Study On E/Z Isomerization Of Lycopene Catalyzed By Common Metal Salts And Stability Of Lycopene Products

Due to its special multi-conjugated double bond structure,lycopene has various physiological functions such as reducing the risk of chronic diseases like cancer and cardiovascular disease,and improving the immunity,and on the other hand,it can form a variety of isomers.More than 90%of lycopene is（all-E）-configuration exist in nature,and its bioavailability,antioxidant activity and other physiological activities are significantly lower than those of Z-lycopene.Therefore,seeking an effective method to promote the conversion of（all-E）-lycopene into Z-isomers has become the focus of research in the field of efficient utilization of lycopene.In this paper,we attempted to construct a catalytic system using natural lycopene extract as raw material and use metal salts as catalysts to realize the E/Z configuration conversion of（all-E）-lycopene.Then,the stability of high Z-lycopene products obtained by metal salts and other isomerous methods will be studied,and the effectiveness of the metal salt-catalyzed process in other carotenoids E/Z isomerization reactions will be verified.The main research results of the paper are as follows:（1）Firstly,the optimal metal salts catalyzed lycopene system was explored.The effects of eleven types of metal salts,different forms of metal salts,the volume ratio of metal salt solvent to lycopene solvent,and lycopene solvent on the E/Z configuration conversion of lycopene were studied.The results showed that five metal salts,namely Al Cl₃,Al₂（SO₄）₃,Fe Cl₃,Fe₂（SO₄）₃,Cu SO₄,could significantly promote the Z-isomerization of lycopene（p<0.05）.When the volume ratio of metal salt solution to lycopene acetone solution is 1:40,a high proportion of total cis-lycopene can be obtained.（2）Secondly,the best lycopene E/Z isomerization catalyst was obtained by studying by studying the effects of metal salt concentration,heating time and heating temperature on the E/Z isomerization of lycopene.When the concentration of lycopene was 10 mmol/L,the total content of lycopene Z-isomers was in the order of Fe Cl₃（70.8%）>Fe₂（SO₄）₃（54.0%）>Al Cl₃（50.2%）>Cu SO₄（40.0%）>Al₂（SO₄）₃（29.3%）,and when the concentration of lycopene was greater than 10 mmol/L,the degradation of lycopene promoted by ferric chloride and ferric sulfate was serious,but the retention rate of lycopene by Al Cl₃still remained above 70%.Then,the kinetic tools showed that equilibrium values of total Z-lycopene and 5-Z-lycopene reached to 81.1%and 33.0%in the presence of Al Cl₃,respectively,higher than other metal salts.At the same time,The activation energy of the degradation of lycopene was 23.9 k J/mol in the presence of Al Cl₃,it is more conducive to the retention of lycopene compared with Fe Cl₃and Fe₂（SO₄）₃.Therefore,considering the comprehensive higher total Z-lycopene content,higher（5Z）-lycopene content and retention rate,Al Cl₃is an ideal lycopene catalyst.The difference in solubility of lycopene and Al Cl₃in different solutions was used to separate lycopene and Al Cl₃,and the result showed no significant difference between the separation group and the control group（p>0.05）,which met the national standards,and n-hexane and acetone residues are also met the production standards.It is confirmed that the preparation of high Z-lycopene by Al Cl₃catalytic process is feasible and safe.（3）Then,the advantages and disadvantages and the stability of high Z-lycopene product obtained by the metal salts,polysulfide and thermal method were studied and compared.The results showed that the total Z-ycopene is 76.3%catalyzed by Al Cl₃,higher than 55.1%and25.7%of total Z-ycopene catalyzed by dimethyl trisulfide and thermal isomerization.After being stored in acetone for 25 days,the lycopene produced produced by Al Cl₃still had a retention rate of 58.1%,while the lycopene prepared by the other two methods was almost completely degraded.The storage kinetics in oil showed that the lycopene isomers catalyzed by Al Cl₃had the best product stability,of which（5Z）-lycopene had the best stability in all studied isomers.（4）Finally,the effectiveness of the established Al Cl₃catalytic process in other carotenoid E/Z isomerization reactions was discussed.The results showed that Al Cl₃can not only catalyze lycopene,but also catalyzeβ-carotene,astaxanthin,and lutein.Catalytic isomerization by Al Cl₃can not only improve the antioxidant activity of carotenoids but also improve their bioavailability.This shows that the production of Z-carotenoids by Al Cl₃has great prospects in the health care products industry.