Modeling the hydration step of the rice ( Oryza sativa ) parboiling process

Hydration behavior and kinetic studies of paddy cultivars: optimization of process variables for improved physical, milling and textural properties

The optimization of hydration temperature and duration were determined in six basmati and non-basmati paddy cultivars varying in grain size, shape, and amylose content based on kinetic parameters and effect of hydration temperature on physical, milling, textural and color attributes. Based on higher R2, lower Chi square and RMSE values, Peleg model fitted more suitably compared to Singh and Kulshrestha model. Hydration process significantly altered geometric, gravimetric and mechanical properties as evident by regression analysis. Physical properties except length and L/B ratio positively correlated with increasing hydration temperature. Head rice yield significantly improved in the hydrated treatments and showed a linear increase with the increase in hydration temperature. Head rice yield significantly correlated with hardness of grain (r = 0.684, p ≤ 0.01). Variable physico-chemical properties of cultivars led to establishment of cultivar specific optimum hydration temperature. Based on improvement in hardness, milling efficiency, head rice yield, color and textural attributes, the optimized temperature emerged as 75 °C for long slender grained cultivars (PB1509, PB1718, PS17) and 80 °C for medium grained cultivars (PD18, KJ, AL). The results revealed that optimum hydration temperature should be cultivar specific to get better output of parboiling process.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-024-05925-1.

Drying kinetics and quality dynamics of ultrasound-assisted dried selenium-enriched germinated black rice

Black rice is a functional food due to its higher protein, fiber, iron, antioxidant compounds, and other health benefits than traditional rice. The ultrasonic (US) pretreatments (10, 20, and 50 min) followed by hot-air drying (50, 60, and 70 °C) were applied to study the drying kinetics, mathematical modeling, thermodynamics, microstructure, bioactive profile, volatile compounds and to lock the nutritional composition of selenium-enriched germinated black rice (SeGBR). Ultrasonic-treated samples exhibited a 20.5% reduced drying time than control ones. The Hii model accurately describes the drying kinetics of SeGBR with the highest R2 (>0.997 to 1.00) among the fifteen studied models. The activation energy values in US-SeGBR varied from 3.97 to 13.90 kJ/mol, while the specific energy consumption ranged from 6.45 to 12.32 kWh/kg, which was lower than untreated. The obtained thermodynamic attributes of dried black rice revealed that the process was endothermic and non-spontaneous. Gallic acid, kaempferol, and cyanidin 3-glucoside were present in high concentrations in phenolics, flavonoids, and anthocyanins, respectively. The HS-SPME-GC-MS investigation detected and quantified 55 volatile compounds. The US-treated SeGBR had more volatile compounds, which may stimulate the release of more flavorful substances. The scanning electronic micrograph shows that the US-treated samples absorbed high water through several micro-cavities. Selenium concentration was significantly higher in US-treated samples at 50 °C than in control samples. In conclusion, ultrasound-assisted hot-air drying accelerated drying and improved SeGBR quality, which is crucial for the food industry and global promotion of this healthiest rice variety.

Bioactive Nutrient Retention during Thermal-Assisted Hydration of Lupins

Lupin, an arid pulse, is gaining popularity as a super food due to its superior nutritional properties. However, it has not been considered for large scale thermal processing, e.g., canning. The present work evaluated the best time/temperature combination to hydrate lupins for canning with minimum losses of bioactive nutrients, pre-biotic fibre, and total solids during hydration. The two lupin species showed a sigmoidal hydration behaviour, which was adequately modelled by the Weibull distribution. The effective diffusivity, D_eff, increased from 7.41 × 10^-11 to 2.08 × 10^-10 m²/s for L. albus and 1.75 × 10^-10 to 1.02 × 10^-9 m²/s for L. angustifolius with increasing temperature, namely, from 25 °C to 85 °C. The lag phase decreased from 145 min to 56 min in L. albus and 61 min to 28 min in L. angustifolius. However, based on the effective hydration rate, reaching the equilibrium moisture, minimum loss of the solids, and prebiotic fibre and phytochemicals, 200 min hydration at 65 °C can be regarded as the optimum temperature of hydration. The findings are thus relevant for designing the hydration protocol to achieve the maximum equilibrium moisture content and yield with the minimum loss of solids (phytochemicals and prebiotic fibres) for L. albus and L. angustifolius.

Impact of chemical modification by immersion with malic acid on the physicochemical properties and resistant starch formation in rice

The effects of immersion time on the physicochemical properties and resistant starch (RS) formation of malic acid-treated rice were investigated. Malic acid treatment decreased the frequency of cracks within the rice kernel. The color (lightness) was significantly affected by the immersion time, reflecting the browning of rice. The degree of substitution gradually increased with the immersion time and reached a plateau after 12 h, and the intensity of the C=O bond peak detected in the Fourier-transform infrared spectroscopy showed a similar trend. However, the crystallinity of rice decreased as the immersion time increased, which was confirmed by the X-ray diffraction and thermal transition properties. A gradual increase in RS was observed as the immersion time and DS increased, ranging from 44.5% to 73.3%, reaching a maximum after 12 h of immersion. Therefore, 12 h was determined to be the optimal immersion time for maximizing RS content. This information about the structural characteristics and heat-stable properties of malic acid-treated rice in starch digestion can be used to develop a low-digestible food ingredient and lead to further application of the study. PRACTICAL APPLICATION: This study reported the preparation and physicochemical properties of malic acid-treated resistant starch with different immersion times. This information could contribute to the structural characterization of resistant starch and the development of low-calorie processed rice products.

Sono-hydro priming process (ultrasound modulated hydration): Modelling hydration kinetic during paddy germination

Application of ultrasound technology in modulating the hydration process during paddy germination was analyzed in this study. The effect of hydropriming (24 h) and sono-hydro priming (ultrasound priming, 12 h) on the hydration behaviour of paddies was determined at different temperatures (25-40 °C). Ultrasound pulse was applied for 10 min after every one hour for sono-hydro priming. Germination potential and microstructure analysis of treated paddies were also performed. Downward concave curve observed in hydration process of paddies indicates initial high-water absorptionthrough diffusion process. Sono-hydro priming process showed higher hydration rate compared to hydropriming. The changes in moisture content during hydration processes fitted to theoretical (Fick's model) and empirical model (Peleg model) exhibited high regression coefficient (R² > 0.95) indicating suitability for predicting hydration behaviour in both paddies for germination. The Peleg model adequately predicted saturation moisture content and sono-hydro priming efficiently increased the water absorption rate. Effective moisture diffusivity determined from Fick's diffusion model increased for sono-hydro priming. Activation energy estimated from effective moisture diffusivity required in sono-hydro priming (E_a = 20.32 and 19.19 KJ/mol respectively) for pigmented rice and non-pigmented rice was lower than hydropriming (E_a = 27.11 and 32.15 KJ/mol respectively). Both hydration processes were endothermic and non-spontaneous inferred from thermodynamic properties. Sono-hydro priming exhibited < 95% germination potential with shorter soaking time (12 h) owing to the high mass transfer rate. SEM micrograph revealed water absorption through various micro-cavities during sono-hydro priming. Thus, sono-hydro priming potentially reduced the soaking process (approximately 50%) with higher germination rate in paddies beneficial for commercial malting of grains.

Empirical characterization of hydration behavior of Indian paddy varieties by physicochemical characterization and kinetic studies

Temperature is an important factor in the determination of hydration kinetics in paddy, and it varies with variety. To understand this hydration behavior, the current study analyses the hydration kinetics of 12 different paddy varieties of India that were exposed to different soaking temperatures. The protein content of the paddy samples was found to be in the range of 6.13 to 9.19%; whereas, starch content was between 67.79 and 84.88%. The physicochemical composition of paddy varieties as well as variation in time-temperature of hydration was found to be decisive in ascertaining the hydration behavior. An increased hydration rate was observed with increasing hydration temperature as well as with higher amylose content of paddy. Among the varieties studied, the ratio of amylose to amylopectin was between 0.37 and 0.77. For all samples, the gelatinization temperature was in the range of 65.60 to 83.10 °C, which in turn was negatively correlated with amylose content, and influenced the hydration behavior of paddy. The optimum time-temperature condition range for hydration for each paddy variety was between 50 and 60°C for 2 to 3.5 hr, depending upon the variety. The activation energy for the paddy samples in this investigation was found to be in the range of 8.70 to 23.10 kJ/mol. The kinetic modeling of hydration was conducted using Peleg's model, with a good fit. The data indicated that with increment in hydration temperature, the rate of hydration was enhanced in all varieties with a decrease in the Peleg's rate constant (K₁ ) and capacity constant (K₂ ). These constants indicate a direct temperature-dependence of water absorption in paddy. PRACTICAL APPLICATION: The hydration of paddy is an important procedure in paddy processing, and across the world, many industries are working on it. Irrespective of the variety, paddy processing globally has remained tricky. Knowledge about the hydration behavior of paddy would enable food processors to better understand the effect of process parameters and to model their experimental setup to obtain the desired physicochemical attributes, as well as process yield. Customers would benefit from adequately processed paddy with better digestibility for which industry would have to invest less in terms of time and resources, thereby making the hydrated paddy more affordable.

Absorption of Phenolic Acids in Rice Kernels after Boiling in Spearmint Aqueous Extracts of Different Concentrations. A Diffusion Study

In this study, an attempt was made to fortify white milled rice grains with phenolic compounds using a hydrothermal process and spearmint aqueous extracts of different % w/v concentrations. In addition, a mathematical model was acquired in order to simulate the diffusion of specific phenolic acids in rice kernels during boiling inside the extracts. Results showed that the amount of phenolic acids in rice, the potential equilibrium concentration values, as well as the diffusivity of these compounds in rice material were positively affected by the increase in % w/v bulk concentration of the aqueous extract. It was also shown that the diffusion process could be sufficiently described by a Fickian model and the estimated diffusion coefficients ranged from 6.86 × 10^-12 to 3.56 × 10^-11 m² /s, with the p-coumaric acid presenting the highest average diffusivity in boiling rice material among all examined compounds. The chemical affinity of each phenolic acid to rice macromolecules was believed to play the most important role concerning their diffusivity in rice during fortification process. PRACTICAL APPLICATION: Consumer's interest for functional food products is constantly growing during the last decades. This study may act as preliminary for the production of fortified rice products, possessing adjusted bioactive content, in industrial scale. The proposed methodology for the production of quick-cooking or ready-to-eat fortified rice may be adopted by rice industries and applied by only making slight modifications in their existing parboiling units.

Improvement of cooking quality of germinated brown rice attributed to the fissures caused by microwave drying

Germinated brown rice (GBR) contains rich bio-active components, but has poor edible quality. To improve the cooking quality of GBR, fissure generation in kernels caused by microwave drying were investigated considering cooking properties, microstructure and textural attributes. The microwave intensity had significant effects on the fissure percentage of GBR, and microwave intensity of 3-4 W/g may be suitable for the microwave drying of GBR based on the distribution of fissure percentage for the GBR. The fissures of GBR caused by microwave drying provided the suitable penetration routes of water into GBR kernel. Appropriate fissure amount in range of 3-4 in GBR kernels were conducive to increase its cooking quality and rice taste due to the moderate water absorption and starch gelatinization. The results present a new viewpoint from the perspective of fissures inside grain kernels to evaluate the drying quality of cereal materials such as GBR.

Hydration kinetics of little millet and proso millet grains: effect of soaking temperature

Hydration characteristics of little millet (Panicum sumatrense) and proso millet (Panicum miliaceum) were studied at different soaking temperatures (30, 40, 50, 60 and 70 °C) and fitted into hydration models. From the initial moisture contents of 11.02 (d.b.) and 10.45% (d.b), little millet and proso millet grains attained the equilibrium moisture content of 38-50.17% (d.b) and 39.11-47.15% (d.b.), respectively. Little millet took 18.5 h to reach equilibrium moisture content at soaking temperature of 30 °C and 3.5 h at 70 °C. For proso millet, it took 4 h at 70 °C and 19 h at 30 °C. The data of moisture content with time fitted to Lewis, Page, modified Page and Peleg models shown higher coefficient of determination values ranging from 0.92 to 0.99. Among the models, the Peleg model is more suitable for the little millet grains and both Page and Peleg models are more suitable for the proso millet grains, to represent the hydration kinetics in the soak water temperature range of 30-70 °C. The dependency of the coefficients of the hydration models with temperature of soaking was found to be linear for both little and proso millets with coefficient of determination values ranging from 0.88 to 0.97.

Modelling the physical properties change of canned glutinous rice porridge during cooking

In this study, we modeled the water absorption, softening and shear viscosity change kinetics of canned rice porridge during cooking as well as estimated the thermodynamic properties involved in hydration. Moreover, the internal microstructure of rice kernels was observed under different hydrothermal conditions. During cooking, the water absorption and shear viscosity alteration rate increased with temperature, whereas the softening rate decreased. However, the temperature did not significantly affect the equilibrium value of the physical properties. The variation tendencies of the moisture content and hardness of the kernels could be expressed satisfactorily by the exponential and the generalized exponential models. The porridge shear viscosity variations fitted the sigmoidal and its generalized models. Thermodynamic parameters (enthalpy, entropy and Gibbs free energy) revealed that the hydration process was non-spontaneous and exothermic. Furthermore, scanning electron microscopy images and the results of the X-ray diffraction analysis showed the microstructure of the kernels during cooking, and the kernels formed a homogeneous mesh structure at earlier times during the initial stage at higher temperatures. These findings would provide valuable information for the optimization of canned rice porridge production.

Numerical Simulation of Water Absorption and Swelling in Dehulled Barley Grains during Canned Porridge Cooking

Understanding the hydration behavior of cereals during cooking is industrially important in order to optimize processing conditions. In this study, barley porridge was cooked in a sealed tin can at 100, 115, and 121 °C, respectively, and changes in water uptake and hygroscopic swelling in dehulled barley grains were measured during the cooking of canned porridge. In order to describe and better understand the hydration behaviors of barley grains during the cooking process, a three-dimensional (3D) numerical model was developed and validated. The proposed model was found to be adequate for representing the moisture absorption characteristics with a mean relative deviation modulus (P) ranging from 4.325% to 5.058%. The analysis of the 3D simulation of hygroscopic swelling was satisfactory for describing the expansion in the geometry of barley. Given that the model represented the experimental values adequately, it can be applied to the simulation and design of cooking processes of cereals grains, allowing for saving in both time and costs.