粮油种子平衡水分测定方法及数据处理

介绍了采用静态称重法测定谷物和油料种子平衡水分的原理、方法,以期对我国粮食平衡水分研究和应用有参考意义。     

Sorption equilibrium moisture and isosteric heat of cold plasma treated milled rice

To promote industrial adoption of cold plasma as a sustainable and safe processing technology for rice, data on equilibrium moisture content (EMC) for cold plasma treated milled rice of five Chinese varieties were collected by a gravimetric method at 11–96% equilibrium relative humidity (ERH) and a temperature range of 15–35 °C. Nine models were fitted well to the sorption data, with the modified Guggenheim–Anderson–deBoer equation (3-MGAB), modified Henderson equation (MHE), and a polynomial equation being the best fits. At a constant ERH, the EMC was negatively correlated with temperature, whereas there was a strong effect of temperature on the sorption isotherms of the milled rice. Initially, the isosteric heats of sorption for the cold plasma treated rice decreased rapidly with increasing sample moisture content (MC); however, when MC was higher than 15% of the wet basis (w.b.), further increases in MC caused a slight decrease in heat sorption values. The heat of vaporization of the milled rice approached the latent heat of pure water at a moisture content of ~17.5% w.b., which was ~2500 kJ/kg. The isosteric heat of sorption values of the milled rice predicted by the modified Chung-Pfost equation (MCPE) and MHE models negatively correlated with temperature. At 70% ERH, the safe-storage MC of the cold plasma treated rice were ≤14.5% w.b. at 25 °C. In comparison to the untreated milled rice, the cold plasma treated rice with 120 W for 20 s and 60 s significantly decreased the water contact angle and increased kernel broken index, without significantly changing the appearance quality of milled rice. The cold plasma treated rice with 120 W-20 s had insignificantly higher EMC than that of 120 W-60 s at the studied temperature range. This study demonstrates that helium cold plasma treatment insignificantly changed hygroscopic property of milled rice whilst maintaining the appearance quality.     

豆粕平衡水分及吸着等热研究

采用静态称重法测定了国产6个豆粕样品的平衡水分吸附/解吸等温线,并采用修正MCPE、MHAE、MHE、MGAB、MOE及STYE 6个方程进行拟合,得出MGAB、MHAE、MOE均适合描述豆粕平衡水分-平衡相对湿度之间的关系,并可用于分析豆粕水分吸附/解吸等热。当水分小于15%时,豆粕吸附/解吸等热均随水分增大而快速减小,同温度下的解吸吸着等热显著高于吸附吸着等热。当水分大于15%时,豆粕吸附/解吸等热均随水分增大而变化平缓,同温度下的解吸吸着等热趋同于吸附吸着等热。当水分小于15%时,较低温度下的豆粕吸附吸着等热与解吸吸着等热均高于较高温度下的。在水分17.5%的游离水临界点,豆粕的吸着等热(汽化热)接近纯水的潜热,约为2 500 kJ/kg。由等温线分析的25℃豆粕绝对安全水分为12.48%,相对安全水分为13.90%。     

Equilibrium moisture content and sorption isosteric heats of five wheat varieties in China

The moisture sorption isotherm data of five Chinese wheat varieties were investigated via the gravimetric static method at five different temperatures (10, 20, 25, 30, and 35 °C) and relative humidity ranging from 11.3 to 96.0%. The sorption data of wheat decreased with an increase in temperature at a constant relative humidity (r.h.). The hysteresis effect was observed between adsorption and desorption isotherms. The width and span of the hysteresis loop decreased with increased temperature, but was not influenced by the hardness of wheat varieties. Six models, namely the Chen-Clayton (CCE), Modified BET (BET), Modified-Chung-Pfost (MCPE), Modified-Henderson (MHE), Modified-Oswin (MOE) and Strohman-Yoerger (SYE), were employed to describe the experimental data. The BET, MCPE and MOE models were selected to best describe the sorption isotherms of wheat in the ranges of 11.3-49.9, 11.3-96.0 and 11.3-96.0% r.h., respectively. The hygroscopic property difference between hard wheat (cv. ‘Longyuan’ and ‘Nanduan’) and soft wheat (cv. ‘Zhaozhuang’ and ‘Lumai’) was very small. The sorption isosteric heat of wheat decreased with an increase in moisture content until the dry bulb moisture content (m.c.) of 20% was reached, and then decreased smoothly with increasing moisture content. A big difference was found between adsorption and desorption isosteric heats of wheat below 20% m.c., but the sorption isosteric heat difference between hard and soft wheat isotherms was small.     

玉米吸湿特性及其等温线类型研究

对测定的我国16个玉米品种的水分吸着等温线数据,采用9个水分吸着方程进行拟合,并根据修正4-参数Guggenheim-Anderson-de Boer方程(4-MGAB)派生的指标划分等温线类型。结果表明,CAE、修正Chung-Pfost(MCPE)、Strohman-Yoerger(STYE)、Brunauer-Emmett-Teller(BET)、3-MGAB、4-MGAB、修正Henderson(MHE)及修正的Oswin(MOE)方程均适合拟合测定的玉米水分吸着等温线,而Modi-fied Halsey(MHAE)不适合。MCPE和CAE被认为是玉米较佳水分吸着方程,方程参数MCPE的C1和C2、CAE的b1在不同玉米品种之间、黄玉米和白玉米之间差异不明显。但是,同一玉米品种吸附等温线的方程参数不同于解吸等温线的对应方程参数。另外,根据D10、Rfi、awn、X4指标判断玉米水分吸着等温线类型,16个玉米品种的吸附和解吸等温线均属于S型等温线(Ⅱ)。结果表明玉米水分吸附与解吸的MCPE和CAE方程参数可用于玉米收获后干燥及储藏通风操作。     

Dependence of Thermodynamic Characteristics of Amylose‐Lipid Complex Dissociation on a Variety of Wheat

Native wheat starch contains amylose‐lipid complexes (AMLs) that are formed both upon biosynthesis of native starch and upon heating of starch slurries at gelatinization temperature and above. These complexes have a detrimental impact on physicochemical properties of starch, because they reduce water binding by starch granules and retard their swelling. An objective of the presented work was to analyze the chemical composition of wheat starch and characterize the thermodynamics of gelatinization of different wheat starches and to evaluate the stability of AMLs derived from these starches with the aid of differential scanning calorimetry (DSC). Grains of eight wheat varieties were used throughout the studies. The gelatinization behavior of the eight wheat varieties examined was similar. The lowest temperature of the onset of gelatinization (T_k = 57.07°C) was found for the Jawa variety, and the highest (T_k = 60.58°C) for the Torka variety. Enthalpy of gelatinization (ΔH_k) of the examined wheat starch preparations ranged from 9.14 J/g (Sakwa) to 11.95 J/g (Elena). Temperature and enthalpy of AMLs dissociation depended on wheat starch variety. During the first heating the temperature of the minimum of the endotherm (T_d) ranged from 98.41°C to 100.5°C. During the second heating, the minimum was at slightly higher temperatures, varying from 102.02°C to 104.08°C. Enthalpies of AML dissociation (ΔH_d) varied from 1.45 J/g to 2.14 J/g during the first heating. During the second heating the enthalpy values were slightly lower (1.26 J/g to 1.68 J/g). Enthalpies of AML reassociation ranged from 1.29 J/g to 1.72 J/g during the first cooling, and from 1.17 J/g to 1.63 J/g during the second cooling. A correlation was found between the amount of lipids and AML content.     

Determination of safe storage moisture content of soybean expeller by means of sorption isotherms and product respiration

Soybean expeller (SBE) is rich in protein and has a relatively high and variable oil composition (7–15%). With the increasing use of the SBE for animal nutrition there arose a need for understanding the quality deterioration during storage. The goal of this research was to determine the storability of SBE by developing a model for predicting its equilibrium moisture content (EMC), using the EMC model to determine its safe storage moisture content (SSMC), and by measuring dry matter loss (DML) for SBE incubated at 10 °C and 20 °C for 46 days. Samples of SBE with different residual oil contents were collected and an EMC experiment was carried out to determine the sorption isotherms at 65, 70, 75 and 80% RH; at 10 and 20 °C for samples with 6.2, 9.6 and 15.3% oil content. A second set of samples was used for determining the respiration rate at 20 °C. The Enhanced Halsey model was fitted to the SBE EMC/equilibrium relative humidity (ERH) data and it was established that the residual oil content significantly affected the sorption isotherms. By considering an ERH of 67% or below to be a safe storage condition, the SBE should be stored at or below 12.2% moisture content (m.c.) if the temperature is at or below 20 °C and an the oil content is 7%. However, according to the respiration experiments it would be safe to store SBE up to 16% m.c. (equivalent to 75% ERH). Considering a DML limit of 0.1%, the allowable storage time of SBE at a m.c. lower than 15.4% (ERH of 75%) was at least 46 days. The widely accepted practice of incorporating the gums present in the extracted oil, diluted in water, back into the SBE should be avoided since it increases the m.c. of the product and substantially reduces the allowable storage time.     

大米安全水分和吸着等热计算

对静态称重法测定的5个大米样品吸着等温线数据,分别采用Brunauer-Emmett-Teller(BET)、CAE、修正Chung-Pfost(MCPE)、修正Guggenhein-Anderson-de Boer(MGAB)、修正Henderson、修正Oswin及Strohman-Yoerger 7个方程进行拟合,MCPE被判定为大米最佳吸着等温线方程。以M=f(hr,t)形式表达的平均解吸等温线方程MCPE的3个参数C1、C2及C3各是492.539、39.846及0.176,在RH 70%下,对应的101、5、202、5、303、5℃条件下大米样品平均解吸值,分别是15.88%、15.49%、15.13%、14.80%、14.50%及14.21%。3个粳米(方正香米、东北普通米、松花江米)在25℃的安全水分是14.92%～15.39%,低于15.5%;2个籼米(泰国香米和江苏米)安全水分则是13.88%～14.43%,低于14.5%,与GB 1354—2009大米限量水分一致。大米吸着等热在含水率<20%干基条件下,随着米粒含水率增加而快速减少,在高于20%干基含水率则随含水率增加而缓慢减少。在含水率<22.5%干基条件下,较低温度下的大米吸附等热与解吸等热均高于较高温度;大米解吸等热高于吸附等热,但是随着含水率增加则差异减少。     

Investigation of sorption isotherms of wheat germ for its effect on lipid oxidation

This research aimed to investigate the oxidation and sorption isotherm properties of wheat germ and to determine monolayer moisture content (m₀) in particular, because it has a limiting effect on lipid oxidation. This research comprised two stages. The first stage was the determination of sorption properties and m₀ at three temperatures (15, 25, and 35°C). The second stage of the research was to investigate lipid oxidation properties of stored wheat germ at two different temperatures (4 and 25°C) and m₀ for 28 days. As a result, it was determined that wheat germ has a Type II sorption isotherm, Halsey is the best fitting sorption equation, and the average m₀ is 4.25 g moisture per 100 g dry matter. Furthermore, the free fatty acid and peroxide value of wheat germ oil increased with increasing storage moisture content and temperature, determined as 12.63% and 5.01 mEqO₂/kg on average, respectively. In conclusion, storage of impermeably packaged wheat germ at low temperature and m₀ content is an applicable method for decreasing rancidity and prolonging shelf-life.     

Water sorption and cooking time of red kidney beans (Phaseolus vulgaris L.): part I – Effect of freezing and drying conditions on water sorption and cooking time

Water sorption and cooking time of kidney beans were determined. The beans were manually harvested at 19.2 ± 0.1% moisture content and stored at ?20 and ?10 °C for about half a year. The beans were further dried at 30, 40 and 50 °C inside a thin‐layer drier for 7.5 h or under room conditions for 4 week. The freezing storage temperature before the beans were dried did not influence their cooking time and water sorption. The saturated kernel volumes decreased approximately 7% after drying. The beans decreased their sphericity during water sorption and had a larger swelling ratio in the thickness direction than in other directions. Lower initial moisture content, especially with a higher drying temperature, decreased water sorptivity and resulted in higher percentage of uncooked kernels if the beans were not soaked before cooking. However, there was no relationship between initial moisture content and uncooked percentage if the beans were soaked before cooking. High drying temperature resulted in hard‐to‐cook (HTC) phenomenon.     

Moisture Sorption Isotherms of Oolong Tea

The sorption isotherms of Oolong tea were determined at temperatures ranging from 5 to 50 °C. Estimated parameters and fitting ability for nine equilibrium relative humidity (ERH) models were evaluated. The modified Oswin equations were found to be an adequate model of three parameters to describe the sorption data. The Andrieu model was the only adequate model of four parameters. In comparing the results of this study with previously published data, it was found that the sorption properties were affected by species and manufacture techniques. The Guggenheim–Anderson–de Boer (GAB) model was not an adequate model as indicated by checking residual plots. The monolayer moisture content calculated from the Brunauer–Emmett–Teller (BET) model was lesser than that calculated from the GAB model. The errors of moisture content determined by measuring the ERH and temperature of samples was within 0.35%.     

Influence of protein concentration on surface composition and physico-chemical properties of spray-dried milk protein concentrate powders

Surface composition, moisture sorption behaviour and glass–rubber transition temperature (T_gr) were determined for spray-dried milk protein concentrate (MPC) powders over a range of protein contents (35–86 g 100 g⁻¹). Surface characterisation of MPC powders indicated that fat and protein were preferentially located on the surface of the powder particles, whereas lactose was located predominantly in the bulk. Moisture sorption analysis at 25 °C showed that MPC35 exhibited lactose crystallisation, whereas powders with higher protein contents did not and continually absorbed moisture upon humidification up to 90% RH. The GAB equation, fitted to sorption isotherms of MPCs, gave increases in monolayer moisture value (m_m) with protein content. T_gr, measured with a rheometer, decreased significantly (P < 0.05) with increasing water content and increased with increasing protein content (P < 0.05). In conclusion, increasing protein concentration of MPCs resulted in altered surface composition and increased m_m value and T_gr values.     

Effect of water content,temperature and storage on the glass transition,moisture sorption characteristics and stickiness of β‐casein 1

Moisture sorption isotherms at +4 °C and +22.5 °C were obtained for β‐casein after isolation and after 9 months of storage at ‐29 °C and +22.5 °C. Glass transition state diagrams (T_g vs. moisture) were determined for β‐casein after storage. The results showed that effects of storage temperature on moisture sorption isotherms were varied; however, at any a_w differences in moisture content were small (< 0.03g H₂O/g solids at high a_w). β‐casein stored at ‐29°C had lower m_o and T_g values than that of β‐casein stored at +22.5°C. The glass transition temperatures for β‐casein were above room temperature, even at a_w = 0.76. Onset of stickiness occurred above a_w = 0.76.     

Effect of heat-moisture treatment for utilization of germinated brown rice in wheat noodle

Effect of heat-moisture treatment of germinated brown rice (GBR) on the texture and cooking quality of the noodles containing mixtures of wheat and GBR flours was investigated. With the increase in GBR content, hardness and tensile strength of the composite noodles decreased and cooking loss and water absorption increased. Pasting viscosity of the flour mixtures was significantly decreased by increasing the amount of GBR. Heat-moisture treatment of GBR (17 or 20 g/100 g moisture at 100 °C for 4 h), however, apparently increased the pasting viscosity and improved the texture and cooking quality of the composite noodles. The mixture of wheat and a treated GBR (1:1 weight ratio) showed a pasting viscosity similar to pure wheat flour. The noodle containing the heat-moisture treated GBR flours showed the lower cooking loss, and higher hardness and tensile strength than the noodle containing untreated counterparts. Among the treated GBR flours tested, the GBR treated at 100 °C for 4 h at a moisture level of 17 g/100 g was the most acceptable in terms of cooking quality and textural property, close to those of the noodle of pure wheat flour. Substitution with the heat-moisture treated GBR, however, made the noodle darker because of thermal discoloration of GBR.     

Sorption and desorption of sulfuryl fluoride by wheat,flour and semolina

Sulfuryl fluoride (SF) has been developed as a fumigant for control of insect pests in stored grain. However, there is very limited information on the sorption behaviour of this fumigant, which can be critical to its bioactivity, application and potential for residues. We undertook a comprehensive laboratory study of the sorption and desorption of SF by wheat (bread and durum), flour and semolina at 15, 25 and 35 °C, moisture contents 12% and 15%, and concentration × time combinations at CT = 1500 mgh/L (4.167 mg/L × 360 h, 8.928 mg/L × 168 h and 31.25 mg/L × 48 h).At each dosage, sorption rate increased as commodity temperature and moisture content increased. The highest rates of sorption occurred at 35 °C and 15% m.c., and lowest rates at 15 °C and 12% m.c., and the rate was independent of initial concentration. Sorption followed first order reaction kinetics described by the exponential decay equation, C_t = C₀·e^−k*t, where k is the sorption rate constant. The most important factors determining the rate of sorption were commodity particle size (exposed surfaces) and temperature. Little sorption of fumigant occurred within the first 24 h whereas longer fumigation times resulted in significant sorption. Unbound SF was rapidly lost from the commodity upon aeration with no further desorption detected under any of the test conditions.SF possesses a number of characteristics that recommend it as a commodity fumigant. It is sorbed slowly by commodities relative to methyl bromide and carbonyl sulphide although it is sorbed about 4–5 times faster than phosphine. It desorbs rapidly upon aeration, and the lack of continued desorption has practical workplace health and safety benefits. On the other hand, sorbed SF appears irreversibly bound to the commodity matrix indicating the need to be alert to the possibility of excessive residues, particularly in longer term fumigations.     

Influence of packaging material on moisture sorption and the multiplication of some toxigenic and non-toxigenic Aspergillus spp. infecting stored cereal grains,cowpea and groundnut

The moisture sorption isotherms of jute sack were determined at 12, 22, and 32°C by a standard procedure using glycerol:water mixtures providing equilibrium relative humidities (ERH) of 65, 70, 75, 80, 90 and 95%. The equilibration period of jute sack kept at 65–85% was found to be between 6–8 days whereas the moisture content (MC) and weight of jute sack kept at 90–95% continued rising. The amount of moisture absorbed at 12°C was significantly greater (P < 0.05) than at 32°C. Analysis of variance applied to collected data of adsorption at ERH 85% (a_w 0.85) and desorption ERH 20% (a_w 0.20) showed that incubation period, type of commodity and type of packaging material as well as the interaction of these factors significantly influenced the moisture sorption and desorption by cowpea, groundnut (shelled), white maize, millet and sorghum. Each food commodity absorbed water differently in the jute and woven polypropylene sacks. However, food commodities stored in jute sack significantly absorbed and desorbed moisture to a greater extent than the same produce stored in woven polypropylene. Mould and yeast count on seed and grain lots in woven polypropylene at ERH 20% were 1.0–1.5 log cycles lower after 6 months storage than same seed and grain lots kept in jute sack. Correspondingly, mould and yeast count on seeds stored in woven polypropylene at ERH 85% were 2–3 log cycles lower than same produce kept in jute sack. Both ambient sttorage humidity and type of storage sack had profound effect on the occurrence of toxigenic and non-toxigenic mould species on cowpea, groundnut, maize, millet and sorghum. The toxigenic moulds and non-toxigenic Aspergillus species reduced considerably the self-life of seeds kept particularly in jute sacks. Practical implications of these findings are discussed in relation to grain food storage in the tropics.     

Effect of drying temperature and beeswax content on moisture isotherms of whey protein emulsion film

The objective of this investigation was to study the effect of drying temperature and beeswax (BW) content on moisture sorption behavior of whey proteins emulsion films. For this purpose, films were obtained by the casting method and dried at two selected temperatures (5 and 25 °C) and constant relative humidity (RH) (58%). After drying, films were removed from the casting plates and were conditioned in the environmental chamber set at 25 °C and 58% RH for 3 days. Subsequently, portions of 400 mg of film were placed in glass bottles and pre-dried in desiccators containing drierite (a_w=0) during 10 days. Then, the bottles were placed in hermetically sealed glass jars containing 10 different desiccants to achieve a_w ranging from 0.11 to 0.90, and allowed to reach equilibrium. The analyses were made in quintuplicate at 25 °C. The equilibrium moisture content (EMC) was determined by drying samples in an oven and the experimental data were fitted by the Brunauer-Emmett-Teller (BET) and the Guggenheim-Anderson-De Boer (GAB) models. The results showed that both models were effective to describe the moisture sorption behavior of the films. The GAB model gave better fit than the BET model. The increase of the drying temperature of 5 to 25 °C and the incorporation of lipids reduced the EMC of whey protein emulsion films. Finally, data from experimental sorption isotherms are a useful tool to predict the effect of the environmental conditions that surround the film on its properties; particularly considering that the stability of an edible film is function of its mechanical and moisture barrier properties and both are strongly influenced by the presence of water, film formulation and drying and storage conditions.     

Glass transitions of barley starch and protein in the endosperm and isolated from

When studying the glass-to-rubber transition inside natural materials, it is important to take into account not only the moisture content but also the moisture distribution over the components in the material. We measured the T_g of protein and starch isolated from barley at different moisture contents using differential scanning calorimetry (DSC) (heating rate 10 °C/min) and by thermo mechanical compression tests (TMCT) (heating rate 2 °C/min). The measurement of the T_g of partially crystalline materials, such as barley starch, is more difficult using TMCT because the mechanical effect of expansion of these materials is smaller. For both measurement sets the glass transition lines were modeled using the Gordon–Taylor equation. The lines were adapted for the differences in moisture content over the endosperm by using the sorption isotherms of isolated barley starch and protein and whole barley endosperm. The glass transition lines measured by TMCT were closer together than the ones measured by DSC.     

Thermal Properties of Sorghum Starch

The differential scanning calorimeter (DSC) was used to measure thermal properties of sorghum starch and flour. DSC gelatinization temperatures of 24 nonwaxy sorghum varieties were: T_o (onset temperature): 71.0 ± 1.0°C; T_p (peak temperature): 75.6 ± 0.9°C and T_e (end temperature): 81.1 ± 1.1°C, respectively. The gelatinization energies ranged from 2.51 to 3.96 cal/g. There were no consistent relationships between DSC gelatinization temperatures or gelatinization energies and grain characteristics or physicochemical starch properties. DSC gelatinization temperature for nonwaxy, heterowaxy and waxy sorghum tended to increase as the number of waxy alleles (wx) increased. However, it appeared that at least a difference of two waxy alleles was required before differences in thermal properties of the samples were significant.     

Some Physico-chemical Properties of Dioscorea Starch from Ethiopia

The chemical composition, amylose content and physio-chemical properties of dioscorea starch (Dioscorea abyssinica, Fam. Dioscoreaceae) from Ethiopia have been investigated. The proximate composition of the starch on dry weight basis was found to be 0.1% ash, 0.5% protein, 1.0% fat and 98.4% starch. The amylose content was 29.7%. Scanning electron microscopy (SEM) showed rounded granules. Particle size analysis revealed granule size distribution with a mean particle size of 29.2 μm. X-ray diffraction study showed a pattern that is typical of B-type with a distinctive maximum peak at around 17° 2 T. The moisture sorption pattern, the swelling power and the solubility values were determined and found to be lower than potato starch. Brabender viscosity curves of 6% starch paste showed a peak viscosity of 781 BU. The breakdown and retrogradation of dioscorea starch were 25 and 501 BU, respectively. DSC parameters of starch-water mixture (1:2) exhibited an onset temperature (T_o) of 64.2°C, a peak temperature (T_p) of 68.2°C and an endset temperature (T_e) of 74.8°C. The enthalpy of gelatinization (ΔH) was 19.2 mJmg⁻¹.