Whole-grain oats (Avena sativaL.) as a carrier of lactic acid bacteria and a supplement rich in angiotensin I-converting enzyme inhibitory peptides through solid-state fermentation

Abstract

This study explored a novel strategy to develop solid-state whole-grain oats as a novel carrier of lactic acid bacteria and a nutraceutical supplement rich in ACE inhibitory peptides. Oats were fermented by Lactobacillus plantarum B1-6, Rhizopus oryzae, or a combination of L. plantarum B1-6 and R. oryzae. L. plantarum showed a much better growth performance in oats when it was combined with R. oryzae than when it was cultured alone, as evidenced by an increase in viable cell count to 9.70 log cfu g-1 after 72 h of fermentation. The coinoculated fermented oats (CFO) and the R. oryzae-fermented oats (RFO) were then selected for investigations on protein hydrolysis and on the functional properties of the released bioactive peptides. The results showed that the soluble protein contents changed from 7.05 mg g-1 to 14.43 and 10.21 mg g-1 for CFO and RFO, respectively. However, the degree of hydrolysis and the content of peptides with molecular masses less than 10 000 Da indicated that the CFO proteins can be degraded to a greater degree. As analyzed by electrophoresis and reversed-phase high-performance liquid chromatography, the protein and peptide profiles of CFO and RFO demonstrated that the proteins from CFO were more obviously hydrolyzed and more small peptides were obtained. In addition, both CFO and RFO presented higher ACE inhibitory activities than unfermented oats, whereas the protein extracts from CFO exerted a lower IC50 value of 0.42 mg protein per mL compared with the protein extracts from the other samples. This research has broadened our knowledge on the development of whole-grain oat products as a probiotic carrier and on the difference between mixed solid-state fermentation (SSF) and fungi SSF in terms of protein degradation and the capacity to release ACE inhibitory peptides. Our approach could be used to obtain probiotic food products and probably to develop oats as a potential therapeutic ingredient targeting hypertension.

Evaluation of biochemical and antioxidant dynamics during the co‐fermentation of dehusked barley with Rhizopus oryzae and Lactobacillus plantarum

“…Although LAB are commonly used as probiotic starters, they are rarely used in solid‐state fermentation alone because of their fastidious requirement of moisture and nutrition. R. oryzae , a generally recognized as safe fungal species, has the ability to degrade polymeric materials and provide nutrients for the growth of LAB culture (Souza et al, ; Wu et al, ). In this study, the viable L. plantarum colonies were as high as 7.94 ± 0.05 log CFU/g FDB after fermentation, indicating that barley could be developed as a good food carrier of LAB by solid‐state fermentation using LAB mixed with R. oryzae .…”

“…Ten milliliters of boric acid‐sodium hydroxide buffer (pH 9.0) was added to 200 mg of freeze‐dried powder, after vibrating for 1 hr at 28°C, the sample was centrifuged at 10,000× g for 20 min to remove the insolubles. The soluble protein content was determined by a Bradford method with bovine serum albumin as the standard protein (Wu et al, ).…”

“…SDS‐PAGE analysis was carried out as described by Wu et al () with some modifications. One milliliter of 0.1 M Tris–HCL (pH 8.8) was added to 40 mg of FDB freeze‐dried powder, after vibrating for 1 hr, it was centrifuged at 10,000 g for 20 min to obtain the protein extracting solution.…”

“…During solid‐state fermentation, microbial metabolism resulted in the improvement of protein digestibility, enrichment of free phenolic compounds, and enhancement of antioxidant and other physiological activities (Oliveira, Cipolatti, Furlong, & Soares, ; Xiao et al, ). Wu et al () reported that the soluble protein contents, degree of hydrolysis, and angiotensin I‐converting enzyme inhibitory activity of oats co‐fermented with R. oryzae and L. plantarum were significantly increased. Studies by Sánchez‐Magaña et al () showed that solid‐state fermentation using R. oligosporus could improve the total phenolic content, antioxidant activity, and hypoglycemic functionality of chickpea extracts.…”

“…Rhizopus oryzae , a generally recognized as safe fungal species, has the ability to degrade polymeric materials and provide nutrients for the growth of LAB culture. (Souza, Massarolo, Tralamazza, & Furlong, ; Wu et al, ). Therefore, the co‐fermentation of dehusked barley with R. oryzae and LAB could not only endow barley with sweet and sour taste, but also develop barley as a carrier for probiotics.…”