ASSESSMENT OF ENDO-1,4-BETA-D-GLUCANASE ACTIVITY BY A RAPID COLORIMETRIC ASSAY USING DISODIUM 2,2'-BICINCHONINATE

It is widely accepted that viscometric assays are the most sensitive methods for evaluation of endoglucanase activities, because of the preferential attack of these enzymes on internal bonds of the substrate. However, due to the high sensitivity of the disodium 2,2′-bicinchoninate assay, we could measure, in a onestep method, the initial stages of the degradation of cellulose derivatives by endo-1,4-β-D-glucanases, by determining the reducing end-groups released. We report the applicability of the method for the determination of activity, and the K_m for the endoglucanase-I from Trichoderma reesei. This assay can be extended to the evaluation of reducing groups released by the action of many other carbohydrases, either with endo- or exo-type activity.     

Kinetic model for osmotic dehydration and its relationship with Fick's second law

A two-parameter equation was developed from mass balance considerations and used to predict the kinetics of osmotic dehydration and the final equilibrium point. The model was tested using kinetic data from ten different experiments and was able to predict water loss and solids gained over long periods of drying. The final equilibrium point was estimated using data obtained during a relatively short period of time. Simple equations were obtained when the model was related to Fick's second law for non-steady one-dimensional diffusion through a thin slab, and apparent diffusion coefficients were readily estimated from these equations.     

Partial Characterization of the Action of An A. niger Lipase on Butteroil Emulsions

A commercially available lipase (A. niger, APF-12) was employed to hydrolyze an emulsified butteroil substrate. HPLC analyses of the reaction products indicated that short chain fatty acid residues (e.g., butyric acid) were preferably hydrolyzed at pH 5 whereas the overall rate of hydrolysis for all major fatty acids showed a pH optimum between 6 and 7. This indicated the possibility of directing the selectivity of lipolysis in butteroil to enhance production of short-chain fatty acids associated with flavor development. The optimal temperature was ca. 35°C. Different cations also affected rate of hydrolysis.     

COMPOSITION OF THREE FOOD PRODUCTS CONTAINING DEFATTED CORN GERM FLOUR

Incorporation of defatted corn germ flour in a standard cookie formula improved amino acid and mineral composition of the baked product. Similar effects, but of less magnitude, occurred in corn muffins. Addition of defatted germ flour to ground beef increased yield of the broiled meat product. Amino acid composition remained essentially constant, but mineral composition changed considerably     

Starch Transformation During Banana Ripening: The Amylase and Glucosidase Behavior

Banana starch disappearance during ripening originated at the central portion of the fruit radiating, afterwards, to the surface; the amylose/amylopectin ratio remained constant during the process. The amyloplast was investigated by light and scanning electron microscopy. The surface of starch granules was smooth, and the unique modification obsenred during ripening was the reduction of the granule dimensions; at advanced ripening stages, some striations were detected on the surface of both small and large granules. Several amylolytic enzymes were followed during banana ripening. Seven amylases were detected at all stages, presumably three a- and four p-amylases and, like glucosidases, their activity increased at the climacteric phase; only p-amylase activity increased before the onset of the respiratory peak. For the first time α-l, 6-glucosidase activity was detected in banana.     

GROWTH/SURVIVAL OF NATURAL FLORA AND LISTERIA MONOCYTOGENES ON REFRIGERATED UNCOOKED PORK AND TURKEY PACKAGED UNDER MODIFIED ATMOSPHERES

Listeria monocytogenes was inoculated onto fresh pork and turkey slices. Inoculated and control samples were packaged under modified atmospheres (100% N₂, and 20%/80% and 40%/60% CO₂O₂) or air in plastic bags of low gas permeability. Samples were stored at 1 and 7C. Samples stored in air showed a similar microbiological pattern to that usually observed in fresh meat stored aerobically. Packaging under modified atmospheres extended the meat shelf-life. Bacterial growth was strongly inhibited at 1C, particularly in samples stored under CO₂/O₂ enriched atmospheres. Temperature and pH were critical factors for L. monocytogenes growth. This pathogen grew only on pork (initial pH 5.3) packaged in air and stored at 7C. No L. monocytogenes growth was observed at 1C in any atmosphere assayed. However, growth on turkey (initial pH 6.0) was marked at 7C in all atmospheres tested, while at 1C, this bacterium grew weakly only on samples stored in air .     

DNA nanomechanical switches under folding kinetics control

Existing DNA nanodevices operate at equilibrium under changes in solution composition. We propose an alternative DNA switch design that can be driven and maintained out of equlibrium, under fixed chemical conditions. Moderate cooling rate after heat denaturation drives the switch to its lowest energy conformation, while rapid cooling (>100 degrees C/ms) locks the molecule in a unique alternative conformation that is retained over weeks at room temperature. This reversible process is probed using fluorescent energy transfer. DNA switches operating out of equilibrium should be more amenable to nanotechnology applications and scalable integration.