From cheese whey permeate to Sakacin-A/bacterial cellulose nanocrystal conjugates for antimicrobial food packaging applications: a circular economy case study.

Applying a circular economy approach, this research explores the use of cheese whey permeate (CWP), by-product of whey ultrafiltration, as cheap substrate for the production of bacterial cellulose (BC) and Sakacin-A, to be used in an antimicrobial packaging material. BC from the acetic acid bacterium Komagataeibacter xylinus was boosted up to 6.77 g/L by supplementing CWP with ß-galactosidase. BC was then reduced to nanocrystals (BCNCs, 70% conversion yield), which were then conjugated with Sakacin-A, an anti-Listeria bacteriocin produced by Lactobacillus sakei in a CWP based broth. Active conjugates (75 Activity Units (AU)/mg), an innovative solution for bacteriocin delivery, were then included in a coating mixture applied onto paper sheets at 25 AU/cm2. The obtained antimicrobial food package was found effective in reducing Listeria population in storage trials carried out on a fresh Italian soft cheese (named "stracchino") intentionally inoculated with Listeria. Production costs of the active material have been mainly found to be associated (90%) to the purification steps. Setting a maximum prudential 50% cost reduction during process up-scaling, conjugates coating formulation would cost around 0.89 €/A4 sheet. Results represent a practical example of a circular economy production procedure by using a food industry by-product to produce antimicrobials for food preservation.

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

Cheese Whey Permeate (CWP) is the by-product of whey ultrafiltration for protein recovery. It is highly perishable with substantial disposal costs and has serious environmental impact. The aim of the present study was to develop a novel and cheap CWP-based culture medium for Lactobacillus sakei to produce the food-grade sakacin A, a bacteriocin exhibiting a specific antilisterial activity. Growth conditions, nutrient supplementation and bacteriocin yield were optimized through an experimental design in which the standard medium de Man, Rogosa and Sharpe (MRS) was taken as benchmark. The most convenient formulation was liquid CWP supplemented with meat extract (4 g/L) and yeast extract (8 g/L). Although, arginine (0.5 g/L) among free amino acids was depleted in all conditions, its supplementation did not increase process yield. The results demonstrate the feasibility of producing sakacin A from CWP. Cost of the novel medium was 1.53 €/L and that of obtaining sakacin A 5.67 €/106 AU, with a significant 70% reduction compared to the corresponding costs with MRS (5.40 €/L, 18.00 €/106 AU). Taking into account that the limited use of bacteriocins for food application is mainly due to the high production cost, the obtained reduction may contribute to widening the range of applications of sakacin A as antilisterial agent.

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

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.

The Paxillin-like protein AgPxl1 is required for apical branching and maximal hyphal growth in A.gossypii.

The development from young, slowly growing hyphae to fast growing hyphae in filamentous fungi is referred to as hyphal maturation. We have identified the Paxillin-like protein AgPxl1 in Ashbyagossypii as a developmental protein that is specifically required for hyphal maturation. The early development of A.gossypii strains lacking AgPxl1 is indistinguishable from wild-type. However, at later developmental stages the maximal hyphal extension rate is less than half compared to wild-type and apical branching is affected. Apical branching is characterised as the symmetric division of fast growing hyphal tips resulting in two sister hyphae. In Agpxl1Delta strains two thirds of the apical branching events lead to asymmetric sister hyphae where growth of one branch is either completely aborted or slowed down while extension of the other branch is not affected. This suggests that AgPxl1 plays a role in the organisation of growth and efficient division of growth upon apical branching in mature mycelia. The conserved C-terminal LIM domains are necessary for AgPxl1 function and also contribute to tip localisation. AgCLA4, a PAK-like kinase, is epistatic to AgPXL1 and robust localisation of AgPxl1 depends on AgCla4. This suggests that AgCla4 acts upstream of AgPxl1.