INHIBITION OF SHIKIMATE DEHYDROGENASE FROM HEART-OF-PALM (EUTERPE OLERACEA MART.)

Shikimate dehydrogenase (E.C.1.1.1.25), extracted from heart-of-palm, was purified by precipitation with ammonium sulphate and elution from columns of Sephadex G-25, and DEAE-Sephadex A-50. The enzyme was unstable and it was not possible to maintain the activity by the addition of cysteine and 2-mercaptoethanol to the buffer. The heart-of-palm contained two isoenzymes which were separated by polyacrylamide gel electrophoresis. The enzyme was inhibited by metal ions and p-CMB. The p-CMB inhibition was reversed by cysteine. The shikimate dehydrogenase was competitively inhibited by protocatechuic acid (Ki 7.5 × 10^?4M), and Km values of 0.021 mM and 0.011 mM for shikimic acid and NADP⁺, respectively, were obtained at pH 9.5 in Tris-HCl-glycine buffer. The molecular weight determination was performed on Sephadex G-100 and the MW was estimated to be 50,000 daltons.     

Prediction of pH Change in Processed Acidified Turnips

The acetic acid uptake by turnips was studied during an acidification process in containers. The process was successfully described by a Fickian diffusion, using a correlation for the buffer effect. Diffusion coefficients (0.629 to 3.99 × 10^-9 m²/sec) and partition coefficients (0.8 to 1.1) were obtained by optimization of the fit between experimental and theoretical values, using the simplex method. The partition coefficient did not show an evident dependence on temperature, while diffusivity followed an Arrhenius type behavior. The relationship between acid concentration and pH was described using a cubic model with parameters independent of temperature. Results showed that the combination of these models describing the acid diffusion into the food and the buffering effects of the food allowed accurate prediction of pH evolution in the acidification process.     

Effect of Surface Freezing on Ascorbic Acid Retention in Water Blanched Potato Strips

The average retention of ascorbic acid in potato strips (10 × 10 × 80 mm) blanched in water at 50°C and 65°C over various blanching times, with and without surface freezing pre-treatment was determined. The strips were frozen in Freon Freezant-12 for 15 sec, with the freezing front penetrating 0.4–0.5 mm. Average retention of ascorbic acid in the surface-frozen potato strips was significantly lower than that in fresh strips and lower at 65°C than at 50°C. At an equal average retention of ascorbic acid, at 50°C the fresh strips required a blanching time four times higher than that for the surface-frozen strips; at 65°C it was twice as high.     

Analytical TEM study of annealed nanocrystalline cobalt–phosphorous electrodeposits

Investigation of thermal stability of two nanocrystalline Co–P alloys shows that P atoms segregate to the grain boundaries upon annealing until precipitation of Co₂P and CoP precipitates takes place. The P-rich precipitates formed have been investigated by analytical transmission electron microscopy to obtain statistical results of precipitate size, volume fraction and spatial distribution. Electron spectroscopic imaging maps show that the P-rich precipitates are 33 ± 9 nm in Co–1.1at.%P and 33 ± 12 nm in Co–3.2at.%P. The main differences between the alloys are the precipitate size distribution (Co–3.2at.%P having broader distribution) and precipitate volume number density (Co–3.2at.%P has 1.8 times more precipitates than Co–1.1at.%P). The volume fraction of precipitates is 3.0% in Co–1.1at.%P and 4.4% in Co–1.1at.%P. Most of the precipitates are of nearly spherical or slightly elongated shape, and only a few have a platelet-like shape as expected from previous tomographic atom probe measurements. Due to the truncation and projection effects, the composition of the precipitates could not be determined.     

ANTIOXIDANT PROPERTIES OF LENTINUS EDODES AND AGARICUS BLAZEI EXTRACTS

ABSTRACT

This work aimed to evaluate the antioxidant activity of Lentinus edodes and Agaricus blazei mushrooms, as well as to measure the content of total phenolic compounds of mushroom extracts and verify the oxidative stability of soybean oil added with mushroom extracts that showed higher antioxidant activity according to the methods of the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH^•) free radical scavenging and the β‐carotene/linoleic acid system. According to the DPPH^• method, the maximum antioxidant activity for L. edodes and A. blazei methanol extracts was 92.84 and 95.10%, respectively. For the β‐carotene/linoleic acid system, the highest values of antioxidant activity were 93.06% for L. edodes and 78.96% for A. blazei. The content of total phenolic compounds ranged from 7.21 to 128.44 and 26.67 to 134.67 mg gallic acid equivalent/g for L. edodes and A. blazei, respectively. The oxidative stability values provided by the Rancimat method indicated that the two varieties presented similar induction period of 19.85 h.

PRACTICAL APPLICATIONS

Mushrooms present high content of antioxidant compounds that are capable of reducing the harmful effects of free radicals. Among the antioxidants present in mushrooms, phenolic compounds stand out as phenolic acids, flavonoids and tocopherols. To decrease or prevent lipid oxidation, synthetic antioxidants are used as food additives. Nevertheless, studies have revealed that these compounds are likely to pose risks to human health. The concern regarding the safety of synthetic antioxidants has motivated the search of natural antioxidants that can substitute them totally or partially.

     

Optimizing Processing Conditions for Chemical Peeling of Potatoes using Response Surface Methodology

Using Response Surface Methodology the effects of NaOH concentration (4–20%), process temperature (55–95°C) and time (1–7 min) was determined on the yield, peeling quality, unpeeled skin and total usage of NaOH. Also evaluated were titratable NaOH in the potato tissue, NaOH penetration and “heat ring” depths during one stage chemical peeling of potatoes (Huincul variety). The best peeling quality, maximum yield and minimum total usage of NaOH was obtained for the following ranges: concentration, 11–13%, time 5–5.70 min and temperature, 90–95°C. The maximum temperature for which the “heat ring” and NaOH penetration depths were equal was 72°C where, at 20% NaOH and 7 min, peeling quality was very good and “heat ring” was absent.