Analysis of food and emulsions

Recent advance in nondestructive imaging technology for detecting quality of fruits and vegetables: a review

As an integral part of daily dietary intake, the market demand for fruits and vegetables is continuously growing. However, traditional methods for assessing the quality of fruits and vegetables are prone to subjective influences, destructive to samples, and fail to comprehensively reflect internal quality, thereby resulting in various shortcomings in ensuring food safety and quality control. Over the past few decades, imaging technologies have rapidly evolved and been widely employed in nondestructive detection of fruit and vegetable quality. This paper offers a thorough overview of recent advancements in nondestructive imaging technologies for assessing the quality of fruits and vegetables, including hyperspectral imaging (HSI), fluorescence imaging (FI), magnetic resonance imaging (MRI), thermal imaging (TI), terahertz imaging, X-ray imaging (XRI), ultrasonic imaging, and microwave imaging (MWI). The principles and applications of these imaging techniques in nondestructive testing are summarized. The challenges and future trends of these technologies are discussed.

Innovations in nondestructive assessment of baked products: Current trends and future prospects

Rising consumer awareness, coupled with advances in sensor technology, is propelling the food manufacturing industry to innovate and employ tools that ensure the production of safe, nutritious, and environmentally sustainable products. Amidst a plethora of nondestructive techniques available for evaluating the quality attributes of both raw and processed foods, the challenge lies in determining the most fitting solution for diverse products, given that each method possesses its unique strengths and limitations. This comprehensive review focuses on baked goods, wherein we delve into recently published literature on cutting-edge nondestructive methods to assess their feasibility for Industry 4.0 implementation. Emphasizing the need for quality control modalities that align with consumer expectations regarding sensory traits such as texture, flavor, appearance, and nutritional content, the review explores an array of advanced methodologies, including hyperspectral imaging, magnetic resonance imaging, terahertz, acoustics, ultrasound, X-ray systems, and infrared spectroscopy. By elucidating the principles, applications, and impacts of these techniques on the quality of baked goods, the review provides a thorough synthesis of the most current published studies and industry practices. It highlights how these methodologies enable defect detection, nutritional content prediction, texture evaluation, shelf-life forecasting, and real-time monitoring of baking processes. Additionally, the review addresses the inherent challenges these nondestructive techniques face, ranging from cost considerations to calibration, standardization, and the industry's overreliance on big data.

Brewing alcohol 101: An undergraduate experiment utilizing benchtop NMR for quantification and process monitoring

In recent years there has been a renewed interest in benchtop NMR. Given their lower cost of ownership, smaller footprint, and ease of use, they are especially suited as an educational tool. Here, a new experiment targeted at upper-year undergraduates and first-year graduate students follows the conversion of D-glucose into ethanol at low-field. First, high and low-field data on D-glucose are compared and students learn both the Hz and ppm scales and how J-coupling is field-independent. The students then acquire their own quantitative NMR datasets and perform the quantification using an Electronic Reference To Access In Vivo Concentration (ERETIC) technique. To our knowledge ERETIC is not currently taught at the undergraduate level, but has an advantage in that internal standards are not required; ideal for following processes or with future use in flow-based benchtop monitoring. Using this quantitative data, students can relate a simple chemical process (fermentation) back to more complex topics such as reaction kinetics, bridging the gaps between analytical and physical chemistry. When asked to reflect on the experiment, students had an overwhelmingly positive experience, citing agreement with learning objectives, ease of understanding the protocol, and enjoyment. Each of the respondents recommended this experiment as a learning tool for others. This experiment has been outlined for other instructors to utilize in their own courses across institutions, with the hope that a continued expansion of low-field NMR will increase accessibility and learning opportunities at the undergraduate level.

Raman Spectroscopy of Emulsions and Emulsion Chemistry

Emulsions are dispersed systems widely used in various industries. In recent years, Raman spectroscopy (RS), as a spectroscopic technique, has gained much attention for measuring and monitoring emulsions. In this review, we explore the use of RS on emulsion structures and emulsification, important reactions that use emulsions such as emulsion polymerization, catalysis and cascading reactions, as well as various applications of emulsions. We explore how RS is used in emulsions, reactions and applications. RS is a powerful and versatile tool for studying emulsions, but there are also challenges in using RS to monitor emulsion processes, especially if they are rapid or volatile. We also explore these challenges and difficulties, as well as possible designs that can be used to overcome them.

Recognition-Enabled Automated Analyte Identification via 19F NMR

Nuclear magnetic resonance (NMR) is an indispensable tool for structural elucidation and noninvasive analysis. Automated identification of analytes with NMR is highly pursued in metabolism research and disease diagnosis; however, this process is often complicated by the signal overlap and the sample matrix. We herein report a detection scheme based on ¹⁹F NMR spectroscopy and dynamic recognition, which effectively simplifies the detection signal and mitigates the influence of the matrix on the detection. It is demonstrated that this approach can not only detect and differentiate capsaicin and dihydrocapsaicin in complex real-world samples but also quantify the ibuprofen content in sustained-release capsules. Based on the ¹⁹F signals obtained in the detection using a set of three ¹⁹F probes, automated analyte identification is achieved, effectively reducing the odds of misrecognition caused by structural similarity.

Non-Invasive Rheo-MRI Study of Egg Yolk-Stabilized Emulsions: Yield Stress Decay and Protein Release

A comprehensive understanding of the time-dependent flow behavior of concentrated oil-in-water emulsions is of considerable industrial importance. Along with conventional rheology measurements, localized flow and structural information are key to gaining insight into the underlying mechanisms causing time variations upon constant shear. In this work, we study the time-dependent flow behavior of concentrated egg-yolk emulsions with (MEY) or without (EY) enzymatic modification and unravel the effects caused by viscous friction during shear. We observe that prolonged shear leads to irreversible and significant loss of apparent viscosity in both emulsion formulations at a mild shear rate. The latter effect is in fact related to a yield stress decay during constant shearing experiments, as indicated by the local flow curve measurements obtained by rheo-MRI. Concurrently, two-dimensional D-T₂ NMR measurements revealed a decrease in the T₂ NMR relaxation time of the aqueous phase, indicating the release of surface-active proteins from the droplet interface towards the continuous water phase. The combination of an increase in droplet diameter and the concomitant loss of proteins aggregates from the droplet interface leads to a slow decrease in yield stress.

An in situ stretching instrument combined with low field nuclear magnetic resonance (NMR): Rheo-Spin NMR

An in situ stretching instrument combined with low field nuclear magnetic resonance (LF-NMR) was designed and developed, namely, Rheo-Spin NMR. The time resolved stress-strain curve together with the corresponding NMR signal can be simultaneously obtained. The Rheo-Spin NMR contains the functional modules, including (1) the in situ stretching module, (2) the NMR signal acquisition module, and (3) the cavity of the NMR positioning module. The unique ring-like shape of the sample is used to replace the traditional dumbbell sample due to limited space in the NMR probe, and the whole ring-like sample will be deformed during the uniaxial stretching process, which avoids the generation of interference signals from the undeformed sample. The designed stretching assembly made by zirconia ceramics is manufactured to match and stretch the ring-like samples. The strain rate can be tuned within the range of 10^-5-10^-2 s^-1 with the maximum stretching ratio λ_max of ∼3.8. The in situ stretching experiments combined with LF-NMR were carried out successfully with natural rubber of different fractions of carbon black. The time-resolved T₂ relaxometry was adopted to evaluate segmental relaxation during uniaxial deformation which, for the first time, provides the direct and in situ molecular dynamics information. The Rheo-Spin NMR is promising to provide more in-depth insights into the structure and dynamics evolution of polymer products under real service conditions.

Benchtop NMR for the monitoring of bioprocesses

This mini-review highlights the potential of benchtop nuclear magnetic resonance (NMR) for the monitoring of bioprocesses. It describes recent perspectives opened by the reduced size of devices in relaxometry, magnetic resonance imaging and NMR spectroscopy. In particular, the recent emergence of the benchtop NMR spectroscopy gives access to many applications thanks to the implementation of advanced experiments.

Progress in low-field benchtop NMR spectroscopy in chemical and biochemical analysis

The employment of spectroscopically-resolved NMR techniques as analytical probes have previously been both prohibitively expensive and logistically challenging in view of the large sizes of high-field facilities. However, with recent advances in the miniaturisation of magnetic resonance technology, low-field, cryogen-free "benchtop" NMR instruments are seeing wider use. Indeed, these miniaturised spectrometers are utilised in areas ranging from food and agricultural analyses, through to human biofluid assays and disease monitoring. Therefore, it is both intrinsically timely and important to highlight current applications of this analytical strategy, and also provide an outlook for the future, where this approach may be applied to a wider range of analytical problems, both qualitatively and quantitatively.

Desktop NMR and Its Applications From Materials Science To Organic Chemistry

NMR spectroscopy is an indispensable method of analysis in chemistry, which until recently suffered from high demands for space, high costs for acquisition and maintenance, and operational complexity. This has changed with the introduction of compact NMR spectrometers suitable for small-molecule analysis on the chemical workbench. These spectrometers contain permanent magnets giving rise to proton NMR frequencies between 40 and 80 MHz. The enabling technology is to make small permanent magnets with homogeneous fields. Tabletop instruments with inhomogeneous fields have been in use for over 40 years for characterizing food and hydrogen-containing materials by relaxation and diffusion measurements. Related NMR instruments measure these parameters in the stray field outside the magnet. They are used to inspect the borehole walls of oil wells and to test objects nondestructively. The state-of-the-art of NMR spectroscopy, imaging and relaxometry with compact instruments is reviewed.

Class-modelling in food analytical chemistry: Development, sampling, optimisation and validation issues - A tutorial

Qualitative data modelling is a fundamental branch of pattern recognition, with many applications in analytical chemistry, and embraces two main families: discriminant and class-modelling methods. The first strategy is appropriate when at least two classes are meaningfully defined in the problem under study, while the second strategy is the right choice when the focus is on a single class. For this reason, class-modelling methods are also referred to as one-class classifiers. Although, in the food analytical field, most of the issues would be properly addressed by class-modelling strategies, the use of such techniques is rather limited and, in many cases, discriminant methods are forcedly used for one-class problems, introducing a bias in the outcomes. Key aspects related to the development, optimisation and validation of suitable class models for the characterisation of food products are critically analysed and discussed.

Ultrafast NMR diffusion measurements exploiting chirp spin echoes

Standard diffusion NMR measurements require the repetition of the experiment multiple times with varying gradient strength or diffusion delay. This makes the experiment time-consuming and restricts the use of hyperpolarized substances to boost sensitivity. We propose a novel single-scan diffusion experiment, which is based on spatial encoding of two-dimensional data, employing the spin-echoes created by two successive adiabatic frequency-swept chirp π pulses. The experiment is called ultrafast pulsed-field-gradient spin-echo (UF-PGSE). We present a rigorous derivation of the echo amplitude in the UF-PGSE experiment, justifying the theoretical basis of the method. The theory reveals also that the standard analysis of experimental data leads to a diffusion coefficient value overestimated by a few per cent. Although the overestimation is of the order of experimental error and thus insignificant in many practical applications, we propose that it can be compensated by a bipolar gradient version of the experiment, UF-BP-PGSE, or by corresponding stimulated-echo experiment, UF-BP-pulsed-field-gradient stimulated-echo. The latter also removes the effect of uniform background gradients. The experiments offer significant prospects for monitoring fast processes in real time as well as for increasing the sensitivity of experiments by several orders of magnitude by nuclear spin hyperpolarization. Furthermore, they can be applied as basic blocks in various ultrafast multidimensional Laplace NMR experiments. Copyright © 2016 John Wiley & Sons, Ltd.