R. Paul Singh

Optimization of Air Drying of Foods

Abstract Several optimization problems related with the air drying of foods are studied: maximization of nutrient or enzyme retention, minimization of process time, maximization of nutrient retention with a constraint on the final retention of an enzyme, and maximization of energy efficiency. These problems are successfully solved for three different model systems using an stochastic optimal control algorithm. The air dry bulb temperature and its relative humidity are used as the control variables. The optimal policies obtained are significantly superior to the classical processes in several cases. This suggests further research in order to experimentally evaluate these advantages.

Modes of Disintegration of Solid Foods in Simulated Gastric Environment

A model stomach system was used to investigate disintegration of various foods in simulated gastric environment. Food disintegration modes and typical disintegration profiles are summarized in this paper. Mechanisms contributing to the disintegration kinetics of different foods were investigated as related to acidity, temperature, and enzymatic effect on the texture and changes in microstructure. Food disintegration was dominated by either fragmentation or erosion, depending on the physical forces acting on food and the cohesive force within the food matrix. The internal cohesive forces changed during digestion as a result of water penetration and acidic and enzymatic hydrolysis. When erosion was dominant, the disintegration data (weight retention vs. disintegration time) may be expressed with exponential, sigmoidal, and delayed-sigmoidal profiles. The different profiles are the result of competition among the rates of water absorption, texture softening, and erosion. A linear-exponential equation was used to describe the different disintegration curves with good fit. Acidity and temperature of gastric juice showed a synergistic effect on carrot softening, while pepsin was the key factor in disintegrating high-protein foods. A study of the change of carrot microstructure during digestion indicated that degradation of the pectin and cell wall was responsible for texture softening that contributed to the sigmoidal profile of carrot disintegration.

Digestion of Raw and Roasted Almonds in Simulated Gastric Environment

Knowledge of digestion kinetics of solid foods in human stomach, as affected by food processing methods, is critical in establishing processing conditions at the manufacturing stage to achieve desirable release of nutrients in the gastrointestinal tract. The objective of this study was to investigate how roasting affected disintegration and solid release properties of almond in simulated gastric environment. In vitro trials were performed for raw and roasted almonds by using static soaking method and a model stomach system. The changes in sample weight, dry mass, and moisture during the trials were determined. Both compression and penetration tests were used to investigate the texture of almonds with a focus on the influence of absorption of gastric juice. Light microscopy and transmission electronic microscopy were used to study the change in microstructure of the raw and roasted almonds after simulated digestion. The results suggested that the slow disintegration rate and the high amount of swelling of the almonds in the stomach may contribute to their high satiety property. Roasting significantly improved the disintegration rates of almonds and increased loss of solids during simulated digestion, which is well correlated with the decrease in the rigidity of almond samples after absorbing gastric juice. Microstructure of digested almonds showed breakage and breach of cell walls due to acid hydrolysis. Intercellular and intracellular channels formed in almonds during roasting are important for penetration of gastric juice that may facilitate an effective digestion.

Solid Loss of Carrots During Simulated Gastric Digestion.

The knowledge of solid loss kinetics of foods during digestion is crucial for understanding the factors that constrain the release of nutrients from the food matrix and their fate of digestion. The objective of this study was to investigate the solid loss of carrots during simulated gastric digestion as affected by pH, temperature, viscosity of gastric fluids, mechanical force present in stomach, and cooking. Cylindrical carrot samples were tested by static soaking method and using a model stomach system. The weight retention, moisture, and loss of dry mass were determined. The results indicated that acid hydrolysis is critical for an efficient mass transfer and carrot digestion. Internal resistance rather than external resistance is dominant in the transfer of soluble solids from carrot to gastric fluid. Increase in viscosity of gastric fluid by adding 0.5% gum (w/w) significantly increased the external resistance and decreased mass transfer rate of carrots in static soaking. When mechanical force was not present, 61% of the solids in the raw carrot samples were released into gastric fluid after 4xa0h of static soaking in simulated gastric juice. Mechanical force significantly increased solid loss by causing surface erosion. Boiling increased the disintegration of carrot during digestion that may favor the loss of solids meanwhile reducing the amount of solids available for loss in gastric juice. Weibull function was successfully used to describe the solid loss of carrot during simulated digestion. The effective diffusion coefficients of solids were calculated using the Fick’s second law of diffusion for an infinite cylinder, which are between 0.75u2009×u200910−11 and 8.72u2009×u200910−11xa0m2/s, depending on the pH of the gastric fluid.

Gastric emptying rate and chyme characteristics for cooked brown and white rice meals in vivo.

BACKGROUNDnRice structure is important to rice grain and starch breakdown during digestion. The objective of this study was to determine the gastric emptying and rice composition during gastric digestion of cooked brown and white medium-grain (Calrose variety) rice using the growing pig as a model for the adult human.nnnRESULTSnBrown and white rice did not show significantly different gastric emptying rates of dry matter or starch, but brown rice had slower protein emptying (P < 0.05). Moisture content was greater and pH was lower in the distal stomach compared to the proximal stomach (P < 0.0001), and varied with time (P < 0.0001). The mechanism of physical breakdown for brown and white rice varied. Brown rice exhibited an accumulation of bran layer fragments in the distal stomach, quantified by lower starch and higher protein content.nnnCONCLUSIONnThe quantity of gastric secretions observed after a brown or white rice meal may be related to the meal buffering capacity, and are accumulated in the distal stomach. The delayed rate of protein emptying in brown rice compared to white rice was most likely due to the accumulation of bran layers in the stomach.

Optimal control of heat and mass transfer in food and bioproducts processing

Abstract Many processes in the food and bioproducts industry are of the batch type. The increased public awareness about product quality and environmental impact has stressed the need to improve this processes. This can be achieved using computer-aided optimal control methods. The selection of an appropriate algorithm is therefore critical. The advantages of alternative discretized decision methods over the traditional maximum principle have been indicated in the literature. Following these ideas, we have developed a computer package, ICRS/DS ( I ntegrated C ontrolled R andom S earch for D ynamic S ystems) for the optimization (optimal control) of batch processes, including distributed parameter systems. In a first step, the original optimal control problem is transformed in a constrained nonlinear optimization problem using an adequate parameterization of the control function(s). Finite differences/finite elements methods are used for the solution of PDEs. In a second step, the constrained NLP problem is solved using a stochastic optimization algorithm. This procedure assures convergence with reasonable computation times. Two important operations were optimized using this algorithm: thermal processing of canned foods and air dehydration of bioproducts. Different objective functions (overall nutrient retention, quality factor retention, process time, energy efficiency, etc.), control functions and constraints were considered, resulting in several complex optimal control problems. In all cases, ICRS/DS proved to be a reliable and easy-to-use computational tool. In many cases, the calculated optimal control policies have significant advantages over the present operation conditions.

Dynamic optimization of double-sided cooking of meat patties

Optimal operating procedures for double-sided cooking of frozen hamburger patties were computed using dynamic optimization techniques. The mathematical statement was to find the optimal control (e.g., heating surface temperature) over cooking time to minimize (or maximize) the performance index J, for example minimize cooking loss, and to ensure the required lethality and safe cooking temperature. The control vector parameterization framework was applied, and stochastic algorithm was used to locate the global optimum with reasonable computation effort (Integrated Controlled Random Search for Dynamic Systems). The performance index improved when the heating temperature profile was considered as control variable and when two control elements of variable size were used (compared with the constant-temperature process or nominal case, ΔJ<3%). When the lower bound was relaxed and two control elements were used, the performance index improved significantly (ΔJ<7%). However, when the top and bottom plate temperatures were considered as two different controls, the plate temperature profiles obtained did not significantly improve the results compared with the nominal cases. When the temperature of the top and bottom plates and gap thickness were considered as control variables, and when two control elements of variable size for gap thickness were used, the performance index improved for long periods of cooking time (ΔJ<2.5%).

Properties of Gastric Chyme from Pigs Fed Cooked Brown or White Rice

Specific effects of food processing on food digestion remain to be clearly established. The objective of this study was to determine the effect of rice processing (cooked brown and white rice) on the rheological properties, chemical composition (water, starch, fiber, protein) and pH of gastric chyme in pigs over a two hour post-ingestion period in the proximal and distal regions of the stomach. Results showed the distal region having a higher moisture content, lower pH, and lower viscosity compared to the proximal region for both brown and white rice. Starch content was significantly affected by the region x time x rice interaction (pu2009=u20090.0259), protein content by both the rice x time (pu2009=u20090.0143) and the region x time (pu2009=u20090.0181) interactions, and total dietary fiber by rice type (pu2009=u20090.005). Rice digesta behaved as a gel, with G’ (42288–1911xa0Pa) greater than G” (6307–360xa0Pa). The extent of particle breakdown for brown and white rice was different. Overall, the results indicated a connection between food processing and food breakdown during gastric digestion. These findings have implications in the management of nutrient absorption and satiety control that can be used in future food design.

Particle Size Distribution of Brown and White Rice during Gastric Digestion Measured by Image Analysis

The particle size distribution of foods during gastric digestion indicates the amount of physical breakdown that occurred due to the peristaltic movement of the stomach walls in addition to the breakdown that initially occurred during oral processing. The objective of this study was to present an image analysis technique that was rapid, simple, and could distinguish between food components (that is, rice kernel and bran layer in brown rice). The technique was used to quantify particle breakdown of brown and white rice during gastric digestion in growing pigs (used as a model for an adult human) over 480 min of digestion. The particle area distributions were fit to a Rosin-Rammler distribution function. Brown and white rice exhibited considerable breakdown as the number of particles per image decreased over time. The median particle area (x(50)) increased during digestion, suggesting a gastric sieving phenomenon, where small particles were emptied and larger particles were retained for additional breakdown. Brown rice breakdown was further quantified by an examination of the bran layer fragments and rice grain pieces. The percentage of total particle area composed of bran layer fragments was greater in the distal stomach than the proximal stomach in the first 120 min of digestion. The results of this study showed that image analysis may be used to quantify particle breakdown of a soft food product during gastric digestion, discriminate between different food components, and help to clarify the role of food structure and processing in food breakdown during gastric digestion.

Physical Property Changes in Raw and Roasted Almonds during Gastric Digestion In vivo and In vitro

The rate of almond breakdown during gastric digestion may be influenced by structural changes that occur during roasting. The primary objective of this study was to investigate in vivo physical property changes of raw and roasted almonds during gastric digestion, using the growing pig as a model for an adult human. Seventy two male pigs were fed a meal of raw or roasted almonds and digested samples were taken 20, 60, 180, 300, 480, and 720xa0min after meal consumption from the proximal and distal stomach regions. Particle size distribution, rheological flow behavior, and textural attributes of gastric digesta were measured. Particle size distributions were fit to the Rosin-Rammler function to determine the median particle diameter (x50) and distribution spread (b) parameters. Median particle diameter was statistically influenced by stomach region (pu2009<u20090.0001). Evidence of gastric sieving was observed by an increased median particle diameter and narrower distribution spread in the distal region. To elucidate on textural changes of diced almonds during digestion, an in vitro study was conducted in a static gastric environment. Results indicated that a majority of textural changes occurred during the first hour of digestion, a trend unobserved in the in vivo trial. No significant differences in physical property changes were observed between raw and roasted almonds during gastric digestion in vivo as measured by particle size distribution, textural attributes, and rheological flow behavior. This suggests that raw and roasted almonds break down at a similar rate in the gastric environment.