EFFECT of UNIT OPERATIONS of PRODUCTION ON the CYANIDE CONTENT and ACCEPTABILITY of GARI

The effect of holding, pressing, initial moisture content, sunheating, and garifying, on pH, total titratable acidity (TTA) and residual cyanide content of cassava mash, cake and gari, were evaluated. A new method to make gari with very low residual cyanide was developed.
Increasing holding time decreased pH, cyanide content, but increased TTA of mash and gari when initial moisture content of mash was greater or equal to 63–65%. Reducing the initial moisture content of mash below 60% increased pH, reduced the residual cyanide, but increased the TTA in the mash. the optimum holding period was 72 h beyond which there was no reduction in residual cyanide content. Pressing and garifying further reduced the residual cyanide of cassava mash and gari, respectively. Sensory properties of gari prepared by the new laboratory method were similar to those of gari produced by the traditional method.     

Influence of selected process variables on the elimination of cyanide from cassava

The effects of selected methods of size reduction, holding periods and drying on elimination of cyanide from cassava roots of variety MCol 1684 were investigated. Drying at 50°C eliminated approximately 50% of the total cyanide from mechanically prepared chips, and 25% from manually prepared chips. Mechanical chipping and drying at 50°C eliminated 65% of the total cyanide from small chips and 47% from large chips. Mincing of whole roots completely degraded the glucoside, and rasping and mechanical chipping degraded 70–80% and 30% of the initial glucoside respectively. The results indicate that the method of size reduction and particle size control the rate of glucoside degradation, and that the drying rate limits the quantity of glucosidic cyanide eliminated. The results are compared with those of other researchers.     

Hydrocyanic acid levels in fermented cassava

The extent of loss of hydrocyanic acid during the fermentation of cassava tubers selected from both sweet and bitter varieties in the traditional method (whole unpeeled tubers) compared with the fermentation of peeled tubers and crushed pulps with or without the addition of water. Although the traditional fermentation is terminated after 3–4 days, in this study the fermentation was allowed to proceed for 8 days. Loss of cyanide from the whole tubers was 8047% after 8 days and was only 51–53% after 4 days. Loss of cyanide from the whole sweet tuber was not significant after 5 days. The loss of cyanide from the peeled tubers was comparable to the whole tubers after 8 days of fermentation. However, there was a marked decrease in free cyanide in the 1st day of fermentation of the peeled tubers compared to whole tubers. The loss in cyanide in the crushed pulp, which occurred primarily in the 1st day, appears to be due to the action of endogenous linamarase rather than hydrolysis by fermentation. When water is added to the crushed pulp the reduction in cyanide was 83–91% with marked decrease in bound cyanide in the 1st day of fermentation. It seems that autohydrolysis is enhanced by addition of water to the crushed pulp.     

Addition of fumaric acid and sodium benzoate as an alternative method to achieve a 5-log reduction of Escherichia coli O157:H7 populations in apple cider

A study was conducted to develop a preservative treatment capable of the Food and Drug Administration-mandated 5-log reduction of Escherichia coli O157:H7 populations in apple cider. Unpreserved apple cider was treated with generally recognized as safe acidulants and preservatives before inoculation with E. coli O157:H7 in test tubes and subjected to mild heat treatments (25, 35, and 45 degrees C) followed by refrigerated storage (4 degrees C). Fumaric acid had significant (P < 0.05) bactericidal effect when added to cider at 0.10% (wt/vol) and adjusted to pH 3.3, but citric and malic acid had no effect. Strong linear correlation (R2 = 0.96) between increasing undissociated fumaric acid concentrations and increasing log reductions of E. coli O157:H7 in apple cider indicated the undissociated acid to be the bactericidal form. The treatment that achieved the 5-log reduction in three commercial ciders was the addition of fumaric acid (0.15%, wt/vol) and sodium benzoate (0.05%, wt/vol) followed by holding at 25 degrees C for 6 h before 24 h of refrigeration at 4 degrees C. Subsequent experiments revealed that the same preservatives added to cider in flasks resulted in a more than 5-log reduction in less than 5 and 2 h when held at 25 and 35 degrees C, respectively. The treatment also significantly (P < 0.05) reduced total aerobic counts in commercial ciders to populations less than those of pasteurized and raw ciders from the same source (after 5 and 21 days of refrigerated storage at 4 degrees C, respectively). Sensory evaluation of the same ciders revealed that consumers found the preservative-treated cider to be acceptable.     

Moisture-pressure combination treatments for cyanide reduction in grated cassava

Several cyanide-associated health disorders have been linked with frequent consumption of mildly toxic cassava (Manihot esculenta crantz) products in individuals on a low-protein diet. Production of bread from cassava often involves application of prolonged physical pressure (pressing) to the freshly grated root for several hours. This study aimed to determine effects of pressure and wetting on grated cassava. Six treatments were applied: confining pressure for 12 h, wetting for 4 h at 25 °C, 2 h at 25 °C, 2 h at 40 °C, and 2 h at 50 °C, or each of the above followed by pressure for 12 h. Treatments released cyanide from samples in the order: 2-h wet at 50 °C + pressing >4-h wet at 25 °C + pressing = 2-h wet at 40 °C + pressing >2-h wet at 25 °C + pressing = 4-h wet at 25 °C >12-h pressing. Wetting for 2 h at 50 °C followed by pressure for 12 h reduced cyanide levels by at least 20% more than that of any other treatment. The combination of moisture and pressure enhanced the contact time between linamarin and linamarase to increase the release of hydrogen cyanide.     

Improved enzymic assay for cyanogens in fresh and processed cassava

The assay for cassava cyanogens developed at the Natural Resources Institute has been modified to overcome some of the problems encountered when the assay is applied to cassava products. Inclusion of 25% ethanol in the extraction medium increased the volume of recovered extract from heat-processed cassava products, eliminated the need for centrifugation and did not interfere with any aspect of the assay. Greater cyanohydrin recovery was noted and the calculation for cyanogen contents was changed to take into account the total extract volume. The separate assay of the three cyanogens (glucosides, cyanohydrins and free cyanide) was achieved by buffering aliquots of the extract followed by appropriate treatment. The importance of assaying for free cyanide (HCN) at pH 4 was demonstrated. Above this pH, cyanohydrin degradation also produces free cyanide, giving rise to misleading values. The efficiency of the extraction medium in recovering added linamarin and cyanohydrin from cassava foods was determined. Recoveries of cyanohydrin were improved using the ethanol/acid medium. The stability of the cyanogens in the ethanol/acid extraction medium was tested at ambient and refrigeration temperatures. Over a two-month period, refrigerated extracts showed acceptable variation as compared with normal variation within the assay (5%) for total and non-glycosidic cyanogens but the levels of free cyanide showed heavy losses (15–56% lost). Since the relative toxicities of the three cyanogens have yet to be ascertained, the relative amount of each cyanogen may be important when assessing the safety of cassava products.     

Short Duration Processing for High Quality Gari Production

High quality, cyanide-free gari was produced within 24 h by separating the process into distinct detoxification and flavour development phases. Grated cassava was rapidly detoxified by adding water (3:4 parts, v/w) and holding at 50°C for 6 h before dewatering in a screw press. Development of the characteristic gari flavour was initiated in the detoxified cassava mash by inoculating with detoxified, 3-day-fermented cassava liquor (2:5 parts, v/w) and holding the mixture at 50°C or ambient temperature for 12–18 h. Flavour development was then completed by dewatering the inoculated mash and toasting/garifying. Extensive sensory evaluation by a panel familiar with gari but which was otherwise untrained showed that there was no significant difference ( P> 0·01) between the product and traditionally processed gari in aroma, flavour and overall acceptability. The value of the rapid production of gari in providing this staple food for millions in developing countries, without exposing them to nutritional hazards from residual cyanide, is stressed.     

Simple method to reduce the cyanogen content of gari made from cassava

The lactic acid content of gari, was determined by pH titration to be about 10 g lactic acid/kg gari. As the size of the gari particles increased from 400 to >1000 μm their total cyanide content increased from 5 to 21 ppm. The acetone cyanohydrin content of gari samples exposed to ambient laboratory conditions of temperature and relative humidity gradually decreased by 58% in 38 weeks whereas linamarin in cassava flour is 100% stable for 6 months. Cyanogens could not be removed from wet gari samples at 30 or 50 °C and were only slowly removed by repeated heating at 100 °C and rewetting. By mixing equal weights of gari (pH 4.1) and low cyanide cassava flour (pH 6.5), wetting and heating at 50 °C for 5 h, the cyanide content was reduced by about one half. Wetting a gari/flour (1:1) sample with 1.5 times its weight of water and standing in a 1 cm thick layer in the sun for 4 h reduced the cyanide content by about one half. This treated mixture may be cooked to prepare stiff porridge with lowered cyanide content, and may help reduce tropical ataxic neuropathy in West Africa.     

Influence of holding temperature on the growth and survival of Salmonella spp. and Staphylococcus aureus and the production of staphylococcal enterotoxin in egg products

In this study, growth and survival of Salmonella spp. and Staphylococcus aureus in steamed egg and scrambled egg held at 5, 18, 22, 37, 55 and 60 degrees C are investigated. The production of staphylococcal enterotoxin in steamed egg is also examined. Results reveal that Salmonella spp. and Staph. aureus in the egg products multiply best at 37 degrees C, followed closely by 22 and 18 degrees C. Neither pathogen showed growth in the egg products held at 5 degrees C. Initial inoculation dose, holding temperature and holding time affected the population of both organisms found in the egg products. Staphylococcal enterotoxin A (SEA) and B (SEB) are detected only in the egg products held at 37 or 22 degrees C. After holding at 37 degrees C for 36 h, scrambled egg inoculated with ca. 5.0 log cfu/g Staph. aureus contains the highest levels of SEA (> 64 ng/g) and SEB (> 64 ng/g). Although Salmonella spp. and Staph. aureus grow better in steamed eggs than in scrambled eggs, production of staphylococcal enterotoxin, in general, was higher in scrambled eggs than in steamed eggs. On the other hand, a repaid destruction of the test organisms in steamed eggs held at 60 degrees C was observed. Holding the steamed eggs at 60 degrees C, Salmonella spp. and Staph. aureus with an initial population of ca. 5.9 and 5.6 log cfu/g, respectively, reduced to a non-detectable level in 1 h.     

The use of a starter culture in the fermentation of cassava for the production of "kivunde", a traditional Tanzanian food product

Three cassava fermentation methods (spontaneous fermentation, back-slopping and the use of starter culture) for the production of kivunde, executed in three trials at 30 degrees C, were compared in terms of cyanide level reduction, microbiology and product quality improvement. Among the isolates from spontaneously fermented cassava batches, four strains were selected on the basis of their enzymatic activities and acid production. All were identified as Lactobacillus plantarum and were used as starters in this study. Lowest residual cyanide levels were detected after 120 h fermentation time in samples fermented with the starter culture and were below the maximum value of 10 mg/kg recommended by the Codex/FAO for cassava flour. This finding seems to be related to the alpha-glucosidase activity of the inoculated strains of which API-zyme (Bio-Merieux) tests showed activities of between 20 and > or = 40 nmol/4 h. The total residual cyanide levels of the spontaneous and back-slopping fermentations at 96 h were respectively 43.5 and 47.7 mg/kg dry weight of cassava. Extension of the fermentation period to 5 days, lead to further substantial reduction in the residual cyanide level in both these processes, but not below the recommended maximum value as in the case of starter culture fermented products. The spontaneous and back-slopping fermented cassava showed signs of deterioration after 3 days of fermentation. There was a sharp drop of pH and an increase of titratable acidity for all three batches during the first 48 h followed by a slow rise of pH and drop in titratable acidity towards the end of fermentation. The samples fermented with the starter culture had a smooth texture and pleasant fruity aroma, as opposed to the course and dull appearance and more complex flavour of the samples of spontaneous and back-slopping batches. During fermentation with starter culture, Enterobacteriaceae and yeasts and moulds could not be isolated throughout the period of fermentation (detection limit: 10 colony forming units/g). The present findings indicate the suitability of these Lb. plantarum strains as starter cultures for cassava fermentation in the kivunde process. The paper highlights the potential for the improvement of a traditional African fermented food (kivunde) through the use of a starter culture.     

Mild methods of processing cassava leaves to remove cyanogens and conserve key nutrients

Current methods for processing cassava leaves to remove cyanogens involve pounding followed by boiling in water or boiling intact leaves for 30 min or longer. Boiling in water rapidly removes cyanogens but also breaks down vitamins, proteins and S-containing amino acids, which are necessary to detoxify ingested cyanide. Two methods have been developed to remove cyanogens whilst conserving these key nutrients present in cassava leaves. The first method involves pounding leaves in a pestle and mortar for a minimum of 10 min until the leaves are well macerated, followed by washing the pounded leaves twice in twice their weight of water at ambient temperature, which reduces the total cyanide remaining to 8%. Two further washes reduce the total cyanide to 3%. The second method is to immerse cassava leaves in ten times their weight of water at 50 ± 3 °C for 2 h followed by one change of water and further immersion for 2 h at 50 °C which reduces the total cyanide remaining to 7%.     

Effect of temperature and sanitizers on the survival of feline calicivirus, Escherichia coli, and F-specific coliphage MS2 on leafy salad vegetables

We conducted a series of experiments to compare the survival of Escherichia coli, feline calicivirus, and F-specific coliphage MS2 on lettuce and cabbage with and without disinfection. Inoculated produce was held at 4, 25, or 37 degrees C for 21 days or was treated with different concentrations of sodium bicarbonate, chlorine bleach, peroxyacetic acid, or hydrogen peroxide. Survival was measured by the decimal reduction value (time to 90% reduction in titer) and the change in log titers of the test organisms. A stronger correlation of survival measures was observed between feline calicivirus and MS2 than between E. coli and either of the viral agents at 25 and 37 degrees C. The maximum time to detection limit for MS2 at all temperatures was 9 days, whereas feline calicivirus was detected for a maximum of 14 days at 4 degrees C. In contrast, E. coli was detectable for 21 days at 4 and 25 degrees C and for 14 days at 37 degrees C. Significant increases in E. coli titer occurred within the first 5 days, but virus titers decreased steadily throughout the experiments. E. coli was also highly susceptible to all disinfectants except 1% sodium bicarbonate and 50 ppm chlorine bleach, whereas the viruses were resistant to all four disinfectants.     

In vitro binding of mutagenic pyrolyzates to lactic acid bacterial cells in human gastric juice

The binding of mutagenic pyrolyzates to freeze-dried cells of Streptococcus cremoris Z-25 was investigated in human gastric juice and compared with the ability of these pyrolyzates to bind in distilled water (pH 6.30). The pH of donated gastric juice ranged from 1.2 to 7.8. Binding that occurred in gastric juice was pH dependent, and binding was affected by NaCl, CaCl2, and MgCl2. Les sof Trp-P-2 was bound in gastric juice at low pH (1.2, 1.48, and 2.1) than at pH 4 to 8. The strain bound simultaneously Trp-P-1, Trp-P-2, and Glu-P-1. The maximum amounts of Trp-P-2 bound to S. cremoris Z-25 were approximately 47.50 micrograms/mg of cells. Freeze-dried cells treated at 120 degrees C for 15 min or 80 degrees C for 3 h showed increased binding of Trp-P-2. However, binding decreased 10% after heating at 120 degrees C for 15 min. Cells nonthermally killed by gastric juice (pH 1.5) had the same Trp-P-2 binding capacity as viable cells. Lactobacillus acidophilus IFO 13951 and Bifidobacterium bifidum IFO 14252 representation of the intestinal bacteria nonthermally killed by gastric juice also showed larger binding of Trp-P-2.     

Detoxification of cassava during fermentation with a mixed culture inoculum

The efficacy of a mixed culture inoculum in detoxifying intact cassava tuber and peel pieces was investigated. Fermented cassava tuber and peel pieces had more linamarase activity than the non-fermented control samples and this might have resulted partly from the release of endogenous linamarase from the retted tuber/peel pieces and partly due to the microbial linamarase. Approximately 24–26% of the total cyanide remained in the bound form in the fermented tuber while 67–79% existed as bound cyanide in the non-fermented controls. In cassava peels, only 15–33% of total cyanide remained in bound form after 72 h fermentation while 58–59% cyanide existed in bound form in the parallel non-fermented control peels. Free cyanide which could be easily eliminated through sun-drying was present at higher concentrations in the fermented tuber and peel compared with the non-fermented samples. The study showed that cassava tuber and peel could be extensively detoxified through fermentation with a mixed culture inoculum.     

Effect of modified atmosphere packaging on the shelf life of sliced wheat flour bread

The application of modified atmospheres packaging (MAP) of sliced bread with different aw, moisture content and pH values, with or without preservative added (calcium propionate) and at different storage temperatures, has been studied with the aim of establishing the effect of MAP on the shelf-life of the selected product. Four atmospheres were tested per batch: 100% N2, 20% CO2/80% N2, 50% CO2/50% N2 and a standard air control. In samples without added preservative in CO2:N2 (50:50), the increases in shelf life were 117% and 158% at 22-25 degrees C and 15-20 degrees C, respectively. In samples with added preservative in 100% N2, shelf life was increased by 116%. Samples with added preservative in 20% CO2:80% N2 increased shelf life by 150% and 131% at 22-25 degrees C and 15-20 degrees C, respectively. By increasing the CO2 concentration to 50%, the increases in shelf life of the samples with added preservative were 167% and 195% at 22-25 degrees C and 15-20 degrees C, respectively.     

Milk pH as a function of CO2 concentration, temperature, and pressure in a heat exchanger

Raw skim milk, with or without added CO2, was heated, held, and cooled in a small pilot-scale tubular heat exchanger (372 ml/min). The experiment was replicated twice, and, for each replication, milk was first carbonated at 0 to 1 degree C to contain 0 (control), 600, 1200, 1800, and 2400 ppm added CO2 using a continuous carbonation unit. After storage at 0 to 1 degree C, portions of milk at each CO2 concentration were heated to 40, 56, 72, and 80 degrees C, held at the desired temperature for 30 s (except 80 degrees C, holding 20 s) and cooled to 0 to 1 degree C. At each temperature, five pressures were applied: 69, 138, 207, 276, and 345 kPa. Pressure was controlled with a needle valve at the heat exchanger exit. Both the pressure gauge and pH probe were inline at the end of the holding section. Milk pH during heating depended on CO2 concentration, temperature, and pressure. During heating of milk without added CO2, pH decreased linearly as a function of increasing temperature but was independent of pressure. In general, the pH of milk with added CO2 decreased with increasing CO2 concentration and pressure. For milk with added CO2, at a fixed CO2 concentration, the effect of pressure on pH decrease was greater at a higher temperature. At a fixed temperature, the effect of pressure on pH decrease was greater for milk with a higher CO2 concentration. Thermal death of bacteria during pasteurization of milk without added CO2 is probably due not only to temperature but also to the decrease in pH that occurs during the process. Increasing milk CO2 concentration and pressure decreases the milk pH even further during heating and may further enhance the microbial killing power of pasteurization.     

Fate of Escherichia coli O157:H7 during composting of bovine manure in a laboratory-scale bioreactor

Inactivation profiles of Escherichia coli O157:H7 in inoculated bovine manure-based compost ingredients were determined by composting these ingredients in a bioreactor under controlled conditions. A 15-liter bioreactor was constructed to determine the fate of E. coli O157:H7 and changes in pH, moisture content, temperature, and aerobic mesophilic and thermophilic bacterial counts during composting. Fresh cow manure, wheat straw, cottonseed meal, and ammonium sulfate were combined to obtain a moisture content of ca. 60% and a carbon/nitrogen ratio of 29:1. The compost ingredients were held in the bioreactor at a constant external temperature of 21 or 50 degrees C. Self-heating of the ingredients due to microbial activity occurred during composting, with stratified temperatures occurring within the bioreactor. At an external temperature of 21 degrees C, self-heating occurred for 0 to 3 days, depending on the location within the bioreactor. E. coli O157:H7 populations increased by 1 to 2 log10 CFU/g during the initial 24 h of composting and decreased by ca. 3.5 log10 CFU/g near the bottom of the bioreactor and by ca. 2 log10 CFU/g near the middle and at the top during 36 days of composting. At an external temperature of 50 degrees C. E. coli O157:H7 was inactivated rapidly (by ca. 4.9 log10 CFU/g at the top of the bioreactor, by 4.0 log10 CFU/g near the middle, and by 5.9 log10 CFU/g near the bottom) within 24 h of composting. When inoculated at an initial level of ca. 10(7) CFU/g. E. coli O157:H7 survived for 7 days but not for 14 days at all three sampling locations, as indicated by either direct plating or enrichment culture. At the top of the bioreactor a relatively constant moisture content of 60% was maintained, whereas the moisture content near the bottom decreased steadily to 37 to 45% over 14 days of composting. The pH of the composting mixture decreased to ca. 6 within 1 to 3 days and subsequently increased to 8 to 9. Results obtained in this study indicate that large populations (10(4) to 10(7) CFU/g) of E coli O157:H7 survived for 36 days during composting in a bioreactor at an external temperature of 21 degrees C but were inactivated to undetectable levels after 7 to 14 days when the external temperature of the bioreactor was 50 degrees C. Hence, manure contaminated with large populations (e.g., 10(7) CFU/g) of E. coli O157:H7 should be composted for more than 1 week, and preferably for 2 weeks, when held at a minimum temperature of 50 degrees C.     

Fate of Staphylococcus aureus in whey, whey cream, and whey cream butter

Fresh Cheddar cheese whey was inoculated with ca. 10(6) Staphylococcus aureus/ml and held at 4, 25, and 37 degrees C for 48 h. Numbers of staphylococci decreased in whey at 25 and 37 degrees C and decreased or remained constant in whey at 4 degrees C. When Cheddar cheese whey was neutralized with sodium hydroxide before inoculation with ca. 10(2) or 10(6) S. aureus/ml, numbers of the bacterium increased at all incubation temperatures. Viability of S. aureus strains in whey butter made from inoculated whey cream (from Cheddar cheese whey) was determined. Whey cream was either neutralized to a titratable acidity of .15% or untreated before inoculation with ca. 10(4) S. aureus/ml. Butter churned from the whey cream was held at 4, 25, and 30 degrees C for up to 4 wk. Viability of S. aureus was enhanced in lightly salted (1%) whey cream butter and in butter made from neutralized whey cream. Strains of S. aureus did not survive in unsalted or in salted (1.5%) butter made from untreated whey cream.     

Water pressure effectively reduces Salmonella enterica serovar enteritidis on the surface of raw almonds

The effects of continuous high hydrostatic water pressure treatments (414 and 483 MPa with a holding time of 6 min) on the viability of two strains of Salmonella enterica serovar Enteritidis (PT 9c and PT 30) inoculated onto raw almonds were evaluated at 25 degrees C. The concentrations of both Salmonella Enteritidis isolates were reduced to undetectable levels when the almonds were directly suspended in water, pressurized at 414 MPa and 25 degrees C for 6 min, and then dried at 115 degrees C for 25 min. When the almonds were pressurized at 414 MPa and dried at 55 degrees C for 5 min, a more than 3.58-log reduction was achieved for both isolates. Increasing the drying temperature to 65 degrees C resulted in a more than 3.96-log reduction for both isolates. Increasing the water pressure to 483 MPa further decreased the Salmonella Enteritidis concentration on the surface of the raw almonds. When the almonds were treated at 414 MPa, the decimal reduction times were less than 35 s for both isolates. High hydrostatic water pressure treatment of certain dry foods appears to be feasible when the food is suspended directly in the pressurizing medium (water).     

Amylase activities and cyanide tolerance of five cassava tuber spoilage molds

Studies on the amylase activities and tolerance to cyanide by five spoilage molds of cassava tuber were carried out. None of the test fungi grew in 0.1 g/ml concentration of potassium cyanide while only Aspergillus aculeatus and A. niger grew in 0.05 g/ml. Except for B. theobromae, all the other four molds synthesised amylases on the 2nd day of incubation. Highest amylase activities by the molds were recorded between pH 6–7 and at 25°C. The molds degraded satisfactorily the raw starch and protein contents of the blended cassava tuber pulp. Total reducing sugars were detected in large quantities from the mold deteriorated cassava tuber.