| Ginkgo is a precious relict plant in China,which has the value of development and application in many aspects.Ginkgo is the seed nucleus of Ginkgo biloba,which is a dual-purpose food for medicine and food.it is rich in nutrients such as starch and protein,as well as effective bioactive components such as flavonoids and terpene lactones,which has great nutrition and health care value.Edible plant enzyme is a fermented product with a variety of active enzymes and bioactive substances obtained by microbial fermentation of plants,which has a certain health care function.Because the shelf life of fresh ginkgo is short,and there is still some waste of ginkgo resources in our country,making ginkgo into enzyme product by microbial fermentation can not only improve the utilization rate of ginkgo,but also produce new bioactive components to improve the health effect of ginkgo.In this paper,Ginkgo biloba was selected as the fermentation raw material,and Angel brand fruit and vegetable enzyme starter(Lactobacillus plantarum N13,Lactobacillus bulgaricus,Streptococcus mesenteric subspecies,Streptococcus thermophilus)was used as fermentation bacteria.through the determination of the physicochemical indexes and sensory experiments of ginkgo after fermentation,the best pretreatment method of ginkgo was selected.On this basis,the fermentation process of ginkgo enzyme was optimized by single factor experiment and response surface experiment Finally,a variety of bioactive components of ginkgo enzyme under the optimal fermentation process were determined in order to explore the development of ginkgo biloba enzyme.The main results are as follows:(1)Fresh ginkgo was selected as the best pretreatment method.Three pretreatment methods of fresh ginkgo,boiling water for 5 minutes and boiling water for 10 minutes were set up.The pretreated ginkgo was fermented under the same fermentation conditions,and the activities of total flavonoids,total phenols and amylase were used as screening indexes,and then sensory evaluation was carried out.The experimental results showed that the screening index and sensory evaluation of fresh ginkgo were better than those of the other two pretreatment methods.Therefore,fresh ginkgo was selected as the best pretreatment method.(2)Through single factor experiment and response surface experiment,the optimum fermentation conditions of ginkgo enzyme were as follows:fermentation time 74.45h,sugar 20.41%,inoculation 2.09%.Three factors affecting fermentation time,amount of sugar and amount of inoculation were set,and each factor was set at three levels.The optimal fermentation conditions were selected by determining the screening index and sensory evaluation after fermentation.The results of single factor experiments show that the optimal fermentation time is 72h,the optimal amount of sugar is 20%,and the optimal amount of inoculation is 2%.Furthermore,the response surface experiment results show that,in order to maximize the sensory evaluation score,the optimal fermentation conditions are as follows:fermentation time 74.45h,sugar 20.41%,,inoculation 2.09%.Under these conditions,the highest sensory score predicted by the model is 86.157.The influence degree of three factors on the comprehensive quality of ginkgo enzyme is C>A>B,that is,inoculation amount>fermentation time>sugar content.(3)On the basis of the above experiments,the changes of antioxidant activity and various enzyme activities of ginkgo enzymes before and after fermentation under the optimal fermentation conditions were studied.The results showed that under the optimal fermentation conditions,the antioxidant activity and enzyme activity of ginkgo enzyme were significantly improved after fermentation.The scavenging rate of DPPH was 81%±0.01,the scavenging rate of hydroxyl radical was 81%± 0.05,and the content of ascorbic acid was 7.92±0.21 ug/L,which increased by 19%,3.8%and 32%respectively compared with that before fermentation.Protease activity,SOD enzyme activity and amylase activity reached 2.50±0.08U/mL,58.53±0.63U/mL and 24.51±1.6 U/dL after fermentation,which were 15%,13%and 18%higher than those before fermentation,respectively.(4)The evaluation index of ginkgo enzyme was determined to evaluate whether the ginkgo enzyme conforms to the national quality standard under the optimal fermentation conditions.The pH value of ginkgo enzyme is 3,7±0.21 and the alcohol content is 0%,which meets the general physical and chemical characteristics of edible plant enzymes in the national standard.The total acid,crude polysaccharide and total phenol of ginkgo enzyme were determined.The results showed that the total acid,crude polysaccharide and total phenol content of ginkgo enzyme were 1.7±0.43g/100g,0.19±0.03g/100g and 20.71±0.66 mg/ml,respectively,which met three characteristic physical and chemical indexes.Ginkgo enzyme taste mellow and pleasant moderate sweet and sour,silky texture without a sense of particles,with a hint of ginkgo aroma,in line with the sensory requirements of edible plant enzymes.Therefore,under the optimal fermentation conditions,the ginkgo enzyme in this paper accords with the national quality standard of edible plant enzyme,and the preliminary development of ginkgo enzyme is successful.(4)The biological activities of five kinds of naturally fermented ginkgo biloba enzymes were analyzed to explore the antioxidant activity and.enzyme activity of naturally fermented ginkgo biloba enzymes.The results showed that the hydroxyl radical scavenging rate,DPPH scavenging rate and protease activity of ginkgo biloba enzymes added in the formula were relatively high,suggesting that ginkgo biloba leaves or ginkgo biloba fruits can be used with grapes to develop ginkgo enzyme products.The SOD enzyme activities of five kinds of ginkgo biloba enzymes were about the same,but the amylase activity of ginkgo biloba enzyme added ginkgo biloba was higher than that of ginkgo biloba enzyme and ginkgo pericarp enzyme amylase.In summary,the preparation process of ginkgo enzyme was determined as follows:fresh ginkgo kernel 40g,fermentation time 74.45h,inoculum 2.09%,PH 6.5,fermentation temperature 34℃.The supernatant was centrifuged and pasteurized(the supernatant was heated to 65℃ kept at this temperature for 30min,and finally preserved at about 4℃.In this paper,ginkgo and compound lactic acid bacteria were used for the first time to select the best pretreatment method of ginkgo,optimize the technological conditions of ginkgo enzyme fermentation,and determine the antioxidant activity,enzyme activity and sensory index of ginkgo enzyme respectively.A ginkgo enzyme was developed successfully;which provides some theoretical basis and technical guidance for the development and utilization of ginkgo biloba resources. |
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