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

Effects of microwave vacuum drying on drying characteristics, quality attributes and starch structure of germinated brown rice

Germinated brown rice (GBR) has high nutritional and health-promoting value, but the influence mechanism of microwave vacuum drying (MVD) on the quality properties of GBR is still unclear. This study investigated the effects of MVD parameters including microwave intensities (9, 12, and 15 W/g), drying temperatures (50, 60, and 70 °C), and vacuum pressures (0.03, 0.05, and 0.07 MPa) on the drying characteristics, quality attributes and starch structure of GBR. A falling-rate phase dominated the MVD process of GBR and temperature-controlled MVD significantly preserved the GABA content in GBR. MVD caused microstructural changes with rearrangement and gelatinization of starch granules in GBR. For the GBR under MVD, increasing the drying temperature resulted in a significant decrease in enthalpy (ΔH) and an increase in the degree of starch gelatinization (DSG) (P < 0.05), however, no significant effect of microwave intensity and vacuum pressure on ΔH and DSG (P > 0.05) was found. MVD reduced the relative crystallinity but hardly changed the crystal type or formed functional groups of starch molecules in GBR. Overall, temperature-controlled MVD conduced to the final quality of GBR. This study may provide a potential method to improve the quality attributes of GBR in product development applications.

Effect of microwave drying and tempering on color attributes, fissure formation, and cooking characteristics of fortified rice kernels

Fortified rice kernels (FRK) are a vitamin-mineral enriched extruded rice-shaped product blended with raw or parboiled rice in a 1:100 ratio to prepare fortified rice. In FRK manufacturing, drying is one of the essential steps that affect the quality of FRK. In the present study, the microwave technique was explored to dry FRK continuously at 180, 360, and 540 W and with the tempering (1, 2, and 3 min) at 180 W to evaluate the effects on the drying curves, color attributes, fissure formation, and cooking characteristics. Thin layer modeling suggested the Two-term exponential model (two parameters), diffusion model (three parameters), and Midilli Kucuk (four parameters) as the best models to predict moisture based on Akaike and Bayesian information criteria. The higher MWP (360 and 540 W) significantly lowered the L* and WI while increasing the a*, b*, and BI compared to 180 W, which was undesirable. Image processing showed fissures in all FRK samples; however, 1 min and 2 min tempering could somewhat restrict the fissure. The fissures caused higher solid losses and increased splitting of kernels during cooking. It can be concluded that the low MWP (< 180W) with appropriate tempering time can be used to dry FRK.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05871-4.

Verification of rice quality during storage after drying with hot air and radio frequency heating

The objectives of the study were to observe the milling and cooking qualities of paddy rice dried with hot air (HA) and hot air and radio frequency heating (HA/RF) at 38 °C and 42 °C, and to observe these qualities after 6 months of storage under average temperature and RH of 28.4 °C and 70%, respectively. During storage, the average moisture content of paddy rice decreased from 13.66% to 11.37% in HA, 13.66% to 11.40% in HA/RF38, and 13.58% to 11.63 in HA/RF42. The milling qualities of rice were affected by the RF heating temperature and storage period. Rice dried with HA/RF38 and HA/RF42 could be safely stored for up to 5 months and 4 months, respectively, with satisfactory fissure percentage and head rice yield. The whiteness index significantly increased from 63.37 ± 0.58 to 64.46 ± 0.75 at HA, 62.78 ± 0.97 to 63.75 ± 1.55 at HA/RF38, and 62.77 ± 1.90 to 64.45 ± 0.95 at HA/RF42 during storage. For cooking qualities, elongation ratio (ER) was affected by RF and storage period, while texture profiles and pasting properties were only affected by storage period. The ER increased from month 3, by 10%, 11%, and 11% in HA, HA/RF38, and HA/RF42. The hardness of cooked rice reached its peak value between months 4-5. However, adhesiveness decreased as the storage period increased. The peak viscosity and setback increased with increasing storage period while breakdown conversely decreased. This study showed that hot air drying and RF heating temperatures of 38 °C could replace hot air drying without undesirable changes in milling and cooking properties during storage up to 5 months. Therefore, this is a promising drying technology for the rice milling industry.

Impact of different microwave treatments on food texture

Electromagnetic waves are frequently used for food processing with commercial or domestic type microwave ovens at present. Microwaves cause molecular movement by the migration of ionic particles or rotation of dipolar particles. Considering the potential applications of microwave technique in food industry, it is seen that microwaves have many advantages such as saving time, better final product quality (more taste, color, and nutritional value), and rapid heat generation. Although microwave treatment used for food processing with developing technologies have a positive effect in terms of time, energy, or nutrient value, it is also very important to what extent they affect the textural properties of the food that they apply to. For this purpose, in this study, it has been investigated that the effects of commonly used microwave treatments such as drying, heating, baking, cooking, thawing, toasting, blanching, frying, and sterilization on the textural properties of food. In addition, this study has also covered the challenges of microwave treatments and future work. In conclusion, microwave treatments cause energy saving due to a short processing time. Therefore, it can be said that it affects the textural properties positively. However, it is important that the microwave processing conditions used are chosen appropriately for each food material.

Effect of Large-Scale Paddy Rice Drying Process Using Hot Air Combined with Radio Frequency Heating on Milling and Cooking Qualities of Milled Rice

The objectives of the study on a continuous flow hot air dryer combined with radio frequency heating at different temperatures (HA/RF) (38 °C, 42 °C, 46 °C, and 50 °C) in a large-scale process compared with conventional continuous flow hot air drying (HA) were (1) to investigate the drying characteristics, drying kinetics, and milling quality of the process and (2) to observe the cooking quality and compare the sensory differences of the cooked rice after treatment. The drying characteristics and moisture diffusivity showed that the higher the radio frequency (RF) heating temperature, the shorter the drying time. The specific energy consumption and energy cost decreased when the RF heating temperature increased. The optimal condition in terms of fissure percentage was HA/RF42. In addition, there were no significant differences in head rice yield and white rice color determination, amylose content, texture profiles, and pasting properties in all HA/RF treatments. In the triangle test, it was found that at least 6% of the population could perceive a difference between HA and HA/RF50. In conclusion, this study proposes the further development of the HA/RF drying process at low-temperature profiles and shows the great potential of RF technology for commercial drying in rice industry.

Quality of Milled Rice from Large-Scale Dried Paddy Rice by Hot Air Combined with Radio Frequency Heating

A scaled-up process for paddy drying was developed using hot air (HA) combined with radio frequency (RF) heating. The study was conducted using hot air (control treatment) arranged in descending order in four temperature levels, namely 80 °C at moisture content of 25–26%, 70 °C at moisture content of 20–25%, 60 °C at moisture content of 17–20%, and 50 °C at moisture content of 13–17%, as well as with hot air combined with radio frequency (HA/RF) at different paddy temperatures (45–60 °C) by adjusting the appropriate RF energy when passing through RF heating chamber, namely HA/RF45, HA/RF50, HA/RF55, and HA/RF60. Each treatment was performed in three replicates and data were statistically analyzed in a randomized complete block design. The quality attributes of paddies affected by the drying process were assessed: fissure percentage, color, milling quality, and sensory evaluation. The drying efficiency showed that the drying time and the specific energy consumption could be decreased by up to 54.44% and 23.17% at HA/RF60 and HA/RF45, respectively. As the RF heating temperature increased, the fissure percentage of brown rice kernels at HA/RF45 and HA was not significantly impacted. Regarding color evaluation, combining RF heating and convective drying at all given conditions could be statistically applied in terms of the b*, WI, and ΔE* value. Considering the milling yield of HA as the baseline, head rice yield was maximized at HA/RF45, while bran yield reached the maximum at HA/RF60. The liking score of cooked rice after it was dried using the HA method was the highest. This study concludes that the HA/RF45 was the most appropriate drying condition, and this may provide preliminary exposure to the industrial drying of paddies.

Formation of texture quality of raspberry snack under microwave puffing

Raspberry snack, as a novel berry product, has rich favor and high crisp taste, where controllable texture quality is conducive to the palatability of the snack. Determinative factors of microwave puffing in microwave intensity and duration and key property of material in Young's modulus were introduced to investigate the formation of texture quality of berry snack under microwave puffing. The results indicate that the microwave intensity has negative correlation with Young's modulus of raspberry chips, which causes the more porosity inside under microwave puffing. Reasonable Young's modulus of raspberry chips enhances the interior porosity and exterior expansion volume of raspberry snack due to the water vapor wrapped other than escaped. The greater microwave intensity results in the higher volume expansion of raspberry chips, in which the great volume expansion from porous pores structure confers moderate hardness. In microwave puffing, the formation of hardness and crispness of raspberry snack depend on microwave puffing parameters, leading to high temperature and great dehydration rate in quick puffing duration, in addition to Young's modulus of raspberry chips, where high dehydration rate accelerates water removal inside raspberry chips to form a harder texture with decreasing springiness, whereas low dehydration rate leads to the gentle change of springiness. Raspberry snack with uniform internal pores and regular shape forming desirable texture may be achieved under the microwave intensity of 7.5 W/g and the puffing duration of 6 min. This study indicates that high-quality raspberry snack may be achieved via controlling heating rate in microwave puffing.

Analysis of Sour Porridge Microbiota and Improvement of Cooking Quality via Pure Culture Fermentation Using Lacticaseibacillus paracasei Strain SZ02

The microbial composition of sour porridge at different fermentation times was analyzed through high-throughput sequencing, and a pure culture fermentation process was established to optimize production process and improve the edible quality of the porridge. In natural fermentation, Firmicutes and Proteobacteria were abundant throughout the process. Specifically, Aeromonas, Acinetobacter, and Klebsiella were dominant on fermentation days 1–5 (groups NF-1, NF-3, and NF-5), while Lactobacillus and Acetobacter gradually became the dominant bacteria on fermentation day 7 (group NF-7). Further, we isolated one strain of acid-producing bacteria from sour porridge, identified as Lacticaseibacillus paracasei by 16SrRNA sequencing and annotated as strain SZ02. Pure culture fermentation using this strain significantly increased the relative starch and amylose contents of the porridge, while decreasing the lipid, protein, and ash contents (P < 0.05). These findings suggest that sour porridge produced using strain SZ02 has superior edible qualities and this strategy may be exploited for its industrial production.

Influence of microwave heating as accelerated aging on physicochemical, texture, pasting properties, and microstructure in brown rice of selected Indian rice varieties

Most of the population does not prefer to consume brown rice because of its strong nutty and chewy texture imparted by bran and germ. The present study has been undertaken to investigate the influence of accelerated aging through microwave (MW) heating at a lower and higher MW power levels of 950 and 1,400 W for 72 and 91 s to observe the changes in physicochemical, texture, pasting properties, sensory attributes, and microstructure of selected rice varieties (Sona masuri and RNR-15048) stored as brown rice for 6 months. The results revealed a significant decrease in moisture, amylose, free fatty acids (FFAs) with changes in color (L*, a*, and b* values) in both the varieties treated at 1,400 W for 91 s. An increase in kernel elongation ratio, water uptake, and a decrease in cooking time and solid loss was noted in both the varieties. After cooking, the texture of both the varieties showed an increase in hardness with reduced stickiness at both lower and higher MW power levels of 950 W for 72 s and 1,400 W for 91 s compared to untreated brown rice with an improved porous structure when observed under SEM analyzer followed by better water absorption and organoleptic properties after cooking. The reduction in final viscosity has been noted in both the varieties at 1,400 W for 91 s due to the binding of FFA with starch. Thus, the MW power level of 950 W for 72 s and 1,400 W for 91 s showed the better results for short-grain varieties like Sona masuri and RNR-15048 stored as brown rice.

Improvement of germinated brown rice quality with autoclaving treatment

Germinated brown rice (GBR) is a popular functional food containing considerable amounts of beneficial nutrients and bioactive compounds. Here, autoclaving at 115°C for 20 min was employed to process GBR (AGBR) to evaluate the effect of autoclaving on the nutritional and health function of GBR in microstructure, taste value, aroma, as well as the physiological ingredients. The results showed that autoclaving treatment influenced the starch gelatinization and aroma to improve the taste of cooked AGBR. Autoclaving treatment significantly increased the gamma‐aminobutyric acid (GABA) and ferulic acid levels of AGBR (p < .05). In addition, consuming AGBR for 1 month significantly decreased the fasting plasma glucose (FPG), 0.5, 1, and 2 hr postprandial plasma glucose (PPG), triglyceride (TG), total cholesterol (TC), high‐density lipoprotein cholesterol (HDL‐c), and low‐density lipoprotein cholesterol (LDL‐c) in metabolic syndrome (MS) patients (p < .05). Therefore, autoclaving treatment, as a promising processing strategy, may both improve the sensory attributes and the nutrition of GBR.

Application of image analysis technique to determine cleaning of ohmic heating system for milk

Cleaning of equipment is one of the major areas of concern in food industry. Image analysis technique was used to assess the cleaning effectiveness and optimize the CIP protocol for ohmic heating setup. Process parameters selected for optimization of cleaning were caustic concentration (1.0, 1.5, 2.0 and 2.5%), caustic temperature (70, 75, 80 and 85 °C), acid concentration (0.00, 0.25, 0.5 and 0.75%), and acid temperature (40, 50, 60 and 70 °C). Time for caustic treatment was varied from 5 to 20 min at an interval of 5 min, while time acid treatment was kept at a constant of 10 min. Taguchi orthogonal array design was used generate different combinations of acid and alkali concentration and temperature. Images of ohmic heating plates were taken before and after the cleaning procedure. MATLAB program was developed to analyze and extract Gray-Level Co-occurrence (GLCM) matrix properties from the image. Optimized combination was selected based on the highest value of desirability factor among all the experimental set of trials. Treatment with 1.5% caustic concentration at 70 °C for 5 min followed by 0.5% nitric acid concentration at 60 °C was found optimum effective CIP of the heating plates used in ohmic heating setup. GLCM properties correlation, cluster prominence, cluster shade, entropy, homogeneity and inverse difference moment normalized were found suitable for analysis of cleaning effectiveness and optimization of the CIP protocol.