Effect of wet incubation time and temperature on infection, and of storage time and temperature on soft rot lesion expansion in potatoes inoculated withErwinia carotovora ssp.Carotovora

Summary Infection and lesion expansion studies were carrried out on potato tubers. In the infection study, the tubers were inoculated withErwinia carotovora ssp.carotovora (Ecc) and exposed to incubation temperatures of 10–25 °C for 3–48 h of wetness. In the lesion expansion study, the tubers were exposed to 12 h of wetness at 20 °C to establish infection, and then·stored at temperatures of 4–16 °C for 15–90 d, at 95% RH. The volume of diseased tissue was determined and the data were transformed to proportion of maximum volume diseased (PVD). Infection was close to zero for 3 and 6 h wet incubation time, regardless of incubation temperature, and reached the maximum in 12 h of wetness at 20 °C. Significant lesion expansion occurred at a storage temperature of 16 °C after about 60 d of storage time. Cubic models of infection and lesion expansion potentials explained 95 and 96% of the variations in infection and lesion expansion, respectively.     

Influence of storage temperature on rate of potato tuber tissue infection caused byPhytophthora infestans (mont.) de bary estimated by digital image analysis

Summary Potato tubers were inoculated with two biotypes ofPhytophthora infestans then stored at 3,7, 10 and 15°C. Image analysis quantified average reflective intensity (ARI) of diseased tissue from cut surfaces of sample tubers. Tuber tissue infection and infection rate were measured by calculating Mean ARI of samples. Average tuber tissue infection and infection rate was minimal at 3°C (P.i.-US8 orP.i.-US1). Tuber tissue infection increased at temperatures >3°C, from 220 Mean ARI seven days after inoculation (dai) to 190–150 Mean ARI 50 dai (depending on cultivar and biotype ofP. infestans). Rate of tuber tissue infection caused byP.i.-US1 at 7°C was about zero in cv. Snowden but greater than −0.2 ARI day⁻¹ (cvs Russet Burbank and Superior). Rate of late blight infection in tuber tissue generally increased with temperature from −0.2 ARI day⁻¹ (at 7°C) in all cultivars to a maximum of −0.8 ARI day⁻¹ (10°C).     

Biochemical Properties of Red Currant Varieties in Relation to Storage

Eleven red currant varieties (Ribes rubrum L.) cultured in Serbia were evaluated for some of their biochemical properties such as total phenolics, anthocyanins, ascorbic acid, invert sugar, soluble solid content, and acidity. The average amount of ascorbic acid varied from 50.5–71.6 mg/100 g FW, while concentration of invert sugars ranged from 6.0%–9.0%. The highest amounts of total phenolics and anthocyanins were detected in variety Redpoll (153.4 mg GAE/100 g FW and 19.3 mg/100 g, respectively). Red currants were processed to juice, and the phenolic and anthocyanin contents changed as a result of processing. Berries and juices were long-term stored at −18 °C and changes in phytochemicals were monitored. In berries, storage caused the decrease of ascorbic acid content up to 49%, and a general reduction of total phenolics was also noticed. In juices, total phenolics content increased after one year of storage. In both berries and juices total anthocyanins increased during storage by up to 85% and 50%, respectively. This study demonstrates that certain varieties, namely Redpoll, Jonkheer and London Market are good source of phytochemicals, retaining the nutritional value during processing and storage.     

Amylolytic activity in stored potato tubers. 2. The effect of low-temperature storage on the activities of α-and β-amylase and α-glucosidase in potato tubers

Summary Tubers of the potato cultivars Record, Wilja, Pentland Dell and Brodick (formerly clone 137371) were sampled before and after storage at either 4°C or 10°C. Reducing sugar content stayed constant during storage at 10°C in all four cultivars but rose greatly during the first 6–12 weeks of storage at 4°C in Record, Wilja and Pentland Dell but not in Brodick. Amylolytic activity was determined after 5 weeks storage using blockedp-nitrophenyl maltoheptaoside as substrate for α-amylase,p-nitrophenyl maltopentaoside as substrate for β-amylase, andp-nitrophenylglucopyranoside as substrate for α-glucosidase. The values obtained from tubers stored at 4°C were higher than those from tubers stored at 10°C, the differences being much less in Brodick than in the other three cultivars.     

Evaluation of growth of Neosartorya spp. on some Nigerian fruit products

Growth of Neosartorya fischeri, N. fischeri var. spinosa and N. quadricincta on inoculated fruit juice agars (FJAs) consisting of 1% agar and juices from mango (MJA), orange (OJA) and pineapple (PJA) containing various levels of added sucrose was studied in terms of the average number of colonies produced by their ascospores, time (days) required before colonies were formed and developed to confluent mycelial mat as well as the level of reproductive spores produced. The means of the number of colonies on PJA and OJA without added sucrose were significantly (p =0.05) higher than that of MJA. Addition of sucrose at levels of 10% to PJA, 11.5% to OJA and 9% to MJA increased the numbers of colonies whereas sucrose levels of 30% or more in PJA, 31.5% or more in OJA and 29% or more in MJA decreased the number of colonies produced. At any level of added sucrose to FJAs, a significant (p =0.05) delay occurred before the colonies were formed and developed to confluent mycelial mat except in PJA containing 10% sucrose. All cultures produced abundant cleistothecia on all FJAs without added sucrose. Addition of sucrose at levels of 30% to PJA, 31.5% to OJA and 29% to MJA resulted in the production of abundant conidial heads with a corresponding decrease in the proportion of cleistothecia.     

Effect of Low Storage Temperature on Some of the Flavour Precursors in Garlic (Allium Sativum)

Garlic (Allium sativum) cloves were stored at ambient temperature and 4 °C for periods up to six months to establish the effect of position of the individual clove within the bulb and of low storage temperature on the composition of several flavours precursors and other organic sulphur compounds, measured by gradient High Pressure Liquid Chromatography. Levels of alliin, γ glutamyl allyl cysteine sulphoxide and γ glutamyl isoallyl cysteine sulphoxide were statistically significantly higher in outer than in inner cloves. There was no statistically significant change in levels of alliin, the major flavour precursor, in cloves stored at 4 °C, remaining in the average range 17.5±3.8–39.1±7.5 mM. However, isoalliin increased significantly during storage at 4 °C, rising from an average 0.6±0.2 mM (outer cloves)—0.7±0.4 mM (inner cloves) to 7.1±1.7 mM (outer cloves)—4.1±0.7 mM (inner cloves). A decline in other sulphur-containing compounds, most likely to be the peptides γ-glutamyl allylcysteine sulphoxide and γ-glutamyl isoallylcysteine sulphoxide, occurred at the same time and possibly contributed to the increase in the flavour precursor compounds. The degree of chemical changes during storage will be of interest to the food and pharmaceutical industries.     

Influence of post-harvest storage temperature and gamma irradiation on potato carotenoids

Summary A comparative study of nine Indian potato varieties showed a good correlation between their total carotenoid content and the tuber flesh colour. Regardless of varietal differences, carotenoid level showed an increase during storage at ambient temperature (25–30°C) and to a lesser extent at 2–4°C and 15°C. Tubers exposed to an irradiation dose of 10 krad for sprout inhibition showed decreased levels of carotenoids during storage, particularly at 15°C where 50% loss was observed after 6 months of storage. Irradiated tubers stored for seven months at 15°C, on reconditioning at 34–35°C for 6 to 12 days showed a 2- to 6-fold increase in their carotenoid content.     

Slow-growth in vitro conservation of potato germplasm at normal propagation temperature

Summary In-vitro conservation of microplants at 24±1 °C was investigated in six potato genotypes belonging to different maturity groups. Growth was controlled by using different concentrations of sucrose (20, 40 and 60 g 1⁻¹) alone or in combination with either mannitol (20 and 40 g 1⁻¹) or sorbitol (20 and 40 g 1⁻¹) in Murashige and Skoog medium. Maximum microplant survival (55.5–77.8%) after 12 months of storage was on medium supplemented with 20 g 1⁻¹ sucrose plus 40 g 1⁻¹ sorbitol. Microplants so conserved were in good to very good condition, without phenotypic abnormalities and had enough nodes for sub-culturing. Microplant survival and microplant condition were closely associated with each other but not with root growth. The success of conservation was unaffected by maturity group of the genotypes. This conservation approach at 24±1 °C can be an effective alternative to low temperature (6–8 °C) storage, especially in tropical and sub-tropical conditions, where the ambient temperatures in summer can reach 45–50°C.     

Effects of soil temperature and moisture on stem canker (Rhizoctonia solani) disease of potatoes

Summary Potato seed pieces bearing one sprout were inoculated with cultures ofRhizoctonia solani, planted in pots of compost at 45, 60, 75 or 90% water holding capacity (whc) and incubated at 5, 10 or 15 °C. Shoots emerged after 2–3 wk at 15°C, 3–4 wk at 10 °C and after 9–11 wk at 5 °C and stem canker recorded after emergence, was severe at 10 and 15 °C but slight at 5 °C. Soil moisture had less effect on emergence but stem canker was more severe in dry (45 % whc) than moist soils (75 and 90 % whc). The relationship between time of shoot emergence and stem canker severity is discussed.     

Chemical composition and organoleptic evaluation of juice from steamed cashew apple blended with orange juice

Fully riped cashew apples (yellow variety) were steamed for 7 minutes prior to juice extraction. The extracted juice was blended with various proportions of sweet orange juice. Chemical composition and organoleptic evaluation were carried out on both the blended and unblended juices. The ascorbic acid content of unsteamed cashew apple juice was 287 mg/100 ml. Steaming of the cashew apple prior to juice extraction resulted in a decreased (230 mg/100 ml) content of ascorbic acid. It also led to slight decreases in soluble solids and titratable acidity. A comparison of the chemical composition of the two juices showed that the orange juice contained more sugars, titratable acidity and soluble solids but less ascorbic acid than cashew apple juice. Consequently, the soluble solids, titratable acidity, reducing and total sugars of the blends increased with increase in the proportions of orange juice while the content of ascorbic acid was decreasing. In spite of the decrease in ascorbic acid content of the blends, results showed that blended juice would no doubt be a very good source of ascorbic acid. Result of the organoleptic evaluation revealed that a 60% cashew apple and 40% orange juice gave a good quality juice in terms of flavor, after taste and overall acceptability.     

Dormancy and sprout development of some South African potato cultivars during cold storage

Summary Observations were made on dormancy and sprout growth of nine potato cultivars stored at 3–4°C, 7–8°C and 11–12°C, respectively. Tubers of the cultivar Vanderplank had a very long dormant period (232 days at 3–4°C) and showed little sprout growth at 180 days. The cultivar Koos Smit had a very short dormant period (92 days at 3–4°C) and developed considerable sprout growth at the higher temperatures. The reaction of tubers of Up-to-date and BP₁ were approximately the same, and intermediate between those of Vanderplank and Koos Smit.     

Influence of nitrogen fertilization on quality,respiration and storage life of Washington navel oranges

Summary The effects of N on quality and storage life of oranges were investigated in a factorial field experiment at Griffith N.S.W., Australia. The trees that did not receive any ammonium sulphate (N₀) produced fruit with the best quality of juice. However, such trees had only one quarter of the total yield (by weight) of trees receiving 2 kg ammonium sulphate (N₁) per annum. Higher levels of ammonium sulphate (4 and 8 kg; N₂ and N₄ respectively) did not increase in yield or quality as judged by the total soluble solids (T.S.S.) to titratable acid ratio of the juice. N₁ — trees had produced more juice and total soluble solids than other treatments. Organoleptic tests favoured juice with the highest T.S.S./acid ratio and the lowest percentage titratable acid. Although fruit stored at 0°C had the least fungal wastage, that stored at 15°C had less rind breakdown and total wastage (fungal + rind breakdown). Low temperature rind breakdown was particularly evident at 7.5°C and most oranges were affected irrespective of nitrogen treatment. At 20°C and 25°C, a high temperature rind breakdown was found with N4 — fruit on short storage, and in other fruit after longer storage. Associated with the rind breakdown and preceding its appearance was a higher rate of respiration. Some typicalSeptoria spot (with pycnidia) was found at 20°C and the high temperature rind breakdown is possibly related to this disease or its due to another pathogen; it was not possible to decide definitely its origin, whether pathogenic or physiological. In general N₀ — and N₁ —fruits stored better at most temperatures than N₂ — and N₄ — fruits. Respiration rate at 20°C was similar irrespective of treatment; a climacteric rise in evolution of carbon dioxide was not found. Yield, internal quality and storage life of fruit, considered collectively, indicated that trees receiving 2 kg sulphate of ammonia per tree per annum were, superior to all other treatments in this experiment.     

Use of Banana (<Emphasis Type="Italic">Musa acuminata</Emphasis> Colla AAA) Peel Extract as an Antioxidant Source in Orange Juices

Using banana peel extract as an antioxidant in freshly squeezed orange juices and juices from concentrate was evaluated. Free radical scavenging capacity increased by adding banana peel extracts to both types of orange juice. In addition, remarkable increases in antioxidant capacity using 2,2′-azino-bis-(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) radical were observed when equal or greater than 5 mg of banana peel extract per ml of freshly squeezed juice was added. No clear effects were observed in the capacity to inhibit lipid peroxidation. Adding 5 mg banana peel extract per ml of orange juice did not substantially modify the physicochemical and sensory characteristics of either type of juice. However, undesirable changes in the sensory characteristics (in-mouth sensations and colour) were detected when equal or greater than 10 mg banana peel extract per ml of orange juice was added. These results confirm that banana peel is a promising natural additive that increases the capacity to scavenge free radicals of orange juice with acceptable sensory and physicochemical characteristics for the consumer.     

Comparative susceptibility of some potato cultivars to dry rot caused byFusarium sulphureum andF. solani var.coeruleum

Summary The susceptibility of 15 potato cultivars to dry rot caused byFusarium sulphureum andf. solani var.coeruleum was examined over 8 years. Tubers were wounded, inoculated, incubated at 10°C for 7–8 weeks and the size of the rot assessed.F. sulphureum was the more aggressive species. There was little correlation between the rank order of susceptibility of the cultivars to the two pathogens, but a higly significant correlation between years. Two years' tests are deemed sufficient to assess susceptibility to both species.     

Environmental factors influencing aphid transmission of potato virus Y and potato leafroll virus

Summary The effect of temperature, relative humidity (RH) and light on aphid transmission of potato virus Y (PVY) and potato leafroll virus (PLRV) was studied using as vectorsMyzus persicae Sulz. andAphis gossypii Glov. Host susceptibility was enhanced by 48 h pre-inoculation exposure at 25°C and by 48 h post-inoculation exposure to 30°C. High RH (80%) in both pre- or postinoculation phases enhanced host susceptibility. Continuous fluorescent light (4000 lux) did not alter the rate of transmission of either virus. High RH (80–90%) and high temperature (25–30°C), when combined, increased virus transmission by 30–35%. Transmission rates were reduced by nearly 50% if RH was maintained at 50% in either of the two phases even if the temperature was 25 or 30°C. Both viruses were acquired by aphids earlier (13–20 days after inoculation) when the source plants were incubated at 25 or 30°C. Most virus was transmitted from plants inoculated with PVY 13 to 16 days and with PLRV 15 to 20 days previously. Transmission rates of PVY were enumerated from symptom expression on test plants and by Enzyme Linked Immunosorbent Assay (ELISA) whereas those of PLRV were enumerated from symptom expression alone.     

The effect of controlled atmosphere storage at 4°C on crisp colour and on sprout growth,rotting and weight loss of potato tubers

Summary After three weeks curing at 10°C, potato tubers cv. Record were stored at 4°C under different controlled atmospheres (CA) for six months to study the effect on crisp fry colour, sprout growth and rotting. Combinations of low levels of CO₂ (0.7–1.8%) and low levels of O₂ (2.1–3.9%) gave a significantly lighter crisp colour, low sprout growth and fewer rotted tubers compared with 0.9% CO₂ and 21.0% O₂. Tubers stored in these conditions. showed a significantly higher weight loss and shrinkage after reconditioning. High CO₂: low O₂ combinations during storage completely inhibited sprout growth and caused the darkest crisp colour, but after reconditioning tubers gave the same level of sprouting and crisps as light as the other CA combinations. Furthermore these combinations, especially CO₂ at 10 or 15%, increased the onset of rotting. Also our results showed that at low concentrations of CO₂ (0.7–1.6%), and low O₂ (2–2.4%) there was an increase in tuber rotting.     

Effect of a continuous hot water treatment of potato tubers on seed-borne fungal pathogens

Summary The viability of five pathogens was decreased by treatment with hot water when tested in vitro.Polyscytalum pustulans was most sensitive andRhizoctonia solani least sensitive. Potato tubers were exposed to 55°C for 5 min in a commercial continuous hot water treatment plant using naturally contaminated seed tubers and tubers which had been inoculated by dipping in comminuted cultures. The frequency of eyes colonised byP. pustulans, Helminthosporium solani, andR. solani was reduced to virtually zero and the effect persisted on tubers subsequently stored at 4°C and at 15°C for up to 16 wk. Results withColletotrichum coccodes were inconclusive. Treatment suppressedPenicillium spp. which, however, rapidly recolonised the eyes during storage, leading to higher contamination levels in the treated than in the untreated tubers. With tubers inoculated withPhoma foveata, good control was achieved when the incubation period before treatment was 10 d but not when the period was 42 d.     

Hydrolysis of glycoalkaloids fromSolanum tuberosum L. haulm by enzymes present in plant material and by enzyme preparation

Summary This paper deals with the kinetics of enzymatic hydrolysis of glycoalkaloids from potato (Solanum tuberosum L.) haulm. The hydrolysis was carried out by the action of the enzymes present in fresh haulm, juice of fresh haulm and in haulm dried at various temperatures. The highest degree of enzymatic hydrolysis of 90% was obtained during fermentation of haulm dried at 40 °C after 30 h incubation time. The enzyme preparation was obtained from the juice of fresh potato haulm by using capillary dialysator HM 16 (AQM 1681, 1.6 m² Hemofan 8 υ). The best degree of enzymatic hydrolysis by enzyme preparation, 68%, was achieved after 20 h time of incubation. The enzyme preparation from juice of fresh haulm was characterized by K_m of 0.70 mM at pH 5.5 and 35 °C.     

Accumulation of sugars in microtubers of potato node cuttings (cv. Kennebec) during cold storage

Summary Microtubers of potato cultivar Kennebec were stored for two months at 2 or 8°C and sampled at selected intervals for the determination of glucose, fructose, sucrose and sprout weight. The aim of this experiment was to determine whether these microtubers show the same response to storage temperature with respect to sweetening as field grown tubers. During storage at 2 °C, reducing sugars and sucrose increased rapidly to a concentration of over 1.0 and 0.7 g/100 g fresh weight, respectively. In contrast, in tubers kept at 8°C, only a relatively slight increase in reducing sugar concentration to 0.3 g/100 g fresh weight was observed and sucrose concentration remained virtually the same.