Faculty of Food Technology and Biotechnology, University of Zagreb
Abstract
The aim of this work is to demonstrate the role of conidial spores as a reservoir of glucose oxidase and their stability as a biocatalyst in the bioconversion reaction for the production of gluconic acid. Solid-state fermentation (SSF) was carried out in fixed-bed column bioreactor for the production of Aspergillus niger spores. Growth parameters, sporulation and kinetics of gluconic acid production were analysed at different time intervals during the course of SSF. Spores of different age (48–216 h) were used as biocatalysts in the bioconversion reaction. Spores harvested at a later period of SSF (196 h) produced high titres of gluconic acid (30 g/L) in the bioconversion medium when compared to the spores harvested at early (48 h) stages of SSF (2.2 g/L). Spores (harvested at 200 h and stored in freezer for 91 days) exhibited the same glucose oxidase activity and served as an active and stable catalyst when compared to the fresh spores, showing that aging (storage) did not affect enzymes present in the spores, which suggested that the spores acted as an efficient enzyme reservoir. Yields close to 93 % were obtained with 98 g/L of gluconic acid production, corresponding to an average productivity of 1.7 g/(L·h). The stability of the enzyme in the spores and the ability of conidia to be stored for a long time without the loss of activity add specific advantage to the bioconversion process.Svrha je rada bila dokazati važnost konidijskih spora kao izvora glukoza-oksidaze, te istražiti stabilnost tih biokatalizatora pri proizvodnji glukonske kiseline. Spore plijesni Aspergillus niger proizvedene su uzgojem na čvrstoj podlozi u kolonskom bioreaktoru s nasutim slojem. Tijekom fermentacije, u različitim vremenskim intervalima, ispitani su parametri rasta, sporulacija i kinetika proizvodnje glukonske kiseline. Kao biokatalizator upotrijebljene su spore različite dobi (48-216 h). Spore dobivene nakon 196 h uzgoja proizvele su biokonverzijom mnogo glukonske kiseline (30 g/L), za razliku od spora prikupljenih nakon 48 h, koje su proizvele samo 2,2 g/L glukonske kiseline. Spore prikupljene nakon 200 h, čuvane 91 dan u zamrzivaču, imale su istu aktivnost glukoza-oksidaze kao i svježe spore, pa su upotrijebljene kao aktivni i stabilni katalizator. Time je dokazano da sazrijevanje (skladištenje) ne utječe na enzime u sporama, te da one mogu biti učinkovito spremište enzima. Pri proizvodnji 98 g/L glukonske kiseline, tj. produktivnosti od 1,7 g/(L·h) postignuto je skoro 93 %-tno iskorištenje. Prednosti su procesa biokonverzije stabilnost enzima u sporama i sposobnost skladištenja konidija duže vrijeme bez gubitka njihove aktivnosti
