SOURCES OF VARIATION IN THE NUTRIENT CONTENT OF AGRICULTURAL COMMODITIES FROM THE FARM TO THE CONSUMER

Raw agricultural commodities vary widely in nutrient composition at the point of sale to the consumer. Sources of this variation in fresh and fruits and vegetables include genetics, preharvest conditions of the plant, maturity of the edible product at harvest, postharvest handling and storage conditions, and any minimal processing techniques employed. Similar sources of variation exist for other plant products and for animal products. Current research knowledge is primarily limited to compositional information on ascorbic acid and β-carotene. A concerted, systematic effort is needed with specific attention focused on the effects of refrigerated storage on composition and bioavailability.     

A REVIEW OF THE CAUSES OF VARIATION IN MUSCLE GLYCOGEN CONTENT AND ULTIMATE pH IN PIGS

Muscle glycogen at slaughter causes variation in pork technological qualities, since it affects the ultimate pH (24 h postmortem). This review addresses various factors influencing muscle glycogen storage and the ultimate pH of pig meat. Results discussed in this paper indicate that breed and preslaughter handling, i.e., waiting time in lairage, mixing, and to a lesser extent fasting, significantly influence ultimate pH. Furthermore, interactions between handling procedures and breed could be highly significant, as with PSE meat. Since the recent discovery of the major gene rn⁺/RN⁻ which is assumed to influence glycogen concentration in the muscle of live pigs, genotype is considered an important source of variation in ultimate pH. All factors likely to influence glycogen concentration must be considered relative to the metabolic and contractile properties of muscle. These play an important role in the amount of glycogen at rest and in its depletion during chronic stress or muscular exercise.     

GENETIC AND ENVIRONMENTAL VARIATION OF GUM CONTENT IN BARLEY

The influence of genetic vs environmental factors on the gum content of the barley grain has been studied by growing 4 varieties of barley, at 4 locations in the South of Spain, with 6 sowing dates at each location. The genetic factors proved to be the more important, accounting for 89% of the variation over locations and 71·5% of the variation among locations and sowing dates. Of the environmental factors studied, the sowing date was the most important. The variety × sowing date interaction was also statistically significant. Furthermore, the later the sowing date the higher the gum content of the grain. There was no variety × location interaction and, therefore, the varieties ranked in the same order at each location. It was also demonstrated that there was a different pattern of response for the varieties when grown in environments which were able to induce high or low gum content, suggesting that low gum content-low response varieties should be grown if the grain is to be used as an adjunct in brewing.     

EFFECT OF SELENIUM FERTILIZATION ON THE GLYCOALKALOID AND NITRATE-NITROGEN CONTENT OF POTATOES

The effect of soil applications of sodium selenite (Na₂SeO₃) on the total glycoalkaloid (TGA) and nitrate-nitrogen (NO₃-N) contents of Katahdin potatoes was studied over two storage periods (0 and 5 month) during each of two years. Sodium selenite was banded to the soil at rates of 0.0, 5.6 (2.5), 11.2 (5.0) and 18.0 (7.5) kg/ha (ppm). Selenium treatment, at all levels, resulted in significantly lower TGA and NO₃-N contents than the controls. Applications of Na₂SeO₃ greater than 5.6 kg/ha did not result in further decreases in the TGA and NO₃-N content. These results were consistent for the two storage periods.     

VARIATION OF CELL WALL CONTENT IN FLOCCULENT AND NON-FLOCCULENT YEAST STRAINS

Estimation of the wall content of a number of flocculent and non-flocculent yeast strains taken in both the growth and stationary phases reveals that flocculent yeasts almost invariably increase their wall content to a greater extent as the cells pass to the stationary phase than do non-flocculent strains. This variation of increase is observed whether the yeasts are grown in hopped wort or in a synthetic malt-yeast-peptone-glucose medium. There are considerable variations in wall content from strain to strain in both types of yeast. Cells of flocculent strains are more difficult to disrupt than those of powdery strains. The nitrogen, phosphate and carbohydrate contents of the walls of all strains varied between the growth and stationary phases but no significant trends were noted in any of the components which could be related to flocculent or non-flocculent behaviour.     

硒及微生物富硒研究进展

介绍了硒与人体健康、富硒食品中硒的检测方法和微生物富硒等方面的研究进展。     

黄曲霉生长预测模型的建立及毒素含量变化

黄曲霉在适合条件下易污染储藏的粮食、饲料，产生对人畜有害的黄曲霉毒素。用两种模型模拟黄曲霉的生长规律，测定了黄曲霉毒素含量的变化情况，初步探索了二者之间的关系，并为风险评估提供了数据基础。     

EFFECT OF SELENIUM FERTILIZATION ON THE CONCENTRATION OF SELENIUM, OTHER MINERALS, AND ASCORBIC ACID IN POTATOES

The effect of selenium fertilization on the concentration of selenium, other minerals, and ascorbic acid of Katahdin potato tubers was studied during each of two years. Sodium selenite was banded to the soil at rates of 5.6 (2.5), 11.2 (5.0) and 16.2 (7.5) kg/ha (ppm of soil). The tuber selenium concentration was increased significantly (p<0.01) from 0.47 ppm to 0.93 ppm fresh weight. However, selenium levels in the soil greater than 5.0 ppm did not result in further increases in the selenium concentration of tubers. No significant effects due to selenium fertilization were observed for the concentration of other minerals and ascorbic acid. Similar trends were observed during both years of the study. In areas where the soil is low in selenium, addition of this element could prove useful in increasing the selenium content of potatoes, a very important vegetable in the American diet.     

聚酯二甘醇含量测定方法的改进

用玻璃毛细管柱代替不锈钢填充柱在色谱仪上进行二甘醇含量测定,可以克服原不锈钢柱存在的吸附、不稳定现象,提高分析的稳定性及准确度。     

牛奶中尿素含量的测定

根据二乙酰-肟与在酸性条件下尿素的反应,建立了一种分光光度法快速测定牛奶中尿素含量的方法,该方法可以定性和定量测定牛奶中尿素含量.在0.125g/L～1g/L之间线性良好.平均回收率为99.4%.该方法在实际的原料奶质量控制中得到了很好的应用.     

灵芝不同部位多糖含量测定

采用苯酚-硫酸法对灵芝菌盖表皮层、木栓层、菌柄、孢子粉、发酵菌丝体等部位中的灵芝多糖进行了测定,结果发现,灵芝发酵菌丝体中的多糖含量明显高于灵芝的其它部位,其含量顺序分别为：发酵菌丝体〉菌盖表皮层〉孢子粉〉菌柄〉木栓层。     

ESTIMATION OF CHANGES IN THE AVAILABILITY OF EACH INDIVIDUAL ESSENTIAL AMINO ACID IN FOOD PROTEINS

A technique has been developed for determining decreases in the availability of individual essential amino acids in a food as a result of processing, cooking or other treatments. Diets containing casein and free L-amino acids were used to establish critical dietary amino acid levels. These critical levels were such that reductions of 20% in the level of any of nine essential amino acids significantly reduced protein utilization as estimated by rat bioassays. When these critical levels were used in evaluating amino acid availability in unheated and heated lactalbumin, each of the nine essential amino acids was found to be affected by the heat treatment.     

纺织品中纤维含量检测结果的评定

分析了影响纺织品纤维含量准确测定的主要因素,并对检测结果的不确定度表述方式进行了评定,为更科学和准确地测定纺织品中纤维的实际含量提供参考和指导。     

煮制对菠菜中草酸含量的影响

研究煮制方法对菠菜中草酸含量的影响,以期了解煮制对草酸的作用,尤其研究不同煮制时间及不同水量对波菜煮制时草酸含量的影响情况.另外根据不同食物在煮制后其草酸的变化情况,了解不同食物间的差异.