MICROBIAL FOOD FERMENTATIONS: INNOVATIVE APPROACH USING INFRARED SPECTROSCOPY

Interest in food quality and production has increased in recent decades, mainly due to changes in consumer habits and behaviour, and the development and increase in the industrialisation of food chains. The growing demand for quality and safety in food production obviously calls for high standards for quality and process control, which in turn requires appropriate analytical tools for the analysis of food. In particular, many unit operations in industrial food processes are related to microbial fermentation, namely milk coagulation in dairy, dough in bakery, as well as must fermentation in wine and beer productions. Fermentation is one of the earliest methods adopted to obtain value-added food products with an extended shelf life. Humans applied fermentation to make products such as wine, mead, cheese and beer long before the biochemical process behind was understood. Even now the biochemistry of fermentations commonly applied in food processes has many aspects which have not been fully investigated yet. Briefly, fermentation is any metabolic process in which an organism converts a carbohydrate, such as starch or sugar, into an alcohol and/or organic acids entailing modifications in the final product. The transition to industrial productions entailed a standardisation of the fermentation processes and the obtained products. Currently, the main objective is to develop instruments able to be implemented in the process in order to closely monitor the products of interest and to detect in real time the smallest changes bringing to a more effective process control and management. In this contest, spectroscopy revealed to be an interesting analytical method to monitor food fermentations processes. Spectroscopy is a secondary analytical method which consists in recording the absorption changes due to the interaction of electromagnetic radiation with the matter. The basic principle is that every chemical compound absorbs, transmits or reflects light (electromagnetic radiation) over a certain range of wavelengths. The information recorded can, thus, be used to measure the amount of a known chemical substance if correlated to a reference analysis. Spectroscopy reveals to be one of the most useful methods for quantitative analysis in various fields such as chemistry, physics, biochemistry, material and chemical engineering and clinical applications. Indeed, any application that deals with chemical substances or materials can use this technique. Moreover, the improved instrumentation for performing in-line and on-line analyses at industrial level has rose in the last decades giving the opportunity to obtained real-time information about the progression of any process and allowed its implementation as strategy to monitor complex systems as food production. The food monitoring with spectroscopic devices has become possible thanks to Chemometrics (i.e. multivariate data analysis). Chemometrics has widely demonstrated to be the perfect partner to spectroscopy to deal with the complex chemical/physical systems that food matrix conforms. Chemometrics is able to extract relevant information from redundant and noisy spectra. In the last years the combination of spectroscopic analysis and Chemometrics was applied crosswise in food processes for qualitative and quantitative modelling in industrial applications. In particular, for the determination of compositional parameters affecting quality and safety of fermented food products such as wine, beer, yoghurt, vinegar and bakery products. Nevertheless, concerning complex biotransformations spectroscopy and Chemometrics are emerging techniques in food fermentation monitoring. The purpose of this PhD Thesis is the demonstration of the feasibility in the combination of spectroscopy and Chemometrics as an innovative working procedure for real time monitoring of food fermentation processes. The thesis consists of five main chapters Chapter 1 Chapters 2 and 3 present an introduction to the main fermentations and their control from an historical prospective, the employed analytical techniques (Near infrared and Mid Infrared spectroscopy) and to Chemometrics, respectively. Chapter 4 presents the experiments carried out on various fermentation food processes. In this section seven studies represent examples of applications of different spectroscopic methods in strong combination with Chemometrics to food fermentation processes as yogurt fermentation (Paper I, II and Paper III), wine malolactic transformation (Paper IV and V) and beer (Paper VI and VII). In addition to the mentioned contributions a brief state of the art and some preliminary results are reported regarding sourdough leaving process monitoring. The two basic Chemometrics tools, principal component analysis (PCA) and partial least squares (PLS) regression were mainly applied to the spectroscopic data collected from the fermentation processes in order to evaluate the results and focus on the relevant information and to correlate the spectral features with different relevant physical and/or chemical parameters such as the concentration of the main chemical species involved in the biotransformation. In particular, the principal components (PCs) scores obtained by monitoring wine and yoghurt fermentations were modelled as function of time to find out kinetic parameters, as maximum acceleration and deceleration of the transformation, important for the process control (PAPER I and V). The spectroscopic data obtained during yoghurt and beer fermentation monitoring were also investigated with multivariate curve resolution- alternating least squares (MCR-ALS), proving to be able to resolve multi-component mixtures into a simpler model (PAPER II and VII). The main conclusive remarks on the presented studies are given in Chapter 5 (CONCLUSIONS), including a discussion of challenges and future perspectives for further application of spectral monitoring and chemometrics in fermented food processes.