Cellulose nanofiber (CNF)–sakacin‐A active material: production, characterization and application in storage trials of smoked salmon

Abstract

BACKGROUND Sakacin‐A due to its specific antimicrobial activity may represent a good candidate to develop active packaging solutions for food items supporting Listeria growth. In the present study a protein extract containing the bacteriocin sakacin‐A, produced by Lactobacillus sakei Lb 706 in a low‐cost culture medium containing deproteinized cheese whey, was adsorbed onto cellulose nanofibers (CNFs) to obtain an active material to be used as a mat (or a separator) in direct contact with foods. RESULTS The applied fermentation conditions allowed 4.51 g L −1 of freeze‐dried protein extract to be obtained, characterized by an antimicrobial activity of near 16 700 AU g −1 , that was used for the preparation of the active material by casting. The active material was then characterized by infrared spectra and thermogravimetric analyses. Antimicrobial trials were carried out in vitro using Listeria innocua as indicator strain; results were also confirmed in vivo, employing smoked salmon fillets intentionally inoculated with Listeria innocua : its final population was reduced to about 2.5—3 Log cycles after 28 days of storage at 6 °C in presence of sakacin‐A, compared with negative control mats produced without the bacteriocin extract. CONCLUSION This study demonstrates the possibility of producing an antimicrobial active material containing sakacin‐A absorbed onto CNFs to decrease Listeria population in smoked salmon, a ready‐to eat‐food product. © 2019 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

From Cheese Whey Permeate to Sakacin A: A Circular Economy Approach for the Food-Grade Biotechnological Production of an Anti-Listeria Bacteriocin

“…As previously explained, pH time course cannot be considered totally representative of sakacin A production due to the possible activation of the ADI pathway with consequent NH 3 production. On the contrary, as lactic acid production is directly linked to bacterial growth, its concentration can be correlated to the presence of sakacin A [27]; concentrations of lactic acid higher than 2 g/L were found when YE concentration was set at its maximum level and above all when in presence of ME, while arginine seems not to be correlated with microbial growth and lactic acid production. Table 3.…”

“…Even if slightly higher L. sakei growth (final OD) was obtained in MRS, growth rates were always higher in SAK, highlighting that the formulation containing CWP can effectively support L. sakei growth. The quantification of the antimicrobial activity confirmed that the highest sakacin A production was reached at the end of the exponential phase of each curve [27,35], i.e., at 8 h for cultures inoculated at 5% (v/v) (300 and 333 AU/mL in MRS and SAK respectively) and 16 h for 0.1-0.5% (v/v) (233-267 AU/mL). As expected, the lag phase significantly decreased with the increase of inoculum percentage for both media and, regardless to the inoculum, longer in SAK.…”

“…Compared with the values obtained in MRS (5.40 €/L, 18.00 €/10 6 AU), a 70% decrease in the production costs was reached in this study. Mapelli et al [27] employing the non-optimized SAK formulation, resulted in 2.33 €/L and 8.06 €/10 6 AU, around 30% higher. Trinetta et al [30] reported, for sakacin A, higher production costs (2.9 €/L), 50% more expensive medium containing bacto peptone, meat peptone, cheese whey, yeast autolysate, glucose and calcium carbonate.…”

“…A culture medium for L. sakei (SAK-medium) was initially used, having the following composition: meat extract, ME (VWR) 8 g/L; yeast extract, YE (Costantino srl, Turin, Italy) 8 g/L; arginine, ARG (Merck K GaA) 0.5 g/L; Tween-80 (Merck K GaA) 0.5 mL/L, minerals and vitamins mix 1 mL/L as reported by Mapelli et al [27]. Ingredients were dissolved in liquid CWP, kindly supplied by Latteria Soresina (Soresina, Italy).…”

“…All minerals present in MRS (sodium acetate, MgSO 4 , MnSO 4 , ammonium citrate, potassium phosphate) were avoided and replaced by those naturally present in CWP. The initial concentration of ME, YE and the other ingredients, dissolved in CWP, have been chosen on the basis of previously published data [26,27]. The presence of arginine was evaluated to investigate the possibility of promoting the arginine deiminase (ADI) pathway, adopted by a variety of bacterial species for obtaining further ATP for cell growth and NH 3 that helps in maintaining the pH to physiological levels.…”