In a recent article published in the journal Food Chemistry, researchers from Denmark investigated the potential of using advanced spectroscopies, specifically near-infrared spectroscopy (NIRS) and proton nuclear magnetic resonance (1H NMR) spectroscopy, for monitoring the quality of semi-hard cheeses.
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They aimed to explore the discriminative patterns in the quality of semi-hard cheeses manufactured using lactic acid bacteria (LAB) and propionic acid bacteria (PAB) by analyzing spectral data and identifying metabolites associated with different culture-specific metabolic pathways.
Background
Cheese production has advanced significantly with modern technology. Semi-hard cheeses like Cheddar, Gouda, and Emmental are popular for their diverse flavor profiles and textures.
These characteristics result from a complex ripening process involving microbes and biochemical reactions, including the metabolism of residual lactose, lactate, and citrate, followed by the breakdown of fatty acids and amino acids.
About the Research
The study employed NIRS and 1H NMR spectroscopy as rapid, non-destructive tools to monitor cheese quality. Researchers analyzed 48 commercial semi-hard cheese samples, categorized by fat content and microbial cultures (LAB or mixed LAB/PAB).
The analysis included expert sensory evaluations, bulk compositional analysis using a NIRS-based instrument (DairyQuant), and detailed chemical analysis with bench-top NIRS and high-resolution 1H NMR spectrometers.
Cheese samples for 1H NMR analysis were prepared using a modified Folch protocol to extract metabolites. The protocol separated hydrophilic and hydrophobic fractions, followed by drying and reconstitution in appropriate solvents. The 1H NMR spectra were acquired using a Bruker Avance III spectrometer, with data undergoing rigorous pre-processing for referencing, noise removal, normalization, alignment, and metabolite quantification.
Experts conducted sensory evaluations based on surface characteristics, consistency, mouthfeel, taste, and flavor. The DairyQuant instrument provided an overview of compositional parameters, with the data undergoing correlation analysis to understand intercorrelations among different quality parameters.
Research Findings
The study demonstrated NIRS's effectiveness in differentiating cheese varieties based on microbial cultures. The DairyQuant instrument accurately determined bulk compositional parameters, with pH and dry matter (DM) serving as weak discriminators between LAB and PAB cheeses. Notably, bench-top NIRS exhibited superior sensitivity, distinguishing between cultures based on the subtle lactate signal in the first overtone carbon-hydrogen (C-H) stretching region (1674 nm).
1H NMR spectroscopy provided a comprehensive understanding of metabolic profiles associated with LAB and PAB cheeses, identifying 25 metabolites. PAB cheeses had higher concentrations of propionate, acetate, and glutamate, while LAB cheeses showed elevated levels of lactate and acetoin. This highlighted the significant influence of microbial cultures on the flavor profile of semi-hard cheeses.
Principal component analysis (PCA) scores from the 1H NMR spectra of the hydrophilic fraction revealed clear discrimination between LAB and PAB cheeses. Box plots of discriminant metabolites such as lactate, acetate, choline, and glutamate underscored the differences in concentrations between the cheese types. The hydrophobic extract analysis indicated no significant impact of microbial culture on the fat profile, as evidenced by the identical spectral profiles of LAB and PAB cheeses.
Applications
These findings hold promise for the dairy industry by streamlining cheese production and ensuring consistent quality. NIRS and 1H NMR spectroscopy offer rapid, reliable methods for monitoring cheese ripening, optimizing flavor development, and early detection of potential quality issues like spoilage or unwanted bacterial growth.
These techniques can reduce waste, increase production efficiency, and enhance consumer satisfaction. Developing in-line sensors based on these spectroscopic techniques could enable real-time quality monitoring, ensuring consistent product standards.
Conclusion
The researchers demonstrated the effectiveness of NIRS and 1H NMR spectroscopy in characterizing and differentiating semi-hard cheeses based on microbial cultures. Their findings highlighted the significant impact of LAB and PAB cultures on the cheese's chemical composition and flavor profile.
This enhanced understanding can provide valuable insights for optimizing cheese production processes, potentially leading to reduced production times, improved consistency, and targeted flavor development. Future research could refine these techniques and explore their applications in other cheese types and dairy products, contributing to advancements in the dairy industry.
Journal Reference
Patel, H., Aur, V., Sorensen, KM., Engelsen, SB. (2024). Towards online cheese monitoring: Exploration of semi-hard cheese using NIR and 1H NMR spectroscopy. Food Chemistry. doi.org/10.1016/j.foodchem.2024.139786
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