Effect of temperature on nitrite and water diffusion in pork meat

Microbial succession and its correlation with the dynamics of flavor compounds involved in the fermentation of Longxi bacon

Introduction

Longxi bacon is a traditional fermented meat from Gansu province, China. The ripening process of the bacon is crucial for quality and flavor. The aim of this study was to gain deeper knowledges on the bacterial and fungal community diversity and the changes of chemical components including fatty acids and volatile compounds at different time points during the ripening of the bacon and to understand the relationship between microbial profiles and the chemical components related the bacon flavor.

Methods

Bacon samples were collected from days 0, 15, 30, 60 and 90. The bacterial and fungal compositions were analyzed with next generation sequencing targeting the 16S rDNA loci for bacteria and ITS loci for fungi. The fatty acids and the volatile components were analyzed by headspace solid phase micro extraction followed by gas chromatography/mass spectrometry (HS-SPME-GC/MS).

Results

We found that the abundance of bacteria in bacon was higher than that of fungi, and Psychrobacter, Brochothrix, Phoma and Trichoderma was the dominant bacon's population. The largest contributors of volatiles were aldehydes, ketones and esters, and the main fatty acids were palmitic, oleic and linoleic acids. Pearson correlation analysis between microbial succession and key flavor substances showed that the production of Longxi bacon flavor is the result of a combination of bacteria and fungi. Ten bacteria genera and six fungi genera were determined as functional core microbiota for the flavor production based their dominance and functionality in microbial community. In addition, bacteria and fungi are involved in the oxidation and hydrolysis of fatty acids during the ripening of bacon, which also contributes to the formation of bacon flavor.

Discussion

This study provides a comprehensive analysis of the key microbiota involved in shaping bacon's distinctive flavor. Here, the results presented should provide insight into the influence of the microenvironment on the microbial community in bacon and lay a foundation for further investigations into the food ecology of bacon.

Mass transfer modeling during wet salting of caiman meat (Caiman crocodilus yacare) at different brine temperatures

Caiman meat is considered exotic and its consumption has significantly increased due to its nutritional quality. This study aimed to evaluate the kinetics of water content (WC) and salt content (SC) at different temperatures (1, 5, 10 and 15 °C) and to evaluate the use of mathematical models to predict the mass transfer kinetics until equilibrium conditions during the wet salting of caiman tail fillets. Moisture and chloride analyses were performed throughout the wet salting process. Four models (Peleg; Weibull; Zugarramurdi and Lupín; Diffusion) were tested to predict WC and SC kinetics in caiman tail fillets subjected to wet salting. The increase in the temperature resulted in a reduction (P < 0.05) in WC and an increase (P < 0.05) in SC. Nonlinear effects on WC and SC kinetics were observed between the different temperatures evaluated. Furthermore, the effective diffusion coefficients (D_w and D_s) increased (P < 0.05) with increasing temperature. Peleg, Weibull, Zugarramurdi and Lupín, and the Diffusion model satisfactorily represented WC and SC rates throughout the process. The kinetic behavior of the parameters of the models corroborated the effects of temperature on those parameters. Peleg was the best model for predicting WC and SC kinetics, and Zugarramurdi and Lupín was the best for predicting the equilibrium conditions of the process (WC^∞ SC^∞), all parameters which can be used to describe the mass transfer kinetics during wet salting of caiman tail fillets.

Advanced Glycation End Products and Nitrosamines in Sausages Influenced by Processing Parameters, Food Additives and Fat during Thermal Processing

Advanced glycation end products (AGEs) and nitrosamines (NAs) in sausage are associated with pathogenic and carcinogenic risks. However, the multiple reaction parameters affecting the production of AGEs and NAs during sausage processing remain unclear. This experiment evaluated the effects of processing parameters, food additives and fat ratios on the formation of AGEs and NAs in sausages. The results showed a 2-3-fold increase in N^ε-(carboxymethyl)lysine (CML) and N^ε-(carboxyethyl)lysine (CEL) when the sausage processing temperature was increased from 90 °C to 130 °C, and N-nitrosodimethylamine (NDEA) increased from 3.68 ng/g to 6.41 ng/g. The addition of salt inhibited the formation of AGEs and NAs, and the inhibitory ability of 2 g/100 g of salt was 63.6% for CML and 36.5% for N-nitrosodimethylamine (NDMA). The addition of 10 mg/kg nitrite to sausages reduced CML formation by 43.9%, however, nitrite had a significant contribution to the formation of NAs. The addition of fat only slightly contributed to the production of CML. In addition, the relationship between α-dicarbonyl compounds and the formation of AGEs was investigated by measuring the changes in α-dicarbonyl compounds in sausages. The results showed two trends of AGEs and α-dicarbonyl compounds: AGEs increased with the increase in α-dicarbonyl compounds and AGE level increased but α-dicarbonyl compound level decreased.

Changes in moisture, colour, residual nitrites and N-nitrosamine accumulation of bacon induced by nitrite levels and dry-frying temperatures

The effects of different nitrite levels (50, 100, and 150 mg/kg meat) and dry-frying temperatures (100, 150, 200 and 250 °C) on the moisture movement, colour, sensory variables and residual nitrite and N-nitrosamine levels in smoked bacon were investigated. Increasing the dry-frying temperatures significantly increased the cooking loss and decreased the moisture content (P < 0.05). The bacon L*-values showed an increasing trend at first and then decreased, with the highest value of the bacon with 150 mg/kg nitrite was obtained at 100 °C and 150 °C. In addition, a*-values were significantly affected by the nitrite level and dry-frying temperature (P < 0.05), with the highest value of the bacon samples with 100 and 150 mg/kg nitrite observed at 250 °C. The residual nitrite content level initially increased (from unheated control to 150 °C) and then decreased (from 150 to 250 °C) sharply with increasing dry-frying temperatures in the bacon samples with the same sodium nitrite levels. N-methyl-N-nitrosoaniline (NMPhA) and N-nitrosomorpholine (NMOR) were measured in a number of smoked bacon samples, and a significant positive correlation (R² = 0.772) was found for N-nitrosamines (NA) contents and nitrite levels (P < 0.05). The maximum levels of NMPhA and NMOR were detected when the bacon with 150 mg/kg sodium nitrite was pan-fried at 200 °C and 150 °C, respectively.

New application for TiO2 P25 photocatalyst: A case study of photoelectrochemical sensing of nitrite ions

Developing photoelectrochemical (PEC) sensors based on photocatalytic materials has recently attracted great interest as an emerging technology for environmental monitoring. TiO₂ P25 is a well-known highly active photocatalyst, cheap, and produced commercially on a large scale. In the current work, a practical and durable TiO₂-based PEC sensor has been fabricated by immobilizing TiO₂ P25 nanoparticles at disposable screen-printed carbon substrates using drop-casting method. The fabricated PEC sensor has been applied for the anodic-detection and determination of nitrite (NO₂^-) ions under UV(A) light (LED, 365 nm) using chronoamperometry (CA) and differential pulse voltammetry (DPV). Linear calibration curves were obtained between the photocurrent responses and the concentrations of NO₂^- ions in the ranges of 0.1-5.0 and 0.5-10 mg L^-1 for CA and DPV, respectively. Surprisingly, the detection limits (sensitivities) of the fabricated sensor towards NO₂^- ions under light were enhanced by a factor of 4.75 (4.1) and 8.3 (37.4) for CA and DPV, respectively, in comparsion with those measured in the dark. It is found that the photo-excitation of TiO₂ facilitates the photooxidation of NO₂^- ions via the photo-generated holes whereas the photogenerated electrons contribute to the enhanced photocurrent and consequently the enhanced detection limit and sensitivity. The fabricated TiO₂-based PEC sensor exhibits a good stability, durability, and satisfying selectivity for NO₂^- ions determination. These results indicate that the TiO₂-based PEC sensor fabricated by utilizing cheap and commercially available components has great potential for being transferred from lab-to-factory.

Dielectric properties of fresh rabbit meat in the microwave range

Dielectric properties (DPs) of fresh rabbit meat in the microwave range (0.5 to 20 GHz) were determined. Three different muscles (Biceps femoris, Tensor fasciae latae, and Longissimus thoracis) from California rabbits (male and female) were measured with the open-ended coaxial probe method at temperatures of 20, 40, and 60 °C. To assess the possible effect of age, females of 100 and 180 days old were analyzed. DPs were affected by frequency, muscle type, age, gender, and temperature (p < 0.05). Dielectric constant decreased with increasing frequency. Loss factor decreased from 0.5 to 2.5 GHz due to ionic conduction, followed by an increase up to 20 GHz, dominated by dipolar relaxation. PRACTICAL APPLICATION: These results are key parameters for further quality sensing applications and for heating processes of meat rabbit using microwaves. Longer penetration depths were achieved at 915 MHz; this frequency is recommended for further applications. Besides, dielectric properties have potential to be a tool for identification of gender and age for slaughtered rabbits.

Effect of Acid Marination Assisted by Power Ultrasound on the Quality of Rabbit Meat

The consumption of rabbit meat is scarce in Mexico, despite its good taste and high protein content. Acid marination may be an option to introduce this meat into new markets and add value to this food. The use of ultrasound has been reported as an accelerator in the impregnation process and improving the product quality. The objective of this study was to evaluate the effect of acid marination assisted by power ultrasound on quality of rabbit meat. Marinating solutions were prepared with 70, 140, or 200 g NaCl/L, 3 g NaNO2, and 1.5% citric acid. Rabbit meat slices were immersed in every solution in static and ultrasonic bath at 40 kHz and 110 W of output power. Marinating time, NaCl concentration in the marinating solution, and US application increased weight losses and meat hardness but reduced water content, WHC, and pH. The color parameters L⁎ and a⁎ increased with the NaCl concentration in marinating solution and with the ultrasound application. NaCl content increased in meat with increased marinating time, NaCl concentration in marinating solutions, and higher rate in ultrasonic treatment. Application of ultrasound has high potential to be employed in the marinating of rabbit meat samples, diminishing the immersion time, and maintaining the quality.