LOCATION EFFECTS ON OXIDATIVE STABILITY OF CHÉTOUI VIRGIN OLIVE OIL

The effect of growing area on the natural antioxidant and oxidative stability of Chétoui virgin olive oil was studied. Total phenolic content, tocopherol composition, fatty acid composition and oxidative stability were analyzed. The results obtained in this study showed that Chétoui virgin olive oil composition is greatly influenced by growing environment, i.e., mainly by the climatic and pedologic factors. The cumulative rainfall appears to have a major influence on phenolic and o‐diphenol content. Among studied samples, Amdoun oil had the highest total phenolic content, which exceeded 700 mg/kg. Moreover, it contained the highest amounts of o‐diphenols 286.08 ± 6.74 mg/kg and total tocopherols 405.65 ± 4.17 mg/kg. The amounts of total phenols and o‐diphenols showed a good correlation (P ≤ 0.001) with stability while tocopherols showed a very low relation to oxidative stability.     

A Comparison of Dogfish and Bovine Chymotrypsins in Relation to Protein Hydrolysis

An extracellular protease, chymotrypsin, from a low temperature-adapted poikilotherm (dogfish) was compared with the bovine enzyme against several protein substrates to determine potential advantages in the use of an enzyme adapted to functioning in a low temperature environment. In general, the dogfish enzyme showed a higher rate of reaction and hydrolyzed more peptide bonds than did the bovine enzyme whether the substrates were soluble or insoluble proteins. Dogfish chymotrypsin was slow to produce clotting of milk, but once formed the clot had good stability. The bovine enzyme was more efficient in incorporating methionine into soy protein in a piasteintype reaction.     

DISCRIMINATION OF SOME TUNISIAN OLIVE OIL VARIETIES ACCORDING TO THEIR OXIDATIVE STABILITY, VOLATILES COMPOUNDS AND CHEMOMETRIC ANALYSIS

Oxidation stability is a key property of olive oil quality and is affected by different antioxidant compounds whose levels may be influenced by several factors such as cultivar and place of production. Polyphenols, carotenoids, chlorophylls, fatty acids levels and some volatiles were correlated to oxidative stability in olive oils in five samples studied. Total polyphenols and saturated to polyunsaturated fatty acids (and/or oleic to linoleic acid ratio) ratio were shown to be the major parameters in oil antioxidant stability, according to analysis of variance and principal component analysis. The hexanal/E-2-hexenal ratio is a very important indicator of the freshness of the oils and can estimate their oxidation degree.

PRACTICAL APPLICATIONS

The present study gives information about the importance and the variability of some Tunisian olive oil varieties in both their quality (high oxidative stability) and good organoleptic properties which could be appreciated by consumers.     

PHENOLIC COMPOUNDS, TOCOPHEROLS AND OTHER MINOR COMPONENTS IN VIRGIN OLIVE OILS OF SOME TUNISIAN VARIETIES

The phenols, α‐tocopherols, fatty acids and oxidative stability of six monovarietal virgin olive oils (VOOs) were determined. Fourteen phenolic compounds were detected and quantified by solid phase extraction and reversed phase‐high performance liquid chromatography. Dialdehydic form of elenolic acid linked to tyrosol and hydroxytyrosol, oleuropein and ligstroside aglycones were the main components in all samples. Pinoresinol was the most abundant component in lignan fraction. The total phenol content of these monovarietal oils varied from 66.82 mg/kg in “Neb Jmel” oil to 662.74 mg/kg in “El Hor” oil. A wide range of α‐tocopherol contents was also noticed; it varied from 141.94 mg/kg in “Semni” variety to 364.23 mg/kg in “Jdallou” variety. With regard to pigments, chlorophylls and carotenoids were found at variable concentrations: with median values of 11.33 and 3.10 mg/kg, respectively. Among the studied varieties, “Oueslati” and El Hor were characterized by the lowest levels of palmitic and linoleic acids and the highest values of oleic acid.     

THE ROLE OF CALCIUM IONS IN THE ACTIVITY OF AN ENDO-PECTIC ACID LYASE ON OLIGOGALACTURONIDES1

A pectic acid lyase was purified from the culture filtrates of Cephalosporium sp. Tetragalacturonic acid was the shortest chain of oligogalacturonides attacked and calcium ions were required for activity. The enzyme was most active at pH 9.9. The kinetic data showed that while Vmax was relatively constant, the Km decreased with increasing chain length of the substrate. The Km was independent of chain length for the substrates containing seven or more galacturonic acid units. Both kinetic data and paper chromatographic analyses of degradation products from the different oligomers indicated that the enzyme was an endo-pectic acid lyase. In the presence of 0.002 N Cacl₂, substrate (tetramer through octamer) concentrations above 0.001 N caused inhibition of activity. The role of calcium was studied by measuring enzymic activity at different concentrations of calcium and tetramer. The data indicated that the true substrate for the lyase activity was the calcium salt of tetramer. The observed substrate inhibition was due to competition between the free oligomer and its calcium salt. The dissociation constant (K_i) for the tetramer as an inhibitor was 1.25 mM and the Km for the calcium salt was 0.14 mM. The data also suggested the possible additional role of calcium as an activator for the lyase.     

THE PROTEINS OF WASHED, MINCED FISH MUSCLE HAVE SIGNIFICANT SOLUBILITY IN WATER

After washing the minced muscle tissue of 5 species of white-fleshed fish twice with water and a third time with 0.15% (26 mM) NaCl solution, a considerable, portion of the remaining protein was soluble when extracted with water at a 1:20 ratio. The amount of protein extracted was 20–36% of the protein extracted by buffered 1 M Lid solution, a good protein extractant. This amount of protein indicates that the extracted proteins were primarily myofibrillar. When soluble protein was plotted versus the logarithm of the NaCl concentration in the extracting solution, an inverse linear relationship was observed. The moisture content of the fish paste was related linearly to the log of the water-soluble protein with a correlation coefficient of 0.945. The solubility of the proteins of washed, minced Atlantic mackerel was much less than that of the five white-fleshed species tested.