Stability of whey-protein-stabilized oil-in-water emulsions during chilled storage and temperature cycling

The stability of heat-treated and/or acidified, partly-crystalline-fat-based, whey-protein-stabilized oil-in-water (o/w) emulsions against partial coalescence was investigated during chilled storage (at 5 degrees C) and repeated temperature cycling (three times between 5 and 25 degrees C). Experiments focused on the evolution of firmness and droplet size (using pulsed field gradient NMR and scanning electron microscopy). Besides the effects of denaturation and/or acidification, the influence of the droplet size of the dispersed phase on emulsion stability was investigated also. It was found that heat treatment or acidification before emulsification led to unstable emulsions during temperature cycling, whereas heat treatment after acidification resulted in stable emulsions.     

赴加拿大森林航空消防吊桶培训考察报告

为进一步增强森林航空消防直接灭火特别是吊桶灭火的能力,受加拿大SEI责任有限公司的邀请和局领导的安排,我们组成森林航空消防吊桶技术培训考察团于2006年10月16～29日赴加拿大进行了培训和考察。     

Osmotic Properties of Gluten

A model for dough is proposed in which the distribution of water between hydrated gluten and starch paste explains a number of practical observations such as 1) the extreme sensitivity of the consistency of dough to the amount of water in the recipe, and 2) the fact that working of the material results in an increase in consistency. The model assumes dough to be a composite material consisting of a starch paste and gluten filaments. During kneading, the starch granule paste in dough dries to become a phase with a yield stress as a result of the uptake of water by the stretching gluten filaments. This study focused on one particular aspect of this model: the osmotic properties of gluten during stretching. The results suggest that gluten can be hydrated more efficiently in the stretched state than in an unstretched conformation. Gluten hydration tends to change slowly over a period of weeks, which is accompanied by water expulsion or uptake, depending on the osmotic properties of the solvent. The rate of change does not seem to depend very much on pH and osmotic pressure for the current experimental conditions. The level of hydration of relaxed gluten depends strongly on pH, as expected. The experiments allow the construction of an osmotic pressure versus gluten concentration diagram over the range 4.6 < pH < 5.8. The level of hydration of the gluten is consistent with the proposed model for dough.     

Differential Scanning Calorimetric Study on the Effects of Frozen Storage on Gluten and Dough

Water transport from the gluten to the starch paste during frozen storage of a dough was studied by analysis of the differential scanning calorimetry (DSC) peak shape for gluten and dough. The results indicate that in gluten stored at ‐15°C, the water content in the gluten phase decreased by ≈1% over the first three weeks. An apparent steady state was attained over this period and the amount of ice did not increase further. Such changes were not observed for samples stored at ‐25°C. Qualitatively similar observations were made for dough stored at either ‐15 or ‐25°C. The greater sensitivity of dough to frozen storage is tentatively attributed to a slightly lower glass transition temperature in dough.     

Environmental conditions alter the effect of organic acid salts on digestibility and intestinal morphology in Nile tilapia (Oreochromis niloticus)

The impact of two dietary organic acids (OAs) on nutrient digestibility and intestinal morphology was determined in Nile tilapia under conditions of dissolved oxygen in the water: normoxia and hypoxia. Four diets designated as control (0 g/kg organic acid salt), KDF (2 g/kg potassium diformate), CAB (2 g/kg calcium butyrate) and their combination (4 g/kg of a mixture of KDF and CAB, ration 1:1) were formulated with 520 g/kg of soybean meal in order to produce soybean meal enteritis‐like symptoms. The four diets were tested first under normoxic conditions (6 mg/L) for a period of 5 weeks, followed by a test period under hypoxic conditions (3 mg/L). The results showed that OAs were unable to significantly improve growth and nutrient digestibility under normoxic conditions but under hypoxic conditions, there was a significant enhancement of the growth and nutrient digestibility. Fish fed OA‐supplemented diets showed improvements in the intestinal morphology under the normoxic conditions, and these effects were more pronounced under the hypoxic conditions. Experimental findings suggest that OAs can improve the nutrient digestibility and intestinal morphology under hypoxic conditions. A synergistic effect by the combination of formic and butyric acid on growth, digestibility and intestinal morphology was not found.     

<Emphasis Type="Italic">Pectobacterium carotovorum</Emphasis> subsp. <Emphasis Type="Italic">carotovorum</Emphasis> can cause potato blackleg in temperate climates

It is well established that the pectinolytic bacteria Pectobacterium atrosepticum (Pca) and Dickeya spp. are causal organisms of blackleg in potato. In temperate climates, the role of Pectobacterium carotovorum subsp. carotovorum (Pcc) in potato blackleg, however, is unclear. In different western and central European countries plants are frequently found with blackleg from which only Pcc can be isolated, but not Pca or Dickeya spp. Nevertheless, tubers vacuum-infiltrated with Pcc strains have so far never yielded blackleg-diseased plants in field experiments in temperate climates. In this study, it is shown that potato tubers, vacuum-infiltrated with a subgroup of Pcc strains isolated in Europe, and planted in two different soil types, can result in up to 50% blackleg diseased plants.     

Heat treatment and meristem culture for the production of virus-free plant material

To obtain virus-free material from plant species or cultivars which are vegetatively propagated and totally infected with virus, three methods were developed. Heat treatment (with hot water or hot air) resulting in an inactivation or an inhibition of the multiplication of the virus has been successful in several cases (a.o. sugar-cane, fruit trees). However, there are viruses which are not inactivated by heat; to obtain virus-free material from plants infected with such viruses the small tip meristems are isolated and cultivated on nutrient media because in several cases the tip meristem of systemically infected plants appeared to be virus-free. The possibilities of this method and the difficulties in composing suitable nutrient media for further shoot development and rooting are treated in detail. Because the tip meristem is very small (0.1 mm) the percentage of growing meristems is not always satisfactory. To increase this percentage a combination of heat treatment and meristem culture has been applied. This gives the possibility of using somewhat larger stem tips (1 mm) which grow better on the nutrient media and may still be virus-free. It always remains necessary to test the treated material for presence of virus. A list is given of crop plants from which virus-free stocks are obtained in The Netherlands and other countries.Samenvatting Directe chemische bestrijding van virussen in de plant is niet mogelijk zonder de gastheer te schaden. De verspreiding van virussen, die op andere wijze dan door vectoren worden overgebracht, kan evenmin door chemische middelen voorkomen worden. Daardoor kunnen soorten en cultivars, die uitsluitend vegetatief vermeerderd worden, volledig met virus besmet raken. Voor deze plantesoorten of cultivars zijn methoden ontwikkeld door middel waarvan virusvrij plantenmateriaal verkregen kan worden, nl. toepassing van warmte, van meristeemcultuur en van een combinatie van beide. Warmte kan worden toegepast op twee manieren nl. als warm water en als warme lucht. Bij de eerste wordt het zieke gewas behandeld en bij de tweede uit het behandelde gewas virusvrij vermeerderingsmateriaal geïsoleerd en opgekweekt. De eerste methode werd met succes toegepast op sereh-zieke suikerrietstekken; verscheidene fruitgewassen zijn door middel van warme lucht virusvrij gemaakt.Wanneer warmtebehandeling niet tot het gewenste resultaat leidt, kan men door middel van meristeemcultuur proberen virusvrije planten te verkrijgen. Het meristematisch weefsel aan de top blijkt nl. in vele gevallen geen virus te bevatten. Door deze topjes te isoleren en op een voedingsbodem over te brengen is het mogelijk een plant op te kweken, die geen virus bevat. Deze cultuur stelt hoge eisen aan de voedingsbodems; deze zijn voor de scheutvorming en de beworteling zeer verschillend en dikwijls voor elke plantesoort en cultivar ook. Door de plant vóór de isolatie van het topmeristeem een warmtebehandeling te laten ondergaan kan men de stengeltopjes iets groter nemen d.w.z. met twee bladprimordia; daardoor wordt de kans dat het geïsoleerde weefsel zich ook verder tot een plantje ontwikkelt groter. Het blijft altijd noodzakelijk om het behandelde of het opgekweekte materiaal op aanwezigheid van virus te toetsen. Van verscheidene gewassen worden met behulp van meristeemcultuur — al of niet in combinatie met warmtebehandeling — reeds grote hoeveelheden virusvrij materiaal gekweekt. Behalve praktisch belang heeft dit laatste ook grote betekenis voor het onderzoek naar de invloed van een bepaald virus op de produktie en de kwaliteit van een gewas. Plantesoorten en cultivars waarvan in Nederland en andere landen virusvrij materiaal verkregen is worden opgenoemd.Lecture held at the VIth Int. Congr. Plant Protection, Vienna, 30 aug.–6 sept. 1967