https://doi.org/10.1080/19476337.2022.2112298
“The current study was conducted to measure the manganese content in nine different food groups. A cross-sectional study was designed; a total of 89 food items were randomly purchased from the main markets and hypermarkets in Alexandria Governorate, then digested by wet ashing procedure and finally analyzed using ICP-OES. The highest mean Mn value was obtained in the fat group (6.75 µg/g) compared to the other eight groups, followed by nuts (4.64 µg/g) and the protein-rich food group (4.52 µg/g), while meat and its products have the lowest mean of Mn (0.53 µg/g). Manganese content in food groups is strongly correlated with the food matrix, soil composition, and fortification process. Local butter, margarine, sunflower oil, corn oil, Scomberomorus commerson, poulty fish, pistachio, and walnuts had the highest content of manganese.”
2.1. Chemicals
All standard solutions were purchased from Germany (Merk), including; Manganese standard solution, Nitric acid, Hydrochloric acid, and Hydrogen peroxide, while Deionized water was obtained from Petroleum Company with resistively <18.6 Ohm
2.2. Data collection methods and tools
A cross-sectional study was conducted. Food items were classified into nine different food groups including; beverages, carbohydrate-rich food, milk, and its product, meat and its products, fruits and vegetables, protein-rich food, nuts, fats, and sweetened products. Nine to ten food items were collected from each food group giving a total of eighty-nine food items. A total of one kilogram or one liter of each food samples were purchased from different main hypermarket, fish market, or herbal market in Alexandria Governorate depending on the type of purchased food item. Each food item was purchased four times from four different markets in Alexandria governorate giving a total of 356 samples. Pooling was done for each food item (four replicates) by mixing them well together to obtain random and representative sample for each. Samples were purchased from January to April 2021.
2.2.1. Sample storage and preparation
Samples were collected and protected from manganese loss or contamination throughout the analysis. Meat, fish, and seafood were stored at −20°C till analysis. Yogurt, fruit, vegetables, and cheese were analyzed once purchased, while oil, nuts, and beverages were stored in opaque glass bottles at room temperature at 27°C until analysis. Dry solid samples were ground to give fine particles using a blender, while muscular samples such as meat and its products, and poultry were minced after discarding fats and connective tissue. On the other hand, only edible parts of seafood were analyzed; head, skin, viscera, scales, and tail were removed, vegetables and fruits were homogenized well in a porcelain mortar to obtain homogeneous samples. All prepared samples were kept in plastic pages till they were digested.
2.3. Sample digestion and quantification
Samples were digested according to the EPA method (Martin et al., Citation1994) using the ETHOS microwave digestion system. All samples were digested either by using HNO3 (65%) or H2O2 (40%) and HCL according to the sample matrix. Samples were filtered through Whatman paper 0.4 then using syringe filter 0.2 µml pore. The obtained solution will make up to 50 ml. All the wet digested samples were ready for manganese quantification using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES).
2.4. Preparation of the standard curve for manganese
The standard curve was prepared from stock solution (1000 ppm) using deionized water. The following concentrations were prepared; 0.005, 0.05, 0.01, 0.5, 1.5, 10, and 15 ppm.
2.5. ICP-OES conditions
2.5.1. Instrumentation
ICP-OES measurements were performed using ICAP-Pro Series ICP-OES (Qtegra ISDS-2.11software) Dual-view, Qua Ex-Cell (Thermo Fisher Scientific, Germany).
2.5.2. Operating conditions of ICP-OES
Table
| Power | 1.2 KW |
|---|---|
| Wavelength | 257.610 nm |
| Plasma flow | 15 L/min |
| Aux. flow | 1.5 L/min |
| Neb. flow | 0.75 L/min |
| Replicate read time (S) | 10 Sec. |
| Sample uptake time | 30 Sec. |
| Rinse Time | 10 S |
| Pump rate | 15 rpm |
| Instrument stabilization delay | 15 S |
2.5.3. ICP – OES analysis
Manganese concentrations were calculated from the regression line (R2 = 0.999) obtained using Mn standard solution (Merk) according to the EPA 200.7 method (Martin et al., Citation1994).
3. Statistical analysis of the data
The data was fed to the computer and analyzed using the IBM SPSS software package version 20.0. (Armonk, NY: IBM Corp).
Qualitative data was described using numbers and percentages. The Kolmogorov-Smirnov test was used to verify the normality of the distribution. Quantitative data were described using range (minimum and maximum), mean, standard deviation, and median. The significance of the obtained results was judged at the 5% level. The used tests were the Kruskal Wallis test; for abnormally distributed quantitative variables, to compare between more than two studied groups, and Post Hoc (Dunn’s multiple comparisons test) for pairwise comparisons.