THE NITRATE DETINNING REACTION IN MODEL SYSTEMS

SUMMARY– As part of a coordinated research program on internal can corrosion, the action of nitrates on tinplate was studied in model systems simulating foods of varying acidities. Detinning rates were measured in citrate buffered nitrate solutions ranging in pH from 3.0–7.0. At pH values less than about 5.2–5.5 the detinning is extremely rapid, with slower rates at higher pH values. Nitrate concentrations of 125 ppm in pH 4 buffers completely detinned cans in about 2 months at ambient temperatures. Ammonia is the principal nitrate reduction product in the pH range of acid products. Nitrous oxide is also produced and acts as an effective detinner at pH 4 and 5. Nitrogen may also be produced at pH 5.     

EFFECTS OF NITROGEN NUTRITION AND DAY TEMPERATURE ON COMPOSITION, COLOR AND NITRATE IN TOMATO FRUIT

The effects of nitrogen nutrition and day temperature on composition, color and nitrate in VF–145 tomatoes were investigated in growth chambers kept at 20, 25, 30 and 35°C respectively during the days for 14 hr, and at 20° C during the nights for 10 hr. Nitrogen fertilizer application was altered in half the pots in each chamber by supplying them with half-strength −N Hoagland's #1 solution during the fruit growth period. Tomatoes from fertilized plants (+N) were slightly higher in titratable acidity but lower in solids content than those from the −N plants. Fruits ripening at high day temperature were poor in color while those ripening at below 30°C were more attractive in color. The total, amino, ammonium and nitrate nitrogen contents of the tomato fruits were higher in the +N series than those of –N series. Tomatoes from plants receiving +N treatments contained more nitrate than those receiving −N treatments. Day temperature greatly affected the nitrate content in the tomatoes. In the +N series the nitrate content of the tomatoes decreased from 72.9 ppm to 0.37 ppm as the day temperature increased from 20: to 35°C. In the −N series, the nitrate content ranged from 0.35–1.15 ppm. Accumulation of nitrates in tomatoes appears to be related to the level of nitrate in the nutrient solution and the day temperature. Low day temperature results in accumulation of nitrate because of the low nitrate reductase activity.     

Investigation of fish product–metal container interaction using scanning electron microscopy–X-ray microanalysis

Scanning electron microscopy (SEM) and X-ray microanalysis (EDS) were used to investigate metal can discoloration and lacquer adhesion failure in enameled food cans containing tuna in vegetable oil and octopus in brine, respectively. Black and brown spots on the internal surface of the can body were caused by the formation of FeS and SnS, respectively. The source of metal can discoloration was traced to inadequate lacquering of the tin plated steel, exposing both tin and iron to sulfur containing amino acids originating from the tuna product. Enamel adhesion failure in canned octopus was also traced to local defects in the lacquer coating enabling both NaCl and citric acid contained in the brine to cause enamel blisters on the can body leading to lacquer peeling and in turn to local detinning and steel corrosion. The first defect known as “sulfide staining” is harmless to human health and does not usually affect the product. The second defect may cause extensive detinning and steel corrosion possibly affecting the safety of the canned product. This postulation is supported by iron and tin concentrations both in the product and liquid medium carried out by atomic absorption spectroscopy.     

Nitrogen form affects yield and taste of tomatoes

Different nitrogen forms in organic or mineral fertilizers affect yield, quality and taste of tomatoes. Tomato plants were grown in a greenhouse for 10 weeks and fertilized with two different organic fertilizers (manure or grass and clover mulch) or with three different mineral nutrient solutions (NO₃^?:NH₄⁺) ratios 4:1 or 1:4). In an attempt to mimic the nutrient supply of the organic production systems, mineral fertilizers with ammonium as the dominating N‐source were combined with two chloride levels. Total nitrogen supply was 650 mg N plant^?1 week^?1 in all treatments. There was no difference in the yield of red tomatoes between the treatments (mean 1.95 kg FW plant^?1). However, the yield of green tomatoes at the final harvest was significantly higher in the mineral nutrient treatments (mean 1.37 kg FW plant^?1) compared with the organic treatments (mean 0.88 kg FW plant^?1). Plant biomass was higher for the mineral nutrient treatments (mean 1.05 kg FW plant^?1) compared with the organic treatments (0.89 kg and 0.72 kg FW plant^?1 in the manure and the grass and clover mulch treatments, respectively). Significantly higher scores were achieved for sweetness, acidity, flavour and acceptance for the tomatoes grown with the organic or the ammonium‐dominated treatments compared with the tomatoes grown with the nitrate dominated nutrient solution. It is suggested that ammonium is an equivalent nitrogen source for tomato plants compared with nitrate and that, when tomato plants are supplied with reduced nitrogen forms such as ammonium or organic nitrogen, an improved tomato fruit taste can be observed. Copyright © 2005 Society of Chemical Industry     

马口铁包装水果罐头中锡的浓度变化和形态分布研究

目的 研究马口铁包装水果罐头中锡的浓度变化和形态分布。方法 采用电感耦合等离子体串联质谱法(inductively coupled plasma tandem mass spectrometry, ICP-MS/MS)测定马口铁包装水果罐头的锡含量,并分析锡浓度随储存时间、加热次数的变化特点;采用高效液相色谱电感耦合等离子体串联质谱法(high performance liquid chromatography-inductively coupled plasma tandem mass spectrometry, HPLC-ICP-MS/MS)测定并分析罐头中锡的形态分布。结果 镀锡马口铁包装水果罐头中锡含量在生产日期3个月内为27.17~183.81 mg/kg,生产日期12个月时为54.56~265.44 mg/kg,锡浓度随储存时间、加热次数而明显增加,溶出锡为无机形态,以二价锡Sn[II]为主,未检测到锡的有机形态。结论 马口铁包装水果罐头中锡随储存时间和加热次数而大量增加,但都以无机锡的形态存在,因吸收利用率低,毒性较低;尽量选择靠近生产日期的产品,且不要罐内加热食用。     

Lead, chromium, tin, iron and cadmium in foods in welded cans

The levels of lead, chromium, tin, iron and cadmium in fruit and vegetables in welded tinplate cans were determined by atomic absorption spectrophotometry. The levels found were compared with those in foods in soldered tinplate cans and fresh foods. The results show that the lead levels in foods in welded cans were much lower than those in similar foods in soldered cans. Foods in unlacquered welded cans contain much more lead, chromium and tin than foods in lacquered welded cans. The cadmium and iron levels in canned fruit and vegetables in welded cans were similar to those found in the corresponding fresh foods.     

Tin and Iron Content of Canned and Bottled Foods

The tin and iron content of 14 different types of canned foods and of 5 different types of bottled foods were determined. No tin was detected in most bottled foods, but tin was detected in all canned foods. Storage of foods on the shelf for 4 months or in open cans in the refrigerator for 1 wk resulted in increased amounts of tin and iron in some of the canned foods. Those foods which were packed in totally lacquered cans accumulated little tin or iron during storage; those foods which were packed in unlacquered or partially lacquered cans generally accumulated significant amounts of iron and tin during storage. The tin content of the canned foods was not statistically correlated to the pH of the foods.     

The effect of sulphur-containing fungicides on the corrosion of plain cans of fruit

The addition of 2–5 ppm of TMTDS (tetramethylthiuramdisulphide) or ziram markedly decreased the shelf life of canned pears, but 1 ppm of these materials had little effect. The addition of trace levels of sulphur or captan to canned pears appeared to increase the shelf life; addition of sodium sulphide appeared to have a negligible effect on shelf life. The shelf life of canned peaches, apricots, pineapple, apples, and citrate solution was also decreased by the addition of 5 ppm TMTDS or ziram. TMTDS and ziram caused pitting of the base steel of the tinplate with little attack on the tin coating. Pitting was not seen in cans containing added sulphur, sulphide, or captan and the rate of corrosion of the tin coating was less than in cans containing no added chemicals. Formation of passive films and reduction of the hydrogen overpotential were considered to be important factors influencing corrosion of cans containing the added agricultural chemicals.     

Analysis of fruit juice by atomic absorption spectrophotometry. I. The determination of iron and tin in canned juice

Atomic absorption spectrophotometry has been used to compare the concentrations of iron and tin in canned fruit juice with those in juice not stored in cans. No significant difference was found in the level of iron, but the amount of tin was considerably higher in canned samples. The determination is rapid, and no ashing procedure is required.     

High Vacuum Flame Sterilized Fruits: Influence of Can Type on Storage Stability of Vacuum Packed Peach and Pear Slices

The feasibility of using enameled tin and tin-free steel (TFS) cans for processing oxygen sensitive fruits by high vacuum flame sterilization was evaluated. Through 18 months storage at ambient temperatures, the appearance and quality of the HVFS peaches and pears remained acceptable for all can types. Fruits packed into plain tin cans appeared brighter and tasted tangier than those packed into TFS or inside-enameled tin cans. Texture, pH and titratable acidity of fruit were not measurably affected by variation in can types. Mechanical deaeration followed by flame sterilization, produced a product with quality comparable to that achieved in flame deaerated packs.     

Detinning Factors from the Shoots of Bamboo Leleba oldhami

Concentrated fresh juice of bamboo shoots was filtered through a Sephadex G-75 column under aseptic and anaerobic conditions. The detinning activity in the filtrate was assayed by an oxygen monitor in the presence of tin powder. A large amount of peptides with molecular weights about 1300, some nucleotides and p-hydroxybenzaldehyde were identified as the detinning substances. Twenty peptides were isolated by means of cation and anion exchange chromatography. The primary structures of these peptides were elucidated by the subtractive Edman degradation, in which a high performance liquid chromatograph was used for amino acid and sugar analysis.     

Corrosion behaviour of tinplate cans in contact with tomato purée and protective (inhibiting) substances

The dissolution of iron and tin from tinplate cans filled with tomato purée (pH 4.34) and dioctyl sebacate oil (DOS), essential onion oil (EOO) or potassium nitrate was studied using atomic absorption spectroscopy (AAS), while nitrate was determined using high-performance liquid chromatography (HPLC). The maximum values found in cans were up to 284 mg kg^?1 for tin and 513 mg kg^?1 for iron at elevated storage temperature. Results indicated that the addition of EOO to tomato purée prevents the corrosion process in the case of tin, where concentrations were lowered from 223 to 28 mg kg^?1 for cans with DOS oil and EOO at 20°C, respectively (inhibition rate of 87%). On the other hand, the presence of EOO enhanced the corrosion process for iron increasing the concentration from 15 to 46 mg kg^?1 during 7 months of storage, although this value did not exceed maximum permitted value (50 mg kg^?1). In cans with tomato purée and potassium nitrate, dissolution of tin started after 30 (36°C) and 60 (20°C) days of storage as a consequence of nitrate action, which act as a corrosion accelerator. Since the addition of EOO improves the taste of canned tomato purée, its potential use as a corrosion inhibitor would be of interest.     

Effect of Ammonium Nitrate and Low-Level Foliar Treatments of Simazine on Some Chemical Components and Protein Quality of'Pinkeye Purple Hull' Pea Seeds

Southern pea seeds were grown 2 yrs with treatments of ammonium nitrate fertilizer 0, 30, and 60 kg/ha and simazine 0, 2,000, and 4,000 ppm applied as a foliar spray. Yield, proximate analysis, amino acid content, and protein quality were determined. No differences were found in yield, crude fat, and crude fiber. Ash, protein, and several of the amino acids increased with the 30 and 60 kg/ha nitrogen fertilizer treatments. Treatments with simazine had no effect on the essential amino acid content. In the Southern pea seeds, protein quality was decreased by the treatments with nitrogen fertilizer, simazine, and combinations of these treatments.     

CHEMICAL COMPOSITION OF TOMATOES AS AFFECTED BY MATURITY AND FERTIGATION PRACTICES

The objective of this study was to determine the effect of various fertigation practices and maturity stages on tomato fruit composition. Soluble solids, reducing sugar content, and sugar/acid ratio of tomatoes increased with maturity. Fertigation treatments had less of an effect on the chemical composition of the fruit than the stage of maturity. Mineral (P, K, Ca, Mg) levels of tomato fruits in fertigated treatments were higher than in the control plot treatments receiving no supplemental water during the production season. Ascorbic acid content in whole mature-red fresh tomatoes was 13.24% and 25.71% higher than that in mature-pink and mature-light pink tomatoes, respectively. The locule section contained more ascorbic acid than other parts of the fruit at maturity. Intensive mineral fertigation and harvesting at the ripe stage contributes toward higher nutritional quality in fresh tomatoes.     

FREEZE PEELING IMPROVES QUALITY OF TOMATOES

SUMMARY— A process of peeling tomatoes using low temperature-short time freezing was perfected. Liquid nitrogen (BP-196°C was used as the refrigerant for freezing the skin and only a thin layer of cells just beneath the skin. The fruit was immediately thawed, after which the skin was quickly and easily removed from the fruit. Liquid nitrogen-peeled samples were evaluated for loss of peel and trim, as well as lycopene and carotene in the peeling process and these losses compared with samples peeled in boiling water. The losses in peel and trim were reduced by approximately 50%, and significantly less lycopene was lost by nitrogen peeling. The peel and trim of fall tomatoes had a greater amount of lycopene and carotene than spring tomatoes. The nitrogen-peeled samples were canned without additives, with sodium chloride and with calcium chloride added and compared with samples peeled with boiling water. There was a decrease in the percentage of broken fruit in the canned tomatoes peeled by liquid nitrogen. Titratable acidity and °Brix were higher and pH was lower in these samples. Color of the homogenized canned product was not statistically different; however, the nitrogen-peeled tomatoes had a better visual color. The calcium chloride added-nitrogen-peeled samples possessed a higher degree of firmness than the comparably treated boiling-water-peeled samples, indicating that the nitrogen-peeled tomatoes utilized the added calcium to a greater extent in firming.     

Iron and tin content of canned fruit juices and nectars

A survey of the iron and tin content of twelve different types of canned fruit juices and nectars revealed that, of the 122 cans examined, 23 (or 18·9%) contianed iron in excess of 15 mg kg^?1 and 16 (or 13·1%) contained tin in excess of 250 mg kg^?1. Apple juice and tomato juice were found to contain particularly high levels of iron, the maximum level recorded being 42·6 mg kg^?1. Mango juice and orange juice exhibited significant non-compliance with recommended Codex tolerance limits for tin. Statistical analysis showed that, at the 5% probability level, the mean iron contents of products packed in completely unlacquered and end-lacquered cans were not significantly different from each other, but were significantly lower than the mean iron content of products packed in fully lacquered cans. The mean tin content fell in the order unlacquered > end-lacquered > fully lacquered cans.     

Crop thinning (hand versus mechanical), grape maturity and anthocyanin concentration: outcomes from irrigated Cabernet Sauvignon (Vitis vinifera L.) in a warm climate

Crop thinning subsequent to fruit set can help regulate yield and improve fruit composition at harvest. Accordingly, an experiment was established in two vineyards (Site 1 Riverland District of South Australia; Site 2 Sunraysia District of Victoria) to investigate effects of crop removal after fruit set (when berries were pea size) using a machine harvester. Specific zones of the canopy were targeted for thinning to remove a predetermined percentage of the fruit and avoid over‐thinning. Cropping responses to mechanical thinning were compared with control (un‐thinned) vines, and with hand thinned vines (where fruit was removed from a similar portion of the canopy as for mechanical thinning). In a fourth treatment, bunches damaged by mechanical thinning were removed by hand. Inclusion of hand thinning treatments enabled us to distinguish between the potential benefits of reduced yield and the potential damage caused by the mechanical harvester to foliage and/or remaining fruit. Both the mechanical and the hand thinning treatments reduced bunch number as well as yield by a similar amount (approximately 24% on Site 1 and approximately 45% on Site 2) and advanced fruit maturity (soluble solids accumulation at harvest), relative to un‐thinned controls, by approximately 1.6 % and 1.7% respectively. Soluble solids accumulated at a similar rate for all treatments at sites, despite differences in yield, implying that the impact of thinning treatments originated prior to veraison. Berry weight was increased by hand thinning at Site1, and by all thinning treatments at Site 2. Anthocyanin concentration (berry fresh weight basis) was higher in fruit from the mechanically thinned vines compared to controls (un‐thinned). Mechanical thinning successfully reduced crop level to the target yield, and improved fruit quality. Mechanical thinning, via modified use of a machine harvester, thus offers some potential to regulate yield over large and minimally pruned vineyards, in a timely and cost‐effective fashion.     

Effect of simulated reclamation on nitrification of ammonium sulphate applied to saline and alkali soils from West Pakistan

Nitrification of ammonium sulphate (100 ppm nitrogen) applied to alkali, saline-alkali, highly saline and moderately saline soils was studied during 12 weeks of incubation before and after simulated reclamation treatments, in which water plus calcium sulphate was used for the two alkali soils and water alone for the two saline soils. Before reclamation there were considerable differences in the pattern of nitrification due to soil type; this was accounted for mainly by the high loss of ammonia by volatilisation (61-96% of the ammonium-nitrogen applied) from the two alkali soils; from 0 to 80% of the nitrogen applied was recovered as nitrate after 12 weeks of incubation. After reclamation the pattern of nitrification was similar for all soils; 58-68% of the applied nitrogen was recovered as nitrate after 12 weeks. The moderately saline soil was the only one to show a lower recovery of applied nitrogen as nitrate after than before reclamation. There was some nitrite accumulation early in incubation in all the original soils, but after reclamation only in the two alkali soils.     

The decrease in pesticides in fruit and vegetables during commercial processing

Samples of tomatoes, peppers, asparagus, spinach and peaches were exposed to three insecticides (acephate, chlorpyrifos and cypermethrin), three ethylenebisdithiocarbamate fungicides (mancozeb, maneb, propineb) and the tetramethyldithiocarbamate fungicide thiram to study the effect of commercial processing on the residues. In most cases, canning operations led to a gradual decrease in residue levels in the finished products, particularly through washing, blanching, peeling and cooking processes. The results indicated that washing plus blanching led to more than 50% loss in pesticide residues, except for in peaches. Ethylenebisdithiocarbamates (EBDCs) were completely removed from tomatoes and spinach by washing followed by hot water blanching. The total amount of pesticide removed by all of the combined canning operations ranged from 90 to 100% in most products. Pepper retained 61% of chlorpyrifos but these residues disappeared during 3‐month storage of finished cans. Acephate showed a surprising tenacity in peaches, as 11% of the original residues were still present in 2‐year stored cans.     

Inactivation of Listeria innocua, Salmonella Typhimurium, and Escherichia coli O157:H7 on Surface and Stem Scar Areas of Tomatoes Using In-Package Ozonation

A novel in-package ozonation device was evaluated for its efficacy in inactivating three microorganisms (viz., Listeria innocua, attenuated Salmonella Typhimurium, and Escherichia coli O157:H7) on tomatoes and for its effect on fruit quality. The device produced ozone inside sealed film bags, reaching a concentration of 1,000 ppm within 1 min of activation. The three bacterial cultures were inoculated onto either the smooth surface or the stem scar areas of the tomatoes, which were then sealed in plastic film bags and subjected to in-package ozonation. L. innocua on tomatoes was reduced to nondetectable levels within 40 s of treatment on the tomato surface, with inactivation of ca. 4 log CFU per fruit on the stem scar area. An increase in treatment time did not result in a proportional increase in bacterial reduction. For E. coli O157:H7 and Salmonella, there was little difference (<1 log) in the effectiveness of the system when comparing surface and scar-inoculated bacteria. Both bacteria were typically reduced by 2 to 3 log CFU per fruit after 2- to 3-min treatments. No negative effects on fruit color or texture were observed during a 22-day posttreatment storage study of ozone-treated tomatoes. These results suggest that the three bacteria responded differently to ozonation and that in-package ozonation may provide an alternative to chemical sanitizers commonly used by the industry.