Production Of Soluble Protein Powder From Low-value Protein Material By Solid-state Fermentation

Recently, with the increase of salmon products, it has become a problem that howto deal with salmon processing by-products. Meanwhile, there are many kinds ofnutrients in soybean meal, but anti-nutritional factors of soybean meal limit itsapplication areas. In the paper, fermentation process of soybean meal and salmonprocessing by-products to produce protein powder is investigated.Firstly, according to National food safety standards, the contents of nutritivecomposition are measured in soybean meal and salmon processing by-products. Theresults show that the contents of moisture, crude ash, crude protein and crude fat ofsalmon processing by-products are67.27%,0.36%,21.55%and10.11%.There are avariety of amino acids in salmon processing by-products. The total content of aminoacid (TAA) is19.31%, the essential amino acids (EAA) account for40.84%of TAA,and the ratio between EAA and non-essential amino acid (NEAA) is69.03%. Thecontents of moisture, crude ash, crude protein and crude fat of soybean meal are12.56%,5.94%,53.76%and2.08%. Soybean meal also has various amino acids. TheEAA account for35.75%of TAA, and the ratio between EAA and NEAA is55.64%.Based on ideal protein profiles recommended by FAO/WHO, salmon processingby-products and soybean meal are both high-quality protein-rich raw material.Secondly, salmon processing by-products and soybean meal are solid-statefermented separately on each of them. Recording the extraction rate of soluble proteinin water as the index, the optimum fermentation process of soybean meal and salmonprocessing by-products is determined respectively by a serious of single-factorexperiments. When salmon processing by-products is selected as fermentationmedium, the main procedure parameters are fermentation temperature32℃, the ratioof salmon processing by-product to water1:0.5, pH value8, inoculation quantity6%-10%, fermentation time4days. The soluble protein extraction yield is53%-55%,and the soluble peptide extraction yield is45%-47%. When soybean meal is selected as fermentation medium, the main procedure parameters are fermentation temperature32℃, the ratio of soybean meal to water1:1, pH value7, inoculation quantity4%-8%,fermentation time6days. The soluble protein extraction yield is87%-89%, and thesoluble peptide extraction yield is72%-74%.Thirdly, the soluble protein extraction yield of fermented salmon processingby-products is only about50%, which is much lower than fermented soybean meal.Because of this disadvantage, mixture of salmon processing by-products and soybeanmeal is fermented in order to find better process about production of protein powder.Several factors including the ratio between salmon processing by-products andsoybean meal, the ratio of material to nutrient solution, the composition of nutrientsolution, pH value, inoculation quantity, fermentation time are analyzed on the impactof soluble protein and peptide extraction yield. Regarding the extraction yield ofsoluble protein as the index, choosing the ratio between salmon processingby-products and soybean meal, the ratio of material to nutrient solution, sucrosedosage and fermentation time as factors, the optimal process parameters of mixedsoybean meal and salmon processing by-products by fermentation are obtained byorthogonal experiment are the ratio of soybean meal to salmon processing by-products6:10, the ratio of material to nutrient solution1:0.5, nutrient solution including2%sucrose,0.6%KH2PO4,0.3%MgSO4,fermentation time5days, pH value7,inoculation quantity6%-8%. Under these conditions, the extraction yield of solubleprotein is93.25%and the soluble peptide extraction yield is81.47%.Lastly, processes about how to extract soluble protein from fermented mixture ofsalmon processing by-products and soybean meal in order to prepare protein powderare discussed. Results show that the optimum solution is as follows: the ratio ofmixture to water1:10and extracting3times (40minutes each time). The extractingsolution can be freeze-dried into required protein powder. The producing proteinpowder is totally re-dissolved, without granular impurities. It owns light yellow color,strong sweet flavor of soybean and fish without fishy smell. At the same time,according to National food safety standards, the contents of nutritive composition aremeasured in the producing protein powder. The results show that the contents of moisture, crude ash, crude protein and crude fat of protein powder are5.87%,6.11%,69.73%and11.74%. About95%of protein can dissolve in water, of which solublepeptide account for more than80%. The protein powder has various amino acids. TheEAA account for41.26%of TAA, and the ratio between EAA and NEAA is70.24%.Based on ideal protein profiles recommended by FAO/WHO, the producing proteinpowder is high-quality protein-rich food.The issues about deep processing of by-products from processing of aquaticproducts and high-value utilization of the low value marine are continuous inindustrial production. The high-quality protein-rich protein powder is produced withmaking full use of soybean meal and salmon processing by-products. The productionprocess provides methods to produce animal and plant protein powder withenvironmental protection.