In order to developing new colorful potato products and promoting the development of potato processing industry,Yellow Rose,Red Rose and Purple Rose potato were used as test materials to optimize the liquefaction and saccharification process of potato pulp.Then the effects of potato varieties and three fermentation methods(Mode 1 was inoculating yeast first,then inoculating Lactobacillus plantarum after fermenting for 18 h.Mode 2 was first inoculating Lactobacillus plantarum and inoculating yeast after fermenting for 24 h.Mode 3was inoculating yeast and Lactobacillus plantarum simultaneously.)on physical and chemical properties,active ingredient content,in vitro antioxidant capacity,organic acid content and sensory index of potato ferment were studied.And the metabolite changes during the fermentation process of Purple Rose potato ferment were explored.The suitable conditions for liquefaction and saccharification of potato pulp before fermentation,and the suitable fermentation varieties and fermentation methods for potato ferment were obtained.The law of material transformation during the fermentation of potato ferment was also found.The results were as follows:(1)The optimal liquefaction conditions of Purple Rose potato pulp were as follows:adding 0.3%(m/m)ofα-amylase,liquefying at temperature 55℃for 60 min.The saccharification conditions of potato pulp which had been liquefied was been optimized.The optimal saccharification conditions were as follows:adding 0.2%(m/m)glucoamylase,saccharifying at temperature 60℃for 2 h when p H value of potato pulp was 5.5.Under this condition,the content of reducing sugar in potato pulp was the highest,which was 90.16mg/m L.The optimized liquefaction and saccharification process can significantly improve the reducing sugar content in potato pulp,which can provide the enough and favorable nutritional conditions for subsequent fermentation of potato ferment.(2)The fermentation methods had a significant effect on the p H value,alcohol,titratable acid and reducing sugar content of potato ferment,and the potato variety can affect the physicochemical quality of the ferment.Among the nine kinds of potato ferment,the total phenol content of the Purple Rose potato ferment obtained by fermentation mode 1 was the highest.The SOD activity of the Red Rose potato ferment obtained by fermentation mode 2was the highest.The Purple Rose potato ferment’s anthocyanins content obtained by fermentation mode 3 was the highest.The nine kinds of potato ferment had a certain in vitro antioxidant capacity.The differences of ABTS~+·scavenging capacity and reducing power between nine kinds of ferment were significant(P<0.05).Under the same fermentation mode,the ABTS~+·,·OH scavenging capacity and reducing power of three varieties of potato ferment from strong to weak were:Purple Rose>Red Rose>Yellow Rose.The DPPH·scavenging capacity of the Red Rose potato ferment fermented by fermentation mode 3 was significantly lower than that of the other eight kinds of potato ferment.The order of three organic acids with higher contents in the nine kinds of potato ferment was:lactic acid>citric acid>succinic acid,when the content of oxalic acid was the lowest.The synthetic sensory evaluation of Purple Rose potato ferment was the highest.In summary,potato varieties and fermentation methods have a significant impact on the quality of ferment,and the Purple Rose potato ferment has the best overall quality.(3)During the fermentation of Purple Rose potato ferment,the content of soluble solids showed a downward trend,when p H value,anthocyanins and total phenol content decreased first then increased slightly.The alcohol content,titratable acid content and SOD activity increased rapidly and then stabilized during the fermentation.Tartaric acid,lactic acid,acetic acid,citric acid,and succinic acid content all showed a significant increase trend(P<0.05),and the contents of oxalic acid and malic acid decreased overall.The content of lactic acid changed the most.From the beginning of fermentation to the end of fermentation,the content of lactic acid increased from 0.79 mg/m L to 7.70 mg/m L.Its content increased by nine times.The optimum process for potato ferment in this study was:After ripening and beating of Purple Rose potato,0.3%(m/m)α-amylase was added to the resulting slurry,liquefying at 55℃for 60 min.Then the potato pulp’s p H was adjusted with citric acid to 5.5,adding 0.2%(m/m)glucoamylase,saccharifying at 60℃for 2 h.After inactivating enzyme and sterilization,the potato pulp,which had been liquefied and saccharified,inoculated yeast,fermenting at 25℃for 18 h,then inoculated Lactobacillus plantarum,fermenting at 36℃for 24 h,then fermenting at 30℃for 30 h,post-fermenting at 4℃for 24 h.Under this condition,the high quality potato ferment can be obtained. |