Stepen zrelosti voća – važan činilac kvaliteta sirovine u proizvodnji voćnih rakija

Abstract

Stepen zrelosti voća je jedan od faktora koji, pored sorte, podneblja na kojem se voće gaji, načina gajenja i zdravstvenog stanja plodova definišepogodnost voća za preradu u rakiju. Tokom zrenja, u voću dolazi do senzornih, biofizičkih i biohemijskih promena, koje se mogu pratiti korišćenjem odgovarajućih metoda analize. Izbor metoda analize zavisi od pristupa praćenju promena u plodovima tokom zrenja. Reč je o tzv. „omskim“ pristupima – senzor(om)skom, metabolomskom, proteomskom, transkriptomskom i genomskom pristupu. U praksi se za utvrđivanje stepena zrelosti u momentu berbe koriste prva dva pristupa, odnosno senzorne, fizičke ili hemijske karakteristike koje se menjaju sa zrenjem voća. Ove specifične karakteristike plodova nazivaju se indikatori zrelosti. Indikatori zrelosti mogu da budu više ili manje pouzdani, pa je za određivanje stepena zrelosti potrebno koristiti nekoliko indikatora. Postoji više vrsta (tipova) zrelosti voća što, ponekad, može dovesti do nesporazuma u definisanju optimalnog stepena zrelosti plodova za različite namene. Kod određenih voćnih vrsta, neke vrste zrelosti, definisane različitim terminima, se vremenski podudaraju. Nasuprot tome, kod drugih voćnih vrsta, za definisanje tipa zrelosti plodova različitih karakteristika, koji se beru u različitim momentima i koriste u različite svrhe, može se ponekad koristiti istovetan termin. Najčešće se koriste termini fiziološka (botanička, biološka) zrelost, komercijalna (hortikulturna, berbena) zrelost, konzumna zrelost i tehnološka zrelost. Tehnološka zrelost je stadijum zrelosti u kojem voće ima odgovarajući hemijski sastav, fizičke i organoleptičke karakteristike neophodne za dobijanje željenih svojstava (optimalnog tj. vrhunskog kvaliteta) gotovog proizvoda, uz maksimalno mogući prinos (najekonomičniju proizvodnju). Tehnološka zrelost se mora definisati za svaku vrstu, pa i sortu voća, a takođe i za vrstu proizvoda za koji je sirovina namenjena. U proizvodnji rakije, plodovi većine vrsta voćaka se beru u odgovarajućem stepenu zrelosti (tehnološka zrelost) i koriste za preradu neposredno po berbi. Neke vrste voća (jabuke, kruške, dunje) mogu da se beru i pre nego što dostignu tehnološku zrelost, nakon čega, radi postizanja odgovarajućih karakteristika neophodnih za preradu u rakiju, treba da dozrevaju, najčešće u kontrolisanim uslovima u pogledu temperature i vlažnosti vazduha. Tehnološka zrelost voća za proizvodnju voćnih rakija nastupa kada se plodovi nađu u stadijumu pune zrelosti, ponekad i u stadijumu delimične, blage prezrelosti, a samo u izuzetnim slučajevima pre pune zrelosti. Pri određivanju optimalne tehnološke zrelosti plodova za proizvodnju rakije, najveća pažnja se, uobičajeno, poklanja karakteristikama sirovine koje su od značaja za ekonomičnu proizvodnju, odnosno dobijanja najvećih prinosa rakije. Tradicionalno se, u tehnologiji voćnih rakija i rakija od grožđa, smatra da su u odgovarajućoj tehnološkoj zrelosti oni plodovi koji su dostigli punu zrelost. Takvi plodovi imaju maksimalni sadržaj fermentabilnih šećera, a kod koštičavog voća i najmanji udeo koštice u plodu, što omogućava dobijanje visokih prinosa rakije. Zrelost plodova ubranih u ovom stadijumu, neki autori opisuju i terminima šećerna zrelost, odnosno alkoholna zrelost, s obzirom da većina šećera u toku alkoholnog vrenja biva transformisana u etanol. Drugim rečima, maksimalni sadržaj šećera u plodu, kao najbolji pokazatelj optimalne zrelosti, definiše potencijalni sadržaj alkohola u fermentisanoj sirovini, odnosno prinos rakije. Postoje i drugi kriterijumi za određivanje optimalne zrelosti voća za preradu u rakiju, pa se optimalna zrelost za preradu može opisati i drugim terminima. Pri zrenju dolazi i do povećanja vrednosti odnosa ukupnih šećera i pektina, što je od značaja za potencijalni sadržaj metanola u rakiji. Promene u sadržajima pektina i drugih polisaharida dovode do omekšavanja plodova (teksturalna zrelost), što ima veliki značaj za preradu pojedinih vrsta koštičavog i jagodastog voća na tradicionalan način, bez predhodne pripreme plodova za alkoholno vrenje. Tradicionalno se smatra da plodovi u punoj zrelosti imaju razvijenu, intenzivnu i izraženu sortnu aromu i da su, kao takvi, pogodni za preradu u rakiju. Kod grožđa se, na primer, smatra da se, u idealnom slučaju zrelosti, maksimalna koncentracija šećera podudara sa razvijenom aromom grožđa. Od ovoga postoje i izuzeci, naročito danas, pri izraženim klimatskim promenama, pa se radi dobijanja rakija sa izraženijom voćnom aromom voće bere pre pune zrelosti. Postizanje maksimalne koncentracije pojedinih poželjnih aromatičnih komponenata u plodu (npr. terpenskih alkohola - linalola idr.) može da nastupi pre akumulacije maksimalne količine šećera u plodu, a zatim dolazi do njihove degradacije i smanjenja koncentracije. Stadijum zrelosti u kojem je postignut maksimalni sadržaj pojedinih sortno specifičnih sastojaka arome, uz istovremeni nestanak vegetativne note - zelenčivosti (uslovljene smanjenjem sadržaja pojedinih S6 aldehida i alkohola), naziva se aromatična zrelost. Različite vrste i sorte voća imaju različite sastojke koji daju specifičnu aromu potpuno zrelih plodova. Na primer, pri zrenju plodova šljive povećava se vrednost odnosa dva važna sastojka arome, nonanala i E-2-heksenala. Kod kajsija i bresaka, plodovi tek u fazi prezrelosti razvijaju specifičnu aromu od koje zavise karakteristična senzorna svojstva kajsijevača i breskovača. Višnje koje prelaze iz stadijuma pune zrelosti u fazu prezrelosti, imaju intenzivniju karakterističnu aromu na košticu (na benzaldehid). Ukoliko se plodovi ovih vrsta prerađuju u punoj zrelosti ili nešto pre pune zrelosti, dobijaju se rakije sa nešto drugačijim profilom arome. Kod kruške viljamovke, sa prezrevanjem plodova dolazi do nepoželjnih transformacija pojedinih estara dekadienske kiseline, pa se od takvih plodova dobija rakija manje finoće i slabije izražene arome karakteristične za ovu sortu. Ukoliko se voće pri preradi dezintegriše na odgovarajući način, stepen zrelosti plodova ne utiče značajnije na dužinu alkoholne fermentacije. Sadržaji većine isparljivih sastojaka (bez obzira na to da li vode poreklo iz plodova ili nastaju tokom primarne prerade, alkoholne fermentacije i destilacije) iz grupe alkohola, estara, kiselina, aldehida i acetala, koji presudno utiču na aromu voćnih rakija, se menjaju u zavisnosti od stepena zrelosti voća koje se koristi za preradu. Obično se najbolje senzorne karakteristike rakije dobijaju preradom plodova u punoj zrelosti. Ima, međutim, i izuzetaka, a to je da plodovi pojedinih vrsta i sorata voćaka ubrani pre pune zrelosti ili u stadijumu prezrelosti daju rakije koje se po senzornim karakteristikama mogu klasifikovati u rakije vrhunskog kvaliteta.

Degree of fruit ripeness is one of the factors which, apart from the cultivar, climate, growing method and health condition of fruits, determine the suitability of fruit for processing into brandy. During fruit maturation, sensory, biophysical and biochemical changes occur, which can be monitored using appropriate analysis methods. Selection of the analysis method depends on the approach for monitoring changes in fruits during maturation. This is the so-called “omics”approach– sensoromic, metabolomic, proteomic, transcriptomic and genomic approach. In practice, the first two approaches are used for determining ripeness degree at harvest time, i.e. sensory, physical or chemical properties changed with fruit ripening. These characteristics of fruits are called maturity indicesand may be more or less reliable; therefore, several indices are needed to be used for determining ripeness degree. There are several types of fruit maturity that can sometimes lead to misconception in defining optimal ripeness degree for different purposes. In certain fruit species, some types of maturity, defined by different terms coincide in time. Contrary to that, the same term can be used in other fruit species to determine the type of maturity of fruits with different characteristics, harvested at different times and used for different purposes. The most common terms are physiological (botanical, biological) maturity, commercial (horticultural, harvesting) maturity, consumption and technological maturity. Technological maturity is a stage of ripeness in which fruit has certain chemical composition, physical and organoleptic characteristics necessary for obtaining required properties (optimal, i.e. top quality) of the finished product with highest yield possible (the most economical production). Technological maturity should be defined for each fruit species and cultivar, as well as for the type of product for which raw material is intended. In brandy production, fruits of most fruit species are harvested in appropriate ripeness degree (technological maturity) and are used for processing immediately after harvest. Some fruit species (apple, pear and quince) can be harvested even before reaching technological maturity after which, in order to achieve adequate characteristics required for processing into brandy, they should ripen further, mostly in controlled conditions regarding air temperature and humidity. Technological maturity of fruit intended for brandy production occurs at full maturity and sometimes in the stage of partial, mild over-ripeness while, in exceptional cases only, prior to full maturity. While determining optimal technological maturity of fruits for brandy production, the greatest attention is commonly paid to raw material characteristics, which are of importance to economical production, that is, for obtaining the highest yields of brandy. Traditionally, in processing fruit brandies and those obtained from grapes, fruits that have reached full maturity are considered to be at appropriate technological maturity. Such fruits have the highest content of fermentable sugars and in stone fruits the lowest stone share in the fruit, which enables obtaining high yields of brandy. Ripeness degree of fruit harvested in this stage is described by some authors as sugar ripeness, i.e. alcoholicripeness, since most sugars are transformed into ethanol during alcohol fermentation. In other words, the highest sugar content in fruit, as the best indicator of optimal maturity, determines the potential alcohol content in fermented raw material, i.e. yield of brandy. There are other criteria to determine optimal fruit ripeness for processing into brandy, thus the optimal ripeness for processing can be described in other terms. During ripening, there comes to an increase of the ratio of total sugar and pectin concentrations, which is of significance for potential methanol content in brandy. Changes in contents of pectin and other polysaccharides lead to fruit softening (textural maturity) which is of large importance for processing certain types of stone and berry fruits in a traditional way, with no prior preparation of fruits for alcoholic fermentation. It is traditionally considered that fruits at full maturity have a developed, intense and pronounced aroma and that as such are suitable for processing into brandy. In grapes, for example, it is considered that at ideal maturity, maximal concentration of sugar coincides with a fully developed aroma of grape. There are exceptions to the rule, particularly today, with severe climatic changes, so in order to obtain brandy with pronounced fruityaroma, the fruit is harvested before full maturity. Reaching the highest concentration of some desirable aromatic components in the fruit (for example, terpenic alcohol – linalool and other) can occur before accumulation of the maximum sugar content in fruit followed by degradation, i.e. lowering concentration of these. Ripeness degree where the highest content of certain cultivar specific aromatic components is reached, with simultaneous loss of vegetative, green note (conditioned by decreasing content of certain С6 аldehydes and alcohols), is called aromatic maturity. Different fruit species and cultivars have different components giving specific aroma of fully ripen fruits. For example, during ripening of plum fruit, the value of the ratio of two important aromatic (nonanal and Е-2-hexenal)components increases. In apricot and peach, it is at full maturity stage that fruits develop specific aroma on which distinctive sensory properties of apricot and peach brandy depend. Sour cherries passing from the stage of full maturity into stage of overripeness have more intense distinctive stone-like aroma (benzaldehyde). If fruits of these species are processed at full maturity or prior to full maturity, brandies with somewhat different aroma profile are obtained. In Williams pear, overripening of fruits leads to undesirable transformations of certain esters of decadienoic acid, hence brandy of lower degree of fineness and less pronounced aroma typical for this cultivar is obtained. If the fruit is disintegrated appropriately during processing, degree of fruit ripeness has no significant effect on duration of alcoholic fermentation. Contents of numerous volatile ingredients in fruit brandies (regardless of whether they originate from fruits or are formed during primary processing, alcoholic fermentation and distillation) from the group of alcohols, esters, acids, adehydes and acetals, which crucially affect the aroma of fruit brandy, depend on ripeness degree of the fruit used for processing. Best sensory characteristics of brandy are usually obtained by processing fruits at full maturity (fully ripe fruits). Still, there are exceptions to this, which is that fruits of certain fruit species and cultivars harvested before full maturity or in the stage of overripeness give brandies which, according to sensory characteristics can be classified into brandies of top quality.