Effects of High Pressure and Heat Treatments on Physicochemical and Gelation Properties of Rapeseed Protein Isolate

High pressure (HP, 200, 400, and 600 MPa)- and heat (60, 80, and 100 °C)-induced gelation, aggregation, and structural conformations of rapeseed protein isolate (RPI) were characterized using gel permeation–size-exclusion chromatography, differential scanning calorimetry, and circular dichroism (CD) techniques. HP treatments significantly (p?<?0.05) increased the content of soluble protein aggregates and surface hydrophobicity of RPI. In contrast, heat treatments at 80 and 100 °C led to significant (p?<?0.05) decreases in the amount of soluble protein aggregates. At pressure treatment of 200 MPa, there was a significant (p?<?0.05) increase in free sulfhydryl group content of RPI, whereas 400- and 600-MPa treatments as well as temperature treatments (60–100 °C) caused significant decreases. Protein denaturation temperature was increased by about 6 °C by HP and heat treatments. The far-UV CD spectra revealed increases in α-helix content of RPI after HP treatments with 400 MPa producing the most increase. Near-UV data showed that HP and heat treatments of RPI led to increasing interactions among the aromatic amino acids (evidence of protein aggregation), and between aromatic amino acids and the hydrophilic environment, which indicates protein unfolding. Least gelation concentration of RPI was significantly (p?<?0.05) reduced by HP and heat treatments, but HP-treated RPI produced gels with better textural properties (hardness increased from ~7.7 to 81.1 N, while springiness increased from ~0.37 to 0.99). Overall, pressure treatments (200–600 MPa) were better than heat treatments (60–100 °C) to modify the structure and improve gelation properties of RPI.     

Production of high-fructose rice syrup and high-protein rice flour from broken rice

The objective of this study was to develop a process for the production of both high-fructose rice syrup and high-protein rice flour from broken rice. The rice flour was obtained from broken rice by using either a dry or wet milling method. The glucose produced from the slurry of various raw materials by treating with α-amylase and glucoamylase was compared. Results indicated that cassava and corn starch were better raw materials than rice flour. However, the filtered residue of liquefied rice slurry could be recovered as high-protein rice flour. The particle size of rice flour had a small effect on the glucose yield. The orthogonal-array table (L₂₇) method of experimental design was employed to determine optimum conditions for liquefaction. The glucose yield based on starch was 90.8±3.6% under the following optimum conditions α-amylase, 0.12%; rice flour, 20%; temperature, 96°C; time, 90 min. The filtrate from liquefied rice slurry was saccharified at 60°C with three different concentrations of glucoamylase. The higher the enzyme concentration, the shorter the time required to reach the maximum yield. After saccharification, the glucose solution was decolourised, desalted and concentrated to 40% d.s. and then isomerised to fructose at 60°C under continuous operation by using immobilised glucose isomerase packed in a column. The isomerised syrup was then purified and concentrated to 71% d.s. The final high-fructose rice syrup contained 50% glucose, 42% fructose and 3% maltose. After liquefaction, the rice slurry was centrifuged and the precipitate was dried by either spray or drum drying. The composition of these two high-protein rice flours was almost the same and the protein content was about three times as high as the raw material. There were significant differences in surface structure of rice flour and high-protein rice flours, as observed by the scanning electron microscope.     

Production and Nutritional Evaluation of High-Protein Rice Flour

Optimal processing conditions for the production of high-protein rice flour from two rice varieties were determined. Gelatinized rice flour slurry was treated with 0.25 mg α-amylase per milliliter of slurry at 60°C for 90 min. The hydrolyzed starch was removed by centrifugation. The precipitated paste was then freeze-dried to yield high-protein rice flour which had 38% protein. The amino acid composition of the high-protein rice flour was similar to that of the dehulled rice flour. The protein efficiency ratio of the high-protein rice flour was 2.17. Supplementation with limiting amino acids, lysine and threonine, or with a laboratory-prepared freeze-dried soy isolate increased protein efficiency ratios above that of casein.     

Preparation and characterization of protein from heat-stabilized rice bran using hydrothermal cooking combined with amylase pretreatment

Hydrothermal cooking (HTC) combined with amylase pretreatment (AP) was used to improve protein extraction from heat-stabilized rice bran. The physicochemical and emulsifying properties of rice bran protein isolate (RPI) were evaluated. Depending on HTC temperature (120 and 150 °C), HTC alone significantly increased extraction yield, while protein purity was decreased. In contrast, HTC combined with AP significantly improved both extraction yield and protein purity (about 45-50% and 72-74%, respectively). The AP avoided the co-precipitation of gelatinized starch during the acidic precipitation. Electrophoresis and size exclusion chromatography profiles indicated that HTC led to the dissociation of insoluble protein aggregates in rice bran, with subsequent increase of soluble aggregates in RPI, linked by non-covalent (e.g., hydrophobic interaction) and covalent bonds (disulfide bond). This result was evidenced by the increased disulfide bond contents and surface hydrophobicity of RPI. In addition, HTC-prepared RPI exhibited excellent emulsifying property.     

Physicochemical properties of high amylose rice starches purified from Korean cultivars

The physicochemical and pasting properties of high amylose rice starches isolated using alkaline steeping method from different Korean rice cultivars, Goamy2 and Goamy, and from imported Thai rice were examined. The protein and lipid contents of the Goamy2 starch were higher than those of the other two starches. The amylose and total dietary fiber contents were ranged from 31.4 to 36.8% and from 6.3 to 8.6%, respectively. Total dietary fiber was positively correlated to amylose content. Water binding capacity was higher in the Goamy2 starch (172.2%) than in the Goamy and Thai rice starches (112.7–115.6%). The swelling power of the Goamy2 starch showed lower values, but its value at 95°C was similar to others because of its rapid increment at 85°C. The granular size of Goamy2 starch was widely distributed compared to those of others. The Goamy2 starch showed a high initial pasting temperature (92.0°C) and low breakdown and setback viscosities. The Goamy and Thai rice starch granules were polygonal‐shaped with A‐type crystals, whereas the Goamy2 starch granules were round‐shaped with B‐type crystals. Goamy and Goamy2 starches showed a single endotherm at 60.8 and 76.0°C for peak temperature and 10.0 and 11.5 J/g for gelatinization enthalpies, respectively. The Thai rice starch presented an endotherm with a shoulder peak at 68.3°C (75.3°C for the main peak) and a gelatinization enthalpy of 12.4 J/g.     

Freezing and Thawing Conditions Affect the Gel Stability of Different Varieties of Rice Flour

The freeze‐thaw stabilities of three different rice flour gels (amylose rice flour with 28% amylose, Jasmine rice flour with 18% amylose and waxy rice flour with 5% amylose) were studied by first freezing at –18 °C for 22 h and subsequent thawing in a water bath at 30 °C, 60 °C and 90 °C, or by boiling in a microwave oven. The freeze‐thaw stability was determined for five cycles. Starch gels thawed at higher temperature exhibited a lower syneresis value (percent of water separation) than those thawed at lower temperature. Amylose rice flour gels gave the highest syneresis values (especially at the first cycle). The Jasmine rice flour gels gave a higher syneresis value than the waxy rice flour gel. Except for freezing by storage at –18 °C and thawing at 30 °C, there was no separation of water at any cycle when waxy rice flour gel was thawed at any temperature, irrespectively of the freezing methods used. Cryogenic Quick Freezing (CQF) followed by storage at –18 °C and then thawing (by boiling or by incubation at any other temperatures) gave lower syneresis values than all comparable samples frozen by storage at –18 °C. The order of syneresis values for the three types of rice flour was waxy rice flour < Jasmine rice flour < amylose rice flour. The syneresis values and the appearance of starch gels, which had gone through the freeze‐ thaw process, suggested that the order of freeze‐thaw stability of gels for the three types of rice flour was waxy > Jasmine > amylose rice flour.     

鸭血糯蛋白的提取及功能性研究

采用碱溶酸沉法制备鸭血糯分离蛋白,并对其氨基酸组成和功能性质进行检测。结果表明,鸭血糯总蛋白含量为8.72%。鸭血糯分离蛋白得率为4.63%,纯度为65.8%。鸭血糯氨基酸组成均衡,其中谷氨酸含量最高,半胱氨酸含量最低。鸭血糯分离蛋白表面疏水性为114,二硫键含量15.1μmol/g,吸油能力、乳化性较好,起泡性稍差。1%~10%的鸭血糯分离蛋白添加量对鱼糜制品的凝弹性、品质等无显著影响。可考虑鸭血糯蛋白在各类食品中添加应用。     

Insights into the effects of dynamic high-pressure microfluidization on the structural and rheological properties of rapeseed protein isolate

The application of dynamic high-pressure microfluidization (DHPM) provides interesting modifications in food structures. However, the effects of DHPM on the structural and rheological properties of rapeseed protein isolate (RPI) were scarcely investigated. In this study, the average hydrodynamic size of RPI treated by DHPM significantly declined from 239.2 nm to 170 nm with the pressure and time rising to 60 MPa and 2 min. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis found that DHPM did not affect the molecular mass of the RPI. The changes in the intrinsic fluorescence and circular dichroism spectra showed that tertiary and secondary structures of RPI were altered, as proved by the higher fluorescence intensity and greater conversion of random coils and β-sheets into α-helices compared with the control (unprocessed RPI). The spatial unfolding of the RPI structure and the dissociation of chemical bonds influenced its rheological behavior. All RPI suspensions (15%, w/v) processed by DHPM had lower apparent viscosity, moduli, higher gelling temperature (up to 69.7 °C) than control, and the differences in rheological performance were closely dependent on the treatment pressure and time. In conclusion, through this study of the effects of DHPM on RPI, DHPM was shown to be a potential method for modifying proteins and reducing the consistency of high-protein fluid foods.     

Dephosphorylation of Phytic Acid in Rice Bran

Incubation time and temperature, moisture content, and pH were examined to determine the conditions necessary for the hydrolysis of phytic acid in rice bran. The extent of hydrolysis increased with increase in moisture content, and autoclaving for 1 hr at 121°C destroyed a significant proportion of the phytic acid at high moisture contents. Maximum hydrolysis of phytic acid occurred by heating at pH 4.5. Incubation of rice bran slurry for 24 hr at 55°C, pH 5.1 reduced the phytic acid level by approximately 80%.     

Impacts of storage temperature and rice moisture content on color characteristics of rice from fields with different disease management practices

Rice downgrading due to discoloration in storage presents a significant loss to growers and processors. The objective of this study was to investigate impacts of storage temperature and rice moisture content (MC) on color characteristics of milled hybrid rice (cv. XL 745) from fields with differing production practices. Freshly-harvested rough rice from field plots treated with and without fungicide for rice disease control during production were procured and stored at four MC levels (12.5%, 16%, 19% and 21% wet basis), and at five temperatures (10 °C, 15 °C, 20 °C, 27 °C, 40 °C) for 16 weeks, with samples taken every 2 weeks. Kinetics of mold growth and rice color were determined. It was observed that at 12.5% MC, discoloration was abated across all studied temperatures and treatments until 6 weeks of storage and increased not in excess of 20% thereafter 16 weeks. As the storage MC increased to 16%, discoloration increased and became significantly notable at the highest temperature of 40 °C. By week 16, at 40 °C storage temperature, discoloration increased significantly to 87.9% and 73% for sample lots from fungicide and non-fungicide treated plots, respectively. At the highest MC (21%), increase in rice discoloration was notable as early as after 2 weeks, across all storage temperatures, and continued to increase, especially for the highest storage temperature of 40 °C, to as high as 99.1% and 96.47%, after 16 weeks, for sample lots from fungicide and non-fungicide treated plots, respectively. There was more expression of discoloration patterns on samples stored at the highest temperature of 40 °C compared to that at lower temperatures, for both categories of sample treatments and ranges of studied MCs. Although not yet widely used for rice, this study suggested that cooling technology for rice, may have potential to extend rice storability, especially by retarding discoloration in the first few weeks after harvest.     

Slurry Sampling for the Determination of Mercury in Rice Using Cold Vapor Atomic Absorption Spectrometry

This paper proposes a procedure for the determination of mercury in rice samples using slurry sampling and cold vapor atomic absorption spectrometry (CV AAS). The first step in the preparation of the slurry is to cook the rice in a closed system for 20?min at 60?°C. The suspension is then sonicated for 30?min at 60?°C in the presence of 6?mol?L^?1 hydrochloric acid and thiourea. Finally, mercury cold vapor is generated using an aliquot of the acidified slurry. During the quantification step, isoamylic alcohol is added to prevent the formation of bubbles. The experimental conditions were optimized using a full two-level factorial and a Box?CBehnken design. The mercury content in rice samples can be determined using external calibration technique that employs aqueous standards; the limits of detection and quantification of this method are 0.95 and 3.18?ng?g^?1, respectively, and the precision, expressed as relative standard deviations, was 1.98% and 12.10% for rice samples with mercury contents of 10.32 and 4.90?ng?g^?1, respectively. The accuracy was confirmed by analysis of the NIST standard reference material for rice flour, SRM 1568a. This method was used to determine the mercury content in seven rice samples that were purchased at supermarkets in Salvador City, Bahia State, Brazil. The mercury content varied from 4.10 to 13.72?ng?g^?1, with an average of 8.36?ng?g^?1. Some of the samples were also analyzed by CV AAS after a complete microwave-assisted digestion. A statistical test showed that there was no significant difference between the results obtained using slurry sampling and those obtained after a complete digestion of the sample by microwave radiation.     

Influence of sodium pyrophosphate on thermal inactivation of Listeria monocytogenes in pork slurry and ground pork

The thermal inactivation (55–62·5°C) of Listeria monocytogenes in pork slurry and ground pork that contained 0, 0·25 or 0·5% sodium pyrophosphate (SPP) was evaluated. Surviving cells were enumerated on Modified Oxford Medium. Decimal reduction (D)-values in pork slurry control (0% SPP) were 8·15, 2·57, 0·99, and 0·18 min, at 55, 57·5, 60 and 62·5°C, respectively; D-values in ground pork ranged from 15·72 min at 55°C to 0·83 min at 62·5°C. D-values in pork slurry that contained 0·25% SPP (w/v) were 4·75, 1·72, and 0·4 min, at 55, 57·5, and 60°C respectively; the values in ground pork ranged from 16·97 at 55°C to 0·80 min at 62·5°C. At 62·5°C,L. monocytogenes in slurry that contained SPP were killed too rapidly to allow determination of the D-value. Addition of 0·5% SPP further decreased (P<0·05) the heat resistance of L. monocytogenes in pork slurry but not in ground pork. The z-values in slurry ranged from 4·63 to 5·47°C whereas higher z-values (5·25 to 5·77°C) were obtained in ground pork. Degradation of SPP to orthophosphates in ground pork was two or three times greater than in pork slurry. Possible reasons for failure of SPP to reduce the thermal resistance of L. monocytogenes in ground pork are discussed.     

RICE PUFFING IN RELATION to ITS VARIETAL CHARACTERISTICS and PROCESSING CONDITIONS

The effect of rice varietal characteristics, namely, length (L): breadth (B), ratio, amylose and protein contents and processing conditions namely, extent/degree of hydrothermal treatment, degree of milling and percentage of salt addition to rice, on puffing quality were studied in detail. the L:B ratio of varieties tested showed a positive correlation (r = 0.69) with expansion ratio (ER) of puffed rice produced. Total amylose and hot water insoluble amylose contents revealed a definite pattern of relationship, with ER showing predicted peaks at 28.5% total amylose (db) and 13.5% insoluble amylose (db) for highest ER. Protein content showed a negative relationship (r =^?0.79) with ER. A new method for determining extent/degree of starch gelatinization, based on Brabender hot paste peak viscosity value (viscosity of 15% slurry retained at 95°C for 20 min.) was used in this study. Normal parboiled and pressure parboiled rice having 425 BU and 240 BU peak viscosities produced highest ER of 7.5 and 9.7% respectively. A 6% milling (minimum) and a 2% salt (NaCl/CaCl₂) addition during preconditioning of rice resulted in maximum ER.     

Optimization of Rice Bran Fermentation Conditions Enhanced by Baker’s Yeast for Extraction of Protein Concentrate

The rice bran fermentation conditions for extraction of protein concentrate was enhanced by the use of baker’s yeast at optimized conditions using response surface methodology (RSM). A central composite design with three independent variables: fermentation temperature (25 to 35°C), yeast concentration (1 to 5%) and fermentation time (10 to 24 h) was used to study the response variable (protein yield). Results indicated that the generated regression model represented the relationship between the independent variables and the responses. Also, all linear terms, two quadratic terms (fermentation temperature and time) and all interactive terms had significant (p < 0.05) effect on the protein yield. The optimum conditions for yeast pretreatment of rice bran protein extraction were achieved at 30°C for 17 h using 3% yeast concentration to obtain a protein yield of 23.37%, which showed no significant difference (p > 0.05) from the response surface methodology predicted protein yield (23.02%). The use of baker’s yeast in the fermentation of rice bran for extraction of protein concentrate can be more effectively used to improve the extraction yield compared to natural fermented (15.43%) and untreated rice bran (10.16%).     

Changes in physicochemical characteristics of rice during storage at different temperatures

This study investigated the changes in the physicochemical properties of rice during storage at different temperatures. Milled rice stored at high temperatures showed higher fat acidity than rice stored at low temperatures. Although the moisture content of milled rice stored at 30 °C and 40 °C decreased below 15.5% (15.33% and 15.22%, respectively) after 1 month, adequate values were maintained with storage at 4 °C for 3 months (15.50%) and at 20 °C for 2 months (15.53%). Rice stored at low temperatures retained its white coloration, whereas low color retention values were obtained at higher storage temperatures. Peak viscosity increased during 4 months of storage and larger changes were found at higher storage temperatures. Breakdown decreased and setback increased with storage, regardless of storage temperatures. Storage at higher temperatures increased cohesiveness and hardness in compared with storage at lower temperatures. High temperatures also led to a decrease in adhesiveness with age. High temperatures (30 °C and 40 °C) significantly decreased all sensory values even after 1 month of storage. These results are similar to those obtained in an analysis of cooked rice texture. The results of this study indicate that storage temperature is an important factor affecting the physicochemical properties of rice. Short storage periods below room temperatures are recommended to maintain rice quality.     

THE FATE OF LIVE BREWERS' YEAST SLURRY IN BOVINE RUMEN FLUID

Live brewers' yeast slurry was incubated under carbon dioxide at 27°C and 39°C in 0·1% peptone solution and in bovine rumen fluid which had been clarified by removal of the population of bacteria and protozoa normally present. Numbers of viable yeast in both media remained constant for 12 h at 27°C; at 39°C loss in viability was 81 % in peptone and 94% in rumen fluid during the same period. When glucose was added to clarified or unclarified rumen fluid containing yeast slurry and incubated for 6 h at 39°C, ethanol was produced. Ethanol production was prevented if the slurry was treated with heat or chemical preservatives before addition to the rumen fluid. Unclarified rumen fluid from a steer fed a brome-alfalfa hay-grain ration contained 10²–10³ yeasts and moulds per ml. The results suggested that the feeding of live brewers' yeast slurry to ruminants could result in ethanol toxicity if fermentable carbohydrate were also present, though many of the yeast cells would succumb to heat inactivation at normal rumen temperatures. This risk could be eliminated by prior treatment of the slurry with heat or chemical preservatives.     

Yield and Quality of Soymilk Processed by Steam-Infusion Cooking

Traditional soymilk is boiled for approximately 60 min at 99°C pH 6.7, which reduces trypsin inhibitor (TI) activity by more than 90% to improve nutritional value. We evaluated continuous, direct steam-infusion cooking that facilitated higher temperatures (99-154°C) than that traditionally used for cooking soymilk. At temperatures above 120°C in steam-infusion cooking we observed consistent temperature-dependent patterns in yields of soymilk, solids, and protein, characterized by an initial decrease, followed by a rise to maximum recovery, then by a final decrease. At 154°C, pH 6.7, maximum recovery occurred at the same point as did adequate in-activation of TI. As much as 90% of the slurry, 86% of the soybean solids, and 90% of the protein were recovered as soymilk after centrifuging at 1050 × G for 5 min. Under optimum conditions for steam-infusion cooking the soymilk also retained less than 8% residual TI activity, and less chemical browning. Using traditional cooking methods, about 72% of the slurry, 61% of soybean solids, and 73% of the protein are recovered.     

Developing radio frequency technology for postharvest insect control in milled rice

Since methyl bromide fumigation has an adverse effect on human health and environment, it is urgently needed for developing a non-chemical method to replace chemical fumigation for disinfesting milled rice. The purpose of this research was to study possible applications of radio frequency (RF) energy for disinfesting milled rice without affecting product quality. A pilot-scale, 27.12 MHz, 6 kW RF system was used to study RF heating uniformity and develop a treatment protocol for achieving 100% insect mortality and finally evaluating quality attributes in RF treated milled rice during storage. The results showed that the heating time needed only 4.3 min to heat the 3.9 kg milled rice from 25 °C to 50 °C using RF energy, but 480 min for milled rice to reach 48 °C using hot air at 50 °C. After comparing three selected electrode gaps, an appropriate gap of 11 cm was obtained to achieve the heating rate of 5.8 °C/min for further heating uniformity tests. An RF treatment protocol was finally developed to combine 1.0 kW RF power with a forced hot air heating at 50 °C, movement of the conveyor with the speed of 12.4 m/h, two mixings, and holding at 50 °C hot air for 5 min, followed by forced room air cooling through single-layer (2 cm thick) samples. There were no significant differences in quality parameters (moisture, protein, fat, starch, hardness, and color) between RF treatments and untreated controls during storage (P > 0.05). Therefore, RF treatments may provide a practical, effective and environmentally friendly method for disinfesting milled rice.     

Physical Basis for Separation of Rice Starch using Various Density Gradient Systems and its Effect on Starch Recovery,Purity, and Pasting Properties

A 32% waxy and non waxy rice flour slurry containing starch‐protein agglomerates was physically disrupted in presence of water by use of high pressure homogenizer called Microfluidizer®. Microfluidized rice flour slurry from passes 2 and 4 was collected followed by isolation of starch using three different density gradient solutions/systems (CeCl, NaCl/sucrose and ZnSO₄·7H₂ O). Complete deagglomeration was obtained after passing the rice flour slurry four times through the Microfluidizer®. The recovery of isolated starch varied from 76.28% to 91.20% for different density gradient systems. The degree of deagglomeration did not seem to affect recovery but affected the purity of the isolated starches. All starches produced from pass 4 rice slurry resulted in starches with residual protein below 0.5%. Higher density of the gradient solution resulted in higher recovery and purity of starch. The isolation method had a significant effect on the pasting properties of the isolated starch. Residual protein in isolated starch had a negative correlation with peak viscosity and setback of pass 2 waxy and nonwaxy starches. The salts were retained in purified starch despite rigorous washing (at least 75 times greater than the control) and could affect starch properties.     

大米分离蛋白的酶法提取及其性质

本文研究了以糖渣为原料,用淀粉酶法水解法制备大米分离蛋白(E-RPI)的反应条件,并测定了蛋白质的溶解性、乳化性及其氨基酸组成。结果表明,反应中固液比为1:12.96、加酶量为0.096％、反应时间为2.3h时效果最好,使糖溶出量达到原料重量的25.7％,产物中的蛋白含量为88.6％,回收率为90.5％;E-RPI的乳化活性随pH值的升高而增大,与大豆蛋白相比,乳化活性低而稳定性高。E-RPI中除赖氨酸外,其它必需氨基酸的含量均高于大豆蛋白和酪蛋白。