Bronwen G. Smith

The polysaccharide composition of Poales cell walls: Poaceae cell walls are not unique

Abstract Monocotyledon families can be divided into two groups depending on the presence (Group A) or absence (Group B) of ferulic acid ester-linked to their unlignified cell walls. The two groups also differ in the major types of non-cellulosic polysaccharides in their unlignified cell walls: in Group A they are glucuronoarabinoxylans (GAXs), and in Group B they are pectic polysaccharides. Previous studies suggested that among the Group A families, the Poaceae (grasses and cereals) was the only family with unlignified cell walls containing (1→3,1→4)- β - d -glucans. Moreover, the unlignified cell walls of the Poaceae contain a smaller proportion of pectic rhamnogalacturonans than those of the other Group A families. However, these studies did not include other families in the order Poales. We examined the polysaccharide compositions of unlignified cell walls from species of six Poales families: Anarthriaceae, Centrolepidaceae, Ecdeiocoleaceae, Flagellariaceae, Poaceae, and Restionaceae. The cell walls of all the species examined contained (1→3,1→4)- β -glucans with the exception of two Restionaceae species; these cell walls also contained similar, small proportions of pectic rhamnogalacturonans. Glucuronoarabinoxylans were a major component of these cell walls and smaller amounts of xyloglucans and glucomannans or galactoglucomannans were also present. We found the polysaccharide compositions of the lignified cell walls were similar and differed in similar ways from the polysaccharide compositions of unlignified cell walls from the same species. Our results are discussed in relation to the possible evolution of Poales families.

Polysaccharide Composition of Unlignified Cell Walls of Pineapple [Ananas comosus (L.) Merr.] Fruit

The polysaccharides of cell walls isolated from the fleshy, edible part of the fruit of the monocotyledon pineapple [Ananas comosus (L.) Merr.] (family Bromeliaceae) were analyzed chemically. These cell walls were derived mostly from parenchyma cells and were shown histochemically to be unlignified, but they contained esterlinked ferulic acid. The analyses indicated that the noncellulosic polysaccharide composition of the cell walls was intermediate between that of unlignified cell walls of species of the monocotyledon family Poaceae (grasses and cereals) and that of unlignified cell walls of dicotyledons. Glucuronoarabinoxylans were the major non-cellulosic polysaccharides in the pineapple cell walls. Xyloglucans were also present, together with small amounts of pectic polysaccharides and glucomannans (or galactoglucomannans). The large amounts of glucuronoarabinoxylans and small amounts of pectic polysaccharides resemble the noncellulosic polysaccharide composition of the unlignified cell walls of the Poaceae. However, the absence of (1 ->3,1 ->4)-[beta]-glucans, the presence of relatively large amounts of xyloglucans, and the possible structure of the xyloglucans resemble the noncellulosic polysaccharide composition of the unlignified cell walls of dicotyledons.

State diagram of apple slices : glass transition and freezing curves

Abstract The state diagram of apple flesh was developed by measuring and modeling its freezing points and glass transition temperatures. The freezing curve and glass transition lines were developed using Clausias–Clapeyron and Gordon–Taylor models, respectively. The state diagram of apple pieces developed in this work can be used in determining the stability during frozen storage and in dried conditions as well as in designing drying and freezing processes.

Cell wall structures leading to cultivar differences in softening rates develop early during apple (Malus x domestica) fruit growth

BackgroundThere is a paucity of information regarding development of fruit tissue microstructure and changes in the cell walls during fruit growth, and how these developmental processes differ between cultivars with contrasting softening behaviour. In this study we compare two apple cultivars that show different softening rates during fruit development and ripening. We investigate whether these different softening behaviours manifest themselves late during ethylene-induced softening in the ripening phase, or early during fruit expansion and maturation.Results‘Scifresh’ (slow softening) and ‘Royal Gala’ (rapid softening) apples show differences in cortical microstructure and cell adhesion as early as the cell expansion phase. ‘Scifresh’ apples showed reduced loss of firmness and greater dry matter accumulation compared with ‘Royal Gala’ during early fruit development, suggesting differences in resource allocation that influence tissue structural properties. Tricellular junctions in ‘Scifresh’ were rich in highly-esterified pectin, contributing to stronger cell adhesion and an increased resistance to the development of large airspaces during cell expansion. Consequently, mature fruit of ‘Scifresh’ showed larger, more angular shaped cells than ‘Royal Gala’, with less airspaces and denser tissue. Stronger cell adhesion in ripe ‘Scifresh’ resulted in tissue fracture by cell rupture rather than by cell-to-cell-separation as seen in ‘Royal Gala’. CDTA-soluble pectin differed in both cultivars during development, implicating its involvement in cell adhesion. Low pectin methylesterase activity during early stages of fruit development coupled with the lack of immuno-detectable PG was associated with increased cell adhesion in ‘Scifresh’.ConclusionsOur results indicate that cell wall structures leading to differences in softening rates of apple fruit develop early during fruit growth and well before the induction of the ripening process.

Monolignol ferulate conjugates are naturally incorporated into plant lignins

Plants have convergently evolved to use monolignol ferulate conjugates to produce lignins containing chemically labile backbone esters. Angiosperms represent most of the terrestrial plants and are the primary research focus for the conversion of biomass to liquid fuels and coproducts. Lignin limits our access to fibers and represents a large fraction of the chemical energy stored in plant cell walls. Recently, the incorporation of monolignol ferulates into lignin polymers was accomplished via the engineering of an exotic transferase into commercially relevant poplar. We report that various angiosperm species might have convergently evolved to natively produce lignins that incorporate monolignol ferulate conjugates. We show that this activity may be accomplished by a BAHD feruloyl–coenzyme A monolignol transferase, OsFMT1 (AT5), in rice and its orthologs in other monocots.

Color and density of apple cubes dried in air and modified atmosphere

Abstract The color, density and porosity of apple cubes dried in air and modified atmospheres were measured to identify the potential of modified atmosphere drying for foods. The modified atmospheres were achieved by flushing nitrogen gas through a specially designed laboratory dryer. The drying temperature was varied from 17 to 75°C. The results indicated that dried apple cubes with no browning could be produced under low oxygen atmospheres. Thus, chemical additives, such as sulfur dioxide can be completely eliminated from the process. The temperature and oxygen levels in the drying atmosphere were important factors in achieving the best quality in terms of color. Apple cubes dried in low oxygen atmospheres gave more porous products than those dried in air. Moreover, apple cubes dried in a nitrogen atmosphere had the greater number of open pore structures connected to the the exterior surface of the cubes.

Cell wall compositions of raw and cooked corms of taro (Colocasia esculenta)

The monosaccharide compositions of parenchyma cell walls of raw and cooked corms of taro, Colocasia esculenta cv Tausala Pink, were determined. The cell wall constituents were sequentially extracted using CDTA, Na2CO3, 1 M KOH, 4 M KOH and water to leave a final residue (α-cellulose). The monosaccharide compositions of the cell walls and cell wall fractions from the raw and cooked corms were consistent with the presence in these cell walls of large amounts of cellulose and pectic polysaccharides. The monosaccharide composition of the cell walls of the raw corms resembled the monosaccharide compositions of primary cell walls of other non-commelinoid monocotyledons and dicotyledons. Cooking of the corms resulted in alteration of the cell walls, with solubilisation of pectic polysaccharides occurring earlier in the sequential fractionation and possibly changes in the extractability of xyloglucans and/or xylans. © 2000 Society of Chemical Industry

Antioxidant capacity, polyphenolics and pigments of broccoli-cheese powder blends.

Novel products were developed by combining freeze dried and conventionally dried broccoli sprouts powder with the commercially available cheese powder. Quality assessment of the blended products during the development process and of the final product was done by sensory analysis and estimation of total antioxidant capacity, total polyphenolics, total chlorophyll and total carotenoids. Freeze drying was more efficient in preserving the original nutritional and sensory characteristics of the dried broccoli sprouts. Blending of the samples including the blend with a least weight proportion of broccoli sprouts powder showed an improved content of healthy compounds. Based on chemical data and sensory analysis, it was concluded that the blended cheese powder containing up to 20% freeze dried broccoli powder was an acceptable product.

Creep test observation of viscoelastic failure of edible fats

A rheological creep test was used to investigate the viscoelastic failure of five edible fats. Butter, spreadable blend and spread were selected as edible fats because they belong to three different groups according to the Codex Alimentarius. Creep curves were analysed according to the Burger model. Results were fitted to a Weibull distribution representing the strain-dependent lifetime of putative fibres in the material. The Weibull shape and scale (lifetime) parameters were estimated for each substance. A comparison of the rheometric measurements of edible fats demonstrated a clear difference between the three different groups. Taken together the results indicate that butter has a lower threshold for mechanical failure than spreadable blend and spread. The observed behaviour of edible fats can be interpreted using a model in which there are two types of bonds between fat crystals; primary bonds that are strong and break irreversibly, and secondary bonds, which are weaker but break and reform reversibly.

Highly Decorated Lignins in Leaf Tissues of the Canary Island Date Palm Phoenix canariensis

Phoenix canariensis leaf lignins vary between tissue region and contain an array of pendent groups. The cell walls of leaf base tissues of the Canary Island date palm (Phoenix canariensis) contain lignins with the most complex compositions described to date. The lignin composition varies by tissue region and is derived from traditional monolignols (ML) along with an unprecedented range of ML conjugates: ML-acetate, ML-benzoate, ML-p-hydroxybenzoate, ML-vanillate, ML-p-coumarate, and ML-ferulate. The specific functions of such complex lignin compositions are unknown. However, the distribution of the ML conjugates varies depending on the tissue region, indicating that they may play specific roles in the cell walls of these tissues and/or in the plant’s defense system.