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.
Vitamin D, Fish, Daily value, Processed fish
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 [1]. The dietary intakes of vitamin D have been estimated to be low ranged between 3 to 7 μg/day, depending on diet, age, sex and fortification practices [2]. Fish are considered as nutritionally valuable part of the human diet, mostly due to the content of long chain polyunsaturated n-3 fatty acids. Furthermore, fish is also an excellent source of vitamin D3 especially oily fish including salmon and mackerel [3,4]. In animal products including fish, vitamin D3 is found together with its metabolite 25(OH)-D3. This metabolite is biologically active and its bioactivity is higher than vitamin D3 [5]. Cholecalciferol (D3) intervention was more efficacious than ergocalciferol (D2) in improving serum levels of total 25(OH)D and 25(OH)D3 irrespective of the participant demographics, dosage and vehicle of supplementation [6]. Vitamin D3 content of some fish products ranged between about 2 and 196 μg/kg. Large variations were found between different fish species and also between the same species from different locations. The variations in vitamin D content between the same species of fish looked not correlated to the weight, age, or sex of fish but depends on the vitamin d content in fish food and feed. Contrary to general belief, no significant correlation between vitamin D and fat content was reported [7]. Generally, fish processing methods, high and low temperature treatments, could be including, chilling, freezing, canning, smoking, drying, salting, frying and fermenting, sun-drying, grilling and frying, and various combinations of these, to give the fish product a form which is attractive to consumers and prolong storage life [8]. Dried fish from low-cost 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.
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.
Table 1: List of selected processed fish products collected from local markets. View Table 1
Moisture and fat content were determined using standard protocol [11]. The data were expressed on the wet and dry weight basis.
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).
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).
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.
Vitamin D (μg/100g) = (Sample Absorbance/standard Absorbance)*(Standard Weight/sample weight)*(Standard Dilution/Sample Dilution)*Standard potency*Average Weight
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].
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.
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%).
Table 2: Some physicochemical analysis of selected processed fish products. View Table 2
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 in dried mackerel to 48.86g/100g in dried sardine. Which is approximately 325.73 and 207.67% of the recommended dietary allowance of 15 μg, respectively [16]. Anchovies and sardines canned in soy oil (100g) were found to contain 101.47 and 61.47% of the RDA, respectively. Smoked herring and smoked salmon satisfy 80.8 and 60.47% of the RDA, respectively. The vitamin D content of canned tuna in oil was found to be significantly higher than that of canned tuna in water. Sardine canned in oil, rather than dried sardine, is a good source of vitamin D with 9.22 μg/100g and covers 61.47% of the recommended dietary allowance.
Table 3: Vitamin D content and DV% of selected processed fish products. View Table 3
The data analysis (Table 4) revealed a positive 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.
Table 4: Correlation between vitamin D and physicochemical characters of selected fish products. View Table 4
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 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.
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.
This work is not financially supported.
All of the authors contributed equally to this work, and they all read and approved the published version of the manuscript.
The authors declare that they have no conflicts of interest.