Depolymerization Of Proanthocyanidins From Chinese Quinces And Inhibition Of Heterocyclic Amines In Fried Foods By Their Depolymerization Products

High-protein foods are indispensable in our daily diet,and the high temperature frying of these foods will generate harmful substances such as heterocyclic amines（HCAs）,which will increase the risk of cancer in humans if consumed in excess.There is an inseparable link between fried foods,HCAs and human health,and how to effectively suppress the production of HCAs in food processing is of great significance.The addition of antioxidants is a commonly used mean of heterocyclic amine inhibition.With the concern for food safety and human health,natural antioxidants have become the first choice for food applications to inhibit the production of HCAs.Currently,a large number of polyphenolic plant extracts have been proven to be effective in inhibiting the production of HCAs.It has been found that Chinese quince（Chaenomeles sinensis）is rich in polyphenols,with the highest proportion of proanthocyanidins.Proanthocyanidins have strong antioxidant activity,and the application of Chinese quince proanthocyanidins as a new natural antioxidant for the inhibition of heterocyclic amines in fried foods is an valid way to increase the added value of Chinese quince.This study intends to extract the oligomeric proanthocyanidins from Chinese quince by ball mill-assisted enzymatic digestion to improve the separation efficiency of proanthocyanidins,and then degrade the proanthocyanidins by ultrasonication combined with acid-catalyzed degradation,optimize the degradation conditions to improve the degradation rate and provide a theoretical basis for the preparation of oligomeric proanthocyanidins from Chinese quince with high purity and low cost.The oligomeric proanthocyanidins were then applied to fried foods,frying oils and simulated systems to analyze their conformational and quantitative relationships as antioxidants to inhibit HCAs production,providing new ideas for obtaining highly effective HCAs inhibitors.The main research contents and conclusions are as follows:（1）The extracts of proanthocyanidins from Chinese quince were obtained by ball mill-assisted enzymatic pretreatment,and their contents were determined and analyzed for their structure and biological activities.The results showed that the highest yield of 7.72%was obtained by the ball mill-assisted complex enzymatic（Combination enzyme of cellulase,xylanase and pectinase）pretreatment method（BEP-4）,which was much higher than that of the conventional organic solvent method（3.02%）.BEP-4 had the highest total phenolic and total proanthocyanidin contents of 750.98±6.95 and 948.72±3.50 mg/g DW extracts,respectively.The proanthocyanidins extracted from different pretreatments were structurally similar and consisted mainly of B-type procyanidins（PC）structure.BEP-4 had a higher percentage of PC structure（98.35%）and flavan-3-ol content（87.88%）.BEP-4 had the highest antioxidant activity with IC₅₀values for DPPH,ABTS,OH radical scavenging capacity andα-amylase inhibitory capacity of 131.45±0.97,22.66±0.32,134.05±0.71,and 182.07±0.28μg/m L.The ball-mill-assisted enzymatic extraction method improved the efficiency of proanthocyanidin isolation and the purity of the extracts with higher antioxidant activity.（2）The degradation of Chinese quince proanthocyanidins was performed by ultrasonication combined with acid catalysis,followed by determination of the degree of polymerization of different depolymerization products,and then their structural characterization,content determination and bioactivity analysis.The results showed that the average polymerization degree decreased from 17.93 to 4.59 under the conditions of p H=1.0,ultrasonic power 360 W,reaction time 60 min and reaction temperature 45℃,and the degradation rate reached 77.40%,which was 1.35 times that of the conventional acid digestion method（57.50%）and 1.95 times that of the ultrasonic degradation method（39.71%）.The degradation product UAPA-360 had the lowest degree of polymerization（4.59）,the highest purity（937.13±6.16 mg/g DW extract）and the strongest antioxidant activity,and its antioxidant capacity was increased by 1.46～10.26 times.The characteristic peaks of proanthocyanidins before and after depolymerization were similar,and the degradation did not destroy their basic structures.That is,sonication combined with acid-catalyzed degradation yielded oligomeric proanthocyanidins with lower degree of polymerization and stronger antioxidant activity.（3）The thermal stability of the oligomeric proanthocyanidins UAPA and the polymeric proanthocyanidins PPA from Chinese quince in the simulated frying system was investigated,and their contents were measured after the reaction to calculate the residual rate and analyze the changes of their antioxidant activities and structures.The results showed that the residual rate of UAPA was higher than that of PPA,which was more than 70%;PPA and UAPA still had strong antioxidant activity in the simulated system,and the oligomer was higher than the polymer;after the high temperature reaction,the core structures of PPA and UAPA were not changed;the addition of both UAPA and PPA to the HCAs simulated system could,to some extent,inhibit the formation of Ph IP,Norharman,and Harman formation was inhibited,and the inhibitory effect of UAPA was more significant（p<0.05）.（4）The inhibitory effects of the oligomeric proanthocyanidins UAPA and the polymeric proanthocyanidins PPA from Chinese quince were investigated on the inhibition of HCAs in fried chicken and tofu.The basic physicochemical parameters of fried foods were also measured.The results showed that the inhibition of HCAs by proanthocyanidins was dose-dependent,and the inhibition ability of UAPA was higher than that of PPA（p<0.05）,and the inhibition of HCAs in chicken and tofu was the highest at 57.84%and 54.17%;Proanthocyanidins can slow down food lipid oxidation,and reduce the consumption of precursors such as glucose,creatine,and amino acids,thereby inhibiting the production of heterocyclic amines.The total HCAs production in chicken epidermis（14.33 ng/g）was higher than that in tofu epidermis HCAs production（6.11 ng/g）;the inhibitory effect of proanthocyanidins on both tofu and chicken epidermis HCAs was higher than that internally,and the inhibition of epidermis HCAs by oligomeric proanthocyanidins could be as high as70.31%.（5）The effect of oligomeric proanthocyanidin modifiers on the formation of HCAs in fried foods was investigated.The proanthocyanidins were first modified by oxyacetylation with stearic acid chloride,then qualitative and quantitative analyses and structural characterization of the modifiers were performed,and then they were added into frying oil and conducted a 14 h continuous frying experiment to analyze their effects on HCAs generation and oil quality.The results showed that the yield of the modifier L-UAPA was46.44%,and the fat solubility reached 87.13%much higher than that of UAPA（39.80%）.The formation of HCAs was significantly and positively correlated with the quality oxidation index of frying oil（p<0.05）.The addition of L-UAPA helped to delay the oxidative rancidity of frying oil,thus also reducing the formation of HCAs,with the inhibition rates of 3.85%and 15.89%for total heterocyclic amines in the oil used for frying tofu and chicken,respectively;and 5.73%and 21.62%for total HCAs in frying tofu and chicken food,respectively.In conclusion,L-UAPA can inhibit the formation of HCAs in fried foods and frying oils,which has positive guidance significance for improving the safety of fried foods and promoting the comprehensive utilization of proanthocyanidins as antioxidants.