Evaluation of Vitamin D3 Content in Selected Dried, Canned and Smoked Fish

The aim of the current study was to shed light on vitamin D3 content in some fishery products that may help the consumers to meet their requirement of vitamin D. The selected products included dried shrimp and fish (sardines and mackerel), canned tuna, sardines, salmon, anchovies and smoked salmon and herring. Vitamin D3, moisture, fat content, antioxidant activity and pH values were estimated for these products, and the percent daily value of vitamin D was calculated. The results revealed that dried sardine showed the highest vitamin D content (48.86 μg/100g), followed by canned anchovy (15.22 μg/100g), then Smoked herring (12.12 μg/100 g). The lowest content of vitamin D was found in white tuna meat canned in water (6.81 μg/100g) and pink salmon in water (3.58 μg/100g). The percent daily value of vitamin D in the selected fishery products extended between 325.73% for dried sardine and 33.87% for salmon canned in water per serving. In conclusion, the daily requirement of vitamin D could be covered by consuming 30.70g of dried sardine, 98.55g of canned anchovy or 123.76g of herrings. The present results may assist the consumers to get their daily value of vitamin D3 from some natural sources. However, studies are needed to renew the use of dried fish or shrimp in future dishes as a high source of vitamin D.


Introduction
Vitamin D deficiency is still a major public health problem worldwide in all age groups, even in countries with low latitude, where the UV radiation was enough to prevent this deficiency, and in industrialized countries, where vitamin D fortification has been implemented traditional industries and citizens exercised on the Blue Nile and White Niles. Completely dried-shrimp or powdered-shrimps have been widely accepted, as they can be used as spices in soups or foods for flavor and protein source [9,10]. The lack of studies about vitamin D content in the processed fish may play a role in decreasing the intake of vitamin D. Therefore, the aim of this study was to determine the vitamin D content of certain fishery products and explain the percent daily value for each product in order to assist consumers in obtaining their requirement of vitamin D through an array of choices.

Materials and Methods
Fourteen processed fish products were purchased from local markets in Al-Ahsa, Saudi Arabia. Table 1 shows the purchased samples, which included dried, smoked, and canned fish.

Chemical analysis
Moisture and fat content were determined using standard protocol [11]. The data were expressed on the wet and dry weight basis.

The pH measurement
After homogenizing one gram of sample with 10 ml of distilled water, the pH was measured at 17 °C using a digital pH meter (Model 320, Mettler-Toledo Ltd., Essex, UK).

Antioxidant activity (AA)
The free radical scavenging capacity of sample extract against DPPH (1,1-diphenyl-2 picryl hydrazyl) was estimated [12]. One milliliter of extract was mixed with one milliliter of a 0.4 mmol in methanolic solution containing DPPH. The mixture was left in the dark for 30 minutes before the absorbance at 516 nm was measured (UV-VIS spectrophotometer, Apel, Japan).

Determination of vitamin D3
Vitamin D as Cholecalciferol was determined according to the method described by [13].
Preparation of Samples: Weight equivalent to 40,00000 IU vitamin D3 of samples were dissolved in 25 ml of solution mixture (chloroform and methanol in a 1:9 ratio). At 264 nm, its absorbance was measured.
Preparation of vitamin D3 (cholecalciferol): Accurately 25 mg vitamin D3 working standard was dissolved in 25 ml of solution mixture (chloroform and methanol in a 1:9 ratio). The absorbance was recorded at 264 nm.

Calculation of percent daily value of vitamin D
The potential contribution of fish products to daily value of foods (V%) was calculated using recommended daily allowance of 15 µg/day for all life-stage groups except those aged 71 and up [14]. Hundred grams of samples has been used as serving size of meats to calculate the DV% [15].

Statistical analysis
Gen-Stat Release 7.2 (PC/Window XP) program was used to define the significance of differences between samples at significance levels of P ≤ 0.05.

Physicochemical properties
Fourteen Fisher products were examined for physicochemical properties ( Table 2). The moisture and fat content of the samples varied greatly depending on the process used; the highest moisture content was found in samples canned in water, ranging from 76.91% in salmon to 72.44% in white tuna. Dried samples, on the other hand, had the lowest moisture content (10.19-39.81% in shrimp and mackerel, respectively). Sardine and tuna canned in oil were found to have a high fat content, with values ranging from 14.55% in tuna/olive oil to 19.39% in sardine/soy oil. The low fat content was observed in canned fish filled with water or tomato paste (2.45% in average). The pH ranged from 5.65 in canned anchovy to 7.1 in dried shrimp. Antioxidant activity showed a higher percent in sardine canned in soy oil (90.58%), followed by dried mackerel (82.74%) and dried sardines (81.51%).

Vitamin D content of selected products
The results presented in Table 3 provide details about the vitamin D content of the selected products as well as their contribution to the daily value of vitamin D. Vitamin D content in products ranged from 31.15g/100g

Correlations between vitamin D content and some physicochemical properties
The data analysis (   Table 3: Vitamin D content and DV% of selected processed fish products.

Samples Vitamin D (µg/100gWB) Percent daily value (%DV)
The amount to get % DV may be in arrears to the exchange of fish oil by vegetable oil during the canning process, that resulted in vitamin D dilution or leaching in these products. Moreover, the higher temperature used in canning in oil process (121 °C) rather than other processing such as smoking and drying, may play a significant role in vitamin D alteration in canned products.
The positive relationship between vitamin D content and antioxidant activity could be related to the antioxidant activity of vitamin D itself as suggested by previous study that vitamin D3 has a role in regulation of oxidative metabolism [23,24]. Our findings demonstrated that all selected products in this study are a high source of vitamin D with more than 20% of DV. The percent daily value of vitamin D in the selected fishery products extended between 325.73% in dried samples and 33.87% in salmon canned in water (per serving). Finally, about 30.70g of dried sardine, 98.55g of canned anchovy or 123.76g of herrings could present the daily value of vitamin D. The present study may help in presenting different choices for vitamin D that help the consumers to get their recommended daily allowance of vitamin D.

Conclusion
The findings concluded that the selected fish products, specially the dried ones, could ensure the daily value of vitamin D. More studies are needed to incorporate dried fish and shrimp into new dishes, or as spices in sea food soups, or to revitalize old traditional meals that use dried fish to minimize vitamin D deficiency.

Funding
This work is not financially supported.

Contribution
All of the authors contributed equally to this work, and they all read and approved the published version of the manuscript. correlation between vitamin D content and both pH (R = 0.3534) and antioxidant activity (R = 0.2815), while significant inverse correlations between vitamin D and moisture content (R = -0.8441) as well as fat content (R = -0.5575) were detected.

Discussion
Fish has been recognized as the best natural source of vitamin D3. Some dried, canned and smoked fish products examined for their vitamin D content and other physicochemical properties in this study. Due to the variation in fish type and the process used, the content of moisture, fat, and vitamin D in the samples varied greatly between samples. Owing to the dehydration and concentration of the nutrients, dried samples had the lowest moisture content but the highest fat. Sardine and tuna canned in oil were found to have a high fat content compared to canned fish filled with brine or tomato paste, which may be attributed to the incorporation of vegetable oil during the canning process. These findings of fat content in fish canned in oil was closed to previous findings [17,18], but higher than the results obtained by other [19]. The pH values between samples varied narrowly and were closed to the pH recorded in the earlier study with average of 6.2 [20]. The antioxidant activity of vitamin D and the antioxidants added during processing may be responsible for the significant increase in antioxidant activity in canned samples compared to other samples as stated previously [21]. As shown in the results of vitamin D estimation, dried fish and shrimp are excellent sources of vitamin D in the diet. The high vitamin D content of dried fish and shrimp may be due to the stability of vitamin D in drying conditions such as the presence of oxygen, long time, and low temperature, which are the main factors influencing the nutritional value of fish in addition to the low moisture content [8]. The decrease in vitamin D content of canned products could be attributed to the fact that canned foods are subjected to high thermal treatment during cooking and sterilization [22]. Furthermore, the addition of vegetable oil to canned fish may alter the content of vitamin D in this product and this alteration may depend on the fish type or the vitamin D content of vegetable oil used. Moreover, leaching of nutrients, in particular vitamin D, into cooking liquors is becoming more widely recognized as a major source of nutrient loss [8]. Unpredictably, the inverse correlation between vitamin D content and fat content found in this study