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Plasmin is by far the predominant and most completely studied endogenous protease in bovine milk. Plasmin-induced proteolysis can have either beneficial or detrimental effects on the texture and flavor of dairy products, depending on the extent of hydrolysis and type of dairy product. In cheese, the breakdown of protein can help develop desirable flavors and texture during ripening, whereas in pasteurized milk and ultra-high-temperature milk, proteolysis causes undesirable gelation. Plasmin is part of a complex protease-protease inhibitor system in milk that consists of active and inactive forms of the enzyme, activators, and inhibitors. Considerable research has been done to isolate and characterize components of the plasmin system, determine how they interact, develop and compare quantitation methods, and determine how they are affected by cow characteristics, processing conditions, other milk components, storage conditions, and bacterial proteases. Considerable research has focused on enhancing or minimizing the activity of plasmin system components. The intent has been to control protease activity in casein and whey fractions, depending on the final food or ingredient application. Controlling the activity of plasmin has a great potential to improve dairy product quality and reduce their processing costs.

Diverse functions for three soybean (Glycine max L. Merr.) cysteine proteinase inhibitors (CysPls) are inferred from unique characteristics of differential regulation of gene expression and inhibitory activities against specific Cys proteinases. Based on northern blot analyses, we found that the expression in leaves of one soybean CysPl gene (LI) was constitutive and the other two (N2 and R I ) were induced by wounding or methyl jasmonate treatment. Induction of N2 and R I transcript levels in leaves occurred coincidentally with increased papain inhibitory activity. Analyses of kinetic data from bacterial recombinant CysPl proteins indicated that soybean CysPls are noncompetitive inhibitors of papain. The inhibition constants against papain of the CysPls encoded by the wound and methyl jasmonate-inducible genes (57 and 21 nM for N2 and R1, respectively) were 500 to 1000 times lower than the inhibition constant of L1 (19,000 nM). N2 and R1 had substantially greater inhibitory activities than L l against gut cysteine proteinases of the third-instar larvae of western corn rootworm and Colorado potato beetle. Cysteine proteinases were the predominant digestive proteolytic enzymes i n the guts of these insects at this developmental stage. N2 and R1 were more inhibitory than the epoxide trans-epoxysuccinyl-~-leucylamide-(4-guanidino)butane (E-64) against western corn rootworm gut proteinases (50% inhibition concentration = 50, 200, and 7000 nM for N2, R1, and E-64, respectively). However, N2 and R1 were less effective than E-64 against the gut proteinases of Colorado potato beetle. These results indicate that the wound-inducible soybean CysPls, N2 and R1, function in host plant defense against insect predation, and that substantial variation in CysPl activity against insect digestive proteinases exists among plant CysPl proteins.Proteinaceous CysPIs, which specifically inhibit sulfl~y-dryl proteinase activities, are distributed ubiquitously among animal, plant, and microorganism species. The an-

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Three cysteine proteinase inhibitor cDNA clones (pL1, pR1, and pN2) have been isolated from a soybean (Glycine max 1. Merr.) embryo library. The proteins encoded by the clones are between 60 and 70% identical and contain the consensus QxVxC motif and W residue i n the appropriate spatial context for interaction with the cysteine proteinase papain. L7, R7, and N2 mRNAs were differentially expressed in different organs of plants (juvenile and mature) and seedlings, although NZ mRNA was constitutive only i n flowers. R I and N2 transcripts were induced by wounding or methyl jasmonate (M-JA) treatment in local and systemic leaves coincident with increased papain inhibitory activity, indicating a role for R I and N2 in plant defense. The L I transcript was constitutively expressed in leaves and was induced slightly by M-JA treatment in roots. Unlike the chymotrypsin/trypsin proteinase inhibitor II gene (H. Peiia-Cortes, J. Fisahn, 1. Willmitzer [19951 Proc Natl Acad Sci USA 92: 41 06-41 13), expression of the soybean genes was only marginally induced by abscisic acid and only in certain tissues. Norbornadiene, a competitive inhibitor of ethylene binding, abolished the wounding or M-JA induction of R I and N2mRNAs but not the accumulation of the wound-inducible vspA transcript. Presumably, ethylene binding to its receptor is involved in the wound inducibility of R I and N2 but not vspA mRNAs. Bacterial recombinant L I and R1 proteins, expressed as glutathione S-transferase fusion proteins, exhibited substantial inhibitory activities against vicilin peptidohydrolase, the major thiol endopeptidase i n mung bean seedlings. Recombinant R I protein had much greater cysteine proteinase inhibitor activity than recombinant L I protein, consistent with the wound inducibility of the R7 gene and its presumed role in plant defense.Injury to plants due to phytophagous insects or mechanical damage induces accumulation of proteinase inhibitor proteins (Ryan, 1981(Ryan, , 1990. Inhibitor proteins with specificity against Ser proteinases have been well characterized and there is direct evidence of their involvement in host plant defense against herbivorous insects (Johnson et al.,

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The effects of storage temperature and humidity were monitored on several physical and chemical components of cowpeas and beans. Seeds stored at 29"C, 65% RH required prolonged cooking times; however, seeds stored in other conditions (YC, 30% RH; 29°C 30% RH; and YC, 65% RH) maintained short, stable cooking times throughout storage. As cooking time increased, phytate, phytase activity, amylose solubility, high methoxyl pectin and protein solubility decreased. Solids leached during soaking and low methoxyl pectin increased as cooking time increased. These results were consistent with the proposed theory that the hard-to-cook defect involves interactions between phytate, minerals, and pectin. However, they did not eliminate possible roles of starch and protein solubility.

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