Effect of Storage on Iodine Content in salts sold in Port Harcourt Metropolis, Nigeria

Essien*E.B. and Oshionya N.V.

Department of Biochemistry, University of Port Harcourt, Choba, Rivers State, Nigeria

ABSTRACT:

Iodine content of six brands of salt samples (two imported and four locally produced), stored in their original salt packages (plastic container with lid and polythene plastic salt packet) commonly sold in Port Harcourt metropolis, were estimated at intervals of fourteen days, for two months. Of the two imported samples (A and B), Sample A had iodine content of 10.10mg/kg while sample B had no iodine. All of the iodine in sample A was lost after 2 weeks of storage. Iodine content of the locally produced Salt samples (D-F) ranged from 26.50±0.61mg/kg (Sample E) to 59.75±0.61mg/kg (Sample F).Iodine content of Sample E was significantly (P<0.05) below the minimum legal requirement of 50 mg/kg in contrast to the declaration on the packet. Highest percentage loss of iodine, accounting for 18.50% was observed in Sample E (from 26.50±0.61mg/kg to 21.15±2.21mg/kg) after four weeks of storage. Other samples recorded losses ranging from 5.27% to 8.29% after storage. Even though there were slight decreases in iodine content in most of the salt brands, the contents were still within the recommended levels of 30mg/kg at retail level.

KEYWORDS: Iodine content, Salt, Storage

INTRODUCTION:

Iodine is an essential trace element required for human growth and development, necessary for the production of thyroxine- a hormone which regulates a variety of physiological functions and critical for optimal development of the brain (Rosenfeld, 2000; WHO, 2003).

Iodine deficiency is the single most common cause of preventable mental retardation and brain damage in the world. It is a major health problem in many parts of the world. IDD causes goitres and decreases the production of hormones (T4 and T3) vital to growth and development. In pregnant women, IDD causes mental retardation or cretinism with possible physical disability in children, and can also lead to miscarriage or still birth (WHO, 2003; Anderson et al., 2005). Children with IDD can grow up stunted, mentally retarded and incapable of fast learning. Children in iodine depleted populations can have an Intelligent Quotient (IQ) of 10-15 percentage points lower than those of iodine- replete populations. The reduction in IQ is irreversible (Vitti et al., 2001; Babikir, 2004).

The use of iodized edible salt to reduce the risks associated with iodine deficiency has been incorporated in many nutrition programs and legislation worldwide (WHO/NUT, 1994; WHO, 2003). Globally, 70% of households in countries with iodine deficiency disorders (IDD) now consume iodized salt (UNICEF, 2007).

Salt Iodization was established by law in 1993 in Nigeria and made mandatory. The law (Nigeria Industrial Standard, NIS, 168:1992) stipulates that all food grade salt be fortified at 50ppm at ports and factories, 30ppm at retail.

The Law is enforced through inspection and testing by the Regulatory Agencies, namely, the Standard Organization of Nigeria (SON) that sets the standards, and the National Agency for Food & Drug Administration and Control (NAFDAC) that enforces the standards (Egbuta and Onyezili, 2002; Akunyili, 2005).

Studies have shown, however, that the iodine content of iodized salt decreases continuously during the whole process from the salt plant to the consumer, depending on manufacturing methods, packaging materials, and storage time. The shortest half-life was found to be 12 weeks (Mannar and Dunn, 1995). Data regarding losses in iodized salt during storage at house hold level are not available. Therefore the aim of this research was to evaluate iodine retention in salts during storage at house hold level.

MATERIALS AND METHODS:

Two brands of imported (samples A and B) and five brands of salt (samples C-F) produced in Nigeria were purchased both from the super markets and open air-markets in Port Harcourt Metropolis. All the brands were well packed in plastic (1kg) bags. The salt samples were left intact in their original retail packages.

Chemical analysis
The amount of potassium iodate in the samples was determined by titrimetric method according to Demeyer et al., 1999. Analysis was carried out at the time of purchase and every fourteen days for eight weeks (2 months).

Data were analyzed using the SPSS. Significant difference between the data was determined at P<0.05 using Duncan multiple range test.

RESULTS AND DISCUSSION:

Results in Table 1 show the iodine content of the imported and locally produced salts at purchase time. Salt sample A had iodine content of 10.10±0.01mg/kg, while sample B had no iodine. The locally produced samples had iodine contents ranging from 26.50±0.61mg/kg in sample E to 59.75±0.01mg/kg in sample D. The labels on the locally produced salts sold in the open-air markets clearly indicated that the salt brands were iodized while the labels on the imported salts did not indicate whether they were iodized or not (Table 1). That there was no iodine in Sample B confirms reports by (Wright, 2002) that contrary to popular belief, the vast majority of salt in the U.S. is not iodized. Most of the locally produced salt samples had iodine contents above values declared on their labels (50mg/kg). It is probable that the manufacturers deliberately put in excess iodate to compensate for the loss due to storage. However, Studies have shown the possibilities of adverse effects of salt consumption above tolerable upper intake level of iodine in individuals living in iodine sufficient area (UNU, 1996; Laurberg et al., 2001). Salt sample E had significantly lower (P<0.05) content than the label declaration (50mg/kg). This may be attributed to exposure of the salts sold in open-air markets to direct sunlight and air before purchase. Iodine loss in iodized salt is reported to be greater for salt stored at a temperature of 37 ºC and humidities of 76% than in that stored at 20-25 ºC (Wang et al., 1999).

Table 1: Iodine contents of imported and locally produced salt samples at purchase time.

Sample description	Production Date	Expiry Date	Iodine content (mg/kg)	Label declaration (mg/kg)
A	January 2007	January 2009	10.10±0.01	None
B	July 2007	July 2009	nil	None
C	April 2007	March 2009	58.70±0.50	50
D	January 2007	January 2009	59.75±0.61	50
E	July 2007	July 2009	26.50±0.61	50
F	January 2007	January 2009	58.70±0.50	50

Table 2: Iodine contents of salts during storage (56 days)

Sample Description	Iodine content during storage (mg/kg)
Sample Description	Purchase day	14 days	28 days	42 days	56 days
A	10.10±0.01	Nil	Nil	Nil	Nil
B	nil	Nil	Nil	Nil	Nil
C	58.70±0.50	58.70±0.52	58.15±2.21	56.60±0.50	54.50±0.50
D	59.75±0.61	59.75±0.63	59.26±2.22	58.15±2.21	56.60±0.50
E	26.50±0.61	26.50±0.65	24.85±0.61	22.75±0.50	21.15±2.21
F	58.70±0.50	58.70±0.53	57.65±0.62	56.60±0.50	53.45±0.61

Values represent means ±SEM of triplicate analysis

Table 3: Percentage loss of Iodine during storage of salt samples

Sample description	Percentage loss of Iodine content during storage (%)
Sample description	14 days	28 days	42 days	56 days
A	Nil	Nil	Nil	Nil
B	Nil	Nil	Nil	Nil
C	Nil	0.94	3.58	7.16
D	Nil	0.84	2.68	5.27
E	Nil	4.24	12.33	18.50
F	Nil	1.79	3.58	8.94

Tables 2 and 3 show the iodine content of the salt samples and percentage losses during storage for 56 days (2 months). There was no loss of iodine in the locally produced samples after Storage for 14 days. The imported salt sample (sample B) lost all its iodine at the 14th day. There was slight insignificant losses of iodine at 28 days ranging from 0.94% in sample C to 4.24% in sample F. Loss of iodine in Sample C was however significant when compared to the other samples. At 42 days, sample C had iodine content of 56.60±0.50mg/kg when compared with an initial iodine content of 58.70±0.52 (mg/kg). This amounted to a 3.58% loss. Sample D, E, and F had significant reductions in their iodine contents ranging from 22.75±0.50mg/kg (Sample E) to 58.15±2.21mg/kg (sample D) resulting to 2.68-12.33% loss. Loss of iodine on the 56^thday was significant (P<0.05) compared to the first day with sample E recording the highest percentage loss (18.50%). Except for sample E, all the locally produced salt samples still had iodine contents significantly above the NAFDAC recommended range of 30mg/kg at the retail level. This could be due to the effectiveness of the packaging material used for the salts- low-density polyethylene (LDPE) bags. It has been reported that solid low density polyethylene provided an excellent moisture barrier and thus maintained the total water content of the bags approximately constant, near the level at time of packaging such that iodine losses could be significantly reduced in the range of 10-15% for up to six months (Diosday et al., 1998).

CONCLUSION:

Strict and periodic monitoring by NAFDAC to make salt producers adhere to the set national standards is required, taking into account expected losses and local salt consumption. Monitoring should be at the factory level as well as the retail level. Monitoring for compliance is very important, since excessive levels could cause adverse effects and inadequate levels would be ineffective.

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Received on 30.01.2011

Modified on 21.03.2011

Accepted on 12.04.2011

Research J. Science and Tech. 3(3): May-June. 2011: 158-160