Improving the application of gibberellic acid to prolong dormancy of yam tubers (Dioscorea spp)

With the aim of reducing the cost and time needed to treat yam tubers with gibberellic acid (GA₃), this study compared several new methods of application with the established dipping procedure (150 mg kg^?1 for 1 h). Both GA₃‐containing soil paste (25 mg kg^?1) and gelatinized starch (860 mg kg^?1) were applied to tuber heads of Dioscorea alata and D cayenensis‐rotundata in the Ivory Coast. Soil paste, gelatinized starch and dipping consistently prolonged dormancy and reduced fresh matter losses by 23–39% in D cayenensis‐rotundata 3‐year means. Although dipping reduced the storage losses most efficiently, soil paste and gelatinized starch used considerably less GA₃. Both new treatments were easily prepared and quickly applied. Soil paste was most effective when the treatment was repeated before the end of dormancy. The third new method, spraying the tubers with a GA₃ solution (150 mg kg^?1), was not effective. In general, the optimal time of application was immediately post‐harvest. For D alata, treatment only 1 month after harvest was particularly ineffective, whereas D cayenensis‐rotundata tubers could be treated with some effect up to the end of dormancy. To achieve extended storage periods of healthy tubers of D cayenensis‐rotundata, GA₃ application may be recommended as post‐harvest practice. Copyright © 2003 Society of Chemical Industry     

Effects of gibberellic acid (GA3) on strawberry PAL (phenylalanine ammonia-lyase) and TAL (tyrosine ammonia-lyase) enzyme activities

Gibberellic acid (GA₃) treatments (30 and 60 μg litre⁻¹) were applied to young plants (Fragaria ananassa cv Chandler). Fruits were harvested at various developmental stages (14, 21, 28 and 35 days from fruit set). Weight and size, phenolic compounds (total polyphenols and anthocyanins) and enzyme activities, phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) were determined. Our aim was to obtain detailed information about PAL and TAL activities related to the strawberry colour during development and ripening processes and to determine the effects of exogenous treatments of GA₃ on PAL and TAL activities. Exogenous treatments of GA₃ improve weight, size and colour of strawberry fruits, and affect PAL and TAL activities. We found that the anthocyanin content and PAL activity are enhanced by the exogenous treatment of GA₃ in the range of 30 μg litre⁻¹. However, with the higher GA₃ treatment, only the anthocyanin content is affected in that way. These findings suggest that gibberellic acid effect on PAL, TAL and ultimately anthocyanin enhancement is dosage related and saturation of the response occurs at 30 μg litre⁻¹. © 1998 SCI.     

Extension of Postharvest Life of Bell Peppers with Low Oxygen

Green bell peppers ( Capsicum annum L cv California Wonder) were stored in oxygen/nitrogen mixtures at 10, 30, 50, 70 and 210 (air) ml O₂ litre⁻¹ for 4 weeks at 10°C. Decay, weight loss, colour, titratable acidity and soluble solids contents, internal CO₂ and ethylene were evaluated. After 2 weeks, 33% of the air-stored peppers had decayed while only 9% of those stored in 10 ml litre⁻¹ O₂ had decayed. The benefit of 10 ml litre⁻¹ O₂ in reducing decay continued through 4 weeks of storage. The 30 and 50 ml litre⁻¹ O₂ atmospheres slightly reduced decay for a short time while the incidence of decay in 70 ml litre⁻¹ O₂ was not different from the control. Peppers stored in 10 ml litre⁻¹ O₂ had significantly lower internal CO₂ than the air control and other low O₂ treatments. A slower decrease in green colour of peppers stored in low O₂ indicates a retardation of colour change by low O₂ treatments during storage. Low respiration and ethylene synthesis rates may be the primary factors in quality retention.     

Effects of explant source,culture medium: Strength and growth regulators on the in-vitro propagation of three Jamaican yams: (Dioscorea cayenensis,D trifida and d rotundata)

Explants of tuber, meristem and vines from three widely cultivated yam species in Jamaica—D cayenensis, D rotundata and D trifida—were examined for their responses to mineral media strength, inorganic ammonium and growth regulator supplements. Tuber pieces (5mm³) showed some positive growth responses but did not produce in-vitro plantlets on all the media tested. Meristem tips of D trifida grew rapidly on basal media (BM) supplemented with either 0.1 mglitre^?1 6-benzylamino purine (BAP) and 0.01 mg litre^?1indole butyric acid or 0.2 mg litre^?1 BAP and 1.0 mg litre^?1 naphthalene acetic acid (NAA) producing plantlets by 28 weeks. The nodal explants grew rapidly with plantlets obtained from all the cultivars within 4 weeks. Use of young, vigorously growing vines of 8 weeks or less, as explant source, gave low contamination levels (16–25%) in culture when sterilised for 30 min in 200 g litre^?1 NaOCl in the case of D trifida and 300 g litre^?1 NaOCl in the case of D cayenesis prior to culturing. Initiation of growth was optimal when explants were taken from monopodial vines grown in October or January and placed on BM supplemented with 0.5 mg litre^?1 BAP (BM0.5BAP). Addition of 0.5 mg litre^?1 kinetin to the BM or 0.05 mg litre^?1 NAA to BM0.5BAP depressed shoot production, while 5.0 mg litre^?1 kinetin increased swelling of the nodal region in explants from sympodial shoots and from vines grown in March. The results suggest that nodal segments excised from young, fast growing vines of these species are the best explant source for the purpose of commercial micropropagation.     

Factors affecting the in-vitro establishment of Jamaican yams (Dioscorea spp) from nodal pieces

Factors such as inorganic ammonium, growth regulator supplements, propagule type and subculture period affecting the in-vitro establishment of Dioscorea cayenensis and D trifida have been examined. The results indicate that for D cayenensis, transfer of whole plantlets to fresh initiation media prior to cutting into nodal segments and transfer to establishment media was beneficial. Addition of 800 mg litre^?1 NH₄NO₃ to basal medium (BM) containing 0.5 mg litre^?1benzylamino purine (BAP) caused a significant improvement in nodal numbers and resulted ir. 11.8 propagules per original explant after 8 weeks or 184.1 propagules after 16 weeks in-vitro. Rapid establishment of D trifida cv Short Neck Yampie depended on the original explant source. Explants obtained from small tuber vines grew faster on establishment than those obtained from leafy cuttings. Initiation on BM supplemented with 0.5 mg litre^?1 kinetin (BM0.5K) and establishment on BM supplemented with 0.5 mg litre^?1 BAP (BM0.5BAP) produced the optimum result for the vines obtained from small tubers (24.0 propagules after 8 weeks of culture). For explants obtained from leafy cuttings, initiation on BM0.5BAP and establishment on BM0.5K gave optimum results (15.8). Quick establishment of initiated plantlets shown by increased shoot response and high multiplication rates were achieved in this study.     

Injury,Inhibition and Inactivation ofEscherichia coli O157:H7 by Potassium Sorbate and Sodium Nitrite as Affected by pH and Temperature

The effect of potassium sorbate (0–2 g litre⁻¹) and sodium nitrite (0–1 g litre⁻¹) on the growth of four strains of Escherichia coli O157: H7 in tryptic soya broth at various pH levels (pH 4·0–7·0 for sorbate, pH 5·0–8·0 for nitrite) were determined at 37°C and 4°C. Among the pH levels tested, sorbate and nitrite exhibited the highest antimicrobial activity at pH 4·0 and 5·0, respectively. At pH 5·0 and 37°C, the presence of 500 mg litre⁻¹ sorbate or 200 mg litre⁻¹ nitrite completely inhibited the growth of E coli O157: H7. While at higher pH levels, 2 g litre⁻¹ sorbate or 1 g litre⁻¹, nitrite, the highest concentration tested, did not show significant antimicrobial action against the test organisms. At 4°C and pH 5·0, the inoculated test organisms did not showed any significant growth in preservative-free control media. Different degree of inactivation and injury was observed when E coli O157: H7 strain 933 was stored in TSB (pH 5·0) containing 1 g litre⁻¹ sorbate or nitrite at 37°C. At 4°C, inactivation and injury of E coli O157: H7 cells was not observed in the medium containing sorbate or nitrite throughout the 24 h experimental period.     

Antimicrobial effects of butylated hydroxyanisole alone or in combination with potassium sorbate on quality changes in palm oil co-inoculated with Aspergillus flavus and Bacillus spp

Palm oil was sterilised and subjected to different concentrations (0.2 to 1.0 g litre⁻¹) of butylated hydroxyanisole (BHA) alone or in combination with potassium sorbate (KS) and co- inoculated with Aspergillus flavus and Bacillus species, the most prevalent organisms isolated from the palm oil. A dramatic increase of c3.43, 3.16 or 1.83 log₁₀ cfu ml⁻¹ microbial populations occurred in control samples or those treated with 0.2 or 1.0 g litre⁻¹ of BHA alone respectively. On the contrary, populations lower by approximately 1.0–1.3 log₁₀ cfu ml⁻¹ occurred in samples subjected to the combination treatment. Bi-phasic minima-extended-lag-phases were observed in the samples treated with BHA + KS. Mycelial growth was markedly inhibited in samples preserved with BHA + KS, being more apparent at concentrations of between 0.4 and 0.8 g litre⁻¹ of BHA in combination with potassium sorbate. Similarly, significantly (P = 0.05) lower free fatty acid content was observed in samples subjected to the combination treatment particularly at concentrations ranging from 0.6 litre⁻¹. Changes in pH were minimal suggesting less microbial activity, but significantly lower values occurred in samples treated with BHA alone after 14 days of ambient (30(±3) °C) storage. Better sensory qualities (less ‘separation’ i.e enhanced stability and aroma) were exhibited by samples preserved with the combination of BHA with KS. These various induced changes demonstrate the importance of concentration, residence time and synergism in relation to the effectiveness of antimicrobial agents. The benefits of the application of combination treatments have been shown and could be exploited by palm oil processors and importers. However, samples treated with the low concentrations are more likely to present potential hazards to consumers. © 1999 Society of Chemical Industry     

Solid State 13C NMR and Diffuse Reflectance Mid-Infrared Spectroscopic Analysis of the Effects of Retting on the Chemical Composition of KenafFibre

Bast ribbons from Tainung 1 (T₁) and Guatemala 45 (G₄₅) cultivars of kenaf ( Hibiscus cannabinus ) were subjected to a chemical retting process. The resulting changes at the base and tip regions of each cultivar were analysed using solid-state ¹³C NMR and diffuse reflectance mid-infrared spectroscopies. Chemical retting was performed by boiling the substrates in NaOH (70 g litre⁻¹) +NaHSO₃ (5 g litre⁻¹) for 1 h, after which they were neutralised, washed and air dried. This process produced large decreases in the non-cellulosic components, though 25% of the phenolic component was left undegraded, and cellulose crystallinity was increased by ∽5% over that in unretted samples.     

Effect of drought and irrigation on the fate of nitrogen applied to cut permanent grass swards in lysimeters: Leaching losses

Nitrogen losses were measured in water draining from cut permanent grass swards growing in monolith lysimeters containing clay loam (Salop series) or silt loam (Bromyard series) soils. The swards were cut at 6-week intervals during the summer and were fertilised with calcium nitrate at rates of 0 and 400 kg N ha^?1 in each of five successive years (1977–81); in the first year the fertiliser was labelled with ¹⁵N. Four differing rainfall regimes were imposed from spring to autumn in each year. Mean annual losses of nitrogen by leaching from unfertilised swards were 3.8 kg N ha^?1 with mean nitrate-N concentrations in the water of about 1 mg N litre^?1. In fertilised lysimeters where rainfall distribution was that of the long-term average the mean annual total nitrogen losses were 41 kg N ha^?1 in the Salop soil and 15 kg N ha^?1 for the Bromyard soil; mean nitrate-N concentrations were 11.6 mg N litre^?1 and 5.1 mg N litre^?1, respectively. Losses of nitrogen and nitrate concentrations were similar to these quantities when irrigation increased the rainfall total to 120% of average. Where a drought was imposed for 2 weeks before and after each cut, mean nitrate-N concentrations increased to 20.3 mg N litre^?1 on Salop soil and 13.1 mg N litre^?1 on Bromyard soils; total annual nitrogen losses were 74 kg N ha and 33 kg N ha^?1, respectively. The largest losses were recorded when the drought period extended for four weeks before each cut and mean nitrate-N concentrations increases to 28.8 mg N litre^?1 on Salop soil and 34 mg N litre^?1 on Bromyard soil, with total annual nitrogen losses of 104 kg N ha^?1 and 109 kg N ha^?1, respectively. Losses of nitrogen derived from the fertiliser labelled with ¹⁵N were 7.3–8.4% of that applied in the Salop soil (29–33 kg N ha^?1), with little effect by the differing rainfall distributions. On the Bromyard soil, losses were 3.7% (14 kg N ha^?1) of the applied fertiliser in lysimeters not subjected to droughts. When the period of the drought extended before and after each cut, losses were 8.2% (32 kg N ha^?1) and increased to 17.9% (70 kg N ha^?1) when the drought period occurred entirely before each cut. Fertiliser nitrogen contributed 48–69% of the total nitrogen in drainage water from both soils in the first year.     

Influence of nitrogen form and concentration on the nitrate reductase activity of winter barley (Hordeum vulgare L cv Igri)

Winter barley (Hordeum vulgare L cv Igri) plants were grown for 5 weeks in a controlled environment room using a recirculating nutrient solution culture system at a root and shoot temperature of 10°C. When solution NO₃-N concentration was varied between 0 and 64 mg litre^?1, shoot endogenous and induced nitrate reductase activity (NRA_e and NRA_i respectively) increased asymptotically from zero in plants grown with O mg NO₃-N litre^?1 to a maximum activity in solutions containing ? 16 mg NO₃-N litre^?1. Shoot Nitrogen Response Index (NRI = NRA_i/NRA_e) showed an opposite trend decreasing from a maximum of 2.6 at 2 mg NO₃-N litre^?1 to a minimum approaching unity when ? 32 mg N litre^?1 was supplied. In a separate experiment, nitrogen form (NO₃-N, NH₄-N or a 1:1 mixture) had a marked influence on shoot NRA. Enzyme activity was negligible in tissue from plants absorbing NH₄-N, highest in NO₃-fed plants and intermediate in those supplied with both N forms. NRI, however, approached unity in all treatments. The results provide evidence to suggest that NRI may be used as an indicator of the N status of barley plants grown with varied N nutrition.     

Changes in flour gelatinisation of trifoliate yam (Dioscorea dumetorum) tubers after harvest

BACKGROUND: Changes in the properties of starch during postharvest hardening of trifoliate yam (Dioscorea dumetorum) tubers need to be investigated. In this work the starch gelatinisation kinetics of D. dumetorum cv. Yellow stored under prevailing tropical ambient conditions (0.98–2.32 kg vapour per 100 m³ airflow) for 0, 2, 7, 14, 21 and 28 days was studied using a 3 × 5 factorial experiment with three cooking temperature (75, 85 and 95 °C) and five cooking times (0, 5, 10, 20 and 40 min). Samples were also evaluated for starch properties and gelatinisation temperature. RESULTS: Storage of D. dumetorum tubers caused starch damage. However, the starch gelatinisation temperature was between 70 and 75 °C irrespective of the tuber storage duration. The starch gelatinisation reaction followed first‐order kinetics defined by the relationship ln(1 ? α) = ? k_Gt. The gelatinisation rate was significantly influenced (P≤0.05) by cooking temperature and increased with tuber storage duration. The activation energy also increased with tuber storage duration. CONCLUSION: Although the gelatinisation temperature of D. dumetorum starch was not influenced by tuber storage, the starch gelatinisation process was affected by tuber storage duration, since tuber storage involved a greater need of energy for starch gelatinisation, which may be an effect of the postharvest hardening phenomenon. Copyright © 2008 Society of Chemical Industry     

Maintenance of rumen protozoa populations in a dual outflow continuous fermenter

Using a 2^5–2 fractional factorial design, five factors were screened for their ability to promote rumen protozoa growth in a dual outflow fermenter and on their influence on fermentation. The tested factors were the addition of bovine serum (BS, 20 ml litre⁻¹) and of a 100 g litre⁻¹ yeast extract solution (20 ml litre⁻¹) to artificial saliva, the addition of diethystilbestrol (15 mg day⁻¹) to fermentation broths, the reduction of shear stresses by lowering the stirring speed from 260 rpm to 230 rpm, and the improvement of ciliate sequestration by the use of a polyurethane foam belt. In the fermentors, the ciliate population density ranged from 10 μl⁻¹ to 58 μl⁻¹. The genus Isotricha was rarely observed, with a population density estimated at <0·7 μl⁻¹ while Dasytricha was not maintained. All the experimental factors markedly influenced total protozoa numbers. Lowering the stirring speed was the sole beneficial treatment. Nutritional supplements, in particular BS, were all detrimental to Entodinium. Their association was characterised by a significant antagonism. The population size of Polyplastron and Eudiplodinium was lowered only by BS addition, possibly through the changes induced in the fermentation pattern. ©1997 SCI     

Oven drying improves the nutritional value of Calliandra calothyrsus and Gliricidia sepium as supplements for sheep given low-quality straw

Leaves from the tree legumes Gliricidia (Gliricidia sepium) and Calliandra (Calliandra calothyrsus) were fed as supplements (200 g dry matter) to sheep (n=3) given a basal diet of barley straw ad libitum. Tree leaves were fed either freshly harvested (F=fresh) or after drying at 60°C in a forced draught oven (D=dried). Voluntary intakes, digestibility and aspects of nitrogen (N) and phenolic compound metabolism were measured in all sheep. Drying decreased the condensed tannin (CT) content of Calliandra (F 117, D 82 g CT kg⁻¹ DM). Total phenolics (TP) were significantly decreased when Gliricidia was dried (F 39, D 21 g TP kg⁻¹ DM), and CT content was reduced from 20 g CT kg⁻¹ DM to zero. Sheep given Gliricidia had higher rumen ammonia concentrations (73–85 mg N litre⁻¹) than did sheep given Calliandra (37–40 mg N litre⁻¹). For both species, drying significantly increased the voluntary consumption of straw, increased DM digestibility, decreased faecal N excretion and increased N balance. For calliandra, drying decreased the apparent degradability of N in the rumen (DNR) from 0·40 to 0·28 g N g⁻¹ N ingested, and increased the apparent digestibility of N (ADN) in the post-ruminal tract from 0·20 to 0·52 g N absorbed g⁻¹ N flowing into the small intestines. For Gliricidia, DNR decreased from 0·64 to 0·51 and ADN increased from 0·41 to 0·56. There were no significant effects of drying on rates of microbial N synthesis. The above changes were discussed in relation to changes in tannin content and it was concluded that drying facilitates the formation of protein–tannin complexes which protect proteins from degradation in the rumen. These proteins are subsequently released in the small intestines, thereby promoting an increased efficiency of dietary N utilisation. ©1997 SCI     

Characterisation of an oleuropein degrading strain of Lactobacillus plantarum. Combined effects of compounds present in olive fermenting brines (phenols,glucose and NaCl) on bacterial activity

This study aims to examine the effects of glucose and NaCl on the ability of an oleuropein degrading strain of Lactobacillus plantarum, strain B21, to grow in the presence of oleuropein, its degradation product, hydroxytyrosol, and p-coumaric acid. Oleuropein (10 g litre⁻¹) and 2 g litre⁻¹ hydroxytyrosol combined with NaCl did not inhibit bacterial growth, whereas 1 g litre⁻¹ p-coumaric acid showed low inhibitory activity. This study also presents that bacterial β-glucosidase and esterase are involved in the breakdown of oleuropein. Oleuropein (10 g litre⁻¹) incorporated in the cultivation medium without glucose was completely degraded to derivative products within 20 days, whereas in the presence of glucose, at concentrations up to 50 g litre⁻¹ β-glucosidase activity was partially inhibited, and 30–70% of oleuropein residual content remained in the cultivation medium. Esterase activity involved in the second step of biodegradation process, was not influenced by glucose. Incorporation of glucose in the growth medium adversely affected the ability of L plantarum to break-down oleuropein. The findings of this study are significant since it could lead to the development of a new biotechnology for removing the bitter principle, oleuropein, from olives replacing the traditional alkali treatment used for debittering olives. © 1998 SCI.     

Kinetic Modeling of Anthocyanin Degradation and Microorganism Growth during Postharvest Storage of Açai Fruits (Euterpe oleracea)

Abstract: The unavoidable damage of açai (Euterpe oleracea) fruits (AF) during picking leads to microbial contamination and anthocyanin degradation, which prejudice the consumed fruit drink. Thirteen lots of AF (24 kg) from different municipal districts of the Pará State (Brazil) were monitored during a 75‐h‐long storage in the dark at 30 °C for microbial growth, and 7 lots for anthocyanin degradation. On arrival at the laboratory, anthocyanins presented a mean concentration of 828 mg kg⁻¹ fruits with a standard deviation of 323 mg kg⁻¹ fruits whereas mean microbial contamination was 2.64 10⁶ CFU g⁻¹ of dry matter for total mesophilic bacteria, 1.98 10³ MPN g⁻¹ DM for fecal coliforms, and 1.11 10⁵ CFU g⁻¹ DM for moulds and yeasts. Kinetic growth of the microbes could be fitted to a quadratic equation with an unusual rapid growth during the 1st 24 h. The kinetics of anthocyanin degradation fitted a 1st‐order equation. The mean velocity constant of the reaction (k₁) was of 0.0137 h⁻¹ and the mean half‐life (t_½) of the anthocyanins was 50 h. These results indicate that the AF simultaneously suffer extensive anthocyanin degradation and explosive microbial growth during the postharvest period needing a special care. Practical Application: The data presented in this article help the industrial sector of açai (Euterpe oleracea) juice to understand: (1) the rapid kinetics of anthocyanin oxidation and (2) the uncommon kinetics of microorganism growth during a postharvest storage of açai fruits for up to 75 h. Our results allow to predict the global deterioration of açai fruits and pointed out the necessity of blanching the fruits or pasteurizing the juice.     

Physicochemical and microbiological changes in postmortem crayfish (Procambarus clarkii) stored at 4 °C and 25 °C

The physicochemical and microbiological parameters of postmortem crayfish stored at 4 °C and 25 °C were evaluated in order to reduce safety risks of crayfish from temperature abuse during transportation and storage. Results showed that hepatopancreas of postmortem crayfish had significantly higher contents of total volatile basic nitrogen, biogenic amines (BAs) and higher microbial loads than tail meat, regardless of storage temperature. Enterobacteriaceae and Pseudomonas counts reached log 6.41 log₁₀ CFU g⁻¹ and 6.31 log₁₀ CFU g⁻¹ in hepatopancreas of crayfish at 25 ℃ for 6 h. Putrescine and cadaverine were the main BAs in tail meat with levels of 28.18 ± 0.73 mg kg⁻¹ and 187.32 ± 3.57 mg kg⁻¹, respectively, whilst cadaverine, spermidine and spermine were the major BAs in hepatopancreas, reaching 283.45 ± 3.95 mg kg⁻¹, 62.87 ± 9.02 mg kg⁻¹ and 155.31 ± 4.55 mg kg⁻¹, respectively, after postmortem storage at 25 °C for 12 h. With time increasing, Acinetobacter, Flavobacterium, Aeromonas and Chryseobacterium at 25 °C and Acinetobacter, Flavobacterium, Psychrobacter at 4 °C in tail meat as well as Bacteroides and Muribaculaceae at 25 °C, and Acinetobacter, Psychrobacter at 4 °C in hepatopancreas, gradually became the major genus at the end of storage. Based on the results of spoilage microorganisms and biogenic amines, crayfish stored at 4 °C and 25 °C could be edible within 24 h and 6 h, respectively.     

Respiratory parameters of onion bulbs (Allium cepa) during storage. Effects of ionising radiation and temperature

The O₂ and CO₂ respiration rates of untreated and irradiated onion bulbs (Allium cepa) at 0.15 and 0.30 kGy were measured at 4, 10 and 20 °C. The O₂ respiration rate increased for 24 h after treatment from 0.19 mmole kg⁻¹ h⁻¹ at 20 °C for control samples up to 0.26 and 0.39 mmole kg⁻¹ h⁻¹ for 0.15 and 0.3 kGy irradiated onions respectively. Respiratory quotient (RQ) increased with temperature. The Q₁₀ of the respiration of the control samples (1.61) was lower than that of any other plant tissue, but it increased with storage duration and irradiation dose. The respiration rate of control onions increased steadily over 25 weeks of storage at 4 °C, while that of the irradiated samples decreased during the same period after a peak observed after irradiation treatment. The apparent K_m for the Menten–Michaelis equation was determined on a new respirometer and averaged 1.6 kPa at 10 °C and 6.3 kPa at 20 °C. However, at this higher temperature (20 °C) apparent K_m varied with O₂ partial pressure, proving that the respiration of onion bulbs does not follow a Menten–Michaelis‐like process. The Fermentative Index (FI) of onions was measured under anoxic conditions as CO₂ production rates in mmole kg⁻¹ h⁻¹ at 4, 10 and 20 °C. © 2000 Society of Chemical Industry     

Long-Term Cell Suspension Culture and Regeneration of the Single-Leafed Strawberry Fragaria vesca monophylla

Cell suspensions have been used for obtaining somaclonal variability and for the production of secondary metabolites, such as aroma compounds, natural dyes and drugs. Undifferentiated growing cells completely lose their regeneration capacity due to the formation of cells with abnormal DNA content during this phase. Callus culture of Fragaria vesca monophylla was obtained on agarised media supplemented with different growth regulators. Afterwards, a stable cell suspension was obtained on an SH (1972) medium supplemented with BSAA 0·25 mg litre⁻¹ and BA 0·1 mg litre⁻¹. The cells were poured onto an agarised regeneration medium, where it was possible to obtain regenerants. This is the first report of a stable cell suspension of a diploid Fragaria and regeneration after 2 years of unorganised cell culture.     

O-dihydroxyphenoloxidase action on natural polyhydric phenolics and enzymic browning of edible yams

Ten cultivars of five edible yam species were examined for o-dihydroxyphenoloxidase (o-DPOase) activity against yam extracts containing phenolic compounds, and for their propensity to brown when cut slices are exposed to air. (+)-Catechin levels in Dioscorea cayenensis (260 mg kg^?1) and D. bulbifera (240 mg kg^?1) were similar to those in D. dumetorum (270 mg kg^?1), but the latter contained less o-DPOase and showed less tendency to browning. D. alata contained more (+)-catechin than other yams, and one cultivar with a higher (+)-catechin content (660 mg kg^?1) showed more browning than another cultivar containing 430 mg kg^?1 (+)-catechin. Five cultivars of D. rotundata showed less tendency to brown, and had lower (+)-catechin content (90–190 mg kg^?1) than the other yams examined, but showed marked variation in o-DPOase activity. o-DPOase activity, assayed by recording the rate of oxygen consumption, varied between 75 units (1 unit=μmol O₂ consumed min^?1 100 g^?1 fresh yam tissue) in D. dumetorum and 2380 units in one D. rotundata cultivar when a crude extract of phenolic compounds diluted to contain 10 mM (+)-catechin was used as substrate and from 60 to 3480 units for these same two enzyme extracts when assayed using crude extracts of phenolic compounds (also adjusted to contain 10 mM (+)-catechin) prepared from the same yam as the enzyme extract. However, in general, the o-DPOase activities recorded using the D. alata extract showed little correlation with the activity when the phenolic extract was prepared from the same yam as the enzyme extract. Incubation of crude extracts containing phenolics with crude extracts of o-DPOase at 20°C for 24 h resulted in a decrease in the quantity of (+)-catechin estimated by h.p.l.c. Cyanidin released by hydrolysis with HCl under mild conditions was also measured. The level in D. alata was sufficiently high to account for ‘pinking’ when this species is boiled. It is concluded that the o-DPOase-catalysed oxidation of (+)-catechin is largely responsible for the browning of yams. The possible influence of other factors, including the reducing agent ascorbic acid in moderating the rate and extent of browning observed, is discussed.     

Properties of polyphenol oxidase in mango (Mangifera indica) kernel

Polyphenol oxidase (PPO) activity of filtered extract of ground mango kernel suspension (400 g litre⁻¹) was studied spectrophotometrically at 420 nm using catechol as substrate. The enzyme was most active at pH 6·0 and 25°C. Activity was reduced by 50% at pH values of 5·0 and 7·1, and also at temperatures of 14°C and 30°C. The calculated activation energy and the Michaelis constant (K_m) were 21·4 kcal mol⁻¹ °C⁻¹ and 24·6 mM , respectively. The V_max value was 2·14 units g⁻¹ mango kernel. The time to heat inactivate PPO decreased rapidly to < 10 min with increasing temperature of ⩾ 70°C at 50% activity. © 1998 SCI.