Study On The Production And Stability Improvement Of High Cis-isomers Ratio Lycopene

Lycopene is a well-known bioactive ingredient with many functions. More than90%naturally existing lycopene is in All-E form, but in the human body Z-isomers take more than80percent. Compared with All-E-lycopene, Z-isomers have relatively higher bioactivity andbioavailability, but tending to degradation and conversion to E-isomer.Inorder to prepare high cis-isomer content lycopene, the author tried to isomerizelycopene in organic solvents by conventional heating and microwave heating, combined witha separation of All-E lycopene from the mixture by low-temperature crystallization to increasethe ratio of Z-isomers.The results showed that the ratio of Z-lycopene could reach43%-45%, the yield ofisomerization product was up to85%-90%after refluxing All-E-lycopene in ethyl acetate for10-12h. The time achieved equilibrium by microwave heating and conventional heating were4h and10h in ethyl acetate.6.2-folds and3.3-folds increase in9-Z-lycopene,4.4-folds and3.7-folds increase in All-Z-lycopene were expected at equilibrium in heating process bymicrowave and conventional respectively. The time to reach equilibrium in ethyl lactate was120min,25min,15min and5min at the temperature of90oC,110oC,130oC and150oCrespectively. By crystallization technology (-20oC) for24hours and suitable separation，theratio of Z-isomers increased to78%-85%. Microwave heating in ethyl acetate and heating athigh temperature in ethyl lactate improved the conversion rate and content of Z-isomers,9-Zespecially. The developed technology works more efficiently than existing methods oflycopene isomerization and is conducive to promoting the product with higher ratio ofZ-lycopene to be widely used in the functional food industry.To improve the stability of high ratio of Z-isomers lycopene, the author studied the typesand the ratio of the isomers, additive. The results showed retro-isomerization was observed inlycopene isomers with13-Z-lycopene being the least stable. When isomerization productplaced three weeks under37oC with TBHQ, the retention rate of Z-isomers and product were30%，44.7%; and product without antioxidant degraded almost completely. The oil layermakes the products yield increased from37.7%to52%-56%, and the Z-isomers ratio from41.6%to65%-70%. The study results indicated that antioxidants and oil layer can reducehigh ratio of Z-isomers lycopene oxidation degradation, and the oil layer can suppressZ-isomers conversion to E-isomer.To improve the stability of high ratio of Z-isomers lycopene, the environment system wasstudied. When isomerization product placed three weeks under37oC, the retention rate ofproduct by nitrogen, carbon dioxide, air-dried and filled were39.4%,38.6%,27.8%and theratio of Z-isomer were64.12%,58.1%,40.27%respectively. The degradation rate constants(k) of the Z-isomers in dark and daylight at room temperature for50days were0.0266d-1,0.0321d-1and the ratio of Z-isomer were55.5%,46.2%; the k of isomerization products were0.0188d-1and0.0212d-1respectively. The k of isomerization products were0.0011d-1,0.0049d-1,0.0075d-1,0.0245d-1and the ratios of Z-isomers were79.95%,72.99%,70.26%,64.04%at the temperature of-18oC,4oC,25oC and37oC for3months respectively; The activation energies of9-Z,13-Z, All-E, All-Z isomers and product were46.42kJ/mol,29.19kJ/mol,56.94kJ/mol,32.45kJ/mol and33.76kJ/mol during storage. The study indicated that driedand filled by nitrogen, storage in dark and at low temperature can reduce oxidationdegradation of the high ratio of Z-lycopene isomers, suppress Z-isomers conversion toE-isomer, thereby improving the stability of product.