Mohammad Shafiur Rahman

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.

Food Stability Beyond Water Activity and Glass Transtion: Macro-Micro Region Concept in the State Diagram

The water activity concept proposed that a food product is the most stable at its monolayer moisture content. Recently, the limitations of the water activity concept were identified and the glass transition concept was proposed in order to overcome the limitations of water activity. Based on the glass-transition concept, a food is the most stable at and below its glass transition point. Recently it has also become evident that the glass transition concept is not universally valid for stability determination when foods are stored under different conditions. The glass transition concept was used to develop the state diagram by drawing another stability map using freezing curve and glass line. Currently, other components indicating different characteristics are being included in the state diagram. It is being emphasized in the literature to combine the water activity and glass transition concepts. In this paper, an attempt is made to combine these two concepts in the state diagram and to propose a macro-micro region concept for determining the stability of foods.

Allicin and Other Functional Active Components in Garlic: Health Benefits and Bioavailability

Traditionally, the medical properties of garlic were recognized as early as 3000 BC. The functional benefits of garlic are its antimicrobial activity, anticancer activity, antioxidant activity, ability to reduce cardiovascular diseases, improving immune functions, and anti-diabetic activity. Recent studies identify the active functional components providing the medicinal benefits, as well as their mechanisms of action including the best possible ways to consume garlic. Allicin (diallyl-thiosulfinate) is one of the major organosulfur compounds in garlic considered to be biologically active. In this article, I review the chemistry of allicin and its stability during processing and storage, in-vivo and in-vitro functionality of allicin, and other functional components. In addition, I explore other potential alternative approaches of making its derivatives and their use for health benefits.

An improved thermal conductivity prediction model for fruits and vegetables as a function of temperature, water content and porosity

Abstract An improved general thermal conductivity prediction model has been developed for fruits and vegetables as a function of water content, porosity and temperature. Thermal conductivity values of apple, pear, com starch, raisin and potato were used to develop the model using 164 data points obtained from the literature. Raisin has the maximum mean percent deviation of 15.1% (standard deviation 10.1) and pear gave minimum mean percent deviation of 6.8% (standard deviation 7.3). The errors for predicting the thermal conductivity using this improved model for fruits and vegetables are therefore within the range of 6.8–15.1%, which is acceptable for general engineering practice.

Freezing‐Melting Process and Desalination: I. Review of the State‐of‐the‐Art

Abstract A thorough literature survey was conducted on the freezing‐melting (FM) process for desalination. Collected literatures were studied and analyzed to identify the current state‐of‐the‐art of the FM process, and its practical limitations. The main advantages of the FM process are the requirement of low energy and low temperature operation compared to thermal desalination. Other advantages are less scaling or fouling and fewer corrosion problems, ability to use inexpensive plastics or low‐cost material, and absence of pretreatment. The three broad classes of FM process are: direct contact freezing, indirect contact freezing, and vacuum freezing. Different types of processing options in each class are discussed with their operating principles and merits and downsides of each process.

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.

Dynamic Isopiestic Method (DIM): Measuring Moisture Sorption Isotherm of Freeze-Dried Garlic Powder and Other Potential Uses of DIM

Moisture sorption (adsorption and desorption) isotherm of freeze-dried garlic powder was measured by static and dynamic isopiestic methods. Isotherms measured by static isopiestic method produced deviations from the dynamic method at the lower and higher water activity ranges. Dynamic method showed that the temperature had more effects on desorption isotherms compared to the adsorption isotherm, and the degree of isotherm hysteresis reduced with the increase of equilibration temperature. The isotherm was fitted with BET, GAB, and Norrish models. Critical evaluations on the physical meaning of the model parameters are presented. The dynamic method has the potential to be used in studying other structural and drying characteristics of foods.Moisture sorption (adsorption and desorption) isotherm of freeze-dried garlic powder was measured by static and dynamic isopiestic methods. Isotherms measured by static isopiestic method produced deviations from the dynamic method at the lower and higher water activity ranges. Dynamic method showed that the temperature had more effects on desorption isotherms compared to the adsorption isotherm, and the degree of isotherm hysteresis reduced with the increase of equilibration temperature. The isotherm was fitted with BET, GAB, and Norrish models. Critical evaluations on the physical meaning of the model parameters are presented. The dynamic method has the potential to be used in studying other structural and drying characteristics of foods.

Instrumental texture profile analysis of gelatin gel extracted from grouper skin and commercial (bovine and porcine) gelatin gels

Mechanical compression was used to study the gelling characteristics of gelatin gels. Texture profile analysis (TPA) showed that the hardness of fish and mammalian gelatin increased significantly as the concentrations of gels increased. TPA attributes of 10% fish skin gel showed significant differences from those obtained from 20% and 30% gels. In bovine and porcine cases, such generic trends were not observed. Mechanical characteristics of 10% gels of gelatin from fish skin, determined from one cycle compression, were significantly lower than other sources of gelatin gels, while bovine and porcine gels did not show any significant differences. In the case of TPA, hardness of bovine gelatin gel was highest at 41 N for 10% gel, followed by porcine (30 N) then fish skin (5 N) gelatin gels. The gels prepared from different sources did not show any generic trends when all other mechanical attributes were considered.

A structural generic model to predict the effective thermal conductivity of fruits and vegetables during drying

A generic structural model to predict the effective thermal conductivity of fruits and vegetables during drying is proposed. The model was applied successfully in the case of apple. It combines a generic structural model for shrinkage and the distribution factor concept for thermal conductivity. The shrinkage coefficient and the distribution factor were used to develop the proposed physical model. Apparent density and thermal conductivity of the material can be calculated as a function of material moisture content and temperature using a minimum number of material characteristics.