cfu/ml, respectively) compared with 2% barley beverage (Bb) fermented with the same cultures (8×107 and 4×107 cfu/ml, respectively). However, B. lactis showed less population in both Ob and Bb samples (4×107 and 1×107 cfu/ml, respectively). In all cases, pH dropped rapidly during the first 8 h of fermentation. After 24 h, the pH was found to be below 3.5 in cereal beverages fermented with both L. plantarum and L. acidophilus. Also, more lactic acid was produced by L. plantarum at 24 h in Ob and Bb (1.41 and 1.65 lactic acid g/L) than by L. acidophilus (1.0 and 1.12 lactic acid g/L).
Application of different concentrations of oat and barley meal:
Fermentation of 2.0, 3.5 and 5.0% (w/v) of oat and barley meal with pure bacterial cultures showed that the population densities of L. plantarum, L. acidophilus and B. lactis, respectively reached 9×107 and 3×107 and 3×107 cfu/ml, respectively in 3.5% Ob and 1×108 and 9×107 and 6×107 cfu/ml, respectively in 3.5% Bb at the end of fermentation. Different Bb samples showed higher DROP in pH values and an increase in titratable acidity (TA) than Ob at 24 h of fermentation. The obtained results showed that 3.5% Ob and Bb was the most preferable concentration in order to obtain good consistency and intensive fermentation of the beverages.
Application of mixed bacterial cultures:
The next step of the study was to ferment oat and barley beverages (3.5%) with mixed cultures of the selected probiotics for their potential application in functional food development. At the end of fermentation, the pH values ranged between 4.6 and 3.9 for Ob and Bb samples. The viable cell counts in the fermented beverages were above 108 cfu/ml for all cultures. The highest cell count increase was registered for mixed culture of L. plantarum and L. acidophilus, L. plantarum and B. lactis and the combination of the three cultures.
Higher DROP in pH values and increase in titratable acidity were observed in Bb than Ob when fermented with different mixed probiotic cultures of LAB. Also, the maximum concentration of lactic acid observed in Bb fermented with mixed cultures of L. plantarum and L. acidophilus (1.55 lactic acid g/L) was lower than that fermented with single culture of L. plantarum (1.8 lactic acid g/L).
Application of mixed cereal substrates:
Fermentation of mixed oat-barley beverage (OBb) with pure or mixed probiotic cultures showed considerable differences in cell population, pH and acid production. Different tested pure cultures showed good growth in mixed cereal media than single cereal media. A slight increase in cell population was observed in mixed cereal beverage fermented for 24 h with mixed culture than pure culture. The results showed that the fermentation of single or mixed cereal beverage by combination of three probiotic cultures achieved higher cell population (over 108 cfu/ml) which is above the levels required for probiotic products (106-107 cfu/ml). More rapid DROP in pH and increase in TA was observed in mixed cereal beverage fermented with L. plantarum and L. acidophilus or L. plantarum and B. lactis followed by sample fermented with combination of three cultures.
In conclusion, mixed cultures fermentation produced approximate amount of cell populations in mixed or single cereal beverage. However, the resultant lactic acid was slightly lower, which could have a slight impact on the organoleptic properties of the products.
Supplementation of cereal beverages:
Supplementation of single and mixed cereal beverages (3.5%) with 4% sugar, 0.5% whey protein concentrate, and 0.2% inulin were applied to increase fermentation rate and enhance the sensory properties of the beverages fermented with combination of the three probiotic cultures. The results showed that supplementation of cereal beverages increased cell counts by 3 log order in comparison to 2 log order in unsupplemented beverages. More rapid DROP in pH and an increase in TA were observed during 4 and 10 h of fermentation. At the end of fermentation, the pH and TA values of the supplemented beverages ranged between 3.32-3.37 and 1.41-1.68 lactic acid g/L, respectively compared to 4.05-4.53 and 0.90-1.0 lactic acid g/L for unsupplemented beverages.
Based on these results, fermentation process of supplemented beverages was carried out for 10 h, at which the viable cell counts were increased to about 8-9 log10 cfu ml-1 and the pH values reached about 4.5 or less.
Sensory evaluation of cereal-based fermented beverages:
Sensory evaluation of cereal-based fermented beverages showed that flavored (strawberry) fermented oat beverage recorded the highest scores of appearance, taste and flavor, whereas flavored fermented mixed-cereal beverage recorded the highest value of consistency. Fermentation of single and mixed cereal beverages with combination of three probiotic cultures significantly (pp≤0.05) improved consistency, taste, flavor and overall acceptability. Flavored fermented samples had significantly (p≤ 0.05) the highest overall acceptability (8.2-8.5 on a 9-point hedonic scale) among all tested samples. Sensory evaluation clearly indicates that fermentation improves the sensory quality of the beverages.
Shelf-life of cereal-based fermented beverages:
Changes in viable cell counts, pH and titratable acidity of single and mixed cereal-based beverages fermented for 10h with three probiotic cultures were determined at 0. 7, 14 and 21 days of storage at 4℃ . During storage, viable cell counts remained within the required range (108-109 cfu/ml) which ensured the probiotic characteristics of the drink for 21 days. There was a slight DROP in pH values and an increase on titratable acidity of the product during storage.
Addition of whole cereal grains meal as a source of dietary fiber and antioxidant for the development of tarhana as a value-added functional food. The effect of substituting wheat flour (72% extr.) with different ratios of whole wheat meal (WMM), oat flakes meal (OFM), whole barley meal (WBM) and mixed cereal meal of oat and barley on the physical, rheological, color, functional and sensory properties of tarhana samples were determined.
Physical properties of tarhana:
Changes in pH values of different tarhana samples were observed during fermentation at 0. 24, 48 and 72h. Long fermentation period significantly (p≤ 0.05) decreased pH values of tarhana samples from 5.22-5.89 to 4.81-5.09. Tarhana sample formulated with 100% WWM showed the highest pH value of 5.09 at the end of fermentation. On the other hand, pH values decreased to 4.70 and 4.82 after 24h of fermentation for the samples formulated with 25 and 50% of oat flakes, respectively. No significant difference (p≤0.05) was observed in pH values between the samples with 25 and 50% of barley meal.
Rheological properties of tarhana soup:
Results of rheological properties of tarhana soup samples showed that the flow curves are non-linear indicating a non-Newtonian behavior of all tested samples. Tarhana sample formulated with 50% of oat flakes meal showed the highest shear stress response values indicating a thick consistency character for this sample. Meanwhile, control and barley 50% samples showed the lowest shear stress values. The flow behavior index of tarhana soup samples ranged between 0.11 to 0.19 which indicate the pseudoplasticity of samples. The higher value of consistency coefficient was recorded for 50% OFM sample followed by 100% WWM sample. The substitution of wheat flour with different ratios of whole cereal grains meal increased the consistency of samples.
Fermentation loss percentage:
Fermentation loss values of tarhana samples ranged between 7.12% and 12.61%. Long fermentation process of tarhana by lactic acid bacteria and baker’s yeast is the main reason for fermentation losses. Over-fermentation of tarhana causes dry matter loss up to 25% and a decrease in functionality. Highest values of fermentation loss were recorded for tarhana samples formulated with high substitution ratios of whole cereal grains’ meal. Fermentation loss values were 12.61, 10.26% for mix 50%, OFM 50% and WWM 100% samples respectively, compared with 9.38% for control sample.
According to the color results, L* values ranged between 73.51-68.2. OFM 25% sample showed the highest L*-value followed by the control sample, while WWM100% sample showed the lowest L*-value because of whole cereal grains’ meal used. Concerning a*, WBM 50% sample achieved the highest value of 2.88 and that may be due to the distribution of anthocyanin pigment in the outer layer of barley grains, while oat flakes meal (OFM) 50% & mixed-cereals 50% samples showed the lowest a*-values of 1.58 & 1.45, respectively. Substitution of wheat flour (72%) in tarhana formulation with whole cereal grains’ meal reduced the yellowness of other samples which led the control sample to be the most yellowish sample among other samples.
Substitution of wheat flour (72% extr.) with different ratios of whole cereal grains meal has significantly (p≤ 0.05) increased water and oil absorption capacity of tarhana sample. The sample with 50% WBM recorded the highest value of water absorption capacity, where the sample with 50% OFM recorded the highest value of oil absorption capacity compared to control sample. Substitution of wheat flour (72% extr.) with different ratios of whole cereal grains meal has significantly (p≤ 0.05) increased the foaming capacity and stability of the final product. The tarhana sample formulated with 50% of mixed-cereal meal of oat and barley recorded the highest value of foaming capacity, where the lowest value was for 100% WWM sample. Emulsification activity results showed that there was no significant difference (p≤ 0.05) among samples as they ranged between 96.2 – 96.7% (except for 100% WWM sample which recorded the lowest value of 93.1%).
Sensory evaluation of tarhana soup samples:
Results of sensory evaluation of tarhana soup samples showed that, substitution of wheat flour 72% with OFM 50% has improved the taste of traditional tarhana and scored the highest value superior to the control sample. Concerning the color, tarhana soup samples supplemented with OFM 25 and 50% were the most liked samples scoring 8.2 and 8.5, respectively. Control soup recorded the highest flavor score of 8.5. Substitution with whole cereal grains meal has increased the consistency and thickness of samples which negatively affected their score in comparison to the control sample. However, the taste of these samples was the highest. Concerning sourness, no significant difference (p<0.05) was observed among samples. Tarhana soup with OFM 25% had the highest score in overall acceptability than control sample. The overall sensory analysis results indicated that, utilization of whole cereal grains’ meal in tarhana production resulted in acceptable soup properties concerning most of the sensory properties.
from this study it could be concluded that whole cereals meal had the ability to enhance and stimulate the growth of probiotic bacteria in cereal-based fermented beverages with good survival during production and storage. Also, the substitution of wheat flour (72% ext.) with different ratios of whole cereal meals had positively affected the functional, rheological and sensorial properties of traditional tarhana. Such functional fermented cereal products are combining the nutritional value of whole grains and the health benefits of probiotic bacteria, they also can be greatly improved and developed by using different raw materials or additives.
Based on the results of this study, it can be recommended to apply oat flakes meal in the production of some functional fermented cereal-based products. In addition to the high nutritional value of oats, they are characterized by good palatability and sweet taste and that could be observed from the results of the sensory evaluation of cereal-based fermented beverages or tarhana, where oat samples were the most liked and preferable.