The health benefits of soybeans have been known for some time. For centuries, soybeans have been the primary source of protein in Asian countries, and in recent years the popularity of soy-based products has increased in the United States. Along with a tendency to lower cholesterol levels, soybeans have recently been linked with, or suggested as having, a possible role in inhibiting cancerous or tumor cells. Additionally, soy protein contains an amino acid profile that is among the most complete of all vegetable protein sources, and resembles, with the exception of the sulfur-containing amino acids, the pattern derived from high-quality animal protein sources. Thus, efforts have been made to incorporate soy into a wide variety of foods.
In order for the maximum nutritional value to be realized from soy protein, inhibitors of proteolytic enzymes such as the trypsin inhibitor must be deactivated, typically by heat treatment. Oligosaccharides, which are also found in soybeans, may cause flatulence, if the level of soy protein ingested is sufficiently high. The flatulence is generally attributed to the fact that humans do not possess the enzyme a-galactosidase, necessary for hydrolyzing the α-galactodidic linkages found in oligosaccharides to yield readily absorbable sugars. It is therefore desirable to remove the oligosaccharides from soybeans prior to their incorporation in foodstuffs.
Prior attempts have been made to process soybeans to deactivate enzymes and remove oligosaccharides. For example, U.S. Pat. No. 4,137,339 (Jan. 30, 1979) describes a method of preparing a processed food material from soybeans wherein whole soybean grains are soaked in water, heated to 80–200° C., and then crushed and homogenized prior to being treated with a protein coagulating agent to precipitate the soybean solids. Other processes have been used to remove oligosaccharides from soy milk (e.g., ultrafiltration and hydrolytic enzymes) and to deactivate soy enzymes (e.g., extrusion). The oligosaccharides remained in solution are were discarded with the supernatant liquid. Process such as these, while effective in deactivating enzymes and/or removing oligosaccharides, involve expensive equipment as well as many complicated and time-consuming steps; moreover, they are generally result in the development of off-flavors and the loss of valuable soy solids. Such processes generally require hydration and/or disrupting the cellular structure of the soybeans prior to the enzyme deactivation, typically by thermal treatment alone; this generally results in the formation of off-flavor precursors. Dry heat and/or roasting can also be used to deactivate the enzymes. Generally, however, these processes significantly and adversely alter the characteristics of the soybeans (i.d., flavor and/or color). Additionally, since such methods generally require that the soybeans be crushed in order to deactivate enzymes and remove oligosaccharides, the resulting products cannot be utilized for applications requiring the use of whole soybeans.
It is therefore desirable to provide a process for deactivating inhibitors of proteolytic enzymes (such as trypsin inhibitor (TI)) and flavor degrading enzymes (such as lipoxygenase) and removing oligosaccharides which is simple and efficient and which avoids the development of off-flavors. It is also desirable that such a process can be operated in a manner in which the integrity of the soybeans is maintained; in other words, it is desirable that the process can, if desired, provide such soybeans in the form of whole soybeans.