CHANGES IN LEAD CONCENTRATION OF FOODS STORED IN THEIR OPENED CANS

A study was made of the effect on the concentration of lead in canned fruits and juices when these food products are stored in their original containers after opening. Samples stored in a refrigerator were analyzed for lead upon initial opening, 2 days after opening, and 5 days after opening. Products in nonlacquered cans showed significant increases in lead concentration with time. The increase of lead in the food product could have an effect on estimates of average dietary intakes of lead if this practice is found to be widespread.     

MULTIELEMENT ANALYSIS OF FOODS STORED IN THEIR OPENED CANS1

A multielement analysis of canned foods was performed on foods stored in their opened containers. Canned fruits and fruit juices were sampled upon initial opening as well as two and five days after opening. After mineralization, the samples were analyzed for 25 elements using an inductively coupled argon plasma. The following elements were quantitated: Al, Ca, Cu, Fe, Mg, Mn, Ni, P, Sn, Ti, and Zn. The concentration of Fe and Sn increased between successive sampling days. These increases did not exceed permissible limits of Sn in canned foods and the Fe concentrations may be of nutritional interest. A decrease in the concentration of P between successive sampling days was associated with insoluble material formation. Scanning electron microscope micrographs coupled with X-ray fluorescence analysis of the can interior surfaces were used to characterize the corrosion of the interior surface of the cans.     

Lead content in grapefruit juice and its uptake upon storage in open containers

The lead contents of 52 samples of grapefruit juice, 14 packaged in glass, eight in waxed paperboard, and 30 in tin-coated carbon steel containers, were determined. Only those juices packaged in metal cans contained measurable amounts of lead, (< 1–27 μg litre-¹) averaging 7-7 μg litre-¹. Leaching studies were carried out on juices stored, under refrigeration, in opened containers for up to 30 days. The lead content increased considerably with time in juices stored in tin-coated cans. For example, after 6 days of storage the lead contents of these juices ranged from 3 to 90 μg litre-¹, and averaged 30 μg litre-¹. The lead content did not increase in juices that were stored in glass, paperboard or polyethylene containers. The source of lead in the cans was traced to lead impurities in the tin coating. Higher lead impurities in the tin coating produced higher lead contents in the juice. The implications of these findings are discussed.     

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.     

Lead and tin in canned foods: results of the UK survey 1983-1987.

Concentrations of tin and lead in canned foods have been monitored since 1983 to determine the effects of recent changes in can-making technology. In the sample studied the proportion of foods contained in non-soldered as opposed to soldered cans has risen consistently during the survey and now accounts for 83% of all samples (excluding sardines). Foods contained in non-soldered cans have lower lead concentrations than those contained in soldered cans and this changeover is likely to result in a decrease in dietary lead intakes in the UK.     

Migration of bisphenol A from can coatings—effects of damage, storage conditions and heating

Bisphenol A (BPA) is an important monomer used in the manufacture of epoxy resins for internal food can linings. Experiments were conducted to investigate the effects of different storage conditions and can damage on the migration of BPA to foods. These experiments were conducted in a systematic fashion by filling empty epoxyphenolic coated cans with four foods: soup, minced beef, evaporated milk and carrots and a food simulant (10% ethanol). Filled cans of each food type or simulant were then sealed and processed using appropriate conditions, before storage at three different temperatures: 5°C, 20°C and 40°C. For each of the storage regimes, 50% of the cans were dented to establish if this would lead to increased BPA migration. Cans were removed from these stocks at intervals of 1, 3 and 9 months storage at 5°C and 20°C or 10 days, 1 and 3 months at 40°C. Some initial problems of heterogeneity between samples was overcome by determining the amount of BPA in food as well as in the can lining. It was found that 80-100% of the total BPA present in the coating had migrated to foods directly after can processing by pilot plant filling with food or simulant, sealing and sterilization. This level was not changed by extended storage (up to 9 months) or can damage, indicating most migration was occurring during the can processing step. There was no noticeable difference, in this respect, between the different foods or the food simulant. Analysis of control samples (foods fortified with ∼0.1 mg kg^-1 BPA and contained in Schott bottles) showed that BPA was stable under both processing and storage. Experiments were also conducted to investigate the potential effects, on the migration of BPA from can coatings, of cooking or heating foods in the can prior to consumption. Food cans were purchased and the food either cooked or heated in the can. BPA was analysed prior to and after the heating/cooking process. It was concluded from the results that there were no appreciable differences in the BPA level before and after cooking or heating.     

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.     

Stability of enterocin AS-48 in fruit and vegetable juices

Enterocin AS-48 is a candidate bacteriocin for food biopreservation. Before addressing application of AS-48 to vegetable-based foods, the interaction between AS-48 and vegetable food components and the stability of AS-48 were studied. Enterocin AS-48 had variable interactions with fruit and vegetable juices, with complete, partial, or negligible loss of activity. For some juices, loss of activity was ameliorated by increasing the bacteriocin concentration, diluting the juice, or applying a heat pretreatment. In juices obtained from cabbage, cauliflower, lettuce, green beans, celery, and avocado, AS-48 was very stable for the first 24 to 48 h of storage under refrigeration, and decay of activity was markedly influenced by storage temperature. In fresh-made fruit juices (orange, apple, grapefruit, pear, pineapple, and kiwi) and juice mixtures, AS-48 was very stable for at least 15 days at 4 degrees C, and bacteriocin activity was still detectable after 30 days of storage. Gradual and variable loss of activity occurred in juices stored at 15 and 28 degrees C; inactivation was faster at higher temperatures. In commercial fruit juices (orange, apple, peach, and pineapple) stored at 4 degrees C, the bacteriocin was completely stable for up to 120 days, and over 60% of initial activity was still present in juices stored at 15 degrees C for the same period. Commercial fruit juices stored at 28 degrees C for 120 days retained between 31.5% (apple) and 67.71% (peach) of their initial bacteriocin activity. Solutions of AS-48 in sterile distilled water were stable (120 days at 4 to 28 degrees C). Limited loss of activity was observed after mixing AS-48 with some food-grade dyes and thickening agents. Enterocin AS-48 added to lettuce juice incubated at 15 degrees C reduced viable counts of Listeria monocytogenes CECT 4032 and Bacillus cereus LWL1 to below detection limits and markedly reduced viable counts of Staphylococcus aureus CECT 976.     

果蔬汁等液态食品之冻结点的经验计算

冻结点是果蔬汁等液态食品冷冻加工与保藏中的重要参数，冻结点和冻结点的下降与果蔬汁等液态食品的组成分及浓度有关。本文介绍了几种通过计算冻结点下降值求得冻结点的经验公式。     

Lead and cadmium levels in commercial infant foods and dietary intake by infants 0-1 year old

Lead and cadmium levels were determined in 131 infant foods. Mean lead and cadmium levels were 19.3 and 3.3 ng/g for meats, 8.4 and 4.1 ng/g for vegetables, 14.9 and 0.58 ng/g for fruits and desserts, 9.6 and 0.53 ng/g for juices and drinks, and 32.8 and 33.6 ng/g for dry infant cereals. These data, combined with those from other recent surveys, yielded average dietary (food and water) intakes of lead and cadmium by infants 0-1 year old of 2.4 and 0.37 microgram/kg/day, respectively. Lead intakes were most strongly influenced by storage of infant formulas in lead-soldered cans. For infants 0-1 month old, they ranged from 0.5 microgram/kg/day when human or cow milk was fed to infants to 5.3 micrograms/kg/day (exceeding the FAO/WHO provisional tolerable daily intake, PTWI, of lead by children of 3.5 micrograms/kg) when ready-to-use formula stored in lead-soldered cans was fed. Cadmium intakes were most strongly affected by soya based formulas, and ranged, for 0-1 months olds, from 0.16 microgram/kg/day for infants fed human or cow milk to 0.50 microgram/kg/day for infants fed soya-based concentrated liquid formula. Cadmium intakes were all below the FAO/WHO PTDI of cadmium by adults of 0.96-1.2 micrograms/kg.     

The Impact of Nonthermal Technologies on the Microbiological Quality of Juices: A Review

Fruit and vegetable juices are rich sources of nutrients that support microbiological growth and ultimately undergo rapid deterioration of safety and quality. The loss of nutritional quality of juices due to intensive thermal processing is a major problem encountered during the treatment of commercially preserved liquid foods. Conventional thermal processing technologies inactivate microorganisms and enzymes and extend the shelf life of foods but exert negative effects on nutritional and organoleptic properties of juices, for example, a loss of vitamins, of a desirable flavor, and of bioactive compounds and development of different sensory profiles as a result of heating. Nonthermal technologies including ultrasonication, a pulsed electric field, high‐pressure processing, irradiation, and their combinations are suitable alternatives for achieving the same preservation effect without the adverse effects of heat on the quality of juices and meet consumer demand for clean‐label, safe, and wholesome products without compromising their nutritional properties.     

Effect of refrigerated storage on vitamin C and antioxidant activity of orange juice processed by high-pressure or pulsed electric fields with regard to low pasteurization

A better knowledge of the effect of refrigerated storage on the nutritional and antioxidant characteristics of foods processed by emerging technologies with regard to thermal traditional technology is necessary. Thus, freshly squeezed orange juice was processed by high-pressure (HP) (400 MPa/40 °C/1 min), pulsed electric fields (PEF) (35 kV/cm/750 μs) and low pasteurization (LPT) (70 °C/30 s). The stability of vitamin C and antioxidant activity was studied just after treatment and during 40 days of refrigerated storage at 4 °C. The determination of total vitamin C (ascorbic acid plus dehydroascorbic acid) was achieved by HPLC whereas the antioxidant activity was assessed by the measurement of the DPPH• radical scavenging. Just after treatment, all treated orange juices showed a decrease lower than 8% in vitamin C content compared with the untreated one. At the end of refrigerated storage, HP and LPT juices showed similar vitamin C losses (14 and 18%, respectively) in relation to untreated juice, although HP juices maintained better the vitamin C content during more days than LPT juices. Regarding antioxidant activity, after 40 days at 4 °C, differences among treated juices were no significant in terms of antiradical efficiency (AE=1/EC₅₀T_EC50). HP and PEF may be technologies as effective as LPT to retain antioxidant characteristics of orange juice during refrigerated storage.     

Freeze concentration of fruit juices

Concentration of aqueous foods such as fruit juices, milk, beer, wine, coffee, and tea, is a major unit operation in the food industry. Technically feasible processes that are commercially available for the concentration of liquid foods include evaporation, freeze concentration, reverse osmosis, and ultrafiltration. Evaporation is considered to be the most economical and most widely used method of concentration. However, it is not suited for food products with very delicate flavors. Commercial processes for the concentration of such products by membrane separation techniques are not yet available. As compared to the conventional evaporation processes, concentration by freezing is potentially a superior and economic process for aroma-rich liquid foods. In the past, the process, however, was seldom used because of the investment cost and the considerable loss of concentrate in the withdrawn ice, and hence, the quality. Recent technological developments have minimized these two drawbacks associated with the earlier freeze concentration processes. In the coming decade, freeze concentration is seen as a potentially attractive method for the concentration of aroma-rich liquid foods, including fruit juices, coffee, tea, and selected alcoholic beverages. In this article, several aspects of the theoretical considerations behind freeze concentration of fruit juices, the development of new and cheaper designs, and commercially available freeze concentration processes are reviewed. The economics of the process and its application to several other areas of the food industry are also discussed.     

Benzol in Lebensmitteln – ein Überblick

Benzene is an environmental contaminant and humans are mainly exposed by ambient air, but benzene may also occur in drinking water and foods. Benzene is carcinogenic to humans causing acute non-lymphocytic leukemia. In foods, critical benzene concentrations were detected in the past mainly in alcohol-free beverages, because benzene was formed from benzoic acid. For this reason, the soft-drink industry nowadays abstains from using this preservative, and our results show that benzene is not problematic anymore in this group of beverages (contents below the EU drinking water limit of 1 µg/L). During the monitoring of beverages, however, benzene was detected in carrot juices intended for babies and young children (average 2 µg/L). In this case, a heat-induced formation mechanism is predominant. Model experiments have proven that benzene may be formed by the thermally induced degradation of different precursors contained in carrots (e.g., carotene, phenylalanine, and flavour compounds). This mechanism also leads to benzene contamination in commercial carrot-containing baby menus (complimentary foods) as well as carrots in cans, while freshly pressed carrot juices and home prepared baby foods were found to be benzene-free. Significantly lower benzene concentrations were found in commercial baby menus sold in plastic containers compared to the conventionally used glass jars. Preliminary risk assessments have shown that even for babies the exposure from foods is below thresholds, above which a health risk would be assumed. For reasons of precautionary public health protection and the minimization principle for carcinogenic contaminants, the concentrations in carrot products should be reduced, especially as these products are intended for babies and children, the most sensitive consumer group. The focus should be set on improving the sterilization conditions.     

Storage Stability of Lactobacillus paracasei as Free Cells or Encapsulated in Alginate-Based Microcapsules in Low pH Fruit Juices

The main objective of this research effort was to study whether microencapsulation could be a viable alternative to obtain probiotic orange or peach juices. In order to be considered probiotic food, probiotic bacteria must be present in sufficient viable numbers to promote a benefit to the host. The survival and viability of Lactobacillus paracasei L26 in juices over 50?days of storage at 5°C was assessed, evaluating the potential use of encapsulated cells in alginate microcapsules. L. paracasei L26 demonstrated good viability in both orange and peach juices despite the low pH values of both juices. Microencapsulation in alginate, with or without double coating, revealed to be suitable to protect L. paracasei L26 since viable cells were approximately 9 log cfu/g after 50?days of storage at 5°C. In general, the probiotic fruit juices showed a decrease in pH during storage. Glucose and fructose contents as well as citric acid contents decreased during storage, whereas an increase in formic acid was observed. The outcome of this study points to L. paracasei L26 as having promising potential, especially in an encapsulated form, as functional supplements in fruit juices without dairy ingredients due to their tolerance in an acidic environment over 50?days of storage at 5°C. Further studies are warranted to prove the functionality of juices with encapsulated probiotic strains.     

Internal corrosion and shelf‐life of food cans and methods of evaluation

Internal corrosion in food cans is characterized by metallic dissolution which is an electrochemical reaction. In lacquered cans, corrosion may also cause disruption in the continuity of the lacquer film. These reactions may cause organoleptic changes in the product, loss of vacuum, swelling, and leaking in extreme cases. In some instances the metal dissolution (i.e., lead) may give rise to toxicological problems. Therefore, these phenomena are often the limiting factor in the shelf life of canned products. Changes in color, texture, and sensoric properties of the foods, which take place simultaneously, affect the aesthetic and nutritional value of the product and thus its shelf life. These changes are often related to interactions with the container. For example, tin dissolution prevents browning and loss of ascorbic acid. Shelf life of canned foods is governed by the quality of the raw materials, the processing technology, quality of the container and storage conditions which will be reviewed in this paper. Can manufacturing technologies, mechanisms of electrochemical corrosion, methods of their measurement and prediction of shelf life will be discussed.     

Detection of Adulterants and Contaminants in Liquid Foods—A Review

Milk and fruit juices have paramount importance in human diet. Increasing demand of these liquid foods has made them vulnerable to economic adulteration during processing and in supply chain. Adulterants are difficult to detect by consumers and thus necessitating the requirement of rapid, accurate and sensitive detection. The potential adulterants in milk and fruit juices and their limits set by different regulatory bodies have been briefly described in this review. Potential advantages and limitations of various techniques such as physicochemical methods, chromatography, immunoassays, molecular, electrical, spectroscopy with chemometrics, electronic nose, and biosensors have been described. Spectroscopy in combination with chemometrics has shown potential for rapid, precise, and sensitive detection of potential adulterants in these liquid foods.     

COLOR OF PROCESSED SWEET POTATOES: EFFECTS OF CAN TYPE

Sweet potatoes packed in four types of enamel-lined cans were darker in color and less attractive than those packed in tin-coated cans. The differences in color among can types was more pronounced after opening the canned product and exposure to air for an hour. The tin content of the product from the tin-coated cans was much greater than that from the enamel-lined cans. The brighter color of the product from the tin-coated cans is assumed to result from the substitution of tin for iron or other metals in the complex formed in the pheno-lase reactions.     

Apple pomace liquefaction with pectinases and cellulases:analytical data of the corresponding juices

Apple juices were produced by way of a two-stage process consisting of traditional enzyme treatment of the mash with pectinases for the premium juices and pomace liquefaction with different pectinases and cellulases for the extraction juices. Premium and extraction juices were analysed separately. Calculated to an equal juice strength of 12° Brix, there was an increase of D-galacturonic acid and cellubiose in the extraction juices. Released galacturonic acid from cell wall material was found at levels ranging from 107 mg/l to 1239 mg/l. This was an essential contribution to the total titrable acid of the extraction juices. The sum of phenolic substances determined by high performance liquid chromatography was significantly higher in all the extraction juices than in the corresponding premium juices. Among the phenolics, the dihydrochalcone phloretin 2′-glucoside (92–110 mg/l) showed an increase of 4 to 5 times the concentration in the respective premium juices. Quercetin derivatives were mainly present in the extraction juices; here the values were between 32 mg/l and 38 mg/l. Under the influence of strong pectolytic or cellulolytic enzyme activities, oligo- and polysaccharides are released from the apple cell wall material, resulting in colloid concentrations of up to 15 g/l in the extraction juices. High concentrations of polyphenols and pectic polysaccharides can lead to technological problems. However, pomace liquefaction may also turn out to be suitable for obtaining value-added foods. In respect to nutritional aspects, enzymatic treatment of pomace offers the opportunity of releasing apple polyphenols and polysaccharides contained in the pomace to a greater extent and obtaining them preparatively. Received: 2 December 1999     

Some factors affecting the formation of furan in heated foods

Levels of furan in various foods were measured before and after heating under heating and laboratory conditions. The effect of contact with can coatings, sealing gaskets and the epoxidized oils used in gasket manufacture on furan formation was studied. The objective was to identify factors affecting furan formation. Furan present in heat-processed food samples persisted during cooking. Furan was shown to form in foods on heating, although it did not accumulate to a significant degree on heating in an open vessel. There were no interactions between foods and cans, can coatings or gaskets that had a significant influence on furan formation. Furan accumulated particularly in heat-processed canned and jarred foods because they are sealed containers that receive a considerable thermal load. Heating epoxidized oils used in sealing gaskets formed furan. At the levels used in gaskets, however, epoxidized oils should not affect the formation of furan in foods.