Abstract
Teff (Eragrostis tef (Zucc.) Trotter) is a tropical cereal used in preparing a staple food in Ethiopia and Eritrea called injera. Phenolic compounds are available in soluble and bound forms in cereals like teff. Therefore, their bioaccessibility depends on their release from the food matrix. Different food processing methods including fermentation have been applied since ancient times to aid bioaccessibility and improve the properties of food products. This study aimed at investigating changes in phenolic profiles and antioxidant activities of white and brown teff grains during mushroom-mediated solid-state fermentation. Fermentation with mushroom considerably increased total phenol contents of the soluble phenol fraction with Ganoderma lucidum showing relatively higher increase than Pleurotus ostreatus. Bound fraction of teff phenol did not show noticeable changes after fermentation with the two mushroom strains. Such changes are suggested to be attributed to activities of fungal enzymes such as amylases, xylanases, and proteases that induce structural breakdown of grain components including cell walls leading to the liberation or synthesis of a variety of phenolic compounds. On the other hand, total flavonoid content of teff significantly decreased after fermentation by both strains. This is also believed to be caused by the action of fungal polyphenol oxidases that catalyze the oxidation of a variety of phenolic compounds including flavonoids to o-quinones.
Highlights
Obesity, cancer, diabetes, and allergies are nowadays becoming critical global health concerns. ese chronic diseases are mostly caused by increased intake of refined carbohydrates and high calorie foods [1, 2]
Phenolic Contents. e Total phenolic content (TPC) results of mushroom mycelia-mediated solid-state fermentation and mycelia-free teff grain samples are shown in Figure 1. e G. lucidum (KACC 42231) strain was able to produce significantly higher soluble phenolic contents than the P. ostreatus (KACC 42738) strain and the control in both teff varieties (p ≤ 0.05)
One study with wheat flour fermentation reported an increase in TPC due to the hydrolysis of covalent bonds between the phenolic compounds and cell wall matrices by β-glucosidase from Aspergillus awamori [24]
Summary
Cancer, diabetes, and allergies are nowadays becoming critical global health concerns. ese chronic diseases are mostly caused by increased intake of refined carbohydrates and high calorie foods [1, 2]. One recent study on teff phenolics identified 32 compounds in both the white and brown grains. Solid-state fermentation using fungi has been applied to enhance the production of phenolic compounds and improve the antioxidant capacity of plant materials such as rice, bean, cranberry pomace, brown rice, oat, and maize; fermented cereals are suitable for making of different functional ingredients [15,16,17]. Changes in the phenolic profiles of teff due to fermentation are important in improving the tastes of its food products and predicting its potential effects in preventing chronic diseases. E present study aimed to investigate the changes in phenolic contents and antioxidant activities of white and brown teff grain during mushroom-mediated solid-state fermentation. It evaluated changes in total phenolic content, total flavonoid content, and FRAP activities after six days of fermentation
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