Enzymatic High Digestion of Soybean Milk Residue (Okara)

Abstract

The objective of this study was to digest okara in high yield by food-processing enzymes. Autoclaving of okara was effective in increasing cellulase digestion for the primary cell wall, and the digestion was accelerated by the formation of single cells by stirring. Most of the residual okara after autoclaving and cellulase digestion was found to be the secondary cell walls compared with the cellulase-treated soybean single cells. The secondary cell wall was found to be composed of galacturonic acid, neutral sugars, and protein and was considered to be a complex of these compositions. Many cellulolytic and proteolytic enzymes could not digest the secondary cell wall; however, it was found that two pectinases could digest the secondary cell wall. A series of digestions resulted in yields of 83-85% from the raw okara, and the final residues were identified as oil body complexes in the soybean cells and fiber-like organ between the cells.

Are Agricultural Plant Products and the Residues Indigestive Fibers?

“…The major part of the oil and protein bodies of soybean cells was removed into the soybean milk in the case of okara, and most of the remaining indigestible okara was considered to be the secondary cell walls of soybeans. 2) Staining with PAS, fast green, and acrolein Schiff reagent did not produce clear positive staining for the secondary cell walls; all stainings were pseudo positive. Alkaline treatment of the remaining okara after the cellulase digestion was done with 1 N sodium hydroxide and boiling for 10 min, and the soluble part was subjected to gel filtration on Toyopearl HW 50 and eluted with water.…”

“…Secondary cell walls from okara after remaining cellulase digestion, and the visible changes in the secondary cell walls of okara were monitored by light microscopy. 2) Most of the tested enzymes were not effective in digesting the remaining secondary cell walls from okara. Only two enzymes, Pectinex Ultra SP from Aspergillus aculeatus and pectolyase from Aspergillus japonicas, digested the remaining secondary cell walls of okara.…”

“…Therefore, a simple cellulase or hemicellulase could not digest the cell wall. 2) Screening of enzymes for the digestion of remaining okara. The secondary cell wall was complex, but the compositions were simple.…”

“…Pectinex Ultra SP resulted in good digestion. 2) Series of enzymatic hydrolyses of okara. The result is shown in Fig.…”

“…1,2) This extract would be the residual of soybean milk and the materials between cells as determined by HPLC analysis and staining results. 3) It is noted that sugar and protein were digested and solubilized as a result, although cellulase digestion was to digest the primary cell walls of okara.…”