COMPARISON OF WET-CHEMICAL METHODS FOR DETERMINATION OF LIPID HYDROPEROXIDES

Five methods for determination of lipid hydroperoxides were evaluated, including two iodometric procedures involving a titration and a spectrophotometric micro method, and three other spectrophotometric methods namely the ferro, International Dairy Federation (IDF) and FOX2 (ferrous oxidation in xylenol orange). Peroxide values determined in a range of food products by these five methods gave different results. The ferro method required large amounts of solvent (50 mL/sample); the FOX2 method had a low range (0.005–0.04 μmol hydroperoxide); the end point detection of the titration method was subjective and required a large amount of sample (1 g); and the micro method was sensitive to interruptions during execution. Therefore, only the modified IDF method was chosen for further testing and validation. Stability tests of the standard curve showed a variation coefficient of 4% and within runs the highest variation was 5.9% (for blank) and a maximum of 9.6% between runs variation for the lowest concentration. Among the antioxidants tested, only ethylenedi-aminetetraacetic acid (EDTA) affected the peroxide determinations.     

Low-temperature Blanch Improves Textural Quality of French-fries

Potatoes, CV. Alpha, were sorted (specific gravity), peeled, cut, and blanched at four temperatures (55—70°C) for several times (0—60 min.) before frying in vegetable oil (200°C, 4 min). Multiple puncture (raw potatoes) and single puncture and Texture Profile Analysis (TPA) of French-fries were used. Limpness angle and oil retention (Carver press) were also evaluated. Firmness and some TPA parameters (chewiness, cohesiveness) were increased (>200%) by blanch. Limpness and oil content were reduced by treatment. Improvement of French-fries texture resulted after blanching for 30—45 min. at 60—65°C.     

THE EFFECT OF TRINITROPHENYL NUCLEOTIDE DERIVATIVES ON THE ADENOSINE TRIPHOSPHATASE ACTIVITIES IN MAIZE TONOPLAST VESICLES

The effects of trinitrophenyl (TNP) derivatives of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and adenosine monophosphate (AMP) on the coupled activities of the tonoplast ATPase in corn roots were investigated. The addition of TNP-ATP at micromolar concentrations (0.5–0.25 mM) significantly decreased both the ATP hydrolytic activity and the coupled proton pumping activity. The presence of TNP-ATP resulted in an increased Km for ATP and a reced maximum enzyme velocity. Unlike TNP-ATP that strongly inhibited proton transport at low concentration, TNP-ADP inhibited this activity only slightly. TNP-AMP stimulated proton transport at low concentrations. ADP and AMP inhibited the initial rate of proton transport in a different manner. The concentrations required to inhibit half of the initial rate of proton transport activity for ADP and AMP were 80 μM and 2 mM, respectively. The results suggest that tonoplast vesicles may contain at least two kinds of nucleotide binding sites.