Absolute stability results for non-linear systems using logarithmic plots

Absolute stability of non-linear systems is examined using the conventional techniques, and a representation of Popov line in the logarithmic gain and phase versus frequency plane. A grapho-analytical procedure is advanced for the Popov line transference to the Bode plane. The technique may be used either as an analytical tool for investigating absolute stability of systems with specified non-linearity sector, or as a synthesis technique for compensator design. The application of the proposed method for substantiating compensator design results is illustrated by two examples.     

MICROBIOLOGICAL QUALITY OF ARTISAN-MADE MEXICAN BOTANERO CHEESE IN THE CENTRAL HIGHLANDS

Artisan-made Mexican Botanero cheese in the northwest of the state of Mexico in the central highlands is a soft-paste, fresh product made from raw cow milk. The microbiological quality was determined in cheese from 10 cheese producers. Milk and cheese samples were taken, and the hygienic process was recorded. Milk was analyzed for aerobic mesophil bacteria (AMB) and total coliform bacteria (TC), and in cheese TC and fecal coliforms (FCs) were determined. Results were compared with the Mexican COFOCALEC (milk) and NMX-462 (cheese). All bacterial counts were above those allowed for AMB (100,000 cfu/mL) and TC (1,000 cfu/mL). The norm allows up to 100 cfu/g of TC, but all cheese samples were above the norm. FC should always be negative, but all cheese samples were also positive. Raw milk is bought in with microbiological problems, and the artisan-manufacturing process further contaminates the final product, which constitutes a risk for human health. Even more rigorous legislation could not be met by artisan cheese makers in the highlands of central Mexico under the current conditions.

PRACTICAL APLICATIONS

In Mexico, there is an ample variety of artisan-made cheeses with a potential to be positioned in regional, national and even export markets by obtaining quality certification either as appellation controleé or as collective trademarks. However, in order to obtain this certification, it is necessary to analyze the situation of all the characteristics of the cheeses such as bacteriological quality. Before carrying out this study, the bacteriological quality of the Botanero cheese was unknown. Taking into account the obtained results, it is intended to carry out joint collaboration with cheese producers, so that their products can achieve the required standards and can reach a better position in the market, without being a risk for human health.     

ISOLATION AND CHARACTERIZATION OF THE 11S GLOBULIN FROM AMARANTH SEEDS

Globulins of Amaranthus hypochondriacus were extracted with two different buffer systems which varied in ionic strength. SDS-PAGE analysis demonstrated that subunit patterns were different between the two extracting systems. Amarantin, the native 11S globulin of amaranth, and its subunits were purified by gel filtration chromatography and preparative electrophoresis. The native amarantin exhibited two heterogeneous forms of MW 330 and 400 kDa, which yielded the same subunit composition after reduction. SDS-PAGE analysis showed that prior to reduction, the 50–52 kDa subunit was the major band, and that after reduction, two new bands of 32–34 kDa and 22–24 kDa appeared. This is a typical characteristic of 11S proteins whose subunits consist of an acidic polypeptide (27–37 kDa) and a basic polypeptide (20–24 kDa) linked by a disulfide bond. Ultracentrification analysis showed that amarantin has a 11.9S sedimentation coefficient whereas DSC demonstrated that the denaturation temperatures in the presence of H₂O, Tris-HCl and K₂HPO₄-KH₂PO₄ are 99C, 99.8C and 103C, respectively.     

MOLECULAR CHARACTERIZATION OF THE β-CONGLUTIN OF LUPIN SEEDS

β‐conglutin from Lupinus campestris was extracted and purified by gel filtration chromatography. The protein with molecular mass around 190 kDa showed by SDS‐PAGE three major polypeptides of 53, 60 and 63 kDa and a minor polypeptide of 30 kDa. Isoelectric focusing of the native protein gave three isoforms with isoelectric points of 6.2, 6.3 and 6.4. Its sedimentation coefficient was 8.0S, with a hydrodynamic diameter of 110 Å and possessed antigenic determinants in common with 7S proteins from common bean and soybean.     

THE LECTINS AND LECTIN-LIKE PROTEINS OF TEPARY BEANS (PHASEOLUS ACUTIFOLIUS) AND TEPARYCOMMON BEAN (PHASEOLUS VULGARIS) HYBRIDS

High levels of lectin activity were found in sixty cultivated and ten wild tepary (Phaseolus acutifolius) accessions. No lectin deficient varieties were observed and all examples studied contained both the phytohemagglutinin-E and L-like lectins previously described (Pusztai et al. 1987). There appeared to be no obvious differences between the wild and cultivated forms of the tepary lectins and all teparies studied contained lectin-like proteins in addition to the tepary lectins. One of the lectin related proteins (40 Kdalton subunit) was present in all teparies and may be comparable to arcelin, a lectin found in certain wild accessions of Phaselus vulgaris. All wild teparies contained a lectin related polypeptide of about 34 Kdaltons which appears to distinguish the wild teparies from the cultivated forms. Three tepary-common bean hybrids were examined and one hybrid was found to be expressing both tepary and common bean lectin genes.     

ASSESSMENT OF GLUCOSINOLATES IN BROCCOLI BY THREE DIFFERENT METHODOLOGIES

ABSTRACT Three different methodologies were used to assess the glucosinolate content in four broccoli cultivars. The assessment was performed by the thymol, enzyme immobilization and gas liquid chromatography (GLC) techniques. The cultivars used were Green Valiant, Green Duke, Marathon and Samurai. The three techniques demonstrated that Samurai and Green Valiant were the cultivars with the highest content of glucosinolates. It was also evident that, compared to stem and leaves, the floret of the four cultivars exhibited in general the highest amount of this component. Of the tested methodologies, the GLC technique showed the lowest data variability, although this technique was unable to estimate all the glucosinolates present in the broccoli samples because of its poor performance for the quantitation of indole and sulfinyl glucosinolates. In conclusion, the thymol technique appeared the most adequate procedure for the assessment of glucosinolates in broccoli samples.     

ANTIGENIC HOMOLOGY BETWEEN AMARANTH GLUTELINS AND OTHER STORAGE PROTEINS

Amaranth seed proteins were sequentially extracted and partially characterized by electrophoresis and immunological analysis using three polyclonal antibodies which were produced against an acidic subfraction of amaranth globulin, an oat globulin, and an acidic subunit of rice glutelin. Significant cross-reactivity was observed among glutelin and globulin fractions with these antibodies. Prolamin fraction did not react. Data suggest that there is some structural homology between amaranth glutelin and globulin fractions and that they could be legumin-like proteins because of their affinity with protein antibodies; such antibodies have been produced from legumin-like proteins. Two-dimensional electrophoretical analysis of a 32 kDa glutelin band clearly showed six acid components from pI 5.7 to 6.3; four of them cross-reacted with the acidic subfraction of amaranth globulin antibody. These results confirm that there is homology between these acidic components (32 kDa) of amaranth glutelin and the amaranth acidic sub-fraction of globulin.     

ISOLATION AND CHARACTERIZATION OF AMARANTIN, THE 11S AMARANTH SEED GLOBULIN

The 11S globulin of seed storage protein of Amaranthus hypochondriacus, termed amarantin, was isolated. This fraction was evaluated for its purity by chromatographic techniques and ultracentrifugation. The 11S globulin was analyzed by sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) without and with prior reduction of disulfide bonds, and by nondenaturing-PAGE. It exhibited an electrophoretic behavior similar to that of 11S-like proteins in other materials. Its apparent relative molecular weight was estimated to be 389 kDa by gel filtration chromatography at low ionic strength. Ultracentrifugation of the freeze-dried extract gave a sedimentation coefficient of 11S.     

Coconut Oil Extraction by a New Enzymatic Process

A new method for coconut oil extraction based on the enzymatic action of polygalacturonases, α-amylase and proteases on a diluted coconut paste was developed. After reaction with enzymes, the solution was centrifuged resulting in three phases: the upper one containing a high quality coconut oil; the middle layer containing water; and the lower phase consisting of coconut meal which has been traditionally used in cattle feed. Eighty percent yields were obtained by this method which was advantageous from the energy point of view compared to the traditional process.     

INFLUENCE OF HEAT TREATMENT AND GRAIN GERMINATION ON THE ISOFLAVONE PROFILE OF SOY MILK

Soy foods have attracted much attention for their possible effects on human health because of their phytochemical content, mainly isoflavones. Twelve forms of isoflavones have been identified in soybeans and soy products. Technological processes like heat treatment or fermentation can change the isoflavone profile of soy products. In this study, the effects of heat treatment and grain germination on isoflavone profile of soy milk prepared from BRS 213 soybean variety were evaluated. Isoflavone forms were separated and quantified by reversed‐phase high‐performance liquid chromatography. Heat treatment by autoclaving for 5 min did not affect the total isoflavone content, but led to a 90% decrease in malonyl forms, whereas β‐glycosides increased by 70%. Autoclaving for 15 min led to a 20% loss of total isoflavones. Germination for 3 days did not change the total isoflavone content, but changed the distribution profile (15% increase of malonyl forms and 30% decrease of β‐glycosides). Germination for 7 days increased the bioavailability of aglycone isoflavones in soy milk by seven times.