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Highlights-PLA nanoparticles loaded with Thymol were prepared for the first time.-The PLA was found to be the key variable in optimizing the nanoparticle preparation.-The nanoparticles exhibited a high storage stability over a wide range of pHs.-The antimicrobial activity of the nanoparticles was tested on apple pieces.

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Acid whey causes a major disposal problem for the dairy industry due to its low pH and high salt concentration. Lactobionic acid (LBA) production by whey fermentation is an inexpensive process. The goal of this work was to employ acid whey for LBA production. Acid whey was fermented in a bioreactor, adding Pseudomonas taetrolens LMG 2336 at 30°C and 6.5 pH, with 1.5-Lpm oxygen aeration and 350-rpm agitation. Three fermentation tests were carried out with a different amount of inoculum (10%, 30% and 10% three times within 24 h). Results indicated that repeatedly adding P. taetrolens inoculum to the acid whey substrate allows a complete lactose conversion into LBA, while the lactose oxidation process was insufficient in the sample where the inoculum was only added at the beginning of the fermentation process (only 29.7% LBA production with 10% inoculum). The physiological heterogeneity of P. taetrolens was determined by multiparametric flow cytometry, and results showed that there was a phenotypic adaptation of the microorganism due to the changes observed in its heterogeneity and physiological state. The results achieved will help to recycle acid whey for value-added product production such as LBA production.