Effect of marination in lemon juice on beef tenderization and in vitro gastric digestibility.

BACKGROUND: There is limited knowledge regarding digestion and absorption of nutrients after cooked marinated meat is ingested. Most of the previous studies on food gastric digestion have focused on chemical digestion and did not reflect upon physical digestion driven by peristalsis. In the present study, we examined the effects of marinating beef in lemon juice on gastric digestibility using a human gastric digestion simulator (GDS) that mimics peristaltic motion called antral contraction waves. RESULTS: Beef thigh slices were marinated in 100% lemon juice for 1 h and then grilled; an image of a stained tissue sample revealed that muscle tissue contraction (i.e. that usually occurs upon cooking) was suppressed. The measurement of physical properties using a rheometer and texture analyzer showed that the meat marinated in lemon juice had a soft texture. In vitro digestion experiments using the GDS revealed that the extent of both physical digestion driven by peristalsis and chemical digestion catalyzed by digestive enzymes was enhanced by the lemon juice marinade. CONCLUSION: The results of the present study suggest that marinating beef in lemon juice affects nutrient digestibility. An integrated evaluation of tissue structure, physical properties and GDS digestion to analyze meat digestion would enhance our understanding of the effects of seasoning and cooking methods on meat. © 2023 Society of Chemical Industry.

Observation of Microstructure Formation During Freeze-Drying of Dextrin Solution by in-situ X-ray Computed Tomography.

In-situ X-ray computed tomography (CT) was used to observe microstructure formations during freeze-drying of a dextrin solution. A specially designed freeze-drying stage was equipped at the X-ray CT stage. Frozen and dried microstructures were successfully observed. The CT images of the frozen solution clarified the ice crystal size increase and obvious boundary formation between the ice and freeze-concentrated phases upon performing post-freezing annealing at -5°C. These structural modifications emerged owing to Ostwald ripening and glassy phase relaxation. During the freeze-drying, pore microstructures formed as a consequence of water removal. The pores were replicas of the original ice microstructures; some pore microstructures newly formed by the removal of water. The latter mechanism was more obvious in the non-annealed sample than in the annealed sample. The glassy phase in the non-annealed solution was not perfectly freeze-concentrated; water was rapidly removed from this phase, losing its original microstructure. At this moment, the freeze-concentrated region piled up to new pore walls, which consequently thickened the pore walls. An image analysis estimated that the mean pore wall thicknesses for the non-annealed and annealed samples were 13.5 and 8.6 µm, respectively. It was suggested that the advantages of annealing are not only to reduce drying time owing to the modification of ice crystal morphologies but also to avoid quality loss related to the structural deformation of the glassy matters.

Observation of glassy state relaxation during annealing of frozen sugar solutions by X-ray computed tomography.

Glassy phase formation in a frozen product determines various properties of the freeze-dried products. When an aqueous solution is subjected to freezing, a glassy phase forms as a consequence of freeze-concentration. During post-freezing annealing, the relaxation of the glassy phase and the ripening of ice crystals (i.e. Ostwald ripening) spontaneously occur, where the kinetics are controlled by the annealing and glass transition temperatures. This study was motivated to observe the progress of glassy state relaxation separate from ice coarsening during annealing. X-ray computed tomography (CT) was used to observe a frozen and post-freezing annealed solutions by using monochromatized X-ray from the synchrotron radiation. CT images were successfully obtained, and the frozen matrix were analyzed based on the gray level values that were equivalent to the linear X-ray attenuation coefficients of the observed matters. The CT images obtained from rapidly frozen sucrose and dextrin solutions with different concentrations gave clear linear relationships between the linear X-ray attenuation coefficients values and the solute concentrations. It was confirmed that the glassy state relaxation progressed as increasing annealing time, and this trend was larger in the order of the glass transition temperature of the maximally freeze-concentrated phase. The sucrose-water system required nearly 20 h of annealing time at -5 °C for the completion of the glassy phase relaxation, whereas dextrin-water systems required much longer periods because of their higher glass transition temperatures. The trends of ice coarsening, however, did not perfectly correspond to the trends of the relaxation, suggesting that the glassy phase relaxation and Ostwald ripening would jointly control the ice crystal growth/ripening kinetics, and the dominant mechanism differed by the annealing stage.