| China Apple production takes the first place in the world,with more than 50% of global output,planting area accounts for about 1/3 of the world’s total.According to Industry Statistics Bureau of Shaanxi Province,Shaanxi province in 2014,apple planting area reached a total area of 10 million 400 thousand mu,total output of 9 million 800 thousand tons,ranking the first place in the world,and the production accounted for China’s total of 1/4,the world’s total of 1/6.Shaanxi is one of the world largest apple planting provinces.At present,apple is the main source of income for local farmers,but apple industry is not optimistic,apple deep processing has become a bottleneck in the development of apple industry,the current consumption of apple is mainly fresh food,the deep processing accounted for about 20% of the total,while the concentrated juice production accounted for the total processing capacity of 90%,the export value of low concentrated juice,has formed a production excess,benefit decrease.As a result,farmers sell fruit difficult and the problems have become increasingly serious,greatly dampened the enthusiasm of farmers.In this study,apple is used as raw material to produce apple vinegar,which can not only increase the added value of agricultural products,but also save a lot of food.The main contents of this paper are as follows:(1)Study on fermentation technology and fermentation kinetics of cider.The main factors influencing in the fermentation of cider were investigated.Response surface methodology was used to optimize the control parameters such as the inoculum size of yeast,the addition of nutrients and the fermentation temperature.The kinetic equations of cell growth,product formation and substrate consumption were established.(2)Study on fermentation technology of apple vinegar.The apple vinegar fermentation process was optimized by response surface method,and the optimum parameters for the fermentation of apple vinegar were determined.Then,the sequential acetic acid fermentation and the synchronous fermentation process were compared.The Logistic,Leudeking-Piret model was used as a kinetics mode to discribe the cell growth,product synthesis and substrate consumption in fermentation of cider and apple vinegar.(3)Separation of lactic acid in apple vinegar.The content of lactic acid is one of the strict control indexes in the production of apple vinegar beverage.In the first,the separation of lactic acid from apple vinegar was studied.Secondly,the clarification technology of apple vinegar was carried out,and the better clarifying agent and its compounding scheme were screened out.Finally,the clarification process was optimized by response surface.The obtained conclusions are as follows:(1)The optimal nutrition for cider fermentation is diammonium phosphate.The optimal conditions of cider fermentations are the temperature of 21℃,nutrient content of 0.4g/L,inoculum size of 0.07%.Under these conditions the alcohol degree of apple wine was 8.01%(v/v),rich in bright and apple flavor,excellent in quality.(2)The fermentation of cider and apple vinegar were in accordance with Logistic and Leudeking-Piret model.In this paper,the model of cell growth,product formation and substrate consumption was established,variance analysis results show that the proposed model significantly.It can predict the dynamic changes of apple vinegar fermentation process well.In the fermentation process of cider,the fitness between the model predicted values and measured data of yeast biomass,alcohol content and sugar content reduction were 0.99724,0.98221,and 0.99076,respectively,average fitting error was 1.89%,5.04% and 9.57%,respectively,being higher fitting degree.In the process of apple vinegar fermentation,the fitness between the model predicted values and the experimental data of acetic acid bacteria biomass,concentration of acetic acid and alcohol reduction were 0.99449,0.96848,and 0.97393,respectively.The average fitting error was 1.78%,7.78% and 5.79%,respectively.According to the model of yeast growth and alcohol production,it is concluded that the production of alcohol and yeast growth are not completely synchronous,but have a certain lag.(3)The most suitable nutrient for apple vinegar fermentation was corn pulp.The optimal fermentation conditions of apple vinegar are the fermentation temperature of 31℃,the rotate speed of 204r/min,nutrient content of 11.12mL/L,the total acid content in apple vinegar under this condition reached 4.45g/100 mL,with a bright orange,sour soft,rich in apple flavor,and high quality.Based on the vinegar technology of alcohol and vinegar fermentation separatively,the effects of acetic acid bacteria inoculation time on the vinegar content were investigated and the results show that: inoculating acetic acid bacteria in the middle stage of cider fermentation can shorten the brewing period of apple vinegar,at the same time the acid production can be improved.(4)The lactic acid content of the original apple vinegar was more than 0.11%,which was more than the requirement of apple vinegar for the content of lactic acid in apple vinegar by 0.05%.So,lactic acid in apple vinegar was separated by D315,a weakly basic anion exchange resin.According to the different elution peak order,lactic acid and acetic acid can achieve a good separation,and the separated vigegar can reach the national standard.The results show that the temperature has little effect on the adsorption of lactic acid,and the adsorption equilibrium time is 340 minutes.(5)By means of single factor test,the effects of six different clarificants on apple vinegar clarification were investigated.The results show that the clarification good effect order is chitosan> PVPP> bentonite> diatomite> pectinase>gelatin.Considering the difference between PVPP and bentonite is not obvious,and the cost of PVPP is high,the chitosan and bentonite are selected to get a mix clarifier in order to improve the clarification effect.The response surface methodology was used to optimize the conditions for the clarification of apple vinegar.The light transmittance of apple vinegar could reach 97.8%,when the clarrifing conditions were the mixture ratio of chitosan and bentonite of 0.07:0.18,the temperature of 28℃ and clarification time of 24 h. |
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