Application Of Amylase-producing Lactic Acid Bacteria In Potato Powder Fermentation

In order to prevent the crisis of food shortage,the potato staple food strategy has been put forward by Ministry of Agriculture.But there are some problems when potato flour added to staple foods,such as the texture will be too sticky,too hard and less pliable,because of the lacking of protein and the structural specificity of its starch.Previous studies have shown that lactic acid bacteria(LAB)fermentation can significantly improve the organoleptic properties of starch-based foods,but most of LAB do not produce amylases.Therefore,our hypothesis is that amylase-producing LAB can improve the fermentation efficiency and may have some contribution to the organoleptic quality of potato staple foods,which is of great significance for the promotion of potato staple food strategy.(1)Screening of amylase-producing LAB.A total of 544 isolates from 7 fermented samples were screened out,and 18 of them possessed starch utilization ability.Among them,strain 430,445 and 472 have strong ability to degrade starch.All 3 strains were identified as Lactobacillus plantarum by API 50 CHL along with 16 S rDNA gene sequence.The optimum condition for amylase production of strain 445(CGMCC 14177)was cultured in pH 6.5 MRS medium with 0.5% starch instead of 0.5% glucose,at 31 ?.Under this condition,the highest amylase activity of CGMCC 14177 was up to 15.89 U/mL at 21 h.Meanwhile,the optimum temperature and pH for amylase reaction were 40 ? and pH 7.(2)The fresh potato slurry was dirctly fermented by CGMCC 14177,and then starch was extarcted to explore the effect of fermentation on the properties of potato starch.The results indicated that the amylose content in starch first increased and then decreased with the extension of fermentation time.The initial gelatinization temperature of fermented potato starch incresed and the gelatinization enthalpy decreased.The Rapid Visco Analyzer(RVA)peak viscosity and setback of fermented potato starch decreased,and the final viscosity and breakdown increased.The hardness and chewiness of potato starch gel increased after fermentation.The starch granules showed surface erosion and the crystallinity of potato starch increased 1.9% after 24 h fermentation.(3)The solid-state fermentation of potato flour with strain CGMCC 14177 was investigated.The suitable condition for the fermentation was: the solid-liquid ratio of 1:1.4,inoculation amount of 8%,and the temperature of 34 °C.Under this condition,the activities of total amylase and ?-amylase were respectively up to 198.9 U/g and 144.5 U/g at 12 h.The starch content was reduced 21.48% after 24 h fermentation by CGMCC 14177,demonstrating its ability to degrade starch was far greater than that of Lactobacillus rhamnosus GG ATCC 53103 and L.plantarum CGMCC 15358,a strain without amylase production.(4)The potato flour fermented by CGMCC 14177 and wheat flour were mixed to produce potato noodles.The results indicated that the optimum time of fermentation was 10 h,and the maximum addition ratio of fermented potato flour for noodles manufacturing was 30%.Compared with noodles added with the unfermented potato flour with the same ratio,the viscosities of noodles with fermented potato flour were significantly reduced and their maximum shearing hardness values were increased obviously.