| The potato starch processing industry is one of the pillar industries in Ningxia’s Guyuan region,and the processing of starch produces a large amount of potato residue every year.The potato residue is usually used as biofodder or stockpiled in the open air.The highwater content of potato residue is prone to deterioration,which seriously pollutes the environment and causes waste of resources.Potato pomace contains organic substances such as proteins and carbohydrates,which provide a good fermentation environment for microorganisms.Lactic acid bacteria are recognised as safe microorganisms in the food industry.Lactic acid bacteria fermentation can improve the nutritional composition,taste and flavour of raw materials,while high viable bacteria entering the human intestine can regulate the balance of intestinal flora,enhance immunity and improve the resistance of pathogens.In this study,a strain of lactic acid bacteria that can directly use the starch in potato pomace was obtained through natural environment screening,and solid-state fermentation conditions were optimised through single-factor and other experiments to obtain lactic acid bacteria products with high viable bacterial counts.The fermentation quality characteristics,microbial safety indicators,in vitro antioxidant capacity and volatile flavour of the products were evaluated,and a meal replacement powder product that meets modern standards was developed.(1)Lactic acid bacteria screening and identification:This experiment used the amylosphere colour development reaction and enzyme activity assay to screen four strains with high enzyme activity.The growth,bile salt tolerance and acid tolerance of the four strains in potato pomace were compared through the experiment.It was determined that strain NX-5 had the best growth stability in potato pomace,with a maximum viable count of 7.8 x 105 CFU/g and an amylase activity of 26.5 U/ml.It also had better bile salt tolerance and acid tolerance than the other three strains,so strain NX-5 was selected as the main bacterium for solid state fermentation.After morphological observation and molecular biology sequencing,it was identified as Lactobacillus plantarum,with an optimum growth temperature and pH of 34℃ and 6.0 respectively.(2)Optimization of the solid state fermentation process of potato residue:The experiments were carried out with inoculum level,fermentation time,feed-to-liquid ratio and nitrogen addition as independent variables,and the optimal fermentation process of strain NX-5 was determined by PlackettBurman experiment and response surface method.The fermentation process was carried out in a pilot experiment using a fermenter,and the number of viable bacteria could reach 8.25±0.406×108 CFU/g.The content of acetic acid,butyric acid,valeric acid and lactic acid in the sample increased after fermentation,and the number of viable bacteria remained at 3.5×107 CFU/g after the sample was stored at 25℃ for 90 days,which has good stability.(3)Study on the changes of the quality characteristics of the solid fermentation of potato pomace:the brightness of the fermented potato pomace was significantly reduced,and the colour was inclined to golden yellow;scanning electron microscopy found that the fermented potato pomace particles were broken in large pieces,and the surface of the particles was rough,and the surface showed signs of serious erosion;the water-holding capacity and oil-holding capacity were reduced;the energy storage modulus,loss modulus and viscoelasticity were all reduced.The starch content of the fermented product is reduced and the content of organic acids,total phenols,total acids,reducing sugars and amino acids is increased.The ABTS+scavenging capacity,total antioxidant capacity(T-AOC)and DPPH radical scavenging capacity of potato pomace were significantly obtained after fermentation;62 volatile substances were detected in the flavour analysis and 59 were characterised,including 11 ketones(18.64%),10 aldehydes(16.95%),9 alcohols(15.24%),8 esters(13.55),5 olefins 5 pyrazines,each accounting for 8.47%;3 acids,accounting for 5.08%;and 9 others,accounting for 15.24%.After fermentation,the active substances of potato pomace increased,and a variety of quality indicators and microbiological safety indicators met the requirements.(4)Study on the formulation and evaluation of meal replacement powder:In order to improve the taste and nutritional balance of solid fermented products,the optimal formulation of potato residue meal replacement powder was determined through a single-factor experimental design,with sensory evaluation and brewing characteristics as the main evaluation indexes,supplemented by in vitro digestive characteristics and electronic nose:the fermented potato residue sample was used as the base material,with the addition of konjac flour at 10%,erythritol at 6%and modified soy lecithin at 2.5%.The powder has a homogeneous colour and flavour,good brewing characteristics and complies with the relevant meal replacement standards. |
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