Isotopic and Elemental Determination in Some Romanian Apple Fruit Juices

1. Introduction

Fruit juices are very popular beverages, and there is an increasing demand for the required raw material all over the world. Quantity and quality of the harvested fruits are subject to significant seasonal variations depending on climatic particularities in the area of production. For example, the partial substitution of a fruit juice concentrate by the much cheaper liquid sugars (beet or cane medium invert sugar or mixture of both) or the preparation of a single-strength juice from concentrate (without proper labeling) could result in a remarkable cost advantage. Such adulteration usually does not affect consumer health; however, they are misleading and cause disadvantages for honest producers [1].

Determination of δ ¹⁸O and δ ²H values of water from fruit juices is today applied in routine analysis as an automated and acknowledged method in order to differentiate between directly pressed and rediluted single-strength juices. Authentic juices have elevated δ ¹⁸O and δ ²H content of water as compared to water from rediluted products made using tap water which is relatively depleted in heavy oxygen and hydrogen isotopes [2]. The principle of this method is an exchange of ¹⁸O between water and carbon dioxide equilibration with the water (juice) to be measured in a closed volume. The δ ¹⁸O values of water can be calculated from the value determinate from the carbon dioxide [2]. Also, the ¹³C/¹²C ratio measured using elemental analyzer—isotopic ratio mass spectrometry in fruit juices—has been shown to be useful for detecting the adulteration of food products [3]. Moreover, ¹³C/¹²C proved to be a good tool for characterizing geographical origin. Indeed, the δ ¹³C values of plant compounds are influenced by the availability of water, relative humidity, and temperature, which control stomata aperture and the internal CO₂ concentration in the leaf [4]. In food sciences, ¹³C/¹²C ratio is a good probe for detecting the addition of cane sugar or maize glucose syrup to fruit juices [5].

The absorption of heavy metals with the diet occurs both in inorganic forms, through the corresponding salts, and as constituents of organic molecules (proteins, fats, carbohydrates, and nucleic acids). Some heavy metals (i.e., zinc, copper, iron, and selenium) are...