Processing Technology And Mechanism Of "Repeated Steaming And Air-exposing" Of Rehmanniae Radix Praeparata

Rehmanniae Radix(RR),a heat-clearing and blood-cooling herb,is changed into Rehmanniae Radix Praeparata(RRP),a blood-replenishing one,which is a representative of effect alteration by traditional processing technique.Historically,RRP prepared by the method of "repeated steaming and air-exposing" is the most widely admired one among the various products.Previously,Maillard reaction was proved to be occured during the steaming process by our research team,but the scientific reason for "air-exposing" remains unknown.Several phenomena have been found recently,for example,the aqueous extract of RR stored in a refrigerator at-18℃ became dark at the surface contacted with air,which suggests that oxygen in the air may take part in the chemical reactions during RRP processing,and accelerate active ingredient formation.In addition,RRP was clinically used to treat blood deficiency syndrome,which resembles hypoferric anemia to some extent.Therefore,whether the concentration of ferrous ion increased by the processing needs further investigation,some related studies were carried out in this paper,and the main results are as follows:Section 1.Effects of repeated steaming and air-exposing on the quality of RRPIn this study,RR slices were used as processing materials,and steaming for 8 hours and then air-exposing for 15 min were used as one processing,time and again,nine kinds of RRP samples were prepared.The results showed that:one-time steaming and air-exposing could make sure that RRP reached to the traditional indexes.However,with the increase of processing times,the contents of stachyose,sucrose,raffinose and catalpol gradually decreased,and those of glucose/galactose,manninotriose and 5-hydroxymethyl furfural(5-HMF)increased rapidly,while the content of fructose increased firstly and then gradually decreased,and the acidity and browning intensity increased,the free radical scavenging ability and NO synthesis inhibiting ability increased gradually.This study further verified that Maillard reaction occurred during the processing of RRP,and RRP quality could be improved by repeated steaming and airexposing.Section 2.Effects of "air-exposing" on RRP processingIn order to evaluate the influence of "air-exposing" on the processing of RRP,the aqueous extract of RR was heated at 95℃ for different times with or without aerating.Compared with control treatment,aeration could significantly reduce pH value,increase the contents of melanoidins,5-HMF,inorganic phosphorus and iron ions,and enhance free radical scavenging ability,but have no significant effect on catalpol degradation.This result indicates that "air-exposing" benefits to RRP processing,and the underlying mechanism may be that supplemented oxygen by aeration promotes the chemical reaction and accelerates the formation of active ingredients.Section 3.Effects of acidity on RRP processingSince RRP acidity increased after repeated processing,RR aqueous extract was adjusted to 10 different levels of acidity(pH:1.0～5.5)in this study,and heated at 95℃ for 8 h with aeration to simulate "steaming" and "air-exposing",and with no aerating system was used as control.It was found that:(1)high acidity could promote catalpol degradation,5-HMF and melanoidins formation,and free radical scavenging the above changes in aerating group were more significant;(2)high acidity could significantly increase the concentration of free iron ions and ferrous ion in the aqueous extract of RR,however,aeration had no significant effect on the changes of iron ions.The results indicate that acidulation during late processing of RRP is beneficial to the transformation of chemical constituents and the improvement of activity,iron ion mainly existed in the form of Fe2+,which is critical to improve RRP quality and enhance its blood-replenishing activity.Section 4.Relationship between fructose alteration and RRP processingSince the hydrolysis of stachyose together with other oligosaccharides could generate fructose in the early processing stage of RRP,while the content of fructose gradually decreased during the late processing stage.Whether this change is related to the change of RRP efficacy?In this study fructose solutions supplemented with Fe2+ and arginine were controlled at pH=3.0 and heated at 95℃ with aerating to simulate the condition of late stage of RRP processing conditions,and those without aerating/Fe2+/arginine were used as controls.It was found that:(1)the effects of supplementing both Fe2+ and arginine in fructose solution on browning,fructose degradation,5-HMF generation and free radical scavenging capacity were better than those of the other treatments;(2)at aerating condition,the above indexes became much more dramatic,and iron ion almost entirely existed in the form of Fe2+;(3)the heated fructose solution supplemented with Fe2+ and inflated with air was analyzed by ion-exchange,molecular sieve and silica gel column chromatography,and the products were found multitudinous,and both neutral and negatively charged fractions have free radical scavenging capacity.The results indicate that oligosaccharides in RR may be the pre-active ingredients of RRP by hydrolysis to generate fructose and various active compounds at an acidic and aerobic condition.In this paper,it was firstly proved that repeatedly "air-exposing" can promote chemical reactions during RRP processing and improve the quality of RRP.This founding lays a foundation for further revealing the scientific connotations of "repeated steaming and air-exposing" in RRP processing.