Microbiological quality of five potato products obtained at retail markets

The microbiological quality of frozen hash brown potatoes, dried hash brown potatoes with onions, frozen french fried potatoes, dried instant mashed potatoes, and potato salad was determined by a national sampling at the retail level. A wide range of results was obtained, with most sampling units of each products having excellent microbiological quality. Geometric mean aerobic plate counts were as follows: dried hash brown potatoes, 270/g; frozen hash brown potatoes with onions, 580/g; frozen french fried potatoes 78/g; dried instant mashed potatoes, 1.1 x 10(3)/g; and potato salad, 3.6 x 10(3)/g. Mean values of coliforms, Escherichia coli, and Staphylococcus aureus were less than 10/g.     

Bacteriological Survey of the Frozen Prepared Foods Industry: III. Potato Products

During sanitation-inspections of 29 potato-processing firms, 2,544 finished product units and 1,654 samples were collected and analyzed bacteriologically. The results of the bacteriological examination of finished French fries, fried potato cylinders, and dehydrated potatoes usually did not reveal the conditions of cleanliness under which they were produced. This was most likely due to the lethal effect of the terminal fry to which the French fries and potato cylinders are subjected, and because of the lethal effect of the dehydration temperatures used in processing the dehydrated potato products. However, as in most food-processing firms, line samples collected at each processing step reflect sanitary conditions and provide bacteriological support of inspectional evidence of plant insanitation. Most of the frozen stuffed baked potatoes examined were produced under poor sanitary conditions. But because this product is usually processed while hot, bacteriological examination of the finished product did not usually reveal the conditions of cleanliness under which they were produced. Again, inspectional observations were necessary for a full evaluation of the conditions of production. In contrast, frozen potato patties and frozen hash brown potatoes were more likely to reveal the conditions of sanitation under which they were produced as evidenced by the varying bacterial counts.     

Statistical analysis and quality control in radioimmunoassays for staphylococcal enterotoxins A, B, and C.

The objective of these studies was to set up a reliable radioimmunoassay (RIA) for staphylococcal enterotoxins A, B, and C (SEA, SEB, and SEC) in a food system. Significant differences (95% confidence limits) were obtained between the 0- and 1-ng/ml enterotoxin standards, so the sensitivity of the RIAs was 1 ng/ml. Polystyrene tubes coated with anti-SEB and stored at 4 degrees C were unstable. The percentage of iodinated SEB bound to these tubes decreased at a rate of 0.33%/day, in contrast to the rate of 0.07%/day obtained with tubes prepared the day before the analyses. Satisfactory precision and maximum sensitivity were obtained by using six replicates for each sample and freshly coated tubes. The antisera used for coating the tubes were reused four times and were frozen between coatings. The process of drum drying mashed potatoes containing 1 mug of SEB per g of mashed potatoes inactivated 83% (wt/wt) of the SEB. Statistical quality control parameters were used to insure that RIAs were performing reliably with a sensitivity of 1 ng/ml. Over 450 samples of potato flakes and granules, which represented different production lots from 12 different manufacturers, were examined for SEA, SEB, and SEC. No enterotoxins were detected.     

Statistical analysis and quality control in radioimmunoassays for staphylococcal enterotoxins A, B, and C.

The objective of these studies was to set up a reliable radioimmunoassay (RIA) for staphylococcal enterotoxins A, B, and C (SEA, SEB, and SEC) in a food system. Significant differences (95% confidence limits) were obtained between the 0- and 1-ng/ml enterotoxin standards, so the sensitivity of the RIAs was 1 ng/ml. Polystyrene tubes coated with anti-SEB and stored at 4 degrees C were unstable. The percentage of iodinated SEB bound to these tubes decreased at a rate of 0.33%/day, in contrast to the rate of 0.07%/day obtained with tubes prepared the day before the analyses. Satisfactory precision and maximum sensitivity were obtained by using six replicates for each sample and freshly coated tubes. The antisera used for coating the tubes were reused four times and were frozen between coatings. The process of drum drying mashed potatoes containing 1 mug of SEB per g of mashed potatoes inactivated 83% (wt/wt) of the SEB. Statistical quality control parameters were used to insure that RIAs were performing reliably with a sensitivity of 1 ng/ml. Over 450 samples of potato flakes and granules, which represented different production lots from 12 different manufacturers, were examined for SEA, SEB, and SEC. No enterotoxins were detected.     

An outbreak of staphylococcal food poisoning caused by enterotoxin H in mashed potato made with raw milk

Mashed potato made with raw bovine milk was suspected to have been the source of a food poisoning outbreak. Almost 8 x 10(8)Staphylococcus aureus CFU g(-1) were detected in the mashed potato. S. aureus was also found in bulk milk from the farm that had supplied milk for the mashed potato. Isolates from mashed potato and bulk milk were positive for the gene encoding staphylococcal enterotoxin H (seh), and the corresponding protein toxin, SEH, was detected by ELISA in the mashed potato. Production of SEH by S. aureus isolates from mashed potato (n = 4) and bulk milk (n = 4) was also demonstrated by ELISA. Sequencing of seh from one mashed potato isolate and one bulk milk isolate confirmed that the gene was a variant seh, and that the genes in both isolates were identical. Macrorestriction of chromosomal DNA with Sma1 followed by pulsed-field gel electrophoresis of seh-positive S. aureus from mashed potato and bulk milk revealed indistinguishable banding patterns between isolates from both sources. It seems likely that raw bovine milk used in the preparation of mashed potato contained S. aureus that subsequently produced sufficient SEH in the mashed potato to cause food poisoning.     

Acrylamide in processed potato products: progress made and present status

Concerns related to higher levels of acrylamide in processed carbohydrate-rich foods, especially in fried potato products, are well known. This article provides updates on various aspects of acrylamide in processed potato products including mechanisms of acrylamide formation and health risks due to its intake. Levels of reducing sugars in potatoes are considered as a main factor contributing towards the formation of acrylamide in processed potato products. Useful approaches in lowering the levels of reducing sugars such as use of suitable varieties, storage methods, storage temperature and duration of storage are described and discussed. Importance and practical utility of various steps before and during the processing that can contribute in reducing the final concentration of acrylamide are highlighted. Progress made and present status of potato processing industry in India are part of this article. The article describes varietal improvement and spread of short-term and long-term storage technologies in India and their contribution towards round the year availability of processing-grade potatoes to the processing industries and how all this has helped in achieving reduced levels of acrylamide in chips and French fries. Outcome and implications of cold-induced sweetening tolerance in potatoes are presented along with other management practices and strategies that can lower the acrylamide levels in processed potato products. Future lines of work have been suggested to make the consumption of fried potato products safer.     

Molecular and physiological properties associated with zebra complex disease in potatoes and its relation with Candidatus Liberibacter contents in psyllid vectors

Zebra complex (ZC) disease on potatoes is associated with Candidatus Liberibacter solanacearum (CLs), an α-proteobacterium that resides in the plant phloem and is transmitted by the potato psyllid Bactericera cockerelli (?ulc). The name ZC originates from the brown striping in fried chips of infected tubers, but the whole plants also exhibit a variety of morphological features and symptoms for which the physiological or molecular basis are not understood. We determined that compared to healthy plants, stems of ZC-plants accumulate starch and more than three-fold total protein, including gene expression regulatory factors (e.g. cyclophilin) and tuber storage proteins (e.g., patatins), indicating that ZC-affected stems are reprogrammed to exhibit tuber-like physiological properties. Furthermore, the total phenolic content in ZC potato stems was elevated two-fold, and amounts of polyphenol oxidase enzyme were also high, both serving to explain the ZC-hallmark rapid brown discoloration of air-exposed damaged tissue. Newly developed quantitative and/or conventional PCR demonstrated that the percentage of psyllids in laboratory colonies containing detectable levels of CLs and its titer could fluctuate over time with effects on colony prolificacy, but presumed reproduction-associated primary endosymbiont levels remained stable. Potato plants exposed in the laboratory to psyllid populations with relatively low-CLs content survived while exposure of plants to high-CLs psyllids rapidly culminated in a lethal collapse. In conclusion, we identified plant physiological biomarkers associated with the presence of ZC and/or CLs in the vegetative potato plant tissue and determined that the titer of CLs in the psyllid population directly affects the rate of disease development in plants.     

Effect of the dates of extraction on the quality of potato pulp

The objectives of this study were to evaluate the fundamental properties of potato pulp and to explore its potential uses. Lactic acid bacteria were the dominant microbes in potato pulp over the season (maximum being 10(8)/g). The water content in potato pulp was approximately 80% in all season. Starch and fiber were the main components of potato pulp, amounting to 80% of the dried matter regardless of the season. The fermentation of potato pulp by Rhizopus oryzae progressed only in the potato pulp extracted at the end of the season. This indicated that the fermentation of potato pulp was influenced by the dates of extraction, and it was assumed that the quality of the components, such as pectin, varied with such dates.     

Effect of Onions on Blood Fibrinolytic Activity

Twenty-two convalescent patients at rest were given a fat-enriched breakfast with and without the addition of 60 g. of fried or boiled onions. Both forms of onions were found to prevent the expected decrease in fibrinolytic activity, and indeed the latter was actually increased.     

Insecticidal Activity of the Granulosis Virus in Combination with Neem Products and Talc Powder Against the Potato Tuberworm Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)

The potato tuberworm Phthorimaea operculella (Zeller) is an important agricultural pest that causes significant economic losses to potato growers worldwide. The addition of an effective method of biological control for the potato tuberworm is greatly needed, and is currently unavailable in Brazil. The granulosis virus (Baculoviridae) is a promising biological control agent to protect post-harvest potatoes and in storage from the potato tuberworm. However, the control measure must be economically feasible. Liquid suspensions of a granulosis virus applied alone or in mixture with two commercial neem oil-based products (DalNeem? and NeemAzal?), and a dry powder formulation of viral granules were evaluated for control of potato tuberworm larvae by treating potato tubers under laboratory conditions. High larval mortality (86.7%) was achieved when DalNeem and virus were applied together at 4?mg of azadirachtin/L and 10⁴ occlusion bodies (OBs)/mL, respectively. This combination resulted in ??50% efficacy in relation to their counterparts alone. Conversely, NeemAzal did not enhance virus effectiveness against larvae of the potato tuberworm. The talc-based virus formulation was used for dusting seed tubers at different concentrations and resulted in 100% larval mortality at 5?×?10⁸ OBs/g. Formulated and unformulated virus provided 50% mortality at 166 OBs/g and at 5.0?×?10⁵ OBs/mL, respectively. As a result, talc-based virus formulation had a better control efficiency on potato tuberworm than the aqueous virus suspension. The granulosis virus combined with DalNeem at low rates or formulated with talc powder is a viable option to control the potato tuberworm under storage conditions.     

Growth and survival of Shigella flexneri in common Bangladeshi foods under various conditions of time and temperature.

Survival and growth of Shigella flexneri were assessed in various foods, including boiled rice, lentil soup, milk, cooked beef, cooked fish, mashed potato, mashed brinjal, and raw cucumber. Growth at 25 and 37 degrees C and survival at 5 degrees C were observed by viable counts on MacConkey agar. The organism grew well in all tested foods and growth increased from 10(5) to 10(8) to 10(10) cells per ml or g within 6 to 18 h after inoculation at 25 and 37 degrees C.     

Effect of a Pulsed Electric Field and Osmotic Treatment on Freezing of Potato Tissue

This work discusses the effects of pulsed electric field (PEF) and osmotic pre-treatments on potato tissue structure and on the freezing and freeze-drying behaviour of this tissue. Potato samples (26-mm diameter, 10-mm height) were treated by PEF (400 V/cm) to high level of disintegration (conductivity disintegration index Z was ≈0.95) and were subjected to osmotic treatment in an aqueous solution of NaCl. The samples were either frozen in an air-blast freezer at air temperature of −80 °C and velocity of 2 m/s or freeze-dried at 0 °C and 0.04-mbar pressure. The scanning electron microscope (SEM) images evidenced similarity in structure of the cell walls and area and morphology of starch granules for untreated and PEF-treated potato tissues. However, sequential (PEF + osmotic) pre-treatment of potato tissue resulted in starch granules with rougher surface. The profiles of freezing curves were strongly dependent on pre-treatment. The longest effective freezing time t _f was observed for untreated tissue, and the values of t _f were decreasing in the following sequence: untreated > PEF pre-treated > PEF + osmotically pre-treated. The faster freezing and freeze drying and visually better quality of the dried samples were observed for PEF or sequential PEF + osmotic pre-treatments. The SEM analysis revealed also a noticeable disorder of starch granule surface morphology inside the cells of the freeze-dried potatoes after sequential PEF + osmotic pre-treatment.     

Plant tissue-based chemiluminescence flow biosensor for determination of unbound dopamine in rabbit blood with on-line microdialysis sampling

A novel plant tissue-based chemiluminescence (CL) biosensor for dopamine combined with flow injection analysis is presented in this paper. The potato roots act as molecular recognition elements. Dopamine is oxidized by oxygen under the catalysis of polyphenol oxidase in the tissue column to produce hydrogen peroxide, which can react with luminol in the presence of peroxidase of potato tissue to generate CL signal. The CL emission intensity was linear with dopamine concentration in the range of 1x10(-5)-1x10(-7) g/ml and the detection limit was 5.3x10(-8) g/ml (3sigma) with a relative standard deviation of 1.7%. Combined with microdialysis sampling, the biosensor was applied to monitor the variation of dopamine level in the blood of rabbit after the administration of dopamine to demonstrate the favorable resolution and reliability of the system for in vivo on-line monitoring.     

The effect of iprodione on sclerotium germination, root infection and mycelial spread of Sclerotium cepivorum in salad onions

Iprodione seed treatment at 125 g a.i./kg seed and stem base sprays at 0–3 and 0.125 g a.i./m row delayed the appearance and reduced the incidence of stem base symptoms and root infection with Sclerotium cepivorum in autumn- and spring-sown salad onions. Viability of sclerotia was unaffected by the treatments but their germination was delayed. The spread of mycelium between plants was suppressed but growth of hyphae within infected roots was much less affected.     

Chemical control of potato cyst-nematode in sandy clay soil

In sandy clay soil in Bedfordshire, potato cyst-nematode (Heterodera rostochiensis Woll.) was controlled and yields of Majestic potatoes greatly increased when i-2g aldicarb, 4-0 g fensulphothion or 10-3 g diazinon, disulphoton, ‘Isolan’ (i-isopropyl-3-methyl-5-pyrazolyl dimethylcarba-mate) or thionazin per m² were incorporated in the top soil before potatoes were planted. Diethyl phosphorothioates controlled H. rostochiensis better than dimethyl phosphates. One hundred and eleven g methyl bromide, 47-6 g carbon disulphide or 45-2 g D-D per m² applied to the soil and covered with polyethylene sheeting greatly increased the yield of potatoes, but also increased the number of nematodes in the soil. Estimates of the number of larvae able to invade potato roots in treated soil after harvest and of cysts, total eggs or live eggs selected the same range of treatments as effective in controlling H. rostochiensis.     

Population dynamics of the potato tuber moth on processing tomatoes in Israel

The potato tuber moth (PTM),Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is a major pest of processing tomatoes,Lycopersicon esculentum Mill. (Solanaceae), in Israel. The larvae penetrate the tomato fruit through the stem end and present a serious threat to crop quality. Foliage and fruit samples were taken in nine commercial tomato fields located in Israel's three main tomato growing areas, two of which are potato growing areas as well. PTM was not found where potatoes were absent. Potato harvest in nearby fields was found to be the most significant factor affecting seasonal trends in PTM population density in tomatoes. All four larval instars were found in foliage on all sampling dates. Significantly higher proportions of first instars were found during the population density increase which followed potato harvest. Damaged fruits did not contain first instar larvae, indicating that PTM never undergoes complete development within tomato fruit. Fruit damage levels at harvest were positively correlated to the peak mean population densities on foliage and the date they were observed. In tomato fields not adjacent to potatoes, infestation was first observed at the edge of the field. Both before and after the potato harvest in nearby fields, population density at the edge of the field was significantly higher than at the center. In tomato fields adjacent to potatoes, no significant differences were found between population densities at the edge and center before the potatoes were harvested. After the potato harvest, population density at the center of tomato fields was higher than at the edge. Deceased, October 1988     

Effects of D-D, Telone or dazomet applied to potato ridges in spring on potato cyst-nematode, Heterodera rostochiensis, in sandy loam and silt loam soils

Large amounts of dazomet (329, 439 kg/ha) applied to potato ridge soil in spring, before potatoes were planted, controlled potato cyst-nematode (Heterodera rostochiensis) in sandy loam and silt loam more effectively than large amounts of D-D (359, 448 kg/ha). In heavily infested sandy loam, 329 kg dazomet/ha or 857 kg methyl bromide/ha applied in spring 1969 or 439 kg dazomet/ha applied in autumn 1968, greatly decreased the number of larvae able to invade potato roots, so Majestic potatoes grew and yielded well without increasing the number of nematodes left in the soil after harvest. Large amounts of D-D or Telone applied to the topsoil in autumn or to the ridges in spring were less effective in controlling potato cyst-nematode or increasing potato yields. Applied in spring 1969 to silt loam ridges, 439 kg dazomet/ha had more effect than 448 kg D-D/ha on potato cyst-nematode and on the increase in yield of Majestic potato. The yield of Maris Piper potatoes (resistant to H. rostochiensis pathotype A) in infested silt loam was increased greatly by D-D, as much by 112 as by 224 or 448 kg/ha.