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.     

The relationship between moisture content and equilibrium relative humidity of pig feed

The moisture content-equilibrium relative humidity relationships at 5, 15 and 25°C of 3 pig meals and pellets made mostly from barley meal and wheatings, with various proportions of soya meals, were very similar to each other. The moisture content in equilibrium with 70% r.h. at 25°C was about 14%, similar to that for cereal grains but these pig feeds should be stored at or below 12% mositure content at this temperature, to avoid the risk of the development of mites.     

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.     

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.     

An accelerated method for adjustment of equilibrium moisture content of foods

The long equilibration period required to attain a desired water activity by traditional methods can lead to microbiological and physico-chemical changes in the food under study. To mitigate these difficulties, a system has been developed for adjusting the relative humidity of food samples to the desired levels in less than an hour. Food samples are exposed to either a saturated or a near zero water vapour pressure thereby greatly decreasing the time required for equilibration. This is mainly due to the increased mass transfer driving force. Evacuation, along with agitation of the head-space, is found to enhance the rate of moisture change. By using the sorption curves prepared using this technique, the time required for a particular food to reach a certain moisture (or a_w) level can then be predicted. The moisture and a_w levels predicted were found to be in good agreement with experiment.     

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.     

Determination of moisture content and equilibrium relative humidity of dried fruit—Sultanas

A vacuum oven method is recommended for the determination of the moisture content of sultanas, drying to constant weight at 70°C, and at a pressure of 5 mm Hg or less, for 24 hr. It is shown that accuracy of better than 0·5 per cent cannot be guaranteed and that day to day variation, and oven position variation are encountered. A distillation method, using toluene as the entrainer, over a period of $\text{2}\text{1}\text{2}\text{hr}$, gives satisfactory estimates of moisture content when a ‘rapid’ but less accurate estimate is required. Data are presented for the moisture content/equilibrium relative humidity (e.r.h.) relationship of Turkish sultanas.     

The moisture content-equilibrium relative humidity relationship of cocoa beans

The moisture content-equilibrium relative humidity relationships for cocoa beans grown in nine different countries were similar to each other, and the maximum safe storage moisture content in equilibrium with 70% relative humidity was between 6.0 and 7.9% at 25°C. There was a large variation between the moisture content of individual beans within each sample, the maximum standard deviation observed in a sample of thirty beans being 0.97, after the moisture content had been increased by adding water.     

控制平衡相对湿度(ERH)与纳他霉素协同作用在夹心糯米点心中防腐效果及机理的研究

夹心糯米点心受微生物污染的程度与其平衡相对湿度(ERH)有关,本文利用不同剂量保湿剂控制产品的平衡相对湿度(ERH),寻找到最佳水分活度的配方,在此配方的基础上使用纳他霉素有效抑制霉菌及酵母的生长。本文研究了不同剂量的纳他霉素及保湿剂在糯米点心中的防霉效果,在常温条件下(25℃)保存,保湿剂含量0.6%～0.8%,10～25mg/kg的纳他霉素可以显著抑制霉菌和酵母的生长,同时保持产品的水分含量及良好的柔软度,延长了糯米点心的货架期,并且对人体安全无害。      

Use of polyols to measure equilibrium relative humidity

Polyols were used to estimate the equilibrium relative humidity (ERH) of foods. Glycerol, ethylene glycol and propylene glycol were found to be suitable for estimating ERH, up to an ERH of 93%, by measuring the refractive index after they had equilibrated in the headspace of a food. The ERH determined by the polyol method agreed with the ERH determined using Sina and Vaisala meters to within 1% ERH for a lithium sulphate slurry, and for foods were usually within 2%. The ERH of prunes determined using the Vaisala meter was about 6% lower than the value obtained by the other methods. Unlike most electronic techniques the polyol method was unaffected by the presence of glycerol, propylene glycol or butylene glycol and so is suitable for measuring the ERH of foods containing these humectants. The polyol method can be used in developing countries where access to sophisticated equipment is limited.     

The moisture content—Equilibrium relative humidity relationship of malt

The equilibrium relative humidity for samples of green malt removed from the kiln during drying at up to 70°C, was higher than that for samples dried in the laboratory at 35°C, the difference being attributed to these drying temperatures. The relationship between moisture content and equilibrium relative humidity of finished malt removed from the kiln after drying and damped up in the laboratory, was also determined. The equilibrium curve for finished malt was closer to the desorption curve obtained by drying in the kiln than to the curve obtained by laboratory drying.     

通风过程中进风相对湿度对仓储粮堆温度和水分的影响研究

温度和水分含量是两个重要的物理变量,在研究谷物储存时品质变化起到很大作用。通风用于冷却粮堆并保持温度恒定,以防止水分迁移。良好的通风条件对粮仓内存储安全有显著影响。目前,通风空气相对湿度对粮堆水分影响的研究相对较少。采用数值模拟和实验研究相结合的方式,探索和比较因不同进风相对湿度而引起的通风过程中仓储的小麦温度和水分变化规律。结果表明:进风相对湿度较低时冷却干燥效率更高,小麦粮堆降温更快速,并将昆虫和霉菌的活动保持在较低水平。     

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.     

A mean moisture content-equilibrium relative humidity relationship for nine varieties of wheat

A mean moisture content-equilibrium relative humidity relationship for nine varieties of wheat at 25°C is presented, for which the curves were fitted by eye. The mean safe storage moisture content in equilibrium with 70% relative humidity (r.h.) for all the wheat varieties adsorbing moisture was 14.7% (wet weight basis) but if varietal differences and errors in measurement are taken into account, the moisture content of stored wheat may need to be as low as 13% to be safe from attack by mites. The hysteresis between adsorption and desorption reached a maximum of 0.7% moisture content at 40–50% r.h. Hysteresis was found to be statistically significant up to 75% r.h. Equilibrium moisture contents were calculated from data transformed using the Chung and Pfost equation and compared with the measured moisture contents.     

Influence of temperature and relative humidity on the efficacy of thiamethoxam for the control of three stored product beetle species

Laboratory bioassays were carried out in order to evaluate the effectiveness of thiamethoxam in different levels of temperature and relative humidity (r.h.) against three major stored-grain beetle species, the lesser grain borer Rhyzopertha dominica (F.), the rice weevil, Sitophilus oryzae (L.) and the confused flour beetle, Tribolium confusum Jacquelin du Val. Adults of the three species were exposed on wheat treated with thiamethoxam at 0.1, 1 and 5 ppm and under six different combinations of temperature (20, 25 and 30 °C) and r.h. levels (55 and 75%). Our study showed that the increase in temperature increased mortality in all insect species, particularly at the lowest concentration. For some of the combinations tested, the low r.h. seemed to play a significant role in thiamethoxam efficacy in the case of R. dominica. Moreover, of the species tested, T. confusum was found to be the least susceptible, while R. dominica the most susceptible. In general, thiamethoxam was found to be effective against all three species, at concentrations that are comparable with most commercially available grain protectants.     

The influence of air temperature and relative humidity on milling performance and flour properties

Three wheats, one Canadian and two from the UK, were used to investigate the effect of ambient temperature and relative humidity (r.h.) on milling performance and flour properties. When the temperature was varied from 25 to 15°C, a decrease in ambient temperature was accompanied by an increase in extraction rate but no change in flour moisture content. When the r.h. was varied from 70 to 50%, a decrease in r.h. was accompanied by an increase in extraction rate and a decrease in flour moisture content. Changes in r.h. had a greater influence on milling performance and flour properties than did changes in ambient temperature.