Study On Edible Carriers For Absorbing Tea Catechin

Tea catechins are a group of abundant polyphenols in tea leaf which has been ascribed with many health benefits and pharmacological functionalities, such as antioxidant and free radical scavenging abilities. However, their application in functional foods and medical area are limited because of their unstability owing to oxidative polymerization, and low bioavailability owing to decomposition in human gastrointestinal tract. Caffeine is a component of tea leaf, which is believed to exert adverse effects on human health as excessively taken. Decaffeination is needed in when tea extract is used in medicine and functional food. Methods for decaffeination and improvement of biovailibility.There has been an increasing interest in the structural design of food-based carriers to encapsulate, protect, and deliver bioactive components. Proteins, phospholipids and polysaccharides are usually used in bio-delivery systems. Byproducts from agriculture and food industry with high contents of proteins, phospholipids and polysaccharides are promising edible carriers. In the present study, we investigated the potentials of rice bran, oat bran and soya milk cake as edible carriers for tea catechins, and the appropriate material was selected for further study, including pretreatment method, optimum parameters of adsorption process, as well as preparation of tablet, and the results were shown as follows:(1) The adsorbabilities of rice bran, oat bran and soya milk cake for catechins were investigated. The adsorption of catechins onto rice bran reached equilibrium within 20 min, which was much less then oat bran (240 min) and soya milk cake (120 min). At the initial tea extract concentration of 0.5 g L-1, the ratio of total catechins to EGCg increased from 2 to 8.5 during the adsorption by rice bran, while the ratio of total catechins to EGCg maintained about 3 during the adsorption by oat bran and soya milk cake. This indicated that rice bran selectively adsorbed EGCg. These three materials had no affinity for caffeine. Hence, rice bran was selected as food carrier for the following study.(2) The pretreatments of rice bran were carried out, including defatting and water washing. The result showed the adsorption capacity of defatted rice bran for total catechins increased by 35.4% while that of water-washed rice bran declined by 48.2%. The selectivity coefficient KTCEGCg of defatted rice bran was 4.29, which was significantly higher than those of originated rice bran (2.81) and water-washed rice bran (0.39) respectively. Thus, defatting pretreatment can further increase the adsorption capacity of rice bran for catechins and the selectivity for EGCg. Based on the enzymolysis reaction and totoal N determination, protein was considered as the major chemical component for carrying rice bran with an assistance of cellulose.(3) The pseudo-first-order model and pseudo-second-order model were used to describe the adsorption kinetics of catechins onto defatted rice bran. Good fitness of the pseudo-second-order model was observed at different temperatures, with a R2 being 0.996 above, indicating that chemisorption was the rate-limiting step for the adsorption of catechins onto rice bran, while diffusion acts partially when temperature was below 25℃. The adsorption systems showed excellent fit to both Langmuir equation and Freundlich equation.(4) Catechin-loaded rice bran (CRB) was used for preparation of tablet. Through screening accessories and optimizing formula, the optimum formula was obtained, viz. CRB:microcrystalline cellulose:sodium cross-linked carboxymethyl cellulose:magnesium stearate=3:2:0.15:0.1. The obtained tablet had a neat and smooth appearance. The stabilities of tea catechins of tea extract, CRB and tablet in the digestive fluids were investigated in a simulated gastrointestinal digestion experiment. The results showed that the percentage of residued catechin were 49.71% for CRB and 39.98% for tablet in intestinal fluids. The residued percentage of EGCg in the intestinal fluids was 59.39% for CRB and 18.84% for tablet in intestinal fluids. These indicated that association with rice bran can significantly increase the stability of catechins in intestinal digestive fluid.