| Oat(Avena L.),belonging to Avena of Gramineae,is an annual herb.As a cereal for human or animal consumption,although consumed in considerably lower quantities worldwide than wheat and rice,oat has received increased interest because of its excellent health-related properties,such as high contents of well-balanced protein and solube dietary fibre,energy in the form of carbohydrate and oil,and several vitamins and minerals.In addition,oats contained abundant biological active compounds such as tocols,phytic acid,sterols,phenolic compounds and so on,which contribute towards protecting foods from rancidity and may also provides its extensive physiologieal functions such as antioxidant activity,reducing blood pressure,blood lipids,blood cholesterol and blood sugar.However,foods from oats have unpleasant taste and difficult to be digested,in addition,the content and bioactivity of biological active compounds were decreased by some processing methods,which limited the development and utilization of oats.Some reported studies demonstrated that germination of seeds from some cereals and beans can decrease antinutritional compounds and enhance the nutritive value and improve sensory quality.Besides,germination can effectively accumulate biological active compounds.The main aim of this research was to study dynamic changes in main nutrient components and biological active compounds in oat groats during germination,as well as to investigate the effect of a highly controlled germination process on their related properties.The main research results of this paper are as follows:1.The content of reduced,soluble sugar and the activity of ?-amylase,?-amylase and total amylase from oat groats increased at first and then decreased rapidly during germination.The content of amylose,amylopectin,total starch from oat groats decreased with the processing of the germintion.During germination,the content of reduced and soluble sugar were highly correlated to the the activity of a-amylase,?-amylase and total amylase,however,the content of amylose,amylopectin and total starch were negativly correlated to the the activity of amylase.2.During germination,the starch granules from oats still maintained the original shape,the A-type characteristics of the X-ray diffraction pattern.Germination increased the solubility and decreased swelling value of starch,and resulted in the poor freeze-thawing stability,which starch is easily gelatinized starch.Moderately germination increased the transparency of starch from oats and enhanced the hot paste stability,cool paste stability and anti-retrogradation,as well as improving starch gel texture properties.3.During germination,the contents of free amino acids,total protein,soluble and insoluble protein and protease activity in oats increased,as well as prolamin.The levels of globulin and glutelin first increased and then decreased,albumin however is quite opposite.The protease activity correlated highly to the content of total,soluble,insoluble protein,albumin,and prolamin,contrary to it for glutelin.The nutritional value of protein from oat groats was improved,but 'lysine was till restricted amino acid during germination.4.With the processing of germination,some albumin subunits in oat groats were degraded and then albumin electrophoretic bands became clear in electrophoresis picture.The higher and medium molecular weight of the globulin subunits were also degraded gradually,the higher molecular weight of band even disappeared and the lower molecular weight of the globulin subunit increased in their content while the molecular weight distribution narrowed,but there were no significant change in the molecular weight and distribution of prolamin.The higher molecular weight of glutelin subunits caused to disappear gradually from 24 h to 48 h of germination,while the molecular weight distribution narrowed.However,with the prolongation of germination time,The higher and lower molecular weight of glutelin subunits increased at the same time,the same as the molecular weight distribution.5.The optimum parameters for extraction technology of peptides from oat groats were determined by quadratic orthogonal rotation regression combination design.The result showed that the effect sequences of three factors for peptide yield were as follows:extraction temperature(X3),liquid-to-solid ratio(X1),extraction time(X2).The regression equation between peptide yield(Y)and three variables was determined by by Data Processing System(DPS),as given in the following equation:Y=5.3712+0.2633X1+0.2454X2+0.3092X3-0.3301X12-0.1958X22-0.1710X32-0.1363 X1X3.The optimal extraction parameters were as follows:liquid-to-solid ratio of 16:1(v/m),extraction time of 72 min,extraction temperature of 34?,and the number of extraction times was one.Under the optimal extract parameters,the peptide yield was 5.54 mg/g,which was in agreement with the predicted value(5.60 mg/g).6.During germination,the content of peptide from oat groats increased significantly as compared with raw groats.The peptide from oat groats exhibited better antioxidant activity and effect of reducing blood pressure,which was highly correlated with the content of peptide.Compared comprehensively,the content and bioactivity(antioxidant activity and angiotensin converting enzyme(ACE)inhibitory activity)of peptide were higher when oat groats were germinated for 60 h.The ultrafiltration membranes with MWCO of 5 KDa and 1KDa were used to classify the extracts of peptide from oat groats.The extracts with lower molecular weights was the lowest in the content,but had higher ACE inhibitory activity.Sephadex G-25 gel filtration chromatography was employed to investigate the molecular weight of the ACE inhibitory peptides(<1 KDa).The result showed that there were two eluting peak with its corresponding molecular weight being 472.3?819.5 Da and 173.3?411.3 Da respectively.7.The peptide from germinared oat groats possessed excellent nutritional values,but its solubility and ACE inhibitory activity were influence by different pH,temperatue,and digestive enzyme.They has higher solubility in range of pH 2.0^12.0,while the ACE inhibitory activity decreased obviously until pH was higher than 9.0.The solubility of peptide first increased to the maximum at 80? then decreased while its ACE inhibitory activity decreased slowly at 20?60?and it decreased sharply at 60? with temperature increasing.The peptides showed no obvious change in ACE inhibitory activity after digested by pepsin or pepsin-trypsin.8.The contents of phenolics and antioxidant activity of oat groats varied with the difference in germination stages and oat cultivars.Compared with raw groats,the contents of free,bound and total phenolics increased in varying degrees during germination.Over all,reducing ability and scavenging ability on DPPH and ABTS radicals of phenolic extracts from oat groats increased along with prolonging the germination time,while the scavenging effects on hydroxyl free radicals and chelating ability on ferrous ions of phenolic extracts first decreased and then increased during germination,as well as inhibition effects on lipid peroxidation.The DNA damage protective effects of phenolic extracts in oats but for free phenolics from Bayou I during germination was better than that of raw groats.The correlation between phenolic content and antioxidant activity indicated that the contents for free,and bound phenolics were highly correlated to the antioxidant activity determined by DPPH,ABTS,FRAP assays.The free phenolics were moderatly correlated to the scavenging activity on site-specific hydroxyl free radicals,chelating ability on ferrous ions and inhibition effects on lipid peroxidation,but negativly correlated to the scavenging activity on non-site-specific hydroxyl free radicals.Conversely,bound phenolics were negativly correlated to antioxidant activity mentioned above.From the regression analysis it can be concluded that changes of antioxidant activity of phenolic extracts from oats during germination can be not only attributed to phenolic contents and assessment methods for antioxidation,but also to phenolic components,including some antioxidative substances contained in extracts besides phenolic compounds. |
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