Development of a low-cost non-destructive system for measuring moisture and salt content in smoked fish products

[EN] In this study, a new method to assess salt content in smoked fish products using impedance spectroscopy has been developed. Two fish species (salmon and cod) from two different brands were analyzed. The analyses carried out were moisture, lipid, and salt contents, as well as a(w). Impedance measurements were performed directly in different locations on smoked product by using a coaxial needle. The modulus and phase of the spectra of impedance were acquired between 1 Hz and 1 MHz, for 50 values of frequency. The impedance modulus and phase values were used to predict the studied physico-chemical parameters, by using the PLS method. In general, the highest lipid contents and the lowest moisture values were observed in salmon samples, independently of the brand and the batch analyzed. The results showed a high variability between batches of a same product, regarding to moisture and salt content. Prediction models were established for all the samples studied and also individually for each product. A higher accuracy of prediction was obtained for the PLS models established for each product compared with the model applied for all samples. In general, the highest R-2 was obtained for prediction of a(w) parameter, followed by moisture content. The best correlations were obtained for smoked cod samples independently of the brand. These results can be explained by the isolating effect of the fat. Due to the differences in the raw material composition, a single model cannot be applied for all the products. A previous characterization of the raw material would improve the accuracy of the developed methodology. These results show the feasibility of the impedance spectroscopy to determine salt and moisture contents.Karaskova, P.; Fuentes López, A.; Fernández Segovia, I.; Alcañiz Fillol, M.; Masot Peris, R.; Barat Baviera, JM. (2011). Development of a low-cost non-destructive system for measuring moisture and salt content in smoked fish products. Procedia Food Science. 1:1195-1201. doi:10.1016/j.profoo.2011.09.178S11951201

Strand specific RNA-sequencing and membrane lipid profiling reveals growth phase-dependent cold stress response mechanisms in Listeria monocytogenes

The human pathogen Listeria monocytogenes continues to pose a challenge in the food industry, where it is known to contaminate ready-to-eat foods and grow during refrigerated storage. Increased knowledge of the cold-stress response of this pathogen will enhance the ability to control it in the food-supply-chain. This study utilized strand-specific RNA sequencing and whole cell fatty acid (FA) profiling to characterize the bacterium's cold stress response. RNA and FAs were extracted from a cold-tolerant strain at five time points between early lag phase and late stationary-phase, both at 4°C and 20°C. Overall, more genes (1.3×) were suppressed than induced at 4°C. Late stationary-phase cells exhibited the greatest number (n = 1,431) and magnitude (>1,000-fold) of differentially expressed genes (>2-fold, p<0.05) in response to cold. A core set of 22 genes was upregulated at all growth phases, including nine genes required for branched-chain fatty acid (BCFA) synthesis, the osmolyte transporter genes opuCBCD, and the internalin A and D genes. Genes suppressed at 4°C were largely associated with cobalamin (B12) biosynthesis or the production/export of cell wall components. Antisense transcription accounted for up to 1.6% of total mapped reads with higher levels (2.5×) observed at 4°C than 20°C. The greatest number of upregulated antisense transcripts at 4°C occurred in early lag phase, however, at both temperatures, antisense expression levels were highest in late stationary-phase cells. Cold-induced FA membrane changes included a 15% increase in the proportion of BCFAs and a 15% transient increase in unsaturated FAs between lag and exponential phase. These increases probably reduced the membrane phase transition temperature until optimal levels of BCFAs could be produced. Collectively, this research provides new information regarding cold-induced membrane composition changes in L. monocytogenes, the growth-phase dependency of its cold-stress regulon, and the active roles of antisense transcripts in regulating its cold stress response