PURIFICATION AND PARTIAL CHARACTERIZATION OF A PROTEINASE INHIBITOR FROM TEPARY BEAN (PHASEOLUS ACUTIFOLIUS) SEEDS

In a qualitative screening of 36 accessions of tepary beans seeds, all the accessions inhibit the activity of bovine trypsin and trypsin-like proteinases from the insect P. truncatus, and the majority of them inhibit α-amylase activity of several important insect pests. A protein proteinase inhibitor was purified from accession L-242-45, using fractional precipitation, gel filtration, ion exchange chromatography and reverse-phase HPLC. The protein showed an apparent molecular weight of 7,100 by PAGE. However, contrary to other inhibitors previously reported, the inhibitory activity was only present in the trimeric form. The protein was characterized as a serine-proteinase inhibitor that recognized trypsin, chymotrypsin and trypsin-like proteinases, but it also recognized aspartic acid proteinases from different insects. It contained no carbohydrate residues and showed a high stability at 96C at low pH.     

EFFECT OF PARTICLE SIZE ON THE WATER SORPTION PROPERTIES OF CEREAL FIBERS1

Six particle size fractions were prepared by grinding and sieving stabilized hard red wheat bran, oat fiber, and corn bran. Water adsorption indices (WAI's) and effective diffusion coefficients (D_eff) were measured for all size fractions. WAI's of wheat bran decreased with particle size. WAI's of oat bran increased as particle size decreased and the WAI's of corn bran fractions did not vary as much as the other fibers. The D_eff's of wheat increased, of oat decreased, and of corn were about the same as the particle size decreased. The wheat D_eff was less than that of corn which was less than that of oats. Monolayer moisture content and bulk moisture content at high A_w were determined from moisture sorption isotherms measured on the smallest particles. There was no difference in the monolayer moistures but both corn and wheat brans adsorbed much more water at high A_w than did the oat bran. Effect of particle size on water sorption and, by inference, some types of functionality cannot be generalized and must be determined for each type of fiber.     

Ultrastructure of Pork Liver after Freeze-Thaw Cycling and Refrigerated Storage

Pork liver was subjected to repeated freezing (-20°C) and thawing (+ 5°C) to simulate conditions of temperature abuse of frozen liver during commercial transport. Ultrastructure was compared to that of refrigerated pork liver. Liver cells deteriorated more with freezing and thawing (F-T) than with refrigerated storage (R-S). After one cycle F-T, hepatocyte organelles were damaged and cytoplasmic components appeared in the sinusoids. After four cycles F-T, membranes were extensively damaged and sinusoids contained organelles. The tissue organization was stable during six days of refrigerated storage, although cell structure deteriorated. Evidence from ultrastructure indicated that drip from F-T liver and R-S liver arose from different kinds of tissue damage.     

USE OF MICROPOROUS PLASTIC FOR IN-PACKAGE CONTROLLED ATMOSPHERES

Ground beef packaged and stored with carbon dioxide-generating reagent packets made from (1) microporous plastic film or (2) non-woven cellulose cloth had significantly (p<0.01) lower bacterial counts than ground meat packaged and stored without packets. There was no significant difference (p>0.05) in bacterial counts of samples stored with the 2 types of packets. Samples with in-package generated carbon dioxide atmospheres had approximately 2–3 days additional shelf-life before spoilage.     

EFFECT OF DIFFERENT COATING TREATMENTS ON THE QUALITY OF MANGO FRUIT

Eight coating formulations were evaluated for beneficial effects on the shelf‐life of mangoes (cvs. Kent, Tommy Atkins, and Lirfa) harvested at different maturity stages. Four coatings were then selected for further study under various conditions of storage including ambient (19–22C and56–60% RH) and simulated commercial (12C and 80% RH) storage. The four coating formulations contained carnauba wax, shellac, zein, and/or cellulose derivatives. All coatings reduced the respiratory rate, the development of external and internal color, and all but carnauba wax retarded the loss of firmness. Changes in acids were also delayed in all coated mangoes. Based on these parameters, fruit maturation was estimated to have been delayed by a few days compared with uncoated fruit. Shellac and cellulose‐based coatings, however, caused elevated levels of ethanol, although this did not lead to significant flavor differences from the control (uncoated fruit) in sensory tests. Only the carnauba wax coating was an effective water loss barrier under conditions of high RH.     

AN IN SITU METHOD TO STUDY THE REACTION CATALYZED BY ALKALINE PHOSPHATASE ON DNPP

The reaction catalyzed by alkaline phosphatase on disodium‐p‐nitrophenyl phosphate was studied in a reaction media composed of sucrose (43.5 and 53.5%, w/w) and sucrose (43.5%, w/w) + polysaccharide (10%, w/w) added with agar‐agar (0.5%, w/w) at low temperatures (20, 0 and ?5C). The results show that temperature and concentration of sucrose and sucrose + dextran in the media affect the enzymatic reaction. The presence of 10% dextran (molecular weight of 10⁴ g/mol, w/w) in the reaction medium decreased the reaction rate. This could be explained by the increase in the viscosity of the medium, due to the presence of this polysaccharide. The experimental data were compared with predicted values, calculated from Atkin's theory. The results show that in our experimental conditions described previously, the reaction catalyzed by alkaline phosphatase cannot be predicted by Atkin's theory, probably because the viscosity was not the main parameter governing the reaction.     

TEXTURE MEASUREMENT IN MEAT BY SENSORY EVALUATION*

Various sensory evaluation methods have been used to measure texture in meat. While some methods are more suitable than others, more work must be done before any one can be recommended as a standard method. Other aspects which require special attention are cooking of samples, selection of reference samples and the multicomponent nature of texture.     

Coating Behavior of Suspensions

The ability of a solid suspension in liquid medium to coat a vertical surface was analyzed. Results with model suspensions, consisting of polystyrene particles (37–147 μm) in volume concentration from 15–40%, show that coating thickness increases linearly with particle concentration in suspension, and then increases sharply at a critical concentration. The coating thickness of sucrose in corn oil shows behavior similar to that of the model system.     

USE OF MASS TRANSFER THEORY TO PREDICT VISCOSITY-SWEETNESS INTERACTIONS OF FRUCTOSE AND SUCROSE SOLUTIONS CONTAINING TOMATO SOLIDS

The perceived sweetness intensity of sucrose and fructose in solutions of varying tomato solids content was studied. Using magnitude estimation it is shown that as the percentage o f tomato solids increased from 0-2.6%, the perceived sweetness intensity decreased substantially for both sucrose and fructose. The sharpest decrease occurred with a 1.66 molar fructose solution where the assessed sweetness intensity of a 2.6% insoluble tomato solids sample is 63% lower than the corresponding Wo tomato solids solution.
The penetration model of mass transfer explains this psychophysical phenomenon with the following relationship: