Abstract: The presence of heavy metals in frozen and canned commercial pork products obtained from retail outlets of Chennai city was determined, by atomic absorption spectrophotometry using dry ashing method. The samples had cadmium from 0.038 to 0.545 mg kg-1, chromium up to 2.244 mg kg-1, copper up to 2.847 mg kg-1, lead up to 6.290 mg kg-1 and zinc from 6.927 to 144.575 mg kg-1. Generally, heavily spiced products had higher levels of heavy metals. Levels of cadmium exceeded the Maximum Permissible Level (MPL) of 0.1 mg kg-1 in 95.83% of the samples as stipulated by Food and Agriculture Organization (0.1 mg kg-1), whereas no samples had copper content exceeding MPL (20 ppm) specified by Meat Food Products Order (MFPO), 25.0% of the samples had lead content exceeding the limit specified by MFPO (2.5 ppm) and 20.83% of the samples had zinc values exceeding the MPL of MFPO (50ppm). The results of this study demonstrate the need for good manufacturing practices (GMP`s) and HACCP to control these heavy metals in pork products.
INTRODUCTION
The risk associated with the exposure to heavy metals present in food products had aroused widespread concern in human health. Improvements in the food production and processing technology had increased the chances of contamination of food with various environmental pollutants, especially heavy metals. Ingestion of these contaminants by animals causes deposition of residues in meat. Due to the grazing of cattle on the contaminated soil, higher level of trace metals have been recorded in beef and mutton (Sabir et al., 2003). Presence of substantiate levels of toxic metals lead and cadmium in meat products have been recorded (González-Weller et al., 2006).
Over the past few decades, both developed and developing countries have experienced equally life and food style changes that have led to an increased demand for processed foods. Some heavy metals get deposited in food as residues during processing (WHO, 1987). When the residue levels go beyond the prescribed standards, they cause deleterious effects on human health, especially when consumed continuously. Hence, food safety can be ensured only by keeping the contamination as low as possible. In the recent times, consumption of pork products has been on the increase in Chennai city. This study was undertaken to determine the levels of heavy metals like cadmium, chromium, copper, lead and zinc in commercially available pork products and to compare the levels of these chemical residues with the specified standards.
MATERIALS AND METHODS
Forty eight samples of commercial pork products, viz., bacon, ham, sausage, salami and canned luncheon meat were obtained from the retail outlets in Chennai city and were examined for the presence of residues of heavy metals.
The samples were allowed to thaw for 16 h at 2°C and 200 g from each product were homogenised in a domestic mixer grinder. Sub-samples were taken out of these representative samples for determining heavy metals. An accurately weighed sample of about five grams of each sample was taken in vycor crucibles to which 2.5 mL of 50% w/v of magnesium nitrate hexahydrate was added. They were then dried for 6 h at 70-75°C and ashed in muffle furnace at 500°C for 1 to 2 h. The ash was again kept in muffle furnace at 500°C after wetting with concentrated nitric acid. The wetting procedure was repeated until the ash turned white in colour. The ash was then made up to 10 mL with triple glass distilled water after adding 1 mL of concentrated nitric acid and two 1 mL portions of dilute (1+3) nitric acid. The stock standard solutions and the working solutions were prepared as per the Cook Book (1982) Perkin-Elmer by utilizing the triple glass distilled water.
Atomic Absorption Spectrophotometer (AAS)-(Perkin Elmer model 2380) was used for estimating the metals. The concentration of the metal to be determined was provided between 0.1 to 0.5 absorbance units. According to the absorbance, the concentration was calibrated and the concentration was measured directly when the sample was within the linear working range. Presence of heavy metals was estimated using respective hollow cathode lamps to give lamp energy. The fuel oxidant was obtained by acetylene - air mixture which provided the flame for determination of metals. For all elements, the fuel/oxidant ratio was used as prescribed. The standard conditions and instructions detailed in analytical methods were followed.
The mean and the standard error were calculated as per the methods outlined by Snedecor and Cochran (1994) and compared with the available standards of maximum permissible limits by using single sample t-test by keeping the corresponding available standards as test value.
RESULTS AND DISCUSSION
Cadmium
The canned luncheon meat had the highest mean cadmium level, followed
by salami (0.296 mg kg-1) and sausage (0.238 mg kg-1).
The observed mean values of the individual products and overall mean of
all the products were significantly (p<0.05) higher than the MPL of
0.1 mg kg-1 (Table 1). In earlier studies
on various ready to eat cured meat products and muscle of food animals,
the cadmium levels were recorded in the range of 0.01 to 0.42 mg kg-1
(Kirkpatrick and Coffin, 1973) and 0.1 to 0.2 mg kg-1 (Coleman
et al., 1992), respectively. Contamination of meat products with
cadmium might occur in three ways, one from animals grazing on lands spread
with sewage sludge or phosphate fertilizers and another from animals grazing
on lands contaminated with industrial cadmium effluent (Yost, 1984; Koh
and Judson, 1986). The cadmium-contaminated mineral components
of commercial feeds and phosphate fertilizers (Linden et al., 2001)
were found to have strong correlation to concentrations in animal tissues
(Sharma et al., 1982). Cadmium from the soil could reach man through
vegetables, milk and meat (Stenstrom and Lonsjo, 1974). The main cause
of the Itai-Itai disease in Japan was the high concentrations of
cadmium in rice over long time as the soil in the valley was polluted
with sludge from a nearby mine. Secondary cadmium contamination of food
occurs as a result of its use in food processing (Zurera-Cosano, 1993).
Muller et al. (1996) reported that sausages had higher
cadmium content than the raw meat. The addition of spices during production
of sausages might be the main reason since spices could contain cadmium
concentrations up to 200 ng g-1 (Muller et al., 1992).
| Table 1: | Mean cadmium levels (mg kg-1) in Pork products
|
| n: No. of observations, SE: Standard Error | |
In this study, sausages and salami were highly spiced and comminuted products and they were found highly contaminated with cadmium. The fact that the luncheon meat had the highest concentration of cadmium among the products analyzed could be due to the processes involved during canning. The lower levels in bacon and ham could be due to the non-addition of spice mix and absence of communication in the product making. In this study, 95.83% of the samples exceeded 0.1mg kg-1 and 64.58% of samples exceeded 0.2 mg kg-1 of cadmium.
A hypothesis has also been put forward that cadmium could play a role in the development of cardiovascular diseases, particularly hypertension. Chronic exposure to cadmium could cause nephrotoxicity in humans, mainly due to abnormalities of tubular re-absorption (Nordberg, 1999). The biological half life of cadmium in the human kidney is long and has been estimated to be 10 to 30 years (Fox, 1987). Due to the slow excretion of the metal, the concentration in the kidney would gradually increase, even at very low concentrations in the food. It has been calculated that with a daily cadmium intake of 250-350 μg, a man might reach hazardous concentrations at the age of 50, with a risk of renal damage (Frieberg et al., 1974) In practice, cadmium levels found in food are normally below 0.1 mg kg-1 (FAO, 1980). The MPL prescribed in Australia for cadmium in muscle of livestock and poultry is 0.2 ppm (Coleman et al., 1992).
Chromium
The highest level of chromium (2.244 mg kg-1) was observed
in pork salami samples (Table 2). Bacon (0.68 mg kg-1),
salami (0.65 mg kg-1) and canned products (0.60 mg kg-1)
(luncheon meat) had higher chromium content than ham and sausage. Statistical
analysis revealed that the observed mean values of the individual products
and overall mean were significantly (p<0.05) higher than the MPL (0.05
mg kg-1) (Codex Alimentarius Commission, 1994). Maggi et
al. (1979) observed ten times higher chromium content in
canned products, compared to fresh beef probably due to release of the
metal from tins, while Marriot et al. (1982) observed
it to be below the detectable level in beef and pork frankfurters. But
in the present study the chromium content of sausages was up to 1.309
mg kg-1. As the ingested chromium is found mainly in liver,
kidneys and blood (Khitrov and Jaeger, 1995), the use of organ meat might
increase the chromium content. Tinggi et al. (1997) reported a
chromium content of 12 to 50 ng kg-1 in various meat products.
Khitrov and Jaeger (1995) documented that dermatosis, nephritis and liver
damage were the results of absorption of large quantities of chromium
over a long period. Kidney damage has also been observed in animal studies.
Chromium is a potent allergen and is a common skin sensitizer in allergic
eczema (Anderson, 1993). Although no MPL has been prescribed by Meat Food
Products Order (MFPO, 1973) for chromium in food products, the MPL in
mineral water has been specified as 0.05 mg L-1 by the (Codex Alimentarius Commission, 1994). In the present study the levels of chromium
estimated in the pork products are higher when compared to this level.
Owing to the toxic effect of this metal, strict regulations and screening
methods have to be implemented.
| Table 2: | Mean chromium levels (mg kg-1) in Pork products |
| n: No. of observations, BDL: Below Detectable Level | |
| Table 3: | Mean copper levels (mg kg-1) in pork products
|
| n: No. of observations, BDL: Below Detectable Level | |
Copper
Out of 48 samples, 45 samples had copper levels of below 2 mg kg-1
(Table 3), which was in accordance with the results
shown by Larkin et al. (1954), Rajmane et al. (1986) and
Brito et al. (1990). Statistical analysis implied that the observed
mean values of all the products were significantly lower (p<0.01) than
the MPL (MFPO, 1973) (20 ppm). In this study, the mean copper level was
the highest in ham followed by salami and bacon. Rajmane et al. (1986)
reported a higher concentration in salami samples (13.8 ppm) and
in ready-to-eat meat products and concluded that the main source of contamination
of foods with copper was copperware used to store or cook foods. Copper,
although not essentially toxic, could cause public health hazards in high
concentrations (Brito et al., 1990). In humans, 10-30 mg of orally
ingested copper from foods stored in copper vessels might cause intestinal
discomfort, dizziness and headaches, while excess accumulation of copper
in liver may result in hepatitis or cirrhosis and in a hemolytic crisis
similar to that seen in acute copper poisoning (Johnson, 1993). However
none of the samples in this study had copper content exceeding the MPL
(20 ppm) prescribed by MFPO (1973) in meat products.
Lead
The present study revealed lead levels being significantly (p>0.05)
closer to the MPL (MFPO, 1973) (2.5 mg kg-1) in ham, bacon
and salami, while sausages had significantly lower (p<0.05) levels
(Table 4). Luncheon meat had significantly higher (p>0.05)
levels of lead. The lead levels determined in this study were in accordance
with that of Rajmane et al. (1986) and Brito et al. (1990).
Among the samples studied, 41.67% samples had lead levels between 2.0-7.0
mg kg-1 which was similar to the results of Rajmane et al. (1986). The canned meat products had higher lead contents and the highest
lead content of 6.29 mg kg-1 was recorded in canned luncheon
pork. Similar findings in canned meat products were reported by Dabeka
and McKenzie (1995) and Muller and Anke (1995). The higher lead content
of the canned products might be due to the release of a substantial quantity
of lead, probably from the soldering line into the food (Maggi et al.,
1979; Larkin et al., 1954). Other than the canned meat
products, some of the other products also had higher lead content (2.500-5.000
mg kg-1), probably due to the presence of higher levels of
lead in the raw meat itself. Lead concentrations in tissues were found
to be higher in samples obtained from sheep raised in former mining areas
than in other samples (Schroeder, 1991). Oskarsson et al. (1992)
reported a high lead concentration (500 μg kg-1) in beef
after accidental exposure to lead. Vreman et al. (1988) found higher
concentrations of lead in the muscle of dairy cows raised on pasture than
in the muscle of dairy cows kept indoors. Humphreys (1991) reviewed the
effects of lead in animals and reported that due to its slow rate of elimination,
harmful levels of lead could accumulate in tissues after prolonged exposure
to even low quantities of lead. The most hazardous heavy metal monitored
on the swine farms in the district of Hodonín, Czech Republic in
1994-1999 was lead, the major source of which being paint coats containing
more than 0.6 g lead kg-1, mineral components of commercial
feeds, scrap lead batteries put away in barns and lead-coated guide bars
of electric lines (Ulrich et al., 2001). Secondary contamination
of food may occur due to processing and addition of spices. Except bacon
and ham, pepper which contains higher levels of lead (>2.5 ppm) (Larkin
et al., 1954) had been added invariably to almost all types of
meat products. Muller and Anke (1995) reported that the lead content of
sausage was higher than that of the meat used for its production, presumably
due to the spices used in sausage production. Bolger et al. (1996)
reported that infants and children are more susceptible to lead toxicity
than adults because they consume more food per unit of body mass, with
the lead getting absorbed more readily. The half life of lead in blood,
soft tissues, spongy bones (pelvis, ribs and skull) and cortical bones
(mid tibia and mid femur) is 35, 40 days, 3-5 and 30 years, respectively
(Pueschel et al., 1996). Tuormaa (1995) reported that an excessive
lead accumulation in children is known to cause hyperactivity, reduced
intelligence and antisocial behaviour. In adults it is associated with
heart disease, cancer and infertility. Lead could cause adverse effects
on the renal and nervous systems and cross the placental barrier, having
potential toxic effects on the fetus (Tuormaa, 1995; WHO, 2003). In the
present study, 25.0% of the samples had lead content exceeding the MPL.
| Table 4: | Mean lead levels (mg kg-1) in Pork products |
| n: No. of observations, BDL: Below Detectable Level | |
| Table 5: | Mean zinc levels (mg kg-1) in Pork products |
| n = No. of observations | |
Zinc
MFPO (1973) has specified the MPL of zinc in meat product as 50ppm.
In the present study, 79.17% of samples had zinc levels below 50 mg kg-1
which is in accordance with the results of Larkin et al. (1954),
Osis et al. (1972), Brito et al. (1990) and Simakova
et al. (1993) who determined the zinc levels in the meat
products. Similar results were also reported in fresh meat samples of
various food animals (Coleman et al., 1992; Jayasekara et al.,
1992). Only 14.58% of samples had values between 50-100 mg kg-1.
Langlands et al. (1987) observed a zinc level upto 70
and 57 mg kg-1 in muscle of cattle and sheep, respectively.
Simakova et al. (1993) reported a zinc level upto 83.2 mg kg-1
in beef and 5.4 mg kg-1 in pork (Table 5).
Food and diets high in protein were found to have high zinc (Osis et
al., 1972). The major source of readily bioavailable zinc in
the US diet is beef (Welsh and Marston, 1982). The second most important
source is pork (Pekarinen, 1973). Leita et al. (1991) reported
that zinc content of sheep grazing in zinc smelter areas generally had
higher zinc content in muscles of and the samples of pasture had 200 ng
g-1 of zinc. Larkin et al. (1954) reported relatively
higher levels of zinc in a number of spices and curry powders, which might
also increase the zinc content of the food products. Ellis et al. (1984) found that storage of wet, damp brewer’s grains, in used galvanized
feed bins even for 24 h could result in zinc levels over 100 ppm in the
material near the galvanized surface of the container. Except salami,
all other observed pork products had the mean zinc levels significantly
(p>0.05) approaching the MPL. In salami, the observed mean level of
the zinc was significantly (p<0.05) lower than the MPL. The abnormally
high levels of zinc found in a few samples might be due to the use of
galvanized equipment or vessels. Diets deficient of copper and zinc may
cause clinical manifestations whereas increased levels could accumulate
in target organs such as liver and kidneys of living organism resulting
in toxic effects (Cherian and Nordberg, 1983). Klevay (1977) hypothesized
that high dietary zinc to copper ratio might be a contributing factor
in the development of coronary heart disease. In this study, 20.83% of
the samples had zinc values exceeding MPL.
CONCLUSIONS
The present study depicts the scenario of the heavy metal levels in selected pork products. The levels of cadmium and lead, which are hazardous metals, exceeded the MPLs in 95.83 and 25.00% of the samples, respectively. Even though, there is no prescribed limit for chromium in the food products, about 95.83% samples exceeded the limit prescribed for drinking water. About 79.17% of samples had zinc levels below 50 mg kg-1 (MPL). None of the samples had copper content exceeding the MPL (20 ppm). Hence, the results of this study demonstrate the need for a systematic control of toxic heavy metals in pork food products. Steps have to be taken to control the environmental contamination, as a primary and effective food safety measure. There is also an absolute need for good manufacturing practices and Hazard Analysis and Critical Control Points to monitor and curtail the contaminants in meat and meat products.