| Abstract | Lješnjak je jedna od najpopularnijih vrsta jezgrastih plodova koji se mogu konzumirati kao svježi
ili prerađeni, najčešće pečeni / tostirani. Osim spomenutog, popularna je proizvodnja i
različitih proizvoda od lješnjaka poput slatkih namaza, ulja i brašna. Izazov prilikom
proizvodnje, odnosno prerade lješnjaka predstavlja građa ploda, a s obzirom da na ljusku
otpada čak 50 % ukupne mase ploda, što u konačnici može predstavljati značajan problem
prilikom zbrinjavanja iste. Naime, ljuska ploda lješnjaka koja zaostaje nakon prerade je
nusproizvod koji se tretira kao kategorija biootpada. Istovremeno, s obzirom na činjenicu kako
je i ljuska vrlo bogata sadržajem specifičnih fitokemikalija, posebno polifenolnih spojeva,
brojne su mogućnosti iskorištenja njenog punog potencijala. Stoga je i cilj ovog rada bio
valorizirati nutritivni potencijal ljuske i jezgre dviju sorti lješnjaka te utvrditi mogućnosti
oporabe ljuske lješnjaka ultrazvukom visokog intenziteta za izdvajanje polifenola. U istraživanju
je analiziran sadržaj polifenolnih spojeva i antioksidacijski kapacitet ljuske i jezgre svježih
plodova lješnjaka dviju sorti, 'Rimski' i 'Istarski', a nakon čega je ljuska ploda za svaku sortu
odvojena ručno i laboratorijskim mlinom usitnjena u prah koji je korišten za testiranje tretmana
ultrazvukom visokog intenziteta (UZV). Za potrebe ultrazvučno potpomognute ekstrakcije
korišten je sustav sonde, a varirana je koncentracija otapala, etilnog alkohola 50 i 80 % (v/v),
amplituda uređaja (40 i 60 %) i vrijeme tretmana (10, 15 i 25 min). Kontrolni uzorak
predstavljao je klasični tretman maceracijom u trajanju od 24 sata 50 i 80 %-im etanolom.
Uspoređujući rezultate ukupnih fenola, flavonoida, neflavonoida i antioksidacijskog kapaciteta
između ljuske i jezgre obje sorte lješnjaka, najviše vrijednosti svih navedenih parametara
utvrđene su za ljusku ploda. Usporedbom načina ekstrakcije, klasično i UZV potpomognuto,
značajno više vrijednosti ukupnih fenola, flavonoida i neflavonoida zabilježene su u ekstraktima
ljuske obje istraživane sorte lješnjaka tretiranim UZV u usporedbi s uzorcima tretiranim
klasično. Također, sukladno visokim vrijednostima polifenolnih spojeva, značajno viši
antioksidacijski kapacitet utvrđen je za ekstrakte ljuske tretirane UZV u usporedbi s klasičnim
načinom ekstrakcije. Prilikom testiranja parametara ekstrakcije, svi varirani faktori utjecali su
na sadržaj ukupnih polifenola i antioksidacijski kapacitet. Koncentracija otapala (alkohola
etanola) značajno je utjecala na prinos polifenolnih spojeva, tako je koncentracija etanola od
80 % (v/v) dala veće prinose u usporedbi s 50 % etanolom. Kod ultrazvučne ekstrakcije varirane
su amplituda i vrijeme tretmana, prilikom čega su duže vrijeme tretmana (25 minuta) te viša
amplituda (60 %) pozitivno utjecali na ukupni sadržaj fenola, flavonoida, neflavonoida i
antioksidacijskog kapaciteta. Za kraj valja istaknuti kako je ljuska obje analizirane sorte
lješnjaka vrlo bogat izvor polifenolnih spojeva te se stoga može smatrati nutritivno visoko
vrijednim nusproizvodom s brojim potencijalnim funkcionalnim svojstvima i mogućnostima
upotrebe u zamjenu za njezino zbrinjavanje kao biootpada. Ultrazvuk visokog intenziteta
pokazao se izuzetno učinkovitim u izolaciji polifenolnih spojeva iz ljuske lješnjaka čime se ta
procesna tehnologija može smatrati potencijalnom za daljnju oporabu nusproizvoda
proizvodnje lješnjaka. |
| Abstract (english) | Hazelnuts are one of the most popular types of nuts, which can be eaten fresh or processed,
usually baked/roasted. In addition, the production of various hazelnut products such as sweet
spreads, oil and flour is also very popular. The challenge in producing and processing hazelnuts
is the structure of the fruit, considering that the shell accounts for up to 50% of the total mass
of the fruit, this can ultimately pose a significant problem when it comes to disposal. The shell
of the hazelnut fruit that remains after processing is a by-product that is treated as bio-waste.
Considering that the shell is also very rich in phytochemicals, particularly polyphenolic
compounds, there are numerous opportunities to exploit its full potential. The aim of this work
was therefore to evaluate the nutritional potential of the shell and kernel of two hazelnut
varieties and to determine the possibilities of extracting polyphenols from the hazelnut shell
using high-intensity ultrasound. As part of the study, the content of polyphenolic compounds
and antioxidant capacity in the shell and kernel of fresh hazelnut fruits of two varieties,
'Rimski' and 'Istarski', was analyzed. The shell of each variety was then separated by hand and
ground into a powder using a laboratory mill, which was used to test the treatment with highintensity
ultrasound (UAE). A probe system was used for the ultrasound-assisted extraction,
and the concentration of the solvent, ethyl alcohol 50 and 80% (v/v), the amplitude of the
device (40 and 60%) and the treatment time (10, 15 and 25 min) were varied. The control
sample represented the classical maceration treatment over 24 hours with 80 and % ethanol.
When comparing the results of total phenols, flavonoids, non-flavonoids and antioxidant
capacity between the shell and the kernel of the two hazelnut varieties, the highest values of
all mentioned parameters were obtained for the shell of the fruit. When comparing the
extraction methods, conventional and UAE-assisted, significantly higher values for total
phenols, flavonoids and non-flavonoids were found in the extracts of the shell of both hazelnut
varieties treated with UAE compared to the classically treated samples. In agreement with the
high levels of polyphenolic compounds, a significantly higher antioxidant capacity was also
found for extracts of the shell treated with UAE compared to the classical extraction method.
When testing the extraction parameters, all varied factors had an effect on the content of
total polyphenols and the antioxidant capacity. The concentration of the solvent (ethanolalcohol)
significantly influenced the yield of polyphenolic compounds, so that an ethanol
concentration of 80% (v/v) resulted in higher yields compared to 50% ethanol. In ultrasonic
extraction, the amplitude and treatment time were varied, with a longer treatment time (25
min) and higher amplitude (60%) having a positive effect on the total content of phenols,
flavonoids, non-flavonoids and antioxidant capacity. In conclusion, the shell of the two
hazelnut varieties studied is a very rich source of polyphenolic compounds and can therefore
be considered a nutritionally valuable by-product with many potential functional properties
and uses in exchange for disposal as bio-waste. High-intensity ultrasound proved to be highly
effective in isolating polyphenolic compounds from the shell of hazelnuts, which means that
this process technology can be considered as a potential for further utilization of the byproducts
of hazelnut production. |
