Nejib Guizani

Thermal characterisation of gelatin extracted from yellowfin tuna skin and commercial mammalian gelatin.

Glass transition and other thermal characteristics of gelatin from different sources were studied by differential scanning calorimetry (DSC) and modulated DSC (MDSC). The initial glass transition temperatures of equilibrated gelatin samples at 11.3% relative humidity, determined from reversible heat flow thermogram of MDSC, were 23, 75 and 59°C, respectively, for tuna skin, bovine and porcine gelatin. When gelatin samples were equilibrated at higher relative humidity of 52.9%, glass transition temperature of fish skin and bovine gelatin decreased to -3 and 57°C, respectively. Further increase of equilibration relative humidity to 75.3% showed increased value in the case of tuna skin, whereas bovine and porcine did not show any significant change. DSC and MDSC results indicated that tuna gelatin showed lower glass transition compared to mammalian source gelatin equilibrated at the same constant relative humidity. In general glass transition measured by DSC was found lower than the values measured by MDSC. The results in this study showed that the degree of plasticization varied with the source of gelatin as well as their extraction methods.

State diagram of tuna meat: freezing curve and glass transition

Abstract The state diagram of tuna meat was developed by measuring and modeling its glass transition temperatures and freezing points. Fresh tuna meat was dried in a freeze drier to vary the moisture content from 73.3% to 6.0% (wet basis). Small deformation dynamic oscillation was employed to identify changes in the viscoelastic properties of tuna as a function of solids. Cooling curve method was used to measure the freezing point and end point of freezing. The state diagram yielded maximally freeze-concentrated solutes at 61% solids with the characteristic temperature of glass formation being −54.2 °C. The freezing curve and glass transition lines were developed using the Clausius–Clapeyron equation adjusted with unfreezable water and Gordon–Taylor model, respectively.

Analysis of cooling curve to determine the end point of freezing

Abstract The cooling curve method used for the measurement of freezing point of food is further analyzed to explore whether it can be used to identify the end point of freezing or glass transition. In this method, slope of the cooling curve is determined and plotted as a function of time to identify the end point of freezing ( T ′ m ). Initially, the slope is decreased and then reached a minimum value, which is identified as the nucleation of ice. Then the slope is increased until the end point of freezing. The end point of freezing is identified when the slope starts to decrease from its highest value or plateau. Sucrose solutions and starch gels were used to measure its T ′ m in identifying validity of the proposed method. The measured values of T ′ m by the proposed method is very close to the literature values.

Pomegranate (Punica granatum) Peel Extract Efficacy as a Dietary Antioxidant against Azoxymethane-Induced Colon Cancer in Rat

Functional foods include antioxidant nutrients which may protect against many human chronic diseases by combating reactive oxygen species (ROS) generation. The purpose of the present study was to investigate the protective effect of pomegranate peel extract (PPE) on azoxymethane (AOM)-induced colon tumors in rats as an in vivo experimental model. Forty Sprague-Dawley rats (4 weeks old) were randomly divided into 4 groups containing 10 rats per group, and were treated with either AOM, PPE, or PPE plus AOM or injected with 0.9% physiological saline solution as a control. At 8 weeks of age, the rats in the AOM and PPE plus AOM groups were injected with 15 mg AOM/kg body weight, once a week for two weeks. After the last AOM injection, the rats were continuously fed ad-libitum their specific diets for another 6 weeks. At the end of the experiment (i.e. at the age of 4 months), all rats were killed and the colon tissues were examined microscopically for lesions suspected of being preneoplastic lesions or tumors as well as for biochemical measurement of oxidative stress indices. The results revealed a lower incidence of aberrant crypt foci in the PPE plus AOM administered group as compared to the AOM group. In addition, PPE blocked the AOM-induced impairment of biochemical indicators of oxidative stress in the examined colonic tissue homogenates. The results suggest that PPE can partially inhibit the development of colonic premalignant lesions in an AOM-induced colorectal carcinogenesis model, by abrogating oxidative stress and improving the redox status of colonic cells.

Instrumental-sensory evaluation of texture for fish sausage and its storage stability

Distinct formulations of fish sausage were developed from commercially underutilized fish caught from the coastal regions of the Sultanate of Oman. The storage stability of the products was evaluated microbiologically at −20°C for 12 weeks and once that was deemed to be satisfactory, quality assessment was implemented. The latter focused on the instrumental and sensory attributes of texture. In a first series of experiments, the level of starch in the formulation was varied from 0 to 48% (w/w of raw fish). Results demonstrated that instrumental hardness correlated strongly with the sensory hardness and both attributes increased in magnitude with higher starch additions to the preparation. However, no correlation was observed for firmness, brittleness and adhesiveness, a result indicating a weakness in the customary definition of these instrumental/sensory attributes for valid implementation of the quantitative descriptive analysis. Finally, affective testing argues that textural desirability is achieved in formulations containing 8% starch, and the overall consumer acceptability is improved further with the addition of selected spices to the product.

MICROBIOLOGICAL, PHYSICOCHEMICAL, AND BIOCHEMICAL CHANGES DURING RIPENING OF CAMEMBERT CHEESE MADE OF PASTEURIZED COW'S MILK

ABSTRACT Camembert cheese was manufactured from pasteurized cows milk by the traditional method in order to determine changes in the microflora, physicochemical, and biochemical characteristics over a 30-day ripening period. The total bacteria counts were high in cheese throughout ripening, with lactic acid bacteria being the main microbial group both on the surface and the center of the curd. However, the microbial activity was more important on the surface than in the center. Each group of microorganisms showed a typical variation during ripening on the surface and in the center. External heterogeneous microflora containing yeasts, molds and halophilic bacteria induced a higher rate of proteolysis and lipolysis on the surface than in the curd of the cheese at the end of ripening (30 days). Migration of salt from the curd reached equilibration after 23 days of ripening. A fast increase in the pH of the surface was observed and the pH differential was maintained between the surface and the center during the ripening period. Rheological analysis demonstrated the softening of Camembert cheese during ripening due to extensive proteolysis.

Papaya epicarp extract protects against hydrogen peroxide-induced oxidative stress in human SH-SY5Y neuronal cells.

Recent studies indicated that regular consumption of antioxidant-rich foods reduces cellular oxidative stress and protects against health-related problems. This study aimed to assess the in vitro antioxidant properties of the papaya epicarp extract against hydrogen peroxide (H2O2)-induced oxidative stress in human SH-SY5Y neuronal cells. Our study revealed that papaya epicarp extract acted as a potent free radical scavenger and provided neuroprotection against H2O2-induced oxidative stress. Papaya epicarp extract ameliorated glutathione depletion, restored total antioxidant capacity and augmented the inhibition of antioxidant enzymes (catalase, glutathione peroxidases and superoxide dismutase). In conclusion, papaya epicarp extract can be used as a functional dietary ingredient that might help in reducing the neurological health problems associated with various oxidative stress insults.

Effects of Salting and Drying on Shark (Carcharhinus sorrah) Meat Quality Characteristics

The effect of drying method and pretreatment with salt on the properties of shark meat was investigated. Water loss during the salting step was faster with dry salting than with brine salting; however, both methods led to the same final water content at the end of the drying process. Moisture desorption isotherms showed that addition of salt prior to sun or air drying resulted in lower equilibrium moisture contents at the same water activity levels. Salting and method of drying had significant effects on the microbial load. Osmo-air-dried samples showed better microbial quality than samples treated by other methods. Molds grew on all samples after two months of storage at room temperature. Color and rehydration ratio were affected by the drying method. Higher dehydration ratios were obtained with air drying.

Nabag (Zizyphus spina-christi) extract prevents aberrant crypt foci development in colons of azoxymethane-treated rats by abrogating oxidative stress and inducing apoptosis.

Zizyphus spina-christi (ZSC) fruit is a rich source of bioactive compounds but any medicinal properties in chemoprevention of colon cancer have hitherto not been studied. The aim of the present study was to examine in vivo protective effects of ZSC water extract on colon carcinogenesis in azoxymethane (AOM)-treated rats. Our results showed that ZSC significantly reduced AOM-induced colonic aberrant crypt foci development and AOM-induced oxidative stress as indicated by restoration of endogenous glutathione depletion and abrogating the impairment of total antioxidant capacity. Caspase-3 cleavage, which has been considered as an apoptotic index, was almost undetectable in AOM-treated rats and ZSC exhibited pro-apoptotic effects evidenced by increased levels of cleaved caspase-3. In the studied model, our findings provide the first in vivo evidence that ZSC extract could inhibit the early stage of colon carcinogenesis by preventing oxidative stress and inducing apoptosis.

Viscoelastic properties of pectin-co-solute mixtures at iso-free-volume states.

Small-deformation oscillatory measurements were performed on pectin-sucrose-glucose syrup systems at a total level of solids of 81%, with the polysaccharide content being fixed at levels of industrial use (1%). The experimental temperature range was between 50 and - 50 degrees C. Analysis of the temperature dependence of viscoelastic processes by the equation of Williams, Landel, and Ferry provides values of fractional free volume for the temperatures covering the glass transition region. The shift factors used in the conversion of mechanical spectra into master curves were normalised at suitably different temperatures so that their temperature dependence becomes coincident. The treatment implies an iso-free-volume state and relates to changes in the monomeric friction coefficient with increasing levels of intermolecular interactions in the mixture. A free-volume related glass transition temperature was defined and manipulated markedly by introducing pectin of variable degrees of esterification to the sucrose-glucose syrup system.