Extraction Of Gossypol And Its Chemical Stability

Free gossypol extraction was studied by single-phase solvent and double solvent and the extraction process was optimized. The antioxidant ability of gossypol was assessed with the Rancimat test and oven experiments. Thermal stability of gossypol and impact of peroxide value and acid value of oils on gossypol losses were described, and the related mechanisms were deduced. The interaction of gossypol and its oxide with bovine serum albumin were investigated.The process of extracting free gossypol from cottonseed kernel by solvent extraction method was studied. On the basis of single-factor experiments, an orthogonal array design was employed for optimization of extracting free gossypol. The results showed that the order of four factors effect on extraction was as follows: extraction times, time, solid-liquid ratio, temperature. The extraction yield of free gossypol reached its maximum 89.58±0.72% under the following conditions: temperature 40 °C, extraction time 50 min, solid-liquid ratio 1:20 g/mL, exacting 3 times and stirring rate 850 r/min. The residue content of free gossypol in cottonseed meal was only 400 mg/kg. On the basis of single factor experiment, the results of extraction conditions using method were optimized by response surface methodology. The results showed that the factors affected the extraction rate of free gossypol significantly, the optimal extraction conditions were obtained as follows: solid-liquid ratio 1:24 g/mL, extraction temperature 35 °C, extraction time 42 min, stirring rate 2600 r/min, extraction times 2, Under the optimal conditions, the extraction rate of free gossypol reached 68.90±0.81%, and the purity was 81.90±0.85%. At this point, the residue of free gossypol in cotton meal was 839.7 mg/kg. The two methods both could reduce the residue of gossypol in cottonseed meal in the range of the feed hygiene standards(GB 13078-2001).The antioxidant ability of gossypol was assessed with the Rancimat test and oven experiments. Gossypol had antioxidant ability and could protect the soybean oil oxidizing. The antioxidant ability had positive correlation with amount of gossypol and negative correlation with temperature. Results of analysis of dynamics and thermodynamics model showed that the antioxidant effect was significantly associated with the amount of gossypol. More gossypol meant higher activation energies and the oils were difficult to oxidize. According to transition state theory, oils oxidation reaction belongs to endothermic reaction. More gossypol meant lower entropy and the oxidation of oil was difficult.The stability of gossypol was investigated using heat treatment method. The results showed that gossypol was unstable and easy to conversion under the action of solvents and high temperature. The stability of gossypol was different in different solvents and its stability was in turn: acetone > acetonitrile > chloroform > ethano > methanol. With the increasing of temperature and heating time, gossypol losses increased significantly in the oil system. In SBO samples under heating conditions, gossypol was involatile and the losses of gossypol were mainly attributable transformation. The quality of SBO could influence the losses of gossypol. Free fatty acids(FFAs) could promote the transformation of gossypol. Peroxide value(PV) could also lead to the losses of gossypol which might be duo to transformation or oxidation of gossypol under the action of hydroperoxides.The interaction of Gossypol and its oxide with bovine serum albumin was investigated by fluorescence spectroscopy and ultraviolet-visible spectroscopy. Results indicated that the quenching mechanism of BSA by gossypol and its oxide was a dynamic-static procedure. Various binding parameters were evaluated. There was one binding site between Gossypol/Gossypol oxide and BSA. The negative value of ΔH, positive value of ΔS and the negative value of ΔG indicated that hydrophobic and hydrogen bonding interactions play major roles in the binding of Gossypol and its oxide with BSA. Based on Forster’s theory of non-radiation energy transfer, the binding distance(r) between the donor(BSA) and acceptor(gossypol and its oxide) was 2.94 nm and 3.12 nm, respectively, and they could interact with BSA the energy transfer way. The results of UV-vis, synchronous fluorescence and three-dimensional fluorescence spectrum showed that the binding of Gossypol/Gossypol oxide to BSA induced conformational changes in BSA.