Changes Of Chlorogenic Acids In The Eucommia-based Vinegar Products Due To Different Processing

Eucommia ulmoides is a well-documented traditional Chinese herb that is often used as functional component in food and medicine fields. Vinegar is a liquid substance consisting mainly of acetic acid and water. Eucommia-based vinegar products are either made from fermented eucommia leaves plus wheat bran or blended via eucommia-leaf hydrolysate and commercial vinegar. The objectives of this study are to:(1) establish a HPLC method for the determination of chlorogenic acids contained in eucommia-leaf vinegar products;(2)assay the levels of chlorogenic acid released form the enzymatically hydrolyzed eucommia leaves; and (3)deal with the changes of chlorogenic acid in various technology steps due to different processing. The following are main results.1. A phase C18HPLC method was set up for detecting chlorogenic acid. HPLC conditions were Diamonsil C18column (250mmx4.6mm,5u m) with the mobile phase of acetonitrile:water:acetic acid (12:88:1). The detection wavelength was325nm with column temperature at30°C plus a flow rate of1.OmL/min. The retention time of reference substance proved that our method was accurate and time-saving, with the average recoveries of99.45%.2. Cellulose was chosen to hydrolyze E. ulmoides leaves collected from Lvyang area of Shaanxi Province of China, to release chlorogenic acid from the herb. It was found that time, temperature, enzyme concentration, and ratio of eucommia-leaf to water were main factors influencing the release of chlorogenic acid during the progress of enzymatic hydrolysis. The optimal conditions for the most formation of chlorogenic acid were enzymatically hydrolyzed temperature at45°C,2h-incubation time, and0.8%enzyme concentration together with a1:10ratio of liquid to material. Under the optimal parameters, about3.34mg/mL chlorogenic acid was produced from the hydrolyzed euconmia leaves.3. Two types of eucommia-based vinegar products were manufactured with the hydrolyzed eucommia leaves. The first was the blending product, i.e., the mixture of eucommia-leaf hydrolyzate with commercial vinegar. The blended eucommia-vinegar had two key stages of processing including hydrolysis and blending procedures. The second was fermented eucommia vinegar which consisted of four key stages of processing, i.e., hydrolysis, saccharification and sterilization, alcohol formation and acetic acid fermentation. HPLC was used to detect the levels of chlorogenic acid from various key steps in the two vinegar products. In the blended eucommia vinegar, the content of chlorogenic acid was3.23mg/mL for hydrolysis stage and0.30mg/mL for blending step, respectively. The rapid decrease in chlorogenic acid mainly resulted from the blending process during the manufacture of eucommia vinegar with water. In the fermented vinegar, the level of chlorogenic acid was3.23mg/mL for the step of enzymatically hydrolysis,1.93mg/mL for the step of saccharification and sterilization,1.78mg/mL for the step of alcohol fermentation, and1.26mg/mL for the step of acetic acid fermentation, respectively. It was seen that chlorogenic acid concentration declined gradually. The lowed chlorogenic acid occurred mainly at the step of saccharification and sterilization, but the exact reason was not clear. Perhaps high temperature during saccharification and sterilization produced a damage to the maintenance of chlorogenic acid. Thus, it are concluded that chlorogenic acid indicate the process steps of eucommia-based vinegar very well, and should be promising for the evaluation of the final quality of different vinegar products containing E. ulmoides as active phytochemicals.