Effect of superheated-steam drying compared to conventional parboiling on chalkiness,head rice yield and quality of chalky rice kernels

Four rice cultivars (Ayutthaya 1, Khao Bahn Nah 432, Plai Ngahm Prachin Buri, and Prachin Buri 2) that usually have a major problem with chalkiness were processed by applying superheated-steam drying and conventional parboiling methods. The main objectives were: (1) to determine the possibility of applying superheated-steam drying to solve the chalkiness and low head rice yield problems and (2) to compare the properties of rice produced using superheated-steam drying and the conventional parboiling process. Both the initial moisture content and superheated-steam drying temperature significantly affected head rice yield. The higher moisture helped to increase starch gelatinization leading to a stronger rice structure and subsequently an increased head rice yield. The rice samples dried in the superheated-steam dryer using an initial moisture content of paddy at 32% w.b. for 6 h under a steam pressure of 1.2 bar and at three drying temperatures (120, 140, 160 °C) had higher milling quality than the conventionally parboiled rice samples. The darker color of the superheated-steam-dried samples was their main drawback. Both parboiling and superheated-steam drying could clearly lessen the percentage of chalky rice kernels compared to the raw paddy. The parboiled rice and superheated-steam-dried rice had more nutrients than normal white rice.     

Vitamin fortified rice grain using spraying and soaking methods

The objective of this work was to fortify three types of rice grains (brown, white milled and parboiled) with B complex vitamins (B₁, B₂, B₃, B₅, B₆, B₁₂), using two different physical treatment methods, (1) soaking of whole dehusked or milled rice kernels in vitamin solutions at 90 °C for 15 min and (2) full spraying of whole kernels with vitamin solution at 35 °C, both followed by oven drying. Various nutrient concentrations were added and the vitamin retention of dried fortified as well as of cooked rice were determined. Fortified rice was evaluated based on vitamin retention, estimated as the percentage of vitamin in rice after fortification treatment versus the total amount of added plus its initially vitamin quantity. It was found that the average retention of all vitamins in dried rice was high and varied from 54.3% to 85.3% for the spraying and from 53.5% to 76.2% for the soaking method respectively. After rice cooking, the retention was maintained in sufficient level (>70%) for all vitamins except for B₁₂. When excess of water was used for cooking, the water-soluble vitamins were leached; however a significant amount of vitamins still remained, varying from 13.5% (B₁₂) to 51.2% (B₁). The good retention of vitamins, even after cooking, achieved applying these relatively simple techniques, may be attributed to the absorption and diffusion of vitamins in the interior of rice kernels in high concentrations. Dried fortified rice samples properties were evaluated.     

Rice degree of milling effects on hydration,texture, sensory and energy characteristics. Part 1. Cooking using excess water

The purpose was to assess the effect of degree of milling (DOM) on cooking kinetics, sensory attributes, and energy requirements when cooking rice in excess water. Commercial milling equipment was adjusted to produce parboiled and non-parboiled rice samples that were milled to varying DOMs, including brown rice lots having no milling. Surface lipid content (SLC) ranged from 0.15% to 0.55% for non-parboiled rice and from 0.40% to 0.95% for parboiled rice. The percentage gelatinized kernels, moisture content, peak force and sensory attributes were determined as a function of cooking duration for all samples. The cooking duration required to attain ‘well-cooked’ rice was determined, after which the energy required for cooking was measured. Within the SLC range tested, DOM did not affect cooking kinetics, texture and flavor of rice. Non-parboiled brown rice required the most energy, expressed as energy per unit mass of uncooked rice, to be cooked, followed by parboiled brown, parboiled milled and non-parboiled milled rice.     

Parboiling of rice. Part I: Effect of hot soaking time on quality of milled rice

This study investigated the effect of soaking time on the quality of parboiled rice. The paddy was soaked in water at 25 and 80 °C for 15, 30, 45, 60 and 120 min. The soaked paddy was steamed, dried, stored and milled. With increasing soaking time a significant increase in water absorption and milling and head rice yield (hence reduction in broken rice) was observed. A significant difference in milling yield, at the 1% level, was obtained between the raw rice control and the hot soaked parboiled samples. A large reduction in fissured grain was observed after soaking. It is suggested that parboiling fills the void spaces and cements the cracks inside the endosperm, making the grain harder and minimizing internal fissuring and thereby breakage during milling.     

The breakage susceptibility of raw and parboiled rice: A review

Rice (Oryza sativa L.) is one of the most important cereals in the world. Before it is consumed, it is common to remove the hull, bran and germ from the rough rice kernel which is either parboiled or not. During such processing, rice kernels are subjected to mechanical stresses which cause some rice grains to break. A main challenge of the rice industry is to minimize the quantities of broken rice. We here review the factors impacting the breakage susceptibility of rice kernels. Their tendency to break is primarily determined by fissures, chalkiness, immaturity and rice kernel dimensions, properties which are both cultivar and rice grain history dependent. The intensity of processing of any given rice feedstock determines the actual level of broken rice kernels. If performed properly, parboiling, a three-step hydrothermal treatment consisting of soaking, heating and drying of rough rice, substantially reduces the level of broken kernels.     

Rice degree of milling effects on hydration,texture, sensory and energy characteristics. Part 2. Cooking using fixed,water-to-rice ratios

The purpose was to assess the effects of degree of milling on hydration and textural characteristics of rice cooked using a range of water-to-rice ratios, and to compare the energy requirements when using these fixed water-to-rice ratios to the energy required when cooking with excess-water. Surface lipid contents (SLCs) ranged from 0.15% to 0.55% for non-parboiled rice and from 0.40% to 0.95% for parboiled rice. Cooking degree was assessed by measuring cooked-rice peak force, moisture content and percentage gelatinized kernels. Milling degree had little to no effect on cooking characteristics of all milled samples. Differences in cooking characteristics between milled and brown rice were less pronounced for parboiled than non-parboiled rice. Non-parboiled milled rice required the least energy to be ‘well-cooked’, followed by parboiled milled rice, non-parboiled brown rice, and parboiled brown rice (there were no significant differences between non-parboiled and parboiled brown rice). In general, excess-water cooking required more energy than fixed water-to-rice ratio cooking.     

干法、半干法和湿法磨粉对糙米粉性质的影响

研究干法、半干法及湿法3种磨粉方式对糙米粉损伤淀粉含量、平均粒径、微观结构、水合特性、热焓特性和流变性质等的影响。结果表明,干法磨粉糙米粉损伤淀粉含量、吸水指数、水溶性和膨胀势显著高于湿法和半干法。但干法磨粉糙米粉平均粒径、凝胶最大弹性模量和最大黏性模量显著小于湿法和半干法。干法和半干法糙米粉糊化焓值低于湿法。干法磨粉糙米粉形成了许多不规则的颗粒碎片,而半干法和湿法的糙米粉淀粉颗粒较完整。磨粉方式和条件显著影响糙米粉的性质,应根据糙米制品品质的要求选择合适的磨粉方式和磨粉条件。     

Folic acid fortification of parboiled rice: Multifactorial analysis and kinetic investigation

Folic acid fortification of parboiled rice has been systematically studied to obtain quantitative insights into the role of key process variables. Parboiling was conducted with brown rice soaked at 70 °C for 1, 2 and 3 h with four different fortificant concentrations added and dried parboiled rice was milled for three durations (i.e. 0, 60 and 120 s). Both residual folate concentration in treated parboiled rice and pH of the soaking water after soaking stages were measured. Multifactorial model was developed to describe the residual folate retention behaviour and suggested that both soaking and milling were significant factors in folic acid fortification. The optimum soaking time was deduced to be 1.97 h. Folate retention rate followed a 1st order kinetics while the rates of natural rice hydrolysis and folate uptake were both time-dependent.     

Effect of Protease Addition on Starch Recovery from Steeped Sorghum and Maize

The effect of protease addition on starch recovery from steeped white regular sorghum (RSOR) compared to yellow maize (YMZ) was determined. An in vitro wet milling method standardized to test dosages from 0 to 1.5 Anson units (AU/100 g grain) indicated that starch yields increased proportionally as enzyme concentration increased. The yields were significantly lower for RSOR. A factorial experiment with a level of confidence of P < 0.05 was performed to study the effect of protease addition (1.25 AU/100 g grain) to coarsely ground kernels for 4 h after 20 h or 44 h SO₂ steeping of whole grains. Calcium oxide (CaO) was used to increase the pH of the steep solution to 5.5 and improve enzyme activity. The in vitro and laboratory tests indicated that the enzyme treatment significantly improved starch yields and recoveries; the effect being more pronounced in RSOR. Protease‐treated kernels yielded 3.2% more starch than those steeped regularly. RSOR steeped for 20 h and then treated with the enzyme for 4 h yielded 6.7% more starch than the counterparts steeped regularly. When steep times were compared, kernels soaked regularly for 48 h produced 1.6% more starch than counterparts steeped for 24 h. The protease treatment reduced the amount of inseparables (gluten‐starch complexes) to zero and also lowered the gluten content of starch by about 1.5%. A comparison of protein and ash contents for the refined starches indicated that the process was more efficient for YMZ than for RSOR and for grains steeped regularly for 48 h. YMZ starch started gelatinization at a lower temperature, required less time to reach peak viscosity and had less shear thinning than RSOR.     

Effect of oxygen absorber on accumulation of free fatty acids in brown rice and whole grain wheat during storage

Because rapid rancidities of lipids in unpolished grains, such as brown rice and whole grain wheat, are often problematic, Suppressions of their lipid degradations during postharvest therefore important for their further utilization. In this study, effect of oxygen absorber on lipid deterioration in unpolished grain during storage was investigated. Kernels and flours of brown rice, rice with germ and whole grain wheat were stored for eight weeks at 4 °C and 26 °C, with and without oxygen absorber. Free fatty acids (FFAs) accumulation in the unpolished grains during storage was accelerated by polishing, milling and storage at high temperature (26 °C), because these storage conditions stimulated activities of their lipid hydrolyses. When oxygen absorber was added and the storage system was sealed, additional FFAs accumulations in these unpolished grains. Decreases both in absolute amounts of linoleic acids of the lipids and in total tocochromanols contained in these unpolished grains were depressed by addition of oxygen absorber to the storage system, which was confirmed by an anti-oxidative effect of oxygen absorber. These results suggested that introduction of oxygen absorber into the storage system of unpolished grains would be effective under the condition where their hydrolytic activities of lipids are suppressed.     

Nature of Starch Crystallinity in Parboiled Rice

A-type X-ray diffraction spectra of raw rice was weakened upon mild parboiling and completely disappeared in moderately severe parboiled rice. A feeble V pattern of lipid-amylose complex appeared in its place. There was no unambiguous evidence of a B-type spectra of retrograded starch, although partial and weak B-like spectra could be seen. Differential scanning calorimetry showed that raw rice flour and starch had a large gelatinization and a small lipid-amylose endotherm, the latter disappearing after defatting. The gelatinization endotherm first decreased and eventually disappeared in samples with moderately severe parboiling, but a small lipid-amylose endotherm was visible in most parboiled rice samples. On the whole, parboiled rice appeared largely amorphous with only minor crystallinity, and the peculiar properties of parboiled rice could not be definitely ascribed to a definite crystalline form of starch.     

Effects of parboiling and infrared radiation drying on the quality of germinated brown rice

This research investigated the physicochemical properties, bioactive compounds, and microstructure of brown rice (BR) and non-parboiled and parboiled germinated brown rice (GBR and PGBR). The GBR and PGBR were treated by sun, hot-air oven, or infrared irradiation (IR) drying. The results showed that IR drying enhanced the bioactive compounds of non-parboiled GBR, including γ-aminobutyric acid, α-tocopherol, and total phenolic compounds, while γ-oryzanol and antioxidant activity were comparable to BR. Meanwhile, IR drying significantly improved the head rice yield (HRY) of PGBR while reducing fissured grains. Parboiling also affected the color values of rice grains, suggesting the diffusion of husk color into endosperm and the formation of brown polymers by the Maillard reaction. In addition, IR drying altered the internal structure of rice grains, resulting in abundant intercellular voids. Specifically, the IR-dried non-parboiled GBR significantly enhanced essential bioactive compounds and improved HRY while maintaining the color of standard BR.     

Impact of parboiling conditions on Maillard precursors and indicators in long-grain rice cultivars

The effect of steaming conditions (mild, intermediate and severe) during parboiling of five different long-grain rice cultivars (brown rice cultivars Puntal, Cocodrie, XL8 and Jacinto, and a red rice) on rice colour, and Maillard precursors and indicators was investigated. Rice colour increased with severity of parboiling conditions. Redness increased more than yellowness when parboiling brown rice. Parboiling turned red rice black. It changed the levels of glucose, fructose, sucrose, and maltose. Losses of the non-reducing sugar, sucrose were caused by both leaching into the soaking water and enzymic conversion, rather than by thermal degradation during steaming. Concentrations of the reducing sugars, glucose and fructose, in intermediately parboiled rice were higher than those of mildly parboiled rice. After severe parboiling, glucose levels were lower than those of intermediately parboiled rice, while fructose levels were higher. These changes were ascribed to the sum of losses in the Maillard reaction (MR), formations as a result of starch degradation and isomerisation of glucose into fructose. It was clear that the ε-amino group of protein-bound lysine was more affected by parboiling conditions and loss in MRs, than that of free lysine. Low values of the MR indicators furosine and free 5-hydroxymethyl-2-furaldehyde (HMF) in processed brown and red rices were related to mild parboiling, whereas high furosine and low free HMF levels were indicative of rices being subjected to intermediate processing conditions. High furosine and high free HMF contents corresponded to severe hydrothermal treatments. The strong correlation (r = 0.89) between the free HMF levels and the increase in redness of parboiled brown rices suggested that Maillard browning was reflected more in the red than in the yellow colour.     

Effect of drying air temperature and storage on industrial and chemical quality of rice grains

The drying air temperature and storage time can change the milling yield and chemical composition of rice grains. Therefore, the objective was to verify the industrial quality and chemical composition of rice grains, white and integral subgroups, in response to drying air temperature and storage time. For such, the rice grains were subjected to drying in a column dryer with a grain capacity of 1 m³, using 55 and 65 °C drying air temperatures. After, they were stored in PP Woven Bags under environmental conditions for 240 days. After drying and every 60 days the milling was performed, aiming to evaluate the industrial quality and chemical composition of the grains. The whole grains yield was negatively affected by the increase in drying air temperature for both subgroups. The increase in the drying air temperature led to a reduction in the lipid content and an increase in the ash content for grains of white subgroup. The storage time promoted an increase in the whole grains yield in the white subgroup when the grains were dried with the highest drying air temperature. The lipids and proteins contents decreased, while the fibers and ash contents increased during storage for the white subgroup grains. The chemical composition of grains from the brown subgroup did not change during storage, regardless of drying air temperature.     

糙米正面破碎特性与裂纹扩展规律

目的:研究碾米室中糙米破碎特性。方法:利用万能材料试验机进行糙米力学试验,通过数字显微镜观察糙米中裂纹及其扩展变化。结果:糙米受力时会经历屈服阶段与强化阶段的交替过程,直至断裂;在挤压载荷作用下,内部微孔洞处产生裂纹,裂纹的快速扩展造成了米粒破碎或断裂,在三点弯曲和剪切载荷下,糙米从支撑端底面产生裂纹,并扩展至正面;糙米的抗挤压变形能力最大、抗三点弯曲变形能力次之、抗剪切变形能力最小;与挤压载荷相比,糙米在三点弯曲和剪切载荷下的破碎强度和破碎能较小。结论:在对碾米机结构进行设计时,要尽量减少弯曲、剪切作用对糙米的影响;同等条件下,粳型糙米的力学特性优于籼型糙米。     

Status of dietary fiber contents in pigmented and non-pigmented rice varieties before and after parboiling

Five different varieties of paddy (four pigmented and one non-pigmented) were shelled and milled in pre and post parboiled form, their dietary fiber contents were estimated. Under similar conditions of milling, raw rice showed a high degree of polish (DOP), 9–12 g/100 g and parboiled rice showed low DOP, 4.6–6.6 g/100 g. Dietary fiber content was high in pigmented rice, 9–10 g/100 g compared to non-pigmented, ∼6 g/100 g. Soluble fiber content in pigmented head rice (dehusked) varied from 1 to 1.5 g/100 g and in its brokens varied from 0.45 to 1.45 g/100 g. Dietary fiber content was low by about 1% in parboiled rice. In the parboiled rice of pigmented varieties, the total fiber content varied from 7.95 ± 0.15 to 9.05 ± 0.25 g/100 g and the soluble fiber content varied from 0.7 to 0.9 g/100 g. In milled parboiled rice the respective values were 5 ± 0.4 to 6 ± 0.1 g/100 g and 0.85 ± 0.05 to 1.25 ± 0.05 g/100 g. However, the soluble fiber content in the non-pigmented brown rice, IR-64 remained same after parboiling, 0.75 ± 0.5 g/100 g. Milled parboiled rice showed higher soluble dietary fiber compared to milled raw rice. In conclusion, dietary fiber was high in pigmented rice varieties when compared with non-pigmented rice.     

Effect of processing on thiamin and riboflavin contents of some high-yielding rice varieties of punjab

Six high-yielding varieties of rice (Oryza sativa L) were taken and subjected to 6 and 8% degree of milling. The raw rice and the parboiled rice were analysed microbiologically for thiamin and riboflavin contents. Milled parboiled rice contained more thiamin and riboflavin that milled raw rice at both the levels of milling because parboiling of paddy results in inward diffusion of water-soluble vitamins to the endosperm. The thiamin content of brown rice is reduced after parboiling. The loss may be due to the partial decomposition of thiamin during the stages of parboiling, but the riboflavin content of brown rice is found to be increased after parboiling.     

The effects of heat–moisture treatment of rice grains before parboiling on viscosity profile and physicochemical properties

The effects of heat–moisture treatment (HMT) (120 °C for 10, 30 and 60 min) on paddy rice grains before parboiling, on head rice yield (HRY), pasting and thermal properties, and colour and cooking characteristics of parboiled rice were studied. The results indicated that the HMT performed intensifies the changes in grains after parboiling, impacting pasting and thermal properties, which results in rice kernels with yellowish colouration and greater cooking time. HMT increased the temperatures of gelatinisation, with increasing HMT time from 10 to 60 min and reduced the gelatinisation enthalpy. HMT also affected the pasting properties of rice flours, reducing setback and viscosity and increased their stability to heat and mechanical agitation. The HMT performed in rice grains before the parboiling process with 60 min of the treatment decreased the HRY and increased the level of metabolic defects only in the treatment with 60 min.     

Rice bolus texture changes due to α-amylase

During mastication, starch hydrolysis caused by salivary α-amylase may influence food bolus formation and subsequent breakdown during gastric digestion. The objective of this study was to examine texture changes of rice boluses after simulated mastication. Boluses were prepared with three varieties each of brown and white rice (short, medium, and long grain). After simulated mastication, rice boluses were incubated from 0 to 180 min at 37 °C prior to texture measurement by bulk compression. Saliva was added at concentrations of 0.1 and 0.2 mL saliva/g rice. Boluses were also formed with 0.1 mL/g saliva without α-amylase. The peak force and area under the compression curve were significantly influenced by rice type, saliva level, and incubation time (p < 0.0001). The peak force of the boluses decreased, on average, from 127 to 52 N for brown rice and 111 to 54 N for white rice. Changes in bolus texture were described by a linear-exponential model. For all rice types, bolus texture was significantly lower in the presence of α-amylase. Saliva amount and presence of α-amylase influenced the textural properties of rice boluses during 180 min of incubation. These factors should be carefully considered in future in vitro studies of carbohydrate-based food products.     

Studies on parboiled rice: Part 1—Comparison of the characteristics of raw and parboiled rice

Various properties of raw and parboiled rice were compared in an effort to elucidate the factors responsible for the changes induced by parboiling.The parboiled rice was less prone to disintegration on cooking, the kernels remaining well separated and less sticky than the non-parboiled sample. The solids leached into the cooking water and the extent of solubilisation of the kernels on cooking were both considerably lowered by parboiling. Amylograms of flour prepared from the rice revealed that this was due to the resistance of the starch in the parboiled rice to swelling and solubilisation in hot water.From the results of X-ray diffraction spectra it was concluded that the behaviour of parboiled rice is influenced by the presence of an insoluble helical amylose complex and not, as is generally assumed, by retrogradation.