Pronounced Odor Research Articles

Study of Physico-chemical and Bacteriological Quality of Water from Ain Mkbrta Source in Morocco

Springs water is underground water, considered purer than surface water. Its nature depends on the rocks and soils through which it flows. They can be highly charged with specific minerals, which explains why these waters do not meet drinking water standards, but they are widely used for therapeutic properties. In this current work, we investigated the physico-chemical and bacteriological analysis of a water source known for its therapeutic effects, particularly in dermatology. We also examined the geological characteristics to understand the origin of the mineralization of these waters, with the aim of making better use of them on both a medical and economical levels. Ain Mkbrta source, 60 km from Fez city. It belongs to the Rif external domains (Rif Chain), and given its chemical composition, this spring is similar to the Moulay Yacoub hydrothermal spring, with a very pronounced odor due to the presence of hydrogen sulfide. The outcome of physico-chemical analysis of Ain Mkbrta spring showed a very high conductivity, a high hydrogen sulfide content and a wide variety of minerals in significant quantities, such as calcium, magnesium, bicarbonate, sulfate, sulfide, and chloride. Furthermore, Bacteriological analysis is moderately satisfactory, with low concentrations of fecal coliforms and revivable germs.

Carvacrol encapsulation into nanoparticles produced from chia and flaxseed mucilage: Characterization, stability and antimicrobial activity against Salmonella and Listeria monocytogenes

Carvacrol is a natural antimicrobial with excellent antimicrobial properties against several foodborne pathogens. Encapsulation can increase carvacrol stability and solubility, and mask its pronounced odor. Mucilages have been studied as wall material for nanoparticles due to their high retention capacity of bioactive compounds and ease of chemical modifications to improve their stability. In this study, 1.67 mg/mL of carvacrol encapsulated into chia mucilage nanoparticles (CMNP) and flaxseed mucilage nanoparticles (FMNP) were produced by high-energy emulsification technique and tested against Listeria monocytogenes and Salmonella. Encapsulation efficiency around 98% of carvacrol was obtained for both formulations. CMNP showed a diameter size of 179 nm and zeta potential of −11.4 mV. Bacterial Inactivation Concentration (BIC) of CMNP was 0.42 mg/mL against Salmonella and 0.83 mg/mL against L. monocytogenes. FMNP showed diameter size of 165.3 nm and zeta potential of −12.6 mV. BIC of FMNP was 0.83 mg/mL against both microorganisms. Scanning electron microscopy analysis showed that the nanoparticles are spherically shaped. Concentrations of BIC and ½ BIC were used to evaluate the kinetics of bacterial growth in the presence of antimicrobials (CMNP, FMNP and carvacrol solution). The results of this test showed that viable counts of Salmonella and L.monocytogenes were below the detection limit (1.69 log CFU/mL) after 2 h incubation (37 °C) using CMNP at the BIC. The wall material, rehydrated chia and flaxseed mucilages, reduced L. monocytogenes growth during 24 h. However, unloaded nanoparticles kept the viable counts of both microorganisms 2–5 log CFU/mL below the control curve of microbial growth during the 48 h experiment, suggesting that nanostructured mucilages potentiate antimicrobial properties. The results indicate that CMNP and FMNP have potential for use as food preservatives.

Application of sensory analysis in the assessment of the quality of meat products with different sodium chloride content

The aim of this paper was to evaluate sensory quality of commercial boiled chicken sausages and boiled pork sausages with different salt content. Descriptive sensory analysis was used. The basic physicochemical parameters of samples were also determined. The results showed that the chicken sausage sample with 3.42% salt and the pork sausage sample with 3.03% salt had better sensory quality compared to the samples with 2.43 and 3.30% salt, respectively. Chicken sausages with lower salt content had a less pronounced odour, aroma, taste, and softer consistency with significant differences (P 0.05) comparing to the sample with higher salt content. The difference in salt content between pork sausages was smaller than between chicken sausages, but also significant (P 0.05). The sample with lower salt content had better sensory quality, but the differences between all sensory properties, except the colour of two samples, were not significant (P 0.05).

Testing of domestic disinfectants in veterinary medicine

In the system of veterinary and sanitary measures against the background of environmental changes , it remains relevant to search for new high effective means for disinfection to prevent infectious diseases. In a short time, drugs should eliminate pathogens, which requires the special approach to the choice of methods and means of disinfection. To carry out effective disinfection, the availability of appropriate drugs is required, but most of them do not meet one or another requirement, namely: some drugs have a high bactericidal effect, but are toxic, others have a high effect, low toxicity, but have a destructive effect on the treated surfaces. For practical veterinary medicine, drugs that provide a complex effect on viruses, bacteria and fungi are of particular interest. As effective disinfectants, including aerosols and electro aerosols, for many bacterial and viral diseases of animals and birds, preparations from the aldehyde group showed a positive result: a formaldehyde solution with an active substance content of 37%, an alkaline formaldehyde solution prepared from paraformaldehyde and 1% sodium hydroxide. However, despite their advantage, these preparations have a number of disadvantages, namely: high toxicity with a pronounced odor, instability of working solutions, selectivity against pathogenic microorganisms, corrosiveness and carcinogenicity. With the constant use of these agents, the microflora develops resistance. In this regard, it remains relevant to create new environmentally friendly disinfectants, taking into account the achievements of domestic and foreign practice, harmless to humans and animals, environmentally safe and available for consumers

Development of a food antioxidant additive technology out of grape pomace

The use of red grape pomaces to develop food antioxidant additive technology is theoretically justified. As a result, it was proposed to use polar solvents for sugar extraction, titratable acids and other organic compounds made from grape pomace. Using the methods of mathematical planning, we studied the influence of extraction time on the process results (τ), treatment temperature (t), active acidity (pH) and concentration of common salt (CNaCI) in the solution. With the use of artificial intelligence, the optimal parameters of the investigated factors were established. The precipitate was separated from the solution, ground and dried at a temperature of 70-80°C. As a result, the technology of producing a food antioxidant additive, which had a dark cherry colour and a powdered consistency without a pronounced odour, was developed. The antioxidant properties of the developed food additive have been studied on the test (no additives) and experimental (with additives) lipid samples. After processing butter at 37oC for 28 days, the test sample was found to have a lower peroxide number than the control number (0.033 compared to 0.055 mmol of active oxygen / kg), which confirms the antioxidant properties of the food additive, enriched flavonoids.

Essential oil and supercritical extracts of winter savory (Satureja montana L.) as antioxidants in precooked pork chops during chilled storage

The effects of winter savory essential oil (EO) and supercritical extracts (first extract 100 bar, 40 °C – SF1, second extract 300 bar, 40 °C – SF2) on oxidative stability of precooked and cold-stored (at 4 °C for 6 days) pork chops were analyzed. Winter savory showed a significant protective effect towards lipid oxidation which occurs during the cooking process. EO and SF1 showed almost the same potential of lipid oxidation inhibition throughout the whole storage period, being higher comparing to SF2. At the end of storage period the TBARS values were 2.42, 1.66, 1.48, 2.06 mg MDA/kg for control, EO, SF1 and SF2, respectively. Also, EO and SF1 showed better antioxidant potential against protein oxidation comparing to SF2. The lowest colour change at the end of storage was determined for SF1 sample. Samples EO and SF1 had better scores for sensory rancidity; where EO had more pronounced odour and flavour of winter savory and SF1 had lower impact in changing dominant aroma, but preserved aroma of cooked meat. Hence, extracts obtained by supercritical fluid extraction, as natural and environmentally friendly technology, could be used to prolong shelf-life of precooked pork.

Tin and Its Native Land

Tin and Its Native Land Xavier Brau De Saint Pol Lias. Source: Popular Science Monthly, vol 37 (June 1890), pp. 233–9. Translated from the Revue Scientifique. TIN, which, every one knows, but which few, except men of science and metallurgists, are acquainted with, is one of the most precious and most interesting metals. After gold and silver, it is intrinsically the most precious of those in use. It is nearly of the same color and almost as bright as silver, but has less resistance and is less valuable. When warmed by friction, it has a pronounced odor and taste. When it is bent, the derangement of the crystals of which its mass is formed causes it, without any fracture taking place, to emit a peculiar sound which metallurgists call its cry, and by means of which an expert can nearly determine its degree of purity. The places where tin is produced are few, scattered sparsely over the surface of the globe; and it disguises itself under the form of a blackish mineral which, to the profane eye, gives no sign of the treasure that is within it. One of the richest as well as most ancient tin mining districts is in the Malay Peninsula, the Golden Chersonesus of the ancients. The name of the province, Pérak, signifies silver; but it is peculiarly the province of tin. A few years ago we visited the mines there, ascending the Larrout River in a Chinese junk to Telok-Kartang, where a warm reception awaited us from the English colonial authorities. Thence we went, in a country wagon, and afoot after it had broken down, through a country where tigers are not rare, to Thaïping, the principal town in the district. We found lodging in the house of the assistant resident on the top of the Boukit Bandéra, which appeared to our eyes at the moment a veritable castle of the fairy tales. Opening the window in the morning, we could look from our elevated position upon the country of tin, which lay in nearly its full extent before us. Large mounds of white earth and water-holes of strange form, breaking up the surface at different points around the kampang, marked where mines had been worked or were still in working. Chinese coolies were climbing up and down the notched tree-trunks which served as ladders to the open pits, bearing on their shoulders bamboos, at each end of which hung the baskets in which the mineral was carried. Hydraulic wheels, which were nothing but primitive wooden Archimedes’ screws, or norias with inclined buckets, were turning with harsh creakings, lifting the water out of the bottom of the excavations. Animation prevailed over the whole plain, in which were to be seen by turns arid spots of mineral refuse, or exuberant tropical vegetation. Farther on the country [End Page 193] grew hilly, and the view was at last shut off by a semicircle of high mountains, in which are found the true mines, in quartz veins charged with tin, intersecting the granitic masses. The washings of these veins, mingled with alluvial sands, have been carried down by the rivers and spread by them through the floods of the ages over the bottom-lands of the country. Taking advantage of this work of Nature, man, instead of quarrying in the mountain for the vein and having to blast the incasing rock, has only to look in the flats for the mineral. Click for larger view View full resolution Fig. 1. Sungei Lembing Tin-Mining District [in Pahang], Peninsula of Malacca1 The mines were worked by the Chinese, no European operator having been as yet established in the country. It did not take long to witness the extremely simple process by which the ore is extracted. After clearing off the ground, the surface and subsoil are removed for one, two, or three metres, till the mineral, tin-bearing bed is exposed; this is sometimes several metres thick. The mineral is carried in baskets, as we have seen, up the cocoa-trunk ladders, to a wooden flume which is washed by a current of water. As the mine grows deeper this labor...

Influence of low methoxyl pectin on the physicochemical properties of sodium caseinate‐stabilized emulsions

AbstractTwo strategies of emulsion preparation, stabilization by sodium caseinate (CAS)/low methoxyl pectin (LMP) complexes formed in advance, and stabilization by the layer‐by‐layer (LBL) method, were compared. In aqueous solution, at a constant CAS concentration (5 g/L), the gradual addition of LMP resulted in an increase in turbidity of the solution caused by the increasing formation of insoluble complexes. The zeta potential change showed that the interactions are mainly due to an electrostatic mechanism. The spectrofluorometric studies as well as the spectroscopic analysis in the UV–visible region have shown that the interactions with LMP caused a change in the secondary and tertiary structures of the protein. Then, these complexes were used for stabilizing oil/water emulsions. The emulsions stabilized by complexes formed in advance and LBL method were characterized by measuring zeta potential, dynamic viscosity, serum index, and particle size distribution. The results showed that, at low LMP concentrations, complexes‐stabilized emulsions were more stable than LBL‐stabilized ones, while at high LMP concentrations, LBL‐stabilized emulsions showed better stability.Practical applicationsThese results would be useful during the development of encapsulation systems having hybrid interfaces in order to better control the release of hydrophobic active molecules like essential oils. These molecules have various benefits like antioxidant and antimicrobial activities, which could be exploited for food biopreservation. One of the major problems for application in food preservation of these active molecules is their great sensitivity to the environmental stress (temperature, pH…), their low water‐solubility, their interactions with food components, and their pronounced odor and flavor. The encapsulation of these molecules in the developed emulsions containing the proper concentration of LMP could be a suitable solution to protect and release these lipophilic molecules in foods.

Modern possibilities ofair pollution estimation by pig industryenterprises

The main problem of pig farms in Ukraine is the mismatch of their capacity to the actual size of the sanitary protection zones, which leads to the risk of negative influence of odor pollution on the health of the population living in nearby settlements. The purpose of the study was to comprehensively assess the pollution of ambient air by emissions from pig breeding complexes containing dust particles and chemicals with pronounced odor properties. The research was conducted between 2012 and 2015 and covered the activities of 14 modern medium and high capacity pig farms. In the course of the study, natural measurements of ambient air pollution were carried out and materials of sanitary and epidemiological examination of these enterprises were examined. Within the framework of the pilot project, a survey of the local population was carried out and a mathematical model of the concentrations of the investigated chemical substances in the surface layer of the atmosphere was calculated, based on data on the odor threshold for these substances. The discrepancy between the existing dimensions of the protection zones of pig complexes and their production capacities was established, while the concentrations of the investigated substances in the air were not exceeded. Out of 126 respondents, 72% complain of a periodic deterioration in their health, which they associate with the pig complex. At mathematical modeling with averaging in 24 hours the excess of a threshold of a smell of hydrogen sulphide (2,8 times) and methylmercaptan (in 2,6 times) is found out. Conclusions are made about the prospects of the method of mathematical modeling of the distribution of chemical substances in ambient air, taking into account their odor threshold.

Acceptance Of Fish Crackers Produced From Tilapia And Catfish

Sensory Evaluation of fish crackers produced from catfish and tilapia was evaluated in attempt to ensure the possibilities of better utilization of underutilized Tilapia and catfish. The product were produced with corn starch (25%), pepper (0.1%) salt (0.5%), magi (2 cubes) vegetable oil (18.5%) Tilapia (35%), catfish (35%). Tilapia and catfish were deboned using a bone separator and grinded with a pepper grinder and mashed together with 25% of cornstarch. The mixture was kneaded and moulded into a cylindrical shape and wrapped in a nylon and steamed in a steaming pot for 45 minutes and then put into a refrigeration for 24 hours. The cooled product was cut into shapes and sprayed on the sun for 3 days and deep fried. The acceptance was evaluated with 25 man panel based on taste, flavor, colour and texture and general acceptability. 75% of the panelist preferred fish crackers from catfish to those made from tilapia in terms of taste. 85% like the texture and flavor of the crackers from tilapia than that of catfish. There was higher consumer acceptability for crackers from catfish in terms of taste to that made from Tilapia. There was significant difference observed between crackers from tilapia and catfish. Diversification of fish industry through better utilization of underutilized tilapia and catfish will help to improve commercialization of these products. This will improve food and nutritional security and also help to create a means of revenue generation and alleviate poverty in Nigeria. I. Introduction A large proportion of the total landed fish from tilapia and catfish. most of these fishes have stunted growth and cannot been utilized in this form and they remain unused due to inherent problems related to unattractive color, flavor, texture, small size and high fat content. Most of these species belong to the abundantly available pelagic species, which are by catch, of some unconventional species. (Akande, 1989). Adding fish as nutritional value to staple foods has been researched by many nutrition scientists and food technologists (ANON 2001). Though considerable research has been carried out on the different ways of utilizing small fishes in minced fish production (Akande 1989; Eyo 1999; King 2001). A variety of fish species are used for fish product, while fish like Alaska Pollock and tropical species such as farmed species like Chineses Carp (Shaviklo 2000). maybe used. The use of fish species with high dark/red muscle and fat content has met with some complication such as how grade protein gel, colour problems and lipid oxidation (Park and Lanier 2000). The production and utilization of fish using locally manufactured pepper grinder (Attrition Mill) was developed by King, M.O of the Nigerian Institute for Oceanography and Marine Research in the processing of ingredients for the preparation of fish cakes, fish burger and fish crackers among others. The processing yield of Tilapia was reported to be 51% for dressed fish and 25.4% for fillet (clement and lovel 1994). Ninan et al., (2010) reported that Tilapia in fresh condition can yield 32-36% mince. The mince is white in colour, has low fat content and pronounced odour, which makes in an ideal raw material for the preparation of value-added products. There is a great interest in using larger quantities of fish for human food (park and lanier 2000). This will lead to better utilization of the fish species. The study is aimed at value addition using Tilapia, a low-value fish which at present has limited scope for consumption in fresh form than catfish which is abundant (Ninan et al., 2010). Studies showed that the mince yield of this species is commercial important in the utilization of underutilized species for the production of cutlets, fish balls and cully fish which are simple and cost-effective. Commercialization of these product can contribute to the fish processing industry through better utilization of a relatively underutilized species. Study Area: The production of fish crackers was done in Nigerian Institute of oceanography and marine research lab.

Variação química no óleo essencial das folhas de seis indivíduos de Duguetia furfuracea (Annonaceae)

Duguetia furfuracea, Annonaceae, a pasture weed, is also used in folk medicine in several Brazilian states. Because of the significant difference in odor between two groups of this plant in a remnant patch of savanna in Campo Grande county, Mato Grosso do Sul, six samples were selected according to the odor intensity in the leaves (In-01, In-03, and In-05: pronounced odor; In-02, In-04, and In-06: weak odor or its absence). The leaves were collected and subjected to steam distillation for extraction of essential oils, which were analyzed by GC-MS. A good agreement was found between CG/MS results and olfactory evaluation of the samples: specimens exhibiting leaf scent had a high percentage of monoterpenes and some sesquiterpenes, as follows: In-01 (β-phellandrene, 42.2%; myrcene, 6.8%; α-phellandrene, 4.6%); In-03 (terpin-4-ol, 21.6%; sabinene, 17.3%; p-cymene, 5.6%); In-05 (sabinene, 25.1%; terpin-4-ol, 16.2%; p-cymene, 8.3%). Only sesquiterpenes were found in the specimens having weakly scented or scentless leaves (main constituent bicyclogermacrene: 21.4%, 24.0%, and 29.1%, respectively, for In-02, In-04 and In-06).

Effect of pork lard content on the chemical, microbiological and sensory properties of a typical fermented meat product ( Pitina) obtained from Alpagota sheep

The aim was to investigate the physicochemical, microbiological and sensory properties of Pitina, a typical fermented meat product and evaluate the effect of two levels of pork lard content (Low Fat, LF, 10% vs. High Fat, HF, 30%) on its attributes. HF attained lower pH than LF Pitina, which reached lower water activity. LAB comprised the major flora with substantial counts of micrococci, enterococci and mould and yeast. Gram negative Enterobacteria were recovered as coliforms and faecal coliforms. Listeria monocytogenes was also isolated. The lard level influenced the count of micrococci and some sensory attributes. LF attained higher scores for both hardness and cohesiveness and differed from HF in having a more marked odour of ewe and smoke and sweeter taste. HF had a more pronounced odour and taste of garlic and mould than LF.

Poly(ethylene oxide) Gel Based Dimexide Ointment

Dimexide (dimethyl sulfoxide, DMSO), approved for medical applications since 1971, is used for the treatment of contusions, strained muscles, edemas of various etiology, lymphostasis, burns, phlegmons, hemarthrosis, acute and chronic thrombophlebitis, erysepilatous inflammations, eczemas, diffuse streptoderma, and other disorders. The main medicinal form of dimexide administration are applications and compresses using 30 – 70% aqueous DMSO solutions (most frequently, 50% solution) [1 – 3]. However, this form is rather inconvenient since a patient has to prepare the solution at home. Another disadvantage is a pronounced specific odor sometimes complicating use of DMSO solutions. Despite the broad range of indications for administration and the wide experience gained on using DMSO in practice, optimum medicinal forms of dimexide have yet to be developed. Creation of an ointment containing 50% DMSO is a complicated task because a base with such a high content of this liquid is difficult to densify. Another problem is related to the fact that DMSO is a strong penetrant facilitating absorption of the base components through the skin. This property of DMSO excludes using hydrocarbon bases for preparation of DMSO ointments because the absorption of hydrocarbons and other lipophilic ointment-forming components detrimentally affects the gas exchange and water metabolism in the skin. Therefore, dimexide ointments should be developed using hydrophilic water-soluble polymer-based components. A promising modern medicinal form of dimexide is offered by analgesic and antiinflammatory gel preparations [4]. Such gels are prepared based on gelatin, poly(vinyl pyrrolidone) (PVP), or starch and additionally contain taurine. We have prepared a series of dimexide gels according to recommendations [4]. It was found that some characteristics of the preparations (appearance, colloidal stability, rheological properties) do not meet the pharmacopoeial requirements. The gels appear as viscous liquids, exhibit strong characteristic odor, and seem “greasy” to the touch. The ointments exhibit separation into layers on standing and cannot be strictly classified as gels due to unsatisfactory elastic-plastic behavior. In contrast, a gel prepared on carbopol base [5] possess valuable organoleptic properties, an attractive appearance, and good spreading capacity owing to the pronounced elastic-plastic properties. This gel is stable on storage, but still has a pronounced odor and was “greasy” to the touch. The purpose of this study was to create a ready-to-use medicinal form – a dimexide ointment – with a DMSO content in the range from 30.0 to 70.0% using bases not containing hydrocarbons (paraffin, vaseline, vaseline oil) and free of the aforementioned disadvantages (odor and “greasy” feel). The work was performed in cooperation with specialists of the Pyatigorsk Pharmaceutical Plant.

Novel chemistry of abdominal defensive glands of nymphalid butterfly Agraulis vanillae.

Abdominal defensive glands of both sexes of the Gulf fritillary butterfly, Agraulis vanillae (Linnaeus) (Nymphalidae:Heliconiinae) emit a pronounced odor when disturbed. We have identified 6-methyl-5-hepten-2-one; oleic, palmitic, and stearic esters of the corresponding alcohol 6-methyl-5-hepten-2-ol; hexadecyl acetate; 1,16-hexadecanediol diacetate; and 1,15-hexade-canediol diacetate in the glandular exudate. Since we have determined that free-flying birds or birds in a butterfly conservatory discriminate against A. vanillae as prey, we suggest that the constituents in the glands may play a defensive role against potential avian predators.

The ontogeny of conditioned odor potentiation of startle.

During development, conditioned responses usually occur first to olfactory, then to auditory, and finally to visual cues. The authors of the present study report that fear potentiation of startle to an olfactory conditioned stimulus emerges relatively late in development (i.e., at 23 days of age; Experiments 1 and 2). The failure to observe conditioned odor potentiation of startle (OPS) in younger rats was not due to a failure to either acquire or remember the odor-shock association (Experiment 3). Surprisingly, the authors also found that rats trained at 16 but tested at 23 days of age failed to exhibit the OPS effect even though they did exhibit pronounced odor avoidance (Experiment 4). The results are discussed in terms of (a) sensory-specific sequential emergence of learned fear, (b) the neural circuit involved in fear potentiation of startle, and (c) the concept that conditioned responding is appropriate to the animal's age at the time of training rather than its age at testing.

Developmental flavor experience affects utilization of odor, not taste in toxiphobic conditioning

Feeding experiences were varied in developing rats and the effects upon flavor neophobia and lithium chloride-induced flavor aversions were observed. In Experiment 1, nursing experience of neonate rats was reduced by artificial feeding via intragastric cannula; the rats then were tested with apple juice paired with lithium chloride injection at weaning or maturity. Conditioned aversions were not affected, but neophobia to novel apple juice was attenuated in artificially-reared rats tested at maturity. In Experiment 2, rats received enriched feeding experience after weaning, which consisted of (a) obtaining many complex flavors, a few of which were paired with poisoning, effortlessly in the home cage, or (b) foraging for various foods on an elevated maze. No dramatic effects on neophobia or conditioned taste aversion for saccharin water were apparent. In Experiment 3, rats were given experience after weaning with vanilla-scented water either paired or unpaired with quinine water, and then tested with the odor of almond or that odor compounded with saccharin water for neophobia and lithium-induced aversions. Flavor-experienced rats exhibited more pronounced odor conditioning and more resistance to extinction of the odor aversion after both simple and compound conditioning. In contrast, saccharin taste aversions were relatively unchanged. Apparently, enriched feeding and drinking experience facilitates the utilization of odor more than taste cues.

Non-enzymic decarboxylation of methionine by ferrous ion.

IN work on the precursors of the volatile sulphur components of vegetable flavours and odours, a non-enzymic oxidative decarboxylation of methionine in the presence of Fe2+ was observed. The final reaction mixture had a very pronounced odour. Unlike other well-known Fe2+ oxidations, there was no need for added hydrogen peroxide1,2 or ascorbic acid3,4. The addition of a metal chelating agent such as ethylenediamine tetraacetate (EDTA) or citrate was very stimulatory. Table 1 shows the absolute requirement for Fe2+. Only Fe2+ was able to carry out this decarboxylation. Mg2+, Mn2+, Ca2+, Co2+, Ni2+, Zn2+, Cu2+ and Al3+ were completely ineffective. Fe3+ was 1 per cent as effective as Fe2+.