Deep (offset) non-invasive Raman spectroscopy for the evaluation of food and beverages – A review

Spatially offset Raman spectroscopy (SORS) technique was developed to overcome the problem with qualitative or quantitative analysis of materials through packaging. To achieve that, the instrument is configured so that the Raman scattered signal is collected at a spatially offset at some distance from the excitation laser spot on the sample. In this way, the Raman spectra are recovered from the sample's sub-surface, providing a characteristic fingerprint of the product that requires a suitable multivariate data analysis to obtain the desired information. Despite the great potential for the technique, SORS applications in the food and agriculture sector are scarce in the literature. This paper is a review of all the studies reported to date where SORS is applied to analyse different foods and beverages. All of them have presented results that demonstrate the ability of SORS to carry out rapid and non-invasive through-the-container measurements and to ensure quality control and authentication of raw materials and end products. The reviewed studies include food analysis of animal and plant origin, through the surface of the food itself, as well as through the original packaging. Using the Raman spectra data, chemometric analyses were used to group, e.g., different varieties or species of the same type of potatoes, cuts of meat or alcoholic beverages, as well as to group them according to differences such as the state of ripeness of tomatoes, or the composition of fish, meat and potatoes, among others. There is a promising future for SORS in foodstuff analysis, so the technique must continue to be studied and evolve in order to obtain the appropriate methodology and instrumentation. In addition, the development of SORS portable instruments greatly facilitates the measurement operation and opens new opportunities for applications in the field or in industrial food processing premises.