Faculty of Food Technology and Biotechnology, University of Zagreb
Abstract
Hydroxycinnamic acids (HAs) have a potential application in the food and pharmaceutical industry because they are rich in phenolics. Feruloyl esterases release phenolic compounds from plant cell walls. Coffee pulp is rich in HAs linked to polysaccharides. A solvent extraction of free HAs was performed with aqueous methanol (80 %). A response surface methodology was applied to optimise the extraction of these compounds from coffee pulp, and the best results were obtained at 56 °C for 34 min. Alkaline and acid hydrolyses were performed to evaluate the content of linked HAs. Treated (extracted) coffee pulp was used to produce feruloyl esterases in solid-state fermentation by Aspergillus tamarii V12307, previously selected by a hydrolysis plate assay. Different dilutions of a culture medium were added to the coffee pulp, and the diluted medium with half the nutrients allowed for higher CO2 production. A specific growth rate (μCO2 ) of 0.25 h^–1 and a lag phase (tlag) of 14.3 h were observed under the selected conditions. Finally, enzymatic activities were 14.0 and 10.8 nkat per g of dried matter when methyl and ethyl ferulate were used as substrates, respectively. Productivities (9.3 and 7.2 nkat per g of dried matter per day, respectively) were higher when compared to other studies carried out in solid-state fermentation. Utilisation of coffee pulp for enzyme production improves the added value of this abundant by-product of the coffee industry.Hidroksicinamične se kiseline mogu upotrijebiti u prehrambenoj i farmaceutskoj industriji, jer su bogate fenolima, koje enzim feruloil esteraza oslobađa iz staničnih stijenki biljaka. Otpad koji nastaje pri proizvodnji kave bogat je hidroksicinamičnim kiselinama vezanim za polisaharide. Ekstrakcija tih spojeva vodenom otopinom metanola (80 %) optimirana je pomoću metode odzivnih površina, a najbolji su rezultati postignuti pri 56 °C tijekom 34 minute. Alkalnom je i kiselom hidrolizom procijenjen udio vezanih hidroksicinamičnih kiselina. Pomoću odabranoga soja Aspergillus tamarii V12307 proizvedena je feruloil esteraza fermentacijom na čvrstoj podlozi od otpada nastalog pri proizvodnji kave. Otpadu su dodana različita razrjeđenja podloge za uzgoj, pri čemu je proizvedeno više CO2 primjenom podloge koja sadržava 50 % hranjiva. Pritom je specifična brzina rasta (μCO2) bila 0,25 h-1, a lag je faza (tlag) iznosila 14,3 h. Uporabom metil ferulata kao supstrata postignuta je aktivnost enzima od 14 nkat/g suhe tvari i produktivnost od 9,3 nkat/g suhe tvari po danu, dok je pomoću etil ferulata dobivena aktivnost enzima od 10,8 nkat/g suhe tvari i produktivnost od 7,2 nkat/g suhe tvari po danu. Produktivnost je procesa bila veća nego u prijašnjim istraživanjima. Primjenom otpada nastalog pri proizvodnji kave u proizvodnji enzima povećala se dodana vrijednost tog nusproizvoda
