Abstract | Cilj istraživanja je bio utvrditi utjecaj sorte i primjene abrazivnog predtratmana na
vrijeme sušenja, stabilnost biološki aktivnih spojeva, senzorska svojstva i nutritivni sastav suhe
šljive u odnosu na konvencionalne predtretmane. Istraživanje je provedeno na plodovima triju
sorti šljive ꞌBistricaꞌ, ꞌPresidentꞌ i ꞌTopend plusꞌ ubranim u pokusnom nasadu Zavoda za
voćarstvo Hrvatskog centra za poljoprivredu, hranu i selo u Donjoj Zelini. Nakon provedenih
pomoloških (masa, visina, širina i debljina ploda) i fizikalno-kemijskih analiza (tvrdoća, topljiva
suha tvar, ukupna suha tvar, pH vrijednost, ukupna kiselost i boja ploda) u vrijeme berbe, na
plodovima namijenjenim sušenju izvršeno je sortiranje, pranje i otkoštičavanje plodova. Prije
postupka sušenja plodovi šljive tretirani su s jedanaest različitih kombinacija predtretmana:
abrazijom pri tri različita vremena vrtnje cilindra 5, 10 i 15 minuta obloženog inertnim
abrazivnim materijalom PW 400 uz konstantnu rotaciju cilindra od 120 rpm, potapanjem
plodova u lužnatu otopinu KOH različitih koncentracija (0,5, 1 i 1,5 %) pri temperaturi 22 i 60
°C u intervalu od 60 sekundi, kao i potapanje plodova u destiliranu vodu pri istim
temperaturama i istom vremenskom intervalu. Plodovi su sušeni u komornoj sušnici pri
konstantnoj temperaturi od 42 °C i brzini strujanja zraka 2,0 msˉ¹ do 35 % vode u plodu. Razlike
između ocjene kvantitativne deskriptivne analize i fizikalno-kemijskih svojstva ploda različitih
sorti s obzirom na predtretmane statistički su analizirane odgovarajućim modelima analize
varijance (ANOVA).
Sva analizirana pomološka svojstva razlikovala su se između istraživanih sorti šljive.
Predtretman je značajno utjecao na vrijeme sušenja. Najkraće vrijeme sušenja utvrđeno je kod
predtretmana abrazijom 15 minuta kod svih sorti, a slijede predtretmani s KOH na 60 °C svih
triju koncentracija (0,5, 1 i 1,5 %) te abrazijom 5 i 10 minuta. Na vrijednosti morfoloških
svojstava osušenih plodava značajno je utjecala sorta. Predtretman je značajno utjecao na
boju osušenog ploda. Veća degradacija boje kožice ploda utvrđena je kod uzoraka koji su
tretirani s KOH svih koncentracija na temperaturi od 60 °C, tj. ista je imala nižu kromatsku
vrijednost L* i više kromatske vrijednosti a* i b*, plodovi su razvili tamnu boju. Plodovi tretirani
abrazijom u svim vremenima vrtnje zadržali su poželjnu svojstvenu boju šljive, tj. kod njih je
izmjerena viša kromatska vrijednost L* i niže kromatske vrijednosti a* i b*. Sorta 'Bistrica' u
interakciji sa svim predtretmanima najbolje je ocijenjena za poželjna senzorna svojstva boje,
okusa, sočnosti, arome i žvakavosti osim za svojstvo mirisa koje je najbolje ocijenjeno kod
sorte 'Topend plus', dok su nepoželjna svojstva izražena kod sorte 'President'. Predtretmani
abrazijom pozitivno su utjecali na poželjna senzorska svojstva: boju, okus, sočnost, aromu i
gumoznost/žvakavost kod svih sorti u istraživanju. Udio ukupnih fenola, hidroksicimetnih
kiselina i flavonola značajno se razlikovao s obzirom na sortiment i ovisio je o predtretmanima.
Predtretmani s KOH koncentracije 1,5 % pri obje temperature pozitivno su utjecali na očuvanje
bioaktivnih spojeva. Sorta 'Topend plus' imala je najveću količinu ukupnih fenola,
hidroksicimetnih kiselina i flavonola kod svih predtretmana u odnosu na druge sorte. |
Abstract (english) | Plum (Prunus domestica L.) is mostly represented in the EU market as fresh or
industrially processed as dried fruit. Production technology of dried plums is based on fruit
drying at high temperatures between 85 and 90 °C, with less fruit water content between 20
and 26 %. This type of fruit dehydration at high temperatures has an influence on fruit quality
decrease in a form of texture, colour, taste and bioactive components loss along with high
energy consumption. In order to keep the texture, colour and taste as well bioactive
components of dried fruits, drying at lower temperatures of 50 °C, with higher final fruit water
content of 35 % is used. Essential parameters in cultivar selection intended for drying are fruit
size, congruent ratio of total soluble solids, total acids, and easiness of stone removal as well
initial fruit water content. Plum fruits intended for drying have to be picked at optimum harvest
window which is determined during continuous monitoring of basic pomological characteristics
such as fruit mass and size as well as physical and chemical parameters - fruit firmness, total
soluble solids content, total acids and pH. Plum drying process is slow and energy demanding
process due to waxy layer that covers plum fruit skin. Removal of waxy layer which enables
free movement of water is therefore needed by means of fruit surface treatment. Pretreatments
are dissolving the waxy layer which consequently creates microscopic fractures
thus enabling water movement. Pre-treated fruits are drying significantly faster from untreated
fruits. Cultivars used in this research – ‘Bistrica’, ‘President’ and ‘Topend plus’, were treated
with 11 different pre-treatments: abrasion of 5, 10 and 15 minutes, KOH in solution
concentration of 0.5, 1.0 and 1.5 % at temperature of 22 °C, KOH in solution concentration of
0.5, 1.0 and 1.5 % at temperature of 60 °C and with distilled water at two temperatures (22 and
60 °C).
Results
Higher precipitation during the vegetation season in which the research was conducted as well
as lower than average temperatures during fruit ripening had influence on fruit firmness,
pomological characteristics, dry matter content, total soluble solids content and total acids.
Pomological characteristics of fresh plum fruit (weight, height, width and thickness of fruit as
well as weight, length, width and thickness of stone) are cultivar dependant. Cultivars
'President' and 'Topend plus' had highest weight as well as height, width and thickness of fruits
in comparison to cv 'Bistrica'.
For all cultivars in the research a significantly shorter drying time of samples pre-treated with
abrasion of 10 and 15 minutes, as well as with alkaline solution (KOH) of 1.0 and 1.5 %
concentration at 60 °C was determined. Parameters such as temperature, solvent types and
concentration have a significantly influence on drying time of plum fruits. Higher temperature
(60 °C) and usage of solvent of higher concentration (1.5 %) had significantly reduced drying
time of plum fruits of all cultivars in the research.
Values of morphological characteristics of dried fruits were significantly influenced by pretreatment.
Cv ‘Bistrica’ had higher weight, height, width and thickens of dried fruit at samples
pre-treated with abrasion; for cv ‘President’ it was highest at KOH pre-treatments of all
concentrations at temperature of 22 °C; for cv ‘Topend plus’ it was the highest at pre-treatment
with KOH of all three concentrations at temperature of 60 °C.
Abrasive pre-treatment had a positive influence on sensory characteristics of dried fruits,
especially on intensity of dark blue/black colour, plum-like taste, sweetness, juiciness, plumlike
aroma and chewiness of all three cultivars in the research. The highest sensory scores
were noted for dried fruits treated with abrasive pre-treatment in duration of 10 minutes. Cv
‘Bistrica’ irrespective of pre-treatment had the highest scores for following sensory
characteristics: intensity of dark blue/black colour, plum-like taste, sweetness, juiciness and
plum-like aroma as well as for chewiness. Cv ‘Topend plus’ had the higher scores for flavour
and firmness/texture sensory characteristics of dried fruits.
The highest content of bioactive compounds (total phenols, total hidroxycinnamic acids and
total flavonols) was determined in dried fruits of all three plum cultivars treated with chemical
and thermal pre-treatments, whilst the lowest values of mentioned bioactive compounds were
determined in fruits pre-treated with abrasion. KOH treatment of 1 and 1.5 % concentrations
at temperatures of 22 and 60 °C had positive influence on the content of bioactive compounds.
Cv ‘Topend plus’ had the highest content of all researched bioactive compounds irrespective
of used pre-treatment in comparison to cv ‘Bistrica’ and ‘President’.
Conclusions
Advantages of chemical pre-treatment application are manifested in significant shortening of
drying time and in preservation of bioactive compounds, whilst the main disadvantage lies in
waste disposal of used chemical reagents and their negative environmental impact. Use of
innovative and ecologically acceptable technique of abrasive pre-treatment of plums fruits
shortens the drying time in comparison to conventional pre-treatments (chemical and thermal).
Efficiency comparison of different pre-treatments used within this research leads to a
conclusion that abrasive pre-treatments contribute to preservation of sensory and qualitative
fruit characteristics as well as to nutritive values. This type of plum fruits pre-treatments can in
the near future replace completely chemical pre-treatments of plum fruits. |