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Soy protein isolate/montmorillonite (SPI/ MMT) nanocomposite films were prepared in which MMT was used as a nanofiller at 0, 3, 6, 9, 12, and 15 wt % relative to SPI dry weight. Effects of MMT on film properties including tensile strength, elongation at break, total soluble matter, water vapor permeability, and oxygen permeability were assessed. X-ray diffraction patterns were determined, and morphologies of SPI and the SPI-MMT composite films were visualized by scanning electron microscopy. Mechanical and barrier properties were improved by evidenced increases in tensile strength and modulus, and decreases in permeability to water vapor and oxygen. MMT concentrations of 3%-12% were optimal for improving functional properties of the composite films. X-ray diffraction and scanning electron microscopy examinations revealed the formation of an intercalated and exfoliated structure on the addition of MMT into the SPI matrix. We conclude that intercalated and exfoliated MMT silicates enhance mechanical and barrier properties of SPI films.

Meju, a brick of dried fermented soybean naturally inoculated with microorganisms, is a starter used for producing traditional Korean fermented soybean products such as soybean paste (doenjang) and soy sauce (ganjang). In order to reduce aging time during production of soybean paste and soy sauce, high pressure (HP) treatment was applied to the meju starter at 500 MPa of pressure for 10 min at 15 degrees C. Fermentative behaviors of normal and HP-treated meju were assessed and compared through physicochemical and (1)H NMR-based metabolomic analysis. All mejues were incubated for 3 weeks at 30 degrees C. At 1 week of incubation, total bacterial population decreased mainly due to a reduction of water content by spontaneous evaporation during the incubation period. As the incubation time increased, glutamate, proline, betain, choline, and phosphocholine levels increased in both normal and HP-treated mejues, indicating that microorganisms in the mejues synthesize these metabolites to endure intracellular hyperosmotic stress induced by the reduction in water content. Through 3 weeks of incubation, the amino-type nitrogen contents and neutral protease activities in HP-treated meju were significantly higher (p < 0.05) than in normal meju, even though total bacterial content in HP-treated meju was 2 or 3 times lower. Moreover, marked increases in glycerol, acetate, tyrosine, and choline levels were observed in HP-treated meju compared to normal meju. In particular, higher levels of tyrosine in HP-treated meju were consistent with the increased neutral protease activities compared to normal meju, indicating an improvement in enzyme stability with HP treatment. These findings highlight a new or better understanding of the influence of the HP or physical treatments on fermentative products in food processing, such as those associated with soybean paste and soy sauce, regarding metabolic behaviors in fermentative starter induced by HP treatment.