The moisture content-equilibrium relative humidity relationships of five varieties of Canadian wheat and of candle rapeseed at different temperatures

The relationship between moisture content and equilibrium relative humidity was determined for five varieties of Canadian wheat over a range of temperatures both for adsorbing and desorbing grains. This was also done for a new variety of oilseed rape. The differences between varieties for wheat were small as were those between the Candle rapeseed and published data for older varieties. A durum variety of wheat maintained an e.r.h. of only 2% above those of the four hard red spring varieties. It seems to be adequate to examine only one or two varieties when determining moisture relationships of hard wheats.     

Moisture relations of dried peas,shelled almonds and lupins

The relationship between moisture content and equilibrium relative humidity (e.r.h.) measured by a dew-point method, was determined over the range 30–90% r.h. for dried peas, shelled almonds and lupins at 15, 25 and 35°C. For dried peas the e.r.h. relationship was conventional, and at 70% r.h. and 25°C the equilibrium moisture contents were 14.8% when desorbing and 14.3% when adsorbing moisture. The relationship for three varieties of almonds was unusual in that there was little hysteresis between adsorption and desorption. The mean moisture content of the two, in equilibrium with 70% r.h. at 25°C was 5.9% for Moroccan sweet, 6.4% for Moroccan bitter and 6.8% for Californian sweet almonds. With dried peas and almonds the e.r.h. increased with temperature, and the moisture contents determined before and after e.r.h. determination were similar, which has been usual with stored products previously studied. However when the moisture of lupins was raised above 11% by adding water as a liquid, the moisture content after e.r.h. determination at 35°C was apparently lower than it had been just previously following e.r.h. determination at the lower temperatures. This implied loss of moisture was not detected when water was added in the vapour phase. At 70% r.h. and 25°C the equilibrium moisture contents were 12.3% when adding liquid water and 13.0% when water was added in the vapour phase.     

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.     

Moisture characteristics of macadamia nuts in relation to storage

The moisture content/relative humidity characteristics of nuts from two species of Macadamia have been examined. For Macadamia tetraphylla the whole nut moisture content corresponding to a relative humidity (r.h.) of 70%, accepted as the maximum for safe storage, was 11.8%. The moisture content can be determined with an electrical moisture meter by calibrating against standard laboratory procedures. The sorption isotherm of M, integrifolia appeared somewhat different.     

The moisture content/equilibrium relative humidity relationship and oil composition of rapeseed

The moisture content/equilibrium relative humidity relationships of a British winter-sown rapeseed variety Hektor, a British spring-sown variety Gulle and a Canadian variety Tower, were found to be similar. The adsorption moisture contents at 25°C in equilibrium with 70% relative humidity, conventionally accepted as the threshold for the growth of fungi, ranged from 8.3% for Tower to 7.5% for Hektor. The three varieties have similar oil contents, but Tower has a low content of erucic acid and glucosinolates.     

Relative humidity control in equilibration studies

The relative humidities in closed containers over both saturated salt solutions and wheat were identical at atmospheric and reduced pressures and reducing the pressure did not alter the relationship between moisture content and equilibrium relative humidity. When using saturated salt or potassium hydroxide solutions to condition samples of wheat, wheatfeed and rapeseed to required humidities, reducing the pressure accelerated the rate of moisture exchange between the product and the atmosphere, without affecting the moisture content-relative humidity equilibria. There was almost total loss of viability of seeds conditioned at 93% r.h., and some loss for seeds that had been wetted prior to exposure at lower humidities, especially for wheat at atmospheric pressure. It is recommended that saturated salt solutions be used for reliable humidity control when conditioning products, but whenever there is any reason to use potassium hydroxide, as much solution as possible should be used with the required quantity of product.     

The influence of the method used for moisture adjustment on the equilibrium relative humidity of stored products

This paper examines some possible causes of differences in the magnitude of the hysteresis effect reported by different workers when studying the moisture content/equilibrium relative humidity relationship of stored products.Three techniques of changing the moisture content during sample preparation were used on Cappelle wheat and the results compared. It was found that the position of the adsorption isotherm was not affected by these techniques, but the position of the desorption isotherm was. At 35% r.h. the moisture content was 0·8 per cent higher on the desorption isotherm by one technique than by the other two. This is equivalent to a difference of 6% r.h.The effect of a fungistat, propylene oxide, on the equilibrium relative humidity, was also included. This caused a ‘reverse’ hysteresis, in that the moisture content at a given relative humidity was lower on the desorption isotherm than on the adsorption isotherm instead of higher, as with previous techniques.     

The sorption isotherms of maize meal

Summary. The equilibrium moisture contents of the three main grades of South African maize meal over a range of 1.4-90.7% relative humidity (r.h.) were determined at 30°C. It was found that the fat content of maize meal influenced the moisture content at equilibrium, i.e. the higher the fat content, the lower the equilibrium moisture content for a specific relative humidity. Both desorption and adsorption isotherms for maize meal were found to be sigmoid and the effects of hysteresis were encountered in all cases. On prolonged storage mould growth occurred in maize meals held in an atmosphere of 84% r.h. and higher. From the sorption isotherms the maximum r.h. at which maize meal could be stored without the danger of mould contamination could be predicted.     

The moisture content/equilibrium relative humidity relationship of macaroni

The moisture content/equilibrium relative humidity relationship obtained at three temperatures is reported. The safe storage moisture content was found to be between 12 and 12·8 per cent, depending on the treatment of the macaroni. There is no hysteresis between the adsorption and desorption isotherms. In the normal storage range of moisture content, the effect of temperature on the equilibrium relative humidity (e.r.h.) was 3–4% r.h., or 0·7 per cent moisture content for every 10°C change in temperature. Samples of macaroni exposed to high controlled r.h.'s took 7 days to reach constant weight. A heavy duty polythene container with a tight fitting lid investigated as to its efficiency in providing an adequate water vapour barrier proved satisfactory. Virtually no change in moisture content of the packed macaroni took place after exposure to 92% r.h. and 30°C for 100 days.     

谷物安全水分估算

采用常用的水分吸着等温线模型对测定的14个小麦品种、15个稻谷品种、10个玉米品种及5个大米品种的平衡水分含量（EMC）/平衡相对湿度（ERH）数据进行拟合,Modified-Chung-Pfost（MCPE）被判定为最佳解吸等温线模型。以M=-1/C3×ln[-（t＋C2）C×1ln（r.h.）/C1]形式表达的平均解吸等温线MCPE方程参数C1、C2及C3对小麦分别是635.479、57.093及0.221,对稻谷分别是502.485、45.276及0.186,对玉米分别是389.939、18.792及0.231,对大米分别是492.539、39.846及0.176。根据RH 70%是霉菌生长的界限,推导10、15、20、25、30、35℃条件下各品种的平均解吸值,对小麦分别是14.84%、14.51%、14.21%、13.93%、13.66%及13.41%;对稻谷分别是14.83%、14.49%、14.17%、13.88%、13.61%及13.35%;对玉米分别是15.74%、15.05%、14.45%、13.93%、13.46%及13.04%;对大米分别是15.88%、15.49%、15.13%、14.80%、14.50%及14.21%。这些数据对谷物安全水分标准制定有参考意义。     

The moisture content-equilibrium relative humidity relationship of rice bran at different temperatures

The moisture content/equilibrium relative humidity relationships at 15, 25 and 35°C, for unextracted rice brans from Burma and Tanzania, unextracted bran from a South African parboiled rice, and a pelleted extracted rice bran from India, are presented and discussed. The relationships differed in shape and position of the curves, and in the magnitude of hysteresis between adsorption and desorption. The equilibrium moisture contents at 65% r.h. and below, of Burmese, Tanzanian and Indian brans were in reverse order of their fibre and ash contents. These moisture contents did not decrease consistently with oil content as they did for those cereal grains and oil-seeds previously investigated. The hysteresis for the parboiled bran was less, and the equilibrium moisture content was generally lower than for the other brans.     

The oviposition and development of Sitophilus oryzae (L.) in different high-yielding varieties of wheat

Studies on the oviposition and development of Sitophilus oryzae in high-yielding varieties of wheat (PV-18, Sonora-64, Kalyan Sona, S-308 and S-307) were conducted at all combinations of the three temperatures, 19°C, 25°C and 30°C and four relative humidities, 45, 60, 75 and 90 per cent. Oviposition and development of the weevil were better on larger kernels. The rates of oviposition and development were affected by certain other factors besides the physical nature of the kernel and its bran and endosperm. According to the development index ($\text{log}\text{n}\text{Av}$) and number of eggs deposited, varieties in increasing order of suitability were Sonora-64 > PV-18 > Kalyan Sona > S-308 > S-307. Oviposition and development were best in varieties with the highest moisture content at any level of relative humidity. Oviposition and development were best at 75% r.h. or 15·0–15·5 per cent moisture content in all varieties. Oviposition and development rates were greater at 30°C and slower at 18°C than at 25°C. Of the conditions examined 30°C and 75% r.h. was the best for oviposition and development of S. oryzae.     

Effect of fungi and fungicides on the preservation of wheat seed stored with high and low moisture content

The protective effect of the fungicides captan, chloratalonil, pentachloronitrobenzene, thiram and the commercial mixture of captan and carboxin against storage fungi, as well as the possible toxic effect on seed viability, were studied on seed of the Salamanca wheat variety. The research was conducted with wheat seed stored at 25°C with a high and low moisture content: (a) seed stored at a high relative humidity of 85%, to allow the development of fungi and (b) seed stored under dry conditions, with seed moisture contents below 13%. The germination of wheat seed, either with high or low moisture content, was slightly inhibited by the fungicide carboxin immediately following seed treatment. It appears that the fungicide temporarily promoted a slight effect of seed dormancy; however, this effect disappeared during the storage period. The fungicides chloratalonil, captan and carboxin+captan prevented the activity of the storage fungi, and protected the germination of the wheat seed stored at 85% relative humidity.     

The relationship between moisture content and equilibrium relative humidity of dried figs

A vacuum oven method is recommended for the determination of the moisture content of figs, by drying sliced quarters of whole figs at 70°C, at a pressure of less than 5 mm Hg for 24 hr. There is a greater variation between the moisture content of whole figs than between quarters of a single fig and the mean moisture content of a sample of figs can be determined with a standard error of 0.2–0.3%, by taking one quarter each from a number of whole figs. Data are presented for the moisture content/equilibrium relative humidity (e.r.h.) relationship of Turkish Lerida figs.     

MICROBIOLOGICAL QUALITY OF WHEAT STORED UNDER DIFFERENT CONDITIONS IN TURKEY

Four different types of wheat storage systems are widely used in the Marmara region. The existing storage conditions were studied and changes in the microbiological quality of the stored wheat under these conditions were assessed.
Depending on the external conditions, ambient temperatures and relative humidities in the stores were 17–26°C and 50–65% RH during summer and 3–10°C and 62–83% RH during winter, respectively. The low relative humidity level during harvesting and subsequent storage was adequate for obtaining low levels of moisture content and water activity in the produci for safe storage. The increase in relative humidity of the air during winter months did not affect the moisture content of the product considerably and the low temperature prevented mold growth. Therefore, all of the four different storage facilities were suitable for safe storage of grain for a period of one year without significant losses in quality due to microbiological load.     

The relationship between moisture content and equilibrium relative humidity of five types of wheat flour

There was little difference at 5, 15 and 25°C between the moisture content-equilibrium relative humidity relationships of three types of bread flour and a biscuit flour made from wheat. A flour made from wheat a about 18% moisture content heated to 70°C for about 15 min, had a higher equilibrium relative humidity than the other types.     

谷物湿热平衡新模型及热力学特性的研究

建立谷物平衡水分与相对湿度在不同温度下的关系模型,并利用小麦、玉米、水稻、大米的静态平衡试验数据进行拟合。结果表明,该方程适合描述小麦、玉米、水稻、大米的等温线,可直接求解出谷物的平衡水分。另外,根据所建立的模型,预测了不同温度条件下的安全储藏水分,并对谷物的热力学性能进行了分析:吸着等热值随着平衡水分值的减小而增加,解吸等热值增加更为显著;解吸和吸附过程中吸着等热值均高于水汽化潜热;平衡水分大于25%后,吸着等热值趋于稳定,与汽化潜热值接近;根据分析所得数据,拟合了小麦、稻谷、玉米解吸与吸附过程的吸着等热曲线回归方程,为以能量化的观念实施粮仓作业管理,实现高效、合理、节能储粮提供了有利依据。     

Moisture content/relative humidity equilibrium of some cereal grains at different temperatures

The concept of the equilibrium relative humidity (e.r.h.) of a product as a measure of storage potential is discussed. It is stressed that whilst moisture content gives an estimate of the amount of water in a product it does not, by itself, indicate the biological activity, or potential activity, of the product. Graphs are presented giving the e.r.h., at a given moisture content, for different temperatures of a soft wheat, barley, American yellow dent maize, flint maize grown in England, and tick beans (Vicia faba L.).     

Sorption equilibrium moisture and isosteric heat of adsorption of Chinese dried wheat noodles

Equilibrium moisture content (EMC) data for dried wheat noodles of ten Chinese varieties were collected by a gravimetric method at 11–96% equilibrium relative humidity (ERH) and 15 °C, 20 °C, 25 °C, 30 °C, and 35 °C. Five models were fitted to the sorption data, namely the modified Chung Pfost equation (MCPE), modified Henderson equation (MHE), modified Guggenheim Anderson deBoer equation (MGAB), modified Oswin equation (MOE), and a polynomial equation. The best fitting equations were MGAB and the polynomial equation. At a constant ERH, the EMC decreased with increasing temperature, despite the minor effect of temperature on the sorption isotherms of dried noodles. Initially, the isosteric heats of adsorption for dried wheat noodles decrease rapidly with increasing sample moisture content (m.c.); however, after the moisture content is more than 15% of the dry basis (d.b.), they decrease slowly with increasing m.c. The heat of vaporization of Chinese dried wheat noodles approaches the latent heat of pure water at a moisture content of ∼20% d.b., which is ∼2500 kJ/kg. The isosteric heats of sorption of Chinese dried noodles predicted by MCPE and MHE models at lower temperatures were higher than those at higher temperatures. When the equilibrium relative humidity (ERH) is 60%, the safe-storage moisture content of Chinese dried wheat noodles are 11.74% and 11.57% d.b. at 25 °C and 35 °C, respectively. Among ten varieties of dried wheat noodles, the egg-flavoured noodle had the highest onset temperature (T_o), peak temperature (T_p), and conclusion temperature (T_c) of gelatinization, but the golden-silk egg noodles had the highest peak enthalpy of gelatinization. The gelatinization T_o, T_p, and T_c of golden-silk egg noodles were the lowest. Most of the ten varieties of dried wheat noodles demonstrated similar thermal properties and hygroscopic behaviour.     

香酥鸭制品贮运过程中的脆性劣变机制

将香酥鸭腿放入恒温恒湿箱中贮存,测定不同温度(5、30℃)、相对湿度(50%、70%、90%)和贮藏时间(0、2、4、6、8、10 h)条件下香酥鸭腿的水分含量、水分活度、剪切力及微观结构,分析香酥鸭腿贮运过程中的水分迁移对脆性的影响,探讨脆性劣变机制。结果显示:5℃鸭皮水分含量先降低后升高,6 h后趋于平缓。鸭皮水分活度先增加,6 h后趋于平缓,鸭肉水分活度0~2 h降低,4 h后趋于平缓。鸭皮剪切力0~6 h增加,6 h后降低;30℃时鸭皮水分含量先升高后降低,水分活度和鸭皮剪切力变化类似5℃。随着相对湿度的升高,鸭皮的水分含量和水分活度增加,剪切力增大,脆性降低。油炸后鸭皮气孔数量少而大,随着水分的迁移,鸭皮气孔数量增加且较小。表明香酥鸭腿贮运过程中温度和相对湿度明显影响了鸭皮和鸭肉中的水分迁移。低温条件下水分迁移速率低,鸭皮水分含量和水分活度小;随着相对湿度增加,鸭皮的水分含量和水分活度增加。由于鸭皮、鸭肉与环境水分不断的迁移,香酥鸭腿的微观结构被破坏,剪切力增大,脆性降低。