FRUCTE Sl LEGUME

Datorita caracterului sezonier si limitat geografic al productiei de legume si fructe se impune conservarea acestora astfel incat sa se asigure necesarul de consum atat pentru perioadele de timp dintre recolte cat si pentru alte zone geografice decat cele in care se cultiva.

Din acest punct de vedere, frigul artificial joaca un rol hotarator in valorificarea legumelor si fructelor.

1. Materia prima

Legumele si fructele reprezinta organisme vii, in tesuturile carora au loc si dupa recoltare procese metabolice complexe (respiratia, maturarea s.a.) sub actiunea catalizatoare a enzimelor proprii. Rolul tehnologiilor frigorifice de conservare consta in reducerea intensitatii acestora si in special a respiratiei si in eliminarea sau diminuarea proceselor de descompunere datorate microorganismelor. Modul in care o tehnologie frigorifica isi atinge scopul de a conserva calitatea legumelor si fructelor depinde in mod esential de caracteristicile si calitatea initiala a acestora.

Caracteristicile legumelor si fructelor care influenteaza asupra conservabilitatii prin frig sunt in principal urmatoarele:

specia, soiul;

caracteristicile fizice si termofizice (marimea, forma, culoarea, gradul de integritate fizica, densitatea, caldura specifica, conductibilitatea termica s.a.);

caracteristicile chimice (continutul in apa, substanta uscata, glucide, lipide, aciditate, celuloza, pigmenti, gust, aroma s.a.);

caracteristici biochimice si fiziologice (intensitatea respiratiei, intensitatea transpiratiei s.a.);

gradul de crestere si dezvoltare la recoltare si in momentul aplicarii tehnologiei de racire.

Trebuie mentionat faptul ca, pe langa caracteristicile propriu-zise ale materiei prime, conservabilitatea legumelor si fructelor tratate prin frig este influentata si de incarcatura microbiologica initiala a acestora .

Din punct de vedere al perisabilitatii, conform recomandarilor Comisiei Economice O.N.U. pentru Europa, produsele horticole se impart in patru grupe si anume:

a)  produse extrem de perisabile (afine, capsuni, agrise, coacaze, mure, zmeura, dude, smochine proaspete, spanac, macris, creson si telina pentru petiol);

b)  produse foarte perisabile (caise, cirese, gutui, mere timpurii,  nuci proaspete, pere timpurii, piersici, prune, struguri cu pielita fina, ceapa verde, ciuperci, castraveti Comichon, dovlecei, fasole verde boabe, mazare verde boabe, morcovi cu frunze in legaturi, morcovi timpurii, patrunjel pentru frunze, praz timpuriu, ridichi de luna, salata, sfecla rosie, sparanghel, telina verde, usturoi proaspat, varza timpurie);

c)   produse perisabile (pere de vara, struguri, masline, anghinare, ardei, bame, bob, conopida de toamna, fasole verde pastai, morcov, pepene galben, praz, telina, tomate, varza de toamna, varza de Bruxelles, vinete);

d) produse mai putin perisabile (mere de toamna, pere de toamna, castane, cartofi, ceapa, dovlecei, hrean, pastarnac radacini, sfecla rosie, usturoi).

2. Conservarea prin refrigerare

Daca refrigerarea se realizeaza rapid (cu durate ale procesului de ordinul a catorva ore sau chiar minute) ca faza tehnologica de sine statatoare, imediat dupa recoltare si inainte de depozitare sau de expediere spre consum sau industrializare, atunci refrigerarea mai este denumita si preracire sau prerefrigerare

Daca depozitarea este de lunga durata, in special in cazul merelor si citricelor, refrigerarea se realizeaza in acelasi spatiu in care se face si depozitarea, in aceste cazuri, refrigerarea propriu-zisa se realizeaza in perioade de timp mai mari, de cel putin cateva zile.

In cadrul lantului frigorific al fructelor si legumelor preracirea are o deosebita importanta. Scopul preracirii este de a scadea rapid temperatura produselor dupa recoltare, prin aceasta incetinindu-se procesele vitale si mentinandu-se calitatea initiala. Produsele cu intensitate mare a respiratiei trebuie preracite cat mai rapid dupa recoltare. Pentru produsele din grupa celor excesiv de perisabile sau foarte perisabile (de exemplu fructele de padure, capsuni, spanacul, sparanghelul s.a.) se recomanda, in general, ca perioadele de timp dintre recoltare si inceperea racirii sa nu depaseasca 29 ore .

2.1. Tratamente preliminare

Inainte de refrigerare legumele si fructele sunt supuse la o serie de tratamente preliminare cum ar fi: spalare, sortare, calibrare, ambalare, tratamente termice pentru prevenirea atacului de putregai, ceruire, iradiere, tratamente cu substante fungicide si cu hormoni pentru incetinirea maturarii s.a.

2.2. Refrigerarea

Principalele metode de refrigerare a fructelor si legumelor sunt refrigerarea cu aer racit, refrigerarea cu apa racita, refrigerarea in vacuum si refrigerarea cu gheata hidrica.

De o deosebita importanta in alegerea metodei de refrigerare si a conditiilor de racire este cunoasterea duratei procesului si a vitezei de racire necesara. Pentru evaluarea duratei de racire este util sa se cunoasca asa numita durata de injumatatire a diferentei de temperatura, definita ca fiind timpul necesar pentru a reduce la jumatate diferenta initiala dintre temperatura medie a produsului si cea a mediului de racire. Aceasta durata de injumatatire depinde de:

dimensiunile produsului;

modul de preluare a caldurii de la produs (modul de ambalare, mediul de racire, modul de aranjare a produselor s.a.);

diferenta de temperatura produs-mediu de racire;

viteza de circulatie a mediului de racire;

natura mediului de racire.

Se poate afirma ca durata de injumatatire a diferentei de temperatura este independenta de temperatura initiala si este constanta pe toata durata procesului de racire.

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