Abstract
Proteins are essential biological nutrients, and the global demand for protein-rich food and feed is increasing with population growth. To promote sustainability, industries are putting efforts to optimize resource utilization, minimize food waste, and improve food and feed quality assessments. For protein quality measurements, industries still rely on conventional, laboratory based analytical methods. The integration of sensor technologies into industrial processes can enable rapid sample analysis and process monitoring. Fourier Transform Infrared (FTIR) spectroscopy is a powerful tool for the analysis of aqueous proteins; however, water interference remains a significant challenge for reliable analysis. Different FTIR sampling approaches and strategies to minimize water interference are currently applied. The dry film approach can be a viable solution because the sample is dried to physically remove water resulting in a thin film of analytes. The main aim of this thesis was therefore to study the feasibility of the dry film FTIR approach for in-process food quality analysis. The thesis focused on using dry film FTIR to analyse the industrial aqueous solution of protein hydrolysates obtained from enzymatic protein hydrolysis (EPH), exploring the industrial process in EPH facilities, designing, and developing a portable dry film FTIR system tailored for industrial use, and developing applications that are relevant for industry. In the current thesis, sampling strategies aimed at minimizing the influence of water in FTIR analysis of aqueous proteins were employed using FTIR-ATR sampling with water background correction and dry film FTIR approach. A comparative analysis of the two FTIR sampling approaches was performed using laboratory-produced salmon hydrolysates and industrially produced poultry hydrolysates. Dry film FTIR demonstrated superior chemical resolution, likely due to physically removing water by drying, higher prediction accuracy for key quality parameters such as average molecular weight (AMW), and reliable analysis of samples of complex protein composition, i.e., poultry hydrolysates, where information from the amide I band of the FTIR spectrum is crucial. FTIR-ATR showed effectiveness in predicting AMW and Brix values in samples of less complex protein composition, i.e., salmon hydrolysates. Here, the calibration models were more dependent on FTIR bands minimally affected by water interference. The dry film FTIR approach was explored as a tool for understanding industrial processes. Aqueous solution of protein hydrolysates from poultry by-products, generated in an industrial enzymatic protein hydrolysis process facility, were characterized in terms of quality and further investigated to gain an understanding of in-process variations. The calibration models developed, based on regression using the FTIR spectra of aqueous solution of protein hydrolysates, demonstrated strong performance in predicting key quality parameters such as AMW, low molecular weight constituents, and collagen content. Dry film FTIR effectively distinguished major variations in raw materials (i.e., turkey and chicken), the significant effect different enzymes have on the key quality parameters, and the heterogeneity of protein hydrolysate compositions. This demonstrated the huge potential of using dry film FTIR to characterize the quality of industrial protein hydrolysates and for monitoring and controlling the hydrolysis process. Central to this thesis has been the design and development of a portable FTIR system that facilitates at-line, dry film measurements in industrial settings. After successful laboratory testing and benchmarking, with a benchtop laboratory FTIR system, using industrially produced aqueous solution of protein hydrolysates, the portable dry film FTIR was deployed in an enzymatic hydrolysis facility for at-line measurements of aqueous solution of protein hydrolysates. The calibration model was reliable in predicting AMW on industrial samples and was successfully validated. There were no significant differences in prediction capabilities between the portable dry film FTIR and the benchtop FTIR systems. The primary findings from dry film FTIR, used to analyse lactate content in cell culture media, indicated its broader application in bioprocess monitoring. The portable dry film FTIR system is expected to simplify the exploration for developing novel industrial applications for assessing protein-rich liquid samples. One prime application would be the analysis of protein composition in milk samples. Overall, the research of this thesis emphasized the potential of dry film FTIR for analysing aqueous protein hydrolysates. The dry film FTIR showed enhanced chemical resolution, promising results in predicting key quality parameters of protein hydrolysates and understanding process variations in the enzymatic hydrolysis facility. The design of the portable dry film FTIR system potentially facilitates integration into process lines for in-line measurements which can be enabled by automation of the sample preparation and drying process. The dry film FTIR can be a reliable tool for rapid sample analysis, quality control, and process exploration in industrial settings, bridging the gap between laboratory and real-world industrial applications.