Abstract
Lactose has become the main byproduct of many dairy products and ingredients. Current applications of lactose are insufficient to use the recovered lactose from manufacturing operations. Here we exemplified a new process for converting aqueous lactose into a sweeting syrup via one-pot synthesis. The synthesis consisted of two-steps: (1) enzymatic hydrolysis of lactose and (2) catalytic isomerization over MgO/SiO2. The hydrolysis of lactose over β-galactosidase converted 95.77 ± 0.67% of lactose into glucose and galactose. The catalytic isomerization was performed over MgO/SiO2 with different MgO loadings (10–40 wt.%). A battery of tests was conducted to characterize the different catalysts, including surface properties, basicity, and microstructure. The one-pot synthesis, enzymatic hydrolysis and catalytic isomerization over 20%-MgO/SiO2, converted 99.3% of lactose into a sweetening syrup made of glucose (30.48%), galactose (33.51%), fructose (16.92%), D-tagatose (10.54%), and lactulose (3.62%). The outcomes of this research present an opportunity for expanding the utilization of lactose.
Highlights
Lactose has become the main byproduct of many dairy products and ingredients
D-tagatose is an isomer of D-galactose, and it can co-exist as α-Dtagato-2,6-pyranose, β-D-tagato-2,6-pyranose, α-D-tagato-2,5-furanose, and β-D-tagato-2,6-furanose[12]
At 4 and 6% of enzyme concentration, the hydrolysis efficiency was more than 98% regardless of the time
Summary
Lactose has become the main byproduct of many dairy products and ingredients. Current applications of lactose are insufficient to use the recovered lactose from manufacturing operations. The one-pot synthesis, enzymatic hydrolysis and catalytic isomerization over 20%-MgO/SiO2, converted 99.3% of lactose into a sweetening syrup made of glucose (30.48%), galactose (33.51%), fructose (16.92%), D-tagatose (10.54%), and lactulose (3.62%). The manufacture of milk protein powders generates as the main by-product streams of lactose, whose concentration is 75–80% on a dry basis. Lactose is commercially available in a wide array of products for diverse uses, including infant foods, confectionery, and pharmaceutical application[3]. Most of the D-tagatose commercialized in the world is produced via isomerization catalyzed L-arabinose isomerase using concentrated lactose or galactose. The chemical synthesis of D-tagatose is base-catalyzed isomerization, where the reaction is operated at high pH values using soluble alkalis (sodium hydroxide, potassium hydroxide, or calcium hydroxide)[14], where
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