Biological Utilization Of Apple Pomace And Research On The Optimization Of Fermentation Conditions

With the increasing development and utilization on the waste of industry and agriculture all around the world, the research on deep processing of agricultural products has been carried out gradually in our country. For the past few years, people have attached more and more importance to the research work producing high value-added goods, especially from some agricultural byproducts with large output and low cost . China is the largest producer of apple. However, the waste from processing apple has not been used effectively all the time. Aiming at this problem, in this thesis, the way of comprehensive utilization of the apple pomace has been explored and the process condition laying a foundation for the industry-scale production has also been optimized.PartⅠ: The optimal pretreatment condition of apple pomace is obtained: apple pomace is treated by the following three reactions according to priority: cooking, pectinase enzymolysis and cellulase enzymolysis. The single factor experiment and orthogonal test are used to determin the pretreatment method. The result shows as follows:(1) The content of reducing sugar is increased remarkably after heat treatment for 30 mins under the normal pressure. (2) The best pectinase enzemolysis condition is as follows: volume of addition of pectinase is 0.2% (v/v), pH is 3.6, reaction temperature is 45℃, time of enzymolysis is 2.5 h.(3) The optimal cellulose amount is 0.6%(v/v).When we used the three steps above to treat the apple pomace, the level of reducing sugar could reach 53.0%. Meanwhile, pectinase and cellulose used in the above experiment are cheap and few consumed. Therefore, the pretreatment conditions can be applied to industrial production.PartⅡ: Using single factor experiment and orthogonal test, the optimal fermentation conditions of apple pomace for producing alcohol is obtained:(1) The medium is supplemented with 0.15% KH₂PO₄ and 0.06% MgSO₄ the best nitrogen source is NaNO₃ or carbamide and the optimal additive amount of NaNO₃ is 0.3%, the optimal pH of the medium is 4.5. The medium is demanded to be sterilized before being used;(2)The optimal inoculated quantity of yeast is 7%(v/v);(3)The fermentation temperature should be controlled between 34℃to 36℃;(4) Aerobic fermentation can increase the output of alcohol. Under these conditions, 344.5ml alcohol can be obtained from 1.0 Kg apple pomace. It can be seen that it is a promising method to produce fuel alcohol by apple pomace.PartⅢ: The optimal fermentation conditions of apple pomace for producing citric acid is obtained. Compared with spore suspension, the liquid seed culture medium has high ability to produce citric acid. The optimal inoculated quantity of the liquid seed culture medium is 1%(V/V), the optimal fermentation pH of Aspergillus niger is 5.0, the best fermentation temperature is 34℃and the optimal fermentation period is four days. Methanol can promote the production of citric acid, and the best dosage is 2% (V/V). Under these conditions, 18.66 g citric acid can be obtained from 1.0 Kg dry residue.PartⅣ: Utilization of fermentation leavings. After ethanol fermentation and citric acid fermentation, there are a lot of yeast and Aspergillus niger in the medium. Then, the medium is dried and crushed by 40 mesh sieve. After being tested, the crude protein content increases from 11.2% to 29.30%, crude fat content increases from 6.8% to 10.33%, ash increases from 2.3% to 5.4%, calcium increases from 0.06% to 0.32% and crude fiber content decreases from 16.8% to 2.6%.