Heat and Mass Transfer in Parboiled Rice during Heating with 915 MHz Microwave Energy and Impacts on Milled Rice Properties

Microwave (MW) heating offers an energy-efficient, fast method to dry high moisture content (MC) parboiled rice to safe storage MC. However, there is limited research that describes the fundamentals of heat and mass transport in rice kernels exposed to MW energy at 915 MHz, the most promising heating frequency for industrialized processing. This information is vital to explain the implications of MW technology on dried rice quality. The overall objective of this study was to develop a microwave heating technology that can sufficiently dry high MC parboiled rough rice kernels in one pass using a 915-MHz industrial microwave system. An industrial type MW system operating at 915 MHz frequency was used to dry high MC long-grain parboiled rough rice samples that were harvested at initial MC of 23% to 24% wet basis (w.b). Long grain rough rice samples were soaked in a lab-scale hot water bath set to soaking temperatures of 71 oC, 73 oC and 76 oC for 3 hours. After soaking, the wet rough rice was steamed in a lab-scale autoclave set to a temperature of 113 oC and a corresponding pressure value of 67 kPa for 5, 10 and 15 minutes (mins). The MW drying was accomplished at MW specific powers that ranged from 0.37 to 8.77 kW. [kg-DM]-1 (power per unit dry matter mass of the grain). During drying, fiber optic sensors were placed within the rice bed to collect real-time parboiled rough rice surface temperature. Results indicate that rough rice should be soaked at temperatures slightly below that of the onset gelatinization temperature of that rice cultivar and steamed for 10 min for optimal physiochemical and milling properties prior to drying by MW. Parboiled rough rice at initial MC of 35.88% reduced to a FMC of 13.48% after being treated with MW power level of 2 kW and drying duration of 31.5 min (MW specific energy of 3780 kJ.[kg-grain]-1) and at a low specific power of 2.92 kW.[kg-DM]-1. Increased MW specific power has a positive effect on parboiled rough rice MC reduction but negatively effects the rice milling characteristics. The head rice yield (HRY) obtained from the treatment was dependent on the specific energy input and reduced at higher specific energies. The drying rate was highest during the beginning of drying then slowed down during the end and can be divided into 2 periods, a first falling rate period (1.5 min to 7.5 min), and the second falling rate period (7.5 min to 31.5 min). Of the Page, Newton, Logarithmic, and Henderson & Pabis semi-empirical drying models, the logarithmic model best represented the MW drying behavior of parboiled rough rice kernels as determined by the R2, Adjusted R2, Reduced χ 2 and RMSE values. The effective moisture diffusivity was determined to be 5.04 × 10-11 m2.s-1. The activation energy was determined to be 3.02 kW.kg-1. The energy consumption was determined to be 1.05 kWh.[kg-grain]−1 with a drying efficiency of 18.89%. The drying cost for a ton of parboiled rough rice was $88.31 at a commercial energy rate of 8.41 cents per kWh in the state of Arkansas (2020). The models and parameters found in this study can be applied to industrial designs and act as an operational guide for the MW drying of parboiled rice

Development Of A One Pass Microwave Heating Technology For Rice Drying And Decontamination

An industrial microwave (MW) system operating at 915 MHz frequency was used to dry high moisture content (MC) (23% to 24% wet basis) medium-grain rough rice samples (cv. Jupiter). The rice beds were contained in a modified tray that accommodated up to 9 kg of rice separated by thin fiberglass mesh in 3 kg increments. Each layer of rice was fitted with fiber optic sensors connected to a real time data logger during MW treatments. It was determined that drying rice to a MC of 14% to 16% was feasible with the application of MW specific energy at 600 kJ/kg-grain followed by 4 hours of tempering at 60°C. Resulting head rice yield (HRY) was not significantly different from that of control samples dried gently using natural air. Increasing MW specific energy resulted in an increase in rice surface lipid content (SLC), rice protein content, final and peak viscosities. Total color differences (TCD) decreased with increasing MW specific energies. Increasing MW specific energy resulted in decreases in rice microbial loads. At the highest specific energy of 900 kJ/kg-grain, the reduction of the aerobic bacterial and aflatoxigenic fungal loads was 4.56 and 2.93 log CFU/g-grain, respectively. Varying rice bed thickness had significant effects (p \u3c 0.05) on rice final surface temperature, HRY, milled rice yield (MRY) and aerobic bacteria count. Highest MRY and HRY were observed at the top and middle layer with bottom layer having the smallest. Similar trends were observed for the aerobic bacteria response. Optimization analyses suggest that a power of 10.00 kW and a heating duration of 6.00 min are preferred for optimum aerobic bacteria and A. flavus mold count, MRY, HRY and FMC of rice beds of equivalent bed thickness of 15 cm. These factor levels equate to a specific energy of 400.00 kJ/kg-grain. At these parameter settings, a ton of freshly harvested rice the energy required to dry a ton of freshly harvested rough rice was 111.11 kWh. Drying at this MW specific energy for batch processes will cost $9.88 per ton of rice

Composition analysis and antioxidant activity evaluation of a high purity oligomeric procyanidin prepared from sea buckthorn by a green method

Procyanidin is an important polyphenol for its health-promoting properties, however, the study of procyanidin in sea buckthorn was limited. In this paper, sea buckthorn procyanidin (SBP) was obtained through a green isolation and enrichment technique with an extraction rate and purity of 9.1% and 91.5%. The structure of SBP was analyzed using Ultraviolet–visible spectroscopy (UV–vis), Fourier-transform infrared spectroscopy (FT-IR), and liquid chromatography-mass spectrometry (LC-MS/MS). The results show that SBP is an oligomeric procyanidin, mainly composed of ( )-epicatechin gallate, procyanidin B, (+)-gallocatechin-(+)-catechin, and (+)-gallocatechin dimer. SBP showed superior scavenging capacity on free radicals. Furthermore, the cleaning rate of the ABTS radical was 4.8 times higher than vitamin C at the same concentration. Moreover, SBP combined with vitamin C presented potent synergistic antioxidants with combined index values below 0.3 with concentration rates from 5:5 to 2:8. SBP also provided significant protection against oxidative stress caused by hydrogen peroxide (H2O2) on RAW264.7 cells. These findings prove the potential of SBP as a natural antioxidant in food additives and support the in-depth development of sea buckthorn resources

Effects of Ball Milling Combined With Cellulase Treatment on Physicochemical Properties and in vitro Hypoglycemic Ability of Sea Buckthorn Seed Meal Insoluble Dietary Fiber

To improve the rough texture and hypoglycemic ability of sea buckthorn insoluble dietary fiber (IDF), a novel combined modification method was developed in this study. The IDF was treated with ball milling and cellulase treatment to obtain co-modified insoluble dietary fiber (CIDF). The physicochemical and functional properties of IDF, milled insoluble dietary fiber (MIDF), and CIDF were studied. After treatments, MIDF had smaller particle sizes and a looser structure, and CIDF exhibited a wrinkled surface and sparse porous structure according to scanning electron microscopy (SEM) and X-ray diffraction. Compared to IDF, MIDF and CIDF showed improved water-holding, oil-binding, and swelling capacities, improved by 16.13, 14.29, and 15.38%, and 38.5, 22.2, and 25.0%, for MIDF and CIDF, respectively. The cation exchange ability of modified samples showed improvement as well. Treatments also changed the fluidity of MIDF and CIDF. Due to the smaller particles and increased stacking, the bulk density (BD) and angle of repose of MIDF improved by 33.3% and 4.1◦ compared to IDF, whereas CIDF had a looser structure and thus decreased by 7.1% and 13.3◦ with increased fluidity. Moreover, the modification also enhanced the effects of CIDF on glucose adsorption, glucose diffusion inhibition, starch digestion inhibition, starch pasting interference, and a-amylase activity inhibition. In summary, IDF modified by ball milling combined with cellulose treatment could be developed as a functional ingredient for regulating glucose content