Effects On Nutrition And Bio-functionality Of Oats By Mixed Solid-state Fermentation With Rhizopus Oryzae And Lactic Acid Bacteria

Oat has the sixth largest yield among the total yield of crops in the world.It is rich in cellulose,essential amino acids,unsaturated fatty acids,vitamins and minerals,etc.Currently,most of the oat crops are treated as livestock and only a handful of resources are brought into food industrial production.To solve this problem,the solid-state fermentation?SSF?technology can be applied.It is not only environmentally friendly,but can take good use of the oat resources.Although lactic acid bacteria?LAB?are generally recognized as safe and probiotics,their ptotease and amylase are less developed than filamentous fungi.In this case,the mixed SSF may provide the possibility of LAB growth in the whole oat,and widely diversify the oat probiotic products.This paper started with discussing the mutual influence of R.oryzae and three LAB strains,including L.plantarum 70810,L.plantarum B1-6 and L.plantarum ZR;then,the core temperature,total acidity,moisture content,reducing sugar content and amino acid nitrogen content were also monitored during the fermentation;the changes in the amino-acid component and soluble protein content both indicated that the mixed SSF could improve the nutritive value of oat;moreover,due to the high level of oat protein and polyphenols,the hydrolysis of protein,ACE-inhibitory activity,total phenolic content and in vitro antioxidant activity were studied to prove that the bio-functionality of oat could be enhanced.All results are described as follows:1.Research on the co-cultured system of R.oryzae and LAB in oatThe growth status of LAB was determined by viable counting method,and the growth indicator of filamentous fungi,ergosterol,was measured using the high-performance liquid chromatography?HPLC?.LAB growth could be improved by fermentation with R.oryzae,the maximum counting number was 8.40?9.82 1g cfu/g,far more then that of solid-state fermentation with lactic acid bacteria.After the mixed SSF,the pH value decreased rapidly and reached the lowest value of 3.69?3.83.Conversely,the microbial synthesis of ergosterol was slightly inhibited in the presence of LAB.However,the continuous increase of ergosterol content could still prove that R.oryzae survived well during the fermentation.2.Effects on the physico-chemical and nutritional characteristics of oats by mixed solid-state fermentation with R.oryzae and LABDuring the mixed SSF,the growth status of LAB was determined by viable counting method,and the growth indicator of filamentous was measured using the high-performance liquid chromatography?HPLC?.The core temperature of oat increased its highest value of 35.60??36.4? at 24 h,and then declined.The total acidity showed a continuous increase to the final value of 1.08%?1.59%.Reducing sugar content and the glycoamylase activity increased rapidly druring 0-48 h and dropped slightly with the highest value of 41.09?47.42 g/100 g,1093.85?1157.46 U/g.The content of soluble protein and amino acid nitrogen augmented to their highest value of 107.478?115.77 mg/?10 g dry matter?and 40.66?41.67 mg/100 g at 48 h,and then remained stable.Continually,the essential amino acid index?EAAI?and biological value?BV?were calculated,respectively 80.77 and 76.34 for SSF with R.oryzae and L.plantarum B1-6.3.Effects on protein degradation and the ACE-inhibitory activity of oats by mixed solid-state fermentation with R.oryzae and LABProtein pofiles of oat isolates were monitored by sodium dodecyl sulfate polyacrylamide-gel electrophoresis?SDS-PAGE?and indicated that oat proteins were degraded or produced during fermentation.The changes of protein contents were predicted by alternations of band intensities.Specifically,several proteins ranged from molecular mass?MM?of 32.75?35.08 kDa were hydrolyzed and the bands of proteins with MM of 12.78?13.38 kDa were evidently enforced.Degree of hydrolysis?DH?and content of peptides with molecular less then 10 kDa were also investigated.During the fermentation with R.oryzae and LAB,the value of DH continually increased from-2.61%to 4.85?6.28%.Peptide contents of molecular weight cut-off at 10 kDa ware equivalent to 359.79?373.93 mg casein tryptone/g dry matter.Furthermore,reverse phase high-performance liquid chromatography?RP-HPLC?showed more disappearance of larger hydrophobic peptides and increased amount of smaller hydrophilic peptides resulted by the mixed solid-state fermentation with R.oryzae and LAB.Consequently,different culture starter enhanced ACE-inhibitory activity of oats in a descending order as:R.oryzae and L.plantarum B1-6>R.oryzae and L.plantarum ZR>R.oryzae and L.plantarum 70810>R.oryzae.4.Effects on the total phenolic content and in vitro antioxidant activity of oats by mixed solid-state fermentation with R.oryzae and LABThe total phenolic content?TPC?of ethanol extract from oat gradually increased during fermentation,the highest value was between 12.37 and 13.17 mg GAE/?10 g dry matter?.Solid-state fermented oat possessed a higher level of TPC and in vitro antioxidant capacity then oat fermented only by R.oryzae.Through experiments,the DPPH radical scavenging activity and the hydroxyl radical scavenging activity were enhanced during 0?36 h,and stayed without change.Their highest values were of 67.54%and 91.81%.However,the ferric reducing power and the potential reducing power were boosted until the end of the SSF,finally reached their highest value of 4.13 ?mol FeSO₄/?10 g dry matter?and 10.93 mg TEAC/?10 g dry matter?.