# Accumulation of Vitamin C in Yeast under Pulsed Electric Field (PEF) Conditions
## 3 Results and Discussion
### Optimal PEF Conditions for Vitamin C Accumulation in Yeast
Ascorbic acid containing liposomes were prepared by rehydration and the stability of this compound was compared with that of unbound ascorbic acid. The results showed that the free ascorbic acid completely disappeared from the solution after 20 days at 4 \({}^{\circ}\)C, and after 6 days at room temperature. In the case of ascorbic acid encapsulated in liposomes at 4 \({}^{\circ}\)C, the loss of vitamin C was 40% after 50 days of storage. At room temperature, the loss was greater, but not as fast as for free ascorbic acid. After 50 days, almost 20% of the ascorbic acid was present in microencapsulated form. In the case of the studies by [PERSON] et al. [42], long-term storage for 12 and 18 months resulted in reductions in the content of vitamin C (enclosed in a bed of maltodext) by less than 2% and by 4%, respectively. Thus, it can be seen that the use of encapsulating materials such as derivatized starch, liposomes, and maltodext resulted in better storage of vitamin C, and its content was much higher compared to ascorbic acid encapsulated in yeast. The likely cause was different encapsulating material that more effectively protected vitamin C against degradation. Figure 7 presents the antioxidant activity of an extract obtained from PEF-treated yeast, fresh and stored for 7, 14, and 28 days. The extract from fresh yeast had the highest antioxidant activity. The storage of yeast with accumulated vitamin C at 20 \({}^{\circ}\)C after prior freeze-drying and at \(-\)22 \({}^{\circ}\)C had only a slight effect on this parameter. A significant reduction was observed in the antioxidant activity of the yeast extract with vitamin C in the samples stored at 4 \({}^{\circ}\)C. After 28 days of storage, it was 2.5 times lower than that of the fresh yeast extract. Figure 6: Effect of storage time (0-fresh yeast, 7, 14, 28 days) on vitamin C content in yeast cultures treated with PEF (vitamin C, 5 mg/mL medium; voltage, 1000 V; pulse width, 10 \(\upmu\)s; treatment time, 20 min; number of pulses, 1200; after 20 h of cultivation). Each value is the mean \(\pm\) standard deviation (\(n=3\)). Bars with the same letter (a–i) are not significantly different (\(p<0.05\)). [PERSON] et al. [43] analyzed the antioxidant properties of vitamin C-rich juices. Antioxidant abilities were tested using the DPPH and ABTS radical methods. It was shown that acerola and rosehip juices had the highest antioxidant capacity tested against the DPPH radical (21.4 mM Trolox), followed by Japanese quince juice (17.9 mM Trolox). The lowest antioxidant capacity was found in cranberry (7.9 mM Trolox) and sea buckthorn (9.8 mM Trolox) juices. Our research showed that the antioxidant activity of the extract from yeast subjected to the electroporation process and not stored (23.5 mM Trolox) is comparable to that of juices containing high amounts of vitamin C.  
Our research also showed that the yeast extract alone, not enriched with vitamin C (control sample C1), has specific antioxidant activity. The likely reason is that other ingredients present in the yeast exhibit this property. [PERSON] et al. [44] assessed the nutritional value, antioxidant activity, and phenolic compound profile of the spent brewer's yeast extract. It was shown that the extract from the inner layer of yeast is a rich source of protein, B vitamins, including vitamins B3, B6, and B9, and minerals such as sodium, potassium, calcium, magnesium, and iron. Chromatographic analysis showed that the yeast extract contained phenolic compounds such as gallic acid, protocatechic acid, \(p\)-coumaric acid, ferulic acid, and cinnamic acid. It can therefore be assumed that thanks to these ingredients the yeast itself has an antioxidant effect and yeast extract may be a potential ingredient for the preparation of functional foods and nutraceuticalals. Conceptualization, M.S. and K.N. ; methodology, M.S. and U.P. ; validation, M.S., E.Z. and U.P. ; investigation, K.N. ; resources, K.N, E.Z. and U.P. ; writing--original draft preparation, K.N. ; writing--review and editing, M.S. ; visualization, K.N.