Combined Effect of Drying Time and Slice Thickness on the Solar Drying of Okra

The effect of slice thickness and drying time on colour, viscosity, microbial load, moisture, crude fibre, vitamin C and ash contents of okra (Hibiscus esculentus) during solar drying was studied using three slice thicknesses (5·0 mm, 10·0 mm, 15·0 mm) obtained from a survey and five drying times (0, 24, 48, 72 and 96 h). The results showed that slice thickness had a significant effect (P<0·01) on moisture, crude fibre and ash contents but not on vitamin C content, viscosity, colour and microbial load. However, the effect of drying time was highly significant (P<0·01) on all the parameters determined. The combined effects of slice thickness and drying time were observed to be highly significant (P<0·05) on ash, crude fibre and moisture contents, viscosity and microbial load but had no significant effect (P<0·05) on colour and vitamin C content. There was a strong correlation between moisture content and ash (R=-0·926), crude fibre (R=-0·94), vitamin C contents (R=0·928) and viscosity (R=-0·963) in all samples during drying. The study showed that a slice thickness of 10·0 mm and a drying time of 48 h was suitable for the solar drying of okra. © 1997 SCI.     

Assessment of Phenolics-Related Antinutritive Levels using the In Vitro Gas Production Technique: A Comparison Between Different Types of Polyvinylpolypyrrolidone or Polyethylene Glycol

The use of different types of phenolic binding agents (PBA) in conjunction with the in vitro gas production technique for the assessment of phenolic related antinutritive factors in browse were compared. During a grazing trial by goats, three fractions, grazed leaves (GL), ungrazed leaves (UL) or stems of ungrazed leaves (US) of Robinia pseudoacacia, together with three harvests of leaves of Cistus incanus and a summer harvest of Fraxinus ornus or Carpinus duinensis were analysed for total extractable phenols (TEPH), total extractable tannins (TETa), condensed tannins (vanillin–HCl) (TECTa) and extractable and total proanthocyanidins (TEPAs and TOPAs). Gas production from the samples with or without adding insoluble polyvinylpolypyrrolidone (IPVP), soluble PVP or polyethylene glycol of different molecular weights was measured. The kinetics of gas production were determined using the equation p=a+b (1-e^−ct). The effects of addition of the PBAs were assessed as percentage changes in the rate and volume of gas production or concentration of volatile fatty acids (VFA). Levels (mg g⁻¹ DM) of TEPH varied from 4·9 to 100·4, TETa from 0·6 to 58·0, TECTa from 1·0 to 64·6, and TEPas or TOPAs from 5·7 to 283·0 and from 12·4 to 331·4. Except for PVP360 which depressed fermentation, addition of 200–500 mg of the other PBAs to rumen liquor/buffer or a tannin free hay, did not affect (P>0·05) fermentation. The highest increase in gas production was achieved with PEG4, PEG8 and PEG10 followed by PVP10, PVP40 and IPVP after 12–24 h incubation. The percentage increase in gas production as a result of adding the PEGs was best associated (r=0·83–0·96; P<0·01) with the higher concentrations of total VFAs after 96 h incubation and was also best related (r=0·89–0·91; P<0.01) to the levels of extractable condensed tannins (TECTa and TEPAs) in the browse. It was concluded that PEGs were more effective than PVPs in eliminating phenolic related antinutritive factors and would be preferred for use in conjunction with the gas technique for the assessment of phenolic related antinutritive factors in feeds.     

Genetic and Environmental Variation for Seed Yield,Protein, Lipid and Amino Acid Composition in Cowpea (Vigna unguiculata (L) Walp)

The genetic and environmental variability for seed yield (kg ha^-1), protein content (g kg^-1 DM), lipid content (mg g^-1 DM) and essential amino acid composition (g per 16 gN) of cowpea seeds using 15 cultivars grown in three locations (Kano (12°00′ N 8°31′ E), Mokwa (9°17′ N 5°04′ E) and Ago-Iwoye (6°58′ N 4°00′ E)) that differ markedly in climate was studied. The environmental effect accounted largely for the variability observed in yield (93%), protein (71%), lipid (100%), threonine (96%), cystine (80%) and arginine (81%) while the genotypic effect accounted largely for the variability observed in methionine (56%) and lysine (51%) contents. Correlation coefficients (pooled data) from the three locations indicated that yield was negatively correlated to protein content (r=-0·87, P<0·001) and positively correlated to lipid content (r=0·73, P<0·001). Protein content was negatively correlated to lipid content (r=-0·67, P<0·001) and positively correlated to threonine (r=0·66, P<0·01), cystine (r=0·69, P<0·001) and methionine (r=0·88, P<0·001) contents. Similarly, yield was positively correlated to threonine (r=0·22, 0·01<P<0·05), cystine (r=0·38, 0·001<P<0·01) and methionine (r=0·67, 0·001<P<0·01). Yield showed a strong negative correlation with protein content (r=-0·81) and a strong positive correlation with lipid content (r=0·97) at the environmental level. Cystine, methionine and to some extent, threonine were the limiting amino acids in the three environments. This research established the degree of variability for these characters in cowpea and indicated that concurrent selection for yield, lipid content, threonine and sulphur amino acids compositions is feasible. © 1997 SCI.     

A SIMPLIFIED ENZYMIC METHOD FOR THE DETERMINATION OF (1→3) (1→4)-β-GLUCANS IN BARLEY

A rapid simplified procedure for the enzymic determination of β-glucans is described. In this method a small sample of ground barley (0·25 g) is heated in 80% ethanol to inactivate enzymes, the β-glucan is hydrolysed by incubation for 1 h with a high concentration of purified β-glucanase and the reducing sugars produced are determined by reaction with p-hydroxybenzoic acid hydrazide. The method was calibrated using β-glucan isolated from barley and the enzymic hydrolysis was shown to be both specific and complete.     

Nutrient contents,rumen protein degradability and antinutritional factors in some colour- and white-flowering cultivars of Vicia faba beans

Six colour-flowering (Scirocco, Alfred, Carola, Condor, Tina and Herz Freya) and six white-flowering (Caspar, Albatros, Gloria, Tyrol, Vasco and Cresta) cultivars of Vicia faba were studied. The crude protein contents of colour- and white-flowering cultivars were 267±13·6 and 283±18·8 g kg⁻¹, respectively, which did not differ significantly at P<0·05. The levels of lipids, crude fibre, starch and ash varied from 14 to 22 g kg⁻¹, 88 to 143 g kg⁻¹, 407 to 485 g kg⁻¹ and 32 to 42 g kg⁻¹, respectively. The calculated organic matter digestibility (OMD) and metabolisable energy (ME) of the white-flowering cultivars were significantly higher (P<0·001) than those of the colour-flowering cultivars (OMD: 889·1±26·6 g kg⁻¹ vs 797·5±17·1 g kg⁻¹; ME: 13·97±0·49 vs 12·30±0·34 MJ kg⁻¹). In all cultivars, sulphur amino acids were lower than adequate concentration when compared with recommended amino acid pattern of FAO/WHO/UNO reference protein for a 2–5-year-old child. The in vitro rumen nitrogen degradability of colour-flowering cultivars was significantly lower (P<0·01) compared to that of white-flowering cultivars (71·4±9·3% vs 88·0±11·1%). Amongst colour-flowering varieties, the contents of total phenols (TP), tannins (T) and condensed tannins (CT) were highest in Alfred (28·3, 21·0 and 35·4 g kg⁻¹, respectively). The contents of TP and T were similar (about 15 and 10 g kg⁻¹, respectively) in Carola, Tina and Herz Freya, and the CT were in the order: Condor>Herz Freya>Carola. The CT were not detected in white-flowering varieties, T were virtually absent and TP were extremely low (4·0–4·9 g kg⁻¹). The activities of other antinutritional factors (white- and colour-flowering cultivars, respectively: trypsin inhibitor activity 3·05±0·34 and 1·85±0·09 mg trypsin inhibited g⁻¹; lectin 27·2±9·4 and 27·1±5·1 mg ml⁻¹ assay medium producing haemagglutination; phytate 15·0±2·7 and 16·6±2·3 g kg⁻¹) were very low. A strong negative correlation (r=-0·92, P<0·001) between tannins and in vitro rumen protein degradability was observed which suggested that tannins have adverse effect on protein degradability. Similarly negative correlations between tannin levels and metabolisable energy (r=-0·89; P<0·001) and organic matter digestibility (r=-0·89; P<0·001) were observed. The correlation coefficient between trypsin inhibitor activity and tannins was negative and highly significant (r=-0·88, P<0·001), whereas between tannins and saponins it was significantly positive (r=0·96, P<0·001). ©1997 SCI     

Inactivation of Endogenous Rice Flour β-Glucanase by Microwave Radiation and Impact on Physico-chemical Properties of the Treated Flour

The apparent reduction of β-glucan (BG) molecular weight in rice-based gluten-free (GF) breads fortified with cereal BG concentrates reveals the presence of β-glucanase activity in rice flour. Inactivation of endogenous β-glucanase in rice flour thus seems to be a necessary step when developing GF breads enriched with BG of high molecular weight. The aim of this work was to study the thermal inactivation of endogenous β-glucanase in rice flour by means of microwave (MW) processing; rice flours preconditioned at four different moisture levels (13, 16, 19, 25 %) were treated by MW radiation at 900 W and five MW treatment times (ranging from 40 s to 8 min, applied stepwise at 20-s intervals). The effects of microwaves on starch crystallinity, pasting, and thermal properties of MW-treated rice flours were also explored. The β-glucanase activity in rice flours was assessed by the rate of decrease in specific viscosity of a dilute solution of a purified β-glucan preparation, upon addition of flour extracts. MW proved to be a useful alternative for thermal inactivation of endogenous β-glucanase in rice flours when applied to moistened samples. The inactivation process followed a first-order kinetic response and the apparent rate constant of thermal inactivation increased exponentially with the moisture content of the flour, M, according to the equation 0.0146·exp (0.212·M) (R ²?=?0.97). The MW time required for complete β-glucanase inactivation was only 4 min when the initial flour moisture increased to 25 %. Following MW treatment, the starch crystallinity was unaffected (p?>?0.05) and the side effects of the treatment on flour pasting and thermal properties were rather negligible.     

Barley β-glucan is effective as a hypocholesterolaemic ingredient in foods

Barley contains high levels of soluble dietary fibre, including mixed linked 1→3, 1→4β-D -glucans (β-glucan). An extract of β-glucan from waxy, hulless barley containing 56% total dietary fibre (TDF) was incorporated into flour tortillas, cornstarch pudding and apple granola bars to provide 2 g soluble fibre as β-glucan per serving. The foods were tested for objective functional properties. Flour tortillas with β-glucan were incorporated into rat diets and compared to diets containing an equivalent amount of cellulose, to test the fibre effect on growth and lipid metabolism parameters. Rats fed β-glucan tortillas had lower feed consumption and body weight (P<0·05) compared to those fed the cellulose tortillas, although feed/gain ratios were not different (P>0·05). Plasma LDL-cholesterol of rats fed β-glucan was lower (P<0·05) than cellulose-fed controls, although total cholesterol and triglycerides did not differ (P>0·05). Rats fed β-glucan tortillas had higher (P<0·05) faecal fat excretion, suggesting impairment of intestinal fat absorption. Liver composition data showed lower (P<0·05) levels of total lipid and cholesterol in β-glucan-fed rats. The results suggest that the barley β-glucan concentrate has potential as a food ingredient to provide supplemental soluble fibre which may be beneficial in reducing plasma LDL-cholesterol in humans. © 1998 SCI.     

Effects of cultivar,nitrogen fertilization rate and environment on yield and grain quality of barley

Ten barley cultivars, including covered and naked types, varying in their content of total starch, amylose, protein and β-glucan, were grown in different years, at various locations and nitrogen fertilization rates. The barley cultivars showed a large variation in yield (3250–6690 kg ha⁻¹), thousand kernel weight (40–50 g), bulk weight (660–815 g litre⁻¹), starch (51–67% of DM), protein (8–15% of DM), β-glucan (3·5–5·9% of DM) and ash (1·9–2·5% of DM). The naked cultivar SW 8775 had the highest starch content and the high amylopectin cultivar (SW 7142-92, waxy) had the lowest. The waxy starch barleys had the highest protein content, while the normal starch barleys (Golf and Lina) had the lowest protein content at each N-rate. Higher content of β-glucan was found in the waxy cultivars (5·0–5·9% of DM) and high amylose cultivars (5·6–5·9% of DM) than in the other barley cultivars (3·5–4·8% of DM). The results were evaluated by analysis of variance (ANOVA) and principal component analysis (PCA), and both confirmed that nitrogen fertilization rate was of great importance for the protein content. PCA revealed that protein and β-glucan were negatively correlated with starch and yield. The ANOVA showed that the cultivar factor was significant for all variables, but especially for the β-glucan content, which responded differently to the nitrogen fertilization rate during the 2 years. In this study, environmental effects were generally of less importance than the barley cultivars for the different variables. © 1998 Society of Chemical Industry.     

ENZYMIC QUANTIFICATION OF (1→3) (1→4)-β-D-GLUCAN IN BARLEY AND MALT

A simple and quantitative method for the determination of (1→3) (1→4)-β-D-glucan in barley flour and malt is described. The method allows direct analysis of β-glucan in flour and malt slurries. Mixed-linkage β-glucan is specifically depolymerized with a highly purified (1→3) (1→4)-β-D-glucanase (lichenase), from Bacillus subtilis, to tri-, tetra- and higher degree of polymerization (d.p.) oligosaccharides. These oligosaccharides are then specifically and quantitatively hydrolysed to glucose using purified β-D-glucosidase. The glucose is then specifically determined using glucose oxidase/peroxidase reagent. Since barley flours contain only low levels of glucose, and maltosaccharides do not interfere with the assay, removal of low d.p. sugars is not necessary. Blank values are determined for each sample allowing the direct measurement of β-glucan in maltsamples.α-Amylasedoes not interfere with the assay. The method issuitable for the routineanalysis of β-glucan in barley samples derived from breeding programs; 50 samples can be analysed by a single operator in a day. Evaluation of the technique on different days has indicated a mean standard error of 0–1 for barley flour samples containing 3–8 and 4–6% (w/w) β-glucan content.     

Rheological Studies of Water-Soluble (1–3),(1–4)-β-D-Glucans from Milling Fractions of Oat

We studied the rheological properties of water-soluble, mixed-linkage β-glucans of high purity (88–99.5%) isolated from oats. Comparing the β-glucan fractions at the same concentration (1.3 mg/g) the mean value of the bran fraction viscosities was larger (by 5X) than the mean viscosity of endosperm fractions. Both mean values had a relative standard deviation of ～20%. Heat treatment of oats did not alter the viscous properties of the extracted β-glucans. Activation energies for the bran fraction at two shear rates were E_r=5.81= 42 kJ/mole and E_r=581= 17 kJ/mole. The variation in G′and G′ with frequency for the β-glucan from bran fractions could be qualitatively described by a superposition of two single Maxwell models with widely different relaxation time. These data can help predict potential processing effects on such fractions incorporated as food components.     

Comparative spectroscopic and rheological studies on crude and purified soluble barley and oat β-glucan preparations

The rheology of crude and purified barley (BBG) and oat (OBG) β-glucan samples were characterized. Sample content and major impurities was characterized by Fourier-transform near infrared Raman and infrared (FT-IR) spectroscopy revealing substantial differences between the β-glucan samples. The purification procedure increased the β-glucan content from 66.7 to 82.4% and from 30.1 to 68.4% for BBG and OBG, respectively. Proton nuclear magnetic resonance (¹H NMR) analysis was applied to estimate the β-(1 → 3) to β-(1 → 4) linkage ratio of the β-glucans. The molar mass of BBG and OBG was determined by high performance size-exclusion chromatography (HPSEC) using β-glucan standards and was found to be 126 and 355 kDa, respectively.The viscosity of crude and purified β-glucans was studied at various concentrations (2.5, 5% w/v), temperatures (10–80 °C) and shear rates (1–100 s^? 1). BBG was characterized as a low-viscosity β-glucan with Newtonian flow behavior while OBG was characterized as a high-viscosity β-glucan with shear thinning flow behavior. At equivalent β-glucan concentration in solutions the viscosity for OBG was found to be ~ 100 fold higher than for BBG. A direct viscosity dependence on exact β-glucan content regardless of amount and composition of α-glucan impurities was found for both OBG and BBG. This study suggests that the structural characteristics of the β-glucan polymers such as molar mass are of greater functional importance than the presence of lager amounts of starch/α-dextrins as long as the β-glucan samples are compared at equivalent β-glucan doses.     

Effect of fermentation on content,molecule weight distribution and viscosity of β-glucans in oat sourdough

This study investigated the effect of fermentation on the physicochemical properties of β-glucans in oat sourdough. Sourdoughs were produced from oat using homo-fermentative lactic acid bacteria, Lactobacillus plantarum 22134. The contents of total β-glucan and soluble β-glucan, the molecular weight (MW) of β-glucan and the viscosity of the extracted β-glucans were determined at 0, 4, 8, 10 and 12 h of fermentation. The total β-glucan content decreased from 4.89% to 4.23% after 12 h of fermentation. The soluble β-glucan concentration increased from 1.89% to 2.18% and then decreased to 1.97% after 8 h of fermentation. The content of β-glucans with MW > 10⁵ decreased from 0 to 4 h of fermentation, followed by an increase and then a decrease after 8 h. The oat sourdough fermented for 8 h had high viscosity, which could be more beneficial for health and bread texture quality, especially for gluten-free breads.     

Effect of Microwave Radiation Pretreatment of Rice Flour on Gluten-Free Breadmaking and Molecular Size of β-Glucans in the Fortified Breads

Cereal β-glucan concentrates can be used in gluten-free breads to improve dough handling properties and quality of final products as well as to enhance their nutritional value; however, the presence of endogenous β-glucanases in rice flour, in combination with prolonged mixing, fermentation, and proofing time, can cause a substantial reduction in β-glucan molecular weight, affecting detrimentally their efficacy for bioactivity. In this study, microwave (MIWA) heating was applied to the rice flours before breadmaking at different flour water contents (13–25%) and treatment times (0-4 min) to reduce β-glucanase activity. Gluten-free breads made from the MIWA-treated rice flours were fortified with oat β-glucan concentrate to enhance their nutritional profile. The molecular weight of added β-glucan in the final products increased with increasing both flour water content and time of MIWA treatment, reflecting the magnitude of residual β-glucanase activity in the flour. Pretreatment with MIWA radiation for 4 min of the rice flour tempered at 25% moisture resulted in negligible residual β-glucanase activity and preserved to a great extent the molecular weight of β-glucans in the enriched breads. End-product quality was not affected by flour MIWA pretreatment, and even a slightly higher loaf specific volume was noted for breads made from the MIWA-treated flours (4 min MIWA at 25% moisture content) compared to that of untreated flour. These findings can contribute to the improvement of nutritional value of rice-based gluten-free breads for celiac consumers as well as of any β-glucan-containing yeast-leavened bakery product without altering its sensorial attributes. Additional studies are still required for further evaluation of the effect of more intense microwave treatment on rice flour and its application on breadmaking.     

Effects of ingredients on the characteristics of rice cakes

Steamed leavened rice cakes made from rice flour, sugar, water, yeast or baking powder were used to study the effects of ingredients on cereal-based cakes. Volume expansion linearly correlates to amylopectin and negatively correlates to amylose content (r²=0·84), with an optimum amylose/amylopectin ratio of approximately 1: 8. Higher amylopectin content resulted in sticky, elastic and unacceptable cake. The optimum water content for volume expansion was in the range of 90±5% by weight of rice flour. Sugar content correlates linearly with volume expansion and tenderness of chemically leavened rice cakes (CLRC) (r²=0·99 and 0·92, respectively). Sugar content above 50% of rice flour weight decreased volume and softness of yeast-leavened rice cakes (YLRC). Tenderness of YLRC correlates linearly to fat content (r²=0·98), but volume expansions correlates negatively to the square root of fat content (r²=0·81 and 0·97 for the two rice cakes). Both tenderness (r²>0·92) and volume expansion (r²>0·93) correlates linearly with emulsifier content up to 3% by weight of rice flour, above which the cake becomes crumbly. A little salt increased hardness, but further increase reduced both volume expansion and hardness of rice cakes. Skimmed milk powder greatly increased the expansion of CLRC. Ovalbumin content correlates linearly to volume expansion of YLRC (r²=0·87) but negatively to the expansion of CLRC (r²=0·96). The proteins that improved the textures of rice cakes were skimmed milk and egg white with an optimum content of 2–4%. Egg yolk, soya protein, whey powder and wheat gluten reduced both tenderness and volume expansion. The effects of the various ingredients interacting together were studied and the optimum formulations was determined using a Random Centroid Optimisation Program. © 1998 SCI.     

Genetic and environmental variability in starch,fatty acids and mineral nutrients composition in cowpea (Vigna unguiculata (L) Walp)

Fifteen cowpea cultivars grown in three locations (Kano (12°00′N 8°31′E), Mokwa (9°17′N 5°04′E) and Ago-Iwoye (6°58′N 4°00′)) between 1993 and 1994 were analysed for genotype, environmental and genotype×environment variability for starch (g kg⁻¹), fatty acids (% of total oil) and mineral nutrients (g kg⁻¹) composition. There were significant environmental as well as genetic effects on these nutritional qualities. The environmental effect accounted largely for the variability observed in starch (60%), palmitic acid (80%), arachidic acid (100%), potassium (100%), phosphorus (81%) and manganese (86%), while the genotypic effect accounted largely for the variability observed in linoleic acid (50%), linolenic acid (50%) and copper (68%) contents. Correlation coefficient (pooled data) from the three locations indicated that starch was positively correlated to palmitic acid (r = 0·21, 0·01< P < 0·05), potassium (r = 0·80, P < 0·001) and phosphorus (r = 0·65, P < 0·001), but negatively correlated to oleic (r = −0·23, 0·01< P < 0·05), linoleic (r = −0·67, P < 0·001) and linolenic acid (r = −0·74, P < 0·001) contents. Starch showed a strong positive correlation with magnesium content (r = 0·75) and a strong negative correlation with copper (r = −0·73) and iron (r = −0·62) at the genetic level. This research established the degree of variability for these characters in cowpea. © 1998 Society of Chemical Industry.     

Physico-Chemical Properties and the Degradation of Oat Bran Polysaccharides in the Gut of Pigs

Physico-chemical properties and the digestibility of carbohydrates (starch, β-glucan and arabinoxylan (AX)) were studied in the gastrointestinal contents of pigs fed diets based on oat bran. One diet was made of commercially prepared oat bran and another of oat bran milled to pass a 1 mm screen. The pigs were slaughtered and samples were collected quantitatively from 10 sites of the gastrointestinal tract either 1 or 3 h after the morning feeding. The viscosity of the liquid phase (obtained by centrifugation) of the stomach and small intestinal contents varied greatly between animals, and was not significantly different between segments of the upper gastrointestinal tract. The molecular weight of β-glucan was reduced up to 20-fold in the upper gastrointestinal tract but was of a relatively low digestibility until the terminal ileum. The solubility (the fraction of the total content in the liquid phase of digesta after centrifugation) of β-glucan varied from 0·25 to 0·58 in the stomach and small intestine, whereas the solubility of AX was in the range of 0·04–0·16. Microscopic examination of digesta showed that β-glucan was retained in intact endospermic cell wall structures, which remained evident until the distal small intestine but was completely disrupted in the caecum. In spite of a cumulative digestibility of non-starch polysaccharides and AX of ∽0·90 in the large intestine, identifiable fragments of aleurone cell walls resistant to complete microbial degradation remained. © 1997 SCI.     

THE MAJOR BIOCHEMICAL CONSTITUENTS OF AN ACID EXTRACT OF BARLEY FLOUR AS USED IN VISCOSITY DETERMINATIONS BY THE FALLING BALL METHOD

The viscosity of an acid extract of barley flour, measured as its ‘falling time’, has been used as a guide to malting potential.²² One such extract, made from a sample of Maris Mink, was examined in detail to identify the principle biochemical constituents and to investigate their contribution to viscosity. The extract contained a high concentration of carbohydrate (3·30 mg/ml) divided into two discrete fractions of high and low molecular weight (in the weight ratio of 39:61) by gel filtration. The high molecular weight component was polydisperse and consisted principally of β-glucan with some starch and pentosan also present. The low molecular weight fraction contained mostly fructose, glucose and some pentose. Protein present in the extract (1·07 mg/ml) was derived almost exclusively from the albumin and globulin (salt soluble) fraction of barley protein. Studies on the viscosities of reconstituted preparations of these components indicated that β-glucan made the major contribution to the viscosity of the extract. This conclusion is supported by observed changes in viscosity after the extract was treated with β-glucanase, α-amylase and protease.     

THE EFFECT OF β-GLUCAN MOLECULAR WEIGHT ON THE SENSITIVITY OF DYE BINDING ASSAY PROCEDURES FOR β-GLUCAN ESTIMATION

An assay procedure has been developed for quantifying β-glucan, based upon its reaction with the dye Congo Red. The sensitivity of this method to changes in β-glucan molecular weight has been determined using β-glucans prepared from standard material by acid hydrolysis and comparison has been made with a Calcofluor-based method for quantifying β-glucans. The Congo Red assay was found to be optimally sensitive to β-glucans with molecular weights of approximately 2.5 × 10⁵ Daltons, whereas the Calcofluor assay was most sensitive to β-glucans with molecular weights in excess of 5 × 10⁴ Daltons. The purity of the β-glucan used during this investigation was determined using an enzyme-based procedure in which the polysaccharide was degraded to glucose by the addition of β-glucanase. The β-glucanase employed was partially-purified from Trichoderma viride cellulase using a novel batch ion-exchange method which is also described.     

Relationships between the back-scatter of polarised light and the fibre-optic detection of connective tissue fluorescence in beef

The back-scatter of light (400–800 nm) from bovine m longissimus lumborum (n=47) was measured with a fibre-optic probe fitted with crossed polarisers to exclude Fresnel reflectance. Unlike normal fibre-optic spectra (which may be relatively flat), back-scatter was approximately proportional to wavelength, being low at 400 nm and high at 800 nm. The shape of the spectrum was modified by myoglobin absorbance, with a Soret minimum at 430 nm. Connective tissue fluorescence (365 nm excitation, 400–550 nm emission) was measured through a single optical fibre moving down the longitudinal axis of the muscle. Back-scatter at 430 nm was correlated positively with minimum fluorescence (r=0·73, P<0·001), the area under the fluorescence signal cm⁻¹ (r=0·81, P<0·001) and fluorescence peaks cm⁻¹ (r=0·46, P<0·005). Back-scatter at 800 nm was correlated weakly and negatively with minimum fluorescence (r=-0·28, P<0·05) and peaks cm⁻¹ (r=-0·26, P<0·05). Thus, in the probe detection of connective tissue fluorescence in meat, errors caused by differences in myoglobin concentration may exceed those caused by differences in pH-related light scattering. © 1997 SCI.     

Cell-Constituents,Tannin Levels by Chemical and Biological Assays and Nutritional Value of Some Legume Foliage and Straws

Twenty six straw and 15 foliage samples of Lathyrus sativus , Vicia narbonensis , V sativa and V ervilia were analysed for ash, crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), extractable phenols (Pe), extractable tannins (Te), extractable condensed tannins (CTe), protein precipitation capacity (PPC) and in vitro characteristics predicted from Hohenheim gas test. The content of crude protein in the foliage was significantly higher than that of the straws (152·6 vs 64·5 g kg⁻¹), while ash (82·8 vs 116·8 g kg⁻¹), NDF (332·7 vs 523·5 g kg⁻¹) and ADF (205·2 vs 369·9 g kg⁻¹) were significantly lower. For straws of L sativus , V narbonensis and V sativa , there was no significant difference in the protein and ADF contents, whereas ash and NDF contents were significantly lower and higher respectively in L sativus as compared to V narbonensis or V sativa . Predicted from gas volumes, the organic matter digestibility (OMD: 70 vs 56%) and metabolisable energy (ME: 9·7 vs 7·3 MJ kg⁻¹) were significantly higher for the foliage compared to straws. The OMD of L sativus straws was significantly lower compared to the straws of V narbonensis and V sativa . The OMD and ME of the straws of second year was significantly lower than those of the first year. The CP, OMD and ME of V sativa foliage were higher than that of V narbonensis . There was no difference in the cell constituents, OMD and ME of foliage samples of V sativa harvested in May 1992 and June 1992. The contents of Pe, Te and CTe of straws were 1·08%, 0·43% and 0·33%, respectively, and those of foliage were 2·27%, 1·30% and 1·63%, respectively. PPC was not detected for any of the foliage and straw samples. The results suggested that the tannin levels of legume straws investigated are negligible and those of the legume foliage are very low. This does not appear to adversely affect their nutritive value since the maximum decrease in OMD by the tannins was about 3% units.