Gopirajah Rajamanickam | Tamil Nadu Agricultural University (original) (raw)

Papers by Gopirajah Rajamanickam

Different models were developed to substitute in vivo studies on gastric digestion of food (for e... more Different models were developed to substitute in vivo studies on gastric digestion of food (for evaluating bio-accessibility) or pharmaceutical formulations (to determine release of active ingredients). However, selecting a suitable method widely depends on operating conditions and how close the model predicts the actual phenomenon occurring. Digestion is well studied in terms of gastric secretion and enzymatic breakdown of food components, but the disintegration kinetics of food and the release of embedded nutrients from the food matrix with effect on various processing conditions still require more attention. This is because, most of the reported models are focused on physiochemical changes during digestion without considering the physical forces exerted on food by accounting actual shape and motility of the stomach. Recently, computational techniques were found to provide unique insight on gastric digestion with its ability to reproduce actual shape and motility of the stomach. All these models help to formulate food and pharmaceuticals. With this background, these comprehensive reviews focustonarrowdown differentgastricmodelsandtheircapabilitieswithmeritsanddemeritstoassistresearchers,manufacturers, and pharmaceutics to select a suitable method for evaluation. This review also includes the latest developments in the area of the computational modeling, particle disintegration, gastric emptying and release of nutrients from food microstructure.

Tef with different oat blend ratio was processed in a single screw extruder and evaluated for opt... more Tef with different oat blend ratio was processed in a single screw extruder and evaluated for optimum physical and protein quality. Effects of oat level (0-30%), feed moisture content (12-16%), extruder die temperature (DT) (80-140 8C), and screw speed (SS) (80-200 rpm) on the extrudate characteristics were investigated using Box-Behnken design. The addition of oat level above 15% increased the extrudate protein availability and water absorption capacity. DT greater than 110 8C and feed moistures greater than 14% results in a steep increase in expansion ratio. The pasting property of tef flour showed higher initial (56 cP) and final viscosity (102 cP) than oat flour with 48 cP initial viscosity and 56 cP final viscosity. In conclusion, tef with 29% oat blend, 16% feed moisture, 140 8C DT, and 80 rpm SS gave an optimum product with high desirability (>0.8). Practical applications The demand for healthy snack formulation with low glycemic index is increasing with the snack industry. Extrusion cooking provides control on minimising the nutrient loss with improved functional qualities. The study provides new experimental data of extrusion process parameters for teff and oat flour formulation. The effect of extrusion process conditions on the extrudate physical and protein quality was optimized using response surface methodology. The pasting profile and gelati-nization temperature of tef-oat formulation indicated their potential application in food textural modifications. The results obtained will be of great significance for formulation and development of healthy snack with minimal loss of nutrients during processing.

Response surface methodology (RSM) based on a five-level-three-factor central composite rotatable... more Response surface methodology (RSM) based on a five-level-three-factor central composite rotatable design (CCRD) was employed for optimisation of formulation for production of a soy-fortified millet-based extruded snack. Effects of amount of ingredients such as ragi (40-50%), sorghum (10-20%) and soy (5-15%) on the physical properties like bulk density, expansion ratio, water absorption index and water solubility index of snacks were investigated. Significant regression models that explained the effects of different percentages of ragi, sorghum and soy on all response variables were determined. The coefficients of determination, R 2 , of all the response variables were higher than 0.90. Based on the given criteria for optimisation, the basic formulation for production of millet-based extruded snack with desired sensory quality was obtained by incorporating with 42.03% ragi, 14.95% sorghum, 12.97% soy and 30% rice.

The chief motor functions of human stomach, namely receiving, storing, mixing and emptying, influ... more The chief motor functions of human stomach, namely receiving, storing, mixing and emptying, influence the absorption of ingested food and hence determine the glycemic response to the meal. However, among these functions, the gastric emptying pattern of the stomach is essentially regulated by the meal characteristics such as particle size, volume, nutrient composition and viscosity. Understanding the complex relationship between the stomach motor functions and the physicochemical characteristics of meal on glycemic control needs more attention in the formulation of functional foods. Hence, the objective of this study is to employ the magnetic resonance imaging (MRI) technique in ten healthy human volunteers to elucidate the relationship between the motor functions of the stomach and the glycemic response to fibre rich foods. For this, wheat and oat based breakfast meals were selected as fibre rich foods with low (0.042 Pa s) and high (0.266 Pa s) viscosity, respectively. Although wheat meal had a lower viscosity compared to oatmeal, the gastric emptying was found to be delayed for the former due to its high caloric density. This was reflected in the glycemic response as well, with wheat meal having a lower area under the curve (AUC) value than oatmeal. The antral contraction frequency is significantly reduced (P < 0.05) with delayed gastric emptying in the case of high nutrient wheat meal. Overall, the study demonstrated the synergistic effect of gastric emptying, stomach motor functions and physicochemical characteristics of food on the glycemic response to a meal. This information will aid in the development of functional foods with specific end applications.

The physical forces exerted by the stomach break down the food particles mechanically facilitatin... more The physical forces exerted by the stomach break down the food particles mechanically facilitating digestion and absorption. Such mechanical action occurs by the powerful peristaltic contractions along the stomach wall, known as gastric motor function. Several in vitro models are developed to understand this mechanical digestion of food particle breakdown. However, the fluid mechanical forces that determine the pressure and flow fields with the effect on shear stress, dispersing food particles remains overlooked. Modern imaging techniques such as magnetic resonance imaging, computed tomogra-phy scan and ultrasound help to visualize the digestion process involving mixing, dilution and dispersion of food. On the other hand, advances in computational methods have proven effective in predicting the interaction between gastric functions and food physical properties. The review discusses the novel imaging and modeling techniques to understand the stomach physical forces that gives information on designing a food formulation (e.g., functional foods) at manufacture stage, targeted for a particular purpose.

Tef with different oat blend ratio was processed in a single screw extruder and evaluated for opt... more Tef with different oat blend ratio was processed in a single screw extruder and evaluated for optimum physical and protein quality. Effects of oat level (0–30%), feed moisture content (12–16%), extruder die temperature (DT) (80–140 8C), and screw speed (SS) (80–200 rpm) on the extrudate characteristics were investigated using Box–Behnken design. The addition of oat level above 15% increased the extrudate protein availability and water absorption capacity. DT greater than 110 8C and feed moistures greater than 14% results in a steep increase in expansion ratio. The pasting property of tef flour showed higher initial (56 cP) and final viscosity (102 cP) than oat flour with 48 cP initial viscosity and 56 cP final viscosity. In conclusion, tef with 29% oat blend, 16% feed moisture, 140 8C DT, and 80 rpm SS gave an optimum product with high desirability (>0.8). Practical applications The demand for healthy snack formulation with low glycemic index is increasing with the snack industry. Extrusion cooking provides control on minimising the nutrient loss with improved functional qualities. The study provides new experimental data of extrusion process parameters for teff and oat flour formulation. The effect of extrusion process conditions on the extrudate physical and protein quality was optimized using response surface methodology. The pasting profile and gelati-nization temperature of tef-oat formulation indicated their potential application in food textural modifications. The results obtained will be of great significance for formulation and development of healthy snack with minimal loss of nutrients during processing.

Fruits and vegetables are porous in nature and undergo pronounced shrinkage during convective dry... more Fruits and vegetables are porous in nature and undergo pronounced shrinkage during convective drying process. Therefore, shrinkage and porosity should be taken into consideration while predicting heat and mass transfer. This work was conducted to study shrinkage and porosity changes along with simultaneous heat and mass transport during the process. Potato slices were subjected to drying for 7 h at 62 °C. It was observed that shrinkage varies linearly with respect to moisture content and reduction in radial dimension of potato slices was around 35%. Porosity undergoes rapid increase after attaining certain moisture content in final stages of drying. The work was extended to study the influence of shrinkage and porosity on heat and mass transfer. Simulated results were validated with experimental values. This model can be employed to predict temperature, moisture, density profiles and to study shrinkage and porosity of various fruits and vegetables.

Tef with different oat blend ratio was processed in a single screw extruder and evaluated for opt... more Tef with different oat blend ratio was processed in a single screw extruder and evaluated for optimum physical and protein quality. Effects of oat level (0–30%), feed moisture content (12–16%), extruder die temperature (DT) (80–140 8C), and screw speed (SS) (80–200 rpm) on the extrudate characteristics were investigated using Box–Behnken design. The addition of oat level above 15% increased the extrudate protein availability and water absorption capacity. DT greater than 110 8C and feed moistures greater than 14% results in a steep increase in expansion ratio. The pasting property of tef flour showed higher initial (56 cP) and final viscosity (102 cP) than oat flour with 48 cP initial viscosity and 56 cP final viscosity. In conclusion, tef with 29% oat blend, 16% feed moisture, 140 8C DT, and 80 rpm SS gave an optimum product with high desirability (>0.8). Practical applications The demand for healthy snack formulation with low glycemic index is increasing with the snack industry. Extrusion cooking provides control on minimising the nutrient loss with improved functional qualities. The study provides new experimental data of extrusion process parameters for teff and oat flour formulation. The effect of extrusion process conditions on the extrudate physical and protein quality was optimized using response surface methodology. The pasting profile and gelati-nization temperature of tef-oat formulation indicated their potential application in food textural modifications. The results obtained will be of great significance for formulation and development of healthy snack with minimal loss of nutrients during processing.