:
1. Introduction
Food chemical analysis is a unique tool for the evaluation of both the quality and safety of foods, and nowadays there is an increasing need to have accurate knowledge of food chemical composition [
1]. This great interest is evidenced by a constantly increasing number of publications on this topic in the more recent scientific literature. Most of these publications are focused on the determination of both chemicals and bio-markers in order to assess toxicity to humans or obtain information on environmental pollution [
2,
3,
4].
It is well known that aluminum (Al) is a widespread natural element (the third most common element in the Earth’s crust [
5]) and as a consequence is contained in different kinds of matrices, such as water, soil, and food [
1,
4,
6,
7,
8]. Additionally, aluminum is widely employed in many industrial activities and present in products such as cosmetics, deodorants (which typically contain aluminum salts), or body care creams. Furthermore, it is widely employed as aluminum foil used for food preparation, cooking, and also for foodstuff storage and packaging [
9,
10]. However, over the last decades, the toxicity of aluminum to humans has been a topic of discussion and is still not completely clarified. The neurotoxicity of Al has been proven [
11], and it has also been found that chronic aluminum intake causes Alzheimer’s disease [
12].
Dietary intake is the main source of exposure to aluminum for humans. From the available data, it is known that cereals and products derived from them, vegetables, and beverages, are the main vectors of exposure.
Aluminum is widely used in the food sector for the production of packaging and containers that are in contact with food, and it is recognized that the release of Al from the packaging into the foodstuff represents a risk [
4,
5,
9]. In the event that aluminum comes into contact with particularly aggressive drinks or foods (i.e., those capable of favoring Al leaching), such as those high in acidity or with high salt content, in order to prevent leaching the containers are internally coated with a layer of polymer that insulates the aluminum from direct contact with food [
13].
Another concern is represented by aluminum utensils, which are ubiquitous in households of developing countries. In particular, aluminum shows pathological effects on the human body (such as anemia, dementia, and osteomalacia) due to its leaching from utensils with long-term usage.
The use of aluminum tools and foils therefore represents another relevant source of aluminum that contributes to increasing the quantities of aluminum consumed through food [
14].
Numerous studies have recently focused on the assessment and quantification of aluminum release [
11,
15,
16,
17]. Al has low bioavailability in healthy humans, but the absorbed dose has a certain capacity for bioaccumulation.
An in-depth study was carried out by the European Food Safety Authority (EFSA), which drafted a detailed report on the safety of aluminum from dietary intake [
18]. The World Health Organization (WHO) and EFSA have established a tolerable weekly intake (TWI) for a human subject of 1 mg of aluminum per kg of body weight per week (i.e., 1 mg/kg bw/w) [
17,
18,
19].
For example, the estimated daily intake of Al was calculated for the Belgian adult population and amounted to 0.030 mg/kg body weight/day [
20] or 21% of the provisional tolerable weekly intake (PTWI), which was established in 2008 and subsequently confirmed by the EFSA [
19].
However, more generally, the limit of 1 mg/kg bw/w is often exceeded by a large part of the population: on average, an adult consumes, through diet alone, a quantity between 0.2 and 2.5 mg/kg bw/w, while for a child the range oscillates between 0.7 and 2.3 mg/kg bw/w [
16].
In Italy, Istituto Superiore di Sanità also published an in-depth study on the release of Al from the contact materials in 2008 [
13] while the Italian Ministry of Health published an opinion paper in 2017 [
16].
It is difficult to establish what effects the long-term intake of limited quantities (chronic toxicity) may have, such as that which occurs due to repeated ingestion of small quantities of Al through the diet. For this reason, extensive research has also been carried out on the different sources of aluminum in order to plan the reduction of the quantities ingested. Children, who generally eat more food than adults in relation to their weight, represent the category with the highest potential for exposure to aluminum per kg bw/w [
18]. In fact, the potential exposures generally come from foods and specific preparations for infants.
In 2013, the European Council (EC) approved limits for metals and alloys that can come into contact with food [
4]: specific release limits (SRLs) from metals and alloys into food have been indicated in this regard, including for aluminum. The SRL for the release of aluminum to food has been specified not to exceed 5.00 mg/kg of food. According to EC regulation n. 1935/2004 [
13], items (for packaging and wrapping) intended for contact with food must not release their constituents in quantities that could represent a danger to human health, lead to an unacceptable change in the composition of the food, or lead to a deterioration of the organoleptic characteristics.
In order to assess the exposure to aluminum for humans, numerous studies have been recently carried out, including the evaluation of Al leaching from aluminum cookware in meat and milk [
21] and the evaluation of leaching from aluminum foil used for cooking food such as meat or fish [
5,
22,
23,
24,
25] that are wrapped with aluminum foil and cooked in an oven.
The complexing effect plays an important role in the aluminum release process [
14] within food. In fact, complexing ions that are present in the food itself (such as organic acids) or within the seasoning used (for example, salt or lemon juice) increase the released Al concentration. Furthermore, at pH values typical of most foods (i.e., between 4 and 8), aluminum is mainly present in the form of organic complexes that are harmful to humans. The release, in fact, consists of the migration of aluminum into the food in the form of Al3+ ions, which can subsequently be complexed.
The quantities released by the foils depend on factors such as pH, salinity, the fat content of the food, temperature, and exposure time. Low pH values favor an increase in release; therefore, aluminum migrates more easily when it is in contact with acidic foods, but also with products rich in salt, with a trend depending on the time and contact temperature [
13,
26]. For example, some studies [
25] on foods wrapped in aluminum foil subjected to different cooking times have shown a correlation between parameters such as temperature, cooking time, and type of food and the Al concentrations found in the sample.
In the present study, the Al content in meat and fish wrapped in aluminum foil and cooked in an oven was quantified by elemental analysis by using inductively coupled plasma optical emission spectrometry (ICP-OES) with the aim of evaluating Al released into these kinds of foods. Furthermore, the appearance and morphological features of the foil after baking were evaluated by scanning electron microscopy coupled with energy dispersion spectroscopy (SEM-EDS), which showed the presence of microscopically small holes.
