L ascorbic acid

Methanol and n-hexane of high purity were purchased from Honeywell Specialty Chemicals Seelze GmbH (Hannover, Germany). L-ascorbic acid and anhydrous sodium sulfate were obtained from Chempur (Piekary Śląskie, Poland), and potassium hydroxide was purchased from POCH (Zabrze, Poland). Water for sample preparations was purified through SolPure XIO P (ELKAR, Kęty, Poland).

Fermented milk was produced from Łaciate milk (2% fat) from SM Mlekpol (Grajewo, Poland). Organic powder of rosehips (Rosa canina L.) (400 mg of vitamin C × 100 g⁻¹) came from RADZIOWI SP. z.o.o. (Częstochowa, Poland). Acerola in powder form (25,000 mg vitamin C × 100 g⁻¹) was purchased from Aliness Health’n’beauty (Karczew, Poland) and L(+) ascorbic acid from Chempur (Piekary Śląskie, Poland). The starter culture of probiotic bacteria (Lactobacillus rhamnosus) was purchased from Chr. Hansen (Hoersholm, Denmark). MRS agars and peptone water came from Biocorp (Warszawa, Poland). Sodium hydroxide, phenolphthalein, ascorbic acid, sodium bicarbonate, oxalic acid, 2,6-dichlorophenolindophenol, were purchased from Chempur (Piekary Śląskie, Poland).
All of the reagents used were of analytical reagent grade.