Production of keto-disaccharides from aldo-disaccharides in subcritical aqueous ethanol

Figures & data

Fig. 1. Isomerization and hydrolysis processes of (♢) maltose to (△) maltulose, (□) glucose, (○) fructose, and (▹) mannose in (a) subcritical water and (b) 60 wt% subcritical aqueous ethanol at 220 °C. The feed concentration of maltose monohydrate was 0.5 wt%.

Fig. 2. ¹H and ¹³C NMR spectra of the standard and purified sample of maltulose. (a) ¹H NMR of standard sample of maltulose, (b) ¹H NMR of purified sample of maltulose, (c) ¹³C NMR of standard sample of maltulose, and (d) ³C NMR of purified sample of maltulose.

Table 1. Effect of ethanol concentration on maltose isomerization in subcritical aqueous ethanol at 220 °C.

Concentration of ethanol (wt%)	Residence time (s)	Maximum yield of maltulose (%)	Selectivity of maltulose (%)	Residence time for maximum yield of glucose (s)	Maximum yield of glucose [%]	Selectivity of glucose [%]
0	100	14	24	400	44	45
20	200	19	26	500	30	31
40	200	19	25	500	15	16
60	100	24	39	400	9	10
80	50	22	37	300	4.4	4.6

Table 2. Effect of temperature on maltose isomerization in 60 wt% aqueous ethanol.

Temperature [°C]	Residence time [s]	Maximum yield of maltulose [%]	Selectivity of maltulose [%]	Total sugar content [%]
180	500	18	48	85
190	500	23	40	71
200	500	28	36	60
210	300	26	37	64
220	100	24	40	72

Fig. 3. Arrhenius plot for the rate constants of maltose to maltulose isomerization in 60 wt% subcritical aqueous ethanol.

Fig. 4. Isomerization and hydrolysis processes of (♢) isomaltose to (△) palatinose, (∇) epiisomaltose, (□) glucose, (○) fructose, and (▹) mannose in (a) subcritical water and (b) 60 wt% subcritical aqueous ethanol at 200 °C. The feed concentration of isomaltose was 0.5 wt%.

Fig. 5. Isomerization and hydrolysis processes of (♢) cellobiose to (△) cellobiulose, (∇) epicellobiose, (□) glucose, (○) fructose, and (▹) mannose in (a) subcritical water and (b) 60 wt% subcritical aqueous ethanol at 200 °C. The feed concentration of cellobiose was 0.5 wt%.

Fig. 6. Isomerization and hydrolysis processes of (♢) lactose to (△) lactulose, (∇) epilactose, (□) glucose, (○) fructose, (▹) mannose, (■) galactose, (●) tagatose, and (►) talose in (a) subcritical water and (b) 60 wt% subcritical aqueous ethanol at 200 °C. The feed concentration of lactose was 0.5 wt%.

Fig. 7. Isomerization and hydrolysis processes of (♢) melibiose to (△) melibiulose, (∇) epimelibiose, (□) glucose, (○) fructose, (▹) mannose, (■) galactose, (●) tagatose, and (►) talose in (a) subcritical water and (b) 60 wt% subcritical aqueous ethanol at 200 °C. The feed concentration of melibiose was 0.5 wt%.

Fig. 8. Isomerization and hydrolysis processes of (♢) palatinose to (△) isomaltose, (□) glucose, (○) fructose, and (▹) mannose in (a) subcritical water and (b) 60 wt% subcritical aqueous ethanol at 200 °C. The feed concentration of palatinose was 0.5 wt%.

Fig. 9. Hydrolysis processes of (♢,♦) trehalose to (○,●) glucose, in subcritical water (open symbols) and 60 wt% subcritical aqueous ethanol (closed symbols) at 200 °C. The feed concentration of trehalose was 0.5 wt%.

Fig. 10. Hydrolysis processes of (♢) sucrose to (□) glucose, (○) fructose, and (△) mannose in 60 wt% subcritical aqueous ethanol at 200 °C. The feed concentration of sucrose was 0.5 wt%.

Fig. 11. Solubility of maltose monohydrate in aqueous ethanol at 25 °C.

Table 3. Isomerization of maltose in 60 wt% aqueous ethanol at 200 °C at different feed concentrations.

Feed concentration of maltose monohydrate [wt%]	Residence time [s]	Maltose conversion [%]	Maximum yield of maltulose [%]	Selectivity of maltulose [%]	Total sugar content [%]	Productivity of maltulose [g/(h kg-solution)]
0.5	500	79	29	36	59	6.6
1	500	70	27	39	67	16
2	500	67	24	35	65	29
5	500	51	18	35	74	41