Kinetics of bubble growth in wheat flour dough during proofing studied by computed X-ray micro-tomography

Bread doughs of various compositions were prepared and studied by computed X-ray microtomography (XRT) with high resolution (5 μm). Their cellular structure was followed during the last stage of proofing, from 40 min to 180 min, to focus on the films separating bubbles and their possible coalescence. Image analysis allowed to determine the porosity, the connectivity index, the bubble size and the cell walls thickness distributions which were fitted by usual mathematical functions. Images showed that different compositions led to different cellular structures. The kinetics of porosity and connectivity had sigmoid shapes with 0.7 and 1 as asymptotic values, respectively. For an average formula, mean cell width grew from 410 μm to 675 μm and the mean cell wall thickness grew from 200 μm to 230 μm. At the end of proofing, most bubbles were interconnected, i.e. they were separated by films of thickness lower than 5 μm. Changes of recipe led to different structures, which were discussed through the influence of the liquid fraction and of the sugar content on the coalescence of bubbles. These results suggested that at the end of fermentation, the dough could be considered as a three phase co-continuous medium: gas/liquid/viscoelastic matrix.     

Morphological development and nutritive value of herbage in five temperate grass species during primary growth: analysis of time dynamics

In a 2‐year field experiment, morphological development and measures of the nutritive value of herbage for livestock during primary growth in Meadow foxtail, Tall oatgrass, Cocksfoot, Perennial ryegrass and Yorkshire fog were investigated. All measured variables were affected significantly by both species and sampling date, and their interaction (P < 0·001), in the period of primary growth. Changes with time in mean stage weight for Meadow foxtail and Cocksfoot were different from the other species due to their indeterminate growth habits. Mean stage weight of Tall oatgrass and Yorkshire fog increased more rapidly than that of Perennial ryegrass with time. Changes in mean stage weight with time were described by linear, parabolic and sigmoid relationships. Crude protein (CP) concentration of herbage was higher for Cocksfoot and Meadow foxtail than for Perennial ryegrass. A parabolic relationship of CP concentration with time was typical for all the species. Concentrations of neutral‐detergent fibre (NDF) and acid‐detergent fibre (ADF) in herbage of the species differed most during the mid‐period of primary growth. Their increases with time showed curvilinear (sigmoid and parabolic) relationships. Perennial ryegrass had lower concentrations of both NDF and ADF in herbage than the other species. Differences between the in vitro dry matter (DM) digestibility among the grasses increased in mid‐ and late periods of primary growth. Perennial ryegrass had higher values for in vitro DM digestibility but the difference from other species was small in the early period of primary growth and from cocksfoot in the late period of primary growth. In vitro DM digestibility showed, in most cases, a sigmoid and, in others, a linear decrease with time. Principal component analysis showed that perennial ryegrass and meadow foxtail were the most distinctive of the species in characteristics relating to morphological development and the nutritive value of herbage to livestock.     

Influence of daylength and temperature during formation of seed potatoes on subsequent growth and yields under long day conditions

Production of high quality seed potatoes is normally favoured by a cool climate with minor pest problems. Growth chamber studies aimed to reveal if daylengths (12 and 24 hrs) and temperatures (18/12 and 12/9°C day/night) during production also might influence progeny growth. Results showed no significant carry-over effect from daylength conditions, while growth vigour and yields were affected by parent plant growth temperature. Further experiments, including a greater range of temperatures, different cultivars and measurements of physiological age, are required to discuss theoretical and practical implications of the results.     

Aspergillus flavus growth and aflatoxin production as influenced by total lipid content during growth and development of cottonseed

Aspergillus flavus infects several food and feed crops, such as corn (Zea mays L.), cotton (Gossypium hirsutum L.), peanuts (Arachis hypogaea L.), and tree nut crops and contaminates the seed with carcinogenic aflatoxins. These susceptible crops contain rich reserves of lipids and fatty acids. The nature of relationship between lipids and the ability of the fungus to infect and produce aflatoxins in mature cottonseed, a protein-rich animal feed, has been addressed previously. In this study, we tracked lipid accumulation in developing cottonseed (15–35 days post-anthesis [DPA]) and also the ability of an aflatoxigenic strain and an isogenic non-aflatoxigenic strain to grow and produce aflatoxins in planta. The aflatoxigenic strain Af-70 green fluorescent protein (GFP) and the isogenic, non-aflatoxigenic strain SRRC 1500 (fungal collections maintained at the Southern Regional Research Center) did not differ much in infection and colonization of cottonseed. The non-aflatoxigenic strain did not produce aflatoxin at all stages of cottonseed development, whereas the aflatoxigenic strain Af-70 GFP produced copious amounts of aflatoxin and it coincided with the increasing levels of lipids, especially in mature cottonseed (30–35 DPA). Fungal growth, as quantified by the GFP expression in the fungus, was highly correlated with toxin production.     

Viscoelastic properties and bubble structure of rice-gel made from high-amylose rice and its effects on bread

Rice gel is a novel form of processed rice, where gelatinized rice is sheared at high speed to create a gel with unique viscoelastic properties, which can partially replace wheat flour in bakery products. In this study, the viscoelastic properties and bubble structures of rice gels made from two high-amylose rice cultivars and two different ratios of rice to water were studied, focusing on the effect of cooling the gelatinized rice before high-speed shearing (cooled rice gel) as opposed to shearing the gelatinized rice while hot (hot rice gel). Increasing the water content and cooling the rice before high-speed shearing generally decreased the dynamic storage (E′) and loss moduli (E″) in the viscoelasticity measurement and introduced fewer but larger and uniform bubbles in the rice gel. In addition, breads made from cooled rice gel showed significantly higher volume than those made from hot rice gel. The application of mechanical shearing to gelatinized starch has a great potential in creating novel food materials with characteristic textures, and can also be used for the processing of cereals other than rice.     

Synchrotron X-ray scattering analysis of the interaction between corn starch and an exogenous lipid during hydrothermal treatment

Lipids have an important effect on starch physicochemical properties. There exist few reports about the effect of exogenous lipids on native corn starch structural properties. In this work, a study of the morphological, structural and thermal properties of native corn starch with L-alpha-lysophosphatidylcholine (LPC, the main phospholipid in corn) was performed under an excess of water. Synchrotron radiation, in the form of real-time small and wide-angle X-ray scattering (SAXS/WAXS), was used in order to track structural changes in corn starch, in the presence of LPC during a heating process from 30 to 85 °C. When adding LCP, water absorption decreased within starch granule amorphous regions during gelatinization. This is explained by crystallization of the amylose-LPC inclusion complex during gelatinization, which promotes starch granule thermal stability at up to 95 °C. Finally, a conceptual model is proposed for explaining the formation mechanism of the starch-LPC complex.     

Impact of frost and plant age on compensatory growth in timothy and perennial ryegrass during winter

Two cultivars of each of two contrasting grass species, timothy ( Phleum pratense L.) and perennial ryegrass ( Lolium perenne L.), sown either in May or July, were sampled for dry matter (DM) weight of roots and herbage in late October (end of main growing season) and examined for regrowth when exposed to a frost treatment (−8 to −10°C in darkness for 48 h) in late January, early March and late April. The frost treatment caused compensatory root and herbage growth, and regrowth of roots in March and April was greater than regrowth of herbage. Early-sown plants had higher DM weights of roots and herbage than late-sown plants in October but had the lowest survival rate when exposed to the frost treatment in April. Compensatory growth of root and herbage in response to moderate frosts occurred in January and March in all cultivars, and in the most frost-resistant timothy cultivar in April. Concentration of total carbohydrates increased from October to March with the greatest increase in the most winter-hardy cultivar of each species, and then decreased in April. An indirect correlation between concentration of total carbohydrates and tolerance to moderate frost was indicated, and plant survival and ability for compensatory growth were also associated with differences in adaptation related to winter survival in the cultivars tested.     

Changes in nutritive value and herbage yield during extended growth intervals in grass–legume mixtures: effects of species,maturity at harvest,and relationships between productivity and components of feed quality

There is a lack of information on the effects of companion species in grass–legume mixtures on herbage yield and quality changes during prolonged growth. Such information is relevant for harvest planning and estimation of consequences for feeding value of conserved feed when harvesting is delayed. Perennial ryegrass was sown with each of four legumes: red clover, white clover, lucerne and birdsfoot trefoil, and white clover was sown with hybrid ryegrass, meadow fescue and timothy. Effects of species composition on herbage yield, contents of N, neutral detergent fibre (NDF), acid detergent fibre (ADF) and lignin, ash and in vitro organic matter digestibility (IVOMD) were studied in entire herbage and in component species during 2 years in a small‐plot cutting trial in Denmark. In May and August, the dynamic development of components of feed value and their interrelationships were investigated by sampling at optimum harvest date (i.e., normal practice) ± 1 week (t = ?1 to t = +1). Herbage digestibility and contents of N and ash decreased while those of fibre compounds increased during the 2 weeks from t = ?1 to t = 1 in all species. In May, contents of ADF and lignin increased at a faster rate in legumes than in grasses; in August, NDF and ADF increased most quickly in legumes. Generally, N contents and IVOMD declined at similar rates in grasses and legumes, but, within each group, differences in yield and quality development occurred among species. The relationship between weekly growth rate and change in quality parameters differed among species and functional groups, i.e., grasses and legumes. Results are discussed in the context of quantifying the impact of delaying the harvest date of grass–legume mixtures and relationships between productivity and components of feed quality.     

Influence of plant growth and root architecture of Italian ryegrass (Lolium multiflorum) and tall fescue (Festuca arundinacea) on N recovery during winter

Nitrate () leaching is an environmental and health concern. In grazed pasture systems, leaching primarily occurs beneath animal urine patch areas due to high nitrogen (N) loading and the inability of pasture plants to capture all of this N. This study investigated the relative importance of plant growth and root architecture to recover soil N. Herbage N recovery, dry matter (DM) yield and root architecture, following injections of ¹⁵N‐enriched urea at different soil depths (5, 25 and 45 cm), were measured for Italian ryegrass (Lolium multiflorum Lam.) and tall fescue (Festuca arundinacea Schreb.) grown in soil monolith lysimeters (18 cm diameter × 70 cm depth) under simulated South Island, New Zealand winter temperature and light levels. Total herbage N uptake and DM yield were on average 24 and 48% greater in L. multiflorum than F. arundinacea respectively. Root length density (cm cm^?3 soil) in the 5‐ to 25‐cm‐depth horizon was similar between species. In the 25‐ to 45‐cm‐depth horizon, F. arundinacea roots were found at higher densities than L. multiflorum. In the 45‐ to 65‐cm‐depth horizon, root length density was fourfold to ninefold higher for F. arundinacea than L. multiflorum, but N uptake efficiency was greater in L. multiflorum (0·48 mg ¹⁵N m^?1 root) than F. arundinacea (0·09 mg ¹⁵N m^?1 root). The results suggest that deep F. arundinacea roots are relatively inactive during the winter period and confirm that plant growth is more important than root architecture (e.g. deep roots) to recover soil N and ultimately reduce nitrate leaching losses.