Moncef Chouaibi

The Influence of Season on the Gonad Index and BiochemicalComposition of the Sea Urchin Paracentrotus lividus from the Golfof Tunis

Seasonal variation in the gonad weight and biochemical composition of the sea urchin Paracentrotus lividus from the Golf of Tunis (Tunisia) were studied between September 2003 and August 2004. The highest gonad indices occurred in March (16.71%). The spawning period occurred between April and July and resulted in a fall in gonad indices to low level (7.12 ± 0.12%). Protein constituted the main component of the gonad, and lipid and carbohydrate were found at appreciable amounts. Consistent with the gonad cycle, sea urchin biochemical components showed clear seasonal variation with a significant decrease during the spawning period. The polyunsaturated fatty acid (PUFA) group was found at high level (40% of the total fatty acids). Of the PUFA group, eicosapentaenoic (C20:5 n − 3) and eicosatetraenoic (C20:4 n − 3) were the most abundant gonadal lipids. The level of PUFA was significantly affected by temperature variation showing an increase during the cold months and a decrease in the hot months.

Effectiveness of almond gum trees exudate as a novel edible coating for improving postharvest quality of tomato (Solanum lycopersicum L.) fruits

The use of coatings is a technique used to increase postharvest life of the fruit. Almond gum exudate was used, in comparison with gum arabic, at concentrations of 10% as a novel edible coating, to preserve the quality parameters of tomato (Solanumlycopersicum). Fruits were harvested at the mature-green stage of ripening. Results showed that the coatings delayed significantly (p < 0.05) the changes in color, weight loss, firmness, titratable acidity, ascorbic acid content, soluble solids concentration, and decay percentage compared to uncoated control fruits. Sensory evaluation proved the efficacy of 10% almond gum and gum arabic coatings to maintain the overall quality of tomato fruits during storage period (20 days). In addition, the difference between gum arabic and almond gum coatings was not significant (p > 0.05) except for pulp color. Therefore, we can suggest the use of almond gum exudate as a novel edible coating extends the shelf-life of tomato fruits on postharvest.

Pumpkin (Cucurbita maxima) Seed Proteins: Sequential Extraction Processing and Fraction Characterization

Seed proteins extracted from Tunisian pumpkin seeds ( Cucurbita maxima ) were investigated for their solubility properties and sequentially extracted according to the Osborne procedure. The solubility of pumpkin proteins from seed flour was greatly influenced by pH changes and ionic strength, with higher values in the alkaline pH regions. It also depends on the seed defatting solvent. Protein solubility was decreased by using chloroform/methanol (CM) for lipid extraction instead of pentane (P). On the basis of differential solubility fractionation and depending on the defatting method, the alkali extract (AE) was the major fraction (42.1 (P), 22.3% (CM)) compared to the salt extract (8.6 (P), 7.5% (CM)). In salt, alkali, and isopropanol extracts, all essential amino acids with the exceptions of threonine and lysine met the minimum requirements for preschool children (FAO/WHO/UNU). The denaturation temperatures were 96.6 and 93.4 °C for salt and alkali extracts, respectively. Pumpkin protein extracts with unique protein profiles and higher denaturation temperatures could impart novel characteristics when used as food ingredients.

Nutritional composition of Zizyphus lotus L. seeds

BACKGROUND Zizyphus lotus seeds are an unutilized source of vegetable oil and protein and nothing has been reported on their physicochemical characteristics which would indicate the potential uses of these seeds. RESULTS The percentage composition of the Zizyphus lotus seeds is (on a dry-weight basis): ash 1.05%, oil 32.92%, protein 19.11%, total carbohydrate 40.87% and moisture 6.05%. Calcium, potassium and magnesium constitute the major minerals of Zizyphus lotus seeds. The seed proteins are rich in threonine, glutamic acid, leucine, arginine and aspartic acid (26.73%, 17.28%, 13.11%, 9.47% and 7.76%, respectively). The main fatty acids of the oil are oleic (61.93%), linoleic (18.31%) and palmitic (9.14%) acids. Glycerol trioleate (OOO; O: oleic acid) was the most abundant triacylglycerol, representing 26.48% of the total triacyglycerols. β-Tocopherol was the major tocopherol (130.47 mg 100 g(-1) ). This oil was rich in Δ7-campestrol and β-sitosterol (147.82 and 82.10 mg 100 g(-1) oil), respectively. CONCLUSION Zizyphus lotus seeds are rich in fat and protein which are of potential industrial significance. In addition, Zizyphus lotus L. seed oil contained many bioactive compounds. This fact is of great economic interest owing to several applications of Zizyphus lotus L. seeds in the food, cosmetics and medicinal industries.

A Comparative Study on Physicochemical, Rheological and Surface Tension Properties of Tunisian Jujube (Zizyphus lotus L.) Seed and Vegetable Oils

The physicochemical, rheological, surface tension and emulsifying properties of Tunisian jujube (Zizyphus lotus L.) seed oil were investigated and compared with six edible vegetable oils ( olive, corn, soybean, sunflower, groundnut and rapeseed). These results showed that total phospholipids and total tocopherols contents were significantly higher (P < 0.05) in jujube seed oil than those in edible vegetable oils. It was also shown that all oil samples exhibited Newtonian behaviors at shear rate ranged from 10 to 1000 s-1 and the highest viscosity η was observed in jujube seed oil, followed by olive, rapeseed, groundnut, corn, soybean and sunflower oils. In addition, the interfacial tension value of jujube seed oil was significantly lower (17.56 mN/m) than the corresponding of edible vegetable oils. The emulsions were prepared with different type of oil samples and they were kept for 60 days under 4, 30 and 55 °C for stability test. Our results showed that mean droplet size d4,3 of jujube seed oil emulsion was significantly smaller ( P < 0.05) than those of vegetable oils studied. Moreover, jujube seed oil emulsions were stable for 2 months with an average diameter of 213.34 nm. According to the results, jujube seed oil has rheological, interfacial tension, and emulsifying properties that may become interesting for specific applications in several segments of food, cosmetic, pharmaceutical and agrichemical industries.

Functional Properties of Protein Fractions Obtained from Pumpkin (Cucurbita Maxima) Seed

Protein fractions were extracted from pumpkin (Cucurbita maxima) seeds with deionized water, salt solution, and alkali solution, and characterized under alkaline (pH 8) and ionic strength conditions for protein solubility, interfacial pressure, and functional properties. The supernatants obtained from the protein fractions after hydration and centrifugation were designed deionized water supernatant, salt solution supernatant, and alkali solution supernatant. All protein fractions showed poor foamability and very low stability. The designed deionized water supernatant presented the highest emulsifying properties. In terms of stability, designed deionized water supernatant emulsions flocculate during storage but with low rates of coalescence compared to the two other fractions.

Physicochemical, Rheological, and Thermal Properties of Six Types of Honey from Various Floral Origins in Tunisia

The present study was undertaken to determine the physicochemical, rheological, and thermal properties of six types of Tunisian honey samples from various floral origins (eucalyptus, orange, thyme, mint, rosemary, and horehound). All the honey samples exhibited non-Newtonian behavior at a shear rate ranging between 0.01 and 500 s–1, with the highest levels of viscosity (µ) being observed for thyme, followed by eucalyptus, rosemary, mint, orange, and horehound honeys, respectively. The effect of temperature on the dynamic viscosity of the samples followed an Arrhenius-like pattern, with activation energy values ranging from 21.23 to 34.91 kJ/mol. The results from oscillatory rheology analysis also revealed that the loss modulus predominated over the storage one in the whole frequency range. As determined by differential scanning calorimetry, the glass transition (Tg) and melting temperatures of the Tunisian honey samples varied between –41.55 and –47.06 °C and between 197.9 and 221.1°C depending on their sugar compositions, respectively.

Extraction of Polysaccharide From Zizyphus Lotus Fruits

Abstract In this study, response surface methodology (RSM) was used to optimize the extraction conditions of polysaccharides from the pulp of Zizyphus lotus fruit. A central composite rotatable design (CCRD) was used for experimental design and analysis of the results to obtain the optimal processing parameters. Ethanol concentration, extraction temperature, extraction time and water to raw material ratio were found to have a significant effect ( p < 0.05) on the yield of Zizyphus lotus polysaccharide. The 3-D response surface and contour plots, derived from the mathematical model, were applied to determine the optimal conditions. The optimum conditions were as follows: water to raw material ratio 22.04:1, ethanol concentration of 83.30 %, extraction time of 2.65 h, and extraction temperature of 66.31 °C. Under these conditions, the experimental percentage value was 17.35±0.07 %, which is in well close agreement with the value predicted by the model (17.29 %). The results of physicochemical analysis showed that the main sugar composition of Zizyphus lotus polysaccharide, purified by Sephadex G-75 gel permeation chromatography, was glucose followed by arabinose, mannose and rhamnose.