Researchers at Chungnam National University in Daejeon, South Korea, working with a colleague at Gadjah Mada University in Indonesia, set out to test whether a short-wave infrared (SWIR) hyperspectral imaging system could reliably predict moisture content in pork meat emulsions while simultaneously revealing how uniformly the batter had been mixed. Their system swept across 1,000 to 1,700 nanometers — a range where water, fat, and protein all leave distinctive spectroscopic fingerprints — and, combined with machine learning models, produced moisture maps of the emulsion in roughly 20 seconds per sample. For an industry racing to build smart factories, the implications are considerable.

The experimental design was deliberately systematic. The team prepared pork ham and back fat batters at three lean meat-to-fat ratios: Group A at 6:2, Group B at 5:3, and Group C at 4:4. Each formulation was mixed in a silent cutter operating at 1,440 rpm for seven different durations: 0, 1, 2, 5, 7, 10, and 15 minutes, with processing temperatures held at approximately 10 to 15 degrees Celsius. Over three batches, the researchers generated 84 samples, each imaged with a line-scan SWIR camera capable of capturing 275 spectral bands across 894 to 2,505 nanometers. Only the cleanest 120 bands, spanning 1,000 to 1,700 nanometers, entered the analysis. Reference moisture values came from the classic, laborious route: oven-drying one-gram subsamples at 105 degrees Celsius for 24 hours, repeated in triplicate for every sample.

The chemical results told a clear story before any photons were analyzed. Group A, richest in lean meat, held the most water at 63.4 percent, followed by Group B at 57.2 percent and Group C at 52.4 percent — differences that were highly statistically significant. This aligns with established meat science: lean muscle proteins form networks that bind water effectively, while increasing fat dilutes that capacity. Mixing time mattered too. Freshly assembled batter at zero minutes averaged 61.8 percent moisture, but after just one minute of cutting the value dropped and then stabilized at roughly 56 to 58 percent through the full 15 minutes. Two-way analysis of variance confirmed both factors as significant main effects, with no meaningful interaction between them — formulation and mixing time independently shape the water content of the final batter.

The spectral data told a parallel story in reflected light. Batters with more moisture absorbed more strongly, since water exhibits intense O–H absorption features in the near infrared; fattier batters reflected more light because fat particles scatter it. Group A showed the lowest overall reflectance, Group C the highest, with the most informative differences appearing near 1,100 nanometers, across 1,250 to 1,350 nanometers, and from 1,600 to 1,700 nanometers — regions corresponding to water O–H overtones and fat C–H overtones. Even more striking was what happened over time: at the start of mixing the spectra varied widely from sample to sample, but as mixing progressed the curves converged into stable, nearly uniform profiles, a direct optical signature of the batter homogenizing.

Turning spectra into numbers required serious modeling. The team extracted 840 mean spectra and trained four different regression approaches — partial least squares regression (PLSR), random forest (RF), Elastic Net, and a weighted ensemble of all three. To avoid the pitfall of a single lucky or unlucky train-test split, they used Monte Carlo random sampling, repeating the random 60/40 calibration-validation partition 100 times for each model and reporting averaged performance metrics. Ten-fold cross-validation guided model selection, with final models judged on the lowest root mean square error of cross-validation. Seven spectral preprocessing techniques, from standard normal variate to Savitzky–Golay derivatives, were tested against raw spectra as well.

The winner was, somewhat counterintuitively, the simplest treatment. Elastic Net regression applied to raw, unpreprocessed spectra delivered the best predictive performance, achieving a prediction coefficient of determination of 0.76 with a root mean square error of prediction of 2.54 percent. The ensemble model, which weighted each base model by the inverse of its cross-validation error squared, performed nearly as well and proved the most stable overall. Random forest posted the highest calibration fit at 0.87 to 0.89, a hallmark of mild overfitting, while PLSR and Elastic Net landed in a comparable band across validation and prediction sets. The researchers also noted that raw spectra often beat preprocessed ones in their experiments — a finding consistent with earlier literature showing that preprocessing is not automatically beneficial when baseline drift and scattering are minimal during acquisition.

Just as revealing was where each model looked. PLSR and Elastic Net concentrated their attention on the lower SWIR wavelengths, around 1,000 to 1,224 and 1,200 to 1,400 nanometers, where water’s O–H second overtone and combination bands dominate — exactly the regions expected to encode moisture. Elastic Net also flagged bands from 1,288 to 1,341 nanometers, hinting at additional fat-related C–H information. Random forest, by contrast, emphasized mid-to-high wavelengths between 1,359 and 1,641 nanometers, corresponding to the first overtone of hydrocarbon C–H bonds and to protein N–H and lipid C–H vibrations, reflecting its nonlinear capacity to capture composite spectral changes. The ensemble blended both perspectives, highlighting water bands near 1,200 and 1,400 nanometers alongside fat and protein regions extending to 1,700 nanometers.

Perhaps the most visually compelling result came from the chemical imaging. Applying the winning Elastic Net model pixel by pixel, the team generated false-color maps of moisture distribution across each batter block. At zero to two minutes of mixing, all groups showed scattered hotspots of locally high moisture exceeding 70 percent — evidence of poorly dispersed muscle proteins and fat particles. By 5 to 15 minutes the maps became visibly homogeneous, mirroring the spectroscopic convergence and the physical reality of proteins encapsulating fat globules into a stable emulsion. Fattier formulations, especially Group C, showed progressively declining moisture across the mixing timeline. The authors caution that the study used a modest sample set under controlled laboratory conditions, and that industrial deployment will demand validation on larger datasets in real processing environments, along with model simplification for low-latency, real-time operation. Still, the demonstration that a 20-second camera scan can replace a 24-hour oven test — while also showing whether a batch is evenly mixed — marks a meaningful step toward moisture monitoring that food processors can actually run on the factory floor.

The SWIR region occupies a particularly informative slice of the electromagnetic spectrum for food analysis. While visible and near-infrared instruments have long been used to assess meat quality, wavelengths beyond 1,000 nanometers probe stronger overtone and combination vibrations of the O–H, C–H, and N–H bonds that define water, lipid, and protein chemistry. This gives SWIR systems inherently richer contrast among the major constituents of a meat batter, though at the cost of weaker detector sensitivity and higher instrument expense, which has historically limited their adoption on processing lines.

The imaging approach also differs fundamentally from the point-sensor methods used in earlier emulsion studies. Fiber-optic probes and benchtop spectrometers average the signal over a small spot, so a single reading can mask pockets of unmixed fat or free water within a batch. By scanning an entire 18 by 10 centimeter block pixel by pixel, the hyperspectral camera turns heterogeneity itself into a measurable quantity, which is why the moisture maps could reveal localized hotspots above 70 percent that a spot measurement would likely have smoothed away.

The choice of reference chemistry matters as well. Oven drying at 105 degrees Celsius for 24 hours remains the AOAC gold standard, but it is destructive, slow, and impractical for in-line control. A prediction error of 2.54 percent moisture, while larger than the 0.291 percent reported in an earlier multispectral study of sausage emulsions, was achieved across a broader range of formulations and mixing times, and with the added benefit of spatial visualization rather than a single averaged value.

The finding that raw spectra outperformed preprocessed ones carries practical weight for industry. Preprocessing pipelines add computational overhead and can amplify noise when scattering conditions are already stable, so a model that tolerates uncorrected spectra simplifies deployment in smart-factory environments where low-latency predictions are essential.

Looking ahead, the authors’ emphasis on validation under real processing conditions points to the next hurdles: variable raw material lots, fluctuating line temperatures, and the calibration transfer needed to move a laboratory model onto multiple production lines without retraining from scratch.

Subject of Research: Non-destructive prediction of moisture content and mixing uniformity in meat emulsions using SWIR hyperspectral imaging and chemometric modeling

Article Title: Monitoring of moisture content in meat emulsion using an SWIR hyperspectral imaging system

Article References: Kim, J., Rho, T.-G., Park, E.-S., Kwon, O.-T., Lee, S.-J., Faqeerzada, M. A., Joshi, R., Amanah, H. Z., & Cho, B.-K. (2026). Monitoring of moisture content in meat emulsion using an SWIR hyperspectral imaging system. Food Science of Animal Resources, 46(1), Article 100. https://doi.org/10.1007/s44463-026-00101-9

Image Credits: AI Generated

DOI: 10.1007/s44463-026-00101-9

Keywords: SWIR hyperspectral imaging, meat emulsion, moisture prediction, chemometrics, Elastic Net regression, PLSR, random forest, ensemble modeling, process monitoring, meat batter quality, food analysis, non-destructive testing

Metalenses represent a radical departure from classical glass optics. Instead of relying on curved glass to refract and focus light, they employ metasurfaces composed of intricately engineered nanostructures. These nanostructures, often mere hundreds of nanometres in size, manipulate light waves by controlling phase, amplitude, and polarization at a scale far below the wavelength of visible light. This nanoscale control enables metalenses to bend and focus light efficiently while being tens of thousands of times thinner than conventional lenses. Such a paradigm shift not only promises to revolutionize consumer electronics by further slimming down camera modules but also opens new horizons for optical applications where space and weight are critical constraints.

A recent breakthrough in this field has been demonstrated by researchers at ETH Zurich, who have successfully developed a novel method to fabricate metalenses from lithium niobate, a well-known crystalline material with exceptional nonlinear optical properties. Lithium niobate is celebrated for its capacity to alter the frequency of light passing through it—a phenomenon known as nonlinear optics. By converting incoming infrared light into visible wavelengths, this material enables devices that can manipulate light in innovative ways beyond simple focusing. However, until now, shaping lithium niobate into nanostructures suitable for metalenses has been technologically challenging due to its robustness and conventional fabrication difficulties.

The team, led by Professor Rachel Grange, devised a groundbreaking nanoimprinting technique that allows lithium niobate to be molded into the complex metasurfaces required for metalenses efficiently and at scale. This fabrication process ingeniously combines chemical synthesis with precision nanoengineering. The liquid precursor containing lithium niobate’s constituent materials is “stamped” in a manner reminiscent of Gutenberg’s printing press, enabling the creation of nanoscale patterns. Subsequently, the imprinted structures are subjected to controlled heating at 600°C, which crystallizes the material and imparts the desired optical properties necessary for frequency conversion.

This innovative method overcomes several limitations previously associated with the production of lithium niobate nanostructures. Traditional fabrication methods struggled with lithium niobate’s remarkable hardness and chemical stability, often resulting in slow, costly, and labor-intensive manufacturing. The nanoimprinting approach not only significantly reduces production costs and time but also allows the repeated use of inverse molds for mass production, potentially accelerating the commercial deployment of these advanced optical elements.

At the heart of the technology lies the capability of the lithium niobate metalenses to not only focus infrared light sharply but also to convert it into shorter wavelengths of visible light in a highly efficient and controlled manner. When infrared laser light with a wavelength around 800 nanometres passes through the metalens, the nonlinear interactions within the engineered lithium niobate structures generate visible violet light at approximately 400 nanometres, concentrated precisely at the focal point. This unusual ability to combine light focusing with wavelength conversion in an ultra-thin device paves the way for multifaceted photonic systems unparalleled in conventional optics.

The nonlinear optical effect utilized here is not confined to a narrow set of incident light wavelengths. This wavelength-agile characteristic means that these metalenses can be adapted for a wide range of optical frequencies, enhancing their utility in various scientific and industrial contexts. Such flexibility extends the reach of this technology into numerous fields, including telecommunications, microscopy, and advanced sensing, where manipulating light of different wavelengths with high precision is essential.

Beyond traditional uses of lenses, this breakthrough prompts exciting possibilities for security and authentication technologies. The minute nanoscale features integrated into the metalenses make them nearly impossible to replicate without sophisticated manufacturing tools, offering robust counterfeit deterrents. By leveraging the nonlinear optical properties, these metasurfaces can be incorporated into banknotes, documents, or artwork as covert security markers that reliably authenticate their origin under specific illumination conditions.

In practical terms, the use of lithium niobate metalenses promises to simplify the complexity of various optical instruments. For example, sensors that require detecting infrared light—ordinarily invisible to most cameras—can incorporate these metalenses to convert infrared signals into visible light, allowing standard camera systems to perform sophisticated measurements. Moreover, the reduced bulk and enhanced functionality facilitate miniaturized apparatuses in fields such as ultraviolet light patterning for semiconductor manufacturing, potentially revolutionizing how microchips are produced.

This convergence of physics, materials science, and chemistry within the emerging field of metasurface optics is propelling photonic research into uncharted territories. The ETH Zurich team’s accomplishment exemplifies how interdisciplinary approaches can unlock new properties of light and overcome manufacturing challenges to create devices with unprecedented capabilities. Though the field remains in its early days, the impact of scalable, cost-effective nonlinear metalenses is poised to ripple across scientific research, industry, and consumer technology.

Looking forward, the continued development of such metasurfaces suggests the possibility of ultra-compact optical systems that integrate multiple functionalities into a single nanostructured layer. The implications cover not only everyday electronics but also the foundational tools used in quantum computing, optical communication, and biomedical imaging. Researchers are optimistic that these scalable fabrication techniques will catalyze innovations resulting in more sustainable, efficient, and versatile optical devices accessible to a broad spectrum of applications.

Nevertheless, translating laboratory success into commercial products requires addressing challenges such as integrating these metalenses with existing device architectures, optimizing their durability and performance under various operating conditions, and further enhancing their efficiency. Continuous collaboration between material scientists, optical engineers, and industrial partners will be essential for realizing the full potential of this technology, ensuring that the extraordinary properties of lithium niobate metalenses become widely harnessed.

In summarizing this advancement, it is clear that lithium niobate nanoimprinted metalenses mark a significant milestone in nanophotonics. They embody the essence of modern scientific progress by marrying intricate nanoscale engineering with the remarkable intrinsic properties of nonlinear optical materials. As research delves deeper into controlling light with ever-greater finesse, we are set to witness a profound transformation in how imaging, sensing, and light manipulation technologies develop in the near future.

Subject of Research: Not applicable

Article Title: Scalable Lithium Niobate Nanoimprinting for Nonlinear Metalenses

News Publication Date: 14-Apr-2025

Web References: 10.1002/adma.202418957

Image Credits: Ülle-Linda Talts, ETH Zurich

Keywords

Metalenses, lithium niobate, nonlinear optics, nanoimprinting, metasurfaces, nanophotonics, wavelength conversion, infrared to visible light, nanostructures, scalable fabrication, optical miniaturization, advanced materials